Haematitum occupies an unusual place in the Chinese Materia Medica. Classified as a mineral-based medicine rather than a plant or animal product, it is used clinically as a hemostatic and antiemetic, and classical texts warn that it should not be taken for long stretches. Modern toxicology has largely confirmed those warnings, documenting lung toxicity in both animal models and clinical observations, but the underlying biology has remained murky. Toxicity studies of mineral medicines often stop at the tissue level, leaving open the question of which cells fail first and which molecular signals carry the injury from one organ system to another.

To answer those questions, the researchers established a mouse model of Haematitum-induced lung injury and then interrogated it with three complementary technologies. Sixteen S ribosomal RNA sequencing mapped shifts in the gut bacterial community, untargeted metabolomics catalogued the small molecules accumulating in lung tissue, and single-cell RNA sequencing constructed a comprehensive atlas of the lung’s cellular landscape, capturing the gene-expression signatures of every major cell type simultaneously. This combined approach allowed the team to connect events at three scales at once: the microbial ecosystem of the intestine, the metabolic chemistry of the lung, and the behavior of individual immune cells within it.

The first domino to fall, according to the data, is the intestinal barrier. Mice receiving high-dose Haematitum showed clear disruption of the gut lining, the selective wall of epithelial cells that normally confines the trillions of microbes in the intestine while allowing nutrients to pass. With that wall compromised, the composition of the microbiome shifted dramatically, and the relative abundance of Klebsiella, an opportunistic bacterial genus notorious for its role in hospital-acquired infections, rose sharply. Microbial metabolites that should have remained sealed within the bowel began entering the bloodstream, hitching a ride through the circulation toward distant organs, including the lungs.

Once those metabolites reached the lung, correlation analysis revealed a striking statistical association between gut dysbiosis and disturbances in a single metabolic network: the glycerophospholipid pathway. Glycerophospholipids are the phospholipid building blocks of cellular membranes and the constituents of pulmonary surfactant, the fatty film that keeps the air sacs of the lung from collapsing. Disruption of this pathway implies that the injured lung was not merely inflamed but was also losing the lipid machinery required for structural integrity and normal immune signaling, creating a metabolically destabilized environment in which immune cells were primed to misfire.

The single-cell data then identified the two cell types at the center of the injury: macrophages and neutrophils. Macrophages, the lung’s resident sentinels, normally enforce calm by patrolling the tissue and suppressing excessive inflammation. The sequencing showed that the PPAR signaling pathway in these macrophages had been inhibited. PPAR, or peroxisome proliferator-activated receptor, is a nuclear receptor that regulates lipid metabolism and anti-inflammatory gene programs; when its activity drops, macrophages lose their anti-inflammatory identity. In the Haematitum-exposed mice, the silenced macrophages began releasing inflammatory factors, most notably tumor necrosis factor-alpha, a potent pro-inflammatory cytokine that functions as a broadcast alarm to the rest of the immune system.

TNF-alpha, in this model, acted as the messenger that recruited and reshaped the second cast member. Colocalization experiments confirmed the spatial relationship between macrophages and the cytokine, while the single-cell analysis showed that neutrophils exposed to the signal activated their own TNF signaling pathway. Neutrophils are the immune system’s shock troops, short-lived cells packed with destructive enzymes and reactive chemicals designed to annihilate pathogens. When appropriately activated, they are lifesavers; when triggered inappropriately, they shred healthy tissue. Under the influence of macrophage-derived TNF-alpha, the neutrophils in the injured lungs acquired what the authors describe as a highly destructive phenotype, and the synergy between the two cell types drove both inflammation and apoptosis, or programmed cell death, across the lung tissue.

Crucially, the team did not stop at correlation. By pharmacologically manipulating the axis they had identified, administering a PPAR-gamma agonist to restore the macrophage pathway, or a TNF-alpha inhibitor to block the cytokine signal, they showed that cellular abnormalities could be effectively reversed and lung injury significantly alleviated. That interventional rescue is the strongest evidence that the PPAR-gamma/TNF-alpha axis is not merely a bystander in the toxicity but its functional core. It also immediately suggests a therapeutic strategy: drugs that prop up anti-inflammatory macrophage programs or mop up excess TNF-alpha could, in principle, mitigate the pulmonary side effects of prolonged mineral medicine use.

