Effects of olanzapine on glucose transport, proliferation and survival in C2C12 myoblasts

Alterations in Skeletal Muscle Insulin Signaling DNA Methylation: A Pilot Randomized Controlled Trial of Olanzapine in Healthy Volunteers

Antipsychotics are associated with severe metabolic side effects including insulin resistance; however, the mechanisms underlying this side effect are not fully understood. The skeletal muscle plays a critical role in insulin-stimulated glucose uptake, and changes in skeletal muscle DNA methylation by antipsychotics may play a role in the development of insulin resistance. A double-blind, placebo-controlled trial of olanzapine was performed in healthy volunteers. Twelve healthy volunteers were randomized to receive 10 mg/day of olanzapine for 7 days. Participants underwent skeletal muscle biopsies to analyze DNA methylation changes using a candidate gene approach for the insulin signaling pathway. Ninety-seven methylation sites were statistically significant (false discovery rate < 0.05 and beta difference between the groups of ≥10%). Fifty-five sites had increased methylation in the skeletal muscle of olanzapine-treated participants while 42 were decreased. The largest methylation change occurred at a site in the Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-Alpha (PPARGC1A) gene, which had 52% lower methylation in the olanzapine group. Antipsychotic treatment in healthy volunteers causes significant changes in skeletal muscle DNA methylation in the insulin signaling pathway. Future work will need to expand on these findings with expression analyses.

The mechanisms underlying olanzapine-induced insulin resistance via the brown adipose tissue and the therapy in rats

A rapid increase has been observed in insulin resistance (IR) incidence induced by a long-term olanzapine treatment with no better ways to avoid it. Our study aimed to demonstrate the mechanism underlying the olanzapine-induced insulin resistance and find appropriate drug interventions. In this study, firstly, we constructed rat insulin resistance model using a two-month gavage of olanzapine and used the main active ingredient mixture of Gegen Qinlian Decoction for the treatment. The activity of brown adipose tissue (BAT) was measured using the PET/CT scan, whereas Western blot and quantitative real-time PCR were used to detect the expression of GLUT4 and UCP1. The results showed that the long-term administration of olanzapine impaired glucose tolerance and produced insulin resistance in rats, while Gegen Qinlian Decoction could improve this side effect. The results of the PET/CT scan showed that the BAT activity in the insulin-resistant rats was significantly lower than that of the Gegen Qinlian Decoction treated rats. Also, the expression of GLUT4 and UCP1 in the insulin resistance group showed a significant decrease, which could be up-regulated by Gegen Qinliane Decoction treatment. The results of both in vivo and in vitro experiments were consistent. we demonstrated that the olanzapine could induce IR in vitro and in vivo by decreasing the expression of UCP1; thus, suppressing the thermogenesis of BAT and impairing glucose uptake. More importantly, we demonstrated a possible novel strategy to improve the olanzapine-induced IR by Gegen Qinlian Decoction.

The protein kinase D1-mediated inflammatory pathway is involved in olanzapine-induced impairment of skeletal muscle insulin signaling in rats

AIMS

Skeletal muscle insulin resistance (SMIR) contributes to the metabolic syndrome. Mounting evidence has demonstrated that the second generation antipsychotic olanzapine causes SMIR. The present study sought to investigate the molecular mechanisms underlying olanzapine-induced SMIR.

MAIN METHODS

Male rats were given olanzapine (5 mg/kg, by a gavage method) for consecutive eight weeks. Plasma glucose and insulin concentrations were determined enzymatically or by ELISA. Gene/protein expression was analyzed by Real-Time PCR, Western blot and/or immunohistochemistry.

KEY FINDINGS

Olanzapine increased fasting plasma insulin concentration, and decreased glucose clearance during insulin tolerance test in rats. In skeletal muscle, it decreased protein expression of membrane glucose transporter (GLUT) 4, the ratio of membrane to total GLUT4, and total insulin receptor substrate 1 (IRS1). However, it increased protein phosphorylation of Ser³⁰⁷ in IRS1, Y⁶⁰⁷ in phosphoinositide 3-kinase p85α and Ser³⁰⁷ in AKT. These results indicate olanzapine-induced impairment of skeletal muscle insulin signaling. Mechanistically, olanzapine upregulated mRNA expression of TNFα, IL6 and IL1β, and protein phosphorylation of both IκB kinase (IKK)α/β and nuclear factor (NF)κB p65. Furthermore, it increased protein phosphorylation of Ser^485/491 in AMPKα2, whereas it decreased AMPKα2 activity. More importantly, both Western blot and immunohistochemical analyses revealed that olanzapine increased protein phosphorylation of Ser^744/748 in protein kinase D1 (PKD1).

SIGNIFICANCE

The present results suggest that the PKD1-mediated inflammatory pathway is involved in olanzapine-induced impairment of skeletal muscle insulin signaling in rats. Our findings may go new insight into the mechanisms underlying olanzapine-induced SMIR.

