The immune-endocrine loop during aging: role of growth hormone and insulin-like growth factor-I

Obesity-induced thymic involution and cancer risk

Declining thymic functions associated either with old age (i.e., age-related thymic involution), or with acute involution as a result of stress, infectious disease, or cytoreductive therapies (e.g., chemotherapy/radiotherapy), have been associated with cancer development. A key mechanism underlying such increased cancer risk is the thymus-dependent debilitation of adaptive immunity, which is responsible for orchestrating immunoediting mechanisms and tumor immune surveillance. In the past few years, a blooming set of evidence has intriguingly linked obesity with cancer development and progression. The majority of such studies has focused on obesity-driven chronic inflammation, steroid/sex hormone and adipokine production, and hyperinsulinemia, as principal factors affecting the tumor microenvironment and driving the development of primary malignancy. However, experimental observations about the negative impact of obesity on T cell development and maturation have existed for more than half a century. Here, we critically discuss the molecular and cellular mechanisms of obesity-driven thymic involution as a previously underrepresented intermediary pathology leading to cancer development and progression. This knowledge could be especially relevant in the context of childhood obesity, because impaired thymic function in young individuals leads to immune system abnormalities, and predisposes to various pediatric cancers. A thorough understanding behind the molecular and cellular circuitries governing obesity-induced thymic involution could therefore help towards the rationalized development of targeted thymic regeneration strategies for obese individuals at high risk of cancer development.

Thymus-Pineal Gland Axis: Revisiting Its Role in Human Life and Ageing

For years the thymus gland (TG) and the pineal gland (PG) have been subject of increasingly in-depth studies, but only recently a link that can associate the activities of the two organs has been identified. Considering, on the one hand, the well-known immune activity of thymus and, on the other, the increasingly emerging immunological roles of circadian oscillators and the rhythmically secreted main pineal product, melatonin, many studies aimed to analyse the possible existence of an interaction between these two systems. Moreover, data confirmed that the immune system is functionally associated with the nervous and endocrine systems determining an integrated dynamic network. In addition, recent researches showed a similar, characteristic involution process both in TG and PG. Since the second half of the 20th century, evidence led to the definition of an effectively interacting thymus-pineal axis (TG-PG axis), but much has to be done. In this sense, the aim of this review is to summarize what is actually known about this topic, focusing on the impact of the TG-PG axis on human life and ageing. We would like to give more emphasis to the implications of this dynamical interaction in a possible therapeutic strategy for human health. Moreover, we focused on all the products of TG and PG in order to collect what is known about the role of peptides other than melatonin. The results available today are often unclear and not linear. These peptides have not been well studied and defined over the years. In this review we hope to awake the interest of the scientific community in them and in their future pharmacological applications.

Cell Therapy Strategies to Combat Immunosenescence

Declining function of the immune system, termed "immunosenescence," leads to a higher incidence of infection, cancer, and autoimmune disease related mortalities in the elderly population. (1) Increasing interest in the field of immunosenescence is well-timed, as 20% of the United States population is expected to surpass the age of 65 by the year 2030. (2) Our current understanding of immunosenescence involves a shift in function of both adaptive and innate immune cells, leading to a reduced capacity to recognize new antigens and widespread chronic inflammation. The present review focuses on changes that occur in haematopoietic stem cells, macrophages, and T-cells using knowledge gained from both rodent and human studies. The review will discuss emerging strategies to combat immunosenescence, focusing on cellular and genetic therapies, including bone marrow transplantation and genetic reprogramming. A better understanding of the mechanisms and implications of immunosenescence will be necessary to combat age-related mortalities in the future.

Vaccination in the elderly: what can be recommended?

The age-associated increased susceptibility to infectious disease would suggest that vaccination should be a route to promote healthy aging and keep our seniors autonomous and independent. While vaccination represents a cost-effective and efficient strategy at community level, the ability of the immune system to mount a protective immune response is still unpredictable at the level of the individual. Thus, at a similar age, some individuals, including the elderly, might still be 'good' responders while some other, even younger, would definitely fail to mount a protective response. In this review, the current burden of vaccine-preventable diseases in the aging and aged population will be detailed with the aim to identify the ideal vaccine candidates over the age of 50 years. This article will conclude with potential strategies to reduce, as best as possible, this burden and the imperative need to overcome barriers in extending current vaccine coverage towards to a lifelong vaccine schedule.

