Recovery of age-related decline of thymic endocrine activity and PHA response by lysin-arginine combination

Immune System and Aging: Neuroimmunological Implications

Intact neuroendocrine-immune interactions are essential for the development and functional maintenance of both systems. Experimental precocious disruption of such interactions causes premature aging-like phenomena affecting various body functions. Normal physiological aging appears to be, in part, dependent on age-related modifications of neuroendocrine-immune interactions. The thymus plays a major role in this context. Experimental manipulation at the thymic or neuroendocrine level may reciprocally correct the age-associated disfunctions, suggesting the reversible nature of such phenomena. Based on these observations, data are presented suggesting that the neuroendocrine-thymus network may represent a biological clock of aging.

Plasticity of neuroendocrine-thymus interactions during ontogeny and ageing: role of zinc and arginine

Thymic re-growth and reactivation of thymic functions may be achieved in old animals by different endocrinological or nutritional manipulations such as, (a) treatment with melatonin, (b) implantation of a growth hormone (GH) secreting tumour cell line (GH3 cells) or treatment with exogenous GH, (c) castration or treatment with exogenous luteinizing hormone-releasing hormone (LHRH), (d) treatment with exogenous thyroxin or triiodothyronine, and (e) nutritional interventions such as arginine or zinc supplementation. These data strongly suggest that thymic involution is a phenomenon secondary to age-related alterations in neuroendocrine-thymus interactions and that it is the disruption of these interactions in old age that is responsible for age-associated immune-neuroendocrine dysfunctions. The targets involved in hormones-induced thymic reconstitution may directly or indirectly involve hormone receptors, cytokines, arginine, and a trace element such as zinc, which is pivotal for the efficiency of neuroendocrine-immune network during the whole life of an organism. The effect of GH, thyroid hormones, and LHRH may be due to specific hormone receptors on thymocytes and on thymic epithelial cells (TECs), which synthesize thymic peptides. Melatonin may also act through specific receptors on T-cells. In this context, the role of zinc, which turnover is reduced in old age, is pivotal because of its involvement through zinc fingers in the gene expression of hormone receptors. In addition, the effects of zinc are multifaceted: from the reactivation of zinc-dependent enzymes, to cell proliferation and apoptosis, to cytokines expression and to the reactivation of thymulin, which is a zinc-dependent thymic hormone required for intrathymic T-cell differentiation and maturation as well as for the homing of stem cells into the thymus. Zinc is also required for arginine action, via NO pathway. The role of zinc is therefore crucial in neuroendocrine-thymus interactions. According to data in animals and humans, the above reported endocrinological manipulations (GH, thyroid hormones, and melatonin) or arginine treatment may also act via zinc pool in restoring thymic activity in ageing allowing improvements on peripheral immune efficiency.

Aging of the vertebrate immune system

We have summarized current knowledge on the aging of the immune system in three vertebrate groups: fish, amphibians and birds. Available data are few due to difficulties in studying ageing in natural populations and in accurately determining age. In all vertebrates, the most obvious evidence of the senescence of lymphoid tissue is the involution of thymus, which courses with decreased numbers of thymocytes, and loss of the histological organization of gland. On the other hand, there is little information on aged secondary lymphoid organs. Possible influence of the endocrine system in the changes observed in aged lymphoid organs is also discussed.

