The new approach, described in Frontiers in Analytical Science by Rong Fu, Diane J. Sutcliffe, Ashok R. Dinasarapu, Ellen J. Hess and H. A. Jinnah, relies on ultra performance liquid chromatography coupled with photodiode array ultraviolet detection, commonly abbreviated UPLC-PDA. Unlike mass spectrometry-based metabolomics, which can be expensive and technically demanding, PDA detection exploits the strong ultraviolet absorbance of purines at 254 nanometers, allowing straightforward identification by retention time and spectral profile. The system consists of a Waters ACQUITY H-Class plus core with a quaternary solvent manager and an eLambda PDA detector, operating on a 2.1 by 100 millimeter reverse-phase C18 column packed with 1.8 micrometer particles at 40 degrees Celsius.

Separation chemistry is the crux of the method. Purines carry ionizable groups whose charge states shift dramatically with pH, so the Emory team designed a stepped gradient between two carefully formulated buffers. Buffer A contains 10 millimolar ammonium acetate and 1.5 millimolar tetrabutylammonium phosphate at pH 5.0, while buffer B contains 10 millimolar ammonium phosphate with the same ion-pairing reagent and 25 percent acetonitrile at pH 7.0. The tetrabutylammonium phosphate acts as an ion-pairing agent, taming the highly polar nucleotides so they interact with the reverse-phase column and elute as discrete peaks rather than co-eluting in the void volume. The gradient holds 100 percent buffer A for 11 minutes, ramps to 75 percent buffer B, then climbs to 100 percent buffer B before the column re-equilibrates for 9.5 minutes ahead of the next injection.

With this configuration, the method resolves all 15 target metabolites: ATP, ADP, AMP, adenosine, adenine, GTP, GDP, GMP, IMP, ZMP, guanosine, hypoxanthine, inosine, xanthine and uric acid. Only 5 microliters of sample are injected per run. Calibration with purified standards confirmed linear detection across a remarkable four-order-of-magnitude range from 0.1 to 100 micromolar, with all metabolites detectable down to approximately 100 nanomolar. Reproducibility proved equally impressive. When the same sample was analyzed five times within a single batch and across three batches on different days, the within-run coefficient of variance averaged 0.8 percent and the between-run variance averaged 1 percent for most analytes, comfortably under the 2 percent threshold the authors cite as evidence of excellent reliability.

The improvements over the team’s earlier HPLC-PDA method are substantial. The original technique required 65 minutes per sample; the new UPLC version cuts that to 33 minutes. Sensitivity is higher with half the sample volume, a critical advantage when working with scarce clinical specimens or small cell cultures. Perhaps most importantly, the new method cleanly discriminates GMP from IMP, two metabolites that co-eluted and could not be separately quantified with the older protocol. Because GMP and IMP occupy distinct positions in purine interconversion pathways, their separate measurement opens new analytical possibilities for studies of guanine nucleotide synthesis and purine salvage.

To demonstrate performance in genuine biological material, the researchers applied the method to induced pluripotent stem cells derived from three publicly available lines: KOLF2.0, NCRM1 and PGP-1. Each line was studied in matched pairs, with and without a c.508C>T stop codon mutation in the HPRT1 gene. This mutation abolishes hypoxanthine-guanine phosphoribosyltransferase, the salvage enzyme whose complete loss causes Lesch-Nyhan disease, a rare X-linked disorder marked by self-injurious behavior, dystonia and severe motor impairment. Cells were grown in six-well plates to roughly one million cells per well, with culture medium freshly replaced 24 hours before collection.

Sample preparation demanded meticulous attention to chemistry. For intracellular purines, cells were released by trypsinization, pelleted, and extracted in 0.2 molar perchloric acid, which instantly denatures the enzymes that would otherwise degrade labile nucleotides. Sonication at 4 degrees Celsius liberated the contents, and after centrifugation the acidic supernatant was neutralized with potassium carbonate, precipitating potassium perchlorate before final filtration through PVDF microcentrifuge tubes. For extracellular purines, 450 microliters of conditioned medium were acidified with perchloric acid to 0.1 molar and processed identically. Intracellular results were normalized to total cellular protein measured with a BCA assay, while extracellular results were corrected for culture volume and duration.

The biological findings were striking. In keeping with decades of prior work, the adenine derivatives dominated the intracellular purine pool, with ATP present in the greatest amounts, roughly 33 to 46 nanomoles per milligram protein across the lines, followed by GTP at 11 to 16 nanomoles per milligram. The adenylate energy charge, calculated as ([ATP] + 0.5 × [ADP]) / ([ATP] + [ADP] + [AMP]), ranged from 0.81 to 0.88, confirming that all cultures retained a healthy nucleotide energy state above the 0.80 benchmark typical of viable cells. Multivariate analysis of variance revealed significant main effects for both mutation status and cell type, along with a significant interaction between the two variables.

Most intracellular purines showed small or no changes in the HPRT1-mutant cells, but the extracellular compartment told a very different story. Conditioned medium contained no detectable purines except hypoxanthine, which was elevated by an average of 30-fold in the mutant lines, with individual increases ranging from 12-fold to as much as 225-fold depending on the genetic background. The explanation is elegant: without functional HPRT, the cells cannot recycle hypoxanthine back into nucleotides, so they simply dump it into the extracellular space. This finding underscores why measuring extracellular purines is essential, since changes outside the cell were far more obvious than those within it.

