Effect of aromatase inhibition on bone metabolism in elderly hypogonadal men

Male subclinical hypogonadism and late-onset hypergonadotrophic hypogonadism: mechanisms, endothelial function, and interplay between reproductive hormones, undercarboxylated osteocalcin, and endothelial dysfunction

BACKGROUND

Pathogenesis and endothelial function in subclinical hypogonadism (SCH) remain unclear. Undercarboxylated osteocalcin (ucOC) participates in atherosclerosis and reproduction. We explored the underlying mechanisms and interplay of endothelial dysfunction, unOC and reproductive hormones in SCH and primary late-onset hypogonadism (LOH).

METHODS

In the SCH, LOH, and healthy eugonadal male groups, we measured serum unOC, calculated luteinizing hormone/testosterone (LH/T), LH.T product, and estradiol/T (E/T) as indicators of impaired Leydig cells, androgen sensitivity index (ASI), and aromatase activity, respectively (LH set-point regulators), and assessed flow-mediated dilation of the brachial artery (FMD%), carotid-intima media thickness (CIMT), and aortic stiffness (AS).

RESULTS

↑LH/T, ↑ASI, ↓aromatase activity, normal T, follicle-stimulating hormone (FSH) and sex hormone-binding globulin (SHBG) levels, ↑unOC, and enhanced atherosclerotic markers (↓FMD%, ↑CIMT, ↑AS) are characteristics of SCH. Testosterone was positively correlated with FMD% in SCH. The independent predictors were: SHBG and LH for FMD% and CIMT, respectively, and LH/T, ucOC, FSH, estradiol, and E/T ratio for AS in the LOH group; and LH for FMD% & AS and LH and LH/T for CIMT in all study subjects.

CONCLUSIONS

SCH is a distinct clinical entity characterized by impaired androgen sensitivity and aromatase activity, compensatory elevated unOC, endothelial dysfunction, and anti-atherogenic role of testosterone.

Role of Aromatase Inhibitors in Managing Hypogonadism in Adult Males Related to Obesity and Aging: A Systematic Review and Meta-Analysis

No meta-analysis is available which has analysed the role of aromatase inhibitors (AIs) in hypogonadism in adult males related to obesity and aging. This meta-analysis intended to address this knowledge gap. Electronic databases were searched for studies involving adult males with hypogonadism. The primary outcomes were changes in total testosterone (TT). Secondary outcomes were alterations in oestradiol, luteinizing hormone (LH), and side-effect profile. From initially screened 177 articles, data from three randomised controlled trials(RCTs) (118 patients) and three uncontrolled studies(52 patients) were analysed. AIs were associated with significantly greater improvement in TT after three months [mean difference (MD) 7.08 nmol/L (95% Confidence Interval (CI): 5.92-8.24); P < 0.01; I2 = 0%], six months [MD 6.61 nmol/L (95% CI: 5.30-7.93); P < 0.01] and 12 months [MD 5.20 nmol/L (95% CI: 3.78-6.62); P < 0.01] therapy. AIs were associated with greater reduction in oestradiol after three months [MD -3.07 pmol/L (95% CI: -5.27- -0.87); P < 0.01; I2 = 40%], six months [MD -5.39 pmol/L (95% CI: -7.18- -3.60); P < 0.01] and 12 months [MD -8.3 pmol/L (95% CI: -15.97- -0.63); P = 0.03] therapy. AIs were associated with greater increase in LH after three months [MD 1.79 IU/L (95% CI: 0.77-2.81); P < 0.01; I2 = 0%], six months [MD 2.20 IU/L (95% CI: 0.29 - 4.11); P = 0.02] and 12 months [MD 1.70 IU/L (95% CI: 0.28-3.12); P = 0.02] therapy. Occurrence of treatment-emergent adverse events[Risk ratio (RR) 1.48 (95% CI: 0.47-4.66); P = 0.45; I2 = 0%] and severe adverse events[RR 2.48 (95% CI: 0.42-14.66); P = 0.32; I2 = 0%] were similar among AIs and controls. Following six-month treatment, AIs were associated with significantly lower bone mineral density (BMD) at lumbar-spine [MD -0.04 gm/cm2 (95% CI: -0.08- -0.01); P = 0.03], but not total hip [MD 0.01 gm/cm2 (95% CI: -0.02-0.04); P = 0.55] and femoral neck [MD 0.02 gm/cm2 (95% CI: -0.01-0.05); P = 0.12] compared to controls. This meta-analysis highlights the good efficacy of AIs in improving TT over 3-12 months of use. Adverse impact on spine bone density remains a concern in obese ageing males and warrants further evaluation.

