Amino acids - lifesaver or killer in patients with diabetes?

Inter-organ crosstalk during development and progression of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is characterized by tissue-specific insulin resistance and pancreatic β-cell dysfunction, which result from the interplay of local abnormalities within different tissues and systemic dysregulation of tissue crosstalk. The main local mechanisms comprise metabolic (lipid) signalling, altered mitochondrial metabolism with oxidative stress, endoplasmic reticulum stress and local inflammation. While the role of endocrine dysregulation in T2DM pathogenesis is well established, other forms of inter-organ crosstalk deserve closer investigation to better understand the multifactorial transition from normoglycaemia to hyperglycaemia. This narrative Review addresses the impact of certain tissue-specific messenger systems, such as metabolites, peptides and proteins and microRNAs, their secretion patterns and possible alternative transport mechanisms, such as extracellular vesicles (exosomes). The focus is on the effects of these messengers on distant organs during the development of T2DM and progression to its complications. Starting from the adipose tissue as a major organ relevant to T2DM pathophysiology, the discussion is expanded to other key tissues, such as skeletal muscle, liver, the endocrine pancreas and the intestine. Subsequently, this Review also sheds light on the potential of multimarker panels derived from these biomarkers and related multi-omics for the prediction of risk and progression of T2DM, novel diabetes mellitus subtypes and/or endotypes and T2DM-related complications.

Metabolic and Metabo-Clinical Signatures of Type 2 Diabetes, Obesity, Retinopathy, and Dyslipidemia

Macro- and microvascular complications of type 2 diabetes (T2D), obesity, and dyslipidemia share common metabolic pathways. In this study, using a total of 1,300 metabolites from 996 Qatari adults (57% with T2D) and 1,159 metabolites from an independent cohort of 2,618 individuals from the Qatar BioBank (11% with T2D), we identified 373 metabolites associated with T2D, obesity, retinopathy, dyslipidemia, and lipoprotein levels, 161 of which were novel. Novel metabolites included phospholipids, sphingolipids, lysolipids, fatty acids, dipeptides, and metabolites of the urea cycle and xanthine, steroid, and glutathione metabolism. The identified metabolites enrich pathways of oxidative stress, lipotoxicity, glucotoxicity, and proteolysis. Second, we identified 15 patterns we defined as "metabo-clinical signatures." These are clusters of patients with T2D who group together based on metabolite levels and reveal the same clustering in two or more clinical variables (obesity, LDL, HDL, triglycerides, and retinopathy). These signatures revealed metabolic pathways associated with different clinical patterns and identified patients with extreme (very high/low) clinical variables associated with extreme metabolite levels in specific pathways. Among our novel findings are the role of N-acetylmethionine in retinopathy in conjunction with dyslipidemia and the possible roles of N-acetylvaline and pyroglutamine in association with high cholesterol levels and kidney function.

Determination of N-acetyl-DL-leucine in the saliva of healthy volunteers and diabetic patients using ultra-performance liquid chromatography with fluorescence detection

BACKGROUND

Recent studies have indicated that N-acetyl-leucine (N-Ac-Leu) is a potential biomarker of diabetes. This study aimed to measure the levels of enantiomers of the chiral molecule N-Ac-DL-Leu in the saliva of patients with type 2 diabetes and further determine the potential association between them.

METHOD

A novel validated method was established using ultra-performance liquid chromatography (UPLC) with fluorescence (FL) detection, in which precolumn derivatization of (R)-(-)-4-(N, N-dimethylaminosulfonyl)-7-(3-aminopyrrolidin-l-yl)-2,1,3-benzoxadiazole [(R)-(-)-DBD-APy] was used for the simultaneous determination and chiral separation of N-Ac-DL-Leu in human saliva.

RESULTS

The labeled N-Ac-DL-Leu diastereomers were completely separated, with a resolution value of 1.93. Additionally, excellent linearity for N-Ac-DL-Leu was observed, with high coefficients of correlation (r² ≥ 0.9999) in the range of 10-300 μM; the limit of quantitation (signal-to-noise ratio=10) was 40-120 pmol/mL, and the mean recoveries of N-Ac-L-Leu and N-Ac-D-Leu were 102.48% and 104.68%, respectively. The levels of N-Ac-Leu in the saliva of diabetic patients and healthy volunteers were determined, and it was found that the levels of N-Ac-DL-Leu in the saliva of diabetic patients were significantly lower than those in healthy volunteers. (p < 0.01).

