Pharmacogenetics of testosterone replacement therapy

Recommendations on the diagnosis, treatment and monitoring of testosterone deficiency in men

The relative proportional increase of the elderly population within many countries will become one of the most significant social transformations of the twenty-first century and, for the first time in history, persons aged 65 or above outnumbered children under five years of age globally. One in four persons living in Europe and Northern America will be aged 65 or over. One of the goals of ISSAM is to raise awareness of the special health needs of older men. Since a significant number of aging men will eventually become testosterone deficient, the Hypogonadism panel of ISSAM updates its guidelines.

[Testosterone replacement treatment in older people with and without co-morbidities]

Testosterone is a natural hormone which is essential to maintaining physical and emotional wellbeing in men, regardless of age. Male hypogonadism is an endocrine condition of testosterone deficiency with the potential to cause multiple morbidities and psychosocial problems. The condition can be of primary (testicular), secondary (hypothalamic-pituitary) or so-called functional origin (as a result of inflammatory conditions, obesity or chronic illness). Testosterone deficiency can cause symptoms of a sexual nature, foster metabolic dysfunction and impair physical abilities as well as cause osteopenia/osteoporosis and anemia. Testosterone replacement therapy should not be initiated in the case of desired paternity, unclear processes of the prostate or mammary gland and high hematocrit. Diagnosis and treatment as well as monitoring of hypogonadism treatment are clearly regulated by international guidelines and replacement therapy is proven to be effective in ameliorating the above-mentioned symptoms when performed according to these guidelines. In functional hypogonadism, which is most often, but not exclusively, found in older men, treatment of the underlying condition/co-morbidity is mandatory prior to starting testosterone substitution.

Androgen actions on endothelium functions and cardiovascular diseases

The roles of androgens on cardiovascular physiology and pathophysiology are controversial as both beneficial and detrimental effects have been reported. Although the reasons for this discrepancy are unclear, multiple factors such as genetic and epigenetic variation, sex-specificity, hormone interactions, drug preparation and route of administration may contribute. Recently, growing evidence suggests that androgens exhibit beneficial effects on cardiovascular function though the mechanism remains to be elucidated. Endothelial cells (ECs) which line the interior surface of blood vessels are distributed throughout the circulatory system, and play a crucial role in cardiovascular function. Endothelial progenitor cells (EPCs) are considered an indispensable element for the reconstitution and maintenance of an intact endothelial layer. Endothelial dysfunction is regarded as an initiating step in development of atherosclerosis and cardiovascular diseases. The modulation of endothelial functions by androgens through either genomic or nongenomic signal pathways is one possible mechanism by which androgens act on the cardiovascular system. Obtaining insight into the mechanisms by which androgens affect EC and EPC functions will allow us to determine whether androgens possess beneficial effects on the cardiovascular system. This in turn may be critical in the prevention and therapy of cardiovascular diseases. This article seeks to review recent progress in androgen regulation of endothelial function, the sex-specificity of androgen actions, and its clinical applications in the cardiovascular system.

Androgen receptor-related diseases: what do we know?

The androgen receptor (AR) and the androgen-AR signaling pathway play a significant role in male sexual differentiation and the development and function of male reproductive and non-reproductive organs. Because of AR's widely varied and important roles, its abnormalities have been identified in various diseases such as androgen insensitivity syndrome, spinal bulbar muscular atrophy, benign prostatic hyperplasia, and prostate cancer. This review provides an overview of the function of androgens and androgen-AR mediated diseases. In addition, the diseases delineated above are discussed with respect to their association with mutations and other post-transcriptional modifications in the AR. Finally, we present an introduction to the potential therapeutic application of most recent pharmaceuticals including miRNAs in prostate cancer that specifically target the transactivation function of the AR at post-transcriptional stages.

Androgen receptor gene polymorphism influence fat accumulation: A longitudinal study from adolescence to adult age

To determine the influence of androgen receptor CAG and GGN repeat polymorphisms on fat mass and maximal fat oxidation (MFO), CAG and GGN repeat lengths were measured in 128 young boys, from which longitudinal data were obtained in 45 of them [mean ± SD: 12.8 ± 3.6 years old at recruitment, and 27.0 ± 4.8 years old at adult age]. Subjects were grouped as CAG short (CAG_S ) if harboring repeat lengths ≤  21, the rest as CAG long (CAG_L ); and GGN short (GGN_S ) if GGN repeat lengths ≤  23, or long if >  23 (GGN_L ). CAG_S and GGN_S were associated with lower adiposity than CAG_L or GGN_L (P < 0.05). There was an association between the logarithm of CAG repeats polymorphism and the changes of body mass (r = 0.34, P = 0.03). At adult age, CAG_S men showed lower accumulation of total body and trunk fat mass, and lower resting metabolic rate (RMR) and MFO per kg of total lean mass compared with CAG_L (P < 0.05). GGN_S men also showed lower percentage of body fat (P < 0.05). In summary, androgen receptor CAG and GGN repeat polymorphisms are associated with RMR, MFO, fat mass, and its regional distribution in healthy male adolescents, influencing fat accumulation from adolescence to adult age.

