Researchers screened physical, pure compounds obtained from African medicinal plants in the pan-African Natural Products Library, abbreviated p-ANAPL. The target was the in vitro interaction between the receptor-binding domain, or RBD, of the SARS-CoV-2 spike protein and ACE2, the host receptor that helps mediate viral entry into cells. Disrupting this molecular interaction could potentially prevent a key step in infection. The library screen selected three compounds with half-maximal inhibitory concentrations, or IC50 values, ranging from 0.5 to 2.4 micromolar, indicating activity within the low-micromolar range in the tested assay.

The compounds showed some selectivity in the screening system. Unlike their effects on the SARS-CoV-2 RBD–ACE2 interaction, oleanolic acid, poinsettifolin B, and rhuschalcone III did not disrupt binding between PD-1 and PD-L1, an unrelated host ligand–receptor pair used as a comparator. This result suggests that the observed inhibitory activity was not simply a nonspecific consequence of broadly interfering with protein interactions. The experiment nevertheless measured binding-related activity in vitro, and the authors did not establish that the same effects would occur in an infected organism or lead directly to an effective COVID-19 treatment.

Cell experiments produced a more limited pattern of antiviral activity. Oleanolic acid and rhuschalcone III inhibited SARS-CoV-2 replication in Vero cells at low micromolar concentrations without cytotoxicity at the tested levels. Poinsettifolin B inhibited the RBD–ACE2 interaction but did not inhibit viral replication in this cell model. The distinction is important because interference with receptor binding alone did not guarantee a measurable reduction in viral replication. The evidence also remains specific to the laboratory conditions and cell line used; the study does not show whether the compounds can be safely or effectively administered to humans.

Computational modelling provided a possible structural explanation for the three molecules’ activity. The models indicated that each compound could interact with numerous residues on the SARS-CoV-2 RBD and human ACE2, including a subset of sites conserved across SARS-CoV-2 variants of concern. Such models can generate hypotheses about binding modes and guide further experiments, but they do not by themselves confirm a physical interaction in cells or in patients. Overall, the research identifies oleanolic acid, poinsettifolin B, and rhuschalcone III as selective, in vitro antiviral candidates that warrant additional investigation, particularly for settings where access to existing vaccines or therapies is limited.

Subject of Research: In vitro antiviral screening of African natural products against SARS-CoV-2 entry and replication

Article Title: The pan-African natural products library compounds oleanolic acid, poinsettifolin B, and rhuschalcone III disrupt SARS-CoV-2 spike-host ACE2 interactions and SARS-CoV-2 replication

Article References: Tjegbe, M. J. M., Onguéné, P. A., Bekono, B. D., Betow, J. Y., Simoben, C. V., Cassel, J., Salvino, J. M., Montaner, L. J., Andrae-Marobela, K., Ntie-Kang, F., & Tietjen, I. (2026). The pan-African natural products library compounds oleanolic acid, poinsettifolin B, and rhuschalcone III disrupt SARS-CoV-2 spike-host ACE2 interactions and SARS-CoV-2 replication. BMC Pharmacology and Toxicology. https://doi.org/10.1186/s40360-026-01264-3

Image Credits: AI Generated

DOI: 10.1186/s40360-026-01264-3

Keywords: SARS-CoV-2, COVID-19, natural products, oleanolic acid, rhuschalcone III, poinsettifolin B, ACE2, spike protein, antiviral screening, Vero cells, pan-African, natural

Anthocyanins are glycosylated forms of anthocyanidins, built on a flavylium ion backbone with a C6-C3-C6 carbon structure: a 15-carbon skeleton of two aromatic rings connected by a three-carbon bridge forming a heterocyclic ring. Six major anthocyanidins—petunidin, malvidin, peonidin, cyanidin, delphinidin, and pelargonidin—account for roughly 90 percent of those found in nature. Beyond their role as plant pigments, these compounds exhibit antioxidant, anti-inflammatory, neuroprotective, and anticancer activities, and previous work has documented broad-spectrum antiviral effects against several RNA viruses, including suppression of influenza neuraminidase.

The review identifies the SARS-CoV-2 main protease, Mpro, as the most extensively investigated molecular target. Because Mpro cleaves viral polyproteins into functional units required for replication and maturation—and because its structure differs substantially from any human protease—it has become one of the most attractive antiviral targets against COVID-19. Numerous independent molecular docking studies have demonstrated favorable predicted interactions between structurally diverse anthocyanins and the Mpro catalytic site, particularly the catalytic residues His41 and Cys145, with no clear cellular cytotoxicity reported. Notably, polyacylated anthocyanins such as tecophilin, cyanodelphin, gentiodelphin, and phacelianin consistently exhibited stronger predicted binding than diacylated or monomeric forms, suggesting that structural modification may enhance inhibitory activity.

Several studies have begun to provide experimental validation of these computational predictions. Cyanidin-3-O-sambubioside isolated from kokum fruit demonstrated approximately 79 percent inhibition of Mpro activity at 100 micromolar in an in vitro enzymatic assay, with favorable docking to the catalytic dyad and no cytotoxicity to BEAS-2B cells. Cyanidin 3-O-galactoside from cranberry showed potent Mpro inhibition with an IC50 of 9.98 micromolar in FRET-based enzymatic assays, while whole cranberry anthocyanin extracts achieved an IC50 of 23.58 micrograms per milliliter. More recently, a high-resolution mass spectrometry-based screening platform identified delphinidin-3-glucoside from blueberry as a covalent Mpro inhibitor, producing dose-dependent inhibition of SARS-CoV-2 replication in Vero E6 cells with an IC50 of approximately 35.8 micromolar—comparable to the established Mpro inhibitor baicalin.

Beyond Mpro, anthocyanins have been proposed to interact with other viral replication proteins, particularly the RNA-dependent RNA polymerase and helicase. A comprehensive virtual screening of naturally occurring polyphenols identified cyanidin-3-O-rutinoside, petunidin-3,5-O-diglucoside, and delphinidin-3-O-rutinoside as the strongest predicted RdRp inhibitors, with binding energies exceeding those of remdesivir. A multitarget docking study found that cyanidin 3-O-glucosyl-rutinoside bound strongly across Mpro, RdRp, and helicase simultaneously. However, the review notes that no studies have conclusively demonstrated direct enzymatic or structural inhibition of these proteins, and the available evidence remains largely limited to computational predictions.