The study also offered a solution rooted in the tradition itself. Haematitum is classically paired with Inula japonica Thunb., a flowering herb used in combination formulas for respiratory complaints, and the researchers evaluated this pairing in their model. The combination reduced lung toxicity, and computational prediction suggested that components within Inula japonica act as natural PPAR-gamma agonists, effectively replenishing the very pathway that Haematitum suppresses. Meanwhile, mice that received Haematitum at a common clinical dose rather than a high dose avoided the severe cascade altogether, reinforcing the traditional dosing guidance and suggesting that the toxicity is dose-dependent rather than intrinsic at all exposure levels.

Beyond its immediate implications for one traditional medicine, the work carries broader lessons for the toxicology of mineral-based drugs and for the rapidly growing field of gut-lung axis research. It demonstrates that organ toxicity can originate far from the organ that suffers it, with a disrupted intestinal barrier serving as the gateway for circulating microbial metabolites that rewire metabolism and immunity elsewhere in the body. It also provides a template for how single-cell transcriptomics, metabolomics, and microbiome sequencing can be braided together to resolve multi-organ toxicity mechanisms that no single technology could untangle alone. For clinicians and regulators weighing the safety of mineral medicines, the message is concrete: protect the gut, respect the dose, and watch the PPAR-gamma/TNF-alpha axis as a biomarker of trouble ahead. The authors note that these findings advance understanding of mineral medicine toxicology and offer a reference framework for the safe clinical application of traditional Chinese medicines whose ancient warnings, it turns out, described a molecular pathway that modern science has only now begun to read.

Subject of Research: Mechanism of Haematitum-induced lung injury mediated by gut dysbiosis and macrophage-neutrophil crosstalk along the gut-lung axis

Article Title: Single-cell transcriptomics reveals macrophage-neutrophil crosstalk in Haematitum-induced lung injury associated with gut dysbiosis

Article References: Single-cell transcriptomics reveals macrophage-neutrophil crosstalk in Haematitum-induced lung injury associated with gut dysbiosis. (n.d.). https://doi.org/10.1186/s12967-026-08954-w

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08954-w

Keywords: Haematitum, gut-lung axis, gut dysbiosis, Klebsiella, macrophages, neutrophils, TNF-alpha, PPAR signaling, glycerophospholipid metabolism, single-cell RNA sequencing, traditional Chinese medicine, lung injury

The relationship begins with anatomy. Blood from much of the intestine travels directly to the liver through the portal vein, carrying nutrients, microbial products and chemical signals absorbed across the intestinal wall. Under healthy conditions, the liver acts as a biochemical filter, while the intestinal barrier limits the passage of potentially harmful substances. This barrier is maintained by mucus, epithelial cells and protein complexes known as tight junctions, which seal the spaces between neighboring cells. When inflammation, infection, dietary stress or metabolic disease weakens these defenses, bacterial components can cross into the circulation and place the liver under sustained immune pressure.

Among the most important signals are pathogen-associated molecular patterns, or PAMPs, such as lipopolysaccharide from the outer membrane of Gram-negative bacteria. Damage-associated molecular patterns released by injured host cells can intensify the same response. In the liver, these molecules are detected by pattern-recognition receptors, including Toll-like receptors and NOD-like receptors, on immune cells and other hepatic cell types. Activation of these sensors stimulates transcription factors such as NF-κB and promotes the production of cytokines including tumour necrosis factor, interleukin-1β and interleukin-6. A short-lived response can be protective, but persistent signalling may drive chronic inflammation and fibrosis.

The review also highlights the microbiome as a chemical partner in gut–liver communication. Intestinal bacteria transform dietary components into short-chain fatty acids, including acetate, propionate and butyrate, which influence epithelial integrity, immune-cell activity and energy metabolism. Other microbial products can be harmful when produced in excess or insufficiently cleared. Changes in bacterial composition, known as dysbiosis, may increase the generation of ethanol, ammonia, indole derivatives or other metabolites that affect hepatic inflammation. The biological impact depends not only on which microbes are present, but also on their activity, the integrity of the intestinal barrier and the liver’s ability to process incoming compounds.

