Aging of the male endocrine system

Low-dose testosterone treatment decreases oxidative damage in TM3 Leydig cells

Testosterone replacement therapy has benefits for aging men and those with hypogonadism. However, the effects of exogenous testosterone on Leydig cells are still unclear and need to be clarified. In this report, we demonstrate that testosterone supplementation can reduce oxidative damage in Leydig cells. The TM3 Leydig cell line was used as an in vitro cell model in this study. Cytoprotective effects were identified with 100-nmol l⁻¹ testosterone treatment, but cytotoxic effects were found with ≥ 500-nmol l⁻¹ testosterone supplementation. Significantly reduced reactive oxygen species (ROS) generation, lipid peroxide contents and hypoxia induction factor (HIF)-1α stabilization and activation were found with 100-nmol l⁻¹ testosterone treatment. There was a 1.72-fold increase in ROS generation in the 500-nmol l⁻¹ compared to the 100-nmol l⁻¹ testosterone treatment. A 1.58-fold increase in steroidogenic acute regulatory protein (StAR) expression was found in 50-nmol l⁻¹ testosterone-treated cells (P < 0.01). Chemically induced hypoxia was attenuated by testosterone supplementation. Leydig cells treated with low-dose testosterone supplementation showed cytoprotection by decreasing ROS and lipid peroxides, increasing StAR expression and relieving hypoxia stress as demonstrated by HIF-1α stabilization. Increased oxidative damage was found with ≥ 500-nmol l⁻¹ testosterone manipulation. The mechanism governing the differential dose effects of testosterone on Leydig cells needs further investigation in order to shed light on testosterone replacement therapy.

Expression of proteinase-activated receptor-2 (PAR2) is androgen-dependent in stromal cell line (hPCPs) from benign prostatic hyperplasia

BACKGROUND

Growth properties of the prostate are regulated by a variety of hormones and growth factors. Benign prostatic hyperplasia (BPH) is characterized by abnormal epithelial and stromal proliferation. Varying androgen hormone levels in elderly men are correlated with abnormal proliferations of the prostate. Proteinase-activated receptor-2 (PAR2), a subtype of G-protein-coupled receptors, is known to induce multiple biological processes. It could also play a key role in the proliferation and metastasis of prostate cancer, but its effect on BPH pathogenesis is to a great extent unknown.

METHODS

Localization of PAR2 was determined both in pathologically altered and in normal prostate tissues by using immunohistochemical techniques. PAR2 activity was assessed by measuring changes in intracellular calcium [Ca(2+)](i) following stimulation of cultured stromal cells with a PAR2 agonist (trypsin) and a synthetic PAR2-activating peptide (AP). DHT-dependence of PAR2 expression in prostate cancer and prostatic stromal cell lines was examined with semi-quantitative and quantitative PCR. Cultured stromal cells (hPCPs) were stimulated with PAR2 AP and cell proliferation was determined through [(3)H]-thymidine incorporation.

RESULTS

In comparison to normal prostate, PAR2 expression was increased in BPH stroma. DHT induced a higher expression of PAR2 when sub-physiological DHT-levels were used. Higher levels of DHT produced reduced PAR2 expression. A mitogenic effect was induced by applying PAR2 AP to hPCPs-cells.

CONCLUSIONS

In conclusion, we found that PAR2 expression is hormone-dependent in prostatic stromal cells with a negative correlation and we consider it to be an important factor in mitogenesis in BPH.

Free radical theory of aging: implications in male infertility

This review examines the effect of mitochondrial generation of reactive oxygen species (ROS) and aging on human spermatozoa and seminal antioxidants. We discuss the effect of continuous ROS production on biomarkers of aging, such as germ cell telomeres and telomerase, lipofuscin, and amyloid. These markers may be responsible for telomere shortening and subsequent decrease in sperm count, decline in testosterone concentration, and decline in motility with aging. Excessive ROS can also damage mitochondrial deoxyribonucleic acid and sperm nuclear DNA, contributing to paternally transmitted diseases. ROS generation has a central role in the pathophysiology of age-related decrease in male fertility.

Arrested germ cell divisions in the ageing human testis

Arrested divisions represent a defective type of germ cell division. The cells are irreversibly arrested in a state marked by strongly condensed chromosomes, a dissolved nuclear envelope and a disturbed spindle apparatus. They finally die. The present ultrastructural study of the ageing human seminiferous epithelium is the first to describe such cells in the human testis. The cells usually lie in small groups and show intercellular bridges connecting them. The bridges lack a bridge-partitioning complex, a structure otherwise characteristic for bridges between dividing germ cells of a clone. Frequently, arrested divisions show signs of cytoplasmic disorganization and severe structural degradation. Centrioles, irregular microtubules, small membranous vesicles and granular electron-dense material are crowded within the circle of chromosomes. Some cells show numerous small vesicles and larger membranous structures distributed throughout the cytoplasm. The presence of arrested germ cell divisions in ageing men might be connected with local dysfunctions of the Sertoli cell barrier, which are known to appear focally in the ageing human seminiferous epithelium as well.

Serum androgen levels in men: impact of health status and age

OBJECTIVES

To investigate the impact of health status on androgen levels in men and to assess the age-related changes in androgen levels.

