The impact of L-citrulline supplementation on glucose homeostasis, lipid profile, and some inflammatory factors in overweight and obese patients with type 2 diabetes: A double-blind randomized placebo-controlled trial

Lactobacillus murinus alleviates insulin resistance via promoting L-citrulline synthesis

AIMS

The role of Lactobacillus murinus as a potential probiotic is being explored. Our objectives were to explore the effects of Lactobacillus murinus on insulin resistance and the underlying mechanism.

METHODS

Insulin resistance animal models were applied to study the effect of L. murinus and the underlying mechanism by six weeks of treatment. Metformin was administered in vitro to analyze the growth and metabolites of L. murinus. Serum metabolites were further analyzed after L. murinus administration. The effect of L-citrulline and the underlying mechanism in alleviating insulin resistance were evaluated.

RESULTS

L. murinus not only reduced body weight gain and postprandial blood glucose (PBG) but improved impaired glucose tolerance (IGT) and insulin resistance. Moreover, L. murinus inhibited the secretion of pro-inflammatory factors (IL-1β, IL-6 and TNF-α) while promoted the secretion of anti-inflammatory factor (IL-10). Further, L. murinus promoted the expression of carnitine palmitoyl transferase 1 (CPT1) while inhibited phosphoenolpyruvate carboxykinase (PCK) and glucose-6-phosphatase (G6Pase). A total of 147 metabolites of L. murinus were identified, in which the content of L-citrulline increased to 7.94 times after metformin regulation. Further, the serum concentration of L-citrulline significantly increased after L. murinus administration. Similarly, L-citrulline reduced body weight gain and PBG, improved IGT and insulin resistance. Additionally, L-citrulline improved inflammation, promoted CPT1 while inhibited PCK and G6Pase.

CONCLUSIONS

L. murinus mediated by L-citrulline alleviated insulin resistance via promoting fatty acid oxidation and inhibiting gluconeogenesis, suggesting that supplementation of L. murinus could be a potential therapeutic approach for type 2 diabetes related to insulin resistance.

Fermented Rice Bran Mitigated the Syndromes of Type 2 Diabetes in KK-Ay Mice Model

Background: Diabetes is a devastating disease that causes millions of deaths. Fermented rice bran (FRB), made by fermenting rice bran with Aspergillus kawachii and a mixture of lactic acid bacteria, was hypothesized to b able to improve diabetes-related symptoms. This study aimed to investigate the effects of FRB supplementation in mitigating type 2 diabetes symptoms and identifying FRB bioactive compounds. Methods: In this study, KK-Ay mice (4 w.o. male) were used as a model for type 2 diabetes. Mice were divided into three different groups. The first group received a control diet, the second received a 12.5% non-fermented rice bran (RB) supplemented diet, and the last group was fed a 12.5% FRB-supplemented diet. Supplementation was done for 4 weeks. Results: FRB supplementation lowered the blood glucose level, OGTT, HOMA-IR, total cholesterol, liver RAGE protein, and glucokinase in KK-Ay mice. Metabolome analysis of RB and FRB showed that fermentation increased bioactive compounds in rice bran, such as GABA, L-theanine, and carnitine. It also increased the levels of various free amino acids while converting some amino acids such as arginine, tyrosine, and tryptophan into other metabolites. Conclusions: This research showed the potency of FRB supplementation as a preventive agent against type 2 diabetes.

Integrated metabolomic and transcriptomic analysis reveals the effects and mechanisms of Jinqi Jiangtang tablets on type 2 diabetes

BACKGROUND

Type 2 diabetes (T2DM) is one of the major metabolic diseases and poses a serious challenge to human life and global economic development. Jinqi Jiangtang Tablets (JQJT) is effective in ameliorating the effects of T2DM, but the mechanism of JQJT is unclear.

PURPOSE

This study integrated metabolomics and transcriptomics to reveal the mechanism by which JQJT improves T2DM.

