Discovery of pancreastatin inhibitor PSTi8 for the treatment of insulin resistance and diabetes: studies in rodent models of diabetes mellitus

Abstract

Pancreastatin (PST) is an endogenous peptide which regulates glucose and lipid metabolism in liver and adipose tissues. In type 2 diabetic patients, PST level is high and plays a crucial role in the negative regulation of insulin sensitivity. Novel therapeutic agents are needed to treat the diabetes and insulin resistance (IR) against the PST action. In this regard, we have investigated the PST inhibitor peptide-8 (PSTi8) action against diabetogenic PST. PSTi8 rescued PST-induced IR in HepG2 and 3T3L1 cells. PSTi8 increases the GLUT4 translocation to cell surface to promote glucose uptake in L6-GLUT4myc cells. PSTi8 treatment showed an increase in insulin sensitivity in db/db, high fat and fructose fed streptozotocin (STZ) induced IR mice. PSTi8 improved the glucose homeostasis which is comparable to metformin in diabetic mice, characterized by elevated glucose clearance, enhanced glycogenesis, enhanced glycolysis and reduced gluconeogenesis. PST and PSTi8 both were docked to the GRP78 inhibitor binding site in protein-protein docking, GRP78 expression and its ATPase activity studies. The mechanism of action of PSTi8 may be mediated by activating IRS1/2-phosphatidylinositol-3-kinase-AKT (FoxO1, Srebp-1c) signaling pathway. The discovery of PSTi8 provides a promising therapeutic agent for the treatment of metabolic diseases mainly diabetes.

Combination of Pancreastatin inhibitor PSTi8 with metformin inhibits Fetuin-A in type 2 diabetic mice

“…Above all, we optimized the Met and PSti8 doses in combination for further in-vitro and in-vivo studies and found that Met 50 μM and PSTi8 100 nM is best possible combination in order to use in in-vitro experiments while Met 150 mg/kg with PSTi8 2.5 mg/kg combination worked best among other combination doses during acute treatment ( Figure 2 A–E) in HFD induced diabetic mice. Considering these aspects, we were intended to speculate implications of combination therapy of Met and PSTi8, at their half of therapeutic dosage, used in preceding studies ( Hossain et al., 2018 ; Tajima et al., 2011 ). Accordingly, we observed that HFD resulted in minimal alterations in the bodyweight while gradually increased FBG, IR, and impaired insulin response ( Figure 2 F and G).…”

“…At 12 th week, HFD group mice were randomly divided into four groups with 6 mice in each group: group first- HFD, group second- HFD + Met, group third- HFD + PSTi8, group fourth- HFD + Comb. Following preliminary study regarding dose selection for combination of Met and PSTi8, Intraperitoneal glucose tolerance test (IPGTT) and intraperitoneal insulin tolerance test (IPITT) were performed with acute drug treatment of Met (300 mg/kg) ( Calixto et al., 2013 ; Salomäki et al., 2013 ), PSTi8 (5 mg/kg) ( Hossain et al., 2018 ) and Comb (Met 150 mg/kg + PSTi8 2.5 mg/kg) to determine the development of glucose intolerance, reduced insulin sensitivity and simultaneously acute effect of treatments on emerging pathophysiology. After successful confirmation of the development of hyperglycemia, glucose intolerance and insulin insensitivity in response to glucose challenge, mice were treated with Met (300 mg/kg), PSTi8 (2 mg/kg) and combination (Met150 mg/kg + PSTi8 1 mg/kg) for 10 days consecutively ( Hossain et al., 2018 ).…”

“…Hence there is an urgent need for combination therapy with Met at lower doses to preserve glycemic control. PSTi8, an emerging peptide, reported to have antidiabetic effects by inhibiting PST derived IR and inflammation ( Bandyopadhyay et al., 2015 ; Funakoshi et al., 1990 ; Hossain et al., 2018 ; Valicherla et al., 2019 ). Chronic treatment of PSTi8 improved glycemic control, glucose tolerance, and IR, as stated in previous research ( Valicherla et al., 2019 ).…”

Does insulin signalling decide glucose levels in the fasting steady state?

“…The way insulin resistance is measured at the clinical level eliminates the chance of separately accounting for other mechanisms of glucose regulation. Even when experiments show that certain agents affect glucose dynamics independent of insulin action, they are typically labelled as "insulin sensitizing" agents (113). As a result, the belief that insulin is the only mechanism of glucose regulation relevant to T2D is artificially strengthened.…”

Pancreastatin

“…Gene deletion studies on CGA have been interpreted as showing an important role of PST on glucose homeostasis (12) but deletion of CGA has multiple effects on the animal many of which are probably not related to PST. Recently, a PST peptide with the eight carboxy terminal amino acids deleted termed PSTi8 has been shown to bind to PST receptors and inhibit the metabolic effects of PST and improve the glucose status in rodent models of diabetes (18).…”