Oral administration of kynurenic acid delays the onset of type 2 diabetes in Goto-Kakizaki rats

Altered neopterin and IDO in kynurenine metabolism based on LC-MS/MS metabolomics study: Novel therapeutic checkpoints for type 2 diabetes mellitus

BACKGROUND

This study assessed the alternations of kynurenine pathway (KP) and neopterin in type 2 diabetes mellitus (T2DM) and explored possible differential metabolites.

METHODS

A fresh residual sera panel was collected from 80 healthy control (HC) individuals and 72 T2DM patients. Metabolites/ratios of interest including tryptophan (TRP), kynurenine (KYN), 5-hydroxytryptamine (5HT), kynurenic acid (KA), xanthurenic acid (XA), neopterin (NEO), KA/KYN ratio and KYN/TRP ratio were determined using a targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) metabolomics approach, and the difference between groups was assessed. Supervised orthogonal partial least squares-discriminant analysis and differential metabolite screening with fold change (FC) were performed to identify distinct biomarkers. The diagnostic performance of KP metabolites in T2DM was evaluated.

RESULTS

Significant decreases of TRP, 5HT, KA, XA, and KA/KYN and increases of KYN/TRP and NEO in T2DM compared to HC group were observed (P < 0.05). The KP metabolites panel significantly changed between T2DM and HC groups (Q2: 0.925, P < 0.005). 5HT (FC: 0.63, P < 0.01) and NEO (FC: 3.27, P < 0.01) were proven to be distinct differential metabolites. A combined testing of fasting plasma glucose and KYN/TRP showed good value in the prediction of T2DM (AUC: 0.904, 95% CI 0.843-0.947).

CONCLUSIONS

The targeted LC-MS/MS metabolomics study is a powerful tool for evaluating the status of T2DM. This study facilitated the application of KP metabolomics into future clinical practice. 5HT and NEO are promising biomarkers in T2DM. KYN/TRP was highly associated with the development of T2DM and may serve as a potential treatment target.

Antiobesity and antidiabetes effects of Cyperus rotundus rhizomes presenting protein tyrosine phosphatase, dipeptidyl peptidase 4, metabolic enzymes, stress oxidant and inflammation inhibitory potential

Diabetes is a significant global health concern that increases the vulnerability to various chronic illnesses. In view of this issue, the current research aimed to examine the effects of administering an extract derived from the tubers of Cyperus rotundus L (CrE) on obesity, type 1 diabetes, and liver-kidney toxicity. Through the utilization of HPLC-DAD analysis, it was discovered that the extract contained several components, including quercetin (47.8%), luteolin glucoside (17%), luteolin (7.56%), apigenin-7-glucoside (6.29%), naringinin (4.52%), and seven others. In vitro experiments they have demonstrated that CrE effectively inhibited key digestive enzymes associated with obesity and type 2 diabetes, such as DPP-4, PTP1B, lipase, and α-amylase, as evidenced by their respective IC50 values are about 23, 51,83, and 67 μg/ml respectively. Furthermore, when diabetic rats were administered CrE, the activity of pancreatic enzymes linked to inflammation, namely 5-lipoxygenase (5-LO), hyaluronidase (HAase), and myeloperoxidase (MPO), was significantly suppressed by 48, 41, 75, and 47%, respectively. Moreover, CrE exhibited protective effects on pancreatic β-cells by inhibiting the formation of thiobarbituric acid reactive substances (TBARS) by 65% and the induction of superoxide Dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) activities by 62, 108, and 112% respectively as compared to diabetic untreated rat. Additionally, CrE significantly inhibited the activities of intestinal, pancreatic, and serum lipase and α-amylase activities. In diabetic rats, CrE administration suppressed glycogen phosphorylase (GP) stimulated glycogen synthase (GS) activities by 45 and 30%; and this increased liver glycogen content by 45%. Furthermore, CrE modulated key hepatic enzymes involved in carbohydrate metabolism, including hexokinase (HK), glucose-6-phosphate dehydrogenase (G6PD), glucose-6-phosphatase (G6P), and fructose-1,6-bisphosphatase (FBP). Notably, the average food and water intake (AFI and AWI) of diabetic rats treated with CrE was reduced by 15 and 16% respectively as compared to those without any treatment. Therefore, this study demonstrated the effectiveness of Cyperus rotundus tubers in preventing and treating obesity and diabetes.

Tryptophanylation of insulin receptor by WARS attenuates insulin signaling

Increased circulating amino acid levels have been linked to insulin resistance and development of type 2 diabetes (T2D), but the underlying mechanism remains largely unknown. Herein, we show that tryptophan modifies insulin receptor (IR) to attenuate insulin signaling and impair glucose uptake. Mice fed with tryptophan-rich chow developed insulin resistance. Excessive tryptophan promoted tryptophanyl-tRNA synthetase (WARS) to tryptophanylate lysine 1209 of IR (W-K1209), which induced insulin resistance by inhibiting the insulin-stimulated phosphorylation of IR, AKT, and AS160. SIRT1, but not other sirtuins, detryptophanylated IRW-K1209 to increase the insulin sensitivity. Collectively, we unveiled the mechanisms of how tryptophan impaired insulin signaling, and our data suggested that WARS might be a target to attenuate insulin resistance in T2D patients.