Pharmacogenetics of erectile dysfunction: navigating into uncharted waters

Sildenafil and other PDE-5 inhibitors have revolutionized erectile dysfunction (ED) treatment. However, a significant number of patients do not respond or present adverse reactions to these drugs. While genetic polymorphisms may underlie this phenomenon, very little research has been undertaken in this research field. Most of the current knowledge is based on sildenafil, thus almost completely ignoring other important pharmacological therapies. Currently, the most promising genes with pharmacogenetic implications in ED are related to the nitric oxide and cGMP pathway, although other genes are likely to affect the responsiveness to treatment of ED. Nevertheless, the small number of studies available opens the possibility of further exploring other genes and phenotypes related to ED. This article provides a comprehensive overview of the genes being tested for their pharmacogenetic relevance in the therapy of ED.

The interaction of serum testosterone levels and androgen receptor CAG repeat polymorphism on the risk of erectile dysfunction in aging Taiwanese men

Testosterone has been found to play important roles in men's sexual function. However, the effects of testosterone can be modulated by androgen receptor (AR) CAG repeat polymorphism. It could also contribute to the risk of erectile dysfunction (ED). The aim of this study is to evaluate the interaction of serum testosterone levels and AR CAG repeat polymorphism on the risk of ED in aging Taiwanese men. This cross-sectional data of Taiwanese men older than 40 years were collected from a free health screening held between August 2010 and August 2011 in Kaohsiung city, Taiwan. All participants completed a health questionnaires included five-item version of the International Index of Erectile Function (IIEF-5) and the International Prostate Symptoms Score, received a detailed physical examination and provided 20 cm3 whole blood samples for biochemical and genetic evaluation. The IIEF-5 was used to evaluate ED. Serum albumin, total testosterone (TT), and sex hormone-binding globulin levels were measured. Free testosterone level was calculated. AR gene CAG repeat polymorphism was determined by direct sequencing. Finally, 478 men with the mean age of 55.7 ± 4.8 years were included. When TT levels were above 330 ng/dL, the effect of testosterone level on erectile function seemed to reach a plateau and a significantly negative correlation between AR CAG repeat length and the score of IIEF-5 was found (r = -0.119, p = 0.034). After adjusting for other covariates, the longer AR CAG repeat length was still an independent risk factor for ED in subjects with TT above 330 ng/dL (p = 0.006), but not in TT of 330 ng/dL or below. In conclusion, both serum testosterone levels and AR CAG repeat polymorphism can influence erectile function concomitantly. In subjects with normal TT concentration, those with longer AR CAG repeat lengths have a higher risk of developing ED.

Age, obesity and inflammation at baseline predict the effects of testosterone administration on the metabolic syndrome

BACKGROUND

Testosterone administration to hypogonadal men improves the metabolic syndrome. This study analyzed whether age, serum testosterone, body mass index/waist circumference, increment in testosterone values and C-reactive protein (CRP) predicted the outcome of testosterone administration.

MATERIALS AND METHODS

A total of 110 mainly elderly men, aged between 18 and 83 years (mean±SD=59.6±8.0) with baseline serum testosterone of 5.8-12.1 nmol/L (mean±SD=9.3±1.7) (n>14.0 nmol/L), received parenteral testosterone undecanoate whereupon serum testosterone normalized between 3 and 24 months.

RESULTS

(i) The lower the baseline testosterone, the stronger the decreases in waist size and triglycerides. (ii) The greater the increment in serum testosterone, the stronger the decreases in low-density lipoprotein (LDL) cholesterol, triglycerides and glucose. (iii) Older age was associated with stronger beneficial effects on waist size, glucose and all lipids, but a small negative effect on high-density lipoprotein cholesterol. (iv) Obese men and men with the largest waist circumference showed the strongest declines over 2 years in weight, waist circumference and body mass index (BMI), and also in total cholesterol, triglycerides and glucose. Baseline BMI predicted a stronger decline in LDL cholesterol, but a smaller decline in CRP levels. (v) Higher baseline CRP predicted larger declines in levels of triglycerides, glucose and CRP. (vi) In the multivariate model, age, BMI and CRP were independent predictors of the strongest benefit of testosterone treatment on the metabolic syndrome.

