The p75 neurotrophin receptor appears in plasma in diabetic rats - Characterisation of a potential early test for neuropathy

Abstract

Aims/hypothesis. This study tested the premise that immunoreactivity representing the p75 neurotrophin receptor (p75NTR) appears in plasma of diabetic rats in association with the early stages of neuronal dysfunction or damage. We also examined whether treatment beneficial to neuropathy might reduce the p75NTR immunoreactivity. Methods. Plasma proteins were fractionated by SDS-PAGE and immunoblots exposed to p75NTR antibody, using receptor protein from cultured PC12 cells as an external standard. Rats were made diabetic with streptozotocin for various periods and exsanguinated. Plasma glucose, HbA1C and plasma proteins were determined. We also studied plasma samples from diabetic mice lacking the gene coding for p75 NTR, as well as the effect of sciatic nerve crush on healthy male Wistar rats. Results. Plasma p75NTR immunoreactivity began to exceed normal levels at 8 weeks after induction of diabates, and was significantly raised at 10 (p<0.05) and 12 weeks (p<0.001). Treatment between 8 and 12 weeks with insulin, fidarestat (an aldose reductase inhibitor), nerve growth factor and neurotrophin 3 all normalised the plasma p75NTR immunoreactivity. Plasma from p75NTR (-/-) mice contained no such immunoreactivity, though it was present in plasma from wild-type mice. Following nerve crush, p75NTR immunoreactivity appeared in plasma of non-diabetic mice, indicating that this can be a result of nerve trauma. Conclusions/interpretation. These observations suggest that plasma p75 NTR immunoreactivity may serve as an early indicator of neuronal dysfunction or damage in diabetes. The time course of its appearance relates well to that of early neuropathy and its response to interventions that are neuroprotective suggests that it might mirror neurological status. © Springer-Verlag 2004.