S Martha, U Veldandi, K Devarakonda, N Pantam, S Thungathurthi
aspirin and type-2 diabetes, insulin like growth factor-i, streptozotocin
S Martha, U Veldandi, K Devarakonda, N Pantam, S Thungathurthi. Role of IGF-I in aspirin pretreatment in streptozotocin induced type-II diabetic rats. The Internet Journal of Pharmacology. 2008 Volume 6 Number 2.
In the present study, we made an attempt to investigate role of insulin like growth factor-I (IGF-I) in aspirin pretreatment in streptozotocin induced type-2 diabetes mellitus in rats. Rat pups were divided in to four groups, on 5th day of their birth, group-I pups were received citrate buffer solution served as normal, group-II were treated only with streptozotocin (80mg/kg,
Type-2 diabetes mellitus is a metabolic disorder with characteristics of hyperglycemia and insufficiency of secretion or action of endogenous insulin . Insulin resistance is one of the major characteristics of type 2 diabetes mellitus. If the insulin resistance can result from oxidative damage, then a prediction would be that chronic oxidative stress would lead to hyperinsulinaemia if plasma glucose is clamped at normal level by infusing the required insulin. Increased oxidative stress, defined as a persistent imbalance between the production of highly reactive molecular species (chiefly oxygen and nitrogen) and antioxidant defenses, is a widely accepted participant in the development and progression of diabetes and its complications . Hyperglycemia was also found to promote lipid peroxidation of low density lipoprotein (LDL) by a superoxide-dependent pathway to generate free radicals . Free radicals can be generated in glucose oxidation, which is believed to be the main source of free radicals, which are not degraded by catalase or glutathione peroxidase, and in the presence of transitional metals, can lead to production of extremely reactive hydroxyl radicals . Aspirin is a derivative of salicylic acid, used as a NSAID, anti thrombotic, antioxidant and anti diabetic drug has new approach in type2 diabetes. Salicylates inhibit serine/ threonine caused insulin resistance and IKK-β activity and restore insulin sensitivity, both in-
Materials and methods
Aspirin pure substance was a kind gift from Natco Pharma Limited, Hyderabad, India. Diphenyl picryl hydrazyl and streptozotocin were purchased from Sigma, St. Louis, USA. Glucose kit was purchased from Excel diagnostics limited, Hyderabad. Ethanol (analytical grade) purchased from E. Merck Limited, Mumbai, India.
Four pregnant female Wistar rats, weighing between 300-350g were obtained from Mahaveer Enterprises, Hyderabad. The rats were housed individually in acrylic cages in standard environmental conditions (20-250C), fed with standard rodent diet and water
Induction of diabetes
On 8.00 AM, the rat Pups were received a single 80 mg/kg intraperitoneal injection of streptozotocin (Sigma, St. Louis, MO) in 0.1 M sodium citrate buffer, pH 4.5. Control nondiabetic animals were fasted and received citrate buffer alone. After 8th week, animals with blood glucose levels greater than 150 mg/dl were considered diabetic .
Rat pups (neonates) were divided in to four groups consisting of group-I 14 pups, group-II 8 pups, group-III 7 pups and group-IV 9 pups. The group-I pups were received citrate buffer solution served as normal control group. Group-II treated only with streptozotocin (80mg/kg,
HOMA-IR = FI in mU/l or µU/ml X FPG in mg/dl / 405
Similarly, insulin sensitivity was assessed by using the previously validated homeostasis model assessment for insulin sensitivity, calculated from the fasting insulin and glucose concentrations according to the formula :
HOMA-S = 1/HOMA-IR
All variables are expressed as means ± SD. Group differences of continuous variables were compared using ANOVA followed by Newman Keuls test. For all analyses, a P value < 0.05 was considered to be statistically significant. All analyses were performed using Graph Pad Prism 4 (Version. 4).
