During the tests in vitro SHP
During the tests in vitro, SHP289-04 showed the beneficial effect on both two important aspects. In human liver carcinoma cell line HepG2, it was found to improve glucose consumption significantly. Otherwise, in pancreas cell line NIT1, it could only promote insulin secretion significantly at high glucose concentration (20 mmol/l), but was not same as glucokinase activator reported by Winzell et al. (2011) to influence insulin secretion at basal glucose concentration, which indicated that the influence of SHP289-04 in insulin secretion depended on the glucose level. Maybe the effect of SHP289-04 on glucose-stimulated insulin secretion in NIT1 DIDS australia through augmenting the concentration of ATP and [Ca]i under high glucose concentration (Lei et al., 2015). In vivo, the advantageous pharmacodynamics of SHP289-04 was observed in spontaneous type 2 diabetes model KKAy mice characterized with hyperinsulinemia and hyperglycemia. It not only decreased blood glucose level and ameliorated glucose tolerance like other glucokianse activators (Winzell et al., 2011, De Ceuninck et al., 2013a, De Ceuninck et al., 2013b), but also regulated lipid metabolism and decreased lipid peroxidation product. At the same time, the plasma insulin level was not elevated like we thought that increasing the activity of glucokinase could promote insulin secretion (Cuesta-Munoz et al., 2004). Compared with the vehicle group, it ameliorated the hyperinsulinemia in KKAy mice, maybe because the promotion of glucose disposition in the liver reduced the quality demand of insulin, which indicated the insulin sensitivity was also improved and the insulin resistance existed in many type 2 diabetes patients. What's more, this effect let us not worry about the hypoglycemia induced by SHP289-04, one of the main adverse effect of most glucokinase activators (Katz et al., 2016, Zhi and Zhai, 2016). Besides, why SHP289-04 down-regulated the food intake of KKAy mice and then body weight, or whether SHP289-04 increased the glucokinase activity of neurons in hypothalamus, which should be studied further. For some other research reported, increased glucokinase activity drove food intake, especially glucose (Hussain et al., 2015, Ma et al., 2015). Therefore, same as the liver-directed glucokinase activators (Erion et al., 2014, Deshpande et al., 2017), SHP289-04 avoid the adverse effect (hypoglycemia) induced by advancing glucokinase activity of beta cells to promote insulin secretion. But, better than those (Erion et al., 2014, Deshpande et al., 2017), SHP289-04 had beneficial effect on islets. It ameliorated morphology of islets and augmented the ratio of beta cells mass/alpha cells mass in KKAy mice, which was also found by other glucokinase activators (Futamura et al., 2012, Lei et al., 2015). Maybe because it stimulated insulin receptor substrate-2 (IRS-2) via calcineurin/nuclear factor of activated T cells (NFAT) signaling (Demozay et al., 2011, Nakamura et al., 2012), or it ameliorated endoplasmic reticulum (ER) stress-mediated apoptosis by suppressing C/-EBP homologous protein (CHOP) expression (Shirakawa et al., 2013). To identify the real mechanism of SHP289-04's advantageous effect in beta cells, further experiments need to be done. In type 2 diabetes patients, besides from high blood glucose level and insulin resistance, they often companied with some other metabolic disorder diseases, such as hyperlipidemia, high blood pressure and so on. Fatty liver was one of common conditions among type 2 diabetes patients due to the dyslipidemia, which was also a risk factor of cardiovascular diseases. Spontaneous type 2 diabetes model KKAy mice not only had the characteristic of hyperglycemia, but also concomitant with disorder of lipid metabolism and obvious fatty liver. Glucokinase, as a glucose sensor in hepatocytes, could promote glucose to be phosphorylated to glucose-6-phosphate, which could enter several metabolic pathways. Glucose-6-phosphate may isomerizate into fructose-6-phosphate, which could synthesize pyruvate and then acetyl-CoA through glycolysis. On the one hand, Acetyl-CoA could be oxidized via entering the tricarboxylic acid cycle; on the other hand, it may produce fatty acid in the cytoplasm (Adeva-Andany et al., 2016). Besides, increased anaplerotic flux into the tricarboxylic acid cycle (TAC) was reported to be related into the nonalcoholic fatty liver disease (Sunny et al., 2011). Therefore, several glucokinase activators were found to induce dyslipidemia and even hepatic steatosis in type 2 diabetes patients and animal models (De Ceuninck et al., 2013a, De Ceuninck et al., 2013b, De Ceuninck et al., 2013a, De Ceuninck et al., 2013b) due to increasing glucokinase activity. Nevertheless, SHP289-04 in this paper was shown to decrease pyruvate content in liver. Furthermore, it not only down-regulated hyperlipidemia and lipid level of liver, but also ameliorated the morphology and function of liver in type 2 diabetes model KKAy mice, which was first reported as one of glucokinase activators. Maybe by regulating the TAC anaplerotic flux and lipid metabolism, SHP289-04 promoted morphology and function of liver in KKAy mice. But the exact reason of the effect of SHP289-04 on anti-dyslipidemia need to be further studied.