Aromatase Inhibitors Plus Weight Loss Improves the Hormonal Profile of Obese Hypogonadal Men Without Causing Major Side Effects

Objective: In obese men, the increased expression of the aromatase enzyme in adipose tissue leads to high conversion of androgens to estrogens contributing to hypogonadotropic hypogonadism (HHG). Our objective is to evaluate efficacy and safety of weight loss (WL) plus aromatase inhibitor (AI) therapy in severely obese men with HHG. We hypothesize that AI+WL will be more effective as compared to WL alone in improving the hormonal profile, thus muscle strength and symptoms of HHG (primary outcomes), with no significant adverse effects on lean mass, metabolic profile, and bone mineral density (secondary outcomes). Design: Randomized double-blind placebo-controlled pilot trial. Methods: Twenty-three obese men (BMI≥35 kg/m²), 35-65 years old, were randomized to weight loss (diet and exercise) plus either anastrozole (AI+WL, n = 12) at 1 mg daily or placebo (PBO+WL, n = 11) for 6 months. Inclusion criteria: total testosterone <300 ng/mL (average of 2 measurements), estradiol≥10.9 pg/ml, LH <9 IU/l. Symptoms of hypogonadism by questionnaires; muscle strength by Biodex dynamometer; body composition and bone mineral density by dual-energy X-ray absorptiometry; bone microarchitecture and finite element analysis by high resolution peripheral quantitative-computed tomography. Results: After 6 months of therapy, AI+WL group had higher testosterone (p = 0.003) and lower estradiol (p = 0.001) compared to PBO+WL. Changes in symptoms and muscle strength did not differ between groups. AI+WL resulted in higher fat mass loss than PBO+WL (p = 0.04) without differences in changes in lean mass. Total and LDL cholesterol reduced more in the PBO+WL group compared to AI+WL (p = 0.03 for both), who experienced a minimal increase with unlikely meaningful clinical impact. Tibial trabecular bone area decreased more in PBO+WL than AI+WL group for which it remained stable (p = 0.03). Conclusions:Although AI+WL is effective in reversing the hormonal profile of HHG in severely obese men without causing major side effects, it does not lead to greater improvements in muscle strength and symptoms of hypogonadism compared to WL alone. Clinical Trial Registration: www.ClinicalTrials.gov, identifier: NCT02959853.

Diagnosis and Treatment of Testosterone Deficiency: Recommendations From the Fourth International Consultation for Sexual Medicine (ICSM 2015)

INTRODUCTION

Testosterone deficiency (TD), also known as hypogonadism, is a condition affecting a substantial proportion of men as they age. The diagnosis and management of TD can be challenging and clinicians should be aware of the current literature on this condition.

AIM

To review the available literature concerning the diagnosis and management of TD and to provide clinically relevant recommendations from the Fourth International Consultation for Sexual Medicine (ICSM) meeting.

METHODS

A literature search was performed using the PubMed database for English-language original and review articles published or e-published up to January 2016.

MAIN OUTCOME MEASURES

Levels of evidence (LoEs) and grades of recommendations are provided based on a thorough analysis of the literature and committee consensus.

RESULTS

Recommendations were given for 12 categories of TD: definition, clinical diagnosis, routine measurement, screening questionnaires, laboratory diagnosis, threshold levels for the biochemical diagnosis of TD, prostate cancer, cardiovascular disease, fertility, testosterone (T) formulations, alternatives to T therapy, and adverse events and monitoring. A total of 42 recommendations were made: of these, 16 were unchanged from the Third ICSM and 26 new recommendations were made during this Fourth ICSM. Most of these recommendations were supported by LoEs 2 and 3. Several key new recommendations include the following: (i) the clinical manifestations of TD occur as a result of decreased serum androgen concentrations or activity, regardless of whether there is an identified underlying etiology [LoE = 1, Grade = A]; (ii) symptomatic men with total T levels lower than 12 nmol/L or 350 ng/dL should be treated with T therapy [LoE = 1, Grade = C]; (iii) a trial of T therapy in symptomatic men with total T levels higher than 12 nmol/L or 350 ng/dL can be considered based on clinical presentation [LoE = 3, Grade = C]; (iv) there is no compelling evidence that T treatment increases the risk of developing prostate cancer or that its use is associated with prostate cancer progression [LoE = 1, Grade = C]; and (v) the weight of evidence indicates that T therapy is not associated with increased cardiovascular risk [LoE = 2, Grade = B].

CONCLUSION

TD is an important condition that can profoundly affect the sexual health of men. We provide guidance regarding its diagnosis and management. Men with TD who receive treatment often experience resolution or improvement in their sexual symptoms and non-sexual health benefits.

Emerging medication for the treatment of male hypogonadism

INTRODUCTION

Male hypogonadism is characterized by inadequate production of Testosterone (T) (hypoandrogenism) and deficiencies in spermatogenesis. The main treatment of male hypogonadism is T replacement therapy (TRT), but for some of the patients, alternative drugs may be more suitable.

AREAS COVERED

The available literature of T and alternative treatments for male hypogonadism are discussed.

