Primary cultures of human synovial macrophages metabolize androgens

Immune Cells as Critical Regulators of Steroidogenesis in the Testis and Beyond

Steroidogenesis is an essential biological process for embryonic development, reproduction, and adult health. While specific glandular cells, such as Leydig cells in the testis, are traditionally known to be the principal players in steroid hormone production, there are other cell types that contribute to the process of steroidogenesis. In particular, immune cells are often an important component of the cellular niche that is required for the production of steroid hormones. For several decades, studies have reported that testicular macrophages and Leydig cells are intimately associated and exhibit a dependency on the other cell type for their proper development; however, the mechanisms that underlie the functional relationship between macrophages and Leydig cells are unclear. Beyond the testis, in certain instances immune cells themselves, such as certain types of lymphocytes, are capable of steroid hormone production, thus highlighting the complexity and diversity that underlie steroidogenesis. In this review we will describe how immune cells are critical regulators of steroidogenesis in the testis and in extra-glandular locations, as well as discuss how this area of research offers opportunities to uncover new insights into steroid hormone production.

An intracrine view of sex steroids, immunity, and metabolic regulation

Background

Over the past two decades, parallel recognition has grown of the importance of both sex steroids and immune activity in metabolic regulation. More recently, these discrete areas have been integrated in studies examining the metabolic effects of sex steroid immunomodulation. Implicit in these studies has been a traditional, endocrine model of sex steroid delivery from the gonads to target cells, including immune cells. Thus, research to date has focused on the metabolic effects of sex steroid receptor signaling in immune cells. This endocrine model, however, overlooks the extensive capacity of immune cells to generate and metabolize sex steroids, enabling the production of sex steroids for intracrine signaling – that is, sex steroid production for signaling within the cell of origin. Intracrine function allows highly cell-autonomous regulation of sex steroid exposure, and sex steroid secretion by immune cells could confer paracrine signaling effects in neighboring cells within metabolic tissues. In this review, immune cell intracrinology will denote sex steroid production within immune cells for either intracrine or paracrine signaling. This intracrine capacity of immune cells has been well established, and prior work has supported its importance in autoimmune disorders, trauma, and cancer. The potential relevance of immune cell intracrine function to the regulation of energy balance, body weight, body composition, and insulin sensitivity has yet to be explored.

Scope of review

The following review will detail findings to date regarding the steroidogenic and steroid metabolizing capacity of immune cells, the regulation of immune cell intracrine function, and the biological effects of immune-derived sex steroids, including the clinical relevance of immune cell intracrinology in fields other than metabolism. These findings will serve as the basis for a proposed model of immune cell intracrinology constituting a new frontier in metabolism research.

Major conclusions

The development of highly sensitive mass spectrometric methods for sex steroid measurement and quantitation of metabolic flux now allows unprecedented ability to interrogate sex steroid production, metabolism and secretion by immune cells. Immune cell intracrinology could reveal key mechanisms underlying immune cell-mediated metabolic regulation.

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Sex steroids exert immunomodulatory effects that may influence metabolic health.

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Immune cells can synthesize, modify, and metabolize sex steroids.

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Immune cell-derived sex steroids may play intracrine, autocrine, paracrine, and possibly even endocrine roles.

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Immune cell steroidogenesis is a largely unexplored area of metabolism research.

Androgen-mediated modulation of macrophage function after trauma-hemorrhage: central role of 5alpha-dihydrotestosterone

Androgens have been implicated as the causative factor for the postinjury immune dysfunction in males; however, it remains unknown whether androgens directly affect macrophages. To study this, male mice were sham operated or subjected to trauma (i.e., midline laparotomy) and hemorrhagic shock (mean arterial pressure, 30 +/- 5 mmHg for 90 min and then resuscitated). The mice received the 5alpha-reductase inhibitor 4-hydroxyandrostenedione (4-OHA) before resuscitation. Plasma TNF-alpha, IL-6, and IL-10 levels were elevated after trauma-hemorrhage and normalized by 4-OHA. TNF-alpha and IL-6 production by splenic macrophages was decreased after injury, whereas Kupffer cell production of these mediators was enhanced. 4-OHA normalized cytokine production. Androgens suppressed cytokine production by splenic macrophages from hemorrhaged mice, whereas it enhanced TNF-alpha and IL-6 production by Kupffer cells. The addition of 4-OHA in vitro normalized cytokine production by cells treated with testosterone, but it had no effect on dihydrotestosterone-treated cells. These results indicate that androgens directly affect macrophage function in males after trauma and hemorrhagic shock and that the intracellular conversion of testosterone to dihydrotestosterone is of particular importance in mediating the androgen-induced effects.