Effect of IGF-I on Hair Growth Is Related to the Anti-Apoptotic Effect of IGF-I and Up-Regulation of PDGF-A and PDGF-B

Background

Insulin-like growth factor-I (IGF-I) shares a high degree of structural and functional homology with insulin and is a potent mitogen supporting cell growth and survival in many kinds of the tissues and cells. It also plays a role in some differentiation and anti-apoptotic functions. In previous reports, it has been shown that IGF-I stimulates hair follicle (HF) growth, maintains the anagen stage, and postpones the catagen stage.

Objective

The exact mechanism of the effect of IGF-I on HF growth is not yet established. Therefore, we investigated the relationships between IGF-I and various other factors (i.e. apoptosis related molecules, pro-inflammatory cytokines, other growth factors, etc.) in the control of HF growth.

Methods

The effect of IGF-I on human hair growth was measured using an organ culture model of human HFs and compared with a control group that did not receive IGF-I. We also measured mRNA expression of factors related to hair growth and apoptosis (which was determined by reverse transcription polymerase chain reaction (RT-PCR). RT-PCR was done on days 2, 4, 6, and 8 of organ culture.

Results

In organ cultured human hair follicles, IGF-I had a positive effect on the rate of linear hair growth. IGF-I maintained the anagen phase. IGF-I increased the expression of platelet-derived growth factor (PDGF)-A, PDGF-B and the expression ratio of Bcl-2/Bax.

Conclusion

The effect of IGF-I on hair growth appears to be related to the upregulation of PDGF-A and PDGF-B and to the anti-apoptotic effect of IGF-I.

Strategies for reconstituting and boosting T cell-based immunity following haematopoietic stem cell transplantation: pre-clinical and clinical approaches

Poor immune recovery is characteristic of bone marrow transplantation and leads to high levels of morbidity and mortality. The primary underlying cause is a compromised thymic function, resulting from age-induced atrophy and further compounded by the damaging effects of cytoablative conditioning regimes on thymic epithelial cells (TEC). Several strategies have been proposed to enhance T cell reconstitution. Some, such as the use of single biological agents, are currently being tested in clinical trials. However, a more rational approach to immune restoration will be to leverage the evolving repertoire of new technologies. Specifically, the combined targeting of TEC, thymocytes and peripheral T cells, together with the bone marrow niches, promises a more strategic clinical therapeutic platform.

Thymic epithelial cells of human patients affected by myasthenia gravis overexpress IGF-I immunoreactivity

Accumulating evidence shows that several kinds of thymic cells express insulin-like growth factor-I (IGF-I), which is known to play an important role in T cell ontogeny under both physiological and pathological conditions. Still, little is known about the mechanisms of IGF-I involvement in the pathological transformation of the thymocyte microenvironment. The present study focuses on a comparative analysis of the IGF-I immunoreactivity of thymic epithelial cells (EC) from human patients with hyperplasia-associated myasthenia gravis (MG) versus physiological thymic tissue from healthy controls using immunohistochemistry and immunoelectron microscopy. We show that myasthenic EC overexpress IGF-I in comparison to EC from control subjects. The IGF-I immunoreactivity in the medullary and cortical EC from MG patients was stronger than in the normal gland. The increased expression of IGF-I and more frequent distribution of IGF-I and IGF-I-receptor (IGF-IR) immunopositive EC correlated with modulation in the immunoreactivity of double (IGF-I/IGF-IR) positive EC. Our data provide new immunocytochemial evidence for alterations of IGF-I and IGF-IR immunoreactivity in EC from pathological thymi. The persisting expression of IGF-I and IGF-IR most likely indicates that the myasthenic thymus is still capable of governing IGF-I signaling pathways, which are involved in the local regulation of T cell development and plasticity.

Immune activation and inflammation in HIV-1 infection: causes and consequences

Thorough research on HIV is progressively enabling us to understand the intricate mechanisms that link HIV-1 infection to the onset of immunodeficiency. The infection and depletion of CD4(+) T cells represent the most fundamental events in HIV-1 infection. However, in recent years, the role played by chronic immune activation and inflammation in HIV pathogenesis has become increasingly apparent: quite paradoxically, immune activation levels are directly associated with HIV-1 disease progression. In addition, HIV-1-infected patients present intriguing similarities with individuals of old age: their immune systems are characterized by a loss of regenerative capacity and an accumulation of ageing T cells. In this review, we discuss the potential reasons for the establishment of sustained immune activation and inflammation from the early stages of HIV-1 infection, as well as the long-term consequences of this process on the host immune system and health. A simplified model of HIV pathogenesis is proposed, which links together the three major facets of HIV-1 infection: the massive depletion of CD4(+) T cells, the paradoxical immune activation and the exhaustion of regenerative capacity.

