Muscle cell palmitate-induced insulin resistance, JNK, IKK/NF-κB, and STAT3 activation are attenuated by carnosic and rosmarinic acid

The worldwide epidemic of obesity has drastically worsened with the increase in more sedentary lifestyles and increased consumption of fatty foods. Increased blood free fatty acids, often observed in obesity, lead to impaired insulin action, and promote the development of insulin resistance and type 2 diabetes mellitus. c-Jun N-terminal kinase (JNK), inhibitor of kappa B (IκB) kinase (IKK)-nuclear factor-kappa B (NF-κB), and signal transducer and activator of transcription 3 (STAT3) are known to be involved in skeletal muscle insulin resistance. We reported previously that carnosic acid (CA) and rosmarinic acid (RA) attenuated the palmitate-induced skeletal muscle insulin resistance, an effect that was associated with increased AMPK activation and reduced mammalian target of rapamycin-p70S6K signaling. In the present study, we examined the effects of CA and RA on JNK, IKK-NF-κB, and STAT3. Exposure of cells to palmitate increased the phosphorylation/activation of JNK, IKKα/β, IκBα, NF-κBp65, and STAT3. Importantly, CA and RA attenuated the deleterious effects of palmitate. Our data indicate that CA and RA have the potential to counteract the palmitate-induced skeletal muscle cell insulin resistance by modulating JNK, IKK-NF-κB, and STAT3 signaling.

Network Pharmacology-Based Dissection of the Active Ingredients and Protective Mechanism of the Salvia Miltiorrhiza and Panax Notoginseng Herb Pair against Insulin Resistance

The Salvia miltiorrhiza and Panax notoginseng herb pair (DQ) has been widely utilized in traditional Chinese medicine for the longevity and for preventing and treating cardio-cerebrovascular diseases. Often associated with cardio-cerebrovascular diseases are comorbidities such as insulin resistance. However, the protective mechanisms of DQ against insulin resistance remain not well understood. Through network pharmacology analysis, a total of 94 candidate active compounds selected from DQ (61 from S. miltiorrhiza Bunge and 33 from P. notoginseng (Burk.) F. H. Chen) interacted with 52 corresponding insulin resistance-related targets, which mainly involved insulin resistance and the AMPK signaling pathway. Furthermore, the contribution index calculation results indicated 25 compounds as the principal components of this herb pair against insulin resistance. Among them, ginsenoside F2, protocatechuic acid, and salvianolic acid B were selected and validated to promote glucose consumption through activating AMPK phosphorylation and upregulating GLUT4 in insulin-resistant cell model (HepG2/IR) cells. These findings indicated that DQ has the potential for repositioning in the treatment of insulin resistance mainly through the AMPK signaling pathway.

Bidirectional regulation of genistein on the proliferation and differentiation of C2C12 myoblasts

Genistein is a widely studied phytoestrogen. The effects of genistein on myoblasts were reported long ago, but the conclusions are controversial. In this study, we evaluated the effects of different concentrations of genistein on C2C12 myoblasts. Genistein treatment promoted myoblast proliferation in a dose-dependent manner in the concentration range of 0-2 µM/L, reaching its maximum effect at 2 µM/L. Proliferation then declined, and a concentration higher than 20 µM/L showed significant inhibition. In addition, genistein treatment promoted myoblast differentiation at a dose of 10 µM/L. However, at treatment concentrations higher than 10 µM/L, the effect on myoblast differentiation was rapidly inhibited as the concentration increased. Genistein treatment also down-regulated the expression of miR-222, resulting in increased expression of its target genes, MyoG, MyoD, and ERα and thereby promoting myoblast differentiation. Our results suggest that genistein has a dose-dependent and bidirectional regulation effect on myoblast proliferation and differentiation. We also found that genistein is a miRNA inducer, and it specifically affects the expression of miR-222 to regulate myoblast differentiation.

Antiobesity Effects of Purple Perilla (Perilla frutescens var. acuta) on Adipocyte Differentiation and Mice Fed a High-fat Diet

Purple perilla (PE) is a medicinal plant that has several health benefits. In this study, the antiobesity effect of PE was studied in 3T3-L1 preadipocytes and C57BL/6J mice fed high-fat diets. Triglyceride quantification and Oil Red O staining in matured adipocytes revealed that PE reduced lipid accumulation in differentiated adipocytes by downregulating adipogenic gene and upregulating lipolytic gene expressions. Mice were fed normal diet, high-fat diet and high-fat diet supplemented with different concentrations of PE. Treatment with PE significantly prevented body weight gain, improved serum lipids, hepatic lipids and reduced the epididymal fat. Furthermore, in the adipose tissue and liver, expression of genes related to lipolysis and fatty acid β-oxidation were upregulated in PE- treated mice. Thus, our results suggested that PE has antiobesity effects in rodents and can be effective in obesity management.

PRACTICAL APPLICATION

Purple perilla, rich in polyphenols such as rosmarinic acid, showed lipid lowering in adipocyte cells and prevented body weight gain in mice. Therefore we conclude that purple perilla may be a potential candidate for the development of functional foods or nutraceuticals in managing obesity in humans.

miR-152 regulates the proliferation and differentiation of C2C12 myoblasts by targeting E2F3

The development of skeletal muscle is a complex process involving the proliferation, differentiation, apoptosis, and changing of muscle fiber types in myoblasts. Many reports have described the involvement of microRNAs in the myogenesis of myoblasts. In this study, we found that the expression of miR-152 was gradually down-regulated during myoblast proliferation, but gradually up-regulated during the differentiation of myoblasts. Transfection with miR-152 mimics restrained cell proliferation and decreased the expression levels of cyclin E, CDK4, and cyclin D1, but promoted myotube formation and significantly increased the mRNA expression levels of MyHC, MyoD, MRF4, and MyoG in C2C12 myoblasts. However, treatment with miR-152 inhibitors promoted cell proliferation and restrained differentiation. Moreover, over-expression of miR-152 significantly decreased E2F3 production in C2C12 myoblasts. A luciferase assay confirmed that miR-152 could bind to the 3' UTR of E2F3. In conclusion, this study showed that miR-152 inhibited proliferation and promoted myoblast differentiation by targeting E2F3.