Malting barley carbon dots-mediated oxidative stress promotes insulin resistance in mice via NF-κB pathway and MAPK cascade.

BACKGROUND: Food-borne carbon dots (CDs) are widely generated during food processing and are inevitably ingested by humans causing toxicity. However, the toxic effects of food-borne CDs on the blood glucose metabolism are unknown. RESULTS: In this study, we brewed beer via a representative strategy and extracted the melting-barley CDs (MBCDs) to explore the toxic effects on blood glucose in mice. We found the accumulation of fluorescent labeled MBCDs in various organs and oral administration of MBCDs can cause visceral toxicity, manifested as liver damage. Mice were orally administered MBCDs (5 and 25 mg/kg) for 16 weeks, and increased levels of fasting blood glucose were observed in both MBCDs-treated groups. Transcriptomic analyses revealed that MBCDs activate oxidative stress, inflammatory responses, the MAPK cascade, and PI3K/Akt signaling in mice livers. Mechanistically, MBCDs exposure-induced reactive oxygen species (ROS) overproduction activates the nuclear factor-κB (NF-κB) signaling pathway and MAPK cascade, thereby promoting phosphorylated insulin receptor substrate (IRS)-1 at Ser307 and inducing insulin resistance (IR). Meanwhile, the IR promoted gluconeogenesis, which enhanced MBCDs-induced hyperglycemia of mice. Importantly, inhibition of the ROS significantly attenuated the MBCDs-induced inflammatory response and MAPK cascade, thereby alleviating IR and hyperglycemia in mice. CONCLUSION: In summary, this study revealed that MBCDs promote ROS overproduction and thus induced IR, resulting in imbalance of glucose homeostasis in mice. More importantly, this study was further assessed to reveal an imperative emphasis on the reevaluation of dietary and environmental CDs exposure, and has important implications for T2DM prevention research.

Polystyrene Nanoplastics Induce Lipid Metabolism Disorder by Activating the PERK-ATF4 Signaling Pathway in Mice.

In recent years, the study of microplastics (MPs) and nanoplastics (NPs) and their effects on human health has gained significant attention. The impacts of NPs on lipid metabolism and the specific mechanisms involved remain poorly understood. To address this, we utilized high-throughput sequencing and molecular biology techniques to investigate how endoplasmic reticulum (ER) stress might affect hepatic lipid metabolism in the presence of polystyrene nanoplastics (PS-NPs). Our findings suggest that PS-NPs activate the PERK-ATF4 signaling pathway, which in turn upregulates the expression of genes related to lipid synthesis via the ATF4-PPARγ/SREBP-1 pathway. This activation leads to an abnormal accumulation of lipid droplets in the liver. 4-PBA, a known ER stress inhibitor, was found to mitigate the PS-NPs-induced lipid metabolism disorder. These results demonstrate the hepatotoxic effects of PS-NPs and clarify the mechanisms of abnormal lipid metabolism induced by PS-NPs.

Methylparaben induces hepatic glycolipid metabolism disorder by activating the IRE1α-XBP1 signaling pathway in male mice.

Methylparaben (MP), a preservative widely used in daily supplies, exists in both the environment and the human body. However, the potential health risks posed by MP remain unclear. This study aimed to unravel the mechanisms by which MP disrupts glucose and lipid homeostasis. For this, we administered MP to mice and observed changes in glucose and lipid metabolism. MP exposure led to hyperglycemia, hyperlipidemia, visceral organ injury, and hepatic lipid accumulation. RNA sequencing results from mice livers indicated a close association between MP exposure and endoplasmic reticulum (ER) stress, inflammatory response, and glucose and lipid homeostasis. Western blotting and quantitative reverse transcription-polymerase chain reaction revealed that MP activated ER stress, particularly the inositol-requiring enzyme 1 (IRE1)/X-box binding protein 1 (XBP1) pathway, which further promoted the activation of the nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways. The activation of these pathways phosphorylated insulin receptor substrate-1 (IRS1) (ser 307), resulting in decreased phosphorylation of protein kinase B (Akt) (ser 473), leading to insulin resistance. Additionally, MP exposure promoted lipogenesis through ER stress. To explore potential remedies, we administered the ER stress inhibitor 4-phenylbutyric acid (4-PBA) and the IRE1α-XBP1 pathway inhibitor toyocamycin to mice, both of which protected against metabolic disorders and organ injury caused by MP. These findings suggest that MP induces disruptions in glucose and lipid metabolism through ER stress, primarily through the IRE1α-XBP1 pathway.