Anthocyanins may also interfere with viral entry by disrupting the interaction between the spike glycoprotein receptor-binding domain and the host ACE2 receptor. In the large-scale multitarget docking study, cyanidin 3-O-glucosyl-rutinoside demonstrated the strongest predicted interactions with both spike protein and ACE2, with docking scores of -10.07 and -13.26 respectively, outperforming the reference compounds remdesivir and hydroxychloroquine. Additional anthocyanins, including pelargonidin-3-rhamnoside and cyanidin-7-arabinoside, were predicted to bind favorably to the spike receptor-binding domain. The review emphasizes, however, that experimental evidence supporting this entry-blocking mechanism remains scarce and should currently be regarded as computational prediction requiring biochemical and cell-based validation.

The review also highlights a complementary mechanism: modulation of host inflammatory responses. Excessive cytokine activation is associated with COVID-19 severity and tissue damage. Using an in vitro model of SARS-CoV-2 spike protein S1-induced inflammation, black rice germ and bran extract rich in cyanidin-3-O-glucoside and peonidin-3-O-glucoside significantly suppressed expression of the inflammatory genes NLRP3, IL-1β, and IL-18, while reducing secretion of IL-6, IL-1β, and IL-18 in A549 lung epithelial cells and THP-1 macrophages. The extract was effective at 12.5 to 100 micrograms per milliliter, with purified constituents active at 1.25 to 10 micrograms per milliliter, operating through inhibition of the NF-κB/NLRP3 inflammasome signaling pathway.

Evidence from anthocyanin-rich plant extracts adds further complexity. Standardized European black elderberry fruit extract, containing 4.6 percent total polyphenols and 3.5 percent anthocyanins, demonstrated in vitro antiviral activity against the original Wuhan strain and the Alpha, Beta, Gamma, Delta, and Omicron variants, with cyanidin-3-sambubioside-5-glucoside exhibiting the strongest inhibition among major components. A subsequent study found that combining elderberry extract standardized to 3.2 percent anthocyanins with quinine produced synergistic antiviral effects against SARS-CoV-2 in Calu-3 lung cells, with a Bliss independence score of 27.8. The review cautions that because extracts contain multiple polyphenols and other phytochemicals, the relative contribution of anthocyanins alone cannot be determined with certainty.

Despite encouraging computational and preclinical evidence, the review identifies poor physicochemical stability and low bioavailability as major translational challenges. Only approximately 2 percent of ingested anthocyanins are reported to retain their intact C6-C3-C6 structure after ingestion. These compounds are highly susceptible to degradation by pH, temperature, oxygen, and light—under acidic conditions they exist predominantly as the red flavylium cation, whereas neutral and alkaline environments promote quinonoidal base formation, reducing both stability and biological activity. Such degradation may occur during food processing, storage, gastrointestinal digestion, and systemic absorption, potentially limiting the concentrations required to achieve the antiviral effects observed in vitro.

Several strategies are being explored to overcome these limitations. Structural modification through glycosylation and acylation, physical protection through microencapsulation and nanoencapsulation, stabilization via complex formation with macromolecules, and co-pigmentation techniques all aim to preserve structural integrity and enhance systemic availability. Encapsulation technologies coat extracted bioactive compounds with protective materials—typically GRAS-classified biopolymers composed of proteins, carbohydrates, or their combinations—to shield them from extreme environments within the body and allow them to reach the small intestine intact. Nanoparticles are of particular interest because their high surface-area-to-volume ratio can enhance stability, solubility, and bioavailability while providing more reactive sites for interaction. The review concludes that while anthocyanins represent promising natural compounds for further antiviral investigation, additional mechanistic studies, in vivo validation using animal models, comprehensive pharmacokinetic evaluations, and well-designed clinical trials are required before their clinical potential against COVID-19 can be established.

Subject of Research: Anthocyanins as potential SARS-CoV-2 antivirals: mechanisms, evidence, and translational challenges

Article Title: Antiviral potential of anthocyanins against SARS-CoV-2: current evidence, translational challenges, and future perspectives

Article References: Lu, P. (2026). Antiviral potential of anthocyanins against SARS-CoV-2: current evidence, translational challenges, and future perspectives. Frontiers in Virology, 6, Article 1897871. https://doi.org/10.3389/fviro.2026.1897871

Image Credits: AI Generated

DOI: 10.3389/fviro.2026.1897871

Keywords: anthocyanins, SARS-CoV-2, COVID-19, antiviral, flavonoids, Mpro, RdRp, ACE2, bioavailability, elderberry, potential, against

Sarbecoviruses, the subgenus of coronaviruses that includes SARS-CoV and SARS-CoV-2, attach to their host cells through the receptor-binding domain, or RBD, of the Spike protein. This domain grips the angiotensin-converting enzyme 2 receptor, ACE2, on the surface of host cells, and it is also the principal target of neutralising antibodies. That dual role creates an intimate link between host range and antigenicity: the same molecular surface that determines which species’ receptors a virus can engage also determines how well antibodies raised against one virus recognise another. The research team, led by scientists at The Pirbright Institute together with collaborators including researchers at King’s College London, set out to map that relationship systematically across a diverse collection of bat sarbecoviruses.

The experimental strategy combined three complementary approaches. First, the researchers used binding assays to test whether the Spike proteins of different sarbecoviruses could attach to ACE2 proteins from a wide panel of mammalian species. Second, they used pseudotype-entry assays, in which harmless lentiviral particles are decorated with each coronavirus Spike protein, to test whether receptor binding actually translates into cell entry. Third, they measured how sera from SARS-CoV-2 convalescent individuals and monoclonal antibodies from vaccinated people who had experienced breakthrough infections neutralised the different viruses. By running the same viruses through all three assays, the team could directly correlate receptor usage with antigenic behaviour.

