Oral histidine affects gut microbiota and MAIT cells improving glycemic control in type 2 diabetes patients

Abstract

Amino acids, metabolized by host cells as well as commensal gut bacteria, have signaling effects on host metabolism. Oral supplementation of the essential amino acid histidine has been shown to exert metabolic benefits. To investigate whether dietary histidine aids glycemic control, we performed a case-controlled parallel clinical intervention study in participants with type 2 diabetes (T2D) and healthy controls. Participants received oral histidine for seven weeks. After 2 weeks of histidine supplementation, the microbiome was depleted by antibiotics to determine the microbial contribution to histidine metabolism. We assessed glycemic control, immunophenotyping of peripheral blood mononucelar cells (PBMC), DNA methylation of PBMCs and fecal gut microbiota composition. Histidine improves several markers of glycemic control, including postprandial glucose levels with a concordant increase in the proportion of MAIT cells after two weeks of histidine supplementation. The increase in MAIT cells was associated with changes in gut microbial pathways such as riboflavin biosynthesis and epigenetic changes in the amino acid transporter SLC7A5. Associations between the microbiome and MAIT cells were replicated in the MetaCardis cohort. We propose a conceptual framework for how oral histidine may affect MAIT cells via altered gut microbiota composition and SLC7A5 expression in MAIT cells directly and thereby influencing glycemic control. Future studies should focus on the role of flavin biosynthesis intermediates and SLC7A5 modulation in MAIT cells to modulate glycemic control.

Keywords: Microbiome; diabetes; histidine; insulin resistance; monocytes.

Figure 1.

Study design. Participants use 4g of histidine daily. At day 14 antibiotics are added to the regimen for 7 days containing ciprofloxacin 500 mg once/day, metronidazole 500 mg twice/day, oral vancomycin 500 mg four times/day. At visit 2, 4, 5 and 6 feces was collected, blood was drawn and anthropometric measurements were performed. V1: visit 1. *mixed meal test was performed. Continuous glucose measure devices were used during the first four weeks and the last two weeks.

Figure 2.

Histidine and clinical parameters. A. Fasting histidine increases after oral supplementation. B. Fasting glucose improves throughout the study in the type 2 diabetes group. C. Mean amplitude of glycemic excursion based on continuous glucose measurements improves in the type 2 diabetes group during the study. Results Mixed Meal test D. Glucose curve during 120 minutes mixed meal test. E. AUC glucose mixed meal test. Linear mixed models, ^#nominal p value, */**FDR corrected. Control n = 19, Type 2 diabetes n = 20. *p < 0.05, **p < 0.01, ***p < 0.001. T2D: n = 20. Control n = 19.

Figure 3.

Immunophenotyping PBMC. A. Percentage of CD8+ MAIT cells is at baseline higher in the control group and increases during two weeks of histidine in the type 2 diabetes group. B. the expression (geometric mean fluorescence intensity) of the MAIT cell specific T cell receptor (TCR Va7.2) is higher at baseline in the control group than in the T2D group in CD8+ MAIT cells. After two weeks of histidine supplementation is the T cell expression in the T2D group also increased compared to baseline. C. the expression (geometric mean fluorescence intensity) of TCR Va7.2 on total MAIT T cells is decreased in T2D at baseline and increased after oral histidine in the T2D group. T2D: type 2 diabetes. T2D: n = 20. Control n = 19. *p < 0.05, **p < 0.01, ***p < 0.001. Paired non-parametric t test. MAIT: mucosa associated invariant T cell. PBMC: peripheral blood monocyte cells. gMFI: geometric mean fluorescent intensity. TCR: T cell receptor.

Figure 4.

Discriminative features for CD8+ MAIT percentages based on A. delta Fecal metagenomics pathways with explained variance: 25.7% B. Delta fecal metagenomics of bacteria belonging to the 20 pathways depicted in A. explained variance 14.6%. XGBoost regression models were applied. Black circumference indicated relation to flavin biosynthesis pathway.

Figure 5.

Correlation heatmap between A. Pathways and MAIT cell proportions and markers B. Bacterial species and genera belonging to the most discriminative pathways and MAIT cell markers. *FDR p < 0.05. Spearman correlation. Pathways and bacterial species and genera were based on fecal metagenomics analysis. FI: mean fluorescence intensity of TCR Va7.2. AUC: area under the curve. MMT: mix meal test.

Figure 6.

SLC7A5 methylation of A. a specific CpG: cg06770731 Chr16 87,863,812 SLC7A5 3’UTR Linear mixed models *p < 0.05, **p < 0.01, ***p < 0.001. Post AB: post antibiotics. B. Spearman correlation between a CpG and mean fluorescent intensity (FI) of CD8+ MAIT cells. Delta of both variables was used for this analysis. C. Gene expression of SLC7A5 in healthy controls and T2D individuals at baseline and after 2 weeks of histidine supplementation. Significant increase in SLC7A5 expression in the T2G group assessed with Mann–Whitney test; *p < 0.05.

Figure 7.

Proposed framework how oral histidine may influence glycemic control. Oral histidine may modulate gut microbiota pathways including vitamin B2 which can bind to MAIT cells, altering MAIT cell methylation. Additionally, abundant systemic availability of histidine may influence MAIT cell activation via SLC7A5 expression, thereby affecting SLC7A5 gene methylation. Altered MAIT cell methylation facilitates proliferation of MAIT cells which is generally associated with metabolic health and could thus thereby improve glycemic control.