Plasmid-mediated growth hormone-releasing hormone efficacy in reducing disease associated with Mycoplasma hyopneumoniae and porcine reproductive and respiratory syndrome virus infection

The purpose of this study was to determine the effects of plasmid-mediated growth hormone releasing hormone (GHRH) supplementation on the clinical outcomes of pigs vaccinated against and challenged with either Mycoplasma hyopneumonia (M. hyo) and/or with porcine reproductive and respiratory syndrome (PRRS) virus. Before the first vaccination, pigs received a single i.m. injection of 0.625 mg of a porcine GHRH-expressing plasmid followed by electroporation of the injection site. Pigs were vaccinated at 2-wk intervals, challenged with either M. hyo and/or PRRS virus 2-wk after the second vaccination, and necropsied at 17 and 36 d after challenge. Clinical parameters associated with M. hyo challenge were improved with the GHRH treatment. Average daily gain between challenge and necropsy was improved (P = 0.04). Respiratory scores for M. hyo-challenged pigs tended to be lower in GHRH-treated animals compared to controls, and coughing scores were improved by the treatment (P = 0.01). Macroscopic lesions associated with M. hyo infection pneumonia were fewer in the group that received the GHRH-expressing plasmid. No differences between treatment groups in the macroscopic pneumonia associated with PRRS virus were observed. No differences in serum antibodies to M. hyo or PRRS virus were observed with GHRH treatment. Nevertheless, IgG in the bronchioalveolar lavage was increased by the GHRH treatment in M. hyo-challenged animals (P < 0.03). The results of this study suggest that GHRH supplementation before vaccination may enhance the protection against M. hyo-induced pneumonia and that a single dose of GHRH-expressing plasmid was sufficient to elicit an improved clinical outcome in this disease challenge model.

Inflammatory cytokines, behaviour and age as determinants of self-rated health in women

Self-rated health is a powerful and independent predictor of long-term health, but its biological basis is unknown. We have shown previously that self-rated health is associated with increased levels of circulating cytokines in women. The main aim of the present study was to increase the understanding of the association between markers of wellbeing, such as self-rated health, and cytokines and to investigate the impact of age on these associations. In 174 female consecutive primary health care patients divided into three age groups, we examined subjective ratings of health and aspects of wellbeing and circulating levels of IL (interleukin)-1beta, IL-1ra (IL-1 receptor antagonist), IL-6 and TNF-alpha (tumour necrosis factor-alpha). Poor self-rated health was significantly associated with higher levels of TNF-alpha in all of the age groups. For IL-1beta and IL-1ra, the correlations with self-rated health were significant only in the oldest age group. Lower ratings of other measurements of health and wellbeing were related to higher levels of cytokines, most pronounced for TNF-alpha and IL-1beta, and in the middle and olderst age groups. More symptoms resembling a sickness response induced by inflammation were implicated to be associated with lower self-rated health. The strength of the association between inflammatory cytokines and poor health perception increased with advanced age, indicating an increased vulnerability for inflammatory activity during aging. It is suggested that higher levels of TNF-alpha are connected to a sickness response that, in turn, is connected to self-rated health. The results provide a possible psychobiological basis to understand better diffuse subjective symptoms and poor subjective health in women.

Reevaluating current models of thymic involution

It is generally accepted that thymic involution commences, or at least accelerates, at puberty due to increases in sex steroid and declines in growth hormone production. As a result of these hormonal changes, the development of the most immature intrathymic progenitors is blocked. However, aspects of this model are now being questioned. The present chapter re-evaluates a number of findings on which traditional models of thymic involution are based and reviews new data that, taken together, indicate a need to revise current views of thymic involution.

Reassessing the role of growth hormone and sex steroids in thymic involution

The concomitant decline in growth hormone (GH) and increase in sex steroid production with age is thought to be responsible for thymic involution. If changes in the production of these hormones trigger or sustain thymic involution, that process should be accelerated in little mice, which have a genetic deficiency resulting in reduced production of thymopoietic GH, and delayed in the hypogonadal strain, which fails to produce thymocytotoxic sex steroids. The results indicated that thymic involution in both strains progressed in a manner similar to their normal littermates. That blocking sex steroid production did not delay thymic involution was surprising since castration reportedly increases thymus cellularity. Re-examination of that phenomenon revealed that, while gonadectomy results in increased thymus size, its effects are transient, and the thymus ultimately undergoes involution. Taken together, these data suggest that age-related changes in the endocrine system do not underlie thymic involution.