Plasticity of neuroendocrine-thymus interactions during aging

Thymic regrowth and reactivation of thymic endocrine activity may be achieved even in old animals by different endocrinological or nutritional manipulations such as, (a) intrathymic transplantation of pineal gland or treatment with melatonin, (b) implantation of a growth hormone (GH) secreting tumor cell line or treatment with exogenous GH, (c) castration or treatment with exogenous luteinizing hormone-releasing hormone (LH-RH), (d) treatment with exogenous thyroxine or triiodothyronine, and (e) nutritional interventions such as arginine or zinc supplementation. These data strongly suggest that thymic, involution is a phenomenon secondary to age-related alterations in neuroendocrine-thymus interactions and that it is the disruption of such interactions in old age that is responsible for age-associated dysfunction. With regard to the mechanisms involved in hormone-induced thymic reconstitution, it is at present, difficult to draw any definitive conclusions. The effect of GH, thyroid hormones, and LH-RH may be due to the presence on thymic epithelial cells supposed to produce thymic peptides, of the specific hormone receptors. Melatonin or other pineal factors may also act through specific receptors, but experimental evidence is still lacking. The role of zinc, whose turnover is usually reduced in old age, is diverse. The effects range from the reactivation of zinc-dependent enzymes, required for both cell proliferation and apoptosis, to the reactivation of thymulin, a zinc-dependent thymic hormone. The role of zinc may even be more crucial. According to recent preliminary data obtained both in animal and human studies, it appears that the above reported endocrinological manipulations capable of restoring thymic activity in old age, may act also by normalizing the altered zinc pool.

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.

Age-dependent changes in thymuses in the European common frog, Rana temporaria

The thymus of the adult frog Rana temporaria is generally small each winter and grows through the spring to reach a large size each summer. The summer thymus has a cortex full of small thymocytes and a medulla in the centre, whereas the winter atrophy is manifested by a loss of distinction between cortex and medulla, an abundance of cells filled with secretory granules, and the formation of intercellular cysts. These seasonal changes are superimposed on age changes. The thymus grows rapidly in froglets. The differences in weight and cell number between winter and summer organs are strongest in middle-aged animals (3-6 years old) and decrease in old specimens. The thymus slowly involutes with age, this being connected with increasing winter atrophy, leading to the formation of huge cysts that fill almost the whole organ in the oldest individuals. In senescent frogs (around 10 years old) seasonal differences still concern corticomedullary division but without pronounced fluctuations in thymic size. The skeletochronological technique applied here for age estimation underestimated rather than overestimated the real age of old animals.

Longevity effect of chromium picolinate--'rejuvenation' of hypothalamic function?

The first rodent longevity study with the insulin-sensitizing nutrient chromium picolinate has reported a dramatic increase in both median and maximal lifespan. Although the observed moderate reductions in serum glucose imply a decreased rate of tissue glycation reactions, it is unlikely that this alone can account for the substantial impact on lifespan; an effect on central neurohormonal regulation can reasonably be suspected. Recent studies highlight the physiological role of insulin as a modulator of brain function. I postulate that aging is associated with a reduction of effective insulin activity in the brain, and this contributes to age-related alterations of hypothalamic functions that result in an 'older' neurohormonal milieu; consistent with this possibility, diabetes leads to changes of hypothalamic regulation analogous to those seen in normal aging. Conversely, promoting brain insulin activity with chromium picolinate may help to maintain the hypothalamus in a more functionally youthful state; increased hypothalamic catecholamine activity, sensitization of insulin-responsive central mechanisms regulating appetite and thermogenesis, and perhaps trophic effects on brain neurons may play a role in this regard. Since both the pineal gland and thymus are dependent on insulin activity, chromium may aid their function as well. Thus, the longevity effect of chromium picolinate may depend primarily on delay or reversal of various age-related changes in the body's hormonal and neural milieu. A more general strategy of hypothalamic 'rejuvenation' is proposed for extending healthful lifespan.

Involution of the thymus revisited: immunological trade-offs as an adaptation to aging

An attempt was made, in previous theories, to find a unifying explanation for two phenomena of thymic involution: stress-induced reversible involution and age-related irreversible involution. It was postulated that in both cases involution is beneficial to the organism, as it serves to reduce the dangers of autoimmune reactions. The modified theory proposed here: (a) relates to the suggestions of I.R. Cohen and D.B. Young (Immunol. Today, 12 (1991) 105-109) and to those of S. Avrameas Immunol. Today, 12 (1991) 154-158) as to the usefulness of autoantibodies to the organism; (b) emphasizes the fact that self components undergo continuous changes throughout the life cycle of the organism, which in turn necessitates continuous adaptations to prevent autoimmune damage; (c) stresses the relevance of these adaptations to the process of natural selection; (d) brings experimental evidence to the effect that thymic involution will reduce the danger of autoimmune damage; and (e) suggests that the adaptations required to prevent autoimmune reactions with aging entail immunological compromises or trade-offs. These measures may by themselves cause autoimmune diseases, result in reduced resistance to neoplasia and to infectious diseases, particularly viral ones, and in accelerated aging.