EXPERT OPINION

Transdermal application of T gels are the most commonly used route of T administration. Some oral T formulations are either associated with hepatic toxicity (i.e. methyltestosterone) or short half-lives that require multiple doses per day (i.e. oral testosterone undecanoate). Short acting, injectable T formulations are also available. If the patient prefers not to use daily drugs or short acting injectable formulations, depot formulations such as injectable testosterone undecanoate (TU) may be a good alternative. If the patient has hypogonadotropic hypogonadism and desires fertility or if he is adolescent, instead of TRT, gonadotropins can be started to stimulate testicular growth and spermatogenesis. In obese patients or for the patients having high risks for TRT, off label aromatase inhibitors (AI) and clomiphene citrate (CC), may be considered to stimulate LH, FSH and T levels. In patients with high prostate disease risk, selective androgen receptor modulators may be an alternative treatment but these latter treatments have not had high level evidence.

Treatment of Hypogonadism: Current and Future Therapies

The treatment of hypogonadism in men is of great interest to both patients and providers. There are a number of testosterone formulations currently available and several additional formulations under development. In addition, there are some lesser-used alternative therapies for the management of male hypogonadism, which may have advantages for certain patient groups. The future of hypogonadism therapy may lie in the development of selective androgen receptor modulators that allow the benefits of androgens whilst minimizing unwanted side effects.

Estrogens and Androgens in Skeletal Physiology and Pathophysiology

Estrogens and androgens influence the growth and maintenance of the mammalian skeleton and are responsible for its sexual dimorphism. Estrogen deficiency at menopause or loss of both estrogens and androgens in elderly men contribute to the development of osteoporosis, one of the most common and impactful metabolic diseases of old age. In the last 20 years, basic and clinical research advances, genetic insights from humans and rodents, and newer imaging technologies have changed considerably the landscape of our understanding of bone biology as well as the relationship between sex steroids and the physiology and pathophysiology of bone metabolism. Together with the appreciation of the side effects of estrogen-related therapies on breast cancer and cardiovascular diseases, these advances have also drastically altered the treatment of osteoporosis. In this article, we provide a comprehensive review of the molecular and cellular mechanisms of action of estrogens and androgens on bone, their influences on skeletal homeostasis during growth and adulthood, the pathogenetic mechanisms of the adverse effects of their deficiency on the female and male skeleton, as well as the role of natural and synthetic estrogenic or androgenic compounds in the pharmacotherapy of osteoporosis. We highlight latest advances on the crosstalk between hormonal and mechanical signals, the relevance of the antioxidant properties of estrogens and androgens, the difference of their cellular targets in different bone envelopes, the role of estrogen deficiency in male osteoporosis, and the contribution of estrogen or androgen deficiency to the monomorphic effects of aging on skeletal involution.

Adult-onset hypogonadism: evaluation and role of testosterone replacement therapy

Testosterone deficiency (TD) has become a growing concern in the field of men’s sexual health, with an increasing number of men presenting for evaluation of this condition. Given the increasing demand for testosterone replacement therapy (TRT), a panel of experts met in August of 2015 to discuss the treatment of men who present for evaluation in the setting of low or normal gonadotropin levels and the associated signs and symptoms of hypogonadism. This constellation of factors can be associated with elements of both primary and secondary hypogonadism. Because this syndrome commonly occurs in men who are middle-aged and older, it was termed adult-onset hypogonadism (AOH). AOH can be defined by the following elements: low levels of testosterone, associated signs and symptoms of hypogonadism, and low or normal gonadotropin levels. Although there are significant benefits of TRT for patients with AOH, candidates also need to understand the potential risks. Patients undergoing TRT will need to be monitored regularly because there are potential complications that can develop with long-term use. This review is aimed at providing a deeper understanding of AOH, discussing the benefits and risks of TRT, and outlining each modality of TRT in use for AOH.

A concise review of testosterone and bone health

Osteoporosis is a condition causing significant morbidity and mortality in the elderly population worldwide. Age-related testosterone deficiency is the most important factor of bone loss in elderly men. Androgen can influence bone health by binding to androgen receptors directly or to estrogen receptors (ERs) indirectly via aromatization to estrogen. This review summarized the direct and indirect effects of androgens on bone derived from in vitro, in vivo, and human studies. Cellular studies showed that androgen stimulated the proliferation of preosteoblasts and differentiation of osteoblasts. The converted estrogen suppressed osteoclast formation and resorption activity by blocking the receptor activator of nuclear factor k-B ligand pathway. In animal studies, activation of androgen and ERα, but not ERβ, was shown to be important in acquisition and maintenance of bone mass. Human epidemiological studies demonstrated a significant relationship between estrogen and testosterone in bone mineral density and fracture risk, but the relative significance between the two remained debatable. Human experimental studies showed that estrogen was needed in suppressing bone resorption, but both androgen and estrogen were indispensable for bone formation. As a conclusion, maintaining optimal level of androgen is essential in preventing osteoporosis and its complications in elderly men.