Effects of aging on early B- and T-cell development

Lymphocyte production in the bone marrow and the thymus is reduced during aging, but why this decline occurs has not been fully elucidated. The ability to isolate hematopoietic stem and progenitor cells using sophisticated flow cytometric strategies and to manipulate them in vitro and in vivo has provided insights into the effects of aging on primary lymphopoiesis. These analyses have showed that intrinsic changes in hematopoietic precursors that affect their proliferative potential are one factor that contributes to the age-related decline in B- and T-cell production. This and other age-related defects may be exacerbated by changes in the lymphopoietic support potential of the bone marrow and thymic microenvironments as well as by age-induced fluctuations in the production of various endocrine hormones. Particular attention with regard to the latter point has focused on changes in the production of sex steroids, growth hormone, and insulin-like growth factor-I. The present review summarizes recent studies of how age-related perturbations affect primary lymphopoiesis and highlights how the data necessitate the reevaluation of a number of existing paradigms.

Perioperative treatment with human growth hormone down-regulates apoptosis and increases superoxide production in PMN from patients undergoing infrarenal abdominal aortic aneurysm repair

BACKGROUND

Recombinant human growth hormone (hGH) therapy has a beneficial effect on catabolism and wound healing after major surgery. Polymorphonuclear neutrophils (PMN) play an important role in this context. In a prospective, double-blind, randomized, placebo-controlled trial we studied the effect of perioperative hGH treatment on postoperative wound healing and on changes in superoxide generation and susceptibility to apoptosis of PMN in elderly patients undergoing elective abdominal aortic aneurysm repair.

METHODS

Seven patients were treated with high-dose hGH (16 U/d) for nine days, seven patients with a placebo. IGF-I, neutrophil count, O2-production induced by opsonized zymosan and apoptosis of PMN were measured and correlated with clinical outcome.

RESULTS

Perioperative hGH treatment more than doubled the O2- production in PMN before and 24 h after surgery (p < 0.01). The long-term capacity of PMN to generate O2 in vitro was prolonged (p < 0.001) in the hGH group. Spontaneous and Fas-inducible apoptosis was strongly down-regulated in PMN after surgery in all patients (p < 0.01). hGH-treatment distinctly reduced apoptosis in PMN before and after surgery (p < 0.01). Clinical outcome was similar in both groups.

CONCLUSION

Perioperative hGH treatment results in an enhanced O2- production in PMN and in a prolongation of the functional life span of these cells. This may improve immune function and help to overcome the postoperative anergic state of the immune system especially in elderly individuals.

Insights into thymic aging and regeneration

The deterioration of the immune system with progressive aging is believed to contribute to morbidity and mortality in elderly humans due to the increased incidence of infection, autoimmunity, and cancer. Dysregulation of T-cell function is thought to play a critical part in these processes. One of the consequences of an aging immune system is the process termed thymic involution, where the thymus undergoes a progressive reduction in size due to profound changes in its anatomy associated with loss of thymic epithelial cells and a decrease in thymopoiesis. This decline in the output of newly developed T cells results in diminished numbers of circulating naive T cells and impaired cell-mediated immunity. A number of theories have been forwarded to explain this 'thymic menopause' including the possible loss of thymic progenitors or epithelial cells, a diminished capacity to rearrange T-cell receptor genes and alterations in the production of growth factors and hormones. Although to date no interventions fully restore thymic function in the aging host, systemic administration of various cytokines and hormones or bone marrow transplantation have resulted in increased thymic activity and T-cell output with age. In this review, we shall examine the current literature on thymic involution and discuss several interventional strategies currently being explored to restore thymic function in elderly subjects.

Immunosenescence and macrophage functional plasticity: dysregulation of macrophage function by age-associated microenvironmental changes

The macrophage lineage displays extreme functional and phenotypic heterogeneity, which appears to be because, in large part, of the ability of macrophages to functionally adapt to changes in their tissue microenvironment. This functional plasticity of macrophages plays a critical role in their ability to respond to tissue damage and/or infection and to contribute to clearance of damaged tissue and invading microorganisms, to recruitment of the adaptive immune system, and to resolution of the wound and of the immune response. Evidence has accumulated that environmental influences, such as stromal function and imbalances in hormones and cytokines, contribute significantly to the dysfunction of the adaptive immune system. The innate immune system also appears to be dysfunctional in aged animals and humans. In this review, the hypothesis is presented and discussed that the observed age-associated 'dysfunction' of macrophages is the result of their functional adaptation to the age-associated changes in tissue environments. The resultant loss of orchestration of the manifold functional capabilities of macrophages would undermine the efficacy of both the innate and adaptive immune systems. The macrophages appear to maintain functional plasticity during this dysregulation, making them a prime target of cytokine therapy that could enhance both innate and adaptive immune systems.