Hypothalamic-pituitary-adrenocortical and gonadal functions in rheumatoid arthritis

Rheumatoid arthritis (RA) as well as most autoimmune disorders results from a combination of several predisposing factors including the relations between epitopes of the trigger agent (i.e., virus, self-antigens) and histocompatibility epitopes (i.e., HLA), the status of the stress response system including the hypothalamic-pituitary-adrenocortical axis (HPA) and the sympathetic nervous system (SNS), as well as the gonadal hormones (hypothalamic-pituitary-gonadal axis, HPG), with estrogens implicated as enhancers of the immune response and androgens and progesterone as natural suppressors. The regular observation of reduced cortisol and adrenal androgen secretion during testing in RA patients not treated with glucocorticoids should clearly be regarded as "relative adrenal insufficiency" in the setting of a sustained inflammatory process, as shown by high interleukin (IL)-6 levels. In polymyalgia rheumatica, several pathogenetic and clinical aspects of the disease might well overlap RA, at least with elderly onset RA (EORA). Therefore, reduced production of adrenal hormones (i.e., cortisol, DHEAS) at baseline in active and untreated patients with polymyalgia rheumatica was detected. The defect was mainly related to altered adrenal responsiveness to ACTH stimulation (i.e., increased 17-OHP), at least in untreated patients with polymyalgia rheumatica. Finally, normal serum estrogen and low androgen levels, but high synovial fluid estrogen and much lower androgen levels, have been found in RA patients, supporting the fundamental role of the peripheral sex hormone metabolism in the manifestations of the disease.

Androgens and coronary artery disease

A significant and independent association between endogenous testosterone (T) levels and coronary events in men and women has not been confirmed in large prospective studies, although cross-sectional data have suggested coronary heart disease can be associated with low T in men. Hypoandrogenemia in men and hyperandrogenemia in women are associated with visceral obesity; insulin resistance; low high-density lipoprotein (HDL) cholesterol (HDL-C); and elevated triglycerides, low-density lipoprotein cholesterol, and plasminogen activator type 1. These gender differences and confounders render the precise role of endogenous T in atherosclerosis unclear. Observational studies do not support the hypothesis that dehydroepiandrosterone sulfate deficiency is a risk factor for coronary artery disease. The effects of exogenous T on cardiovascular mortality or morbidity have not been extensively investigated in prospective controlled studies; preliminary data suggest there may be short-term improvements in electrocardiographic changes in men with coronary artery disease. In the majority of animal experiments, exogenous T exerts either neutral or beneficial effects on the development of atherosclerosis. Exogenous androgens induce both apparently beneficial and deleterious effects on cardiovascular risk factors by decreasing serum levels of HDL-C, plasminogen activator type 1 (apparently deleterious), lipoprotein (a), fibrinogen, insulin, leptin, and visceral fat mass (apparently beneficial) in men as well as women. However, androgen-induced declines in circulating HDL-C should not automatically be assumed to be proatherogenic, because these declines may instead reflect accelerated reverse cholesterol transport. Supraphysiological concentrations of T stimulate vasorelaxation; but at physiological concentrations, beneficial, neutral, and detrimental effects on vascular reactivity have been observed. T exerts proatherogenic effects on macrophage function by facilitating the uptake of modified lipoproteins and an antiatherogenic effect by stimulating efflux of cellular cholesterol to HDL. In conclusion, the inconsistent data, which can only be partly explained by differences in dose and source of androgens, militate against a meaningful assessment of the net effect of T on atherosclerosis. Based on current evidence, the therapeutic use of T in men need not be restricted by concerns regarding cardiovascular side effects. Available data also do not justify the uncontrolled use of T or dehydroepiandrosterone for the prevention or treatment of coronary heart disease.

Androgens and estrogens modulate the immune and inflammatory responses in rheumatoid arthritis

Generally, androgens exert suppressive effects on both humoral and cellular immune responses and seem to represent natural anti-inflammatory hormones; in contrast, estrogens exert immunoenhancing activities, at least on humoral immune response. Low levels of gonadal androgens (testosterone/dihydrotestosterone) and adrenal androgens (dehydroepiandrosterone and its sulfate), as well as lower androgen/estrogen ratios, have been detected in body fluids (that is, blood, synovial fluid, smears, salivary) of both male and female rheumatoid arthritis patients, supporting the possibility of a pathogenic role for the decreased levels of the immune-suppressive androgens. Several physiological, pathological, and therapeutic conditions may change the sex hormone milieu and/or peripheral conversion, including the menstrual cycle, pregnancy, the postpartum period, menopause, chronic stress, and inflammatory cytokines, as well as use of corticosteroids, oral contraceptives, and steroid hormonal replacements, inducing altered androgen/estrogen ratios and related effects. Therefore, sex hormone balance is still a crucial factor in the regulation of immune and inflammatory responses, and the therapeutical modulation of this balance should represent part of advanced biological treatments for rheumatoid arthritis and other autoimmune rheumatic diseases.