The results revealed a striking pattern. Sarbecoviruses in clade 1, the group that contains SARS-CoV-2 itself and the BANAL viruses isolated from bats in Laos, tended to be generalists. Their Spike proteins could productively engage ACE2 receptors from many different bat species, indicating that they are not finely tuned to a single host. In contrast, viruses from clade 3, exemplified by RhGB07, and clade 5, exemplified by Rc-o319, behaved as specialists, using a much narrower range of ACE2 receptors. Rc-o319, which was previously known to be unable to use human ACE2 efficiently, fits this specialist profile, whereas the BANAL viruses, which can use human ACE2, sit firmly in the generalist camp alongside SARS-CoV-2.

To understand the structural basis of this specialism, the team solved a novel structure of the RhGB07 Spike protein. The structure allowed them to identify specific residues within the RBD that are associated with the restricted receptor usage of this clade 3 virus. These residues presumably shape the receptor-binding interface in ways that favour particular bat ACE2 variants while excluding others. Such structural insights are valuable because they point to the molecular features that distinguish viruses capable of flexible receptor engagement from those locked into narrow host ranges, and they may help predict the properties of newly discovered sarbecoviruses from sequence data alone.

When the researchers extended their receptor panel beyond bats to include more diverse mammalian ACE2 proteins, the generalist phenotype largely held. Clade 1 viruses could bind and enter cells expressing ACE2 from humans, non-human primates, livestock, and rodents, as well as from species considered potential intermediate reservoir hosts, such as civets, raccoon dogs, and pangolins. This is significant because intermediate hosts are thought to have played a role in previous coronavirus spillovers, including the emergence of SARS-CoV in 2002. A virus that can already use the receptors of many species faces fewer barriers on the path from bat to human. The specialist viruses, by contrast, showed wider phenotypic diversity across this expanded panel, with RhGB07 exhibiting a more idiosyncratic pattern of receptor usage that did not simply mirror its bat-host profile.

The study also examined how SARS-CoV-2’s ongoing evolution in humans has changed its receptor preferences. Comparing variants that have emerged during the pandemic, the researchers found an expanding and, in some cases, shifting pattern of generalism, particularly for Omicron and its many sub-lineages. Omicron’s Spike has accumulated numerous mutations in the RBD, and these changes appear to have broadened or reconfigured the range of ACE2 molecules the virus can engage. This observation underscores that receptor usage is not a fixed property of a virus but a dynamic trait that can evolve under immune pressure and changing transmission landscapes, with potential consequences for which animal species might serve as new reservoirs for human-derived variants.

The antigenic side of the analysis produced equally important findings. When convalescent sera from people who had recovered from COVID-19 were tested against the panel of bat sarbecoviruses, clade 1 viruses, being phylogenetically closest to SARS-CoV-2, were antigenically the most similar. There was robust evidence for cross-neutralisation of these viruses, meaning that immunity generated against SARS-CoV-2 offers meaningful protection against its closest bat relatives. Importantly, however, the team also found evidence for limited cross-neutralisation across the entire subgenus, suggesting that even the more distantly related specialist viruses are not completely invisible to immunity primed by SARS-CoV-2 infection. This graded pattern of cross-reactivity maps closely onto the phylogenetic and receptor-usage relationships the researchers had established.

Using monoclonal antibodies derived from COVID-19 vaccinees who subsequently experienced breakthrough infections, the researchers were able to pinpoint which classes of antibody epitopes are responsible for the broader neutralisation observed across the sarbecovirus panel. Because antibodies recognise specific structural features of the RBD, identifying the epitope classes that mediate cross-neutralisation provides a rational basis for designing vaccines and therapeutics with deliberately broad coverage. Antibodies directed against more conserved features of the receptor-binding interface, rather than those specific to SARS-CoV-2’s particular configuration, appear to underpin the wider neutralising activity.

Taken together, the study delivers a unifying message: generalist ACE2 usage, phylogenetic proximity to SARS-CoV-2, and antigenic similarity travel together. A bat sarbecovirus that can flexibly use receptors from many mammalian species is likely to be a close relative of SARS-CoV-2 and likely to be partially neutralised by existing human immunity. This constellation of traits offers surveillance teams a practical framework for triage. When a new sarbecovirus is discovered, characterising its receptor-binding breadth through binding and pseudotype assays could provide an early, laboratory-based assessment of both its zoonotic potential and the degree to which current vaccines and antibodies might protect against it. As bat habitats are disturbed and human-wildlife interfaces expand, such tools for distinguishing the generalists from the specialists among the thousands of circulating bat coronaviruses could prove essential for anticipating, and perhaps preventing, the next spillover.

Subject of Research: ACE2 receptor usage breadth as a predictor of host range and antigenic relatedness across bat sarbecoviruses

Article Title: Breadth of ACE2 receptor usage predicts host range and antigenic relatedness across bat sarbecoviruses

Article References: Thakur, N., Newman, J., Ni, D., Seow, J., Hay, A. L., Lee, Y., Upadhyay, A., Ekundayo, B. E., Hammond, J. A., Peacock, T. P., Lau, K., Doores, K. J., & Bailey, D. (2026). Breadth of ACE2 receptor usage predicts host range and antigenic relatedness across bat sarbecoviruses. PLOS Biology, 24(10), e3003944. https://doi.org/10.1371/journal.pbio.3003944

Image Credits: AI Generated

DOI: 10.1371/journal.pbio.3003944

Keywords: sarbecoviruses, ACE2, SARS-CoV-2, host range, receptor-binding domain, antigenicity, cross-neutralisation, bat coronaviruses, zoonotic spillover, Omicron, monoclonal antibodies, pseudotype assays

The review is careful to separate what is established from what remains hypothetical, a distinction that matters in a field where observational data can easily be overinterpreted. The authors distinguish three clinical scenarios that are often conflated in the literature. The first is simultaneous co-infection, in which a patient harbors both SARS-CoV-2 and actively toxin-producing C. difficile at the same time. The second is CDI that develops during hospitalization for COVID-19, a situation in which antimicrobial exposure and disrupted infection-prevention practices during pandemic surges may play dominant roles. The third, and perhaps the most intriguing, is delayed or recurrent CDI after apparent recovery from acute infection, which points toward persistent alterations of the intestinal ecosystem rather than simple nosocomial exposure. Each scenario implies a different balance of contributing causes, and each demands a different study design to disentangle.

