Impact of nutrient excess and endothelial nitric oxide synthase on the plasma metabolite profile in mice

Gut microbial genomes with paired isolates from China illustrate probiotic and cardiometabolic effects

The gut microbiome displays genetic differences among populations, and characterization of the genomic landscape of the gut microbiome in China remains limited. Here, we present the Chinese Gut Microbial Reference (CGMR) set, comprising 101,060 high-quality metagenomic assembled genomes (MAGs) of 3,707 nonredundant species from 3,234 fecal samples across primarily rural Chinese locations, 1,376 live isolates mainly from lactic acid bacteria, and 987 novel species relative to worldwide databases. We observed region-specific coexisting MAGs and MAGs with probiotic and cardiometabolic functionalities. Preliminary mouse experiments suggest a probiotic effect of two Faecalibacillus intestinalis isolates in alleviating constipation, cardiometabolic influences of three Bacteroides fragilis_A isolates in obesity, and isolates from the genera Parabacteroides and Lactobacillus in host lipid metabolism. Our study expands the current microbial genomes with paired isolates and demonstrates potential host effects, contributing to the mechanistic understanding of host-microbe interactions.

Serum metabolomic signatures of plant-based diets and incident chronic kidney disease

BACKGROUND

Greater adherence to plant-based diets is associated with a lower risk of incident chronic kidney disease (CKD). Metabolomics can help identify blood biomarkers of plant-based diets and enhance understanding of underlying mechanisms.

OBJECTIVES

Using untargeted metabolomics, we aimed to identify metabolites associated with 4 plant-based diet indices (PDIs) (overall PDI, provegetarian diet, healthful PDI, and unhealthful PDI) and incident CKD in 2 subgroups within the Atherosclerosis Risk in Communities study.

METHODS

We calculated 4 PDIs based on participants' responses on an FFQ. We used multivariable linear regression to examine the association between 4 PDIs and 374 individual metabolites, adjusting for confounders. We used Cox proportional hazards regression to evaluate associations between PDI-related metabolites and incident CKD. Estimates were meta-analyzed across 2 subgroups (n1 = 1762; n2 = 1960). We calculated C-statistics to assess whether metabolites improved the prediction of those in the highest quintile compared to the lower 4 quintiles of PDIs, and whether PDI- and CKD-related metabolites predicted incident CKD beyond the CKD prediction model.

RESULTS

We identified 82 significant PDI-metabolite associations (overall PDI = 27; provegetarian = 17; healthful PDI = 20; unhealthful PDI = 18); 11 metabolites overlapped across the overall PDI, provegetarian diet, and healthful PDI. The addition of metabolites improved prediction of those in the highest quintile as opposed to the lower 4 quintiles of PDIs compared with participant characteristics alone (range of differences in C-statistics = 0.026-0.104; P value ≤ 0.001 for all tests). Six PDI-related metabolites (glycerate, 1,5-anhydroglucitol, γ-glutamylalanine, γ-glutamylglutamate, γ-glutamylleucine, γ-glutamylvaline), involved in glycolysis, gluconeogenesis, pyruvate metabolism, and γ-glutamyl peptide metabolism, were significantly associated with incident CKD and improved prediction of incident CKD beyond the CKD prediction model (difference in C-statistics for 6 metabolites = 0.005; P value = 0.006).

CONCLUSIONS

In a community-based study of US adults, we identified metabolites that were related to plant-based diets and predicted incident CKD. These metabolites highlight pathways through which plant-based diets are associated with incident CKD.

The Metabolomics of Childhood Atopic Diseases: A Comprehensive Pathway-Specific Review

