Modifications of thymulin titers in patients affected with prolonged low or high zinc circulating levels are independent of patients' age

Different age-related effects of thymectomy in myasthenia gravis: role of thymoma, zinc, thymulin, IL-2 and IL-6

Different age-related immune pathogenetic mechanisms in myasthenia gravis (MG) have been suggested because of restoration after thymectomy (Tx) of altered zinc, thymulin (TH) and T-cell subsets exclusively in early-onset patients (younger <50 years), not in late-onset patients (older >50 years). In this context interleukin-2 (IL-2), interleukin-6 (IL-6) and thymoma are crucial because both involved in MG pathogenesis and correlated with acetylcholine receptors (AchRs) Ab production. Moreover, IL-2 and IL-6 are zinc-dependent, are altered in aging and related with zinc and TH age-dependent declines. Moreover, zinc is relevant for immune efficiency. In order to confirm these different age-related pathogenetic mechanisms further, the role of thymoma, zinc, TH, IL-2 and IL-6 is studied in MG patients with generalized MG with and without thymoma before and 1 month and 1 year after Tx. The high IL-2, IL-6, zinc, and AChR Ab levels observed before Tx are significantly correlated each other in younger MG patients (<50 years) independently by thymoma and in older MG patients (>50 years) with thymoma. No correlations exist in older MG patients without thymoma. Thymulin is not correlated with other parameters considered to be both in younger and older MG patients independently by the thymoma. Thymectomy restores zinc; immune parameters and AChR Ab are exclusively in the younger group, not in the older one. These findings suggest that IL-2 and IL-6, via zinc, rather than TH, may be involved in different age-related pathogenetic mechanisms mainly in early-onset MG. By contrast, thymoma may be involved in MG etiology in late-onset representing, as such, a useful discriminant tool for MG etiology between early and late-onset MG patients. Because autoimmune phenomena may rise in aging, a parallelism with altered immune functions during aging is discussed.

Thymulin, zinc and insulin-like growth factor-I (IGF-I) activity before and during recombinant growth hormone (rec-GH) therapy in children and adults with GH deficiency

Plasma thymulin (active and total) levels; IGF-I and zinc concentrations were evaluated in 9 children and in 8 adults with GH-deficiency (GHD) before and after 3-6 months of recombinant-GH treatment. Before therapy, GH deficient children had lower plasma active thymulin levels (1.0 +/- 0.3 log-2), not due to a peripheral defect in zinc saturation since plasma zinc levels were within the normal range, and total thymulin levels (1.3 +/- 0.3 log-2) than in the age-matched control group. GH therapy significantly increased active thymulin (3rd month: 3.0 +/- 0.2 log-2, 6th month: 4.0 +/- 0.2 log-2), total thymulin (3rd month: 3.3 +/- 0.3 log-2, 6th month: 4.3 +/- 0.2 log-2) and IGF-I levels (3rd month: 283.3 +/- 7.2 micrograms/L, 6th month: 411.2 +/- 44.2 micrograms/L, vs basal: 144.3 +/- 11.5 micrograms/L); at the 6th month of therapy, thymulin levels (active and total) were comparable to those found in controls. A positive correlation existed between zinc and plasma IGF-I levels (r = 0.66, p < 0.05). In adults with GHD, plasma active (1.9 +/- 0.3 log-2) and total thymulin levels (3.9 +/- 0.1 log-2), significantly lower (p < 0.01 and 0.05, respectively) than in controls before treatment, increased after GH therapy (active thymulin, 3rd month: 3.0 +/- 0.2 log-2, 6th month: 4.4 +/- 0.3 log-2; total thymulin, 3rd month: 3.9 +/- 0.3 log-2, 6th month: 4.7 +/- 0.2 log-2), being at 6th month of therapy no more different from the values recorded in the age-matched control group. In conclusion, children and adults with GHD have a marked impairment of the thymic endocrine activity, which can be restored by six months of GH treatment. The effects of GH on thymic functions may be mediated by IGF-I, through the modulation of zinc turnover, suggesting the possible existence of an interplay among GH, zinc, IGF-I and thymulin both in children and adults with GHD.

Zinc, human diseases and aging

Zinc is one of the most important trace elements in the body for many biological functions; it is required as a catalytic component for more than 200 enzymes, and as a structural constituent of many proteins, hormones, neuropeptides, hormone receptors, and probably polynucleotides. Due to its role in cell division and differentiation, programmed cell death, gene transcription, biomembrane functioning and obviously many enzymatic activities, zinc is considered a major element in assuring the correct functioning of an organism, from the very first embryonic stages to the last periods of life. This biological role together with the many factors that modulate zinc turnover explains on one hand, the variety of clinical and laboratory signs resulting from its reduced bioavailability, and on the other, the high number of human pathologies characterized by alterations in the zinc pool. As zinc supplementation is efficacious in most of these conditions, it is regarded more as an oriented therapeutical support, than a simple dietary integrator. Furthermore, the relevance of zinc status to many age-associated diseases and, according to experimental studies, the aging itself of the major homeostatic mechanisms of the body, i.e., the nervous, neuroendocrine and immune systems, places zinc in a pivotal position in the economy of the aging organism.