Growth hormone releasing hormone plasmid supplementation, a potential treatment for cancer cachexia, does not increase tumor growth in nude mice

Growth hormone releasing hormone (GHRH) is known to have multiple anabolic effects and immune-stimulatory effects. Previous studies suggest that treatment with anabolic hormones also has the potential to mitigate the deleterious effects of cancer cachexia in animals. We studied the effects of plasmid-mediated GHRH supplementation on tumor growth and the role of antitumor immune cells with two different human tumor cell lines, NCI-H358 human bronchioalveolar carcinoma and MDA-MB-468 human breast adenocarcinoma, subcutaneously implanted in nude mice. GHRH supplementation by delivery of human GHRH from a muscle-specific GHRH expression plasmid did not increase tumor progression in tumor-bearing nude mice. Male animals implanted with the NCI-H358 tumor cell line and treated with the GHRH-expressing plasmid exhibited a 40% decrease in the size of the tumors (P<.02), a 48% increase in white blood cells (P<.025) and a 300% increase in monocyte count (P<.0001), as well as an increase in the frequency of activated CD3+ and CD4+ cells in the tumors, compared to tumors of control animals. No adverse effects were observed in animals that received the GHRH-plasmid treatment. The present study shows that physiological stimulation of the GHRH-GH-IGF-I axis in mice with cancer does not promote tumor growth and may provide a viable treatment for cancer cachexia in humans.

Immune-enhancing effects of growth hormone-releasing hormone delivered by plasmid injection and electroporation

Growth hormone-releasing hormone (GHRH) is a hypothalamic hormone with both direct and indirect functions in the maintenance of immune status under physiological and pathological conditions. In this study, 52 Holstein heifers were evaluated for the effects of a plasmid-mediated GHRH treatment on their immune function and on the morbidity and mortality of treated animals. In the third trimester of pregnancy, 32 heifers received 2.5 mg of a myogenic GHRH-expressing plasmid by intramuscular injection followed by electroporation, while 20 heifers were used as controls. No adverse effects were associated with either the plasmid delivery or GHRH expression. At 18 days after plasmid administration, GHRH-treated animals had increased numbers of CD2(+) alphabeta T-cells (P < 0.004), CD25(+)CD4(+) cells (P < 0.0007), and CD4(+)CD45R(+) cells (P < 0.016) compared to controls. These increases were maintained long term after treatment and correlated with plasmid expression. At 300 days post-GHRH therapy, CD45R(+)/CD45R0(-) naïve lymphocytes were significantly increased in frequency (P < 0.05). Natural killer lymphocytes (CD3(-)CD2(+)) were also increased. As a consequence of improved health status, body condition scores of treated animals improved (3.55 vs. 3.35, P < 0.0001). Hoof pathology was also reduced with treatment. The mortality of heifers was decreased (3% vs. 20% in controls, P < 0.003). Collectively, these results indicate that the myogenic GHRH plasmid can be successfully electrotransferred into a 500-kg mammal and expressed for prolonged periods of time, ensuring physiological levels of GHRH. The plasmid injection followed by electroporation could prove an efficient method for the systemic production of therapeutic proteins and may provide a useful means for basic research in relevant animal models.

Apparent induction of partial thymic regeneration in a normal human subject: a case report

Magnetic resonance imaging was used to detect signs of regeneration of the thymus after approximately one month of human growth hormone administration. A 46-year-old human volunteer was placed on a regimen of recombinant human growth hormone and pharmaceutical grade dehydroepiandrosterone for one month. Mediastinal magnetic resonance images were collected at baseline and after the study period. Thymic cross sections were analyzed for total area and for the total gray area, which was taken to represent functional mass. Baseline and post-treatment blood samples were taken to follow changes in IGF-1 levels and related metabolites. The setting was an informal, non-institutional trial supervised by a physician will full informed consent of the volunteer. Visual inspection and image analysis demonstrated limited but distinct enlargement of the thymus after treatment, and an increase in the percent of thymic cross section represented by gray-appearing (functional) mass. Estimated total thymic functional volume was within the normal range at baseline, but after treatment was more than three standard deviations above the expected mean for a subject of this age, thus meeting a proposed definition of thymic hyperplasia for individuals. IGF-1 levels were confined to the upper range of normal for young adults. The present observations apparently provide the first demonstration of growth hormone induced partial reversal of established thymic involution in a normal human subject, and are consistent with previous measurements of restored immune function after the administration of human growth hormone to elderly individuals.

