Associations among circulating branched-chain amino acids and tyrosine with muscle volume and glucose metabolism in individuals without diabetes

Causal relationships between gut microbiota, gut metabolites, and diabetic neuropathy: A mendelian randomization study

BACKGROUND

Previous studies have shown a strong correlation between gut microbiota and diabetes and its associated complications. We aimed to evaluate the causal relationships between the gut microbiota, gut metabolites, and diabetic neuropathy.

METHODS

Summary statistics of 211 gut microbiota and 12 gut-related metabolites (β-hydroxybutyric acid, betaine, trimethylamine-N-oxide, carnitine, choline, glutamate, kynurenine, phenylalanine, propionic acid, serotonin, tryptophan, and tyrosine) were obtained from previous genome-wide association studies (GWAS). A two-sample Mendelian randomization (MR) design was used to estimate the effects of gut microbiota and gut metabolites on the risk of diabetic neuropathy based on FinnGen GWAS.

RESULTS

Higher levels of Acidaminococcaceae (OR = 0.62; 95%CI = 0.46 to 0.84; P = 0.002), Peptococcaceae (OR = 0.70; 95%CI = 0.54 to 0.90; P = 0.006), and Eubacterium coprostanoligenes group (OR = 0.68; 95%CI = 0.50 to 0.93; P = 0.016) are genetically determined to provide protection against diabetic neuropathy. Conversely, the presence of Alistipes (OR = 1.65; 95%CI = 1.18 to 2.31; P = 0.003), ChristensenellaceaeR7 group (OR = 1.52; 95%CI = 1.03 to 2.23; P = 0.033), Eggerthella (OR = 1.28; 95%CI = 1.05 to 1.55; P = 0.014), RuminococcaceaeUCG013 (OR = 1.35; 95%CI = 1.01 to 1.82; P = 0.046), and Firmicutes (OR = 1.42; 95%CI = 1.05 to 1.93; P = 0.023) increases the risk of diabetic neuropathy. Moreover, a correlation has been identified between diabetic neuropathy and two gut metabolites: betaine (OR = 0.95; 95%CI = 0.90 to 1.00; P = 0.033) and tyrosine (OR = 1.03; 95%CI = 1.01 to 1.06; P = 0.019). Sensitivity analysis indicated robust results with no sign of heterogeneity or pleiotropy.

CONCLUSION

The present study elucidated the impact of specific gut microbiota and gut metabolites on the susceptibility to diabetic neuropathy. Interventions targeting the improvement of the gut microbiota diversity and composition hold considerable promise as a potential strategy.

Chiral resolution of plasma amino acids reveals enantiomer-selective associations with organ functions

Plasma amino acids reflect the dynamics of amino acids in organs and their levels have clinical significance. Amino acids as clinical indicators have been evaluated as a mixture of D- and L-amino acids because D-enantiomers are believed to be physiologically nonexistent. However, it has become clear that some D-amino acids are synthesized by endogenous enzymes and symbiotic bacteria. Here, using a two-dimensional HPLC system, we measured enantiomers of all proteinogenic amino acids in plasma and urine and analyzed for correlation with other biochemical parameters in humans who underwent health checkups at our institutional hospital. Four D-amino acids (D-asparagine, D-alanine, D-serine, and D-proline) were detected in the plasma, amounting to less than 1% of the quantities of L-amino acids, but in the urine at several tens of percent, showing that D-amino acids have much higher fractional excretion than their L-counterparts. Detected plasma D-amino acids and D-/L-amino acid ratios were well correlated with renal parameters, such as blood urea nitrogen, creatinine, and cystatin C. On the other hand, a set of plasma L-amino acids were associated with body mass index and correlated with metabolic parameters such as liver enzymes, lipids, blood glucose, and uric acid. Thus, chiral resolution of plasma amino acids revealed totally different associations of the enantiomers with organ functions, and warrants further investigation for clinical and laboratory usefulness.

The Effect of Mild Renal Dysfunction on the Assessment of Plasma Amino Acid Concentration and Insulin Resistance in Patients with Type 2 Diabetes Mellitus

BACKGROUND

An increase in the levels of branched-chain amino acids (BCAAs) and certain aromatic amino acids, such as alanine, in plasma is correlated with insulin resistance (IR) in type 2 diabetes mellitus (T2DM). T2DM is a leading risk factor for chronic kidney disease. Meanwhile, renal dysfunction causes changes in plasma amino acid levels. To date, no study has examined how mild renal dysfunction and IR interact with plasma amino acid levels. This study examines the effects of IR and renal dysfunction on plasma amino acid concentrations in T2DM.

