The aim of this review was to examine the evidence for age-related changes of the hypothalamic± pituitary±adrenal (HPA) axis in both physiological and pathological aging, on the basis of the many data in the literature, as well as of our personal findings.A statistically significant circadian rhythmicity of serum cortisol was maintained in elderly subjects, even if with a reduced amplitude of the 24 h fluctuations and a trend to an increase of the serum levels in the evening and at night-time, in comparison with young controls. Furthermore, an age-related impairment of HPA sensitivity to steroid feedback was present in elderly people.The occurrence of senile dementia amplified the changes already present in physiological aging. While the cortisol secretion was generally well maintained in aging, the adrenal production of dehydroepiandrosterone and of its sulfate (DHEAS) exhibited an age-related decline. Therefore, the cortisol/DHEAS molar ratio was significantly higher in elderly subjects and even more in demented ones, than in young controls.Due to the opposite effects of cortisol and DHEAS on the brain and particularly on the hippocampal region, the imbalance between glucocorticoids and androgens occurring in physiological and even more in pathological aging, may have adverse effects on the function of this region, whose key role in learning and memory is well known.

Alzheimer's disease (AD) is a multifactorial disorder characterized by the progressive deterioration of neuronal networks. The primary cause and sequence of its progression are only partially understood but abnormalities in folding and accumulation of insoluble proteins such as p-amyloid and Tau-protein are both associated with the pathogenesis of AD. Mitochondria play a crucial role in cell survival and death, and changes in mitochondrial structure and/or function are related to many human diseases. Increasing evidence suggests that compromised mitochondrial function contributes to the aging process and thus may increase the risk of AD. Dysfunctional mitochondria contribute to reactive oxygen species which can lead to extensive macromolecule oxidative damage and the progression of amyloid pathology. Oxidative stress and amyloid toxicity leave neurons chemically vulnerable. The mitochondrial toxicity induced by p-amyloid is still not clear but may include numerous mechanisms, such as the increased permeability of mitochondrial membranes, the disruption of calcium homeostasis, the alteration of oxidative phosphorylation with a consequent overproduction of reactive oxygen species. Other mechanisms have been associated with the pathophysiology of AD. Inflammatory changes are observed in AD brain overall, particularly at the amyloid deposits, which are rich in activated microglia. Once stimulated, the microglia release a wide variety of pro-inflammatory mediators including cytokines, complement components and free radicals, all of which potentially contribute to further neuronal dysfunction and eventually death. Clinically, novel approaches to visualize early neuroinflammation in the human brain are needed to improve the monitoring and control of therapeutic strategies that target inflammatory and other pathological mechanisms. Similarly, there is growing interest in developing agents that modulate mitochondrial function.Alzheimer's disease (AD) is a neurodegenerative disorder primarily characterized by a progressive deterioration of cognitive functions with consequent reduction of memory, associated with a decrease in

We studied the circadian rhythm of plasma melatonin, growth hormone (GH), prolactin (PRL), adrenocorticotropic hormone (ACTH), and cortisol in 52 mentally healthy old subjects, 35 old demented patients, and 22 clinically healthy young controls. When compared to young controls, the circadian profile of plasma melatonin of old subjects, both demented or not, was clearly flattened, particularly during the night. The selective impairment of nocturnal melatonin secretion was significantly related to both the age and the severity of mental impairment (Mini Mental State Examination [MMSE] score). The PRL and GH circadian profiles were similar in the three groups during the day, but a significant lowering of the values recorded during the night occurred with aging. The impairment of the nocturnal secretion was related to the subjects' age and, for the GH secretory pattern only, also to the MMSE score. The ACTH circadian profile was similar in the three groups studied, even when old subjects exhibited higher ACTH levels throughout the 24 h cycle, compared to young controls. Significantly higher cortisol values at evening- and nighttime occurred in elderly subjects and particularly in the demented group. Both the mean levels and the nadir values of plasma cortisol were positively related to age and negatively to MMSE score. In order to verify the sensitivity of the hypothalamo-pituitary-adrenal (HPA) axis to the steroid feedback, the circadian profile of plasma cortisol was evaluated also after dexamethasone (DXM) administration (1 mg at 23:00 h); the sensitivity of the HPA axis was significantly impaired in old subjects and particularly in the demented ones. These findings suggest that the neuroendocrine alterations already present in physiological aging, due to both anatomical damages and unbalanced central neurotransmitters, are enhanced in senile dementia.