The authors acknowledge limitations. The method focuses on free purines and does not capture purines incorporated into DNA, RNA, NAD(H), NADP(H), FAD(H) or other complex molecules, though it can be adapted for some of these derivatives. Cyclic nucleotides and deoxynucleotides occur at levels too low for direct detection without prior sample concentration. The team also emphasizes the extraordinary speed of purine degradation: within seconds, ATP is dephosphorylated to ADP and then AMP, and within minutes AMP is further catabolized to adenosine, inosine, hypoxanthine and uric acid. Tissue measurements demand freeze-clamping in situ or focused microwave irradiation to halt degradation. Finally, the authors caution that isolated ATP measurements can be misleading, since they cannot distinguish energy impairment from wholesale purine depletion; only the simultaneous measurement of ATP, ADP and AMP, captured by the adenylate energy charge, provides a faithful picture of cellular energy state. With its speed, sensitivity and comprehensive coverage, the new UPLC-PDA method appears well suited to simultaneous analysis of the most abundant biologically relevant purines across blood, urine, cerebrospinal fluid and cultured cells, offering a powerful new lens on disorders of purine metabolism.

Subject of Research: Biomedical Analysis and Diagnostics

Article Title: Comprehensive measurement of purines in biological samples

Article References: Fu, R., Sutcliffe, D. J., Dinasarapu, A. R., Hess, E. J., & Jinnah, H. A. (2025). Comprehensive measurement of purines in biological samples. Frontiers in Analytical Science, 5, Article 1600781. https://doi.org/10.3389/frans.2025.1600781

Image Credits: AI Generated

DOI: 10.3389/frans.2025.1600781

Keywords: purine metabolism, UPLC-PDA, Lesch-Nyhan disease, hypoxanthine, adenylate energy charge, metabolomics, HPRT1, analytical chemistry, Comprehensive, measurement, purines, biological

The logic behind this enduring popularity is structural. Purine is a fused pyrimidine–imidazole ring system whose shape and hydrogen-bonding pattern closely mimic the adenine portion of ATP, the universal energy currency of the cell. Because many disease-driving enzymes, particularly kinases, bind ATP in deep, well-defined pockets, purine-based molecules can slide into those sites and block them with remarkable efficiency. The review emphasizes that this ATP-like architecture is precisely why purine derivatives have become such productive kinase inhibitors, and why the scaffold appears in marketed drugs spanning immunosuppression, antiviral therapy, gout treatment, asthma, and leukemia, including azathioprine, acyclovir, allopurinol, theophylline, and clofarabine.

The most impressive potency numbers in the review come from anticancer work, where purine derivatives have been optimized against an expanding roster of molecular targets. A 2,9-disubstituted purine designed to inhibit the mutant EGFR variant L858R, a common driver of non-small-cell lung cancer, achieved an inhibitory concentration of just 1.9 nanomolar while suppressing receptor phosphorylation and reducing tumor growth in animal models. Other purine compounds have reached similarly low nanomolar potency against the PI3Kα signaling kinase, the mTOR regulator, the FLT3 kinase implicated in acute myeloid leukemia, and the Bcr-Abl fusion protein that defines chronic myeloid leukemia, with one trisubstituted derivative inhibiting Abl1 at 15 nanomolar and another blocking CDK9 at 11.3 nanomolar in leukemia cells.

Structure–activity relationship analysis across these anticancer series reveals consistent design rules. Modifications at the C-6 position of the purine ring are especially influential: arylamine or heteroaromatic substituents placed there create additional hydrophobic contacts within kinase binding pockets and reliably boost potency against CDK, EGFR, VEGFR, FLT3, and mTOR targets. Electron-withdrawing groups such as fluoro, chloro, and trifluoromethyl on attached aromatic rings strengthen binding through hydrophobic interactions, and halogenation is a recurring feature among the most active EGFR inhibitors. Substitutions at C-2, N-7, C-8, and N-9 fine-tune selectivity and cellular uptake, with piperazine rings and other cyclic amines at N-9 repeatedly shown to increase both kinase inhibition and cytotoxicity. Fused frameworks such as triazolopurines and pyrazolopyrimidines generally outperform simple purines because their added rigidity locks molecules into productive binding conformations.

Importantly, the review connects these small-molecule successes to fundamental cell biology. Blocking de novo purine biosynthesis at the enzyme GARFT starves cells of guanine nucleotides, which in turn limits the formation of GTP-bound Rheb, a small GTPase required to activate mTORC1 at the lysosomal membrane. Without that activation, protein synthesis stalls and cancer cell proliferation collapses. This pathway explains why purine metabolism itself, not merely purine-shaped inhibitors, has become a therapeutic target, and it aligns with separate findings that glioblastoma cells resist temozolomide by ramping up one-carbon-mediated purine synthesis, and that breast cancer metastasis depends on purine synthesis regardless of the local nutrient environment.

Beyond oncology, the review catalogs substantial progress against infectious diseases, exploiting a different structural vulnerability: many pathogens cannot make purines from scratch. The malaria parasite Plasmodium falciparum lacks a complete de novo pathway and must scavenge purines from host red blood cells through a salvage route funneled by the enzyme PfHGXPRT. Designers have attacked this dependency from several angles, and the most potent result is a 4-aminoquinoline–purine hybrid that reached 80 nanomolar activity against chloroquine-resistant parasites by combining heme detoxification disruption with purine metabolism interference. Acyclic nucleoside bisphosphonates targeting HGXPRT show moderate but highly selective activity, while nucleoside analogues with sugar-like fragments achieve better uptake through parasite transporters.

