JNK downregulation improves olanzapine-induced insulin resistance by suppressing IRS1Ser307 phosphorylation and reducing inflammation

When IGF-1 Meets Metabolic Inflammation and Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a prevalent endocrine disorder associated with insulin resistance (IR) and hyperandrogenaemia (HA). Metabolic inflammation (MI), characterized by a chronic low-grade inflammatory state, is intimately linked with chronic metabolic diseases such as IR and diabetes and is also considered an essential factor in the development of PCOS. Insulin-like growth factor 1 (IGF-1) plays an essential role in PCOS pathogenesis through its multiple functions in regulating cell proliferation metabolic processes and reducing inflammatory responses. This review summarizes the molecular mechanisms by which IGF-1, via MI, participates in the onset and progression of PCOS, aiming to provide insights for studies and clinical treatment of PCOS.

Korean Red Ginseng Improves Oxidative Stress-Induced Hepatic Insulin Resistance via Enhancing Mitophagy

This study explored the potential of saponins from Korean Red Ginseng to target the PINK1/Parkin mitophagy pathway, aiming to enhance insulin sensitivity in hepatocytes-a key factor in metabolic disorders like metabolic dysfunction-associated steatotic liver disease (MASLD) and type 2 diabetes. Results from both in vitro and in vivo experiments showed increased expression of PINK1 and Parkin, activating mitophagy and reducing oxidative stress through reduction in mitochondrial and total reactive oxygen species. Additionally, improvements in insulin signaling were observed, including the upregulation of phosphorylated IRS and AKT, and downregulation of gluconeogenic enzymes, underscoring the saponins' efficacy in boosting insulin sensitivity. The findings highlighted Korean Red Ginseng-derived saponins as potential treatments for insulin resistance and related metabolic conditions.

miR-486-5p-rich extracellular vesicles derived from patients with olanzapine-induced insulin resistance negatively affect glucose-regulating function

A high risk of glucometabolic disorder severely disturbs compliance and limits the clinical application of olanzapine. MicroRNAs (miRNAs) in extracellular vesicles (EVs) have been reported as emerging biomarkers in glucolipid metabolic disorders. A total of 81 individuals with continuous olanzapine treatment over 3 months were recruited in this study, and plasma EVs from these individuals were isolated and injected into rats via the tail vein to investigate the glucose-regulating function in vivo. Moreover, we performed a miRNA profiling assay by high through-put sequencing to clarify the differentiated miRNA profiles between two groups of patients who were either susceptible or not susceptible to olanzapine-induced insulin resistance (IR). Finally, we administered antagomir and cocultured them with adipocytes to explore the mechanism in vitro. The results showed that individual insulin sensitivity varied in those patients and in olanzapine-administered rats. Furthermore, treatment with circulating EVs from patients with olanzapine-induced IR led to the development of metabolic abnormalities in rats and adipocytes in vitro through the AKT-GLUT4 pathway. Deep sequencing illustrated that the miRNAs of plasma EVs from patients showed a clear difference based on susceptibility to olanzapine-induced IR, and miR-486-5p was identified as a notable gene. The adipocyte data indicated that miR-486-5p silencing partially reversed the impaired cellular insulin sensitivity. Collectively, this study confirmed the function of plasma EVs in the interindividual differences in olanzapine-induced insulin sensitivity.

Chronic intermittent hypoxia-induced oxidative stress activates TRB3 and phosphorylated JNK to mediate insulin resistance and cell apoptosis in the pancreas

This study explores the potential mechanisms of obstructive sleep apnoea (OSA) complicates type 2 diabetes mellitus (T2DM) by which chronic intermittent hypoxia (CIH) induces insulin resistance and cell apoptosis in the pancreas through oxidative stress. Four- and eight-week CIH rat models were established, and Tempol (100 mg/kg/d), was used as an oxidative stress inhibitor. This study included five groups: 4-week CIH, 4-week CIH-Tempol, 8-week CIH, 8-week CIH-Tempol and normal control (NC) groups. Fasting blood glucose and insulin levels were measured in the serum. The expression levels of 8-hidroxy-2-deoxyguanosine (8-OHdG), tribbles homologue 3 (TRB3), c-Jun N-terminal kinase (JNK), phosphorylated JNK (p-JNK), insulin receptor substrate-1 (IRS-1), phosphorylated IRS-1 (Ser307) (p-IRS-1ser307 ), protein kinase B (AKT), phosphorylated AKT (Ser473) (p-AKTser473 ), B cell lymphoma protein-2 (Bcl-2), cleaved-caspase-3 (Cl-caspase-3), and the islet cell apoptosis were detected in the pancreas. CIH induced oxidative stress in the pancreas. Compared with that in the NC group and CIH-Tempol groups individually, the homeostasis model assessment of insulin resistance (HOMA-IR) and apoptosis of islet cells was increased in the CIH groups. CIH-induced oxidative stress increased the expression of p-IRS-1Ser307 and decreased the expression of p-AKTSer473 . The expression levels of TRB3 and p-JNK were higher in the CIH groups than in both the CIH-Tempol and NC groups. Meanwhile, the expressions of Cl-caspase-3 and Bcl-2 were upregulated and downregulated, respectively, in the CIH groups. Hence, the present study demonstrated that CIH-induced oxidative stress might not only induce insulin resistance but also islet cell apoptosis in the pancreas through TRB3 and p-JNK.