Changes of vascular endothelial growth factor (VEGF) secretion have recently been demonstrated in patients with Alzheimer’s disease (AD). Since VEGF has been involved in brain angiogenesis, neuroprotection and cerebromicrovascular exchange of substrates and nutrients, the study of VEGF could have important relapses into the pathogenesis and treatment of AD. Within this context, 35 healthy subjects (16 of young and 19 of old age), 18 patients with dementia of the vascular type (VAD) and 22 with dementia of the Alzheimer’s type (AD) were included in the study. VEGF levels were determined in the supernates of circulating natural killer (NK) immune cells isolated by immunomagnetic separation (pure CD16 + CD56 + NK cells at a final density of 7.75 × 10⁶ cells/ml). VEGF was measured in spontaneous conditions (without modulation) and after exposure of NK cells with IL-2, lipopolysaccharide (LPS), dehydroepiandrosterone sulfate (DHEAS), LPS + insulin, amyloid-β (Aβ) fragment 1–42, the inactive sequence Aβ_40–1 and Aβ_1–42 + insulin. A significant decrease in VEGF released by NK cells was demonstrated in AD subjects compared to the other groups. No differences of VEGF levels were found between healthy subjects of old age and the VAD group. The incubation with LPS and DHEAS significantly increased, in a dose-dependent manner, VEGF levels in AD as well as in healthy subjects of young and old age and in VAD patients. The incubation of NK cells with Aβ_1–42 completely suppressed VEGF generation in AD subjects, also reducing VEGF release in the other groups. The co-incubation of NK with LPS + insulin, at different molar concentrations, significantly restored (4- and 6-fold increase from LPS alone) VEGF in AD, also enhancing VEGF secretion in healthy subjects and the VAD group, while the co-incubation of NK with Aβ_1–42 + insulin promptly abolished the negative effects of Aβ_1–42 on VEGF release. These data might suggest that the decreased VEGF secretion by peripheral immune cells of AD subjects could have a negative role for brain angiogenesis, neuroprotection and for brain microvascular permeability to nutrients, increasing brain frailty towards hypoxic injuries. On the contrary, insulin and DHEAS could have beneficial effects in AD, as well as in VAD and in physiological aging, by increasing, in a dose-dependent fashion, VEGF availability by peripheral and resident immune and endothelial cells, so contributing to increase its circulating pool.

Since dehydroepiandrosterone sulfate (DHEAS) has been involved in the regulation of cellular immunity, the aim of the presence study was to evaluate whether the age-dependent reduction of DHEAS was associated with changes of natural killer (NK) immune function in healthy elderly subjects and in patients with senile dementia of the Alzheimer type (SDAT). Circulating DHEAS was determined throughout 24 h (circadian profile). NK cytotoxic activity was measured as spontaneous and induced cytotoxicity during exposure with DHEAS (10^–7 M), interleukin-2 (IL-2; 100 IU) and IL-2 (100 IU) coincubated with DHEAS (10^–7 M). DHEAS was significantly reduced in healthy elderly subjects (mesor M ± SD = 2.3 ± 0.5 µmol/l) and SDAT (1.6 ± 0.4 µmol/l) patients compared to healthy young subjects (6.7 ± 0.9 µmol/l; p < 0.001); significant differences were also found when healthy elderly subjects and SDAT patients were compared (p < 0.01). A significant inverse correlation between age and DHEAS levels was demonstrated in SDAT and healthy elderly subjects (p < 0.05). The decrease in 24-hour DHEAS secretion was associated with a higher NK cytotoxic response to DHEAS in the healthy elderly subject group than in healthy subjects of young age (p < 0.01). Increased NK cell activity during IL-2 incubation was found in patients with SDAT in comparison with the healthy elderly subject (p < 0.001). On the contrary, NK cell cytotoxic response of SDAT patients was less pronounced during DHEAS exposure and when DHEAS was coincubated with IL-2 (p < 0.001). These data suggest an immunomodulatory role of DHEAS on NK functional activity in physiological aging and SDAT. The antagonizing effect of DHEAS on NK overactivity during exposure with cytokines might counteract some neuroimmune components related to the pathogenesis and progression of the disease.