The host–microbiome interface is rich in metabolite exchanges and exquisitely sensitive to diet. Hydrogen sulfide (H ₂ S) is present at high concentrations at this interface and is a product of both microbial and host metabolism. The mitochondrial enzyme, sulfide quinone oxidoreductase (SQOR), couples H ₂ S detoxification to oxidative phosphorylation; its inherited deficiency presents as Leigh disease. Since an estimated two-thirds of systemic H ₂ S metabolism originates in the gut, it raises questions as to whether impaired sulfide clearance in this compartment contributes to disease and whether it can be modulated by dietary sulfur content. In this study, we report that SQOR deficiency confined to murine intestinal epithelial cells perturbs colon bioenergetics that is reversed by antibiotics, revealing a significant local contribution of microbial H ₂ S to host physiology. We also find that a 2.5-fold higher methionine intake, mimicking the difference between animal and plant proteins, synergizes with intestinal SQOR deficiency to adversely impact colon architecture and alter microbiome composition. In serum, increased thiosulfate, a biomarker of H ₂ S oxidation, reveals that intestinal SQOR deficiency combined with higher dietary methionine affects sulfide metabolism globally and perturbs energy metabolism as indicated by higher ketone bodies. The mice exhibit lower exploratory locomotor activity while brain MRI reveals an atypical reduction in ventricular volume, which is associated with lower aquaporin 1 that is important for cerebrospinal fluid secretion. Our study reveals the dynamic interaction between dietary sulfur intake and sulfide metabolism at the host–microbe interface, impacting gut health, and the potential for lower dietary methionine intake to modulate pathology.

Folate metabolism in mammalian cells is essential for multiple vital processes, including purine and pyrimidine synthesis, histidine catabolism, methionine recycling, and utilization of formic acid. It remains unknown, however, whether these processes affect each other via folate metabolism or can function independently based on cellular needs. We addressed this question using a quantitative mathematical model of folate metabolism in rat liver cytoplasm. Variation in the rates of metabolic processes associated with folate metabolism (i.e., purine and pyrimidine synthesis, histidine catabolism, and influxes of formate and methionine) in the model revealed that folate metabolism is organized in a striking manner that enables activation or inhibition of each individual process independently of the metabolic fluxes in others. In mechanistic terms, this independence is based on the high activities of a group of enzymes involved in folate metabolism, which efficiently maintain close-to-equilibrium ratios between substrates and products of enzymatic reactions.

Functional effectiveness of erythrocytes depends on their high deformability that allows them to pass through narrow tissue capillaries. The erythrocytes can deform easily due to discoid shape provided by the stabilization of an optimal cell volume at a given cell surface area. We used mathematical simulation to study the role of transport Na/K-ATPase and transmembrane Na⁺ and K⁺ gradients in human erythrocyte volume stabilization at non-selective increase in cell membrane permeability to cations. The model included Na/K-ATPase activated by intracellular Na⁺, Na⁺ and K⁺ transmembrane gradients, and took into account contribution of glycolytic metabolites and adenine nucleotides to cytoplasm osmotic pressure. We found that this model provides the best stabilization of the erythrocyte volume at non-selective increase in the permeability of the cell membrane, which can be caused by an oxidation of the membrane components or mechanical stress during circulation. The volume of the erythrocyte deviates from the optimal value by no more than 10% with a change in the non-selective permeability of the cell membrane to cations from 50 to 200% of the normal value. If only one transmembrane ion gradient is present (Na⁺), the cell loses the ability to stabilize volume and even small changes in membrane permeability cause dramatic changes in the cell volume. Our results reveal that the presence of two oppositely directed transmembrane ion gradients is fundamentally important for robust stabilization of cellular volume in human erythrocytes.

The differential diagnosis of hereditary spherocytosis is a great challenge because of the similar clinical and laboratory signs it shares with other hereditary hemolytic anemias as well as due to the limited availability of molecular genetic testing. The development of easy-to-perform laboratory tests for the differential diagnosis of hereditary hemolytic anemias remains as relevant as ever. Here, a method of measuring red blood cell filterability for the diagnosis of hereditary spherocytosis is proposed for the first time. The aim of our study was to compare red blood cell filterability measurement with other diagnostic tests for hereditary spherocytosis as well as to assess its specificity and sensitivity. We included 30 patients (18 girls and 12 boys, with the median age of 8.6 years) with hereditary spherocytosis and 15 patients (9 girls and 6 boys, with the median age of 10 years) with other hereditary hemolytic anemias (pyruvate kinase deficiency (n = 14) and stomatocytosis (n = 1)). The diagnostic work-up for hereditary hemolytic anemia included a complete blood count test using an automated hematology analyzer, an osmotic resistance analysis before and after 24 hours of incubation at 37°С, erythrocytometry with sphericity index calculation, EMA test (eosin-5-maleimide binding assay) and red blood cell filterability measurement using artificial filters with cylindrical pores 3-5 μm in diameter. The study was approved by the Independent Ethics Committee and the Scientific Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. The parents of all of the enrolled children signed a voluntary informed consent form for peripheral blood collection and diagnostic testing. In all the cases of hereditary spherocytosis diagnosed in accordance with the relevant clinical recommendations, red blood cell filterability was very low (0–0.31 units). It was higher only in 3 instances, reaching 0.47, 0.64 and 0.82 units, but in two of these cases there were no genetic data available, and the remaining patient was found to harbor the SPTA1 c.433999CT mutation which was characterized both as spherocytosis and elliptocytosis. Red blood cell filterability in the group of the patients with other hemolytic anemias equalled 0.55 to 0.86 units (with the median of 0.77 units). The sensitivity of the RBC filterability measurement method in diagnosing hereditary spherocytosis was 93% (with 100% specificity), while the EMA test had a sensitivity of 89% and specificity of 95%. Our comparative study showed that red blood cell filterability measurement and the EMA test have similar sensitivity and specificity in diagnosing hereditary spherocytosis but the former is much cheaper and easier to perform since it does not require expensive equipment and can be carried out at any laboratory.