Foodborne Carbon Dots Aggravate High-Fat-Diet-Induced Glucose Homeostasis Imbalance by Disrupting the Gut-Liver Axis.

Foodborne carbon dots (CDs) are generally produced during cooking and exist in food items. Generally, CDs are regarded as nontoxic materials, but several studies have gradually confirmed the cytotoxicity of CDs, such as oxidative stress, reduced cellular activity, apoptosis, etc. However, studies focusing on the health effects of long-term intake of food-borne CDs are scarce, especially in populations susceptible to metabolic disease. In this study, we reported that CDs in self-brewing beer had no effect on glucose metabolism in CHOW-fed mice but exacerbated high-fat-diet (HFD)-induced glucose metabolism disorders via the gut-liver axis. Chronic exposure to foodborne CDs increased fasting glucose levels and exacerbated liver and intestinal barrier damage in HFD-fed mice. The 16s rRNA sequencing analysis revealed that CDs significantly altered the gut microbiota composition and promoted lipopolysaccharide (LPS) synthesis-related KEGG pathways (superpathway of (Kdo)2-lipid A, Kdo transfer to lipid IVA Ill (Chlamydia), lipid IVA biosynthesis, and so on) in HFD-fed mice. Mechanically, CD exposure increased the abundance of Gram-negative bacteria (Proteobacteria and Desulfovibrionaceae), thus producing excessive endotoxin-LPS, and then LPS was transferred by the blood circulation to the liver due to the damaged intestinal barrier. In the liver, LPS promoted TLR4/NF-κB/P38 MAPK signaling, thus enhancing systemic inflammation and exacerbating HFD-induced insulin resistance. However, pretreating mice with antibiotics eliminated these effects, indicating a key role for gut microbiota in CDs exacerbating glucose metabolism disorders in HFD-fed mice. The finding herein provides new insight into the potential health risk of foodborne nanoparticles in susceptible populations by disturbing the gut-liver axis.

Butylparaben induces glycolipid metabolic disorders in mice via disruption of gut microbiota and FXR signaling.

Butylparaben, a common preservative, is widely used in food, pharmaceuticals and personal care products. Epidemiological studies have revealed the close relationship between butylparaben and diabetes; however the mechanisms of action remain unclear. In this study, we administered butylparaben orally to mice and observed that exposure to butylparaben induced glucose intolerance and hyperlipidemia. RNA sequencing results demonstrated that the enrichment of differentially expressed genes was associated with lipid metabolism, bile acid metabolism, and inflammatory response. Western blot results further validated that butylparaben promoted hepatic lipogenesis, inflammation, gluconeogenesis, and insulin resistance through the inhibition of the farnesoid X receptor (FXR) pathway. The FXR agonists alleviated the butylparaben-induced metabolic disorders. Moreover, 16 S rRNA sequencing showed that butylparaben reduced the abundance of Bacteroidetes, S24-7, Lactobacillus, and Streptococcus, and elevated the Firmicutes/Bacteroidetes ratio. The gut microbiota dysbiosis caused by butylparaben led to decreased bile acids (BAs) production and increased inflammatory response, which further induced hepatic glycolipid metabolic disorders. Our results also demonstrated that probiotics attenuated butylparaben-induced disturbances of the gut microbiota and hepatic metabolism. Taken collectively, the findings reveal that butylparaben induced gut microbiota dysbiosis and decreased BAs production, which further inhibited FXR signaling, ultimately contributing to glycolipid metabolic disorders in the liver.

