Corrigendum to "Ginsenoside compound K ameliorates palmitate-induced atrophy in C2C12 myotubes via promyogenic effects and AMPK/autophagy-mediated suppression of endoplasmic reticulum stress" [J Ginseng Res 46(3) May 2022 444-453].

[This corrects the article DOI: 10.1016/j.jgr.2021.09.002.].

Ginsenoside compound K ameliorates palmitate-induced atrophy in C2C12 myotubes via promyogenic effects and AMPK/autophagy-mediated suppression of endoplasmic reticulum stress.

Background: Compound K (CK) is among the protopanaxadiol (PPD)-type ginsenoside group, which produces multiple pharmacological effects. Herein, we examined the effects of CK on muscle atrophy under hyperlipidemic conditions along with its pro-myogenic effects. Further, the molecular pathways underlying the effects of CK on skeletal muscle have been justified. Methods: C2C12 myotubes were treated with palmitate and CK. C2C12 myoblasts were differentiated using CK for 4-5 days. For the in vivo experiments, CK was administered to mice fed on a high-fat diet for 8 weeks. The protein expression levels were analyzed using western blotting analysis. Target protein suppression was performed using small interfering (si) RNA transfection. Histological examination was performed using Jenner-Giemsa and H&E staining techniques. Results: CK treatment attenuated ER stress markers, such as eIF2α phosphorylation and CHOP expression and impaired myotube formation in palmitate-treated C2C12 myotubes and skeletal muscle of mice fed on HFD. CK treatment augmented AMPK along with autophagy markers in skeletal muscle cells in vitro and in vivo experiments. AMPK siRNA or 3-MA, an autophagy inhibitor, abrogated the impacts of CK in C2C12 myotubes. CK treatment augmented p38 and Akt phosphorylation, leading to an enhancement of C2C12 myogenesis. However, AMPK siRNA abolished the effects of CK in C2C12 myoblasts. Conclusion: These findings denote that CK prevents lipid-induced skeletal muscle apoptosis via AMPK/autophagy-mediated attenuation of ER stress and induction of myoblast differentiation. Therefore, we may suggest the use of CK as a potential therapeutic approach for treating muscle-wasting conditions associated with obesity.

Patchouli alcohol ameliorates skeletal muscle insulin resistance and NAFLD via AMPK/SIRT1-mediated suppression of inflammation.

Obesity-induced chronic low-grade inflammation and thus causes various metabolic diseases, such as insulin resistance and non-alcoholic fatty liver disease (NAFLD). Patchouli alcohol (PA), an active component extracted from patchouli, displayed anti-inflammatory effects on different cell types. However, the impact of PA on skeletal muscle insulin signaling and hepatic lipid metabolism remains unclear. This study aimed to investigate whether PA would affect insulin signaling impairment in myocytes and lipid metabolism in hepatocytes. Treatment with PA ameliorated palmitate-induced inflammation and aggravation of insulin signaling in C2C12 myocytes and lipid accumulation in HepG2 hepatocytes. Treatment of C2C12 myocytes and HepG2 cells with PA augmented AMP-activated protein kinase (AMPK) phosphorylation and Sirtuin 1 (SIRT1) expression in a dose-dependent manner. siRNA-mediated suppression of AMPK or SIRT1 mitigated the effects of PA on palmitate-induced inflammation and insulin resistance in C2C12 myocytes and lipid accumulation in HepG2 cells. Animal experiments demonstrated that PA administration increased AMPK phosphorylation and SIRT1 expression, and ameliorated inflammation, thereby attenuating skeletal muscle insulin resistance and hepatic steatosis in high-fat diet-fed mice. These results denote that PA alleviates skeletal muscle insulin resistance and hepatic steatosis through AMPK/SIRT1-dependent signaling. This study might provide a novel therapeutic approach for treating obesity-related insulin resistance and NAFLD.

3-hydroxymorphinan enhances mitochondrial biogenesis and adipocyte browning through AMPK-dependent pathway.

3-hydroxymorphinan (3-HM), a metabolite of dextromethorphan, has previously been reported to have anti-inflammatory, anti-oxidative stress, and neuroprotective effects. However, its effect on energy metabolism in adipocytes remains unclear. Herein, we investigated 3-hydroxymorphinan (3-HM) effects on mitochondrial biogenesis, oxidative stress, and lipid accumulation in 3T3-L1 adipocytes. Further, we explored 3-HM-associated molecular mechanisms. Mouse adipocyte 3T3-L1 cells were treated with 3-HM, and various protein expression levels were determined by western blotting analysis. Mitochondria accumulation and lipid accumulation were measured by staining methods. Cell toxicity was assessed by cell viability assay. We found that treatment of 3T3-L1 adipocytes with 3-HM increased expression of brown adipocyte markers, such as uncoupling protein-1 (UCP-1) and peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC-1α). 3-HM promotes mitochondrial biogenesis and its-mediated gene expression. Additionally, 3-HM treatment suppressed mitochondrial ROS generation and superoxide along with improved mitochondrial complex I activity. We found that treatment of 3-HM enhanced AMPK phosphorylation. siRNA-mediated suppression of AMPK reversed all these changes in 3T3-L1 adipocytes. In sum, 3-HM promotes mitochondrial biogenesis and browning and attenuates oxidative stress and lipid accumulation in 3T3-L1 adipocytes via AMPK signaling. Thus, 3-HM-mediated AMPK activation can be considered a therapeutic approach for treating obesity and related diseases.