METHODS

Data were collected from healthy male participants (controls) and male patients with T2DM between May 2018 and February 2022. Blood samples were collected after overnight fasting. IR and renal function were evaluated using the homeostasis model assessment of IR (HOMA-IR) and serum cystatin C (CysC), respectively.

RESULTS

A total of 49 and 93 participants were included in the control and T2DM groups, respectively. In the T2DM group, eight amino acids (alanine, glutamic acid, glutamine, glycine, isoleucine, leucine, tyrosine, and valine) and total BCAA showed a significant correlation with HOMA-IR (p < 0.01), whereas six amino acids (γ-aminobutyric acid, citrulline, cysteine, glycine, methionine, and valine) and total BCAA showed a significant correlation with 1/CysC (p < 0.02). However, only alanine, glutamic acid, and each BCAA showed significant differences between the control group and the IR T2DM subgroup. Increases in the BCAA levels with T2DM were canceled by renal dysfunction (CysC ≥ 0.93) in patients with intermediate IR.

CONCLUSION

To use plasma BCAA concentration as a marker of IR, renal function must be considered, even in mild renal dysfunction. Increased alanine and glutamic acid levels indicate IR, regardless of mild renal dysfunction.

Changes in plasma-concentration ratios of branched-chain amino acids in acute and convalescent phases of bacterial pneumonia

Branched-chain amino acids (BCAAs) have different immunity-related functions. Thus, BCAAs require evaluation in terms of their plasma concentration ratio. Eighty healthy participants and 57 patients with community-acquired pneumonia were enrolled. Samples from the healthy participants were collected after 12-h fasting; samples from the community-acquired pneumonia group were collected 2–3 h after lunch, during the acute (day 0) and convalescent (day 7) phases. The coefficient “a” of the regression line (Y = aX + b) of each BCAA plasma concentration was calculated from healthy participants and fixed, and each intercept “b” was calculated from the plasma concentration of each BCAA pair. Isoleucine levels increased; no significant changes in leucine concentrations were observed between healthy participants and pneumonia patients on days 0 and 7. In female participants in the pneumonia group, valine concentrations decreased on day 0. The isoleucine concentration was relatively higher than the leucine concentration on day 7 when evaluated with “b”. Changes in “b” on days 0 and 7 differed between men and women. There were sex-related differences in the plasma concentration ratios of BCAAs evaluated by “b”, which indicates a possible sex-related difference in the metabolic response to bacterial infection.

Endogenous Metabolic Modulators: Emerging Therapeutic Potential of Amino Acids

Multifactorial disease pathophysiology is complex and incompletely addressed by existing targeted pharmacotherapies. Amino acids (AAs) and related metabolites and precursors are a class of endogenous metabolic modulators (EMMs) that have diverse biological functions and, thus, have been explored for decades as potential multifactorial disease treatments. Here, we review the literature on this class of EMMs in disease treatment, with a focus on the emerging clinical studies on AAs and related metabolites and precursors as single- and combination-agents targeted to a single biology. These clinical research insights, in addition to increasing understanding of disease metabolic profiles and combinatorial therapeutic design principles, highlight an opportunity to develop EMM compositions with AAs and related metabolites and precursors to target multifactorial disease biology. EMM compositions are uniquely designed to enable a comprehensive approach, with potential to simultaneously and safely target pathways underlying multifactorial diseases and to regulate biological processes that promote overall health.

Cross-correlation of plasma concentrations of branched-chain amino acids: A comparison between healthy participants and patients with chronic kidney disease

BACKGROUND & AIMS

Plasma concentrations of branched-chain amino acids (BCAAs) are known to exhibit strong intercorrelations; however, the associated regulatory mechanism is not sufficiently understood. Furthermore, the mechanisms underlying the intercorrelation changes in metabolic disorders with the disease are unclear. Therefore, plasma BCAAs in patients with chronic kidney disease (CKD) were examined.