Establishment of diabetes mellitus model using Bombyx mori silkworms in a low-temperature environment

Due to the high prevalence of diabetes mellitus, researchers have conducted numerous experimental animal studies. However, the mammalian diabetes model is cumbersome and expensive to operate, while the cheap and simple common silkworm diabetes model has the disadvantage of a short cycle time. Since the growth of silkworms is greatly affected by environmental factors, we extended the five-age cycle of silkworms by lowering the ambient temperature to establish a novel low-temperature silkworm diabetes model. Our goal was to determine whether the low-temperature feeding of a high-sugar diet to silkworms could serve as an effective animal model for diabetes. Also, we aimed to resolve certain issues concerning the normal temperature silkworm diabetes model, such as the short time frame for experiments and erratic fluctuations in blood sugar levels. Silkworms weighing between 0.9 and 1.0 g at the beginning of the fifth instar were selected, and we created diabetic silkworms by feeding mulberry leaves containing 4% glucose daily in a 16-20°C environment. When the silkworms were kept at a cooler temperature, the fifth instar stage lasted for an additional 9-11 days. In the model group, 83.3% of the silkworms had blood glucose levels greater than 7.8 mmol/L, while the total prevalence of diabetic silkworms was 89.8%. Moreover, JNK phosphorylation expression rose in the model group, while PI3K expression fell. Additionally, the JNK and PI3K signaling pathway expressions matched diabetic signals. Therefore, using silkworms to create a diabetes model in a cool environment is a straightforward and cost-effective approach to studying diabetes in animals.

Ginsenoside F4 Alleviates Skeletal Muscle Insulin Resistance by Regulating PTP1B in Type II Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease with increasing morbidity. Protein tyrosine phosphatase 1B (PTP1B) is a major negative regulator of the insulin signaling cascade and has attracted intensive investigation in the T2DM study. Ginseng is widely used to treat metabolic diseases, while the effects of ginsenoside F4 (F4) on T2DM have remained unknown. Here, we identify F4 as an inhibitor of skeletal muscle insulin resistance. The results showed that F4 significantly improved the hyperglycemic state of db/db mice, alleviated dyslipidemia, and promoted skeletal muscle glucose uptake. This phenomenon was closely related to the inhibition of the PTP1B activity. On the one hand, the inhibition of PTP1B activity by F4 resulted in increased insulin receptor (INSR) and insulin receptor substrate 1 tyrosine phosphorylation and enhanced insulin sensitivity. On the other hand, F4 as a PTP1B inhibitor inhibited the inositol-requiring enzyme 1 (IRE-1)/recombinant TNF receptor associated factor 2 (TRAF2)/c-Jun N-terminal kinase signaling pathway and alleviated skeletal muscle endoplasmic reticulum (ER) stress, thereby reducing IRS-1 serine phosphorylation. Both finally activated the PI3K/AKT signaling pathway and promoted glucose transporter protein 4 translocation to the cell membrane for glucose uptake. Taken together, our experiments demonstrate that F4 activates the insulin signaling pathway by inhibiting the activity of PTP1B while inhibiting the IRE-1/TRAF2/JNK signaling pathway, enhancing insulin sensitivity, and alleviating ER stress in the skeletal muscle of db/db mice. Our results indicate that F4 can be used as a PTP1B inhibitor for the treatment of T2DM.

Changes in Lipid Metabolism Enzymes in Rat Epididymal Fat after Chronic Central Leptin Infusion Are Related to Alterations in Inflammation and Insulin Signaling

Leptin inhibits food intake and reduces the size of body fat depots, changing adipocyte sensitivity to insulin to restrain lipid accrual. This adipokine may modulate the production of cytokines that could diminish insulin sensitivity, particularly in visceral adipose tissue. To explore this possibility, we examined the effects of chronic central administration of leptin on the expression of key markers of lipid metabolism and its possible relationship with changes in inflammatory- and insulin-signaling pathways in epididymal adipose tissue. Circulating non-esterified fatty acids and pro- and anti-inflammatory cytokines were also measured. Fifteen male rats were divided into control (C), leptin (L, icv, 12 μg/day for 14 days), and pair-fed (PF) groups. We found a decrease in the activity of glucose-6-phosphate dehydrogenase and malic enzyme in the L group, with no changes in the expression of lipogenic enzymes. A reduction in the expression of lipoprotein lipase and carnitine palmitoyl-transferase-1A, together with a decrease in the phosphorylation of insulin-signaling targets and a low-grade inflammatory pattern, were detected in the epididymal fat of L rats. In conclusion, the decrease in insulin sensitivity and increased pro-inflammatory environment could regulate lipid metabolism, reducing epididymal fat stores in response to central leptin infusion.