CONCLUSIONS

Older men, particularly when obese with chronic low-grade inflammation benefited most of normalizing their testosterone levels, preferably if they reached mid-normal reference values.

Recommendations on the diagnosis, treatment and monitoring of hypogonadism in men

Hypogonadism or Testosterone Deficiency (TD) in adult men as defined by low levels of serum testosterone accompanied by characteristic symptoms and/or signs as detailed further on can be found in long-recognized clinical entities such as Klinefelter syndrome, Kallmann syndrome, pituitary or testicular disorders, as well as in men with idiopathic, metabolic or iatrogenic conditions that result in testosterone deficiency. These recommendations do not encompass the full range of pathologies leading to hypogonadism (testosterone deficiency), but instead focus on the clinical spectrum of hypogonadism related to metabolic and idiopathic disorders that contribute to the majority of cases that occur in adult men.

Clinical genetic testing for male factor infertility: current applications and future directions

Spermatogenesis involves the aggregated action of up to 2300 genes, any of which, could, potentially, provide targets for diagnostic tests of male factor infertility. Contrary to the previously proposed common variant hypothesis for common diseases such as male infertility, genome-wide association studies and targeted gene sequencing in cohorts of infertile men have identified only a few gene polymorphisms that are associated with male infertility. Unfortunately, the search for genetic variants associated with male infertility is further hampered by the lack of viable animal models of human spermatogenesis, difficulty in robustly phenotyping infertile men and the complexity of pedigree studies in male factor infertility. In this review, we describe basic genetic principles involved in understanding the genetic basis of male infertility and examine the utility and proper clinical use of the proven genetic assays of male factor infertility, specifically Y chromosome microdeletions, chromosomal translocations, karyotype, cystic fibrosis transmembrane conductance regulator mutation analysis and sperm genetic tests. Unfortunately, these tests are only able to diagnose the cause of about 20% of male factor infertility. The remainder of the review will be devoted to examining novel tests and diagnostic tools that have the potential to explain the other 80% of male factor infertility that is currently classified as idiopathic. Those tests include epigenetic analysis of the spermatozoa and the evaluation of rare genetic variants and copy number variations in patients. Success in advancing to the implementation of such areas is not only dependent on technological advances in the laboratory, but also improved phenotyping in the clinic.

A critical analysis of the role of testosterone in erectile function: from pathophysiology to treatment-a systematic review

CONTEXT

Androgen modulation of erectile function (EF) is widely accepted. However, the use of testosterone replacement therapy (TRT) in men with erectile dysfunction (ED) has generated an unprecedented debate.

OBJECTIVE

To summarize the relevant data on the incidence, diagnosis, and management of ED coexisting with hypogonadism and to develop a pathophysiology-based treatment algorithm.

EVIDENCE ACQUISITION

We reviewed the relevant medical literature, with a particular emphasis on original molecular studies, prospective observational data, and randomized controlled trials performed in the past 20 yr.

EVIDENCE SYNTHESIS

Testosterone modulates nearly every component involved in EF, from pelvic ganglions to smooth muscle and the endothelial cells of the corpora cavernosa. It also regulates the timing of the erectile process as a function of sexual desire, coordinating penile erection with sex. Epidemiologic studies confirm the significant overlap of hypogonadism and ED; however, most guidelines do not consider the differential diagnosis of hypogonadism or the relevance of subclinical disease. Various clinical tools can help the physician to assess and restore androgen levels in men with ED. Special attention is given to fertility-sparing treatments, due to the increasing number of older men desiring fatherhood. The simultaneous use of phosphodiesterase type 5 inhibitors (PDE5-Is) and TRT has recently been questioned. Originally proposed as a salvage therapy for nonresponders to PDE5-Is, this approach has been inappropriately transformed into a combination therapy. Clinical data are consistent when reinterpreted in the proper framework, whereas molecular evidence remains controversial.

CONCLUSIONS

A body of molecular and clinical evidence supports the use of TRT in hypogonadal patients with ED, although the benefit-risk ratio is uncertain in advanced age. Critical appraisal of this evidence enabled the development of a pathophysiology-oriented algorithm designed to avoid inappropriate treatments and support whether to start with TRT, PDE5-I only, or both. Apparently divergent findings are reconciled when TRT is correctly indicated. An improved diagnosis and individualized management is desirable in light of the many available options.

The impact of androgen receptor CAG repeat polymorphism on andropausal symptoms in different serum testosterone levels

INTRODUCTION

In addition to a depletion of androgen, attenuated action of androgen receptor (AR) might also contribute to andropausal symptoms.