METHODS

The T2DM mouse model was established, and the effects of JQJT on improving T2DM were evaluated by determining the levels of blood lipids, fasting blood glucose (FBG), insulin metabolism and hepatic lipid accumulation in mice after JQJT administration for 8 weeks. Serum metabolites were detected using ultra-performance liquid chromatography/quadrupole time-of-flight-tandem mass spectrometry (UPLC-Q-TOF-MS) technology, and mouse liver differential genes were detected using transcriptomic technology. Correlation analysis was used to extract metabolites and RNA with correlations, and potential pathways were enriched and constructed using the common pathway analysis function of MetaboAnalyst 5.0. Finally, the expression of key target proteins and genes was verified by Western blot (WB) and Polymerase Chain Reaction (PCR) to further elucidate the mechanism by which JQJT improves T2DM.

RESULTS

JQJT reduced FBG and lipid levels, improved insulin resistance (IR) and hepatic lipoatrophy in mice. A total of 35 differentially abundant metabolites were identified by metabolomics, and 328 differential genes were detected by transcriptomics. The integrated metabolomics and transcriptomics results suggested that JQJT may ameliorate T2DM mainly by regulating glucose and lipid metabolic pathways. WB and PCR results showed that JQJT regulates the insulin signaling pathway, involved in fatty acid metabolism, glycogen synthesis and catabolism.

CONCLUSIONS

JQJT improved IR in T2DM mice by regulating the insulin signaling pathway, improving glycogen synthesis and glycolysis, and increasing hepatic triglyceride and fatty acid metabolism.

Gut microbiome shifts in adolescents after sleeve gastrectomy with increased oral-associated taxa and pro-inflammatory potential

Background

Bariatric surgery is highly effective in achieving weight loss in children and adolescents with severe obesity, however the underlying mechanisms are incompletely understood, and gut microbiome changes are unknown.

Objectives

1) To comprehensively examine gut microbiome and metabolome changes after laparoscopic vertical sleeve gastrectomy (VSG) in adolescents and 2) to assess whether the microbiome/metabolome changes observed with VSG influence phenotype using germ-free murine models.

Design

1) A longitudinal observational study in adolescents undergoing VSG with serial stool samples undergoing shotgun metagenomic microbiome sequencing and metabolomics (polar metabolites, bile acids and short chain fatty acids) and 2) a human-to-mouse fecal transplant study.

Results

We show adolescents exhibit significant gut microbiome and metabolome shifts several months after VSG, with increased alpha diversity and notably with enrichment of oral-associated taxa. To assess causality of the microbiome/metabolome changes in phenotype, pre-VSG and post-VSG stool was transplanted into germ-free mice. Post-VSG stool was not associated with any beneficial outcomes such as adiposity reduction compared pre-VSG stool. However, post-VSG stool exhibited an inflammatory phenotype with increased intestinal Th17 and decreased regulatory T cells. Concomitantly, we found elevated fecal calprotectin and an enrichment of proinflammatory pathways in a subset of adolescents post-VSG.

Conclusion

We show that in some adolescents, microbiome changes post-VSG may have inflammatory potential, which may be of importance considering the increased incidence of inflammatory bowel disease post-VSG.

Anti-obesity and anti-diabetic effects of L-citrulline are sex-dependent

AIMS

Anti-diabetic and anti-obesity effects of L-citrulline (Cit) have been reported in male rats. This study determined sex differences in response to Cit in Wistar rats.

MAIN METHODS

Type 2 diabetes (T2D) was induced using a high-fat diet followed by low-dose of streptozotocin (30 mg/kg) injection. Male and female Wistar rats were divided into 4 groups (n = 6/group): Control, control+Cit, T2D, and T2D + Cit. Cit (4 g/L in drinking water) was administered for 8 weeks. Obesity indices were recorded, serum fasting glucose and lipid profile were measured, and glucose and pyruvate tolerance tests were performed during the Cit intervention. White (WAT) and brown (BAT) adipose tissues were weighted, and the adiposity index was calculated at the end of the study.

