Insulin-like growth factor (IGF) gene expression is reduced in neural tissues and liver from rats with non-insulin-dependent diabetes mellitus, and IGF treatment ameliorates diabetic neuropathy.

Neural disturbances are observed in the peripheral and central nervous systems of patients with insulin-dependent diabetes mellitus (IDDM) and non-IDDM (NIDDM). Insulin-like growth factors (IGFs) are neurotrophic growth factors that can support nerve regeneration and neuronal survival in the types of neurons known to be afflicted in diabetes. We tested the hypotheses that IGF gene expression is reduced in neural tissues and liver of spontaneously diabetic obese Zucker (fa/fa) rats and that IGF treatment can prevent neuropathy. There was a significant early reduction in IGF-II mRNA content as measured per mg of wet tissue or per poly(A)+ RNA in sciatic nerves, spinal cord and brain from spontaneously diabetic obese (fa/fa) vs. nondiabetic lean (+/+) adult rats. In addition, IGF-I mRNA content was reduced in liver but not nerve or spinal cord of NIDDM rats. Pain/pressure thresholds were abnormal (hyperalgesia) in diabetic (fa/fa) vs. nondiabetic (+/+) rats, and subcutaneous infusion of IGF-II restored thresholds toward normal. The low dose of IGF-II that prevented hyperalgesia in contrast had no effect on hyperglycemia or obesity. These data suggest that IGF treatment may provide rational therapy for diabetic neuropathy and that therapy may be effective even in patients unable to adequately control their hyperglycemia.

Brain insulin-like growth factor-II mRNA content is reduced in insulin-dependent and non-insulin-dependent diabetes mellitus.

Diabetic encephalopathy, characterized by structural, electrophysiological, neurochemical, and cognitive abnormalities, is observed in insulin-dependent diabetes mellitus (IDDM) and non-IDDM (NIDDM). Identification of early biochemical lesions potentially may provide clues pointing to its pathogenesis. Insulin-like growth factors (IGFs) are neurotrophic factors that recently have been implicated in the pathogenesis of diabetic neuropathy. Because IGF-II is the predominant IGF in adult brain, we tested the hypothesis that IGF-II gene expression is decreased in the CNS in both IDDM and NIDDM. Brain and spinal cord were isolated from streptozotocin-diabetic rats, a model of IDDM with weight loss and impaired insulin production. IGF-II mRNA content was measured by northern and slot blots. After 2 weeks of diabetes, IGF-II mRNA content per milligram of tissue wet weight, as well as per unit of poly(A)+ RNA, declined significantly (p < or = 0.05) in brain and spinal cord. Insulin replacement therapy partially restored IGF-II mRNA levels in brain, cortex, medulla, and spinal cord. The obese, hyperinsulinemic, and spontaneously diabetic (fa/fa) Zucker rat was used as a model of NIDDM. Brain weight (p < 0.025) and IGF-II mRNA contents (p < 0.01) were significantly decreased in (fa/fa) versus lean nondiabetic (+ /?) rats. Therefore, the decline in IGF-II mRNA levels in diabetic brain was independent of the type of diabetes, the direction of change in body weight, and the insulinemic state. We speculate that this early biochemical lesion may contribute to the development of diabetic encephalopathy.