The Role of Estrogen Modulators in Male Hypogonadism and Infertility

Estradiol, normally considered a female hormone, appears to play a significant role in men in a variety of physiologic functions, such as bone metabolism, cardiovascular health, and testicular function. As such, estradiol has been targeted by male reproductive and sexual medicine specialists to help treat conditions such as infertility and hypogonadism. The compounds that modulate estradiol levels in these clinical conditions are referred to as selective estrogen receptor modulators (SERMs) and aromatase inhibitors (AIs). In a certain subset of infertile men, particularly those with hypogonadism, or those who have a low serum testosterone to estradiol ratio, there is some evidence suggesting that SERMs and AIs can reverse the low serum testosterone levels or the testosterone to estradiol imbalance and occasionally improve any associated infertile or subfertile state. This review focuses on the role these SERMs and AIs play in the aforementioned reproductive conditions.

Testosterone inhibits expression of lipogenic genes in visceral fat by an estrogen-dependent mechanism

The influence of the aromatase enzyme on the chronic fat-sparing effects of testosterone requires further elucidation. Our purpose was to determine whether chronic anastrozole (AN, an aromatase inhibitor) treatment alters testosterone-mediated lipolytic/lipogenic gene expression in visceral fat. Ten-month-old Fischer 344 rats (n = 6/group) were subjected to sham surgery (SHAM), orchiectomy (ORX), ORX + treatment with testosterone enanthate (TEST, 7.0 mg/wk), or ORX + TEST + AN (0.5 mg/day), with drug treatment beginning 14 days postsurgery. At day 42, ORX animals exhibited nearly undetectable serum testosterone and 29% higher retroperitoneal fat mass than SHAM animals (P < 0.001). TEST produced a ∼380-415% higher serum testosterone than SHAM (P < 0.001) and completely prevented ORX-induced visceral fat gain (P < 0.001). Retroperitoneal fat was 21% and 16% lower in ORX + TEST than SHAM (P < 0.001) and ORX + TEST + AN (P = 0.007) animals, while serum estradiol (E2) was 62% (P = 0.024) and 87% (P = 0.010) higher, respectively. ORX stimulated lipogenic-related gene expression in visceral fat, demonstrated by ∼84-154% higher sterol regulatory element-binding protein-1 (SREBP-1, P = 0.023), fatty acid synthase (P = 0.01), and LPL (P < 0.001) mRNA than SHAM animals, effects that were completely prevented in ORX + TEST animals (P < 0.01 vs. ORX for all). Fatty acid synthase (P = 0.061, trend) and LPL (P = 0.043) mRNA levels were lower in ORX + TEST + AN than ORX animals and not different from SHAM animals but remained higher than in ORX + TEST animals (P < 0.05). In contrast, the ORX-induced elevation in SREBP-1 mRNA was not prevented by TEST + AN, with SREBP-1 expression remaining ∼117-171% higher than in SHAM and ORX + TEST animals (P < 0.01). Across groups, visceral fat mass and lipogenic-related gene expression were negatively associated with serum testosterone, but not E2 Aromatase inhibition constrains testosterone-induced visceral fat loss and the downregulation of key lipogenic genes at the mRNA level, indicating that E2 influences the visceral fat-sparing effects of testosterone.

Challenges in Testosterone Measurement, Data Interpretation, and Methodological Appraisal of Interventional Trials

INTRODUCTION

Male hypogonadism is a common condition, with an increasing body of literature on diagnosis, implications, and management. Given the significant variability in testosterone (T) from a physiologic and assay perspective, a thorough understanding of factors affecting T values and study methodology is essential to interpret reported study outcomes appropriately. However, despite the large number of publications on T, there are no reference materials consolidating all relevant and potentially confounding factors necessary to interpret T studies appropriately.

AIMS

To create a resource document that reviews sources of T variability, free vs total T, assay techniques and questionnaires, and study methodology relevant to interpreting outcomes.

METHODS

A PubMed search was performed of all the T literature published on T variability, assay techniques, and T-specific questionnaires. Results were summarized in the context of their impact on interpreting T literature outcomes and methodology.

MAIN OUTCOME MEASURES

Effect of various factors on T variability and their relevance to study methodology and outcomes.

RESULTS

Several factors affect measured T levels, including aging, circadian rhythms, geography, genetics, lifestyle choices, comorbid conditions, and intraindividual daily variability. The utility of free T over total T is debatable and must be compared using appropriate threshold levels. Among various assay techniques, mass spectrometry and equilibrium dialysis are gold standards. Calculated empirical estimates of free T also are commonly used and accepted. Hypogonadism-specific questionnaires have limited utility in screening for hypogonadism, and their role as objective end points for quantifying symptoms remains unclear. Numerous aspects of study methodology can directly or indirectly affect reported outcomes, including design (randomized, prospective, retrospective), duration, populations studied (age, comorbid conditions), low T threshold, therapeutic agent used, objective measurements and end points selected, and statistical interpretation.

CONCLUSION

Critical appraisal of the T literature requires an understanding of numerous factors resulting in T variability, study design and methodology, and limitations of assay techniques and objective measurement scales.