KEY FINDINGS

Cit was more effective in decreasing fasting glucose (18 % vs. 11 %, P = 0.0100), triglyceride (20 % vs. 14 %, P = 0.0173), and total cholesterol (16 % vs. 11 %, P = 0.0200) as well as decreasing gluconeogenesis and improving glucose tolerance, in females compared to male rats with T2D. Following Cit administration, decreases in WAT weight (16 % vs. 14 % for gonadal, 21 % vs. 16 % for inguinal, and 18 % vs. 13 % for retroperitoneal weight, all P < 0.0001) and increases in BAT weight (58 % vs. 19 %, for interscapular and 10 % vs. 7 % for axillary, all P < 0.0001) were higher in females than male rats with T2D. The decrease in adiposity index was also higher (11 % vs. 9 %, P = 0.0007) in females.

SIGNIFICANCE

The anti-obesity and anti-diabetic effects of Cit in rats are sex-dependent, with Cit being more effective in female than male rats.

Assessing Metabolic Differences Associated with Exposure to Polybrominated Biphenyl and Polychlorinated Biphenyls in the Michigan PBB Registry

BACKGROUND

Polybrominated biphenyls (PBB) and polychlorinated biphenyls (PCB) are persistent organic pollutants with potential endocrine-disrupting effects linked to adverse health outcomes.

OBJECTIVES

In this study, we utilize high-resolution metabolomics (HRM) to identify internal exposure and biological responses underlying PCB and multigenerational PBB exposure for participants enrolled in the Michigan PBB Registry.

METHODS

HRM profiling was conducted on plasma samples collected from 2013 to 2014 from a subset of participants enrolled in the Michigan PBB Registry, including 369 directly exposed individuals (F0) who were alive when PBB mixtures were accidentally introduced into the food chain and 129 participants exposed to PBB in utero or through breastfeeding, if applicable (F1). Metabolome-wide association studies were performed for PBB-153 separately for each generation and Σ PCB (PCB-118, PCB-138, PCB-153, and PCB-180) in the two generations combined, as both had direct PCB exposure. Metabolite and metabolic pathway alterations were evaluated following a well-established untargeted HRM workflow.

RESULTS

Mean levels were 1.75  ng / mL [standard deviation (SD): 13.9] for PBB-153 and 1.04  ng / mL (SD: 0.788) for Σ PCB . Sixty-two and 26 metabolic features were significantly associated with PBB-153 in F0 and F1 [false discovery rate (FDR) p < 0.2 ], respectively. There were 2,861 features associated with Σ PCB (FDR p < 0.2 ). Metabolic pathway enrichment analysis using a bioinformatics tool revealed perturbations associated with Σ PCB in numerous oxidative stress and inflammation pathways (e.g., carnitine shuttle, glycosphingolipid, and vitamin B9 metabolism). Metabolic perturbations associated with PBB-153 in F0 were related to oxidative stress (e.g., pentose phosphate and vitamin C metabolism) and in F1 were related to energy production (e.g., pyrimidine, amino sugars, and lysine metabolism). Using authentic chemical standards, we confirmed the chemical identity of 29 metabolites associated with Σ PCB levels (level 1 evidence).

CONCLUSIONS

Our results demonstrate that serum PBB-153 is associated with alterations in inflammation and oxidative stress-related pathways, which differed when stratified by generation. We also found that Σ PCB was associated with the downregulation of important neurotransmitters, serotonin, and 4-aminobutanoate. These findings provide novel insights for future investigations of molecular mechanisms underlying PBB and PCB exposure on health. https://doi.org/10.1289/EHP12657.

Obesity- and sex-related metabolism of arginine and nitric oxide in adults

BACKGROUND

There is growing interest in the supplementation of arginine (Arg) and citrulline (Cit) in obesity due to their potential anti-obesogenic and anti-inflammatory properties. However, there is no consensus on the metabolic changes in Arg kinetics in obesity.