Lambda-cyhalothrin induces lipid accumulation in mouse liver is associated with AMPK inactivation.

Lambda-cyhalothrin (LCT) is a critical synthetic Type II pyrethroid insecticide widely applied. Several studies suggest pyrethroids could induce fat accumulation, promote adipogenesis, and impair liver function. Now, the influences of LCT on the hepatic lipid metabolism and the cellular mechanism is still unknown. AMPK has important function in regulating cellular energy balance. To indicate the potential pathogenesis of liver injury caused by LCT exposure, ICR mice were orally administrated with LCT at a dose of 0.4 mg/kg and 2 mg/kg. The results suggest that LCT induced obesity, dyslipidemia and hepatic steatosis. In addition, LCT also induced oxidative stress, liver function injury, and disorganized structure of the liver. Furthermore, upregulation of PPARγ, FASN, and SREBP1c expression, as well as reduction of PPARα and FGF21 expression, bringing with decreases of phosphorylated ratios of AMPK and ACC were found in LCT-L group. These results indicate that LCT at 0.4 mg/kg could result in dyslipidemia and hepatic steatosis in mice. In addition, activation of AMPK in hepatocytes effectively attenuated the effects of LCT. The detailed mechanism of LCT-induced hepatic steatosis is associated with AMPK and its downsteam genes. Activation of AMPK might be a novel protection against the progression of hepatic steatosis induced by LCT.

High-fat diet and palmitate inhibits FNDC5 expression via AMPK-Zfp57 pathway in mouse muscle cells.

Irisin, a muscle-secreted cytokine involved in maintaining glucose homeostasis and improving insulin resistance, is generated from the precursor fibronectin type Ⅲ domain-containing protein 5 (FNDC5) by specific proteases. Zinc-finger protein Zfp57, a transcription factor that maintains the methylation during early embryonic development, is also reported to be associated with diabetes mellitus. However, the association between Zfp57 and FNDC5 is still unclear. In our study, we explored the detailed regulatory effect of Zfp57 on FNDC5 expression. In this study, we found that high-fat diet or saturated fatty acid palmitate increased the Zfp57 expression and decreased FNDC5 expression in muscle tissue or C2C12 myotubes. RNA sequencing analysis disclosed effects of the high-fat diet on genes associated with insulin resistance and the AMP-activated protein kinase (AMPK) signaling pathway in muscle tissue of mice. Chromatin immunoprecipitation experiments revealed that Zfp57 binds the FNDC5 gene promoter at positions -308 to -188. Moreover, Zfp57 overexpression inhibited FNDC5 expression, and Zfp57 knockdown alleviated the inhibitory effect of palmitate on FNDC5 expression in C2C12 myotubes. In addition, in vivo and in vitro studies demonstrated that activation of the AMPK pathway by 5-Aminoimidazole-4-carboxamide riboside (AICAR) or metformin mitigated the inhibitory effect of Zfp57 on FNDC5 expression and improved insulin resistance. These findings collectively suggest that high-fat diet and palmitate inhibit the AMPK pathway to increase Zfp57 expression, which in turn induces FNDC5 inhibition, to further aggravate insulin resistance.

Foodborne Carbon Dot Exposure Induces Insulin Resistance through Gut Microbiota Dysbiosis and Damaged Intestinal Mucus Layer.

