The Long and Tortuous History of the Discovery of Testosterone and Its Clinical Application

The testis, eunuchs, and testosterone: a historical review over the ages and around the world

INTRODUCTION

Testosterone therapy for men with testosterone deficiency is widely used, yet remains controversial. The rich and fascinating history of the testicles, including human castration, provides a valuable perspective on this important topic.

OBJECTIVES

This study reviewed the history of testosterone from antiquity to the modern day.

METHODS

Primary sources consisted of books and relevant articles, augmented by a MEDLINE search using the key words "testis," "testicles," "castration," "eunuchs," "testosterone," and "testicular function."

RESULTS

An early scientific observation was that castration reduced sexual development and activity, originating with domestication of animals approximately 10 000 years ago. Human castration appears in ancient Egyptian mythology more than 4000 years ago, in Greek mythology from 8th century BCE, and in the Bible. The history of eunuchs in China spanned 2000 years, beginning with the Hsia dynasty (2205-1766 BCE). The concept that the testicles produced some factor responsible for male sexual development and behavior was thus known throughout the world since the beginning of recorded history. Testosterone was isolated and synthesized in 1935 and was soon available as a treatment. Multiple benefits of testosterone therapy were apparent by 1940. Recent large, controlled testosterone studies have conclusively demonstrated sexual and general health benefits, with a strong safety profile.

CONCLUSION

Testosterone has been a known substance for <1% of the historical timeline, yet knowledge that the testes were responsible for male sexual development and behavior has been known since the beginning of recorded history. Today, modern evidence has demonstrated the importance of normal levels of testosterone for general health as well as sexual function and desire. Yet, testosterone therapy remains controversial. We believe this historical review provides a helpful perspective on this age-old issue.

Testosterone replacement therapy: clinical considerations

INTRODUCTION

As an increasingly popular therapeutic option, testosterone replacement therapy (TRT) has gained significant notoriety for its health benefits in indicated populations, such as those suffering from hypogonadism.

AREAS COVERED

Benefits such as improved libido, muscle mass, cognition, and quality of life have led to widened public interest in testosterone as a health supplement. No therapy exists without side effects; testosterone replacement therapy has been associated with side effects such as an increased risk of polycythemia, benign prostate hypertrophy (BPH), prostate cancer, gynecomastia, testicular atrophy, and infertility. Testosterone replacement therapy is often accompanied by several prophylactic co-therapies aimed at reducing the prevalence of these side effects. Literature searches for sections on the clinical benefits and risks associated with TRT were performed to include clinical trials, meta-analyses, and systematic reviews from the last 10 years.

EXPERT OPINION

Data from clinical studies over the last decade suggest that the benefits of this therapy outweigh the risks and result in overall increased quality of life and remission of symptoms related to hypogonadism. With this in mind, the authors of this review suggest that carefully designed clinical trials are warranted for the investigation of TRT in symptomatic age-related hypogonadism.

Cholesterol intake and serum total cholesterol levels are not associated with total testosterone levels in men: a cross-sectional study from NHANES 2013-2014

BACKGROUND

Testosterone (T) is an anabolic hormone crucial to the structure and function of skeletal muscle. Testosterone is partially synthesized from cholesterol, but little is known about the relationship of cholesterol intake and serum cholesterol with T levels.

AIM

To investigate whether cholesterol intake and serum total cholesterol (TC) levels are associated with serum total testosterone (TT) levels in men.

METHODS

A cross-sectional study enrolling 1996 men aged 20 to 80 years from National Health and Nutrition Examination Survey (NHANES) 2013-2014 was carried out. Diet assessment was performed using two 24-h food recalls, and TT levels were measured by liquid chromatography coupled with tandem mass spectrometry. Regression analyses were performed to evaluate whether TT was associated with cholesterol intake and serum TC levels.

RESULTS

Neither cholesterol intake nor serum TC levels were associated with TT levels in unadjusted and adjusted analyses (adjustment for energy, total fat and alcohol intake, smoking, age, physical activity, family income, marital status, race, educational level, diabetes, hypertension, and body mass index).