The antimicrobial sections document equally diverse mechanisms. Ethanol-bridged purine–azole hybrids inhibit methicillin-resistant Staphylococcus aureus at micromolar concentrations, apparently through membrane disruption and DNA interactions, while purine–benzimidazole hybrids beat norfloxacin against resistant strains. On the antifungal front, isothiazole–purine hybrids kill the rice pathogen Rhizoctonia solani by inhibiting pyruvate kinase, and a new class of purine analogues targeting fungal inositol polyphosphate kinases suppresses Cryptococcus neoformans by roughly 95 percent and synergizes with amphotericin B. N-9 substituted purines bearing morpholine rings match fluconazole against Candida albicans, with dihydrofolate reductase implicated as the target. In tuberculosis, the standouts include a purine derivative blocking the MbtA enzyme of mycobactin iron acquisition at 0.049 micromoles per liter and compounds inhibiting the cell-wall biosynthesis enzymes DprE1 and MurB, with amino acid conjugation and piperazine substitution emerging as recurring potency enhancers.

Antiviral applications extend the scaffold’s reach from human pathogens to crop protection. Chiral purine derivatives have shown activity against both acyclovir-sensitive and acyclovir-resistant herpes simplex virus type 1, with stereochemistry proving decisive, while purine-based phosphonates inhibit the adenylate cyclase toxin of Bordetella at 16 nanomolar. Against SARS-CoV-2, dimethylxanthine derivatives designed as dual inhibitors of the viral main protease and RNA-dependent RNA polymerase outperformed remdesivir in enzymatic assays, echoing the mechanism by which approved nucleoside analogues corrupt viral genome replication. Plant-virus studies, meanwhile, show purine–chalcone and sulfonamide nucleoside derivatives binding the tobacco mosaic virus coat protein and activating host defense responses, suggesting agricultural as well as pharmaceutical value.

Perhaps the most surprising breadth appears in the miscellaneous activity section, where purine chemistry touches nearly every organ system. Caffeine-based triazoles inhibit acetylcholinesterase at 0.49 micromolar, a dramatic improvement over the parent compound and a plausible route to Alzheimer’s therapeutics; purine-based DPP-4 inhibitors lower glucose in diabetic animal models; xanthine derivatives block adenosine receptors with submicromolar affinity for antifibrotic and cardiovascular indications; and 7-deazapurine nucleosides clear intracellular Trypanosoma cruzi and Leishmania infections in vivo with excellent selectivity. Mechanistic insights threaded through the review, such as the role of urate crystals and the P2X7 receptor in driving NLRP3 inflammasome activation during gout, and the ability of bacterial inosine to open OmpF channels and increase antibiotic uptake, illustrate how purine metabolism itself shapes disease outcomes in ways that new drugs could exploit.

The authors are careful to temper the enthusiasm. Most compounds surveyed remain preclinical, and the translation gap separating nanomolar enzyme inhibition from safe, orally available medicine involves pharmacokinetics, bioavailability, toxicity, and in vivo efficacy that many leads have not yet cleared. Still, the overall picture is one of a scaffold with unmatched versatility, in which deliberate substitution patterns, heterocycle fusion, electronic tuning, and linker engineering can be combined like adjustable dials to hit an extraordinary range of biological targets. As resistance to existing antimicrobials mounts and cancer increasingly exploits its own purine metabolism to survive treatment, the humble fused ring at the core of life’s information molecules looks less like a historical artifact of drug discovery and more like a platform whose most valuable derivatives may still be ahead.

Subject of Research: Structure–activity relationships and biological activities of purine and purine-derived compounds in medicinal chemistry and drug discovery

Article Title: Purine and its derivatives: Structure activity relationships, biological activities, and mechanistic insights

Article References: Gochhayat, S. J., Kavalapure, R. S., Vadivel, E., Shaikh, S. N., Kalakwade, A., Gharge, S., Ranade, S. D., Ramu, R., & Firdose, N. (2026). Purine and its derivatives: Structure activity relationships, biological activities, and mechanistic insights. Results in Chemistry, 31, Article 103896. https://doi.org/10.1016/j.rechem.2026.103896

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103896

Keywords: purine, medicinal chemistry, structure–activity relationship, kinase inhibitors, anticancer agents, antimalarial drugs, antimicrobial resistance, antiviral agents, antifungal agents, tuberculosis, purine metabolism, drug discovery

An international team of researchers from Italy and Brazil, led by Gabriele Rocchetti of the Università Cattolica del Sacro Cuore, used an untargeted metabolomic approach based on ultra-high-performance liquid chromatography coupled to high-resolution Orbitrap mass spectrometry. Rather than testing a pre-selected list of compounds, untargeted metabolomics casts a wide analytical net, capturing and tentatively identifying as many small molecules as possible in a biological sample. In this case, the platform putatively annotated 1,412 metabolites in whole blood, cross-referenced against the comprehensive Bovine Metabolome Database. Amino acids, peptides and their analogues dominated the detectable metabolome with 281 compounds, followed by carbohydrates and their conjugates with 90, and fatty acids and conjugates with 63.

The experimental design took advantage of a long-running field study at São Paulo State University’s experimental station in Araçatuba, Brazil. Twenty-five Nellore and 25 Angus young bulls, half-sibs within each breed to minimize genetic variation, were reared under identical conditions. After an adaptation period with access to shade, half of the animals in each breed were exposed to direct sunlight and high temperature-humidity conditions for 56 days during the height of the southern summer, from early December 2015 to early February 2016. Shading was then restored and the animals entered a recovery phase. Blood was drawn from five sun-exposed animals per breed at the peak of heat stress and again in the cooler season, allowing the researchers to compare each animal against its own baseline. Notably, these were the same animals whose DNA methylation patterns the team had characterized in an earlier study, providing an unusual opportunity to link epigenetic regulation with metabolic chemistry.