The most straightforward explanation for an association between the two diseases is iatrogenic. Patients hospitalized with severe COVID-19 frequently received broad-spectrum antibiotics, either because bacterial co-infection was suspected or as empirical coverage during the chaotic early phases of the pandemic, when distinguishing viral pneumonia from secondary bacterial infection was difficult. Antibiotic exposure is the single strongest risk factor for C. difficile infection because it dismantles colonization resistance, the collective ability of a diverse gut microbiota to suppress pathogen expansion through competition for nutrients, production of bacteriocins, and, critically, the metabolism of bile acids. Primary bile acids such as taurocholate stimulate germination of C. difficile spores, while secondary bile acids generated by commensal bacteria inhibit its growth. When antibiotics deplete the bile acid-metabolizing community, the gut becomes a permissive niche for the pathogen.

Yet the review argues that antibiotics and hospitalization alone cannot fully account for the observed patterns. SARS-CoV-2 is increasingly recognized as an agent capable of perturbing the gut directly. Viral RNA has been detected in intestinal tissue and stool, and the angiotensin-converting enzyme 2 receptor, the cellular entry gate for the virus, is abundantly expressed on intestinal epithelial cells, particularly mature enterocytes of the small intestine. The authors emphasize that ACE2 is not merely a viral docking site. In normal physiology, ACE2 participates in regulating amino acid homeostasis, antimicrobial peptide expression, and the composition of the gut microbiome. Loss or dysregulation of ACE2 function during infection could therefore weaken epithelial barrier integrity and shift the microbial community toward a dysbiotic state, independently of any antimicrobial exposure.

This leads to the renin-angiotensin system, one of the review’s central mechanistic themes. SARS-CoV-2 binding to ACE2 promotes internalization and degradation of the receptor, reducing its protective enzymatic activity. The consequence is an imbalance in the renin-angiotensin axis: less angiotensin II is converted into the vasoprotective angiotensin-(1-7), and unopposed angiotensin II signaling through the AT1 receptor increases. In the intestine, excessive angiotensin II/AT1R signaling is associated with inflammation, increased epithelial permeability, and impaired barrier repair. The authors propose that this signaling imbalance could amplify mucosal damage during COVID-19 and thereby lower the threshold at which residual C. difficile spores, persisting in the lumen after germination conditions improve, can establish infection and produce toxin.

Downstream of angiotensin signaling, the review highlights inflammatory cascades that connect viral injury to bacterial opportunity. Severe COVID-19 is characterized by activation of the transcription factors NF-κB and MAPK in epithelial and immune cells, driving robust production of interleukin-6 and other pro-inflammatory mediators. Persistent inflammatory signaling can disrupt epithelial tight junctions, alter mucus production, and change the metabolic landscape of the lumen in ways that favor pathogenic taxa over obligate anaerobes that maintain colonization resistance. The authors also draw attention to nutritional vulnerability, noting that malnutrition and micronutrient deficiencies, common in hospitalized and older patients, impair epithelial regeneration and immune defense. They further discuss apolipoprotein E-related immunometabolic pathways as a possible link between host lipid metabolism, inflammatory resolution, and susceptibility to intestinal injury, an area they flag as requiring direct experimental validation.

Among the more forward-looking elements of the review is its treatment of extracellular vesicles as a potential biomarker framework. Extracellular vesicles, small membrane-bound particles released by cells into circulation and bodily fluids, carry proteins, lipids, and nucleic acids that reflect the physiological state of their cell of origin. The authors suggest that vesicle cargo could eventually serve as a readout of the combined inflammatory, epithelial, and microbial perturbations that characterize patients at heightened risk of CDI during or after COVID-19. Such biomarkers could, in principle, allow clinicians to identify which recovered COVID-19 patients warrant closer surveillance for delayed intestinal complications, although this remains a hypothesis-generating proposal rather than a validated clinical tool.

The authors are explicit that direct longitudinal evidence linking SARS-CoV-2 infection to subsequent CDI remains limited. Much of the available data come from single-center cohorts, retrospective chart reviews, and studies with heterogeneous testing practices, which complicates interpretation. Distinguishing true C. difficile infection from colonization in patients with diarrhea of other causes is a persistent diagnostic challenge, and pandemic-era disruptions to infection-prevention bundles and testing algorithms further muddy the picture. What the review offers instead is convergence: multiple independent lines of clinical and experimental evidence that all point in the same direction, supporting what the authors describe as a cautious, testable hypothesis rather than a demonstrated causal relationship.

To move the field forward, the review calls for prospective studies with standardized CDI testing protocols, careful quantification of antimicrobial exposure, and integrated microbiome and metabolomic profiling of patients followed from acute COVID-19 through recovery. Such studies would need to track bile acid pools, inflammatory markers, and microbial community structure over time to determine whether SARS-CoV-2 infection produces a durable shift in colonization resistance, and whether that shift translates into elevated risk of primary or recurrent CDI. Mechanistic biomarker discovery, including the extracellular vesicle framework, would ideally proceed in parallel. The authors also underline the importance of clarifying prognosis and long-term consequences, since recurrent CDI carries substantial morbidity and mortality in the same older and medically complex populations that bore the heaviest burden of the pandemic.

The broader significance of the work lies in its reframing of COVID-19 as a condition with potential gastrointestinal sequelae mediated through the microbiome, rather than a purely respiratory illness. If the hypothesis holds, the implications extend beyond the acute pandemic: clinicians managing patients recovering from severe COVID-19 may need to weigh antibiotic stewardship more carefully, monitor for gastrointestinal symptoms after discharge, and consider gut-protective strategies such as targeted microbiome restoration. At the same time, the review’s disciplined separation of established observations from mechanistic speculation serves as a model for how the field should proceed. The interaction between a global respiratory pathogen and an opportunistic intestinal spore-former is almost certainly multifactorial, involving antimicrobial exposure, hospitalization dynamics, dysbiosis, barrier dysfunction, altered bile acid metabolism, and persistent inflammation. Untangling those threads will require exactly the kind of rigorous, longitudinal, mechanistically informed research that the authors advocate.