Bile acids create a second major communication circuit. Produced in the liver and released into the intestine, these molecules aid fat digestion before being modified by intestinal bacteria and returned through the enterohepatic circulation. Beyond their digestive role, bile acids act as signalling molecules through receptors such as the farnesoid X receptor and the G-protein-coupled bile acid receptor TGR5. These pathways help regulate lipid and glucose metabolism, immune responses and the composition of the microbiome. Disrupted bile-acid synthesis, transport or microbial conversion can therefore affect both intestinal inflammation and liver disease, linking metabolic disorders to changes in immune signalling.

This network becomes particularly important in conditions such as metabolic dysfunction-associated steatotic liver disease, alcohol-associated liver disease, inflammatory bowel disease and advanced liver fibrosis. In metabolic liver disease, excess dietary energy and insulin resistance can promote fat accumulation in hepatocytes, while microbial products and inflammatory mediators amplify cellular stress. Kupffer cells, the liver’s resident macrophages, respond to these signals and communicate with stellate cells. Once activated, stellate cells produce extracellular matrix proteins, including collagen, that gradually remodel liver tissue. Persistent matrix deposition can lead to fibrosis and, in severe cases, cirrhosis.

The authors describe the gut–liver axis as a therapeutic opportunity, but the review also suggests why simple solutions have often failed. Antibiotics may reduce selected bacterial signals but can disrupt beneficial communities and promote resistance. Probiotics and prebiotics can influence microbial ecology, although their effects may vary according to the patient’s diet, baseline microbiome and disease stage. Approaches under investigation include targeted microbial consortia, postbiotics, faecal microbiota transplantation, engineered bacteria and dietary strategies designed to restore production of protective metabolites. The central challenge is to modify the ecosystem precisely rather than suppressing it indiscriminately.

Drug development is also moving toward the molecular links that connect intestinal signals with hepatic inflammation. Potential targets include receptors that detect microbial products, enzymes involved in bile-acid metabolism, inflammatory cytokine pathways and mechanisms controlling epithelial tight junctions. Therapies designed to alter bile-acid signalling or reduce fibrogenic activation in the liver could potentially interrupt disease progression. However, the review emphasizes that the gut–liver axis is highly individualized. Sex, age, genetics, medication use, diet and environmental exposures can all influence microbial communities and immune responses, making broad treatment strategies difficult to apply uniformly.

Future progress may depend on combining multiple forms of biological information. Metagenomic sequencing can identify microbial genes, while metabolomics reveals the compounds actually produced in the intestine and transported to the liver. Imaging, immune profiling and computational modelling may then connect these molecular signals to tissue damage and clinical outcomes. Such integrated approaches could help distinguish harmless dysbiosis from the specific microbial and metabolic patterns that predict inflammation or fibrosis. The emerging picture is not of a single disease pathway, but of a dynamic network that can be measured, manipulated and, potentially, reset.

By bringing together immunology, microbiology, hepatology and metabolism, Murao, Aziz and Wang position inflammatory gut–liver crosstalk as a central problem in modern medicine. The review’s message is both cautionary and promising: damage in one organ can reverberate through the entire network, but that same connectivity creates several points for intervention. Treatments that protect the intestinal barrier, rebalance microbial chemistry and calm excessive hepatic immune activation could eventually offer more precise ways to prevent chronic liver disease before irreversible scarring develops.

Subject of Research: Inflammatory communication between the gut and liver, including the roles of the intestinal barrier, microbiome, microbial metabolites, bile acids, immune signalling and potential therapeutic targets.

Article Title: Inflammatory gut–liver crosstalk: mechanisms and therapeutic targets

Article References: Murao, A., Aziz, M. & Wang, P. “Inflammatory gut–liver crosstalk: mechanisms and therapeutic targets.” Experimental & Molecular Medicine (2026). https://doi.org/10.1038/s12276-026-01810-3

Image Credits: AI Generated

DOI: 10.1038/s12276-026-01810-3

Keywords: gut–liver axis, intestinal barrier, microbiome, bile acids, inflammation, liver disease, fibrosis, microbial metabolites, immune signalling, therapeutic targets