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.