When the researchers applied supervised statistical modeling to the metabolomic profiles collected during the challenge period, the two breeds separated cleanly, with a prediction ability of Q² = 0.917. Twenty metabolites showed outstanding discriminating power, each achieving a perfect area under the receiver operating characteristic curve. The single most predictive compound was the steroid 4-hydroxyestrone, which accumulated far more in the blood of heat-stressed Angus than in Nellore, with a log2 fold-change of 3.79. Steroid metabolism is known to be highly responsive to environmental stressors, and this finding points to breed-specific endocrine regulation under thermal load. Other top discriminators included lysine, the membrane lipid LysoPC(16:0), and citric acid, all previously implicated in heat-related metabolic adjustments and consistent with the known effects of heat stress on mitochondrial metabolism, substrate use, and membrane lipid turnover.

The most striking results, however, emerged from the longitudinal comparison of each breed between the heat challenge and the recovery period. Because repeated measurements from the same animals can inflate apparent significance, the team used linear mixed models that accounted for individual identity and then applied stringent false discovery rate correction. Under this rigorous framework, the contrast between the breeds was dramatic. Nellore cattle showed 114 metabolites whose phase-dependent changes remained statistically significant, spanning amino acids and peptides, carbohydrates, purine and pyrimidine derivatives, acyl-carnitines, steroids, and tetrapyrrole-related compounds. Angus, by comparison, retained only three significant metabolites: urobilin, deoxycitidine, and D-1-piperideine-2-carboxylic acid.

Interpreting this asymmetry requires care, the authors caution. The scarcity of significant metabolites in Angus does not mean the breed was unaffected by heat. Multivariate modeling still identified 264 metabolites contributing to class discrimination in Angus, but their univariate changes were modest and variable across animals. The researchers suggest two non-exclusive explanations: either Angus responses are more biologically variable between individuals, or the breed lacks the systemic metabolic plasticity that characterizes its zebu cousin. In Nellore, the large and coherent set of regulated metabolites points to a tightly controlled, network-level reprogramming, precisely the kind of coordinated response one would expect from a breed evolutionarily shaped by tropical climates.

Within the Nellore response, each chemical class told a coherent physiological story. Amino acids and peptides formed the largest affected category, with 34 significant compounds showing a global reduction, consistent with heat-induced shifts in nitrogen metabolism, increased amino acid catabolism, and the redistribution of substrates toward energy production. Carbohydrate-related metabolites also declined, plausibly reflecting altered glucose utilization and gluconeogenic flux. Purine and pyrimidine derivatives were predominantly reduced during heat exposure, a pattern linked to energy balance, redox homeostasis, and stress signaling. Perhaps most intriguingly, acyl-carnitines, key intermediates in fatty acid transport and mitochondrial beta-oxidation, showed a strong cumulative increase, suggesting that heat-stressed Nellore cattle shift their metabolism toward lipid substrates. Steroids and steroid-conjugated metabolites were broadly reduced, while phenolic compounds of dietary origin, including quercetin and enterolactone, also fell during the challenge period.

The metabolic findings dovetail elegantly with the team’s earlier epigenetic work on the same animals. In the previous DNA methylation study, Nellore cattle exhibited hypo-methylation of stress-responsive genes during heat exposure, including ELOVL5 and FADS1, which govern fatty acid chain elongation and desaturation, and PDE5A, a regulator of vascular function and oxidative stress responses. The convergence of epigenetic loosening of lipid-metabolism genes with the observed remodeling of acyl-carnitines and membrane lipids supports the hypothesis that Nellore cattle possess a multi-layered adaptive framework: gene regulation and metabolite chemistry responding in concert to preserve membrane stability, optimize lipid turnover, and limit oxidative damage. Pathway analysis reinforced this picture, identifying porphyrin, purine, and pyrimidine metabolism as the routes most consistently modulated by heat, particularly in Nellore, with porphyrin metabolism standing out as a shared signature in both breeds.

That shared porphyrin signature is biologically telling. Urobilin, a downstream catabolite of heme breakdown, plummeted during heat exposure in both breeds, with log2 fold-changes of −6.08 in Angus and −5.97 in Nellore, and achieved maximal predictive power in the Angus model. Heme is central to oxygen transport, mitochondrial electron transfer, and cellular redox balance, and thermal stress is known to influence mitochondrial activity, oxygen utilization, and reactive oxygen species generation. The marked drop in urobilin thus suggests that heat stress perturbs heme turnover in both breeds, even as their broader metabolic responses diverge. In Angus, the rise of deoxycitidine hints at increased nucleotide turnover, possibly reflecting DNA and RNA damage and repair under oxidative stress, while the fall of D-1-piperideine-2-carboxylic acid, a lysine degradation intermediate, points to perturbed amino acid catabolism.

The study’s authors are careful to frame their conclusions within its limits. The cohort was small, with five animals per breed providing longitudinal samples, and data acquisition was performed exclusively in positive ionization mode, meaning that metabolites preferentially detected in negative mode, including several classes of organic acids, may be underrepresented. Larger cohorts and targeted validation will be needed to confirm the functional roles of the identified metabolites. Even so, the implications are considerable. If heat tolerance in cattle reflects the capacity for controlled, systemic metabolic reprogramming rather than the magnitude of any single molecular change, then breeding programs may eventually be able to use blood metabolite panels as biomarkers to select thermotolerant animals. In an era when climate change is squeezing livestock systems on every continent, the humble blood sample of a Nellore steer may hold a blueprint for building more resilient herds.