CONCLUSIONS

The proposed method was successfully applied for the measurement of N-Ac-DL-Leu enantiomers in the saliva of diabetic patients and healthy volunteers.

Anticipation of Precision Diabetes and Promise of Integrative Multi-Omics

Precision diabetes is a concept of customizing delivery of health practices based on variability of diabetes. The authors reviewed recent research on type 2 diabetes heterogeneity and -omic biomarkers, including genomic, epigenomic, and metabolomic markers associated with type 2 diabetes. The emerging multiomics approach integrates complementary and interconnected molecular layers to provide systems level understanding of disease mechanisms and subtypes. Although the multiomic approach is not currently ready for routine clinical applications, future studies in the context of precision diabetes, particular in populations from diverse ethnic and demographic groups, may lead to improved diagnosis, treatment, and management of diabetes and diabetic complications.

Targeted metabolomics as a tool for the diagnosis of kidney disease in Type II diabetes mellitus

Background: Diabetic kidney disease (DKD) is an increasing health problem and an extra burden to health services. The study of characteristic metabolic alterations of DKD is crucial for a better understanding of pathogenesis to identify new potential biomarkers and drug targets. We hypothesized that metabolic profiling of amino acids, acylcarnitines, and organic acids are useful new biomarkers for the diagnosis of the early stages of DKDMethods: The hypothesis was testing in a case-control study of 232 patients with type 2 diabetes mellitus and 150 healthy controls. Patients were classified according to urinary albumin and estimated glomerular filtration rate (eGFR) into 100 with normoalbuminuria and 132 with microalbuminuria group. Eighteen AcylCNs and 17 amino acids were measured in the blood by tandem mass spectrometry while 17 urinary organic acids were quantitatively measured by gas chromatography - mass spectrometry.Results: Regression analysis found that dodecanoylcarnitines C12 (effect size 2.03 [95%CI 1.73-2.32]), triglylcarnitine C5:1 (2.01 [1.70-2.30]), and isovalerylcarnitine C5 (1.78 [1.48-2.07]) were stronger predictors of albumin/creatinine ratio than HbA1c (1.50 [1.20-1.78]) and hence they could serve as potential biomarkers for the diagnosis of the early stages of DKD.Conclusions: Targeted metabolic profiling offers a new, non-invasive approach for detecting biomarkers for the early diagnosis of DKD suggesting new pathogenetic phases that might be new targets for treatment.

Multiomics Approach to Explore the Amelioration Mechanisms of Glucomannans on the Metabolic Disorder of Type 2 Diabetic Rats

Type 2 diabetes (T2D) is a worldwide epidemic associated with metabolic disorders and intestinal microbiota alterations. Polysaccharides have been considered to be beneficial to the prevention and alleviation of T2D. In the present study, ultra-performance liquid chromatography-triple-time-of-flight-based metabolomics and proteomics and 16S rRNA sequencing methods were employed to evaluate the effects of glucomannans from Dendrobium officinale stem, konjac, and Aloe vera leaves on host metabolism and intestinal microbiota regulation in type 2 diabetic rats and potential mechanisms. The metabolism of amino acids was significantly disturbed in the type 2 diabetic rats, especially the upregulated branched-chain amino acid (BCAA) metabolism. Host-derived BCAA metabolism was significantly decreased in type 2 diabetic rats. However, the levels of BCAAs in host circulation and gene abundance of BCAA biosynthesis in gut microbiota were significantly increased in diabetic rats, which suggested that the disturbed intestinal microbiota might be responsible for the increased circulation of BCAAs in T2D. Glucomannan treatment decreased the abundance of microbial BCAA biosynthesis-related genes and ameliorated the host BCAA metabolism. Also, glucomannan with a higher molecular weight and a lower ratio of mannose/glucose possessed better antidiabetic effects. In summary, the antidiabetic effects of glucomannans might be associated with the amelioration of BCAA metabolism by modulating intestinal microbiota.