Second-Generation Antipsychotics and Dysregulation of Glucose Metabolism: Beyond Weight Gain

Second-generation antipsychotics (SGAs) are the cornerstone of treatment for schizophrenia because of their high clinical efficacy. However, SGA treatment is associated with severe metabolic alterations and body weight gain, which can increase the risk of type 2 diabetes and cardiovascular disease, and greatly accelerate mortality. Several underlying mechanisms have been proposed for antipsychotic-induced weight gain (AIWG), but some studies suggest that metabolic changes in insulin-sensitive tissues can be triggered before the onset of AIWG. In this review, we give an outlook on current research about the metabolic disturbances provoked by SGAs, with a particular focus on whole-body glucose homeostasis disturbances induced independently of AIWG, lipid dysregulation or adipose tissue disturbances. Specifically, we discuss the mechanistic insights gleamed from cellular and preclinical animal studies that have reported on the impact of SGAs on insulin signaling, endogenous glucose production, glucose uptake and insulin secretion in the liver, skeletal muscle and the endocrine pancreas. Finally, we discuss some of the genetic and epigenetic changes that might explain the different susceptibilities of SGA-treated patients to the metabolic side-effects of antipsychotics.

The therapeutic potential of GPR43: a novel role in modulating metabolic health

GPR43 is a receptor for short-chain fatty acids. Preliminary data suggest a putative role for GPR43 in regulating systemic health via processes including inflammation, carcinogenesis, gastrointestinal function, and adipogenesis. GPR43 is involved in secretion of gastrointestinal peptides, which regulate appetite and gastrointestinal motility. This suggests GPR43 may have a role in weight control. Moreover, GPR43 regulates plasma lipid profile and inflammatory processes, which further indicates that GPR43 could have the ability to modulate the etiology and pathogenesis of metabolic diseases such as obesity, type 2 diabetes mellitus, and cardiovascular disease. This review summarizes the current evidence regarding the ability of GPR43 to mediate both systemic and tissue specific functions and how GPR43 may be modulated in the treatment of metabolic disease.

Exploratory study on association of genetic variation in TBC1D1 with antipsychotic-induced weight gain

BACKGROUND

Previous studies have shown that antipsychotics with high propensity for antipsychotic-induced weight gain (AIWG) influence glucose transporter type 4 (GLUT4) mediated glucose intake. Variation in the gene encoding TBC1 domain family member 1 (TBC1D1), a Rab-GTPase activating protein regulating GLUT4 trafficking, has been associated with obesity. Therefore, we investigated the impact of TBC1D1 polymorphisms on AIWG.

METHODS

We analyzed rs9852 and rs35859249 in TBC1D1 in 195 schizophrenia subjects treated mostly with clozapine or olanzapine for up to 14 weeks. Association was tested using analysis of variance and analysis of covariance with change (%) from baseline weight as the dependent variable.

RESULTS

Analysis of covariance showed a non-significant trend for lower weight gain in carriers of the T-allele of rs9852 than in C-allele homozygotes (p = 0.063). This effect was more pronounced in the subgroup of patients treated with clozapine or olanzapine (p = 0.024). For rs35859249, no significant association with AIWG could be detected.

CONCLUSIONS

This is the first study examining the association between TBC1D1 and AIWG. The moderate association of rs9852, located in the 3'UTR near a miRNA binding site, indicates an influence of TBC1D1 on AIWG. Further investigations remain necessary to elucidate the role of this gene in AIWG.

Foxo/atrogin induction in human and experimental myositis

Skeletal muscle atrophy can occur rapidly in various fasting, cancerous, systemic inflammatory, deranged metabolic or neurogenic states. The ubiquitin ligase Atrogin-1 (MAFbx) is induced in animal models of these conditions, causing excessive myoprotein degradation. It is unknown if Atrogin upregulation also occurs in acquired human myositis. Intracellular β-amyloid (Aβi), phosphorylated neurofilaments, scattered infiltrates and atrophy involving selective muscle groups characterize human sporadic Inclusion Body Myositis (sIBM). In Polymyositis (PM), inflammation is more pronounced and atrophy is symmetric and proximal. IBM and PM share various inflammatory markers. We found that forkhead family transcription factor Foxo3A is directed to the nucleus and Atrogin-1 transcript is increased in both conditions. Expression of Aβ in transgenic mice and differentiated C2C12 myotubes was sufficient to upregulate Atrogin-1 mRNA and cause atrophy. Aβi reduces levels of p-Akt and downstream p-Foxo3A, resulting in Foxo3A translocation and Atrogin-1 induction. In a mouse model of autoimmune myositis, cellular inflammation alone was associated with similar Foxo3A and Atrogin changes. Thus, either Aβi accumulation or cellular immune stimulation may independently drive muscle atrophy in sIBM and PM, respectively, through pathways converging on Foxo and Atrogin-1. In sIBM it is additionally possible that both mechanisms synergize.