Subject of Research: Breed-specific blood metabolomic responses of Nellore and Angus cattle to heat stress

Article Title: Metabolomic profiling of blood from Nellore and Angus cattle under heat stress

Article References: Rocchetti, G., Errico, M., Capra, E., Milanesi, M., Fappani, G., Garcia, J. F., de Paula Nogueira, G., Utsunomiya, Y. T., Lucini, L., OBrien, A. M. P., & Marsan, P. A. (2026). Metabolomic profiling of blood from Nellore and Angus cattle under heat stress. Stress Biology, 6(1), Article 31. https://doi.org/10.1007/s44154-026-00303-7

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00303-7

Keywords: heat stress, cattle, metabolomics, Nellore, Angus, thermotolerance, porphyrin metabolism, purine metabolism, pyrimidine metabolism, acyl-carnitines, urobilin, livestock

The scale of the problem the researchers set out to address is substantial. Muscle injuries remain one of the leading causes of time lost from training and competition in professional football, and the biological response to a given training load is highly individual, shaped by a complex web of metabolic, inflammatory, and recovery processes. Current monitoring strategies rely predominantly on external load metrics derived from electronic performance tracking systems, which the authors argue do not fully capture the individual physiological stress and biological cost of training. Metabolomics, the systematic measurement of small molecules that represent the final products of cellular regulation, provides a downstream functional readout of physiology that integrates genomic, proteomic, and environmental influences. Because urine can be collected non-invasively and repeatedly, it is an attractive medium for tracking these processes in athletes who are tested constantly.

The study’s design reflected the realities of elite sport. Of the 287 samples, 30 were collected during ten clinically confirmed muscle injury and rehabilitation periods from ten distinct players, while the remaining 257 came from healthy periods and served as controls. Injuries were defined and recorded according to UEFA consensus recommendations, diagnosed by the same medical staff throughout, and supported by ultrasound and magnetic resonance imaging when clinically indicated. The injury set spanned the spectrum of lesions common in professional football, including grade 2b and 3c hamstring strains affecting the biceps femoris, semimembranosus, semitendinosus, and rectus femoris muscles. Samples were collected at a median of 22 days post-injury, with the majority drawn during early and late rehabilitation phases rather than the acute window.

On the analytical side, the team used targeted ultra-performance liquid chromatography coupled to tandem mass spectrometry to quantify amino acids and tryptophan-related metabolites. Absolute concentrations were normalized to creatinine to correct for urinary dilution, and tryptophan pathway metabolites were additionally normalized to tryptophan itself, yielding 71 metabolite ratios for statistical analysis. Quality control relied on calibration standards, procedural blanks, retention-time matching, and stable isotope-labeled internal standards added to every sample. Before any supervised modeling, principal component analysis confirmed that injury status was not the dominant source of variance in the dataset, an expected result given that injury-related perturbations are subtle against the broad physiological variability inherent to elite athletes. No analytical outliers or season-related batch effects were detected.

Despite that subtlety, univariate statistics combining Welch’s test, fold-change assessment, and Hedge’s g effect sizes revealed a coherent biochemical story. The most striking signals involved tryptophan metabolism: injured players showed substantially elevated levels of xanthurenic acid, kynurenic acid, and elevated tryptamine-to-tryptophan ratios, alongside higher S-adenosylmethionine. The kynurenine pathway, through which tryptophan is degraded, is strongly regulated by immune signaling and inflammatory mediators and has been widely implicated in exercise-induced adaptation, making its perturbation one of the most biologically relevant responses to muscle damage. Conversely, aminophenol, proline, ornithine, and lysine were reduced in the injury group, consistent with altered protein turnover as the body repools amino acids for tissue repair.

Two further metabolic themes emerged. The first involved purine degradation, particularly hypoxanthine, a well-established marker of energetic stress that accumulates when ATP is broken down faster than it can be regenerated. In the context of muscle injury, elevated hypoxanthine likely reflects both localized energy depletion within damaged fibers and the systemic metabolic cost of sustaining tissue repair. The second theme involved amino acids directly implicated in structural remodeling: proline and ornithine are closely linked to collagen synthesis and connective tissue repair, while elevated beta-aminoisobutyric acid, or BAIBA, has been associated with muscle stress adaptation and mitochondrial remodeling. Changes in alanine, glutamic acid, taurine, beta-alanine, and phenylacetylglutamine reinforced the picture of coordinated protein turnover. Pathway over-representation analysis using the KEGG database pointed to significant enrichment of amino acid metabolic pathways, particularly arginine and proline metabolism, although the authors caution that because the panel was targeted, this enrichment is exploratory rather than definitive mechanistic evidence.

The multivariate analysis was where the findings took on their most clinically suggestive form. Using partial least squares discriminant analysis with leave-one-out cross-validation and 300-fold permutation testing to guard against overfitting, the researchers built a model that separated injured from non-injured samples with a cross-validated area under the receiver operating characteristic curve of 0.88, correctly identifying 73 percent of injury samples and 88 percent of controls, with statistical significance at p less than 0.003. The most influential discriminant metabolites were BAIBA, hypoxanthine, xanthurenic acid, beta-alanine, and alanine, largely consistent with the univariate results. Backward stepwise feature selection then pared the model down to a restricted subset of metabolites that preserved an AUROC of 0.81, a simplification the authors highlight as important for translation, since small targeted panels are more analytically robust and easier to validate in routine clinical settings than full metabolomic profiles.

The team was careful to stress-test its own statistics. Because 30 injury samples came from only ten players, they repeated validation using a stricter leave-one-player-out scheme, under which performance dropped to an AUROC of 0.72. They attribute this decline to the severe class imbalance and the concentration of injury samples among few individuals, and they emphasize that independent player-level validation in larger cohorts is essential before any clinical deployment. The imbalance also shaped other performance metrics: the positive predictive value was a modest 41 percent, while the negative predictive value reached 97 percent, meaning the current score is far better at ruling out injury-related metabolic stress than confirming it. The authors also note that nutritional intake, acute workload, and medication, all of which can influence the urinary metabolome, were not recorded and represent potential confounders.