From hormones to immunity: the physiology of immunology

Discoveries in the physiology of immunology have increased at an increasing rate during the past two decades. It is now recognized that the immune system is just another physiological system that regulates, and is regulated by, other physiological systems such as the brain. These advances make it clear that recent findings in genomic biology must be interpreted in the context of the environment in which animals and humans live. Lack of a strong genetic basis for significant human mental health disorders, such as major depression, points to the critical importance of interactions. Several examples of environmental x genetic x disease interactions are presented. Regulation of cells of the hematopoietic lineage by two genes that control over 80% of postnatal growth, growth hormone and IGF-I, are then highlighted. The reciprocal relationship of how proinflammatory cytokines from the immune system regulate the growth hormone/IGF-I axis is also summarized. Particular emphasis is placed upon TNFalpha-induced IGF-I resistance in neurons, muscle cells and epithelial cells. This cytokine regulation of hormone action may ultimately be more important for human and animal health than direct effects of growth hormone and IGF-I on hematopoietic cells. Wasting of AIDS patients is given as an important clinical example of how TNFalpha from an activated immune system reduces IGF-I sensitivity in multiple physiologic systems, including muscle, nervous and hematopoietic tissues.

Age-dependent changes in the nervous and endocrine control of the thymus

The immune system, especially the thymus, undergoes age-related modifications leading to structural and functional changes in the lymphoid organs and immunocompetent cells. Nevertheless, the consequences of thymic involution in the peripheral pool of T-cells are still a matter of controversy. The control of the thymic function is very complex and involves intrathymic signals, the autonomic nervous system, and the endocrine system. Both thymocytes and thymic stromal cells express receptors for a wide range of hormones, as well as for neurotransmitters and neuropeptides, thus affecting thymocytes maturation. This review summarizes the age-dependent variations in the extrathymic components of the thymic microenvironment, i.e., vegetative nerves and hormones, and the possible effects of those changes in the immune function.

Effects of N-acetylcysteine on macrophage and lymphocyte functions in a mouse model of premature ageing

In previous studies, we have observed that mice of the same strain and age show striking interindividual differences in behavior when exposed to a T-maze test. The animals that take longer to explore a T-shaped maze ("slow" animals) show high levels of emotionality/anxiety in other standard behavioral tests, prematurely aged immune functions, and a shorter life span, in comparison to "fast" mice. In these slow mice, which are a model of premature immunosenescence, the immune functions were improved after the ingestion of the thiolic antioxidant thioproline in the diet. In the present work, we studied the effects in vivo (0.1% w/w, for 4 weeks) and in vitro (0.001, 0.01, 0.1, 1, and 2.5 mM) of the thiolic antioxidant N-acetylcysteine (NAC) on different functions of peritoneal macrophages and lymphocytes from slow and fast adult Swiss mice. The results showed an improvement of all the functions studied, namely adherence to substrate, directed migration or chemotaxis, phagocytosis, and reactive oxygen species (ROS) production, after in vivo and in vitro treatment with NAC. The effect of this antioxidant was stronger in the cells from the slow than in those from the fast mice.

Humoral immune response in mice over-expressing or deficient in growth hormone

Effects of growth hormone (GH) levels on the humoral immune response were investigated in metallothionein I (MT)-bovine (b) GH-transgenic (tg) and GH-deficient Ames dwarf (Prop1 df(-/-)) mice. Four-month-old mice were given primary and secondary injections of either normal saline or tetanus toxoid (TT) to induce specific antibody (Ab) production. MT-bGH-tg mice with high peripheral levels of bGH produced less TT-specific Ab than normal nontransgenic (Ntg) littermates, df, or nondwarf (Ndf) control mice. Titers reached maximum levels at 3-4 weeks post-primary immunization (PPI) and declined gradually through 24 weeks PPI in all groups of mice. Peripheral CD4(+) and CD8(+) T cell populations were significantly lower in tg than in Ntg, df, or Ndf mice. No significant differences were found in B cell numbers between tg, Ntg, or df mice. T helper 2 (Th2) cell populations were significantly greater in df mice compared to Ntg control mice. No significant differences were found in CD4(+):CD8(+) T cell ratios, interleukin (IL)-4 concentrations or interferon (IFN)-gamma levels between tg,Ntg, df, and Ndf mice. No patterns of significant sexual dimorphism were found for any of the immune parameters studied. Elevated levels of corticosterone were investigated as a possible immunosuppressant mechanism responsible for low Ab responses in the tg mice. Ab production was not enhanced by decreasing corticosterone in tg mice. Thus, high endogenous GH levels inhibit specific Ab production and peripheral T cell populations but not peripheral B cell numbers, Th2 cell populations, or IL-4 or IFN-gamma production. Elevated corticosterone levels do not appear to be responsible for suppressed humoral immune responses. Low levels of endogenous GH do not inhibit specific Ab production but may contribute to increased peripheral Th2 cell numbers.