Foodborne carbon dots (CDs), an emerging food nanocontaminant, are an increasing risk factor for metabolic toxicity in mammals. Here, we report that chronic CD exposure induced glucose metabolism disorders via disruption of the gut-liver axis in mice. 16s rRNA analysis demonstrated that CD exposure decreased the abundance of beneficial bacteria (Bacteroides, Coprococcus, and S24-7) and increased the abundance of harmful bacteria (Proteobacteria, Oscillospira, Desulfovibrionaceae, and Ruminococcaceae), as well as increased the Firmicutes/Bacteroidetes ratio. Mechanistically, the increased pro-inflammatory bacteria release the endotoxin lipopolysaccharide, which induces an intestinal inflammation and disruption of the intestinal mucus layer, activating systemic inflammation and inducing hepatic insulin resistance in mice via the TLR4/NFκB/MAPK signaling pathway. Furthermore, these changes were almost completely reversed by probiotics. Fecal microbiota transplantation from CD-exposed mice induced glucose intolerance, damaged liver function, intestinal mucus layer injury, hepatic inflammation, and insulin resistance in the recipient mice. However, microbiota-depleted mice exposed to CDs had normal levels of these biomarkers consistent with microbiota-depleted control mice, which revealed that gut microbiota dysbiosis contributes to CD-induced inflammation-mediated insulin resistance. Together, our findings revealed that gut microbiota dysbiosis contributes to CD-induced inflammation-mediated insulin resistance and attempted to elucidate the specific underlying mechanism. Furthermore, we emphasized the importance of assessing the hazards associated with foodborne CDs.

Tris (2-chloroethyl) phosphate (TCEP) induces obesity and hepatic steatosis via FXR-mediated lipid accumulation in mice: Long-term exposure as a potential risk for metabolic diseases.

Tris (2-chloroethyl) phosphate (TCEP) is the most commonly detective organophosphate flame retardant in surroundings. TCEP is also evidenced as endocrine disrupting chemicals and has potential adverse effects on metabolic diseases. In this study, we hypothesized that metabolic diseases are adverse outcomes of TCEP exposure. Adult ICR mice was daily treated with TCEP (20 mg/kg and 60 mg/kg, higher than expected level in people) by gavage administration for 9 weeks. The results demonstrate that TCEP promoted body weight gain, hypertriglyceridemia, and hepatic steatosis, consistent with upregulation of hepatic lipogenesis-related gene expression. Moreover, TCEP altered the levels of several hepatic metabolites, especially bile acids and downregulated bile acid synthesis pathways. Intriguingly, we found a marked downregulation of the bile acid nuclear reporter, FXR, in TCEP-exposed livers. Mechanistically, TCEP directly interacted with FXR at Lys335 and Lys336. Further studies in this work elucidate the mechanisms of long-term TCEP exposure on hepatic steatosis and obesity in mice via FXR-mediated lipid accumulation. Our results provide insight into the possibility of intermediate TCEP exposure in causing metabolic diseases.

Di-(2-ethylhexyl) phthalate increases plasma glucose and induces lipid metabolic disorders via FoxO1 in adult mice.

Di-(2-ethylhexyl) phthalate (DEHP), an endocrine-disrupting chemical (EDC) commonly used as a plasticizer, is responsible for widespread environmental pollution. Epidemiological and experimental data implicate DEHP and its metabolite mono(2-ethylhexyl) phthalate (MEHP) in the occurrence and development of metabolic syndrome. However, the specific effects and potential mechanisms of action of DEHP on glucose and lipid metabolism in adults are currently unclear. In the current study, adult male mice were continuously exposed to DEHP (0, 5, and 25 mg/kg/day) via oral administration and changes in glucose and lipid metabolism explored. Notably, exposure to DEHP led to a significant increase in plasma glucose and hepatic lipid accumulation but had no effect on insulin secretion. Western blot and real-time quantitative PCR showed that DEHP induced insulin resistance and promoted gluconeogenesis and lipid accumulation via overexpression of forkhead box protein O1 (FoxO1), in keeping with hepatic RNA sequencing data. Variations in gut microbiota aggravated these effects while inhibition of FoxO1 reversed the adverse effects of DEHP. Our findings support a key role of FoxO1 in disorders of glucose and lipid metabolism caused by DEHP.

Effects of oral administration of polystyrene nanoplastics on plasma glucose metabolism in mice.