METHODS

This study included a healthy group of older participants (Group C; n = 87, 46 males, 41 females) who had undergone health examinations at Sanyudo Hospital and a group of CKD patients (Group CKD; n = 71, 49 males, 22 females) receiving maintenance hemodialysis at the same hospital. Samples from Group C were collected 12 h after fasting. CKD samples were collected before and after hemodialysis (pre-HD and post-HD, respectively), without 12 h fasting. The samples were analyzed for 38 amino acids by SRL Inc., using liquid chromatography-mass spectrometry (LC-MS).

RESULTS

Differences between the plasma BCAA concentrations of Group C and pre-HD were determined. Dialysis-induced BCAA losses were different for each BCAA. However, strong intercorrelations between the plasma concentrations of each BCAA were maintained. In addition, the regression lines did not converge at the origin and were in different positions for groups C, pre-HD, and post-HD. A different distribution of the constant (b) for each group was observed for each BCAA correlation when a in the regression line (Y = aX + b) was fixed at the value for Group C, and b was calculated.

CONCLUSION

Strong intercorrelations among plasma concentrations of BCAAs were maintained in CKD patients both pre- and post-dialysis, whereas the changes in the plasma concentrations of each BCAA were different. We speculate that there is a novel mechanism that selectively regulates each BCAA and suggest that changes in the constant of the regression formula for correlation may have a novel function as an index for renal contribution to BCAA metabolism.

High Plasma Branched-Chain Amino Acids Are Associated with Higher Risk of Post-Transplant Diabetes Mellitus in Renal Transplant Recipients

Post-transplant diabetes mellitus (PTDM) is a serious complication in renal transplant recipients. Branched-chain amino acids (BCAAs) are involved in the pathogenesis of insulin resistance. We determined the association of plasma BCAAs with PTDM and included adult renal transplant recipients (≥18 y) with a functioning graft for ≥1 year in this cross-sectional cohort study with prospective follow-up. Plasma BCAAs were measured in 518 subjects using nuclear magnetic resonance spectroscopy. We excluded subjects with a history of diabetes, leaving 368 non-diabetic renal transplant recipients eligible for analyses. Cox proportional hazards analyses were used to assess the association of BCAAs with the development of PTDM. Mean age was 51.1 ± 13.6 y (53.6% men) and plasma BCAA was 377.6 ± 82.5 µM. During median follow-up of 5.3 (IQR, 4.2–6.0) y, 38 (9.8%) patients developed PTDM. BCAAs were associated with a higher risk of developing PTDM (HR: 1.43, 95% CI 1.08–1.89) per SD change (p = 0.01), independent of age and sex. Adjustment for other potential confounders did not significantly change this association, although adjustment for HbA1c eliminated it. The association was mediated to a considerable extent (53%) by HbA1c. The association was also modified by HbA1c; BCAAs were only associated with renal transplant recipients without prediabetes (HbA1c < 5.7%). In conclusion, high concentrations of plasma BCAAs are associated with developing PTDM in renal transplant recipients. Alterations in BCAAs may represent an early predictive biomarker for PTDM.

The Association Between Leucine and Diabetic Nephropathy in Different Gender: A Cross-Sectional Study in Chinese Patients With Type 2 Diabetes

OBJECTIVE

This study aimed to evaluate how leucine are associated with diabetic nephropathy (DN) in type 2 diabetes (T2D) patients and the gender difference of this association.

METHODS

We retrieved 1,031 consecutive patients with T2D who meet the inclusion and exclusion criteria from the same tertiary care center and extracted clinical information from electronic medical record. Plasma leucine was measured by liquid chromatography-mass spectrometer. Restricted cubic spline (RCS) was conducted to examine potential non-linear relationship between leucine and the risk of DN. Logistic regression was used to obtain odds ratio (OR) and confidence interval (CI). Additive interaction was used to estimate the interaction effect between leucine and gender for DN.

RESULTS

We found there was a negative correlation between leucine and the risk of DN. After stratifying all patients by gender, this relationship only remained significant in women (OR:0.57, CI:0.41-0.79).

CONCLUSIONS

In conclusion, T2D patients with high levels of leucine have a lower risk of developing DN in female.