Perhaps the most visually compelling element of the study is the longitudinal perspective. For eight of the ten injured players, serial samples collected across rehabilitation allowed the researchers to track individual trajectories of a metabolite-based injury score. In a descriptive, exploratory assessment, these trajectories suggested progressive normalization of the metabolic profile during rehabilitation, approaching baseline values by the return-to-play milestone, and players who never sustained injuries showed baseline stability in the score. The study juxtaposes these chemical trajectories with serial 3-Tesla MRI examinations of a 24-year-old player who suffered a complete proximal hamstring aponeurosis tear, documenting the anatomical progression from acute edema and tendon retraction through scar bridging, maturation, and remodeling over eight weeks. The authors argue that macro-structural healing on MRI does not necessarily reflect the resolution of local energetic or systemic inflammatory stress, so mapping metabolomic trajectories against structural lesion evolution could, in principle, reveal whether cellular homeostasis has truly recovered even when imaging looks normal.

The researchers are measured about what their findings can and cannot support. Urinary profiles reflect systemic metabolic balance rather than local tissue remodeling, and the signatures cannot currently be used to guide return-to-play decisions. The observational design limits causal interpretation, and the single-center cohort restricts generalizability. Nevertheless, the demonstration that a coordinated, statistically robust metabolic signature of muscle injury can be captured non-invasively in urine marks a meaningful step toward complementing external load monitoring with an internal readout of biological stress. Future multicenter studies that integrate longitudinal metabolomics with structural imaging, biochemical markers, and clinical assessment will determine whether this multimodal approach adds clinically meaningful value, potentially transforming how the world’s most expensive athletes are monitored, rehabilitated, and returned to competition.

Subject of Research: Urinary metabolomic biomarkers of muscle injury and recovery in professional football players

Article Title: Urinary metabolomic signatures of muscle injury and recovery in elite football players

Article References: Quintás, G., Pruna, R., Wong, M., Mechó, S., Madrero, P., Sanjuán-Herráez, J. D., & Rodas, G. (2026). Urinary metabolomic signatures of muscle injury and recovery in elite football players. Metabolomics, 22(5), Article 158. https://doi.org/10.1007/s11306-026-02530-5

Image Credits: AI Generated

DOI: 10.1007/s11306-026-02530-5

Keywords: metabolomics, muscle injury, football, sports medicine, urine biomarkers, tryptophan metabolism, purine metabolism, PLS-DA, FC Barcelona, athlete monitoring, rehabilitation, UPLC-MS

The story begins with an untargeted look at metabolism. Using liquid chromatography–mass spectrometry, the researchers compared urea cycle metabolites in Philadelphia chromosome-positive B-ALL cells, which carry the t(9;22) translocation that fuses BCR to ABL, with metabolites in healthy human B cells freshly isolated from peripheral blood. The leukaemia cells stood out for elevated levels of ASA and altered handling of citrulline and arginine, the substrates and products that bracket the ASA step of the cycle. Urea cycle gene expression profiles in patient-derived cells and in the Sup-B15 and Nalm21 B-ALL lines reinforced the picture that this pathway, generally associated with the liver’s ammonia detoxification, was being co-opted in malignant B cells.

Why would BCR–ABL care about a urea cycle enzyme? The answer the authors provide is a phosphorylation event. Through mass spectrometric mapping of tyrosine-phosphorylated proteins, they identified argininosuccinate synthase 1 (ASS1), the enzyme that condenses citrulline and aspartate into ASA, as a direct substrate of the BCR–ABL kinase. Four high-confidence tyrosine residues were detected, and mutation analysis pinpointed tyrosine 282 (Y282) as the functionally important site. In vitro, purified GST-tagged Abl kinase phosphorylated wild-type ASS1 but not an ASS1-Y282F mutant, and in cells the interaction was verified by co-immunoprecipitation in both directions. Treatment with the kinase inhibitor STI571, better known as imatinib, reduced ASS1 phosphorylation, tying the modification directly to BCR–ABL activity.

Notably, Y282 phosphorylation was not a quirk of BCR–ABL alone. When the team co-expressed ASS1 with other fusion tyrosine kinases implicated in haematological malignancies, including ALK, JAK2, FGFR and PDGFR, ASS1 phosphorylation and enzymatic activity rose in each case, and kinase inhibitors lowered urea cycle metabolite levels in a chronic myelogenous leukaemia line and in anaplastic large cell lymphoma cells. This suggests that ASS1 phosphorylation at Y282 is a convergent metabolic endpoint of oncogenic tyrosine kinase signalling, one that boosts the enzyme’s capacity to convert citrulline into ASA.

What does the extra ASA actually do? The key experiments traced the fate of isotopically labelled citrulline in leukaemia cells. When B-ALL cells were fed [13C5]citrulline, labelled carbon flowed through ASA into arginine, confirming active flux through ASS1. Cells expressing a phosphorylation-deficient ASS1-Y282F mutant accumulated less ASA and arginine than cells with the wild-type enzyme. The team then depleted ASS1 with short hairpin RNAs and performed metabolomic profiling of BCR–ABL-positive BAF3 cells recovered from mouse bloodstreams. The most striking changes appeared in purine metabolism: nucleotides and nucleosides dropped when ASS1 was silenced, implicating the urea cycle intermediate in maintaining purine pools.

The mechanistic link turned out to be a direct protein–metabolite interaction. ASA, the authors show, binds cytosolic 5′-nucleotidase II (NT5C2), an enzyme that removes phosphate groups from nucleoside monophosphates to yield nucleosides such as inosine, adenosine and guanosine. Molecular docking and molecular dynamics simulations, performed by Mingjie Liu and Xiaojing He’s groups, indicated that ASA localizes to the effector site of NT5C2 and stabilizes helix A, a structural element (residues Gly355–Glu364) that gates the enzyme’s allosterically activated state. Enzyme kinetics assays confirmed that ASA enhances NT5C2’s nucleotidase activity, whereas arginine and adenylosuccinate did not reproduce the effect. In other words, ASA is not merely a passive intermediate here; it is a small-molecule activator that tells NT5C2 to convert purine nucleotides into nucleosides.

