Joong-Yeol Park

Anti-obesity effects of α-lipoic acid mediated by suppression of hypothalamic AMP-activated protein kinase

AMP-activated protein kinase (AMPK) functions as a fuel sensor in the cell and is activated when cellular energy is depleted. Here we report that α-lipoic acid (α-LA), a cofactor of mitochondrial enzymes, decreases hypothalamic AMPK activity and causes profound weight loss in rodents by reducing food intake and enhancing energy expenditure. Activation of hypothalamic AMPK reverses the effects of α-LA on food intake and energy expenditure. Intracerebroventricular (i.c.v.) administration of glucose decreases hypothalamic AMPK activity, whereas inhibition of intracellular glucose utilization through the administration of 2-deoxyglucose increases hypothalamic AMPK activity and food intake. The 2-deoxyglucose-induced hyperphagia is reversed by inhibiting hypothalamic AMPK. Our findings indicate that hypothalamic AMPK is important in the central regulation of food intake and energy expenditure and that α-LA exerts anti-obesity effects by suppressing hypothalamic AMPK activity.NOTE: In the version of this article initially published online, the name of an author was misspelled. The name of the twelfth author should be “Benoit Viollet”. This error has been corrected for the HTML and print versions of the article

Multifactor-dimensionality reduction shows a two-locus interaction associated with Type 2 diabetes mellitus.

Aims/hypothesisType 2 diabetes mellitus is a complex genetic disease, which results from interactions between multiple genes and environmental factors without any single factor having strong independent effects. This study was done to identify gene to gene interactions which could be associated with the risk of Type 2 diabetes.MethodsWe genotyped 23 different loci in the 15 candidate genes of Type 2 diabetes in 504 unrelated Type 2 diabetic patients and 133 non-diabetic control subjects. We analysed gene to gene interactions among 23 polymorphic loci using the multifactor-dimensionality reduction (MDR) method, which has been shown to be effective for detecting and characterising gene to gene interactions in case-control studies with relatively small samples.ResultsThe MDR analysis showed a significant gene to gene interaction between the Ala55Val polymorphism in the uncoupling protein 2 gene (UCP2) and the 161C>T polymorphism in the exon 6 of peroxisome proliferator-activated receptor γ (PPARγ) gene. This interaction showed the maximum consistency and minimum prediction error among all gene to gene interaction models evaluated. Moreover, the combination of the UCP2 55 Ala/Val heterozygote and the PPARγ 161 C/C homozygote was associated with a reduced risk of Type 2 diabetes (odds ratio: 0.51, 95% CI: 0.34 to 0.77, p=0.0016).Conclusions/interpretationUsing the MDR method, we showed a two-locus interaction between the UCP2 and PPARγ genes among 23 loci in the candidate genes of Type 2 diabetes. The determination of such genotype combinations contributing to Type 2 diabetes mellitus could provide a new tool for identifying high-risk individuals.

Essential Role of Mitochondrial Function in Adiponectin Synthesis in Adipocytes

OBJECTIVE—Adiponectin is an important adipocytokine that improves insulin action and reduces atherosclerotic processes. The plasma adiponectin level is paradoxically reduced in obese individuals, but the underlying mechanism is unknown. This study was undertaken to test the hypothesis that mitochondrial function is linked to adiponectin synthesis in adipocytes. RESEARCH DESIGN AND METHODS—We examined the effects of rosiglitazone and the measures that increase or decrease mitochondrial function on adiponectin synthesis. We also examined the molecular mechanism by which changes in mitochondrial function affect adiponectin synthesis. RESULTS—Adiponectin expression and mitochondrial content in adipose tissue were reduced in obese db/db mice, and these changes were reversed by the administration of rosiglitazone. In cultured adipocytes, induction of increased mitochondrial biogenesis (via adenoviral overexpression of nuclear respiratory factor-1) increased adiponectin synthesis, whereas impairment in mitochondrial function decreased it. Impaired mitochondrial function increased endoplasmic reticulum (ER) stress, and agents causing mitochondrial or ER stress reduced adiponectin transcription via activation of c-Jun NH2-terminal kinase (JNK) and consequent induction of activating transcription factor (ATF)3. Increased mitochondrial biogenesis reversed all of these changes. CONCLUSIONS—Mitochondrial function is linked to adiponectin synthesis in adipocytes, and mitochondrial dysfunction in adipose tissue may explain decreased plasma adiponectin levels in obesity. Impaired mitochondrial function activates a series of mechanisms involving ER stress, JNK, and ATF3 to decrease adiponectin synthesis.