Effects of Transdermal Testosterone Gel or an Aromatase Inhibitor on Prostate Volume in Older Men

CONTEXT

T replacement is being increasingly offered to older men with age-related low T; hence, monitoring prostate health is important during T therapy. Data suggest that estrogens have an independent effect on the prostate and some effects of T on the prostate might be mediated via its aromatization to estradiol. Although some studies have assessed the effects of T replacement on prostate volume, the differential effects of T and estradiol have not been delineated.

OBJECTIVE

The objective of the study was to investigate the relative effects of T and estradiol on prostate volume in older men with low T.

PARTICIPANTS

Thirty-one men, 65 years old or older with total T less than 350 ng/dL (measured by mass spectrometry) participated in the study.

INTERVENTION

The intervention included randomization to 5 g transdermal T gel (TT), 1 mg oral aromatase inhibitor (AI), or placebo daily for 12 months.

MAIN OUTCOME MEASURES

The primary outcome was prostate volume measured by transrectal ultrasound at baseline and 12 months. Secondary outcomes included prostate-specific antigen levels and lower urinary tract symptoms score.

RESULTS

Serum T levels increased in both intervention groups; estradiol levels increased in the TT group, whereas it decreased in the AI group. At 12 months, prostate volume significantly increased (4.5 ± 1.76 cc, P < .05) only in the TT group. Increase in prostate-specific antigen levels were seen in both intervention groups at 6 months (P < .01 and P < .001). The lower urinary tract symptoms score increased only in the TT group (P < .05).

CONCLUSIONS

The tropic effects of T on the prostate are mediated via its aromatization to estradiol. Administration of AI for 12 months to older men was not detrimental to the prostate.

Alternative treatment modalities for the hypogonadal patient

Testosterone (T) deficiency syndrome (TDS) is a prevalent condition, commonly managed with exogenous T. Despite an abundance of T formulations, alternative treatments are often sought for various reasons. To evaluate outcomes of alternative therapies, a PubMed search was performed of all publications that included men with TDS from 1990 through October 2013, with results summarized. Proposed mechanisms of action were also reviewed to provide a pathophysiologic basis for reported outcomes. Nonpharmacologic therapies that increase endogenous T are weight loss, exercise, and varicocelectomy, while medications used off-label include aromatase inhibitors, human chorionic gonadotropin, and selective estrogen receptor modulators. All reported therapies increase T, while changes in estradiol and adverse events vary by therapeutic class. Although limited data preclude direct comparisons between therapies, exercise and weight loss alone or in combination with medications may be considered first line. The role for surgical therapy in TDS remains undefined and requires further study.

Sex steroid actions in male bone

Sex steroids are chief regulators of gender differences in the skeleton, and male gender is one of the strongest protective factors against osteoporotic fractures. This advantage in bone strength relies mainly on greater cortical bone expansion during pubertal peak bone mass acquisition and superior skeletal maintenance during aging. During both these phases, estrogens acting via estrogen receptor-α in osteoblast lineage cells are crucial for male cortical and trabecular bone, as evident from conditional genetic mouse models, epidemiological studies, rare genetic conditions, genome-wide meta-analyses, and recent interventional trials. Genetic mouse models have also demonstrated a direct role for androgens independent of aromatization on trabecular bone via the androgen receptor in osteoblasts and osteocytes, although the target cell for their key effects on periosteal bone formation remains elusive. Low serum estradiol predicts incident fractures, but the highest risk occurs in men with additionally low T and high SHBG. Still, the possible clinical utility of serum sex steroids for fracture prediction is unknown. It is likely that sex steroid actions on male bone metabolism rely also on extraskeletal mechanisms and cross talk with other signaling pathways. We propose that estrogens influence fracture risk in aging men via direct effects on bone, whereas androgens exert an additional antifracture effect mainly via extraskeletal parameters such as muscle mass and propensity to fall. Given the demographic trends of increased longevity and consequent rise of osteoporosis, an increased understanding of how sex steroids influence male bone health remains a high research priority.

Influence of aromatase inhibition on the bone-protective effects of testosterone

The influence of the aromatase enzyme in androgen-induced bone maintenance after skeletal maturity remains somewhat unclear. Our purpose was to determine whether aromatase activity is essential to androgen-induced bone maintenance. Ten-month-old male Fisher 344 rats (n = 73) were randomly assigned to receive Sham surgery, orchiectomy (ORX), ORX + anastrozole (AN; aromatase inhibitor), ORX + testosterone-enanthate (TE, 7.0 mg/wk), ORX + TE + AN, ORX + trenbolone-enanthate (TREN; nonaromatizable, nonestrogenic testosterone analogue; 1.0 mg/wk), or ORX + TREN + AN. ORX animals exhibited histomorphometric indices of high-turnover osteopenia and reduced cancellous bone volume compared with Shams. Both TE and TREN administration suppressed cancellous bone turnover similarly and fully prevented ORX-induced cancellous bone loss. TE- and TREN-treated animals also exhibited greater femoral neck shear strength than ORX animals. AN co-administration slightly inhibited the suppression of bone resorption in TE-treated animals but did not alter TE-induced suppression of bone formation or the osteogenic effects of this androgen. In TREN-treated animals, AN co-administration produced no discernible effects on cancellous bone turnover or bone volume. ORX animals also exhibited reduced levator ani/bulbocavernosus (LABC) muscle mass and elevated visceral adiposity. In contrast, TE and TREN produced potent myotrophic effects in the LABC muscle and maintained fat mass at the level of Shams. AN co-administration did not alter androgen-induced effects on muscle or fat. In conclusion, androgens are able to induce direct effects on musculoskeletal and adipose tissue, independent of aromatase activity.