The hypothalamic-pituitary-adrenal and gonadal axes in rheumatoid arthritis

The hypothalamic-pituitary-adrenal (HPA) and the hypothalamic-pituitary-gonadal (HPG) axes involvement or response to immune activation seems crucial for the control of excessive inflammatory and immune conditions such as autoimmune rheumatic diseases, including rheumatoid arthritis (RA). However, female patients seem to depend more on the HPA axis, whereas male patients seem to depend more on the HPG axis. In particular, hypoandrogenism may play a pathogenetic role in male RA patients because adrenal and gonadal androgens, both products of the HPA and HPG axes, are considered natural immunosuppressors. A significantly altered steroidogenesis of adrenal androgens (i.e., dehydroepiandrosterone sulfate, DHEAS and DHEA) in nonglucocorticoid-treated premenopausal RA patients has been described. The menopausal peak of RA suggests that estrogens and/or progesterone deficiency also play a role in the disease, and many data indicate that estrogens suppress cellular immunity, but stimulate humoral immunity (i.e., deficiency promotes cellular Th1-type immunity). A range of physical and psychosocial stressors are also implicated in the activation of the HPA axis and related HPG changes. Chronic and acute stressors appear to have different actions on immune mechanisms with experimental and human studies indicating that acute severe stressors may be even immunosuppressive, while chronic stress may enhance immune responses. The interactions between the immunological and neuroendocrine circuits is the subject of active and extensive ongoing research and might in the near future offer highly promising strategies for hormone-replacement therapies in RA.

Sex hormone adjuvant therapy in rheumatoid arthritis

RA is an autoimmune rheumatic disorder resulting from the combination of several predisposing factors, including the relation between epitopes of possible triggering agents and histocompatibility epitopes, the status of the stress response system, and the sex hormone status. Estrogens are implicated as enhancers of humoral immunity, and androgens and progesterone are natural immune suppressors. Sex hormone concentrations have been evaluated in RA patients before glucocorticoid therapy and have frequently been found to be altered, especially in premenopausal women and male patients. In particular, low levels of gonadal and adrenal androgens (testosterone and DHT, DHEA and DHEAS) and a reduced androgen:estrogen ratio have been detected in body fluids (i.e., blood, synovial fluid, smears, saliva) of male and female RA patients. These observations support a possible pathogenic role for the decreased levels of the immune-suppressive androgens. Exposure to environmental estrogens (estrogenic xenobiotics), genetic polymorphisms of genes coding for hormone metabolic enzymes or receptors, and gonadal disturbances related to stress system activation (hypothalamic-pituitary-adrenocortical axis) and physiologic hormonal perturbations such as during aging, the menstrual cycle, pregnancy, the postpartum period, and menopause may interfere with the androgen:estrogen ratio. Sex hormones might exert their immune-modulating effects, at least in RA synovitis, because synovial macrophages, monocytes, and lymphocytes possess functional androgen and estrogen receptors and may metabolize gonadal hormones. The molecular basis for sex hormone adjuvant therapy in RA is thus experimentally substantiated. By considering the well-demonstrated immune-suppressive activities exerted by androgens, male hormones and their derivatives seem to be the most promising therapeutic approach. Recent studies have shown positive effects of androgen replacement therapy at least in male RA patients, particularly as adjuvant treatment. Interestingly, the increase in serum androgen metabolism induced by RA treatment with CSA should be regarded as a possible marker of androgen-mediated immune-suppressive activities exerted by CSA, at least in RA and at the level of sensitive target cells and tissues (i.e., synovial macrophages). The absence of altered serum levels of estrogens in RA patients and the reported immune-enhancing properties exerted by female hormones have represented a poor stimulus to test estrogen replacement therapy in RA. The different results obtained with OC use seem to depend on dose-related effects and the different type of response to estrogens in relation to the cytokine balance between Th1 cells (cellular immunity, i.e., RA) and Th2 cells (humoral immunity, i.e., SLE). The androgen replacement obtained directly (i.e., testosterone, DHT, DHEAS) or indirectly (i.e., antiestrogens) may represent a valuable concomitant or adjuvant treatment to be associated with other disease-modifying antirheumatic drugs (i.e., MTX, CSA) in the management of RA.