Causal relationship between insulin resistance and sarcopenia

Sarcopenia is a multifactorial disease characterized by reduced muscle mass and function, leading to disability, death, and other diseases. Recently, the prevalence of sarcopenia increased considerably, posing a serious threat to health worldwide. However, no clear international consensus has been reached regarding the etiology of sarcopenia. Several studies have shown that insulin resistance may be an important mechanism in the pathogenesis of induced muscle attenuation and that, conversely, sarcopenia can lead to insulin resistance. However, the causal relationship between the two is not clear. In this paper, the pathogenesis of sarcopenia is analyzed, the possible intrinsic causal relationship between sarcopenia and insulin resistance examined, and research progress expounded to provide a basis for the clinical diagnosis, treatment, and study of the mechanism of sarcopenia.

A small-molecule JNK inhibitor JM-2 attenuates high-fat diet-induced non-alcoholic fatty liver disease in mice

BACKGROUND

The prevalence of non-alcoholic fatty liver disease (NAFLD) has been deemed a leading cause of end-stage liver disease. As a member of the mitogen-activated protein kinase family, c-Jun N-terminal kinase (JNK) has been shown to play an important role in the pathogenesis of NAFLD. Here, we identified a novel JNK inhibitor, JM-2, and evaluated its therapeutic effects against NAFLD both in vitro and in vivo.

METHODS

In vitro, JNK was blocked by JM-2 in PA-challenged hepatocytes. C57BL/6 mice were fed a high-fat diet for 6 months to develop NAFLD. Mice were treated with JM-2 by intragastric administration.

RESULTS

In primary hepatocytes and AML-12 cells, JM-2 treatment significantly suppressed palmitic acid (PA)-induced JNK activation and PA-induced inflammation and cell apoptosis. In addition, JM-2 restricted the production of fibrosis- and lipid metabolism-related genes in PA-challenged hepatocytes. We evaluated the curative effect of JM-2 against NAFLD using a high-fat diet (HFD)-fed mouse model. Based on our findings, JM-2 administration significantly protected the mouse liver from HFD-induced inflammation, lipid accumulation, fibrosis, and apoptosis, accompanied with reduced JNK phosphorylation in the liver tissue.

CONCLUSION

JM-2 affords a significant protective effect against HFD-induced NAFLD by inhibiting JNK activation and is potential to be developed as a candidate drug for NAFLD treatment.

Gold nanoclusters eliminate obesity induced by antipsychotics

Obesity induced by antipsychotics have plagued more than 20 million people worldwide. However, no drug is available to eliminate the obesity induced by antipsychotics. Here we examined the effect and potential mechanisms of a gold nanoclusters (AuNCs) modified by N-isobutyryl-L-cysteine on the obesity induced by olanzapine, the most prescribed but obesogenic antipsychotics, in a rat model. Our results showed that AuNCs completely prevented and reversed the obesity induced by olanzapine and improved glucose metabolism profile in rats. Further mechanism investigations revealed that AuNCs exert its anti-obesity function through inhibition of olanzapine-induced dysfunction of histamine H1 receptor and proopiomelanocortin signaling therefore reducing hyperphagia, and reversing olanzapine-induced inhibition of uncoupling-protein-1 signaling which increases thermogenesis. Together with AuNCs' good biocompatibility, these findings not only provide AuNCs as a promising nanodrug candidate for treating obesity induced by antipsychotics, but also open an avenue for the potential application of AuNCs-based nanodrugs in treating general obesity.

Opposite Effects of Chronic Central Leptin Infusion on Activation of Insulin Signaling Pathways in Adipose Tissue and Liver Are Related to Changes in the Inflammatory Environment

Leptin modulates insulin signaling and this involves the Akt pathway, which is influenced by changes in the inflammatory environment and with leptin regulating cytokine synthesis. We evaluated the association between activation of the insulin-signaling pathway and alterations in pro- and anti-inflammatory cytokine levels in inguinal fat and liver of chronic central leptin infused (L), pair-fed (PF), and control rats. Signal transducer and activator of transcription 3 (STAT3) phosphorylation was increased in inguinal fat and reduced in liver of L rats. Phosphorylation of c-Jun N-terminal kinase (JNK) and nuclear factor kappa B (NFkB) was increased in inguinal fat of L rats, together with a pro-inflammatory cytokine profile, while in the liver activation of JNK and NFkB were reduced and an anti-inflammatory pattern was found. Phosphorylation of the insulin receptor, Akt and mechanistic target of rapamycin was decreased in inguinal fat and increased in liver of L rats. There was a direct relationship between pSTAT3 and JNK and a negative correlation of Akt with pSTAT3 and JNK in both tissues. These results indicate that the effects of chronically increased leptin on insulin-related signaling are tissue-specific and suggest that inflammation plays a relevant role in the crosstalk between leptin and insulin signaling.