Subject of Research: Potential mechanisms linking COVID-19 and Clostridioides difficile infection through gut dysbiosis

Article Title: COVID-19 and clostridioides difficile infection: clinical overlap, gut dysbiosis, and mechanistic hypotheses

Article References: de Carvalho Leitão, R. F., da Silva Costa, D. V., Nguyen, A., Vieira, L. L., Nunes, P. I. G., Warren, C. A., Oriá, R. B., & de Castro Brito, G. A. (2026). COVID-19 and clostridioides difficile infection: clinical overlap, gut dysbiosis, and mechanistic hypotheses. Gut Pathogens. https://doi.org/10.1186/s13099-026-00862-0

Image Credits: AI Generated

DOI: 10.1186/s13099-026-00862-0

Keywords: COVID-19, Clostridioides difficile, SARS-CoV-2, ACE2, gut dysbiosis, renin-angiotensin system, bile acid metabolism, colonization resistance, inflammation, extracellular vesicles, hospitalization, antibiotic exposure

The stakes of this kind of work are hard to overstate. In the past two decades, three zoonotic coronaviruses—SARS-CoV-1, MERS-CoV, and SARS-CoV-2—have caused major outbreaks, and each emergence began with a virus crossing a species barrier. For sarbecoviruses, that barrier is defined largely by compatibility between the viral receptor-binding domain (RBD) on the spike protein and the host’s angiotensin-converting enzyme 2 (ACE2) receptor. If a virus’s RBD can engage a species’ ACE2 efficiently, that species becomes a plausible host; if it cannot, the chain of transmission breaks at the very first step. Understanding which receptors are vulnerable to which viruses is therefore central to anticipating where the next spillover might come from.

To build the atlas, the researchers first established an evolutionary framework. Phylogenetic analysis of the RBD sequences divided the 46 viruses—31 from bats, 10 from humans, three from civets, and two from pangolins—into three major clades, with clade 1 further splitting into subclades 1a and 1b. Clade 1a contains SARS-CoV-1 and related bat and civet strains; clade 1b contains SARS-CoV-2 and its closest relatives, including the bat virus RaTG13 and pangolin coronaviruses. Clade 2, which comprises most known sarbecoviruses, carries a distinctive double-segment deletion in the receptor-binding motif, while clade 3 viruses from African and European bats carry a single-segment deletion in the same region. These structural differences in the RBM, the loop that physically contacts ACE2, turned out to predict much of the functional variation the team later observed.

The functional screen itself relied on pseudotyped reporter viruses: vesicular stomatitis virus particles decorated with each sarbecovirus spike protein, whose entry into cells expressing a given ACE2 ortholog could be quantified by luminescence. The team confirmed comparable spike expression and incorporation across pseudovirus preparations by western blot and normalized viral input by quantitative RT-PCR, allowing a fair comparison across the roughly 3,000 possible virus-receptor pairings. The result is a heatmap of cross-species infectivity that functions as a kind of vulnerability index for each species’ receptor.

Clade 1 viruses emerged as the clear standouts in receptor breadth. Within clade 1b, the pangolin viruses PCoV-GD and PCoV-GX, which share 89.6 and 92.3 percent spike identity with SARS-CoV-2 respectively, showed broad ACE2 compatibility, with PCoV-GD efficiently infecting nearly all tested non-bat mammalian ACE2s and most bat ACE2s. Intriguingly, RaTG13—despite sharing 97.4 percent identity with SARS-CoV-2 across the full spike protein—displayed a more restricted host range, implying that subtle differences within the receptor-binding motif underlie the expanded tropism of SARS-CoV-2. Within clade 1a, human SARS-CoV-1 isolates used ACE2 orthologs from a wide range of bat families, whereas most bat- and civet-derived relatives showed narrower usage, with the bat virus WIV1 bridging human and bat lineages through its ability to engage ACE2 from multiple Rhinolophus and Myotis species.

Clade 2 and clade 3 viruses told very different stories. None of the clade 2 pseudoviruses, which represent the majority of known sarbecoviruses, mediated entry through any of the 66 ACE2 orthologs, consistent with their double RBM deletion and previously reported ACE2-independent entry mechanisms. Clade 3 viruses showed intermediate phenotypes: BtKY72 used ACE2 from only a few Rhinolophus species and did not engage human ACE2, while Khosta-2 showed broader tropism, infecting cells expressing rabbit ACE2 more than ten-fold more efficiently than those expressing the human receptor—a striking example of lineage-specific adaptation.

The study also delivered a decisive verdict on several proposed alternative receptors. Host factors including NRP1, CD147, AXL, and TMEM106B have each been suggested to facilitate SARS-CoV-2 entry in various experimental contexts. Yet across the entire 46-virus panel, none of these factors supported detectable infection when overexpressed in the assay cells, indicating that none functions as an independent entry receptor for any sarbecovirus tested. The authors are careful to note that context-dependent accessory roles in specific SARS-CoV-2 settings cannot be excluded, but the message is clear: ACE2 remains the only demonstrated primary entry receptor across this viral diversity.

Among the most consequential findings is the identification of two bat species whose receptors behave remarkably like the human version. Only the ACE2 orthologs of Rhinolophus affinis and Miniopterus schreibersii correlated strongly with human ACE2 usage across the viral panel, with correlation coefficients of 0.8314 and 0.8777 respectively. Surface plasmon resonance confirmed that M. schreibersii ACE2 binds the SARS-CoV-1 and SARS-CoV-2 RBDs with high affinity—dissociation constants of 8.14 × 10⁻⁸ M and 8.06 × 10⁻⁷ M, lower than human ACE2’s nanomolar binding but fully consistent with efficient entry. Because both species range across Southeast Asia, Europe, and North Africa in regions overlapping human habitats, the authors argue they should be priorities for ongoing surveillance. The data also flagged rabbits, cattle, sheep, raccoon dogs, badgers, Siberian chipmunks, and pigs as mammalian species whose ACE2 usage correlates strongly with human ACE2, marking them as candidate intermediate hosts worth investigating.