OBJECTIVES

This exploratory cross-sectional study aimed to investigate the association between obesity, sex, and sex-by-obesity interaction on whole-body Arg kinetics in a large group of human subjects.

METHODS

We studied 83 nonobese [BMI (kg/m2) <30] and 80 morbidly obese (BMI >30) middle-aged individuals (40% males) enrolled in the MEDIT (Metabolism of Disease with Isotope Tracers) trial. After body-composition measurement by DXA, we collected arterial(ized) blood samples for amino acid (AA) concentrations, markers of inflammation [high-sensitivity C-reactive protein (hs-CRP)], liver function, and glucose in a postabsorptive state. We administered a pulse of AA stable tracers and measured whole-body production (WBP) of Arg, Cit, ornithine (Orn), phenylalanine, and tyrosine, and calculated their clearance (disposal capacity) and metabolite interconversions [markers for NO and de novo Arg production, systemic Arg hydrolysis, and whole-body protein breakdown (wbPB)]. We measured plasma enrichments by LC-MS/MS and statistics by Fisher's exact test or analysis of (co)variance. Significance was set at P < 0.05.

RESULTS

Obese individuals were normoglycemic and characterized by low-grade inflammation (P < 0.0001) and greater wbPB (P = 0.0298). We found lower plasma Cit concentration (P < 0.0001) in the obese group but no differences in the WBP of Arg, Cit, and Orn. Furthermore, we observed overproduction of NO (P < 0.0001) in obesity but lower de novo Arg production (P = 0.0007). The WBP of Arg was lower in females for almost all Arg-related AAs, except for plasma Cit and NO production.

CONCLUSIONS

Alterations in Arg metabolism are present in morbid obesity. Further studies are needed to investigate if these changes could be related to factors such as increased Arg requirement in obesity or metabolic adaptation.

Current Evidence of Watermelon (Citrullus lanatus) Ingestion on Vascular Health: A Food Science and Technology Perspective

The amino acid L-arginine is crucial for nitric oxide (NO) synthesis, an important molecule regulating vascular tone. Considering that vascular dysfunction precedes cardiovascular disease, supplementation with precursors of NO synthesis (e.g., L-arginine) is warranted. However, supplementation of L-citrulline is recommended instead of L-arginine since most L-arginine is catabolized during its course to the endothelium. Given that L-citrulline, found mainly in watermelon, can be converted to L-arginine, watermelon supplementation seems to be effective in increasing plasma L-arginine and improving vascular function. Nonetheless, there are divergent findings when investigating the effect of watermelon supplementation on vascular function, which may be explained by the L-citrulline dose in watermelon products. In some instances, offering a sufficient amount of L-citrulline can be impaired by the greater volume (>700 mL) of watermelon needed to reach a proper dose of L-citrulline. Thus, food technology can be applied to reduce the watermelon volume and make supplementation more convenient. Therefore, this narrative review aims to discuss the current evidence showing the effects of watermelon ingestion on vascular health parameters, exploring the critical relevance of food technology for acceptable L-citrulline content in these products. Watermelon-derived L-citrulline appears as a supplementation that can improve vascular function, including arterial stiffness and blood pressure. Applying food technologies to concentrate bioactive compounds in a reduced volume is warranted so that its ingestion can be more convenient, improving the adherence of those who want to ingest watermelon products daily.

Carotid Artery Disease in Subjects with Type 2 Diabetes: Risk Factors and Biomarkers