Age-associated loss of bone marrow hematopoietic cells is reversed by GH and accompanies thymic reconstitution

Deterioration of the thymus gland during aging is accompanied by a reduction in plasma GH. Here we report gross and microscopic results from 24-month-old Wistar-Furth rats treated with rat GH derived from syngeneic GH3 cells or with recombinant human GH. Histological evaluation of aged rats treated with either rat or human GH displayed clear morphologic evidence of thymic regeneration, reconstitution of hematopoietic cells in the bone marrow, and multiorgan extramedullary hematopoiesis. Quantitative evaluation of formalin-fixed, hematoxylin and eosin-stained sections of bone marrow from aged rats revealed at least a 50% reduction in the number hematopoietic bone marrow cells, compared with that of young 3-month-old rats. This age-associated decline in bone marrow leukocytes, as well as the increase in bone marrow adipocytes, was significantly reversed by in vivo treatment with GH. Restoration of bone marrow cellularity was caused primarily by erythrocytic and granulocytic cells, but all cell lineages were represented and their proportions were similar to those in aged control rats. On a per-cell basis, GH treatment in vivo significantly increased the number of in vitro myeloid colony forming units in both bone marrow and spleen. Morphological evidence of enhanced extramedullary hematopoiesis was observed in the spleen, liver, and adrenal glands from animals treated with GH. These results confirm that GH prevents thymic aging. Furthermore, these data significantly extend earlier findings by establishing that GH dramatically promotes reconstitution of another primary hematopoietic tissue by reversing the accumulation of bone marrow adipocytes and by restoring the number of bone marrow myeloid cells of both the erythrocytic and granulocytic lineages.

Inhibition of Na,K-ATPase activates PI3 kinase and inhibits apoptosis in LLC-PK1 cells

In the present study we used LLC-PK1 cells, a porcine renal proximal tubular cell line, to investigate whether PI3 kinase activation was involved in the anti-apoptotic effect of ouabain, a specific inhibitor of Na,K-ATPase. Apoptosis was induced by actinomycin D (Act D, 5 microM) and assessed by appearance of hypodiploid nuclei and DNA fragmentation. Ouabain attenuated Act D-induced apoptotic response in a dose-dependent manner. Incubation in a low K(+) medium (0.1 mM) which is another way to decrease Na,K-ATPase activity also had anti-apoptotic effect. Both ouabain and low K(+) medium increased the PI3 kinase activity in p85 immunoprecipitates. Ouabain, as well as incubation in the low K(+) medium, also increased the phosphorylation of Akt. Inhibition of PI3 kinase by either wortmannin or LY294002 reversed the cytoprotective effect of ouabain. These data together indicate that inhibition of Na,K-ATPase activates PI3 kinase in LLC-PK1 cells which could then exert the cytoprotective effect.

Hematopoietic growth factors in the older cancer patient

Aging is associated with a progressive decline in the functional reserve of multiple organ systems, which may lead to enhanced susceptibility to stress such as that caused by cancer chemotherapy. Myelodepression is the most common and the most commonly fatal complication of antineoplastic drug therapy and may represent a serious hindrance to the management of cancer in older individuals. This is already a common and pervasive problem and promises to become more so. Currently 60% of all neoplasms occur in persons aged 65 years and older, and this percentage is expected to increase as the population ages. This well-known phenomenon, sometimes referred to as squaring or the age pyramid, is caused by the combination of an increasing life expectancy and a decreasing birth rate. This article explores the use of hematopoietic growth factors in the older cancer patient after reviewing the influence of age on hemopoiesis and chemotherapy-related complications. The issue is examined in terms of effectiveness and cost. An outline of the assessment of the older cancer patient is provided at the end of the chapter as a frame of reference for clinical decisions.