CONCLUSION

Dietary cholesterol intake and TC levels are not associated with TT levels in men from the USA.

History of testosterone therapy through the ages

The symptoms of testosterone deficiency have been known throughout history with evidence dating back to the twenty-first century BCE when men were castrated to be docile and obedient servants. Experimentation ingesting mammalian testicles began during the reign of the Roman empire and continued through the nineteenth century with claims that the substance found within these testicles could improve energy, erectile function, and urination. In the twentieth century, studies transplanting animal testes onto other castrated animals suggested that a substance produced in the testicle was responsible for systemic effects. Then in 1929, Adolf Butendant was the first to isolate testosterone and shortly after synthetic formulations of testosterone were created. While testosterone therapy is an important treatment for testosterone deficiency, the history of testosterone therapy has not been without abuse from doping scandals in the twentieth century and the use of testosterone therapy for conversion therapy and treatment of psychiatric disease. Today, there are clear and appropriate clinical uses of testosterone set by the American Urological Association to treat clinically significant testosterone deficiency. Still, even with such guidelines, the potential for misuse and abuse remains high in physicians and athletes. There is a long history that has led to the development of testosterone therapy and when used appropriately can significantly improve the quality of life for men with testosterone deficiency.

The Roles of Androgens in Humans: Biology, Metabolic Regulation and Health

Androgens are an important and diverse group of steroid hormone molecular species. They play varied functional roles, such as the control of metabolic energy fate and partition, the maintenance of skeletal and body protein and integrity and the development of brain capabilities and behavioral setup (including those factors defining maleness). In addition, androgens are the precursors of estrogens, with which they share an extensive control of the reproductive mechanisms (in both sexes). In this review, the types of androgens, their functions and signaling are tabulated and described, including some less-known functions. The close interrelationship between corticosteroids and androgens is also analyzed, centered in the adrenal cortex, together with the main feedback control systems of the hypothalamic-hypophysis-gonads axis, and its modulation by the metabolic environment, sex, age and health. Testosterone (T) is singled out because of its high synthesis rate and turnover, but also because age-related hypogonadism is a key signal for the biologically planned early obsolescence of men, and the delayed onset of a faster rate of functional losses in women after menopause. The close collaboration of T with estradiol (E2) active in the maintenance of body metabolic systems is also presented Their parallel insufficiency has been directly related to the ravages of senescence and the metabolic syndrome constellation of disorders. The clinical use of T to correct hypoandrogenism helps maintain the functionality of core metabolism, limiting excess fat deposition, sarcopenia and cognoscitive frailty (part of these effects are due to the E2 generated from T). The effectiveness of using lipophilic T esters for T replacement treatments is analyzed in depth, and the main problems derived from their application are discussed.

Anabolic-Androgenic Steroid Use in Sports, Health, and Society

This consensus statement is an update of the 1987 American College of Sports Medicine (ACSM) position stand on the use of anabolic-androgenic steroids (AAS). Substantial data have been collected since the previous position stand, and AAS use patterns have changed significantly. The ACSM acknowledges that lawful and ethical therapeutic use of AAS is now an accepted mainstream treatment for several clinical disorders; however, there is increased recognition that AAS are commonly used illicitly to enhance performance and appearance in several segments of the population, including competitive athletes. The illicit use of AAS by competitive athletes is contrary to the rules and ethics of many sport governing bodies. Thus, the ACSM deplores the illicit use of AAS for athletic and recreational purposes. This consensus statement provides a brief history of AAS use, an update on the science of how we now understand AAS to be working metabolically/biochemically, potential side effects, the prevalence of use among athletes, and the use of AAS in clinical scenarios.

The Effects of Androgens on Cardiometabolic Syndrome: Current Therapeutic Concepts

INTRODUCTION

Cardiometabolic syndrome (CMS), as a bunch of metabolic disorders mainly characterized by type 2 diabetes mellitus (T2DM), hypertension, atherosclerosis, central adiposity, and abdominal obesity triggering androgen deficiency, is one of the most critical threats to men. Although many significant preclinical and clinical findings explain CMS, new approaches toward common pathophysiological mechanisms and reasonable therapeutic targets are lacking.