Perhaps the most mechanistically revealing part of the study concerns two closely related Miniopterus bats whose receptors sit at opposite ends of the permissiveness spectrum. M. schreibersii ACE2 supported entry by nearly all ACE2-dependent pseudoviruses, while the ACE2 of M. natalensis was entirely non-permissive—despite the two proteins differing by only seven amino acids. Three of those substitutions, at positions 27, 31, and 42, sit directly at the predicted RBD-binding interface. Molecular dynamics simulations using the molecular mechanics generalized Born surface area method showed that mutating M. schreibersii ACE2 residue I27 to lysine raised the binding free energy by roughly 5 kcal/mol, while the K42E substitution raised it by nearly 7 kcal/mol, disrupting a salt-bridge network involving residue D38 and the SARS-CoV-1 RBD residue Y442. Entry assays confirmed the simulations: the I27K mutation selectively impaired civet-derived SARS-CoV-1 entry, N31G had minimal impact, and K42E broadly abolished usage by nearly all pseudotypes. Reciprocally, introducing the corresponding M. schreibersii residues into M. natalensis ACE2 restored entry competence for multiple SARS-CoV-1 pseudotypes. Residues 27 and 42, in short, are the principal molecular switches governing Miniopterus receptor recognition.

The authors are candid about the limits of their approach. Pseudoviruses built from available sequences may not capture the full diversity of natural sarbecoviruses, and receptor compatibility is only one barrier to cross-species transmission; protease availability, replication competence, and immune evasion all matter for productive infection in a living animal. Efficient ACE2 engagement alone does not guarantee disease. Still, the atlas provides exactly the kind of mechanistic framework that field surveillance has lacked: a way to prioritize which of the world’s more than 1,400 bat species, and which of the hundreds of circulating sarbecovirus sequences, warrant the closest monitoring. As the authors put it, identifying species with ACE2 structures resembling the human receptor may help focus receptor-based risk assessment where it matters most—before, rather than after, the next spillover.

Subject of Research: Cross-species ACE2 receptor usage and host-range determinants of sarbecoviruses

Article Title: An atlas of sarbecovirus infectivity across diverse ACE2 orthologs

Article References: Sun, Y., Cheng, Z., Wu, X., Liu, K., Wang, L., Yang, D., Huang, W., & Nie, J. (2026). An atlas of sarbecovirus infectivity across diverse ACE2 orthologs. iScience, 29(10), Article 117769. https://doi.org/10.1016/j.isci.2026.117769

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117769

Keywords: sarbecovirus, ACE2, SARS-CoV-2, SARS-CoV-1, bats, spillover, pseudovirus, receptor-binding domain, host range, surveillance, Miniopterus, Rhinolophus

The research team, led by Franko O. Garcia-Solorzano and colleagues, registered their protocol in advance on PROSPERO and followed the PRISMA reporting guidelines, searching PubMed, Scopus, Embase, Web of Science and SciELO through August 2023. From 2,157 records initially recovered, the authors winnowed the literature down to 17 studies, most of which examined the 2020 to 2021 period of the pandemic. To qualify for inclusion, a study had to compare COVID-19 mortality rates or case fatality rates between high and low altitude populations, with the high-altitude category defined as above 1,500 meters above sea level. The included work fell into two broad types: thirteen population-based ecological studies, which compared aggregate death statistics across provinces, counties or states, and four individual-based cohort studies, which followed hospitalized patients at institutions located at different elevations. More than half of the studies, 58.8 percent, were conducted in Peru or Ecuador, two countries whose dramatic altitudinal gradients make them natural laboratories for this kind of research.

The methodological toolkit of the meta-analysis was deliberately conservative. For studies treating altitude as a dichotomous variable, the authors extracted risk ratios comparing the highest and lowest altitudes reported, along with 95 percent confidence intervals. For studies treating altitude continuously, they collected beta coefficients expressing the change in mortality per 100 meters of elevation, standardizing coefficients when the original studies used different units. All pooling was performed with random-effects models using the DerSimonian-Laird estimator, an appropriate choice given the expected heterogeneity across study sites, populations and outcome definitions. Risk of bias was assessed with the Joanna Briggs Institute critical appraisal tools, and the certainty of the pooled findings was graded using the GRADE framework, which starts observational evidence at a low baseline and can downgrade it further for bias and inconsistency.

That grading proved consequential. Every ecological study in the review carried a moderate or high risk of bias, with recurring failures to specify which COVID-19 diagnostic tests were used, a serious omission given the poor quality of many early-pandemic assays, and to control for confounders in their statistical models. Among the cohort studies, three of four had moderate risk of bias and one was rated high, with all studies showing substantial residual confounding despite identifying potential confounders. This pattern matters because ecological designs, which compare populations rather than individuals, are intrinsically limited in their ability to disentangle altitude from correlated factors such as access to health services, socioeconomic status and the quality of clinical management, and their results cannot be validly interpreted at the individual level.

The headline findings split by population type. In the primary meta-analysis of population-based studies, high altitude showed no statistically significant association with the mortality rate, the number of COVID-19 deaths per 100,000 inhabitants, with a pooled relative risk of 0.63 and a confidence interval spanning from 0.35 to 1.15. When altitude was analyzed as a continuous variable, each 100-meter increase in elevation was associated with a beta coefficient of 0.03, with a confidence interval from negative 0.62 to 0.67, again indicating no detectable gradient. The case fatality rate in the general population likewise showed no significant difference between high and low elevations, with a pooled relative risk of 1.10. However, in a sensitivity analysis that excluded the studies judged to be at high risk of bias, a different picture emerged: living at high altitude was associated with a 51 percent reduction in the mortality rate compared with low altitude, a relative risk of 0.49 with a confidence interval of 0.30 to 0.80.