Alpha‐lipoic acid decreases hepatic lipogenesis through adenosine monophosphate‐activated protein kinase (AMPK)‐dependent and AMPK‐independent pathways

Fatty liver is common in obese subjects with insulin resistance. Hepatic expression of sterol regulatory element binding protein‐1c (SREBP‐1c), which plays a major role in hepatic steatosis, is regulated by multiple factors, including insulin, adenosine monophosphate–activated protein kinase (AMPK), liver X receptors (LXRs), and specificity protein 1. Alpha‐lipoic acid (ALA), a naturally occurring antioxidant, has been shown to decrease lipid accumulation in skeletal muscle by activating AMPK. Here we show that ALA decreases hepatic steatosis and SREBP‐1c expression in rats on a high fat diet or given an LXR agonist. ALA increased AMPK phosphorylation in the liver and in cultured liver cells, and dominant‐negative AMPK partially prevented ALA‐induced suppression of insulin‐stimulated SREBP‐1c expression. ALA also inhibited DNA‐binding activity and transcriptional activity of both specificity protein 1 and LXR. Conclusion: These results show that ALA prevents fatty liver disease through multiple mechanisms, and suggest that ALA can be used to prevent the development and progression of nonalcoholic fatty liver disease in patients with insulin resistance. (HEPATOLOGY 2008.)

Effects of Recombinant Adenovirus-Mediated Uncoupling Protein 2 Overexpression on Endothelial Function and Apoptosis

Increased oxidative stress in vascular cells plays a key role in the development of endothelial dysfunction and atherosclerosis. Uncoupling protein 2 (UCP2) is an important regulator of intracellular reactive oxygen species (ROS) production. This study was undertaken to test the hypothesis that, UCP2 functions as an inhibitor of the atherosclerotic process in endothelial cells. Adenovirus-mediated UCP2 (Ad-UCP2) overexpression led to a significant increase in endothelial nitric oxide synthase (eNOS) and decrease in endothelin-1 mRNA expression in human aortic endothelial cells (HAECs). Moreover, UCP2 inhibited the increase in ROS production and NF-&kgr;B activation, and apoptosis of HAECs induced by lysophophatidylcholine (LPC) and linoleic acid. LPC and linoleic acid caused mitochondrial calcium accumulation and transient mitochondrial membrane hyperpolarization, which was followed by depolarization. UCP2 overexpression prevented these processes. In isolated rat aorta, Ad-UCP2 infection markedly improved impaired vascular relaxation induced by LPC. The data collectively suggest that UCP2, functions as a physiologic regulator of ROS generation in endothelial cells. Thus, measures to increase UCP2 expression in vascular endothelial cells may aid in preventing the development and progression of atherosclerosis in patients with metabolic syndrome.

Inhibitory Effects of Novel AP-1 Decoy Oligodeoxynucleotides on Vascular Smooth Muscle Cell Proliferation In Vitro and Neointimal Formation In Vivo

Excessive proliferation of vascular smooth muscle cells (VSMCs) and neointimal formation are critical steps in the pathogenesis of atherosclerosis and restenosis after percutaneous transluminal angioplasty. In this study, we investigated the hypothesis that the activator protein-1 (AP-1) plays an important role in neointimal formation after vascular injury. A circular dumbbell AP-1 decoy oligodeoxynucleotide (CDODN) was developed as a novel therapeutic strategy for restenosis after angioplasty. This CDODN was more stable than the conventional phosphorothioate linear decoy ODN (PSODN) and maintained structural integrity on exposure to exonuclease III or serum. Transfection with AP-1 decoy ODNs strongly inhibited VSMC proliferation and migration, as well as glucose- and serum-induced expression of PCNA and cyclin A genes. Administration of AP-1 decoy ODNs in vivo using the hemagglutinating virus of Japan (HVJ)-liposome method virtually abolished neointimal formation after balloon injury to the rat carotid artery. Compared with PSODN, CDODN was more effective in inhibiting the proliferation of VSMCs in vitro and neointimal formation in vivo. Our results collectively indicate that AP-1 activation is crucial for the mediation of VSMC proliferation in response to vascular injury. Moreover, the use of stable CDODN specific for AP-1 activity in combination with the highly effective HVJ-liposome method provides a novel potential therapeutic strategy for the prevention of restenosis after angioplasty in humans.

α-Lipoic Acid Prevents Endothelial Dysfunction in Obese Rats via Activation of AMP-Activated Protein Kinase

Objective—Lipid accumulation in vascular endothelial cells may play an important role in the pathogenesis of atherosclerosis in obese subjects. We showed previously that α-lipoic acid (ALA) activates AMP-activated protein kinase (AMPK) and reduces lipid accumulation in skeletal muscle of obese rats. Here, we investigated whether ALA improves endothelial dysfunction in obese rats by activating AMPK in endothelial cells. Methods and Results—Endothelium-dependent vascular relaxation was impaired, and the number of apoptotic endothelial cells was higher in the aorta of obese rats compared with control rats. In addition, triglyceride and lipid peroxide levels were higher, and NO synthesis was lower. Administration of ALA improved all of these abnormalities. AMPK activity was lower in aortic endothelium of obese rats, and ALA normalized it. Incubation of human aortic endothelial cells with ALA activated AMPK and protected cells from linoleic acid–induced apoptosis. Dominant-negative AMPK inhibited the antiapoptotic effects of ALA. Conclusions—Reduced AMPK activation may play an important role in the genesis of endothelial dysfunction in obese rats. ALA improves vascular dysfunction by normalizing lipid metabolism and activating AMPK in endothelial cells.