Capmatinib improves insulin sensitivity and inflammation in palmitate-treated C2C12 myocytes through the PPARδ/p38-dependent pathway.

Capmatinib (CAP) has been used to treat metastatic non-small lung cancer (NSCL) and suppress inflammation. It causes hypoglycemia in NSCL patients. Therefore, it is expected that CAP improves inflammation-mediated insulin resistance due to its anti-inflammatory effect. However, the impacts of CAP on insulin signaling in skeletal muscle cells have not yet been fully elucidated. Herein, we investigated the effect of CAP on insulin resistance in palmitate-treated C2C12 myocytes and explored the related molecular mechanisms. We found that treatment of C2C12 myocytes with CAP reversed palmitate-induced impairment of insulin signaling and glucose uptake. CAP treatment ameliorated phosphorylation of inflammatory markers, including NFκB and IκB, in palmitate-treated C2C12 myocytes. Further, it augmented PPARδ expression and suppressed palmitate-induced p38 phosphorylation in a dose-dependent manner. siRNA-mediated suppression of PPARδ abolished the effects of CAP on palmitate-induced insulin resistance and inflammation as well as p38 phosphorylation. Therefore, it has been shown that CAP treatment ameliorates insulin resistance in palmitate-treated C2C12 myocytes via PPARδ/p38 signaling-mediated suppression of inflammation. These results may represent a novel therapeutic approach that could halt insulin resistance and type 2 diabetes.

Patchouli alcohol improves wound healing in high fat diet-fed mice through AMPK-mediated suppression of inflammation and TGFb1 signaling.

Obesity impairs wound healing with substantial alterations in skin inflammation. Patchouli alcohol (PA), extracted from patchouli, has been reported to ameliorate inflammation in various cell types. However, the effects of PA on inflammation and wound healing have not been reported to date. In the present study, we examined whether PA affects cutaneous wound healing in high fat diet (HFD)-fed mice and explored PA-mediated molecular mechanisms through in vitro experiments. We found that PA administration accelerated wound healing as well as ameliorates inflammation in skin of HFD-fed mice. PA treatment augmented AMP-activated protein kinase (AMPK) phosphorylation and TGFb1 expression. PA enhanced cell migration and suppressed inflammation in LPS-treated HaCaT cells. Further, PA increased dose-dependently AMPK phosphorylation as along with TGFb1 and cell migration markers expression. siRNA for AMPK or TGFb1 abrogated the effects of PA on cell migration and inflammation. TGFb1 siRNA mitigated PA-induced expression of cell migration markers. These results suggest that PA ameliorates wound healing via AMPK and TGFb1-mediated suppression of inflammation. In sum, PA can be used as a novel treatment strategy for wound healing in obesity or insulin resistance.

Valdecoxib improves lipid-induced skeletal muscle insulin resistance via simultaneous suppression of inflammation and endoplasmic reticulum stress.

Valdecoxib (VAL), a non-steroidal anti-inflammatory drug, has been widely used for treatment of rheumatoid arthritis, osteoarthritis, and menstrual pain. It is a selective cyclooxygenase-2 inhibitor. The suppressive effects of VAL on cardiovascular diseases and neuroinflammation have been documented; however, its impact on insulin signaling in skeletal muscle has not been studied in detail. The aim of this study was to investigate the effects of VAL on insulin resistance in mouse skeletal muscle. Treatment of C2C12 myocytes with VAL reversed palmitate-induced aggravation of insulin signaling and glucose uptake. Further, VAL attenuated palmitate-induced inflammation and endoplasmic reticulum (ER) stress in a concentration-dependent manner. Treatment with VAL concentration-dependently upregulated AMP-activated protein kinase (AMPK) and heat shock protein beta 1 (HSPB1) expression. In line with in vitro experiments, treatment with VAL augmented AMPK phosphorylation and HSPB1 expression, thereby alleviating high-fat diet-induced insulin resistance along with inflammation and ER stress in mouse skeletal muscle. However, small interfering RNA-mediated inhibition of AMPK abolished the effects of VAL on insulin resistance, inflammation, and ER stress. These results suggest that VAL alleviates insulin resistance through AMPK/HSPB1-mediated inhibition of inflammation and ER stress in skeletal muscle under hyperlipidemic conditions. Hence, VAL could be used as an effective pharmacotherapeutic agent for management of insulin resistance and type 2 diabetes.

