Gut microbiota mediate melatonin signalling in association with type 2 diabetes.

AIMS/HYPOTHESIS: It has been shown that melatonin plays a general beneficial role in type 2 diabetes in rodents but its role in humans is controversial. In the present study, we investigated the association between serum melatonin and type 2 diabetes risk in a southern Chinese population in a case-control study. We also examined the role of gut microbiota in this relationship. METHODS: Individuals with type 2 diabetes (cases) and healthy individuals (controls) (n=2034) were recruited from a cross-sectional study and were matched for age and sex in a case-control study. The levels of serum melatonin were measured and the association between serum melatonin and type 2 diabetes risk was examined using a multivariable logistic regression model. We further conducted a rigorously matched case-control study (n=120) in which gut microbial 16S rRNA was sequenced and metabolites were profiled using an untargeted LC-MS/MS approach. RESULTS: Higher levels of serum melatonin were significantly associated with a lower risk of type 2 diabetes (OR 0.82 [95% CI 0.74, 0.92]) and with lower levels of fasting glucose after adjustment for covariates (ß -0.25 [95% CI -0.38, -0.12]). Gut microbiota exhibited alteration in the individuals with type 2 diabetes, in whom lower levels of serum melatonin, lower α- and ß-diversity of gut microbiota (p<0.05), greater abundance of Bifidobacterium and lower abundance of Coprococcus (linear discriminant analysis [LDA] >2.0) were found. Seven genera were correlated with melatonin and type 2 diabetes-related traits; among them Bifidobacterium was positively correlated with serum lipopolysaccharide (LPS) and IL-10, whereas Coprococcus was negatively correlated with serum IL-1ß, IL-6, IL-10, IL-17, TNF-α and LPS (Benjamini-Hochberg-adjusted p value [false discovery rate (FDR)] <0.05). Moreover, altered metabolites were detected in the participants with type 2 diabetes and there was a significant correlation between tryptophan (Trp) metabolites and the melatonin-correlated genera including Bifidobacterium and Coprococcus (FDR<0.05). Similarly, a significant correlation was found between Trp metabolites and inflammation factors, such as IL-1ß, IL-6, IL-10, IL-17, TNF-α and LPS (FDR<0.05). Further, we showed that Trp metabolites may serve as a biomarker to predict type 2 diabetes status (AUC=0.804). CONCLUSIONS/INTERPRETATION: A higher level of serum melatonin was associated with a lower risk of type 2 diabetes. Gut microbiota-mediated melatonin signalling was involved in this association; especially, Bifidobacterium- and Coprococcus-mediated Trp metabolites may be involved in the process. These findings uncover the importance of melatonin and melatonin-related bacteria and metabolites as potential therapeutic targets for type 2 diabetes.

[Determination of carbamazepine and 10-hydroxy-carbamazepine in human serum by solid-phase extraction with poly ethylene glycol dimethacrylate monolithic column coupled with high performance liquid chromatography].

A polymeric monolithic solid phase extraction sorbent was fabricated from sole ethylene glycol dimethacrylate in a syringe and applied as a sorbent for the determination of carbamazepine (CBZ) and 10-hydroxy-carbamazepine (MHD) in human serum using high performance liquid chromatography. The effects of reaction temperature and reaction time on the extraction performance of the target compounds were investigated. The parameters, such as washing solvent, and elution solution and its volume, were optimized. Under the optimized condition, the purification and enrichment of CBZ and MHD in human serum were successfully achieved on the proposed poly ethylene glycol dimethacrylate (EDMA) monolithic column. The linear ranges were 0.02-40 µg/mL for CBZ and 0.05-100 µg/mL for MHD. The results indicated that the method exhibited good linearity in the corresponding ranges with the correlation coefficients (r) of 0.999. The limits of detection (S/N=3) of CBZ and MHD were 0.004 µg/mL and 0.01 µg/mL, respectively. The average recoveries at three spiked levels of CBZ and MHD were 92.7% and 94.2%, respectively, with relative standard deviations (RSDs) ≤ 6.1%. Furthermore, the intra column to column (n=3) and inter batch to batch (n=5) RSDs were no more than 5.3%. The RSDs of eight repeated extraction cycles were no more than 5.8%. The developed method is effective and simple, and is suitable for the determination of CBZ and MHD in human serum.