Supplemental arginine and ornithine do not affect splenocyte proliferation in surgically treated rats

The present study was designed to determine whether arginine or ornithine supplementation enhanced immune responsiveness in surgically stressed rats. Young rats (130 to 150 g; n = 72) were fed one of three nonpurified diets: control, arginine-supplemented (30 g/kg of diet), or supplemented with ornithine on an equimolar basis to supplemental arginine. Control and ornithine-supplemented diets were made isonitrogenous to the arginine-supplemented diet with alanine. Food intake and body weight were monitored throughout the experimental period. Eight days after initiation of dietary treatments, 36 rats were given dorsal skin wounds. Rats were killed 7 days later. Blood was collected, spleen and thymus were weighed, and splenocytes were isolated to measure proliferation in response to mitogens and interleukin-2 production. Food intake, body weight gain, and thymus weight were lower in rats subjected to surgery than in controls rats (p < .01). Neither supplemental dietary arginine nor ornithine affected food intake, body weight gain, thymus weight, splenocyte proliferation, or splenocyte interleukin-2 production in any treatment group (p < .1). These data suggest that low-level dietary supplementation of arginine and ornithine did not ameliorate detrimental effects of minor surgery in rats.

Does supplemental arginine alter immune function following major surgery?

Provision to surgical patients of parenteral arginine with minimal additional calories did not enhance proliferation of mononuclear cells. Earlier reports of the immunostimulatory effects of arginine may reflect interactions between arginine and other dietary components rather than exclusive effects of supplemental arginine.

Biomarkers of aging in the neuroendocrine-immune domain. Time for a new theory of aging?

A common and generally accepted assumption is that with advancing age, the thymus undergoes progressive and irreversible involution. This is considered the main cause for the age-related deterioration of various immune functions and, ultimately, for the increased incidence of infectious, neoplastic, and automimmune diseases in old age. This assumption is no longer tenable because of several clear-cut demonstrations that age-related thymic involution is not an intrinsic and irreversible phenomenon. Various neuroendocrine or nutritional manipulations can to induce a regrowth of the thymus, even when applied in old age. This thymic reconstitution is followed by a consistent recovery of peripheral immune functions. These data strongly support the idea that thymic involution is a phenomenon secondary to age-related alterations in neuroendocrine-thymus interactions and that it is the disruption of such interactions in old age that is responsible for most of the age-associated dysfunctions. On the basis of this experimental and clinical evidence and as an alternative to purely immune or neuroendocrine theories of aging, a neuroendocrine-immune hypothesis is proposed. Further work is required to determine if the age-related disruption of neuroendocrine-immune interactions occurs because of progressive accumulation of stressor-dependent consequences at the level of one or the other system or if it may depend on a single common cause.

Recovery of low thymic hormone levels in cancer patients by lysine-arginine combination

Thymic hormones are required for maturation and maintenance of the immune efficiency. It has been previously demonstrated that with advancing age there occurs a progressive reduction of the plasma level of one of the best known thymic peptides, i.e. thymulin, and that the administration of an amino acid combination (lysine-arginine, as present in the commercial preparation Lysargin, Baldacci, Italy) to elderly individuals is able to increase the synthesis and/or release of thymulin to values comparable to those recorded in young subjects. In the present paper we report evidence that cancer patients show much lower thymulin values than those recorded in healthy age-matched individuals and that the oral administration of the amino acid preparation is able to significantly increase thymulin levels even over the values of age-matched controls and to increase the number of peripheral T-cell subsets. It is suggested that such an effect is mediated through the known secretagogue activity of the amino acids on the pituitary release of growth hormone, which has a modulating effect on the thymic endocrine activity.