Asthma, allergic rhinitis, food allergy, and atopic dermatitis are common childhood diseases with several different underlying mechanisms, i.e., endotypes of disease. Metabolomics has the potential to identify disease endotypes, which could beneficially promote personalized prevention and treatment. Here, we summarize the findings from metabolomics studies of children with atopic diseases focusing on tyrosine and tryptophan metabolism, lipids (particularly, sphingolipids), polyunsaturated fatty acids, microbially derived metabolites (particularly, short-chain fatty acids), and bile acids. We included 25 studies: 23 examined asthma or wheezing, five examined allergy endpoints, and two focused on atopic dermatitis. Of the 25 studies, 20 reported findings in the pathways of interest with findings for asthma in all pathways and for allergy and atopic dermatitis in most pathways except tyrosine metabolism and short-chain fatty acids, respectively. Particularly, tyrosine, 3-hydroxyphenylacetic acid, N-acetyltyrosine, tryptophan, indolelactic acid, 5-hydroxyindoleacetic acid, p-Cresol sulfate, taurocholic acid, taurochenodeoxycholic acid, glycohyocholic acid, glycocholic acid, and docosapentaenoate n-6 were identified in at least two studies. This pathway-specific review provides a comprehensive overview of the existing evidence from metabolomics studies of childhood atopic diseases. The altered metabolic pathways uncover some of the underlying biochemical mechanisms leading to these common childhood disorders, which may become of potential value in clinical practice.

Integration of transcriptomic and metabolomic data reveals metabolic pathway alteration in mouse spermatogonia with the effect of copper exposure

Copper is a widespread heavy metal in environment and has toxic effects when exposed. However, study of copper-induced male reproductive toxicity is still insufficient to report, and the underlying mechanisms are unknown. Keeping in view, RNA-Seq and metabolomic were performed to identify metabolic pathways that were distressed in mouse spermatogonia with the effect of copper sulfate, and the integrated analysis of the mechanism of copper administered GC-1 cells from metabolomic and transcriptomic data. Our results demonstrated that many genes and metabolites were regulated in the copper sulfate-treated cells. The differential metabolites analysis showed that 49 and 127 metabolites were significantly different in ESI+ and ESI- mode, respectively. Meanwhile, a total of 2813 genes were up-regulated and 2488 genes were down-regulated in the treatment groups compared to those in the control groups. Interestingly, ophthalmic acid and gamma glutamylleucine were markedly increased by copper treatment in two modes. By integrating with transcriptomic and metabolomic data, we revealed that 37 and 22 most related pathways were over-enriched in ESI+ and ESI- mode, respectively. Whereas, amino acid biosynthesis and metabolism play essential role in the potential relationship between DEGs and metabolites, which suggests that amino acid biosynthesis and metabolism may be the major metabolic pathways disturbed by copper in GC-1 cells. This study provides important clues and evidence for understanding the mechanisms responsible for copper-induced male spermatogenesis toxicity, and useful biomarkers indicative of copper exposure could be discovered from present study.

Branched-chain ketoacid overload inhibits insulin action in the muscle

Branched-chain α-keto acids (BCKAs) are catabolites of branched-chain amino acids (BCAAs). Intracellular BCKAs are cleared by branched-chain ketoacid dehydrogenase (BCKDH), which is sensitive to inhibitory phosphorylation by BCKD kinase (BCKDK). Accumulation of BCKAs is an indicator of defective BCAA catabolism and has been correlated with glucose intolerance and cardiac dysfunction. However, it is unclear whether BCKAs directly alter insulin signaling and function in the skeletal and cardiac muscle cell. Furthermore, the role of excess fatty acids (FAs) in perturbing BCAA catabolism and BCKA availability merits investigation. By using immunoblotting and ultra-performance liquid chromatography MS/MS to analyze the hearts of fasted mice, we observed decreased BCAA-catabolizing enzyme expression and increased circulating BCKAs, but not BCAAs. In mice subjected to diet-induced obesity (DIO), we observed similar increases in circulating BCKAs with concomitant changes in BCAA-catabolizing enzyme expression only in the skeletal muscle. Effects of DIO were recapitulated by simulating lipotoxicity in skeletal muscle cells treated with saturated FA, palmitate. Exposure of muscle cells to high concentrations of BCKAs resulted in inhibition of insulin-induced AKT phosphorylation, decreased glucose uptake, and mitochondrial oxygen consumption. Altering intracellular clearance of BCKAs by genetic modulation of BCKDK and BCKDHA expression showed similar effects on AKT phosphorylation. BCKAs increased protein translation and mTORC1 activation. Pretreating cells with mTORC1 inhibitor rapamycin restored BCKA's effect on insulin-induced AKT phosphorylation. This study provides evidence for FA-mediated regulation of BCAA-catabolizing enzymes and BCKA content and highlights the biological role of BCKAs in regulating muscle insulin signaling and function.