Aromatase activity and bone loss in men

Aromatase is a specific component of the cytochrome P450 enzyme system responsible for the transformation of androgen precursors into estrogens. This enzyme is encoded by the CYP19A1 gene located at chromosome 15q21.2, that is, expressed in ovary and testis, but also in many extraglandular sites such as the placenta, brain, adipose tissue, and bone. The activity of aromatase regulates the concentrations of estrogens with endocrine, paracrine, and autocrine effects on target issues including bone. Importantly, extraglandular aromatization of circulating androgen precursors is the major source of estrogen in men. Clinical and experimental evidences clearly indicate that aromatase activity and estrogen production are necessary for longitudinal bone growth, the attainment of peak bone mass, pubertal growth spurt, epiphyseal closure, and normal bone remodeling in young individuals. Moreover, with aging, individual differences in aromatase activity may significantly affect bone loss and fracture risk in men.

Aromatase inhibitors in men: effects and therapeutic options

Aromatase inhibitors effectively delay epiphysial maturation in boys and improve testosterone levels in adult men Therefore, aromatase inhibitors may be used to increase adult height in boys with gonadotropin-independent precocious puberty, idiopathic short stature and constitutional delay of puberty. Long-term efficacy and safety of the use of aromatase inhibitors has not yet been established in males, however, and their routine use is therefore not yet recommended.

Testosterone and the male skeleton: a dual mode of action

Testosterone is an important hormone for both bone gain and maintenance in men. Hypogonadal men have accelerated bone turnover and increased fracture risk. In these men, administration of testosterone inhibits bone resorption and maintains bone mass. Testosterone, however, is converted into estradiol via aromatization in many tissues including male bone. The importance of estrogen receptor alpha activation as well of aromatization of androgens into estrogens was highlighted by a number of cases of men suffering from an inactivating mutation in the estrogen receptor alpha or in the aromatase enzyme. All these men typically had low bone mass, high bone turnover and open epiphyses. In line with these findings, cohort studies have confirmed that estradiol contributes to the maintenance of bone mass after reaching peak bone mass, with an association between estradiol and fractures in elderly men. Recent studies in knock-out mice have increased our understanding of the role of androgens and estrogens in different bone compartments. Estrogen receptor activation, but not androgen receptor activation, is involved in the regulation of male longitudinal appendicular skeletal growth in mice. Both the androgen and the estrogen receptor can independently mediate the cancellous bone-sparing effects of sex steroids in male mice. Selective KO studies of the androgen receptor in osteoblasts in male mice suggest that the osteoblast in the target cell for androgen receptor mediated maintenance of trabecular bone volume and coordination of bone matrix synthesis and mineralization. Taken together, both human and animal studies suggest that testosterone has a dual mode of action on different bone surfaces with involvement of both the androgen and estrogen receptor.

Aromatase activity and bone loss

Aromatase is a specific component of the cytochrome P450 enzyme system that is responsible for the transformation of C19 androgen precursors into C18 estrogenic compounds. This enzyme is encoded by the CYP19A1 gene located at chromosome 15q21.2, that is expressed in ovary and testis not only but also in many extraglandular sites such as the placenta, brain, adipose tissue, and bone. The regulation of the level and activity of aromatase determines the levels of estrogens that have endocrine, paracrine, and autocrine effects on target issues including bone. Importantly, extraglandular aromatization of circulating androgen precursors is the major source of estrogen not only in men (since only 15% of circulating estradiol is released directly by the testis) but also in women after the menopause. Several lines of clinical and experimental evidence now clearly indicate that aromatase activity and estrogen production are necessary for longitudinal bone growth, attainment of peak bone mass, the pubertal growth spurt, epiphyseal closure, and normal bone remodeling in young individuals. Moreover, with aging, individual differences in aromatase activity and thus in estrogen levels may significantly affect bone loss and fracture risk in both genders.

