Inducible Nitric Oxide Synthase Activity and Expression in Liver and Hepatocytes of Diabetic Rats

Abstract

Inducible nitric oxide synthase (iNOS) is expressed by the liver in a number of physiological and pathophysiological conditions. The aim of this study was to investigate the relationship between the diabetic state, iNOS and oxidative stress in the rat liver and isolated hepatocytes. Hepatic iNOS expression and activity was measured in both healthy and streptozotocin-induced diabetic rats and determined in hepatocytes in the presence and absence of insulin. Cu/Zn superoxide dismutase (SOD) and phosphatidylinositol-3-kinase (PI3K) were also measured. In a separate experiment lasting 3 weeks, diabetic rats received either no treatment, two daily injections of insulin or aminoguanidine in the drinking water. Diabetes led to increased activity (45%) and expression (70%) of liver iNOS, an effect that was attenuated by insulin treatment both in vitro and in whole animals. Hepatocyte iNOS expression increased by 56%. Hepatic SOD expression was elevated in the diabetic state, but activity levels were similar to healthy controls. Insulin treatment in vivo led to increased enzyme activity but expression was not modified. Levels of PI3K protein were significantly lower in diabetic rats while insulin treatment markedly increased expression. Aminoguanidine did not inhibit hepatic iNOS in this study. Glycemic control via insulin administration was able to downregulate enhanced hepatic iNOS activity and expression in the liver observed in the diabetic state and improve SOD activity, responses that can potentially reduce the free radical damage associated with diabetes.

Protective effect ofL-glutamine against diabetes-induced nephropathy in experimental animal: Role of KIM-1, NGAL, TGF-β1, and collagen-1

“…75 It has been well documented that streptozotocin-induced diabetes caused an increase in the activity and expression of iNOS. 76 In the present investigation, intraperitoneal administration of STZ demonstrated the involvement of iNOS in the inflammatory process reflected by the elevated level of NO in renal tissue.…”

Melatonin treatment against remote organ injury induced by renal ischemia reperfusion injury in diabetes mellitus

“…It was reported that melatonin decreases the expression of iNOS by inhibition of the transcription factor NF κB (Gilad et al, 1998) and inhibits iNOS activity (Pozo et al, 1997). It was reported that DM led to increased activity and expression of liver iNOS in streptozotocininduced diabetic rats (Madar et al, 2004) and NO levels were significantly elevated in diabetic liver at a very early stage (Stadler et al, 2003). The iNOS is involved in the inflammatory process and might have a role in distant organ injury induced by renal IR via activated iNOS producing cells.…”

Hyperglycemia Induced Changes in Liver: In vivo and In vitro Studies

“…An elevated level of gamma-glutamyltrans- [5] STZ [10] HepG2 [62] HepG2, hepatocytes [61] Glucose infusion [42] High fat [26] Obese Zucker rat + High fat, db/db mouse [28,34] Db/db mouse [34] Goto-Kakizaki rat [32] Hepatocytes [58] HepG2, OLTF rats [33] HepG2 [71] Huh-7 [74] Hep6-16 [75] Fao hepatoma [76] Obese Zucker rat, hepatic stellate cells [29] STZ [6] STZ, db/db mouse, HepG2, hepatocytes [13,27,47] STZ [6,19] STZ [20] STZ [9] STZ, db/db+high fat [11] STZ [17] Obese Zucker rat +High fat, hepatic stellate cells [77] STZ [19] HepG2 [73] HepG2 [70] HepG2 [63] STZ, ob/ob mouse [18,37] Hepatocytes [54] Hepatocytes [59] Fao hepatoma, STZ, hepatocytes [47] HepG2 [64] to exhibit increased levels of gamma-glutamyltranspeptidase, and supplementation with insulin reduced the level of the enzyme [9].…”

“…The livers of STZ treated rats also showed increased oxidation of GSH, increased formation of lipoperoxides and increased activity of xanthine oxidase, a superoxide-generating enzyme [17]. STZ induced diabetes also led to the increased expression of liver and hepatocyte inducible nitric oxide synthase (iNOS), an effect that was attenuated by insulin treatment both in vitro and in whole animals [18].…”