Plasma Branched-Chain Amino Acids and Risk of Incident Type 2 Diabetes: Results from the PREVEND Prospective Cohort Study

Plasma branched-chain amino acids (BCAAs) are linked to metabolic disease, but their relevance for prediction of type 2 diabetes development is unclear. We determined the association of plasma BCAAs with type 2 diabetes risk in the prevention of renal and vascular end-stage disease (PREVEND) cohort. The BCAAs were measured by means of nuclear magnetic resonance spectroscopy. We evaluated the prospective associations of BCAAs with type 2 diabetes in 6244 subjects. The BCAAs were positively associated with HOMA-IR after multivariable adjustment (p < 0.0001). During median follow-up for 7.5 years, 301 cases of type 2 diabetes were ascertained. The Kaplan-Meier plot demonstrated that patients in the highest BCAA quartile presented a higher risk (p log-rank < 0.001). Cox regression analyses revealed a positive association between BCAA and type 2 diabetes; the hazard ratio (HR) for the highest quartile was 6.15 (95% CI: 4.08, 9.24, p < 0.0001). After adjustment for multiple clinical and laboratory variables, the association remained (HR 2.80 (95% CI: 1.72, 4.53), p < 0.0001). C-statistics, Net reclassification improvement, and −2 log likelihood were better after adding BCAAs to the traditional risk model (p = 0.01 to <0.001). In conclusions, high concentrations of BCAAs associate with insulin resistance and with increased risk of type 2 diabetes. This association is independent of multiple risk factors, HOMA-IR and β cell function.

Association of plasma concentrations of branched-chain amino acids with risk of colorectal adenoma in a large Japanese population

Background

Available evidence from animal studies suggests that branched-chain amino acids (BCAAs) may have a protective effect against colorectal carcinogenesis. However, a possible effect of BCAAs against colorectal neoplasia has not been evaluated in humans. Here, we aimed to evaluate whether plasma concentrations of BCAA are associated with the risk of colorectal adenoma (CRA), a precursor lesion of colorectal cancer.

Patients and methods

CRA cases and controls were identified from examinees who underwent total colonoscopy as part of a cancer screening program between 2004 and 2005 and responded to self-administered dietary and lifestyle questionnaires. We measured plasma concentrations of leucine, isoleucine and valine in 629 patients with adenoma and 584 controls. Unconditional logistic regression models were used to estimate odds ratio (OR) and 95% confidence interval (CI) for the association between BCAA and CRA risk after adjustment for potential confounders.

Results

High plasma concentrations of leucine, valine and total BCAA were inversely associated with CRA risk after adjustment of potential confounders. The multivariate-adjusted ORs for the highest versus lowest quartiles were 0.60 (95% CI 0.42-0.87, Ptrend = 0.006) for leucine, 0.68 (95% CI 0.48-0.97, Ptrend = 0.09) for valine and 0.68 (95% CI 0.48-0.98, Ptrend = 0.10) for total BCAA. Further analysis by gender revealed that this inverse association was clearly evident in men, but not in women: the corresponding OR for leucine, valine and total BCAA was 0.50 (95% CI 0.32-0.80, Ptrend = 0.003), 0.60 (95% CI 0.38-0.95, Ptrend = 0.01) and 0.58 (95% CI 0.37-0.93, Ptrend = 0.04), respectively, in men and 0.78 (95% CI 0.42-1.45, Ptrend = 0.44), 0.77 (95% CI 0.41-1.43, Ptrend = 0.85) and 0.84 (95% CI 0.45-1.57, Ptrend = 0.81), respectively, in women.

Conclusion

Our finding suggests that BCAAs may have a beneficial influence against the process of colorectal carcinogenesis, at least in the early stage. The mechanisms underlying this potential association between BCAA and colorectal carcinogenesis warrant further investigation.

The role of amino acid profiles in diabetes risk assessment

PURPOSE OF REVIEW

The concentrations of plasma-free amino acids, such as branched-chain amino acids and aromatic amino acids, are associated with visceral obesity, insulin resistance, and the future development of diabetes and cardiovascular diseases. This review discusses recent progress in the early assessment of the risk of developing diabetes and the reversal of altered plasma-free amino acids through interventions. Additionally, recent developments that have increased the utility of amino acid profiling technology are also described.

RECENT FINDINGS

Plasma-free amino acid alterations in the early stage of lifestyle-related diseases are because of obesity and insulin resistance-related inflammation, and these alterations are reversed by appropriate (nutritional, drug, or surgical) interventions that improve insulin sensitivity. For clinical applications, procedures for measuring amino acids are being standardized and automated.

SUMMARY

Plasma-free amino acid profiles have potential as biomarkers for both assessing diabetes risk and monitoring the effects of strategies designed to lower that risk. In addition, the methodology for measuring amino acids has been refined, with the goal of routine clinical application.