Antihyperglycemic Activity of Oxidovanadium(IV) Aroylhydrazone–Bipyridine Complexes Featuring Different Hydrazide Moieties in Diabetic Wistar Rats

Five neutral heteroleptic mononuclear vanadium(IV) hydrazone complexes ([VOL(bpy)]), derived from 2-hydroxy-5-methylacetophenone and various acid hydrazides (furoic, thiophene, benzoic, nicotinic, and isoniazid), were synthesized and shown to exhibit improved antidiabetic efficacy in streptozotocin-induced diabetic rats, with reduced toxicity and minimal bioaccumulation compared to maltolato- and picolinato-based vanadium species. Structural identity was established by spectroscopic methods. Crystal structures were obtained for four complexes, providing insight into their solid-state chemistry. Stability studies in simulated intestinal and gastric fluids showed that the complexes largely retained their integrity under intestinal conditions, whereas decomposition occurred in the highly acidic gastric environment within several minutes. In vivo experiments revealed a structure-antihyperglycemic activity relationship. The nicotinic-containing complex showed the highest activity, reducing blood glucose levels by 67% within 7 days of treatment, while the remaining complexes improved glycemic control by more than 50%. Bioaccumulation studies demonstrated <1.1% uptake in the liver and kidneys and negligible accumulation in the brain. The presented vanadium compounds enhance antidiabetic potential by addressing key limitations, particularly bioaccumulation and toxicity, associated with vanadium agents previously evaluated in clinical trials.