AIM

To evaluate the interaction of AR cytosine adenine guanine (CAG) repeat polymorphism and serum testosterone levels and their effect on andropausal symptoms in aging Taiwanese men.

METHODS

From August 2007 to April 2008, a free health screening for men older than 40 years was conducted by a medical center in Kaohsiung City, Taiwan. All participants received physical examination, answered questionnaires to collect their demographic information and medical histories, completed the Androgen Deficiency in the Aging Male (ADAM) questionnaire, and provided 20-cm(3) whole blood samples for biochemical and genetic evaluation.

MAIN OUTCOME MEASURES

The ADAM questionnaire was used to evaluate andropausal symptoms. Serum albumin, total testosterone (TT), and sex hormone-binding globulin levels were measured. Free testosterone level was calculated. AR gene CAG repeat polymorphism was determined by direct sequencing.

RESULTS

Seven hundred two men with the mean age of 57.2 ± 6.5 years were included. There was no significant association between TT levels and the distribution of AR CAG repeat polymorphism. When TT levels were above 340 ng/dL, subjects with AR CAG repeat lengths ~25 showed significantly higher risk of developing andropausal symptoms, as compared with those with AR CAG repeat lengths ~22 (P = 0.006), but this was not observed when TT levels were 340 ng/dL or below. Age and number of comorbidities were also independent risk factors for andropausal symptoms.

CONCLUSION

In subjects with normal TT concentration, those with longer AR CAG repeat lengths have a higher risk of developing andropausal symptoms. Age and number of comorbidities can also influence the appearance of andropausal symptoms. In clinical practice, a multifactorial approach to evaluate andropausal symptoms and the interactions between those risk factors is suggested.

Sex hormone levels, genetic androgen receptor polymorphism, and anxiety in ≥50-year-old males

INTRODUCTION

While associations between somatic changes and sex hormone levels in aging men have been explored in many studies, the association of testosterone and estradiol with psychic symptoms other than depression and the role of the genetically determined CAG repeat (CAGn) polymorphism of the androgen receptor (AR) have received much less attention.

AIM

The purpose of this article is to investigate the associations between general anxiety, phobic anxiety and panic with sex hormone levels and the genetic androgen receptor polymorphism in aging males.

METHODS

This cross-sectional study of males aged ≥50 years included 120 consecutive patients of the Department of Psychosomatics and Psychotherapy, 76 consecutive patients of the Andrology Clinic, and 100 participants from the general population; all of them completed the Brief Symptom Inventory (BSI), the Aging Males' Symptoms (AMS) Scale, and the Patient Health Questionnaire (PHQ-9). Morning blood samples were analyzed for total and free testosterone, estradiol, sex hormone-binding globulin (SHBG), and the CAGn AR polymorphism. Psychosomatic patients also underwent psychiatric assessment.

MAIN OUTCOME MEASURES

Scores on the Anxiety subscales of the BSI and PHQ, Anxiety disorders according to International Classification of Diseases, 10th revision (ICD-10).

RESULTS

The two clinical samples had significantly longer CAGn of the AR and higher anxiety levels compared to the population sample. Anxiety scores were positively correlated with CAGn in psychosomatic patients and in andrological patients, in the latter also with estradiol levels, while the population sample showed no significant correlations between anxiety scores, CAGn and sex hormones. Anxiety cases according to BSI, PHQ, and ICD-10 had significantly longer CAGn of the AR when compared to the other participants, but there were no significant differences in testosterone or free testosterone levels.

CONCLUSIONS

Our results indicate that genetically determined long CAGn of the AR is an independent risk factor for higher anxiety, panic and phobic anxiety levels.

Sex and gender issues in competitive sports: investigation of a historical case leads to a new viewpoint

Based on DNA analysis of a historical case, the authors describe how a female athlete can be unknowingly confronted with the consequences of a disorder of sex development resulting in hyperandrogenism emerging early in her sports career. In such a situation, it is harmful and confusing to question sex and gender. Exposure to either a low or high level of endogenous testosterone from puberty is a decisive factor with respect to sexual dimorphism of physical performance. Yet, measurement of testosterone is not the means by which questions of an athlete's eligibility to compete with either women or men are resolved. The authors discuss that it might be justifiable to use the circulating testosterone level as an endocrinological parameter, to try to arrive at an objective criterion in evaluating what separates women and men in sports competitions, which could prevent the initiation of complicated, lengthy and damaging sex and gender verification procedures.

Recent Publications on Medications and Pharmacy

Hospital Pharmacy presents this feature to keep pharmacists abreast of new publications in the medical/pharmacy literature. Articles of interest regarding a broad scope of topics are abstracted monthly.