AIM

To gain a further understanding of the role of androgen levels in various facets of CMS such as the constellation of cardiometabolic risk factors including central adiposity, dyslipidemia, insulin resistance, diabetes, and arterial hypertension and to define future directions for development of effective therapeutic modalities.

METHODS

Clinical and experimental data were searched through scientific literature databases (PubMed) from 2009 to October 2019.

MAIN OUTCOME MEASURE

Evidence from basic and clinical research was gathered with regard to the causal impact and therapeutic roles of androgens on CMS.

RESULTS

There are important mechanisms implicated in androgen levels and the risk of CMS. Low testosterone levels have many signs and symptoms on cardiometabolic and glycometabolic risks as well as abdominal obesity in men.

CLINICAL IMPLICATIONS

The implications of the findings can shed light on future improvements in androgen levels and add potentially predictive risk for CMS, as well as T2DM, abdominal obesity to guide clinical management in the early stage.

STRENGTHS & LIMITATIONS

This comprehensive review refers to the association between androgens and cardiovascular health. A limitation of this study is the lack of large, prospective population-based studies that analyze the effects of testosterone treatment on CMS or mortality.

CONCLUSION

Low testosterone levels have several common features with metabolic syndrome. Thus, testosterone may have preventive role in the progress of metabolic syndrome and subsequent T2DM, abdominal obesity, and cardiovascular disease and likely affect aging men's health mainly through endocrine and vascular mechanisms. Further studies are necessary to evaluate the therapeutic interventions directed at preventing CMS in men. Kirlangic OF, Yilmaz-Oral D, Kaya-Sezginer E, et al. The Effects of Androgens on Cardiometabolic Syndrome: Current Therapeutic Concepts. Sex Med 2020;8:132-155.

Uncovering sex-specific mechanisms of action of testosterone and redox balance

The molecular and pharmacological manipulation of the endogenous redox system is a promising therapy to limit myocardial damage after a heart attack; however, antioxidant therapies have failed to fully establish their cardioprotective effects, suggesting that additional factors, including antioxidant system interactions with other molecular pathways, may alter the pharmacological effects of antioxidants. Since gender differences in cardiovascular disease (CVD) are prevalent, and sex is an essential determinant of the response to oxidative stress, it is of particular interest to understand the effects of sex hormone signaling on the activity and expression of cellular antioxidants and the pharmacological actions of antioxidant therapies. In the present review, we briefly summarize the current understanding of testosterone effects on the modulation of the endogenous antioxidant systems in the CV system, cardiomyocytes, and the heart. We also review the latest research on redox balance and sexual dimorphism, with particular emphasis on the role of the natural antioxidant system glutathione (GSH) in the context of myocardial infarction, and the pro- and antioxidant effects of testosterone signaling via the androgen receptor (AR) on the heart. Finally, we discuss future perspectives regarding the potential of using combing antioxidant and testosterone replacement therapies to protect the aging myocardium.

Androgen-Regulated Cardiac Metabolism in Aging Men

The prevalence of cardiovascular mortality is higher in men than in age-matched premenopausal women. Gender differences are linked to circulating sex-related steroid hormone levels and their cardio-specific actions, which are critical factors involved in the prevalence and features of age-associated cardiovascular disease. In women, estrogens have been described as cardioprotective agents, while in men, testosterone is the main sex steroid hormone. The effects of testosterone as a metabolic regulator and cardioprotective agent in aging men are poorly understood. With advancing age, testosterone levels gradually decrease in men, an effect associated with increasing fat mass, decrease in lean body mass, dyslipidemia, insulin resistance and adjustment in energy substrate metabolism. Aging is associated with a decline in metabolism, characterized by modifications in cardiac function, excitation-contraction coupling, and lower efficacy to generate energy. Testosterone deficiency -as found in elderly men- rapidly becomes an epidemic condition, associated with prominent cardiometabolic disorders. Therefore, it is highly probable that senior men showing low testosterone levels will display symptoms of androgen deficiency, presenting an unfavorable metabolic profile and increased cardiovascular risk. Moreover, recent reports establish that testosterone replacement improves cardiomyocyte bioenergetics, increases glucose metabolism and reduces insulin resistance in elderly men. Thus, testosterone-related metabolic signaling and gene expression may constitute relevant therapeutic target for preventing, or treating, age- and gender-related cardiometabolic diseases in men. Here, we will discuss the impact of current evidence showing how cardiac metabolism is regulated by androgen levels in aging men.