Those nucleosides, it turns out, are not waste products but fuel. When leukaemia cells were incubated with [ribose-13C5]inosine or [ribose-13C5]adenosine, label from the ribose moiety appeared in glycolytic intermediates, tricarboxylic acid (TCA) cycle metabolites and the pentose phosphate pathway, even when glucose was abundant. The purine nucleosides serve as a carbon source for central carbon metabolism under glucose-replete conditions, an unexpected contribution given that nucleoside salvage is usually framed in terms of nitrogenous bases and nucleotide pools rather than carbon economics. Earlier work had shown that ribose salvaged from uridine can fuel glucose-restricted pancreatic cancer; this study extends the concept to purine nucleosides in glucose-rich leukaemia, where they complement rather than replace glycolysis.

The physiological importance of the axis became clear in vivo. Loss of ASS1 or NT5C2 disrupted central carbon metabolism and inhibited leukaemia progression in mouse models, and supplementing the animals’ leukaemia cells with inosine or adenosine rescued the metabolic and growth defects. In Nalm21-based xenografts, an ASS1-Y282F mutant supported less disease burden than wild-type ASS1, and inosine administration partially restored phenotypes suppressed by imatinib, consistent with the nucleosides acting downstream of the kinase. Serum measurements in leukaemia-bearing mice showed elevated adenosine, inosine and cytidine compared with healthy controls, hinting that the pathway shapes the systemic nucleoside environment as well as the intracellular one.

The study also maps the transport machinery that moves these metabolites across the membrane. Uptake experiments with doubly labelled [13C6,15N4]ASA identified SLC13A2 and SLC13A3 as candidate ASA transporters, while citrulline import depended on SLC7A5, the amino acid transporter also known as LAT1, and was blocked by the LAT1 inhibitor JPH203. These assignments sharpen the metabolic wiring diagram and point to additional potential intervention points.

The findings carry a double significance for leukaemia biology and therapy. First, they identify an ASA–NT5C2 signalling axis that directly links tyrosine kinase activity, urea cycle dysregulation and purine metabolism, adding a concrete molecular mechanism to the growing appreciation of metabolites as signalling molecules. Second, they highlight purine nucleosides as a carbon source that tyrosine kinase-driven leukaemias exploit, and NT5C2 as an enzymatic node essential to that exploitation. NT5C2 is already notorious in the clinic because acquired mutations in relapsed lymphoblastic leukaemia confer resistance to thiopurine chemotherapy by altering the enzyme; this work now gives the protein a second, more fundamental role in leukaemia metabolism that is independent of treatment selection. Whether targeting the ASS1–NT5C2 axis can be translated into combination strategies with existing kinase inhibitors will require further preclinical and clinical evaluation, but the study establishes a clear metabolic vulnerability: cut off the urea cycle’s signalling output, and the leukaemia cell’s carbon supply begins to starve.

Subject of Research: The role of ASS1-derived argininosuccinate in promoting purine nucleoside synthesis and central carbon metabolism in B cell acute lymphoblastic leukaemia.

Article Title: ASS1-derived argininosuccinate promotes purine nucleoside synthesis in B cell acute lymphoblastic leukaemia

Article References: Li, G., He, Z., Liu, M., Zhao, J., Zhu, H., Zhou, C., Wang, Z., He, X., Tang, J., & Jiang, P. (2026). ASS1-derived argininosuccinate promotes purine nucleoside synthesis in B cell acute lymphoblastic leukaemia. Nature Metabolism, 8(9), 1871-1887. https://doi.org/10.1038/s42255-026-01586-w

Image Credits: AI Generated

DOI: 10.1038/s42255-026-01586-w

Keywords: ASS1, argininosuccinate, NT5C2, BCR-ABL, B-ALL, urea cycle, purine metabolism, cancer metabolism, leukaemia, tyrosine kinase, nucleosides, Nature Metabolism

Researchers at the College of Agriculture and Animal Husbandry of Qinghai University, working at the Black Tibetan Sheep Breeding Centre in Guinan County, randomly assigned 60 two-month-old male lambs weighing 13 to 14 kilograms to two groups. One group was castrated after weaning, while the other remained intact. Both groups were housed in separate pens but managed and fed identically, and after a one-week acclimatisation period the formal feeding trial ran for 120 days. At the end of the trial, six animals from each group were humanely slaughtered under animal welfare protocols following a 12-hour fast, and muscle samples were collected bilaterally between the ninth and eleventh ribs, flash-frozen on dry ice, and stored at minus 80 degrees Celsius until analysis. The work was approved by the Animal Ethics Committee of Qinghai University under approval number QUA-2020-0709.

The team then subjected the meat to an unusually rigorous battery of tests combining classical meat-science measurements with modern metabolomics. Conventional quality indicators included pH at 24 hours post-mortem, cooking loss, drip loss, Warner-Bratzler shear force, cooked meat percentage, and texture profile parameters such as hardness, elasticity, chewiness, cohesiveness, and resilience. Nutritional composition, namely crude protein, moisture, and crude fat, was determined using accepted AOAC methods. To peer into the molecular machinery underlying these traits, the scientists deployed untargeted metabolomics on an Agilent 1290 Infinity ultrahigh-performance liquid chromatography system coupled to an AB Triple TOF 6600 mass spectrometer operated in both positive and negative ionisation modes, alongside targeted amino acid quantification using UPLC-ion mobility separation with multiple reaction monitoring on a 5500 QTRAP instrument, and fatty acid profiling by gas chromatography-mass spectrometry after methyl esterification.