Edgeworthia gardneri (Wall.) Meisn. Water Extract Ameliorates Palmitate Induced Insulin Resistance by Regulating IRS1/GSK3β/FoxO1 Signaling Pathway in Human HepG2 Hepatocytes

The flower of Edgeworthia gardneri (Wall.) Meisn is commonly used in beverage products in Tibet and has potential health benefits for diabetes. However, the mechanisms underlying anti-insulin resistance (IR) action of the flower of E. gardneri are not fully understood. This study aims to investigate the effects of the water extract of the flower of E. gardneri (WEE) on IR in palmitate (PA)-exposed HepG2 hepatocytes. WEE was characterized by UPLC analysis. PA-treated HepG2 cells were selected as the IR cell model. The cell viability was determined using MTT assay. Moreover, the glucose consumption and production were measured by glucose oxidase method. The glucose uptake and glycogen content were determined by the 2-NBDG (2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl) amino]-D-glucose) glucose uptake assay and anthrone-sulfuric acid assay, respectively. The intracellular triglyceride content was detected by oxidative enzymic method. Protein levels were examined by Western blotting. Nuclear localization of FoxO1 was detected using immunofluorescence analyses and Western blotting. The expression of FoxO1 target genes was detected by quantitative real-time polymerase chain reaction (qRT-PCR). The viability of PA-treated HepG2 cells was concentration-dependently increased by incubation with WEE for 24 h. WEE treatment remarkably increased the consumption and uptake of glucose in PA-exposed HepG2 cells. Moreover, treatment with WEE significantly decreased the PA-induced over-production of glucose in HepG2 cells. After exposure of HepG2 cells with PA and WEE, the glycogen content was significantly elevated. The phosphorylation and total levels of IRβ, IRS1, and Akt were upregulated by WEE treatment in PA-exposed HepG2 cells. The phosphorylation of GSK3β was elevated after WEE treatment in PA-treated cells. WEE treatment also concentration-dependently downregulated the phosphorylated CREB, ERK, c-Jun, p38 and JNK in PA-exposed HepG2 cells. Furthermore, the nuclear protein level and nuclear translocation of FoxO1 were also suppressed by WEE. Additionally, PA-induced changes of FoxO1 targeted genes were also attenuated by WEE treatment. The GLUT2 and GLUT4 translocation were also promoted by WEE treatment in PA-treated HepG2 cells. Taken together, WEE has potential anti-IR effect in PA-exposed HepG2 cells; the underlying mechanism of this action may be associated with the regulation of IRS1/GSK3β/FoxO1 signaling pathway. This study provides a pharmacological basis for the application of WEE in the treatment of metabolic diseases such as type 2 diabetes mellitus.

Differences in Serum Amino Acid Phenotypes Among Patients with Diabetic Nephropathy, Hypertensive Nephropathy, and Chronic Nephritis

Background

We assessed levels of circulating amino acids in different etiologies of chronic kidney disease (CKD) and the association of amino acids with risk factors of CKD progression.

Material/Methods

High-performance liquid chromatography-based analysis was used to determine amino acid profiles in patients with diabetic nephropathy (DN, n=20), hypertensive nephropathy (HN, n=26), and chronic nephritis (CN, n=33), and in healthy controls (HC, n=25).

Results

All 3 types of CKD patients displayed decreased serum levels of serine, glycine, GABA, and tryptophan compared with healthy controls. Moreover, serine and tryptophan were positively correlated with glucose in DN cohorts. Total cholesterol was positively correlated with tryptophan levels in the DN cohort and negatively correlated with serine levels in the CN cohort. In the HN cohort, glycine was negatively correlated with triglyceride levels, and systolic blood pressure (SBP) was negatively correlated with GABA levels.

Conclusions

Patients with different etiologies of CKD have significantly different amino acids profiles, and this indicates specific supplementary nutritional needs in CKD patients.

Metabolic Fingerprint of Acromegaly and its Potential Usefulness in Clinical Practice

Insulin-like growth factor-1 (IGF-1) and growth hormone (GH) levels are the main targets for monitoring acromegaly activity, but they are not in close relationship with the clinical course of the disease and the associated comorbidities. The present study was aimed at identifying metabolites that could be used as biomarkers for a better disease phenotyping. For this purpose, metabolic fingerprint using an untargeted metabolomic approach was examined in serum from 30 patients with acromegaly and 30 age-matched controls. Patients with acromegaly presented fewer branched-chain amino acids (BCAAs) compared to the control group (valine: 4.75 ± 0.87 vs. 5.20 ± 1.06 arbitrary units (AUs), p < 0.05; isoleucine: 2.54 ± 0.41 vs. 2.80 ± 0.51 AUs; p < 0.05). BCAAs were also lower in patients with active disease compared to patients with normal levels of IGF-1 with or without medical treatment. GH, but not IGF-1, serum levels were inversely correlated with both valine and isoleucine. These findings indicate that low levels of BCAAs represent the main metabolic fingerprint of acromegaly and that GH, rather than IGF-1, might be the primary mediator. In addition, our results suggest that the assessment of BCAAs could help to identify active disease and to monitor the response to therapeutic strategies.