The individual-based evidence told a more consistent story. Pooling the four cohort studies of hospitalized patients, the authors found that COVID-19 patients treated at high altitude had a 29 percent lower risk of death than those treated at lower elevations, with a relative risk of 0.71 and a confidence interval of 0.52 to 0.98. This result held up when the single high-risk study was excluded, with the protective association strengthening to a 33 percent reduction, relative risk 0.67, confidence interval 0.59 to 0.75. Notably, the protective effect was smaller among patients admitted to intensive care units than among hospitalized patients overall, a pattern the authors attribute to the severity of hypoxemia and the inherently elevated baseline mortality in critically ill populations, which may overwhelm any physiological advantage conferred by altitude acclimatization.

What biological mechanisms could underlie such a protective effect? The authors point to the suite of adaptations that high-altitude residents develop through chronic exposure to hypoxia, including increased ventilatory drive, higher hematocrit values, enhanced oxygen delivery at the tissue level and metabolic adjustments that improve tolerance to low oxygen availability. These adaptations could, in principle, blunt the hypoxemia produced by SARS-CoV-2 infection. A second, more molecular hypothesis involves angiotensin-converting enzyme 2, the receptor the virus uses to enter host cells. Chronic hypoxia states are associated with downregulation of ACE2 in the pulmonary epithelium, and infection rates have been correlated with the level of ACE2 expression, offering a plausible route by which altitude could reduce susceptibility. Environmental factors may contribute as well: higher ultraviolet radiation at elevation can inactivate virus, and colder temperatures may reduce the social interactions that drive transmission.

The review also flags important nuances and gaps. Some studies suggest that any protective effect may diminish above roughly 3,500 to 4,000 meters, possibly because chronic mountain illness offsets the benefits of acclimatization, and the authors caution that altitude gradients are difficult to study because each elevation band may carry its own distinct local factors, a point captured in the ecologist Christian Körner’s observation that there is no standard mountain. The heterogeneity of altitude cut-offs across studies, ranging from below 500 meters to 4,000 meters or more, further complicates comparison. The authors also note that no study has yet examined whether altitude modifies the immunological response to COVID-19 vaccination, and that ecological studies generally failed to specify how long their populations had actually lived at the altitudes recorded. A related line of evidence, meanwhile, suggests altitude may influence the proportion of asymptomatic infections, which would distort case fatality comparisons by changing the denominator of detected cases.

The GRADE assessment delivered the sobering bottom line: every outcome in the review, from population mortality rates to hospitalized case fatality, was rated as very low certainty, downgraded for risk of bias and for heterogeneity exceeding 80 percent in the pooled analyses. The authors are candid that residual confounding is almost unavoidable when comparing populations at different elevations, since altitude is inseparable from geography, climate, ethnicity, income and health system capacity. Their conclusion is measured rather than triumphant: the primary analysis suggests high altitude makes little to no difference in COVID-19 mortality in the general population, while the sensitivity analyses hint at a protective effect that remains very uncertain. What the review does establish is a roadmap for future work, calling for studies with standardized altitude definitions, rigorous confounder control and consistent outcome reporting. With hundreds of millions of people living above 1,500 meters worldwide, and with several respiratory viruses remaining on the list of pandemic threats, clarifying how elevation shapes infection outcomes is far more than an academic curiosity.

Subject of Research: The effect of high-altitude residence on COVID-19 mortality and case fatality rates

Article Title: Effect of altitude on COVID-19 mortality: A systematic review and meta-analysis

Article References: Garcia-Solorzano, F. O., Ortiz-Abanto, Y., Pachacama, L. F., Solis-Facho, G. V., & Taype-Rondan, A. (2026). Effect of altitude on COVID-19 mortality: A systematic review and meta-analysis. Heliyon, 12(15), Article e45528. https://doi.org/10.1016/j.heliyon.2026.e45528

Image Credits: AI Generated

DOI: 10.1016/j.heliyon.2026.e45528

Keywords: COVID-19, altitude, mortality, meta-analysis, systematic review, hypoxia, ACE2, epidemiology, Peru, Ecuador, case fatality rate, GRADE

The clinical backdrop to the work is well established. Epidemiological studies have repeatedly shown that patients with Parkinson’s disease face a strikingly elevated risk of osteoporosis and osteoporotic fractures, a burden that exceeds what can be explained by poor mobility, falls, or age alone. Meta-analyses cited by the researchers indicate high rates of osteoporotic fracture in Parkinson’s disease, and cross-sectional clinical work has associated biomarkers such as serum uric acid with reduced bone mineral density in affected patients. Yet the molecular mechanisms that bind neurodegeneration to bone loss have remained murky. The Henan University team set out to interrogate that relationship experimentally, asking whether a single genetic factor—absence of ACE2—could simultaneously perturb dopaminergic neuron survival in the brain and bone homeostasis in the skeleton.

To do so, the researchers used a well-characterized mouse model of parkinsonism in which the neurotoxin MPTP, or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, selectively destroys dopamine-producing neurons in the substantia nigra. Crucially, they crossed this challenge with mice lacking a functional ACE2 gene—specifically Ace2-null males, designated Ace2−/y—because ACE2 sits at the center of the protective arm of the renin-angiotensin system, converting angiotensin II into angiotensin-(1–7), a peptide with documented anti-inflammatory and neuroprotective actions. Previous studies from other groups and from the same team had shown that ACE2 activation mitigates behavioral deficits and neuroinflammation in chemically induced Parkinson’s models, and that the ACE2/Ang-(1–7)/Mas cascade strengthens bone structure and metabolism. The new study asked what happens when this protective factor is removed entirely under parkinsonian stress.

Behavioral testing revealed a clear aggravating effect. MPTP exposure significantly worsened motor dysfunction and depression-like behaviors in the mice, and the combination of MPTP toxicity with ACE2 deficiency produced a particularly severe pathological picture in the brain. Immunohistochemistry, Western blotting, and histopathological staining showed reduced activity of dopaminergic neurons and heightened microglial activation—the inflammatory response of the brain’s resident immune cells. At the molecular level, the researchers measured elevated levels of total α-synuclein, the misfolding-prone protein that defines Parkinson’s pathology, alongside increased abundance of Caspase-3 and Bax, two canonical executioners of programmed cell death. Together, these markers indicate that ACE2 loss intensifies both the protein aggregation burden and the apoptotic pressure on vulnerable neurons.