Microplastic (MP) and nanoplastic (NP) induce neurotoxicity, cytotoxicity, and reproductive system toxicity in mammals. However, the impacts of NPs on the endocrine system are obscure. Here, monodisperse polystyrene nanoplastics (PS-NPs) were prepared by emulsion polymerization and the accumulation of fluorescent PS-NPs in various organs, including the liver, kidney, spleen, and pancreas, was examined. The oral administration of PS-NPs induced visceral organ injury, and the main toxicities were damage to hepatic function and the abnormity of lipid metabolism. Global transcriptome sequencing (RNA-Seq) revealed the impact of PS-NPs on the genes involved in reactive oxygen species (ROS) generation and the PI3K/Akt signaling pathway, which is associated with glucose metabolism in mice. Chronic exposure to PS-NPs significantly increased plasma glucose levels and ROS levels, but did not affect plasma insulin secretion. The phosphorylation of insulin receptor substrate (IRS)-1 at Ser307 was raised, which decreased the phosphorylation of Akt (at Ser473) in the PI3K/Akt pathway. Collectively, these findings suggested that the oral administration of PS-NPs significantly increased ROS, hepatic triglycerides, and cholesterol accumulation. The high levels of ROS disturbed the PI3K/Akt pathway, causing insulin resistance and increased plasma glucose in the mouse liver.

Fatty acid palmitate suppresses FoxO1 expression via PERK and IRE1 unfolded protein response in C2C12 myotubes.

Forkhead Box O1 (FoxO1) is a transcription factor with a unique fork head domain that indirectly participates in a variety of physiological processes and plays an important role in type 2 diabetes. Palmitate as the most abundant free fatty acid, accounting for 28-32% of total free fatty acids in human plasma. There is a direct relationship between palmitate and insulin resistance-induced type 2 diabetes. In addition, palmitate can activate the unfolded protein response signaling pathway induced by endoplasmic reticulum (ER) stress. This study aimed to investigate the response of FoxO1 to palmitate and the relationship with ER stress in C2C12 myotubes. Treatment of palmitate or tunicamycin promoted ER stress-related genes expression but suppressed FoxO1 expression, while 4-phenylbutyrate presented the opposite activity in palmitate-pretreated C2C12 myotubes, indicating that ER stress might be closely associated with FoxO1 expression. Moreover, palmitate-suppressed FoxO1 expression was reversed in C2C12 cells when the PERK and IRE-1 signaling pathway was inhibited by treatment with GSK2656157 or 4µ8C. However, no differences were observed when the ATF6 signaling pathway was suppressed by knockout of the ATF6 gene. These findings suggest that palmitate suppressed FoxO1 expression via the PERK and IRE1 signaling pathways.

Probiotics protect against hepatic steatosis in tris (2-chloroethyl) phosphate-induced metabolic disorder of mice via FXR signaling.

Tris (2-chloroethyl) phosphate (TCEP), the most widely useful and most frequently detective organophosphate flame retardants in environment, has been shown potential relationship with adolescent weight. Probiotics is an effective therapy for metabolic diseases such as obesity and NAFLD with gut microbiota dysregulation. This study aims to explore the protective effects of probiotics against lipid metabolic disorder induced by chronic TCEP exposure and demonstrate the mechanism of this event. The data showed that dietary complex probiotics supplement attenuated TCEP-induced obesity, hyperlipidemia, liver dysfunction, and hepatic steatosis. In addition, dietary complex probiotics suppressed TCEP-promoted ileal FXR signaling, and upregulated hepatic FXR/SHP pathway inhibited by TCEP. Moreover, dietary complex probiotics stimulated PPARα-mediated lipid oxidation and suppressed SREBP1c/PPARγ-mediated lipid synthesis via regulation of FXR signaling. Therefore, this study indicates that dietary complex probiotics could protect against hepatic steatosis via FXR-mediated signaling pathway in TCEP-induced metabolism disorder in mice, resulting in attenuation of systemic lipid accumulation.