Different roles for androgens and estrogens in the susceptibility to autoimmune rheumatic diseases

It is now documented that androgens and estrogens modulate susceptibility and progression to autoimmune rheumatic diseases. At any concentration, androgens seem to be primarily suppressive on cellular and humoral immunity, whereas at physiologic concentrations, estrogens seem to enhance humoral immunity. Further research should focus on the different and frequently opposite effects exerted by physiologic and pharmacologic doses of estrogens (dose-related effects). In addition to the influence of endogenous estrogen fluctuations (i.e., during pregnancy, postpartum, menstrual periods, menopause), estrogen replacement therapy, and the use of oral contraceptives, the susceptibility to autoimmunity might be increased by the environmental estrogens (xenobiotics). Further studies must be directed to the inflammatory mediators (i.e., cytokines) that seem to alter the peripheral metabolism of sex hormones and complicate the effects of sex hormones on susceptibility to autoimmunity. Finally, genetic factors might further interfere with the roles of androgens and estrogens in selected individuals.

Macrophages as effectors of the immunoendocrinologic interactions in autoimmune rheumatic diseases

An intricate balance between soluble mediators, released by activated cells of the immune/inflammatory systems, and products of the neuroendocrine system is implicated in the presence of an autoimmune rheumatic disease. Monocytes/macrophages contribute to autoimmune events in rheumatic diseases, such as rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE), mainly acting as antigen-processing and presenting cells in the presence of an autoimmune rheumatic disease. Clinical symptoms such as morning stiffness and gelling, at least in RA, that peak during the late night and early morning, are consistent with the hypothesis that the immune function of activated cells (i.e., Th1 cells and monocytes/macrophages) and their mediators (cytokines and reactive oxygen intermediates) is increased at these times in relation to neuroendocrine pathway rhythmicity. Therefore, monocytes/macrophages seem to be the "link" between the steroid hormone environment (i.e., gonadal hormones) and the immune response effectors. If gonadal hormones, along with cytotoxic agents, do modulate macrophage apoptosis, such an approach might offer an important pathway to the control of autoimmune diseases. In conclusion, on the basis of a more complete understanding of macrophage effector and immunoregulatory activities, on both a local and systemic level, new hopes arise from the possible development of more sophisticated antimacrophage treatments for the management of autoimmune rheumatic diseases.

Androgenizing effects of cyclosporin A in rheumatoid arthritis

In order to determine the influence of CsA on whole peripheral androgen metabolism, we evaluated 14 patients with RA over a period of 12 months. Patients were treated with low-dose CsA (2.5-3.5 mg/kg/day). Other drugs influencing androgen metabolism were excluded. Plasma levels of Test and of 5 alpha-androstane-3 alpha, 17 beta-diol glucuronide (Adiol-G), an important peripheral Test metabolite, were analyzed. Each patient was monthly examined for the first three months, and thereafter every three months. At each visit, the number of swollen and tender joints, as well as the visual analogic scale of pain, were evaluated. The laboratory parameters of RA activity (ESR, CRP, Hb) were also monitored, along with some safety serological indexes. Statistical analysis was performed by using nonparametrical tests. After 12 months of treatment, an evident increase in mean plasma Adiol-G concentration was observed in patients of both sexes (women's basal levels +/- SE = 2.89 +/- 0.58 ng/mL vs. 12 months = 5.71 +/- 1.33 ng/mL; men's basal levels = 4.87 +/- 0.91 vs. 9.20 +/- 0.68, respectively) (p < 0.001). The increase was already statistically significant after 4-5 weeks of treatment in male patients (p < 0.01) and after 12-14 weeks in female patients (p < 0.05). All the patients experienced the side effect of a low-degree hypertrichosis after a mean period of 4-8 weeks. Concerning clinical parameters, a significant improvement (p < 0.05) of the number of swollen and tender joints was observed after 12 months, as well as a reduction of CRP levels. No statistically significant correlation between hormonal levels and clinical or laboratory indexes of disease activity was observed. In conclusion, the appearance of a dose-related hypertrichosis and the increase in plasma androgen metabolites (Adiol-G) in CsA-treated patients should be regarded as possible markers of the influence of CsA on peripheral androgen metabolism, at the level of target cells and tissues.