The physical results were striking. Meat from the castrated group, designated BTC, showed significantly lower drip loss than meat from intact rams, designated BTN, indicating better water retention during storage, a trait consumers associate with juicier, more tender products. At the same time, cooking loss, elasticity, chewiness, and cohesiveness were all significantly higher in the castrated group, changes the authors attribute to shifts in muscle fibre type and structure that they plan to characterise in future work. The pH values of both groups fell within the normal fresh-meat range of roughly 5.67 to 6.28 at 24 hours, although the castrated animals trended lower, and there were no significant differences in cooked meat percentage, hardness, or resilience. Crucially, castration did not alter the crude composition of the meat: moisture, protein, and fat contents were statistically indistinguishable between the groups, meaning the animal’s fundamental nutritional payload remained intact.

The metabolomics told a richer story. Principal component analysis clearly separated castrated from non-castrated samples, and supervised PLS-DA and OPLS-DA models, with high explained variance and predictive statistics, confirmed significant metabolic segregation between the groups. In the negative ion mode alone the team identified 586 metabolites, dominated by lipids and lipid-like molecules at about 31 percent of the total, followed by organic acids and their derivatives at nearly 24 percent. Applying strict criteria of variable importance in projection greater than 1 and a P value below 0.05, the researchers pinpointed 34 differentially abundant metabolites, 15 of them upregulated and 13 downregulated in castrated sheep. Notable upregulated compounds included uric acid, vitamin C, malate, glutamine, oleic acid, and ammelide, while compounds such as L-malic acid, maltotriose, D-lactose, inosine 5′-monophosphate, and several phospholipid species were reduced.

Pathway analysis using the Kyoto Encyclopedia of Genes and Genomes illuminated the biological circuits most affected by castration. Purine metabolism, general metabolic pathways, bile secretion, the phosphotransferase system, glyoxylate and dicarboxylate metabolism, pyrimidine metabolism, and ABC transporters emerged as the key pathways distinguishing the two groups. The authors propose that DL-2-phosphoglycerate, upregulated in castrated muscle, feeds into glycolysis where it is converted by enolase to phosphoenolpyruvate and then by pyruvate kinase to pyruvate, ultimately contributing to lactate formation and the slight decline in muscle pH observed 24 hours after slaughter. ABC transporters, one of the most extensively studied protein families in biology, may in turn shuttle metabolites across membranes, modulating the amino acid content of muscle tissue in concert with the phosphotransferase system and glyoxylate and dicarboxylate metabolism.

Targeted metabolomics added nutritional depth. Of 31 amino acids and derivatives detected, 11 were significantly elevated in castrated sheep, and the totals for non-essential amino acids, umami amino acids, and overall amino acid content were all significantly higher than in intact rams. Umami compounds such as aspartate and glutamate are central to the savoury taste that makes lamb so prized, and the finding mirrors earlier reports that castrated boars carry more umami amino acids than females. Meanwhile, fatty acid profiling identified 40 fatty acids, 23 of which differed significantly between groups. Levels of saturated, monounsaturated, and polyunsaturated fatty acids were all significantly higher in castrated animals, the n-6 to n-3 ratio shifted significantly, and oleic acid, the dominant monounsaturated fatty acid, was upregulated, consistent with previous castration studies in goats, cattle, and pigs.

Correlation analysis wove these threads together. Drip loss was negatively correlated with uric acid, suggesting that the castration-driven rise in this purine metabolite, routed through purine metabolism, bile secretion, and general metabolic pathways, may help the muscle hold onto its water. Total and non-essential amino acid scores correlated positively with vitamin C, malate, glutamine, oleic acid, and ammelide, all of which were elevated in castrated sheep, while elasticity showed a strong positive relationship with oleic acid and ammelide. The researchers note that prior work links purine metabolism to enhanced umami flavour and that guanine content correlates positively with savoury intensity in pork, lending plausibility to the idea that castration subtly tunes flavour chemistry as well as texture in Tibetan mutton.

The study is not without limits. Given cost and animal ethics considerations, only six castrated and six intact sheep were analysed, and the authors acknowledge that additional quality-relevant metabolites may await discovery in larger cohorts. Still, the practical implications are considerable. Castration improved several eating-quality traits and boosted amino acid and fatty acid levels while reducing drip loss, but it also raised cooking loss and saturated fatty acid content. The team suggests that future feed formulation for castrated flocks, for example incorporating flaxseed to push the fatty acid profile toward beneficial n-3 species, could amplify the benefits while offsetting the drawbacks. For the herders of the Qinghai-Tibet Plateau, and for a growing global market that prizes distinctive, high-quality lamb, an ancient pastoral custom now rests on a firm molecular foundation.

Subject of Research: Effects of castration on meat quality and muscle metabolites in Black Tibetan sheep on the Qinghai-Tibet Plateau

Article Title: The effects of castration on the quality of black Tibetan sheep meat and muscle metabolites

Article References: Xu, X., Han, L., Yue, Q., Hou, S., Luo, Z., Gui, L., Yang, B., Wang, Z., Yuan, Z., & Sun, S. (2026). The effects of castration on the quality of black Tibetan sheep meat and muscle metabolites. Food Science of Animal Resources, 46(1), Article 91. https://doi.org/10.1007/s44463-026-00067-8

Image Credits: AI Generated

DOI: 10.1007/s44463-026-00067-8

Keywords: castration, Black Tibetan sheep, meat quality, metabolomics, amino acids, fatty acids, drip loss, oleic acid, purine metabolism, ABC transporters, Qinghai-Tibet Plateau, lamb meat