Semen Cuscutae Administration Improves Hepatic Lipid Metabolism and Adiposity in High Fat Diet-Induced Obese Mice

Since arginase has been shown to compete with nitric oxide (NO) synthase, emerging evidence has reported that arginase inhibition improves obesity by increasing NO production. Semen cuscutae (SC), which is a well-known Chinese medicine, has multiple biological functions such as anti-oxidant function and immune regulation. In this study, we investigated whether the SC as a natural arginase inhibitor influences hepatic lipid abnormalities and whole-body adiposity in high-fat diet (HFD)-induced obese mice. The lipid accumulation was significantly reduced by SC treatment in oleic acid-induced hepatic steatosis in vitro. Additionally, SC supplementation substantially lowered HFD-induced increases in arginase activity and weights of liver and visceral fat tissue, while increasing hepatic NO. Furthermore, elevated mRNA expressions of sterol regulatory element-binding transcription factor 1 (SREBP-1c), fatty-acid synthase (FAS), peroxisome proliferator-activated receptor-gamma (PPAR-γ)1, and PPAR-γ2 in HFD-fed mice were significantly attenuated by SC supplementation. Taken together, SC, as a novel natural arginase inhibitor, showed anti-obesity properties by modulating hepatic arginase and NO production and metabolic pathways related to hepatic triglyceride (TG) metabolism.

A framework for examining how diet impacts tumour metabolism

The way cancer cells utilize nutrients to support their growth and proliferation is determined by cancer cell-intrinsic and cancer cell-extrinsic factors, including interactions with the environment. These interactions can define therapeutic vulnerabilities and impact the effectiveness of cancer therapy. Diet-mediated changes in whole-body metabolism and systemic nutrient availability can affect the environment that cancer cells are exposed to within tumours, and a better understanding of how diet modulates nutrient availability and utilization by cancer cells is needed. How diet impacts cancer outcomes is also of great interest to patients, yet clear evidence for how diet interacts with therapy and impacts tumour growth is lacking. Here we propose an experimental framework to probe the connections between diet and cancer metabolism. We examine how dietary factors may affect tumour growth by altering the access to and utilization of nutrients by cancer cells. Our growing understanding of how certain cancer types respond to various diets, how diet impacts cancer cell metabolism to mediate these responses and whether dietary interventions may constitute new therapeutic opportunities will begin to provide guidance on how best to use diet and nutrition to manage cancer in patients.

Stereoselective effects of ibuprofen in adult zebrafish (Danio rerio) using UPLC-TOF/MS-based metabolomics

Ibuprofen (IBU), as a commonly used non-steroidal anti-inflammatory drug (NSAID) and pharmaceutical and personal care product (PPCP), is frequently prescribed by doctors to relieve pain. It is widely released into environmental water and soil in the form of chiral enantiomers by the urination and defecation of humans or animals and by sewage discharge from wastewater treatment plants. This study focused on the alteration of metabolism in the adult zebrafish (Danio rerio) brain after exposure to R-(-)-/S-(+)-/rac-IBU at 5 μg L^-1 for 28 days. A total of 45 potential biomarkers and related pathways, including amino acids and their derivatives, purine and its derivatives, nucleotides and other metabolites, were observed with untargeted metabolomics. To validate the metabolic disorders induced by IBU, 22 amino acids and 3 antioxidant enzymes were selected to be quantitated and determined using targeted metabolomics and enzyme assay. Stereoselective changes were observed in the 45 identified biomarkers from the untargeted metabolomics analysis. The 22 amino acids quantitated in targeted metabolomics and 3 antioxidant enzymes determined in enzyme assay also showed stereoselective changes after R-(-)-/S-(+)-/rac-IBU exposure. Results showed that even at a low concentration of R-(-)-/S-(+)-/rac-IBU, disorders in metabolism and antioxidant defense systems were still induced with stereoselectivity. Our study may enable a better understanding of the risks of chiral PPCPs in aquatic organisms in the environment.

