Possible usefulness of growth hormone/insulin-like growth factor-I axis in Alzheimer's disease treatment

Alzheimer's disease (AD) has been traditionally conceptualized as a clinicopathological entity, its definite diagnosis requiring the presence of characteristic pathology together with a dementia clinical picture. The fact that certain AD biomarkers show an acceptable sensitivity and specificity to detect AD pathology has shifted the diagnostic paradigm towards a clinicobiological approach. Neuropathological analysis of AD-affected brains reveals extensive atrophy due to neuronal loss, and accumulation of neurofibrillary tangles and neuritic plaques, surrounded by a tract of neuroinflammation and loss of neurons. Recently, emerging evidence supports the concept that AD is also a disorder of metabolic degeneration. Taken together, the neurochemical changes in the brain from patients with AD indicate multiple disturbances and it seems likely that the changes are secondary to more fundamental changes into the brain. There is a physiological decline of the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis with ageing and the possibility that the GH/ IGF-I axis is involved in cognitive deficits has been recognized for several years. The IGF-I is a potent neurotrophic as well neuroprotective factor found in the brain with a wide range of actions in both central and peripheral nervous system. IGF-I is a critical promoter of brain development and neuronal survival and plays a role in neuronal rescue during degenerative diseases. The investigations of GH releasing stimulation tests especially to GHRH in AD are equivocal and in some cases contradictory. When a cholinesterase inhibitor as rivastigmine, a drug for AD, is acutely administered the area under the curve of the GH response to GHRH doubled, showing that rivastigmine is a powerful drug to enhance GH release. Starting with a more accurate diagnosis not of the clinical syndrome, but of underlying molecular defects, that may eventually lead to a personalized, more effective treatment. Hence, the development of novel therapeutic approaches is urgently needed.