METHODS

Sera were obtained from 526 men (age 20 to 89 years) participating in a health screening project and 35 men selected according to the SENIEUR protocol, which excludes those with underlying disease. The health screening project participants were divided into two groups: healthy men (n = 133; group 1) and the remainder (n = 393; group 2). The total testosterone and sex hormone-binding globulin levels were quantified, and the amount of free testosterone (cfT) was calculated.

RESULTS

The lowest annual declines in androgen level were observed in group 3 (testosterone 0.2%; cfT 0.4%), followed by group 1 (testosterone 0.4%; cfT 0.8%) and group 2 (testosterone 0.8%; cfT 0.9%). Body mass index and levels of cholesterol, triglycerides, and glucose correlated negatively (P <0.01) with testosterone and cfT. Decade-adjusted reference values (mean +/- 2 standard deviations) for testosterone and cfT were defined. The proposed lower testosterone reference value declined gradually from 3.1 ng/mL (20 to 29 years) to 1.7 ng/mL (70 years or older).

CONCLUSIONS

In this cross-sectional study, serum androgens declined in aging men, and the extent of this decrease correlated with health status. A fixed, non-age-adjusted reference value does not adequately reflect this and might lead to a false diagnosis of androgen deficiency, particularly in elderly men. The clinical value of age-related reference values, however, needs to be determined in prospective studies.

A Darwinian-evolutionary concept of age-related diseases

Humans and animals are structurally designed as a compromise to guarantee optimal survival until the time of reproduction based on natural selection that is effective until that age. Modern conditions of life including improvement of hygiene, preventive and curative medicine as well as socio-economic and political developments have led to an increase of the mean life expectancy that allows ever larger proportions of the population to reach an age that is far beyond that of the reproductive phase. The concept of a Darwinian-evolutionary basis for the development of age-related diseases in principle postulates that genetic traits that are beneficial in younger years to allow for successful reproduction may become deleterious in the elderly, i.e. when selective pressure does not seem to be effective anymore. Examples for this mechanism of pleiotropic antagonism taken from the work of the Institute for Biomedical Aging Research in Innsbruck, Austria, include atherosclerosis, benign and malignant prostate hypertrophy, Alzheimer's disease and the reciprocal relationship between cellular senescence and cancer.

Age-related increase in mitochondrial superoxide generation in the testosterone-producing cells of Brown Norway rat testes: relationship to reduced steroidogenic function?

Aging in Brown Norway rats is accompanied by the reduced production of testosterone by the Leydig cells, the testicular cells responsible for synthesizing and secreting this essential steroid. As yet, the mechanism by which Leydig cell steroidogenesis is reduced is unknown. Herein we assess the production of mitochondrial reactive oxygen species by intact Leydig cells isolated from the testes of young and old rats. To this end, Leydig cells were incubated with lucigenin (bis-N-methylacridinium nitrate), a probe that enters cells, localizes to mitochondria, and yields a significant chemiluminescent response following its reaction with intramitochondrial superoxide. Leydig cells from old rats elicited significantly greater lucigenin-derived chemiluminescence (LDCL) than those from young rats. Electron microscopic stereological analysis revealed that the absolute volume of mitochondria in the old cells was reduced from that in the young. These results, taken together, suggest that there are age-related changes in the production of reactive oxygen species by the mitochondria of Leydig cells, with those of old Leydig cells producing significantly greater levels than those of young Leydig cells. The results are consistent with the proposal that mitochondrial-derived reactive oxygen may play a role in the irreversible decline in the ability of old Leydig cells to produce testosterone.

Diseases of aging

By definition, diseases of aging become clinically manifested in elderly patients. However, their pathogenetic basis has to be sought earlier in life. The general thread of this presentation relies on the concept of an evolutionary-Darwinian view of the development of age-related diseases. In essence, this concept states that we may have to "pay" for genetic traits that play a beneficial role earlier in life by the later development of diseases since there is no post-reproductive selective pressure that may have eliminated the potential late onset detrimental effects of such genes. Examples for this kind of trade-off are taken from diseases involving the immune system (infections), the endocrine system (andropause), the nervous system (Alzheimer's disease), the locomoter system (osteoporosis), the cardio-vascular system (atherosclerosis) and cancer.

Hormone replacement in the aging male?

The recent increase in the elderly population, current health trends, and awareness of age-related changes in the male endocrine system have led to discussions about the endocrine system being a "pacemaker" of male aging. Better prevention and treatment of "non-beneficial states of health" in aging men, such as generally decreased well-being and virility, increased visceral fat, osteopenia, atherosclerosis, and impaired cognitive function, is based on improved understanding of aging, particularly the significance of age-associated hormonal changes. Although not as dramatic as in women, men also show declining hormone serum concentrations with aging (Vermeulen and Kaufman, 1995). Because aging is associated with deleterious effects resembling the clinical signs of hypogonadism or states of subnormal hormone concentrations, the potential role of hormone supplementation in aging men paralleling hormone replacement therapy in postmenopausal women is the topic of discussion. The goal of hormone replacement would be to improve body composition and increase muscle strength and quality of life in men, thereby reducing mortality and morbidity. The findings so far support the need for long-term studies of hormonal supplementation in older males showing decreased hormone serum levels. Nevertheless, to date, such a use outside the context of a clinical trial is not justified.