Association of plasma nitrite levels with obesity and metabolic syndrome in the Old Order Amish

OBJECTIVES

Plasma nitrite is a metabolite of nitric oxide and reflects endogenous nitric oxide synthase (NOS) activity. Although plasma nitrites were previously linked with obesity and metabolic syndrome (MetS), the direction of association remains inconsistent, possibly due to sample heterogeneity. In a relatively homogeneous population, we hypothesized that nitrite levels will be positively associated with overweight/obesity and MetS.

METHODS

Fasting nitrite levels were measured in 116 Old Order Amish (78% women). We performed age-and-sex-adjusted ancovas to compare nitrite levels between three groups (a) overweight/obese(-)MetS(-), (b) overweight/obese(+)MetS(-) and (c) overweight/obese(+)MetS)(+). Multivariate linear regressions were conducted on nitrite associations with continuous metabolic variables, with successive adjustments for demographics, body mass index, C-reactive protein and neopterin.

RESULTS

Nitrite levels were higher in the obese/overweight(+)MetS(+) group than in the other two groups (p < 0.001). Nitrites were positively associated with levels of triglycerides (p < 0.0001), total cholesterol (p = 0.048), high-density lipoprotein/cholesterol ratio (p < 0.0001) and fasting glucose (p < 0.0001), and negatively correlated with high-density lipoprotein-cholesterol (p < 0.0001). These associations were robust to adjustments for body mass index and inflammatory markers.

CONCLUSION

Further investigation of the connection between obesity/MetS and plasma nitrite levels may lead to novel dietary and pharmacological approaches that ultimately may contribute to reducing the increasing burden of obesity, MetS and cardiovascular morbidity and mortality.

An extract from the Atlantic brown algae Saccorhiza polyschides counteracts diet-induced obesity in mice via a gut related multi-factorial mechanisms

In this study we addressed the questions whether an Atlantic brown algae extract (BAE) affects diet induced obesity in mice and which would be the primary targets and underlying key mechanisms. Male C57 BL/6 mice were fed a hypercaloric diet, referred to as high fat diet (HFD), supplemented with a freeze-dried aqueous BAE from Saccorhiza polyschides (5 %) for 8 months. Compared to the control group, dietary BAE supplementation significantly attenuated increase in body weight and fat mass. We observed apparent metabolic improvement including normalization of blood glucose, reduced plasma leptin, reduced fecal bile salt hydrolase activity with lower microbial production of toxic bile acid metabolites in the gut and increased systemic bile acid circulation in BAE-fed mice counteracting adverse effects of long term HFD feeding. Survival of mice receiving dietary BAE supplementation appeared slightly enhanced; however, median and maximal life spans as well as hepatic mTOR activation were not significantly different between BAE and control mice. We suggest that the beneficial metabolic effects of our BAE are at least partly mediated by alterations in gut microbiota associated with fermentation of indigestible polysaccharides that are major components of brown algae such as alginates and fucoidans. We moreover propose a multi-factorial mechanism that involves profound alterations in bile acid homeostasis, changes in intestinal and systemic glucose metabolism likely including increased intestinal gluconeogenesis, increased activity of the intestinally derived hormone GLP-1 contributing to promote systemic insulin sensitivity, and inhibition of α-amylase activity, which expectably limits dietary carbohydrate digestion and glucose release.

Obesity and Asthma: A Missing Link

Obesity and asthma are two chronic conditions that affect millions of people. Genetic and lifestyle factors such as diet, physical activity, and early exposure to micro-organisms are important factors that may contribute to the escalating prevalence of both conditions. The prevalence of asthma is higher in obese individuals. Recently, two major phenotypes of asthma with obesity have been described: one phenotype of early-onset asthma that is aggravated by obesity, and a second phenotype of later-onset asthma that predominantly affects women. Systemic inflammation and mechanical effect, both due to the expansion of the adipose tissue, have been proposed as the main reasons for the association between obesity and asthma. However, the mechanisms involved are not yet fully understood. Moreover, it has also been suggested that insulin resistance syndrome can have a role in the association between these conditions. The intestinal microbiota is an important factor in the development of the immune system, and can be considered a link between obesity and asthma. In the obese state, higher lipopolysaccharide (LPS) serum levels as a consequence of a microbiota dysbiosis have been found. In addition, changes in microbiota composition result in a modification of carbohydrate fermentation capacity, therefore modifying short chain fatty acid (SCFA) levels. The main objective of this review is to summarize the principal findings that link obesity and asthma.