8th week analysis
Pups treated with streptozotocin alone and in combination with aspirin for one month and two months were shown significantly raised body weight, fasting blood glucose and insulin resistance levels when compared to the normal control group of pups (P=0.0005, P<0.0001, P<0.0001) respectively[Table-1] Pups treated with streptozotocin alone and in combination with aspirin for one month and two months were shown significantly lowered fasting insulin and insulin sensitivity levels when compared to the normal control group of pups (P<0.0001, P<0.0001) respectively[Table-1] Pups treated with aspirin for one month were shown significantly raised IGF-I levels but two months treatment were shown significantly lowered IGF-I levels when compared to the normal pups (P<0.0001) [Table-1&Figure1-5]
10th week analysis
Pups treated with streptozotocin alone and in combination with aspirin for one month and two months were shown significantly raised body weight, fasting blood glucose and insulin resistance levels when compared to the normal control group of pups (P=0.0006, P<0.0001, P=0.0030) respectively[Table-1] Pups treated with streptozotocin alone and in combination with aspirin for one month and two months were shown significantly lowered fasting insulin and insulin sensitivity levels when compared to the normal control group of pups (P<0.0001, P=0.0068) respectively. Pups treated with aspirin for one month were shown significantly raised IGF-I levels but two months treatment were shown significantly lowered IGF-I levels when compared to the normal pups (P<0.0001) [Table-1&Figure 1-4,6]
Yaun et al., 2001 reported Salicylates inhibits IKK-B activity and restore insulin sensitivity, both
There is a great deal of evidence that aspirin / NSAIDs have effects on insulin resistance. It has been long known that salicylates have a hypoglycemic effect and that they reduce fasting blood glucose in diabetic persons . High doses of salicylates have been shown to reverse hyperglycemia, hyperinsulinemia, and dyslipidemia in obese rodents by sensitizing insulin signaling . In patients with type 2 diabetes, aspirin treatment has been shown to reduce fasting plasma glucose, total cholesterol, C-reactive protein, triglycerides, and insulin clearance; aspirin reduced hepatic glucose production and improved insulin-stimulated peripheral glucose uptake by 20% . Aspirin/NSAID influence on insulin resistance appears to be independent of COX-2 inhibition, instead involving inhibition of nuclear factor-nB and InB and/or activation of peroxisome proliferator-activated receptors .
An interaction between aspirin and IRS1 in antagonizing effects of tumor necrosis factor- α (TNF- α) has also been reported. TNF- α, a major cause of insulin resistance in obesity and inflammation, has been reported to inhibit insulin-induced glucose uptake by targeting components of the insulin signaling cascade, one of which is insulin receptor substrate . IRS1 is the major cytoplasmic substrate of the insulin receptor in most insulin sensitive tissues and is necessary for maintenance of metabolic homeostasis. Aspirin has been shown to inhibit the TNF- α-induced serine phosphorylation of IRS1 through inhibition of multiple serine kinases, including IB kinase .
However, our findings are consistent with the animal studies demonstrating low insulin sensitivity in mice with liver specific deletion of the IGF-I gene that is reversed by treatment with recombinant human IGF-I  which was raised by the aspirin treatment for one and two months. IGF-I has hypoglycemic effects and enhances insulin sensitivity in both experimental and human subjects it is due to its type-1 receptors and / or hybrid insulin / IGF-I receptors .
High levels of IGF-I in one month treated aspirin group when compared to two month treated group, is important to note that short term therapy seems to be beneficial. Preconditioning of hepatocytes with aspirin on short course is better than long term treatment in production of IGF-I. Mechanism of increased levels of IGF-I in one month aspirin treated group is not well understood.
In conclusion, the present study indicates that aspirin pretreatment seems to protect pancreas from damage caused by STZ and maintains glucose levels in diabetic rats and increases insulin sensitivity and reduces insulin resistance. The protection offered by the aspirin treatment in type -2 diabetes, there may a involvement of insulin like pathway particularly IGF-I. The mechanism of increased levels of IGF-I in one month treated group when compared to two month treated group is not well understood and further studies are required to prove this hypothesis.