Mangrove endophytic fungi have recently gained attention among researchers as a replacement of mangrove phytoconstituents to protect critically endangered mangrove species. 2,4,6-triphenylaniline (TPA) is an endophytic secondary metabolite isolated from a novel strain Alternaria longipes strain VITN14G derived from mangrove plant Avicennia officinalis to perceive its role in antidiabetic activity. Antidiabetic efficacy of TPA and TPA loaded nanoemulsion formulation (NE) were validated using low dosage (35 mg/kg bw) of streptozotocin (STZ) induced high-fat diet Albino Wistar rats. The diabetic rats were orally administered with TPA (10 mg/kg bw), nano emulsified TPA (10 mg/kg bw) and the standard drug metformin (10 mg/kg bw) respectively once on a daily basis for a period of 48 days. After intervention period, TPA and TPA loaded NE showed controlled blood glucose, significant effect on electrolytes, liver and kidney function test as comparable to standard drug metformin. TPA loaded NE was found to have lesser toxicity on liver, kidney, pancreas and heart than TPA. Moreover, gene expression studies of TPA and TPA loaded NE showed down regulation of PKA and up regulation of AMPK which was similar to the effect of metformin. Therefore, the antidiabetic effect of TPA and TPA loaded NE can be correlated with PKA regulation and vice versa with AMPK regulation. The outcome of this study paves a way to use a natural substitute for existing synthetic antidiabetic drugs. © 2020