Carotid atherosclerosis (CA) and, especially, carotid artery stenosis (CAS), are associated with a high risk of cardiovascular events in subjects with type 2 diabetes (T2D). In this study, we aimed to identify risk factors and biomarkers of subclinical CA and CAS in T2D individuals. High-resolution ultrasonography of carotid arteries was performed in 389 patients. Ninety-five clinical parameters were evaluated, including diabetic complications and comorbidities; antihyperglycemic, hypolipidemic, and antihypertensive therapy; indices of glycemic control and glucose variability (GV); lipid panels; estimated glomerular filtration rate (eGFR); albuminuria; blood cell count; and coagulation. Additionally, serum levels of calponin-1, relaxin, L-citrulline, and matrix metalloproteinase-2 and -3 (MMP-2, -3) were measured by ELISA. In univariate analysis, older age, male sex, diabetes duration, GV, diabetic retinopathy, chronic kidney disease, coronary artery disease, peripheral artery disease, and MMP-3 were associated with subclinical CA. In addition to these factors, long-term arterial hypertension, high daily insulin doses, eGFR, and L-citrulline were associated with CAS. In multivariate logistic regression, age, male sex, BMI, GV, and eGFR predicted CA independently; male sex, BMI, diabetes duration, eGFR, and L-citrulline were predictors of CAS. These results can be used to develop screening and prevention programs for CA and CAS in T2D subjects.

Effects of L-citrulline supplementation and watermelon consumption on longer-term and postprandial vascular function and cardiometabolic risk markers: A meta-analysis of randomized controlled trials in adults

L-citrulline may improve non-invasive vascular function and cardiometabolic risk markers through increases in L-arginine bioavailability and nitric oxide synthesis. A meta-analysis of randomized controlled trials (RCTs) was performed to examine longer-term and postprandial effects of L-citrulline supplementation and watermelon consumption on these markers for cardiovascular disease in adults. Summary estimates of weighted mean differences (WMDs) in vascular function and cardiometabolic risk markers with accompanying 95% confidence intervals (CIs) were calculated using random or fixed-effect meta-analyses. Seventeen RCTs were included involving an L-citrulline intervention, of which six studied postprandial and twelve longer-term effects. Five studies investigated longer-term effects of watermelon consumption and five assessed effects during the postprandial phase. Longer-term L-citrulline supplementation improved brachial artery flow-mediated vasodilation (FMD) by 0.9 %-point (95 % CI: 0.7 to 1.1, P < 0.001). Longer-term watermelon consumption improved pulse wave velocity by 0.9 m/s (95% CI: 0.1 to 1.5, P < 0.001), while effects on FMD were not studied. No postprandial effects on vascular function markers were found. Postprandial glucose concentrations decreased by 0.6 mmol/L (95% CI: 0.4 to 0.7, P < 0.001) following watermelon consumption, but no other longer-term or postprandial effects were observed on cardiometabolic risk markers. To conclude, longer-term L-citrulline supplementation and watermelon consumption may improve vascular function, suggesting a potential mechanism by which increased L-citrulline intake beneficially affects cardiovascular health outcomes in adults. No effects on postprandial vascular function markers were found, while more research is needed to investigate effects of L-citrulline and watermelon on risk markers related to cardiometabolic health.

Effects of L-Citrulline Supplementation and Aerobic Training on Vascular Function in Individuals with Obesity across the Lifespan

Children with obesity are at higher risk for developing cardiometabolic diseases that once were considered health conditions of adults. Obesity is commonly associated with cardiometabolic risk factors such as dyslipidemia, hyperglycemia, hyperinsulinemia and hypertension that contribute to the development of endothelial dysfunction. Endothelial dysfunction, characterized by reduced nitric oxide (NO) production, precedes vascular abnormalities including atherosclerosis and arterial stiffness. Thus, early detection and treatment of cardiometabolic risk factors are necessary to prevent deleterious vascular consequences of obesity at an early age. Non-pharmacological interventions including L-Citrulline (L-Cit) supplementation and aerobic training stimulate endothelial NO mediated vasodilation, leading to improvements in organ perfusion, blood pressure, arterial stiffness, atherosclerosis and metabolic health (glucose control and lipid profile). Few studies suggest that the combination of L-Cit supplementation and exercise training can be an effective strategy to counteract the adverse effects of obesity on vascular function in older adults. Therefore, this review examined the efficacy of L-Cit supplementation and aerobic training interventions on vascular and metabolic parameters in obese individuals.