Metformin attenuates myocardium dicarbonyl stress induced by chronic hypertriglyceridemia

X-box binding protein 1: A new metabolic mediator and drug target of metformin?

Accumulating evidence has demonstrated that metformin improved hypertriglyceridemia. The present study aim to investigate the molecular mechanism by which metformin improves hypertriglyceridemia via regulation of diacylglycerol O-acyltransferase 2 (DGAT2) and X-box binding protein 1 (XBP1) in the liver and whether AMP-activated protein kinase (AMPK) is involved. Mice were fed a high-fat diet (HFD) or high-fat diet with metformin for 5 weeks to evaluate the effect of metformin on triglyceride (TG) levels and expression of DGAT2 and XBP1 in the liver. In vitro HepG2 cells or XBP1 knockout AML12 hepatocytes were stimulated with metformin, palmitic acid or small interfering RNA inducing XBP1 knockdown, or dominant-negative mutant AMPK plasmid. Metformin treatment reduced hepatic TG levels in the liver of HFD-fed mice. Expression of nuclear and cytoplasmic XBP1 protein and its downstream target gene DGAT2 decreased in the liver of HFD-fed mice and HepG2 cells after metformin treatment. AMPK inactivation or overexpression of XBP1 attenuates this effect. Our preliminary results demonstrate that metformin activates AMPK to reduce TG synthesis by inhibiting the XBP1-mediated DGAT2 pathway, at least in part, suggesting that XBP1 is a new metabolic mediator for metformin treatment of hypertriglyceridemia and associated metabolic disease.

Berberine Improves the Protective Effects of Metformin on Diabetic Nephropathy in db/db Mice through Trib1-dependent Inhibiting Inflammation

PURPOSE

Diabetic nephropathy (DN), one of severe diabetic complications in the diabetes, is the main cause of end stage renal disease (ESRD). Notably, the currently available medications used to treat DN remain limited. Here, we determined whether berberine (BBR) could enhance the anti-diabetic nephropathy activities of metformin (Met) and explored its possible mechanisms.

METHOD

The anti-diabetic nephropathy properties were systematically analyzed in the diabetic db/db mice treated with Met, BBR or with combination of Met and BBR.

RESULTS

We found that both single Met and BBR treatments, and combination therapy could lower blood glucose, and ameliorate insulin resistance. The improvement of lipids metabolism by co-administration was more evident, as indicated by reduced serum cholesterol and less fat accumulation in the liver. Further, it was found that Met and BBR treatments, and co-administration could attenuate the progression of DN. However, anti-diabetic nephropathy activities of Met were enhanced when combined with BBR, as evidenced by improved renal function and histological abnormalities of diabetic kidney. Mechanistically, BBR enhanced renal-protective effects of Met primarily through potently promoting expression of Trib1, which subsequently downregulated the increased protein levels of CCAAT/enhancer binding protein α (C/EBPα), and eventually inhibited fatty synthesis proteins and nuclear factor kappa-B (NF-κB) signaling.

CONCLUSION

Our data provide novel insight that co-administration of BBR and Met exerts a preferable activity of anti-diabetic nephropathy via collectively enhancing lipolysis and inhibiting inflammation. Combination therapy with these two drugs may provide an effective therapeutic strategy for the medical treatment of diabetic nephropathy.

Metformin Affects Cardiac Arachidonic Acid Metabolism and Cardiac Lipid Metabolite Storage in a Prediabetic Rat Model

Metformin can reduce cardiovascular risk independent of glycemic control. The mechanisms behind its non-glycemic benefits, which include decreased energy intake, lower blood pressure and improved lipid and fatty acid metabolism, are not fully understood. In our study, metformin treatment reduced myocardial accumulation of neutral lipids—triglycerides, cholesteryl esters and the lipotoxic intermediates—diacylglycerols and lysophosphatidylcholines in a prediabetic rat model (p < 0.001). We observed an association between decreased gene expression and SCD-1 activity (p < 0.05). In addition, metformin markedly improved phospholipid fatty acid composition in the myocardium, represented by decreased SFA profiles and increased n3-PUFA profiles. Known for its cardioprotective and anti-inflammatory properties, metformin also had positive effects on arachidonic acid metabolism and CYP-derived arachidonic acid metabolites. We also found an association between increased gene expression of the cardiac isoform CYP2c with increased 14,15-EET (p < 0.05) and markedly reduced 20-HETE (p < 0.001) in the myocardium. Based on these results, we conclude that metformin treatment reduces the lipogenic enzyme SCD-1 and the accumulation of the lipotoxic intermediates diacylglycerols and lysophosphatidylcholine. Increased CYP2c gene expression and beneficial effects on CYP-derived arachidonic acid metabolites in the myocardium can also be involved in cardioprotective effect of metformin.