The bone findings were equally striking, and notably they emerged in parallel rather than secondarily. In the skeletal tissue of the Ace2-deficient mice, the team documented reduced abundance of total Wnt ligands, β-catenin, bone morphogenetic proteins (BMP), and insulin-like growth factor 1 (IGF-1), along with diminished phosphorylation ratios of the downstream kinases that transmit these signals. This matters because each of these cascades is a cornerstone of bone formation: Wnt/β-catenin signaling drives osteoblast differentiation and bone accrual, BMPs are potent inducers of bone formation used clinically in spine fusion and fracture repair, and IGF-1 couples muscle and bone metabolism through mTOR-dependent pathways. The researchers are careful to note that the parallel reduction of these signaling proteins suggests potential perturbation of the cascades rather than definitive proof of pathway failure, a distinction that reflects appropriate scientific caution.

In the opposite direction, ACE2 deficiency upregulated mediators of the RANKL/RANK/OPG axis, a triad that governs osteoclast formation and bone resorption. RANKL binding to RANK on osteoclast precursors drives the differentiation of bone-resorbing cells, while OPG acts as a soluble decoy receptor that restrains the process. Dysregulation of this axis tilts bone turnover toward net loss. Intriguingly, the same axis operates in the brain, where it has been identified as a critical inflammatory signaling system in ischemic injury, and Rho GTPases downstream of these pathways modulate osteoclast differentiation directly. The coordinated shift of this inflammatory skeletal axis in both brain and bone tissue under ACE2 deficiency is one of the study’s most suggestive observations, hinting at a common pathological language spoken by the two organs.

To move from candidate pathways to gene-level targets, the team turned to transcriptomics. They mined public GEO datasets and applied weighted gene co-expression network analysis, or WGCNA, a computational method that groups genes into modules based on correlated expression patterns and identifies the hub genes most central to disease-associated modules. This analysis pinpointed ten hub genes, including DNM1, which encodes dynamin 1, a protein essential for synaptic vesicle recycling; OCRL, a phosphatidylinositol phosphate phosphatase linked to the oculocerebrorenal syndrome; and OPA1, a mitochondrial fusion protein whose mutations cause dominant optic atrophy and which has been implicated in mitochondrial parkinsonism through stem cell modeling. The dysregulation of these genes was linked to synaptic dysfunction and inflammation—two processes squarely at the heart of Parkinson’s pathophysiology.

The team then evaluated whether these hub genes could serve as diagnostic biomarkers. Using receiver operating characteristic, or ROC, analysis on public single-disease transcriptome datasets for Parkinson’s disease and osteoporosis separately, they found that the core gene signatures achieved areas under the curve ranging from 0.683 to 0.981, indicating diagnostic accuracy that spans moderate to near-perfect discrimination. Functional enrichment of the core genes pointed to involvement in synaptic signaling, MAPK signaling, and the Rap1 and Ras pathways—small GTPase cascades that regulate cell proliferation, differentiation, and cytoskeletal dynamics in both neurons and bone cells. Such dual-diagnostic performance, if replicated in human cohorts, would suggest that a shared molecular signature underlies both conditions and could be exploited clinically to identify patients at risk of combined neurodegenerative and skeletal decline.

The authors are appropriately measured in their claims. They emphasize that these are preclinical findings obtained under short-term MPTP treatment in growing young male mice, meaning that the observed bone metabolic disturbance was transient and that the results may not translate directly to elderly human patients, in whom Parkinson’s disease typically manifests and in whom bone loss is chronic and sex-dependent. They also stress that the coordinated dysregulation observed in brain and bone is consistent with a bone-brain axis pathological phenotype, but that the current experimental design cannot confirm causal bidirectional cross-talk between the tissues. Distinguishing whether ACE2 deficiency independently damages both organs, or whether pathology in one propagates to the other—perhaps through circulating osteocalcin, sympathetic nervous system output, or inflammatory mediators—will require interventional studies that manipulate one tissue and measure the other.

Even with those caveats, the study offers a compelling framework and a set of concrete targets for follow-up. Restoring ACE2 activity or mimicking its product, angiotensin-(1–7), has already shown neuroprotective effects in experimental Parkinson’s models, including reduced α-synuclein expression through the NEAT1/miR-153-3p axis, and ACE2 activation has been reported to promote hippocampal neurogenesis via Wnt/β-catenin signaling. The present results raise the possibility that such therapies could carry a skeletal benefit as well, protecting against the osteoporosis that so often compounds the disability of Parkinson’s disease. The ten hub genes, meanwhile, provide a molecular shortlist for mechanistic validation, and their diagnostic AUC values justify testing in human blood or tissue datasets. As the bone-brain axis matures from a descriptive concept into a mechanistic research program, work like this demonstrates how a single molecule, studied across two organs at once, can illuminate disease connections that medicine has long observed clinically but struggled to explain at the level of genes and signaling pathways.

Subject of Research: ACE2-dependent molecular mechanisms linking Parkinson's disease neurodegeneration and bone metabolic alterations via the bone-brain axis

Article Title: ACE2 and Parkinsonism‑related bone metabolic alterations: signaling pathways and hub gene analysis

Article References: Liu, T., Ren, Y., Tian, X., & Wei, J. (2026). ACE2 and Parkinsonism‑related bone metabolic alterations: signaling pathways and hub gene analysis. Molecular Genetics and Genomics, 301(1), Article 185. https://doi.org/10.1007/s00438-026-02511-2

Image Credits: AI Generated

DOI: 10.1007/s00438-026-02511-2

Keywords: Parkinson's disease, ACE2, bone metabolism, bone-brain axis, osteoporosis, Wnt/beta-catenin signaling, RANKL/RANK/OPG, IGF-1, hub genes, WGCNA, alpha-synuclein, MPTP mouse model