Hydro-Alcoholic Cinnamon Extract, Enhances Glucose Transporter Isotype-4 Translocation from Intracellular Compartments into the Cytoplasmic Membrane of C2C12 Myotubes

Cinnamon has been used as an anti-diabetic agent for centuries but only in recent few years its mechanism of action has been under investigation. Previous studies showed that cinnamon might exert its anti-diabetic effect via increasing glucose transporter isotype-4 (GLUT4) gene and glycoprotein contents in fat cells. To study if hydro-alcoholic cinnamon extract (HACE) enhances GLUT4 translocation from intracellular compartments of nuclear or endoplasmic reticulum membranes (N/ER) into the cytoplasmic membrane (CM). C2C12 myoblastic cell line were seeded in DMEM plus 20 % FBS and differentiated to myotubes using 2 % horse serum. After myotubes formation, 100 or 1,000 μg/ml HACE, as intervention, and as control 1 % DMSO were added for 3 h. Cells were washed and homogenized followed by ultracentrifuge fractionation, protein separation by SDS-PAGE and GLUT4 detection using semi-quantitative Western blotting. Data analysis was done by two-independent samples t test for comparison of mean ± SD of GLUT4 percent in categories. GLUT4 contents were higher in CM of groups 100 and 1,000 μg/ml HACE and lower in 1 % DMSO treated myotubes (CI = 0.95, P < 0.05). For N/ER reverse results were obtained (CI = 0.95, P < 0.05). As our results have shown HACE induces GLUT4 translocation from intra-cell into cell surface. We conclude that cinnamon maybe a choice of type-2 diabetes mellitus treatment because its extract enhances GLUT4 contents in CM where it facilitates glucose entrance into the cell. However it is necessary to trace the signaling pathways which are activated by HACE in muscular tissue.

AMP-activated protein kinase regulates normal rat somatotroph cell function and growth of rat pituitary adenomatous cells

AMP-activated protein kinase (AMPK) is activated under conditions that deplete cellular ATP and elevate AMP levels such as glucose deprivation and hypoxia. The AMPK system is primarily thought of as a regulator of metabolism and cell proliferation. Little is known about the regulation and the effects of AMPK in somatotroph cells. We present results from "in vitro" studies showing that AMPK activity has a role in regulating somatotroph function in normal rat pituitary and is a promising target for the development of new pharmacological treatments affecting cell proliferation and viability of pituitary adenomatous cells. In parallel, we show "in vivo" data obtained in the rat suggesting that AMPK is an intracellular transducer that may play a role in mediating the effects of the pharmacological treatment with dexamethasone on somatotrophs. In rat pituitary cell cultures, the AMP analog AICAR induced a rapid and clear-cut activation of AMPK. AICAR decreased GH release and total cellular GH content. An appropriate level of AMPK activation was essential for GH3 adenomatous cells. Remarkably, over-activation by AICAR induced apoptosis of GH3 whereas the AMPK inhibitor compound C was more effective at reducing cell proliferation. The role of endocrine or paracrine factors in regulating AMPK phosphorylation and activity in GH3 cells has been also studied. As to "in vivo" studies, western blot analysis revealed a significant decrease of phosphorylated AMPK alpha-subunit in pituitary homogenates of DEX-treated rats versus controls, suggesting reduced AMPK activity. In conclusion, our studies showed that AMPK has a role in regulating somatotroph function in normal rat pituitary and proliferation of pituitary adenomatous cells.

Negative regulation of adiponectin secretion by receptor interacting protein 140 (RIP140)

RIP140 (receptor-interacting protein 140) is highly expressed in mature adipocytes and functions as a co-repressor for gene expression involved in lipid and glucose metabolism. In adipocytes, activated PKCε (Protein kinase C epsilon) phosphorylates nuclear RIP140 which is then subsequently arginine methylated and exported to the cytoplasm. In the cytoplasm, RI140 can elicit additional activities. Here we report a new functional role for cytoplasmic RIP140 in adipocyte in regulating adiponectin secretion. Targeting cytoplasmic RIP140 by knocking down RIP140 itself or its nuclear export trigger, PKCε, promotes the secretion of adiponectin without affecting the production or oligomerization of adiponectin. Consequentially, conditioned media from either RIP140- or PKCε-silenced adipocytes, which contain higher levels of adiponectin, enhance glucose uptake in C2C12 cells and reduce gluconeogenesis in HepG2 cells. Further, these effects can be inhibited by an adiponectin-neutralizing antibody. The effect of cytoplasmic RIP140 in regulating adiponectin secretion is via interacting with AS160, a known RIP140-interacting protein. This study reveals a new functional role for cytoplasmic RIP140 in modulating adiponectin vesicle secretion, and suggests that targeting cytoplasmic RIP140 may be a potentially effective therapeutic strategy to improve adiponectin secretion and possibly to manage metabolic disorders.