Central Administration of an Endoplasmic Reticulum Stress Inducer Inhibits the Anorexigenic Effects of Leptin and Insulin

Leptin and insulin are important anorexigenic hormones acting on the hypothalamus. However, most obese humans and animals have reduced hypothalamic responses to leptin and insulin. Increased endoplasmic reticulum (ER) stress has been shown to cause insulin resistance in the livers of obese animals. In the present study, we investigated a role of ER stress in the development of central leptin and insulin resistance. Intracerebroventricular (ICV) administration of the ER stress inducer thapsigargin (TG) increased food intake and body weight. Furthermore, ICV or intra‐hypothalamic administration of TG inhibited the anorexigenic and weight‐reducing effects of leptin and insulin. ICV administration of TG by itself activated signal‐transduction‐activated‐transcript‐3 (STAT3) and Akt in the hypothalamus, but prevented a further activation of hypothalamic STAT3 and Akt by leptin and insulin. We also found that the expression of the ER stress markers such as phosphorylation of the inositol‐requiring kinase‐1 (IRE1), spliced form of X‐box‐binding protein‐1 (XBP‐1s), glucose‐regulated/binding immunoglobulin protein‐78, and C/EBP homology protein (CHOP) increased in the hypothalami of diet‐induced obese (DIO) mice. Furthermore, treatment of chemical chaperone 4‐phenyl butylic acid significantly improved central leptin resistance in DIO mice. These findings suggest that increased hypothalamic ER stress in obese animals may induce central leptin and insulin resistance.

Endoplasmic Reticulum Stress-Induced Activation of Activating Transcription Factor 6 Decreases Insulin Gene Expression via Up-Regulation of Orphan Nuclear Receptor Small Heterodimer Partner

The highly developed endoplasmic reticulum (ER) structure of pancreatic beta-cells is a key factor in beta-cell function. Here we examined whether ER stress-induced activation of activating transcription factor (ATF)-6 impairs insulin gene expression via up-regulation of the orphan nuclear receptor small heterodimer partner (SHP; NR0B2), which has been shown to play a role in beta-cell dysfunction. We examined whether ER stress decreases insulin gene expression, and this process is mediated by ATF6. A small interfering RNA that targeted SHP was used to determine whether the effect of ATF6 on insulin gene expression is mediated by SHP. We also measured the expression level of ATF6 in pancreatic islets in Otsuka Long Evans Tokushima Fatty rats, a rodent model of type 2 diabetes. High glucose concentration (30 mmol/liter glucose) increased ER stress in INS-1 cells. ER stress induced by tunicamycin, thapsigargin, or dithiotreitol decreased insulin gene transcription. ATF6 inhibited insulin promoter activity, whereas X-box binding protein-1 and ATF4 did not. Adenovirus-mediated overexpression of active form of ATF6 in INS-1 cells impaired insulin gene expression and secretion. ATF6 also down-regulated pancreatic duodenal homeobox factor-1 and RIPE3b1/MafA gene expression and repressed the cooperative action of pancreatic duodenal homeobox factor-1, RIPE3b1/MafA, and beta-cell E box transactivator 2 in stimulating insulin transcription. The ATF6-induced suppression of insulin gene expression was associated with up-regulation of SHP gene expression. Finally, we found that expression of ATF6 was increased in the pancreatic islets of diabetic Otsuka Long Evans Tokushima Fatty rats, compared with their lean, nondiabetic counterparts, Long-Evans Tokushima Otsuka rats. Collectively, this study shows that ER stress-induced activation of ATF6 plays an important role in the development of beta-cell dysfunction.

Effects of Alpha-Lipoic Acid on Body Weight in Obese Subjects

PURPOSE alpha-lipoic acid is an essential cofactor for mitochondrial respiratory enzymes that improves mitochondrial function. We previously reported that alpha-lipoic acid markedly reduced body weight gain in rodents. The purpose of this study was to determine whether alpha-lipoic acid reduces body weight in obese human subjects. METHODS in this randomized, double-blind, placebo-controlled, 20-week trial, 360 obese individuals (body mass index [BMI] ≥ 30 kg/m(2) or BMI 27-30 kg/m(2) plus hypertension, diabetes mellitus, or hypercholesterolemia) were randomized to alpha-lipoic acid 1200 or 1800 mg/d or placebo. The primary end point was body weight change from baseline to end point. RESULTS the 1800 mg alpha-lipoic acid group lost significantly more weight than the placebo group (2.1%; 95% confidence interval, 1.4-2.8; P<.05). Urticaria and itching sensation were the most common adverse events in the alpha-lipoic acid groups, but these were generally mild and transient. CONCLUSION alpha-lipoic acid 1800 mg/d led to a modest weight loss in obese subjects. Alpha-lipoic acid may be considered as adjunctive therapy for obesity.