SMTP-44D prevents negative symptoms of diabetic neuropathy by inhibiting sciatic nerve apoptosis

Diabetic neuropathy (DN) affects more than 50 % of patients with diabetes mellitus (DM). With progression, it causes negative symptoms characterized by sensory numbness. However, no effective treatment drug has been approved for the negative symptoms of DN. In this study, Stachybotrys microspora triprenyl phenol-44D (SMTP-44D), previously reported to inhibit apoptosis and ameliorate axonal damage in immortalized mouse Schwann cells treated with high glucose, was evaluated in a DN mouse model. Streptozocin (STZ)-induced DM models were treated with SMTP-44D for 49 days starting 8 days after STZ administration of SMTP-44D, and effects on mechanical and thermal thresholds, blood flow, and conduction velocity were evaluated. Epoxyeicosatrienoic acid (EET)/dihydroxyeicosatrienoic acid (DHET) measurements in serum, morphological changes in the sciatic nerve, immunohistochemistry, and TUNEL staining were performed to elucidate the mechanism of action. SMTP-44D improved the 11,12-EET/DHET decrease in serum and blood flow in the sciatic nerve. It inhibited sciatic nerve apoptosis and alleviated myelin thinning, thereby preserving the conduction velocity and showing dose-dependent improvements in mechanical and thermal threshold elevation. A hypoglycemic effect with long-term administration is suggested based on the findings. In conclusion, SMTP-44D is a promising therapeutic agent against the negative symptoms of DN.