Alterations in signal transduction cascade in young and adult rat brain and lymphocytes

Signal transduction cascade, phosphoinositide metabolism, and protein kinases were studied from discrete areas of rat brain like cerebral hemispheres, cerebellum, brainstem, and diencephalon as well as lymphocytes isolated from three different age groups of rats; young (1 month), young adult (3-4 months), and adult (12 months) rats. The activities of protein kinase A, protein kinase C, phospholipase A(2) and phospholipase C and inositol 1, 4, 5-triphosphate, diacylglycerol, cyclic adenosine monophosphate contents were assayed from different brain areas and lymphocytes from these three age group rats. An upregulatory effect on the signal transduction system was observed from 1 month to 3-4-month age group, whereas, the brain tissue and lymphocytes of adult rats showed lower contents and activities of signal transduction components as compared to young adults. In view of the established 'cross talk' between signal transduction system, the present results suggests that molecular/cellular changes in brain and immune cells signal transduction pathway along with neuronal cell loss may contribute to age-related decline in nervous as well as immune system functions.

Age-dependent changes in 24-hour rhythms of thymic and circulating growth hormone and adrenocorticotropin in rats injected with Freund's adjuvant

OBJECTIVE

To analyze the 24-hour changes in thymic and serum concentration of growth hormone (GH) and adrenocorticotropin (ACTH) and their correlation with thymic concentrations of glutamate, aspartate, taurine and GABA in young and old rats during the acute phase of adjuvant's arthritis.

METHODS

Young (50-day-old) and old (18-month-old) rats were injected subcutaneously with Freund's adjuvant or its vehicle (paraffin oil containing 15% mannide monooleate). Eighteen days later, they were killed at six different time intervals throughout a 24-hour cycle. Serum and thymic levels of GH and ACTH were measured by radioimmunoassay. Thymic amino acid concentration was measured by HPLC. A quantitative assessment of arthritis was made in an independent group of rats by plethysmography.

RESULTS

Old rats injected with Freund's adjuvant exhibited fewer clinical signs of inflammation than young rats. Significant 24-hour changes in thymic and serum GH occurred, except for serum GH in adjuvant's vehicle-treated old rats. Aging augmented thymic GH and decreased serum GH. Immunization with Freund's adjuvant did not modify GH concentration. Thymic and serum concentration of GH correlated negatively. Thymic ACTH varied significantly over 24 h with maxima during the dark phase, except in Freund's adjuvant-treated young rats. Maximal serum ACTH levels occurred in the late afternoon except in Freund's adjuvant-treated old rats which showed maxima at night. Immunization with Freund's adjuvant augmented thymic and circulating concentrations of ACTH. Thymic and serum concentration of ACTH correlated positively. Thymic concentration of glutamate, aspartate and taurine decreased in aged rats and correlated significantly with thymic ACTH.

CONCLUSION

The results support the existence of a thymic compartment of GH and ACTH that may be independently regulated.

Growth hormone prevents Fas-induced apoptosis in lymphocytes through modulation of Bcl-2 and caspase-3

OBJECTIVE

Growth hormone (GH) has been reported to have a potent effect on the immune system. However, the detailed mechanism of the effect of GH on the immune system has not yet been clarified. This study was designed to investigate the nature of this mechanism.

METHODS

In the present study, we investigated the effects of GH on the susceptibility of both human CEM/C7 lymphocytes and human IM-9 lymphocytes to Fas-induced apoptosis.

RESULTS

Both cell lines expressed GH receptor mRNA. GH rescued Fas-induced suppression of [(3)H]-thymidine incorporation into each cell line. GH prevented Fas-induced apoptosis in each cell line without changing Fas antigen expression. We next investigated the mechanisms of the prevention of Fas-induced apoptosis, by focusing on intracellular molecules related to the apoptotic signal. Bcl-2 expression was increased by GH treatment in both CEM/C7 and IM-9 lymphocytes. GH also downregulated caspase-3 expression and inhibited activation of caspase-3 in both cell lines.

CONCLUSION

These findings suggest that GH regulates the human immune system through inhibition of Fas-induced apoptosis in activated T and B lymphocytes.

Identification of INSL5, a new member of the insulin superfamily

A new member of the insulin gene superfamily (INSL5) was identified by searching EST databases for the presence of the conserved insulin B-chain cysteine motif. Human and murine INSL5 are both polypeptides of 135 amino acids, matching the classical signature of the insulin superfamily. Through the B- and A-chain regions, human INSL5 has 48% identity to shark relaxin, 40% identity to human relaxin, and 34% identity to human Leydig insulin-like factor. Northern blot analysis detected expression of human INSL5 in rectal, colon, and uterine tissue and of murine INSL5 only in thymic tissue. Using quantitative RT-PCR, expression of murine INSL5 was detected in the highest quantity in colon followed by thymus, and minimal expression was seen in testis. By radiation hybrid mapping and the use of surrounding markers, human INSL5 maps to chromosome 1 in the 1p31.1 to 1p22.3 region.