Metformin: A Novel Weapon Against Inflammation

It has become widely accepted that inflammation is a driving force behind a variety of chronic diseases, such as cardiovascular disease, diabetes, kidney disease, cancer, neurodegenerative disorders, etc. However, the existing nonsteroidal anti-inflammatory drugs show a limited utility in clinical patients. Therefore, the novel agents with different inflammation-inhibitory mechanisms are worth pursuing. Metformin, a synthetic derivative of guanidine, has a history of more than 50 years of clinical experience in treating patients with type 2 diabetes. Intense research efforts have been dedicated to proving metformin’s inflammation-inhibitory effects in cells, animal models, patient records, and randomized clinical trials. The emerging evidence also indicates its therapeutic potential in clinical domains other than type 2 diabetes. Herein, this article appraises current pre-clinical and clinical findings, emphasizing metformin’s anti-inflammatory properties under individual pathophysiological scenarios. In summary, the anti-inflammatory effects of metformin are evident in pre-clinical models. By comparison, there are still clinical perplexities to be addressed in repurposing metformin to inflammation-driven chronic diseases. Future randomized controlled trials, incorporating better stratification/targeting, would establish metformin’s utility in this clinical setting.

The Vasoactive Role of Perivascular Adipose Tissue and the Sulfide Signaling Pathway in a Nonobese Model of Metabolic Syndrome

The aim of this study was to evaluate the mutual relationship among perivascular adipose tissue (PVAT) and endogenous and exogenous H2S in vasoactive responses of isolated arteries from adult normotensive (Wistar) rats and hypertriglyceridemic (HTG) rats, which are a nonobese model of metabolic syndrome. In HTG rats, mild hypertension was associated with glucose intolerance, dyslipidemia, increased amount of retroperitoneal fat, increased arterial contractility, and endothelial dysfunction associated with arterial wall injury, which was accompanied by decreased nitric oxide (NO)-synthase activity, increased expression of H2S producing enzyme, and an altered oxidative state. In HTG, endogenous H2S participated in the inhibition of endothelium-dependent vasorelaxation regardless of PVAT presence; on the other hand, aortas with preserved PVAT revealed a stronger anticontractile effect mediated at least partially by H2S. Although we observed a higher vasorelaxation induced by exogenous H2S donor in HTG rats than in Wistar rats, intact PVAT subtilized this effect. We demonstrate that, in HTG rats, endogenous H2S could manifest a dual effect depending on the type of triggered signaling pathway. H2S within the arterial wall contributes to endothelial dysfunction. On the other hand, PVAT of HTG is endowed with compensatory vasoactive mechanisms, which include stronger anti-contractile action of H2S. Nevertheless, the possible negative impact of PVAT during hypertriglyceridemia on the activity of exogenous H2S donors needs to be taken into consideration.

The combination of atorvastatin with silymarin enhances hypolipidemic, antioxidant and anti-inflammatory effects in a rat model of metabolic syndrome

Hypolipidemic and cardioprotective effects of statins can be associated with the development of myopathies and new-onset type 2 diabetes. These adverse effects may be related to increased oxidative stress. The plant extract silymarin (SM) is known for its antioxidant and anti-inflammatory actions. We tested the hypothesis that the combination of atorvastatin (ATV) with SM could improve therapy efficacy and eliminate some negative effects of statin on hypertriglyceridemia-induced metabolic disorders. Hereditary hypertriglyceridemic rats were fed a standard diet for four weeks without supplementation; supplemented with ATV (5 mg/kg b. wt./day) or a combination of ATV with 1 % micronized SM (ATV+SM). ATV treatment elevated plasma levels of HDL-cholesterol (p<0.01), glucose and insulin and decreased triglycerides (p<0.001). The combination of ATV+SM led to a significant reduction in insulin, an improvement of glucose tolerance, and the hypolipidemic effect was enhanced compared to ATV alone. Furthermore, ATV supplementation increased skeletal muscle triglycerides but its combination with SM decreased triglycerides accumulation in the muscle (p<0.05) and the liver (p<0.01). In the liver, ATV+SM treatment increased the activities of antioxidant enzymes, glutathione and reduced lipid peroxidation (p<0.001). The combined administration of ATV with SM potentiated the hypolipidemic effect, reduced ectopic lipid accumulation, improved glucose metabolism, and increased antioxidant and anti-inflammatory actions. Our results show that SM increased the effectiveness of statin therapy in a hypertriglyceridemic rat model of metabolic syndrome.

Adverse Effects of Methylglyoxal on Transcriptome and Metabolic Changes in Visceral Adipose Tissue in a Prediabetic Rat Model

Excessive methylglyoxal (MG) production contributes to metabolic and vascular changes by increasing inflammatory processes, disturbing regulatory mechanisms and exacerbating tissue dysfunction. MG accumulation in adipocytes leads to structural and functional changes. We used transcriptome analysis to investigate the effect of MG on metabolic changes in the visceral adipose tissue of hereditary hypetriglyceridaemic rats, a non-obese model of metabolic syndrome. Compared to controls, 4-week intragastric MG administration impaired glucose tolerance (p < 0.05) and increased glycaemia (p < 0.01) and serum levels of MCP-1 and TNFα (p < 0.05), but had no effect on serum adiponectin or leptin. Adipose tissue insulin sensitivity and lipolysis were impaired (p < 0.05) in MG-treated rats. In addition, MG reduced the expression of transcription factor Nrf2 (p < 0.01), which controls antioxidant and lipogenic genes. Increased expression of Mcp-1 and TNFα (p < 0.05) together with activation of the SAPK/JNK signaling pathway can promote chronic inflammation in adipose tissue. Transcriptome network analysis revealed the over-representation of genes involved in insulin signaling (Irs1, Igf2, Ide), lipid metabolism (Nr1d1, Lpin1, Lrpap1) and angiogenesis (Dusp10, Tp53inp1).