From estrogen-centric to aging and oxidative stress: a revised perspective of the pathogenesis of osteoporosis

Estrogen deficiency has been considered the seminal mechanism of osteoporosis in both women and men, but epidemiological evidence in humans and recent mechanistic studies in rodents indicate that aging and the associated increase in reactive oxygen species (ROS) are the proximal culprits. ROS greatly influence the generation and survival of osteoclasts, osteoblasts, and osteocytes. Moreover, oxidative defense by the FoxO transcription factors is indispensable for skeletal homeostasis at any age. Loss of estrogens or androgens decreases defense against oxidative stress in bone, and this accounts for the increased bone resorption associated with the acute loss of these hormones. ROS-activated FoxOs in early mesenchymal progenitors also divert ss-catenin away from Wnt signaling, leading to decreased osteoblastogenesis. This latter mechanism may be implicated in the pathogenesis of type 1 and 2 diabetes and ROS-mediated adverse effects of diabetes on bone formation. Attenuation of Wnt signaling by the activation of peroxisome proliferator-activated receptor gamma by ligands generated from lipid oxidation also contributes to the age-dependent decrease in bone formation, suggesting a mechanistic explanation for the link between atherosclerosis and osteoporosis. Additionally, increased glucocorticoid production and sensitivity with advancing age decrease skeletal hydration and thereby increase skeletal fragility by attenuating the volume of the bone vasculature and interstitial fluid. This emerging evidence provides a paradigm shift from the "estrogen-centric" account of the pathogenesis of involutional osteoporosis to one in which age-related mechanisms intrinsic to bone and oxidative stress are protagonists and age-related changes in other organs and tissues, such as ovaries, accentuate them.

Tissue selectivity and potential clinical applications of trenbolone (17beta-hydroxyestra-4,9,11-trien-3-one): A potent anabolic steroid with reduced androgenic and estrogenic activity

Recently, the development of selective androgen receptor modulators (SARMs) has been suggested as a means of combating the deleterious catabolic effects of hypogonadism, especially in skeletal muscle and bone, without inducing the undesirable androgenic effects (e.g., prostate enlargement and polycythemia) associated with testosterone administration. 17beta-Hydroxyestra-4,9,11-trien-3-one (trenbolone; 17beta-TBOH), a synthetic analog of testosterone, may be capable of inducing SARM-like effects as it binds to androgen receptors (ARs) with approximately three times the affinity of testosterone and has been shown to augment skeletal muscle mass and bone growth and reduce adiposity in a variety of mammalian species. In addition to its direct actions through ARs, 17beta-TBOH may also exert anabolic effects by altering the action of endogenous growth factors or inhibiting the action of glucocorticoids. Compared to testosterone, 17beta-TBOH appears to induce less growth in androgen-sensitive organs which highly express the 5alpha reductase enzyme (e.g., prostate tissue and accessory sex organs). The reduced androgenic effects result from the fact that 17beta-TBOH is metabolized to less potent androgens in vivo; while testosterone undergoes tissue-specific biotransformation to more potent steroids, dihydrotestosterone and 17beta-estradiol, via the 5alpha-reductase and aromatase enzymes, respectively. Thus the metabolism of 17beta-TBOH provides a basis for future research evaluating its safety and efficacy as a means of combating muscle and bone wasting conditions, obesity, and/or androgen insensitivity syndromes in humans, similar to that of other SARMs which are currently in development.

Effects of aromatase inhibition on bone mineral density and bone turnover in older men with low testosterone levels

CONTEXT

Aging is associated with declining gonadal steroid production, low bone mineral density (BMD), and fragility fractures. The efficacy and safety of testosterone replacement in older men remains uncertain.

OBJECTIVE

The objective of the study was to assess the effects of aromatase inhibition on BMD in older men with low testosterone levels.

DESIGN AND SETTING

This was a 1-yr, double-blind, randomized, placebo-controlled trial that was conducted at a tertiary care academic center in Boston, MA.

PARTICIPANTS

Participants included 69 men aged 60+ yr with borderline or low testosterone levels and hypogonadal symptoms.

INTERVENTION

Intervention included 1 mg anastrozole daily or placebo.

MAIN OUTCOME MEASURES

Changes in gonadal steroid hormone levels, BMD, and bone turnover markers were measured.

RESULTS

Mean serum testosterone increased from 319 +/- 93 ng/dl at baseline to 524+/-139 ng/dl at month 3 (P < 0.0001) and declined slightly to 474 +/- 145 ng/dl by 1 yr. Estradiol levels decreased from 15 +/- 4 pg/ml at baseline to 12 +/- 4 pg/ml at month 3 and then remained stable (P < 0.0001). Posterior-anterior (PA) spine BMD decreased in the anastrozole group as compared with placebo (P = 0.0014). In the anastrozole group, PA spine BMD decreased from 1.121 +/- 0.141 g/cm(2) to 1.102 +/- 0.138 g/cm(2), whereas in the placebo group, PA spine BMD increased from 1.180 +/- 0.145 g/cm(2) to 1.189 +/- 0.146 g/cm(2). Qualitatively similar, but not statistically significant, changes occurred at the other sites. Bone turnover markers were not affected by anastrozole therapy.

CONCLUSIONS

In older men, aromatase inhibition increases testosterone levels, decreases estradiol levels, and appears to decrease BMD. Aromatase inhibition does not improve skeletal health in aging men with low or low normal testosterone levels.