Capmatinib attenuates lipogenesis in 3T3-L1 adipocytes through an adenosine monophosphate-activated protein kinase-dependent pathway.

Recently, there is a rapid increase in the incidence of obesity, a condition for which there are no effective therapeutic agents. Capmatinib (CAP), a novel mesenchymal-to-epithelial transition inhibitor, is reported to attenuate pro-inflammatory mediators and oxidative stress. In this study, the effects of CAP on lipogenesis in the adipocytes were examined. Treatment with CAP dose-dependently suppressed lipid accumulation in, and differentiation of, and increased lipolysis in, 3T3-L1 adipocytes. Additionally, CAP treatment augmented adenosine monophosphate-activated protein kinase (AMPK) phosphorylation and FNDC5 expression in the adipocytes. Transfection with si-AMPK or si-FNDC5 mitigated the CAP-induced suppression of lipogenesis and enhanced lipolysis. Furthermore, transfection with si-FNDC5 mitigated the CAP-induced phosphorylation of AMPK. These results suggest that the anti-obesity effect of CAP is mediated through the irisin/AMPK pathway and that CAP is a novel therapeutic agent for obesity.

Meteorin-like protein (METRNL)/IL-41 improves LPS-induced inflammatory responses via AMPK or PPARδ-mediated signaling pathways.

PURPOSE: Meteorin-like protein (METRNL) (also known as IL-41), recently identified as a myokine, is released in response to muscle contraction. It improves the skeletal muscle insulin sensitivity through exerting a beneficial anti-inflammatory effect. However, no independent studies have been published to verify the effects of METRNL on human umbilical vein endothelial cells (HUVECs) and THP-1 human monocytes. MATERIALS AND METHODS: The levels of NFκB and IκB phosphorylation as well as the expression of adhesion molecules were assessed by Western blotting analysis. Cell adhesion assay demonstrated the interactions between HUVEC and THP-1 â€‹cells. We used enzyme-linked immunosorbent assay (ELISA) to measure the levels of TNFα and MCP-1 in culture medium. RESULTS: Treatment with METRNL suppressed the secretion of TNFα and MCP-1 as well as NFκB and IκB phosphorylation and inflammatory markers in lipopolysaccharide (LPS)-treated HUVECs and THP-1 â€‹cells. Furthermore, treatment with METRNL ameliorated LPS-induced attachment of THP-1 monocytes to HUVECs via inhibition of adhesion molecule expression and apoptosis. Treatment of HUVEC and THP-1 â€‹cells with METRNL enhanced AMPK phosphorylation and PPARδ expression in a dose-dependent manner. Small interference (si) RNA-mediated suppression of AMPK or PPARδ restored all these changes. CONCLUSIONS: It has therefore been shown that METRNL ameliorates inflammatory responses through AMPK and PPARδ-dependent pathways in LPS-treated HUVEC. In sum, the current study may suggest the suppressive potential of METRNL against endothelial inflammation.

Endogenous metabolite, kynurenic acid, attenuates nonalcoholic fatty liver disease via AMPK/autophagy- and AMPK/ORP150-mediated signaling.

Endoplasmic reticulum (ER) stress plays a causative role in the development of nonalcoholic fatty liver disease (NAFLD). Kynurenic acid (KA) is a tryptophan metabolite that has been shown to exert anti-inflammatory effects in macrophages and endothelial cells. However, the role of KA in ER stress-associated development of NAFLD has not been fully explored. In the current study, we observed decreased KA levels in the serum of obese subjects. Treated hepatocytes with KA attenuated palmitate-induced lipid accumulation and downregulated lipogenesis-associated genes as well as ER stress markers in a dose-dependent manner. Furthermore, KA augmented AMP-activated protein kinase (AMPK) phosphorylation, oxygen-regulated protein 150 (ORP150) expression, and autophagy markers. The small interfering RNA-mediated suppression of AMPK and ORP150, or 3-methyladenine also abrogated the effects of KA on ER stress and lipid accumulation in hepatocytes. In accordance with in vitro observations, KA administration to mice fed a high-fat diet ameliorated hepatic lipid accumulation and decreased the expression of lipogenic genes as well as ER stress. Moreover, KA treatment increased hepatic AMPK phosphorylation, ORP150 expression, and autophagy related markers in mouse livers. Knockdown of AMPK using in vivo transfection mitigated the effects of KA on hepatic steatosis and ER stress as well as autophagy and ORP150 expression. These results suggest that KA ameliorates hepatic steatosis via the AMPK/autophagy- and AMPK/ORP150-mediated suppression of ER stress. In sum, KA might be used as a promising therapeutic agent for treatment of NAFLD.