Anti-Obesity Effect of Bombus ignitus Queen Glycosaminoglycans in Rats on a High-Fat Diet

The mechanism of functional insect glycosaminoglycan (GAG) on obesity caused a high fat diet has not yet been elucidated. Therefore, insect glycosaminoglycans derived from Isaria sinclairii, Bombus ignitus (a type of bumblebee) queen, and Gryllus bimaculatus were purified and investigated as a potential functional food. 14-week old male Wistar rats were fed a high-fat diet (HFD) for 6 weeks. There were five groups that received daily intraperitoneal administration of phosphate buffered saline (PBS, control), GbG (GAG from Gryllus bimaculatus) 10 mg/kg, ISG (GAG from Isaria sinclairii) 10 mg/kg, IQG (GAG from Bombus ignites) 10 mg/kg, or Pravastatin (2 mg/kg). All treatments were performed for one month. IQG produced a potential anti-inflammatory effect with the inhibition of c-reactive protein and sero-biochemical parameters of phospholipids and free fatty acids indicative of an anti-hyperlipidemic effect. Abdominal and epididymidal fat weight were reduced in conjunction with a mild increase in body weight. The level of laminin in HMVEC-C cells or fibronectin in HFD rat hepatocytes was significantly affected by these GAG treatments, which regulated adipogenesis and adipocyte function. Compared to the control rats, IQG-treated rats displayed up-regulation of 87 genes (test:control ratio >2.0) including fatty acid synthase and 3-hydroxy-3-methylglutaryl-coenzyme A reductase, with the down-regulation of 47 genes including the uridine diphosphate (UDP) glycosyltransferase 2 families, polypeptidase B, and insulin-like growth factor binding protein 1. The data suggest that IQG could potentially prevent or treat fatty liver or hyperlipidemia.

Glucose and Palmitate Differentially Regulate PFKFB3/iPFK2 and Inflammatory Responses in Mouse Intestinal Epithelial Cells

The gene PFKFB3 encodes for inducible 6-phosphofructo-2-kinase, a glycolysis-regulatory enzyme that protects against diet-induced intestine inflammation. However, it is unclear how nutrient overload regulates PFKFB3 expression and inflammatory responses in intestinal epithelial cells (IECs). In the present study, primary IECs were isolated from small intestine of C57BL/6J mice fed a low-fat diet (LFD) or high-fat diet (HFD) for 12 weeks. Additionally, CMT-93 cells, a cell line for IECs, were cultured in low glucose (LG, 5.5 mmol/L) or high glucose (HG, 27.5 mmol/L) medium and treated with palmitate (50 μmol/L) or bovine serum albumin (BSA) for 24 hr. These cells were analyzed for PFKFB3 and inflammatory markers. Compared with LFD, HFD feeding decreased IEC PFKFB3 expression and increased IEC proinflammatory responses. In CMT-93 cells, HG significantly increased PFKFB3 expression and proinflammatory responses compared with LG. Interestingly, palmitate decreased PFKFB3 expression and increased proinflammatory responses compared with BSA, regardless of glucose concentrations. Furthermore, HG significantly increased PFKFB3 promoter transcription activity compared with LG. Upon PFKFB3 overexpression, proinflammatory responses in CMT-93 cells were decreased. Taken together, these results indicate that in IECs glucose stimulates PFKFB3 expression and palmitate contributes to increased proinflammatory responses. Therefore, PFKFB3 regulates IEC inflammatory status in response to macronutrients.

