Vitamin D deficiency as a potential risk factor for accelerated aging, impaired hippocampal neurogenesis and cognitive decline: a role for Wnt β catenin signaling Aging Dihexa (also known as PNB 0408) is an experimental small molecule derived from angiotensin IV. It was engineered to cross the bloodbrain barrier and has shown synaptogenic effects in preclinical models. The often quoted Dihexa Capsules Research Grade Cognitive Peptide Hepatocyte Growth Factor MET Activator Rescues Working Memory Deficits After Repeated Mild Traumatic Brain Injury