ABSTRACT
Background@#CycloZ, a combination of cyclo-His-Pro and zinc, has anti-diabetic activity. However, its exact mode of action remains to be elucidated. @*Methods@#KK-Ay mice, a type 2 diabetes mellitus (T2DM) model, were administered CycloZ either as a preventive intervention, or as a therapy. Glycemic control was evaluated using the oral glucose tolerance test (OGTT), and glycosylated hemoglobin (HbA1c) levels. Liver and visceral adipose tissues (VATs) were used for histological evaluation, gene expression analysis, and protein expression analysis. @*Results@#CycloZ administration improved glycemic control in KK-Ay mice in both prophylactic and therapeutic studies. Lysine acetylation of peroxisome proliferator-activated receptor gamma coactivator 1-alpha, liver kinase B1, and nuclear factor-κB p65 was decreased in the liver and VATs in CycloZ-treated mice. In addition, CycloZ treatment improved mitochondrial function, lipid oxidation, and inflammation in the liver and VATs of mice. CycloZ treatment also increased the level of β-nicotinamide adenine dinucleotide (NAD+), which affected the activity of deacetylases, such as sirtuin 1 (Sirt1). @*Conclusion@#Our findings suggest that the beneficial effects of CycloZ on diabetes and obesity occur through increased NAD+ synthesis, which modulates Sirt1 deacetylase activity in the liver and VATs. Given that the mode of action of an NAD+ booster or Sirt1 deacetylase activator is different from that of traditional T2DM drugs, CycloZ would be considered a novel therapeutic option for the treatment of T2DM.
ABSTRACT
Mitochondrial dysfunction is a hallmark of metabolic diseases such as obesity, type 2 diabetes mellitus, neurodegenerative diseases, and cancers. Dysfunction occurs in part because of altered regulation of the mitochondrial pyruvate dehydrogenase complex (PDC), which acts as a central metabolic node that mediates pyruvate oxidation after glycolysis and fuels the Krebs cycle to meet energy demands. Fine-tuning of PDC activity has been mainly attributed to post-translational modifications of its subunits, including the extensively studied phosphorylation and de-phosphorylation of the E1α subunit of pyruvate dehydrogenase (PDH), modulated by kinases (pyruvate dehydrogenase kinase [PDK] 1-4) and phosphatases (pyruvate dehydrogenase phosphatase [PDP] 1-2), respectively. In addition to phosphorylation, other covalent modifications, including acetylation and succinylation, and changes in metabolite levels via metabolic pathways linked to utilization of glucose, fatty acids, and amino acids, have been identified. In this review, we will summarize the roles of PDC in diverse tissues and how regulation of its activity is affected in various metabolic disorders.