Targeted overexpression of endothelial nitric oxide synthase in endothelial cells improves cerebrovascular reactivity in Ins2Akita-type-1 diabetic mice

Reduced bioavailability of nitric oxide due to impaired endothelial nitric oxide synthase (eNOS) activity is a leading cause of endothelial dysfunction in diabetes. Enhancing eNOS activity in diabetes is a potential therapeutic target. This study investigated basal cerebral blood flow and cerebrovascular reactivity in wild-type mice, diabetic mice (Ins2(Akita+/-)), nondiabetic eNOS-overexpressing mice (TgeNOS), and the cross of two transgenic mice (TgeNOS-Ins2(Akita+/-)) at six months of age. The cross was aimed at improving eNOS expression in diabetic mice. The major findings were: (i) Body weights of Ins2(Akita+/-) and TgeNOS-Ins2(Akita+/-) were significantly different from wild-type and TgeNOS mice. Blood pressure of TgeNOS mice was lower than wild-type. (ii) Basal cerebral blood flow of the TgeNOS group was significantly higher than cerebral blood flow of the other three groups. (iii) The cerebrovascular reactivity in the Ins2(Akita+/-) mice was significantly lower compared with wild-type, whereas that in the TgeNOS-Ins2(Akita+/-) was significantly higher compared with the Ins2(Akita+/-) and TgeNOS groups. Overexpression of eNOS rescued cerebrovascular dysfunction in diabetic animals, resulting in improved cerebrovascular reactivity. These results underscore the possible role of eNOS in vascular dysfunction in the brain of diabetic mice and support the notion that enhancing eNOS activity in diabetes is a potential therapeutic target.

Associations Between the Serum Metabolome and All-Cause Mortality Among African Americans in the Atherosclerosis Risk in Communities (ARIC) Study

Early and accurate identification of people at high risk of premature death may assist in the targeting of preventive therapies in order to improve overall health. To identify novel biomarkers for all-cause mortality, we performed untargeted metabolomics in the Atherosclerosis Risk in Communities (ARIC) Study. We included 1,887 eligible ARIC African Americans, and 671 deaths occurred during a median follow-up period of 22.5 years (1987-2011). Chromatography and mass spectroscopy identified and quantitated 204 serum metabolites, and Cox proportional hazards models were used to analyze the longitudinal associations with all-cause and cardiovascular mortality. Nine metabolites, including cotinine, mannose, glycocholate, pregnendiol disulfate, α-hydroxyisovalerate, N-acetylalanine, andro-steroid monosulfate 2, uridine, and γ-glutamyl-leucine, showed independent associations with all-cause mortality, with an average risk change of 18% per standard-deviation increase in metabolite level (P < 1.23 × 10(-4)). A metabolite risk score, created on the basis of the weighted levels of the identified metabolites, improved the predictive ability of all-cause mortality over traditional risk factors (bias-corrected Harrell's C statistic 0.752 vs. 0.730). Mannose and glycocholate were associated with cardiovascular mortality (P < 1.23 × 10(-4)), but predictive ability was not improved beyond the traditional risk factors. This metabolomic analysis revealed potential novel biomarkers for all-cause mortality beyond the traditional risk factors.

Metabolomic Endotype of Asthma

Metabolomics, the quantification of small biochemicals in plasma and tissues, can provide insight into complex biochemical processes and enable the identification of biomarkers that may serve as therapeutic targets. We hypothesized that the plasma metabolome of asthma would reveal metabolic consequences of the specific immune and inflammatory responses unique to endotypes of asthma. The plasma metabolomic profiles of 20 asthmatic subjects and 10 healthy controls were examined using an untargeted global and focused metabolomic analysis. Individuals were classified based on clinical definitions of asthma severity or by levels of fraction of exhaled NO (FENO), a biomarker of airway inflammation. Of the 293 biochemicals identified in the plasma, 25 were significantly different among asthma and healthy controls (p < 0.05). Plasma levels of taurine, lathosterol, bile acids (taurocholate and glycodeoxycholate), nicotinamide, and adenosine-5-phosphate were significantly higher in asthmatics compared with healthy controls. Severe asthmatics had biochemical changes related to steroid and amino acid/protein metabolism. Asthmatics with high FENO, compared with those with low FENO, had higher levels of plasma branched-chain amino acids and bile acids. Asthmatics have a unique plasma metabolome that distinguishes them from healthy controls and points to activation of inflammatory and immune pathways. The severe asthmatic and high FENO asthmatic have unique endotypes that suggest changes in NO-associated taurine transport and bile acid metabolism.