Safety and efficacy of testosterone gel in the treatment of male hypogonadism

Transdermal testosterone gels were first introduced in the US in 2000. Since then, they have emerged as a favorable mode of testosterone substitution. Serum testosterone levels reach a steady-state in the first 24 hours of application and remain in the normal range for the duration of the application. This pharmacokinetic profile is comparable to that of testosterone patch but superior to injectable testosterone esters that are associated with peaks and troughs with each dose. Testosterone gels are as efficacious as patches and injectable forms in their effects on sexual function and mood. Anticipated increases in prostate-specific antigen with testosterone therapy are not significantly different with testosterone gels, and the risk of polycythemia is lower than injectable modalities. Application site reactions, a major drawback of testosterone patches, occur less frequently with testosterone gels. However, inter-personal transfer is a concern if appropriate precautions are not taken. Superior tolerability and dose flexibility make testosterone gel highly desirable over other modalities of testosterone replacement. Androgel and Testim, the two currently available testosterone gel products in the US, have certain brand-specific properties that clinicians may consider prior to prescribing.

Indirect androgen doping by oestrogen blockade in sports

Androgens can increase muscular mass and strength and remain the most frequently abused and widely available drugs used in sports doping. Banning the administration of natural or synthetic androgens has led to a variety of strategies to circumvent the ban of the most effective ergogenic agents for power sports. Among these, a variety of indirect androgen doping strategies aiming to produce a sustained rise in endogenous testosterone have been utilized. These include oestrogen blockade by drugs that act as oestrogen receptor antagonists (antioestrogen) or aromatase inhibitors. The physiological and pharmacological basis for the effects of oestrogen blockade in men, but not women, are reviewed.

Therapeutic uses of aromatase inhibitors in men

PURPOSE OF REVIEW

In men estrogens are important for achieving and maintaining bone mass, epiphysial maturation and feedback on gonadotrophin secretion. Potent aromatase inhibitors offer a convenient way to suppress estrogen production in men. This review aims to present an overview of the potential indications for aromatase inhibitors in men and to discuss results of clinical trials.

RECENT FINDINGS

Aromatase inhibitors are particularly useful to delay epiphysial maturation and increase predicted adult height in boys with pubertas praecox, idiopathic short stature and constitutional delay of puberty. In older men with late-onset hypogonadism aromatase inhibitors improve plasma testosterone levels but evidence for long-term benefit is presently lacking. Preliminary evidence shows no detrimental effects of aromatase inhibition on bone metabolism in men.

SUMMARY

Aromatase inhibitors effectively delay epiphysial maturation in boys and improve testosterone levels in adult men and may be used to increase adult height in boys with pubertas praecox, idiopathic short stature and constitutional delay of puberty. Long-term efficacy and safety is not established in adult men and their use in older men with late-onset hypogonadism is therefore not yet recommended.

Letrozole Versus Testosterone. A Single-Center Pilot Study of HIV-Infected Men Who Have Sex with Men on Highly Active Anti-Retroviral Therapy (HAART) with Hypoactive Sexual Desire Disorder and Raised Estradiol Levels

INTRODUCTION

Since the advent of Highly Active Anti-Retroviral Therapy (HAART), men with HIV experience good quality of life and expect to have normal sexual function. However, it appears that men infected with HIV commonly complain of sexual problems. There is evidence that men on HAART develop low sexual desire that is associated with raised estradiol levels. It has been postulated that abnormal metabolism seen in this group of men increases the aromatization of testosterone to estradiol. We hypothesized that letrozole, an aromatase inhibitor that inhibits the conversion of testosterone to estradiol, would be beneficial in these men.

AIM

The aim of this study was to compare the effects of testosterone vs. an aromatase inhibitor, letrazole, in HIV-infected men with raised estradiol and low sexual desire.

METHODS

Thirteen men who have sex with men on HAART with low sexual desire as well as raised estradiol levels (>120 pmol/L) were randomly allocated to receive either parenteral testosterone (Sustanon 250 intramuscular injection) (N = 6) or letrozole 2.5 mg orally daily (N = 7) for 6 weeks.

MAIN OUTCOME MEASURES

Sex steroid hormone assays, sex hormone-binding globulin, virological, hematological, and biochemical parameters were measured before and after treatment. Each subject was given the Spector Sexual Desire Inventory and the Depression/Anxiety Stress Scale before and immediately after treatment. Subjects were also asked to estimate the number of actual sexual acts before and after treatment. Results. Inventory data showed a rise in dyadic desire in both treatment arms. Mean actual sexual acts rose from 0.33 to 1.5 in the testosterone group and from 0.43 to 1.29 for the letrozole group. Luteinizing hormone increased in seven of seven men on letrozole. Serum testosterone increased in seven of seven men on letrozole. There were no adverse events from either medication.

CONCLUSION

Letrozole may be useful in the management of men on HAART who have low sexual desire.