Perfluoroalkyl substances, metabolomic profiling, and alterations in glucose homeostasis among overweight and obese Hispanic children: A proof-of-concept analysis

OBJECTIVE

To examine the prospective associations between exposure to perfluoroalkyl substances (PFASs) and longitudinal measurements of glucose metabolism in high-risk overweight and obese Hispanic children.

METHODS

Forty overweight and obese Hispanic children (8-14 years) from urban Los Angeles underwent clinical measures and 2-hour oral glucose tolerance tests (OGTT) at baseline and a follow-up visit (range: 1-3 years after enrollment). Baseline plasma perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), perfluorohexane sulfonic acid (PFHxS), and the plasma metabolome were measured by liquid-chromatography with high-resolution mass spectrometry. Multiple linear regression models were used to assess the association between baseline PFASs and changes in glucose homeostasis over follow-up. A metabolome-wide association study coupled with pathway enrichment analysis was performed to evaluate metabolic dysregulation associated with plasma PFASs concentrations. We performed a structural integrated analysis aiming to characterize the joint impact of all factors and to identify latent clusters of children with alterations in glucose homeostasis, based on their exposure and metabolomics profile.

RESULTS

Each ln (ng/ml) increase in PFOA and PFHxS concentrations was associated with a 30.6 mg/dL (95% CI: 8.8-52.4) and 10.2 mg/dL (95% CI: 2.7-17.7) increase in 2-hour glucose levels, respectively. A ln (ng/ml) increase in PFHxS concentrations was also associated with 17.8 mg/dL increase in the glucose area under the curve (95% CI: 1.5-34.1). Pathway enrichment analysis showed significant alterations of lipids (e.g., glycosphingolipids, linoleic acid, and de novo lipogenesis), and amino acids (e.g., aspartate and asparagine, tyrosine, arginine and proline) in association to PFASs exposure. The integrated analysis identified a cluster of children with increased 2-h glucose levels over follow up, characterized by increased PFAS levels and altered metabolite patterns.

CONCLUSIONS

This proof-of-concept analysis shows that higher PFAS exposure was associated with dysregulation of several lipid and amino acid pathways and longitudinal alterations in glucose homeostasis in Hispanic youth. Larger studies are needed to confirm these findings and fully elucidate the underlying biological mechanisms.

Metabolites Associated with Vigor to Frailty Among Community-Dwelling Older Black Men

Black versus white older Americans are more likely to experience frailty, a condition associated with adverse health outcomes. To reduce racial disparities in health, a complete understanding of the pathophysiology of frailty is needed. Metabolomics may further our understanding by characterizing differences in the body during a vigorous versus frail state. We sought to identify metabolites and biological pathways associated with vigor to frailty among 287 black men ages 70-81 from the Health, Aging, and Body Composition study. Using liquid chromatography-mass spectrometry, 350 metabolites were measured in overnight-fasting plasma. The Scale of Aging Vigor in Epidemiology (SAVE) measured vigor to frailty based on weight change, strength, energy, gait speed, and physical activity. Thirty-seven metabolites correlated with SAVE scores (p < 0.05), while adjusting for age and site. Fourteen metabolites remained significant after multiple comparisons adjustment (false discovery rate < 0.30). Lower values of tryptophan, methionine, tyrosine, asparagine, C14:0 sphingomyelin, and 1-methylnicotinamide, and higher values of glucoronate, N-carbamoyl-beta-alanine, isocitrate, creatinine, C4-OH carnitine, cystathionine, hydroxyphenylacetate, and putrescine were associated with frailer SAVE scores. Pathway analyses identified nitrogen metabolism, aminoacyl-tRNA biosynthesis, and the citric acid cycle. Future studies need to confirm these SAVE-associated metabolites and pathways that may indicate novel mechanisms involved in the frailty syndrome.