Beneficial effects of troxerutin on metabolic disorders in non-obese model of metabolic syndrome

Background

Troxerutin (TRX) has a beneficial effect on blood viscosity and platelet aggregation, and is currently used for the treatment of chronic varicosity. Recently, TRX can improve lipid abnormalities, glucose intolerance and oxidative stress in high-fat diet-induced metabolic disorders. In this study, we tested the effect of TRX on metabolic syndrome-associated disorders using a non-obese model of metabolic syndrome–the Hereditary Hypertriglyceridaemic rats (HHTg).

Methods

Adult male HHTg rats were fed standard diet without or with TRX (150 mg/kg bwt/day for 4 weeks).

Results

Compared to untreated rats, TRX supplementation in HHTg rats decreased serum glucose (p<0.05) and insulin (p<0.05). Although blood lipids were not affected, TRX decreased hepatic cholesterol concentrations (p<0.01) and reduced gene expression of HMGCR, SREBP2 and SCD1 (p<0.01), involved in cholesterol synthesis and lipid homeostasis. TRX-treated rats exhibited decreased lipoperoxidation and increased activity of antioxidant enzymes SOD and GPx (p<0.05) in the liver. In addition, TRX supplementation increased insulin sensitivity in muscles and epididymal adipose tissue (p<0.05). Elevated serum adiponectin (p<0.05) and decreased muscle triglyceride (p<0.05) helped improve insulin sensitivity. Among the beneficial effects of TRX were changes to cytochrome P450 family enzymes. Hepatic gene expression of CYP4A1, CYP4A3 and CYP5A1 (p<0.01) decreased, while there was a marked elevation in gene expression of CYP1A1 (p<0.01).

Conclusion

Our results indicate that TRX improves hepatic lipid metabolism and insulin sensitivity in peripheral tissues. As well as ameliorating oxidative stress, TRX can reduce ectopic lipid deposition, affect genes involved in lipid metabolism, and influence the activity of CYP family enzymes.

The effect of dicarbonyl stress on the development of kidney dysfunction in metabolic syndrome - a transcriptomic and proteomic approach

Background and aims

Dicarbonyl stress plays an important role in the pathogenesis of microvascular complications that precede the formation of advanced glycation end products, and contributes to the development of renal dysfunction. In renal cells, toxic metabolites like methylglyoxal lead to mitochondrial dysfunction and protein structure modifications.

In our study, we investigated the effect of methylglyoxal on metabolic, transcriptomic, metabolomic and proteomic profiles in the context of the development of kidney impairment in the model of metabolic syndrome.

Materials and methods

Dicarbonyl stress was induced by intragastric administration of methylglyoxal (0.5 mg/kg bw for 4 weeks) in a strain of hereditary hypertriglyceridaemic rats with insulin resistance and fatty liver.

Results

Methylglyoxal administration aggravated glucose intolerance (AUC_0–120p < 0.05), and increased plasma glucose (p < 0.01) and insulin (p < 0.05). Compared to controls, methylglyoxal-treated rats exhibited microalbuminuria (p < 0.01). Targeted proteomic analysis revealed increases in urinary secretion of pro-inflammatory parameters (MCP-1, IL-6, IL-8), specific collagen IV fragments and extracellular matrix proteins. Urine metabolomic biomarkers in methylglyoxal-treated rats were mainly associated with impairment of membrane phospholipids (8-isoprostane, 4-hydroxynonenal).

Decreased levels of glutathione (p < 0.01) together with diminished activity of glutathione-dependent antioxidant enzymes contributed to oxidative and dicarbonyl stress. Methylglyoxal administration elevated glyoxalase 1 expression (p < 0.05), involved in methylglyoxal degradation. Based on comparative transcriptomic analysis of the kidney cortex, 96 genes were identified as differentially expressed (FDR < 0.05). Network analysis revealed an over-representation of genes related to oxidative stress and pro-inflammatory signalling pathways as well as an inhibition of angiogenesis suggesting its contribution to renal fibrosis.

Conclusion

Our results support the hypothesis that dicarbonyl stress plays a key role in renal microvascular complications. At the transcriptome level, methylglyoxal activated oxidative and pro-inflammatory pathways and inhibited angiogenesis. These effects were further supported by the results of urinary proteomic and metabolomic analyses.