Pyrrolidine dithiocarbamate enhances hepatic glycogen synthesis and reduces FoxO1-mediated gene transcription in type 2 diabetic rats

Abstract

The aim of the present study was to examine the effects of pyrrolidine dithiocarbamate (PDTC) on hepatic glycogen synthesis and FoxO1 transcriptional activity in type 2 diabetic rats and the mechanism underlying these effects. Fasting blood glucose and glycogen deposition, together with expressions of two key genes related to gluconeogenesis, were studied in the liver of rats fed a normal diet (NC), high-fat diet (HFD)-induced insulin-resistant rats made type 2 diabetic by a single intraperitoneal injection of streptozotocin (DM), and a DM with intervention of PDTC (DM + PDTC) for 1 wk. The phosphorylation of Akt, GSK-3β, and FoxO1 was assessed in liver extracts of fasted rats by Western blot, whereas indirect immunofluorescence staining was performed to determine the cellular distribution of FoxO1. The DM rats exhibited obvious increases in fasting blood glucose as well as decreased hepatic glycogen content compared with the NC group. Activation of the Akt/GSK-3β pathway and inactivating phosphorylation of FoxO1 were reduced greatly in DM rat livers ( P < 0.01). By contrast, PDTC treatment protected DM rats against high fasting blood glucose and hepatic glycogen deposition loss. PDTC also elicited an increase in Akt/GSK-3β signaling and subsequent inactivation and nuclear export of FoxO1 in DM rat livers, which translated into a significant reduction in the expression of two FoxO1 target genes, phospho enolpyruvate carboxykinase and glucose-6-phosphatase. This study suggests that PDTC enhances hepatic glycogen synthesis, whereas it reduces FoxO1 transcriptional activity in DM rats.

Pyrrolidine dithiocarbamate protects pancreatic β-cells from oxidative damage through regulation of FoxO1 activity in type 2 diabetes rats

“…They were kept at a constant temperature (22 + 18C) with 12 h light and dark cycles and were allowed free access to water. Type 2 diabetes was established as described previously [29]. Briefly, rats were divided randomly into two groups: a normal control (NC) group (n ¼ 11) and a high-fat diet (HFD) group (n ¼ 22).…”

“…Rats in the NC group received a regular diet containing 10.3% fat, and rats in the HFD group received an HFD containing 42% fat for 8 weeks, after which rats in the HFD group were subjected to an oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) to confirm insulin resistance. These determinations were carried out as previously described [29]. Subsequently, HFD rats received an intraperitoneal (i.p.)…”

“…Our recent work [29] established that significant alterations in the rates of blood glucose clearance occurred during OGTT in HFD rats even though FBG levels were not altered. It was found that after glucose ingestion, the levels of blood glucose increased quickly and peaked at 30 min before gradual decrease to preprandial concentrations in the NC group.…”

“…In contrast, the blood glucose levels remained elevated 2 h after glucose ingestion in the HFD group. Moreover, HFD feeding was found to induce insulin resistance as assessed by ITT [29].…”

“…In addition, it has been reported that PDTC lowers blood glucose levels [27], prevents lung injury [24], and reduces abnormal prostanoid signaling [28] in diabetic rats. Our previous study has found that PDTC enhances hepatic glycogen synthesis and reduces FoxO1 transcriptional activity in the liver of diabetic rats [29]. The purpose of this study was to investigate whether PDTC protects b-cells against oxidative damage and improves insulin production through regulation of FoxO1 and PDX-1.…”