Trehalose protects testicular tissue of dairy goat upon cryopreservation

The aim of this study was to investigate whether the addition of trehalose to cryomedia reduces cellular damage and improves gene expression in cryopreserved dairy goat testicular tissues. Testicular tissues were cryopreserved in cryomedia without or with trehalose at a concentration of 5%, 10%, 15%, 20% or 25%. Cryopreserved testicular tissues were analysed for TUNEL-positive cell number, expression of BAX, BCL-2, CREM, BOULE and HSP70-2. Isolated Leydig cells from cryopreserved tissue were cultured, and spent medium was evaluated for testosterone level. The results showed that though the TUNEL-positive cell number increased in cryopreserved testicular tissues, the presence of trehalose reduced apoptotic cell number significantly. Quantitative real-time polymerase chain reaction results showed that although the expression of BAX was upregulated following cryopreservation, the presence of trehalose downregulates it in cryopreserved testicular tissues. Expression of BCL-2, CREM, BOULE and HSP70-2 was downregulated following cryopreservation but the presence of trehalose significantly upregulated their expression in cryopreserved testicular tissues. Leydig cells isolated from testicular tissues cryopreserved with trehalose produced higher testosterone than the one without it (control). These results suggest that trehalose has a protective role in cryopreservation of dairy goat testicular tissue, and the most suitable trehalose concentration for cryopreservation is 15%.

Mechanisms of Sex Disparities in Cardiovascular Function and Remodeling

Epidemiological studies demonstrate disparities between men and women in cardiovascular disease prevalence, clinical symptoms, treatments, and outcomes. Enrollment of women in clinical trials is lower than men, and experimental studies investigating molecular mechanisms and efficacy of certain therapeutics in cardiovascular disease have been primarily conducted in male animals. These practices bias data interpretation and limit the implication of research findings in female clinical populations. This review will focus on the biological origins of sex differences in cardiovascular physiology, health, and disease, with an emphasis on the sex hormones, estrogen and testosterone. First, we will briefly discuss epidemiological evidence of sex disparities in cardiovascular disease prevalence and clinical manifestation. Second, we will describe studies suggesting sexual dimorphism in normal cardiovascular function from fetal life to older age. Third, we will summarize and critically discuss the current literature regarding the molecular mechanisms underlying the effects of estrogens and androgens on cardiac and vascular physiology and the contribution of these hormones to sex differences in cardiovascular disease. Fourth, we will present cardiovascular disease risk factors that are positively associated with the female sex, and thus, contributing to increased cardiovascular risk in women. We conclude that inclusion of both men and women in the investigation of the role of estrogens and androgens in cardiovascular physiology will advance our understanding of the mechanisms underlying sex differences in cardiovascular disease. In addition, investigating the role of sex-specific factors in the development of cardiovascular disease will reduce sex and gender disparities in the treatment and diagnosis of cardiovascular disease. © 2019 American Physiological Society. Compr Physiol 9:375-411, 2019.

Marketing and Testosterone Treatment in the USA: A Systematic Review

CONTEXT

Testosterone replacement therapy (TRT) is currently approved by the Food and Drug Administration only for classic hypogonadism, although off-label indications have resulted in a dramatic expansion in prescriptions in the USA. Marketing may significantly affect prescriber behavior.

OBJECTIVE

To systematically review all available evidence on marketing and TRT in the USA.

EVIDENCE ACQUISITION

PubMed, Embase, and Scopus were searched up to July 2017 for all relevant publications reporting on assessments of the TRT market size, economic costs associated with hypogonadism, trends in TRT prescriptions, drug discontinuation rates, and advertising and sales efforts in the USA.

EVIDENCE SYNTHESIS

Twenty retrospective studies were included in the final analysis. The market size for hypogonadism constitutes 5.6-76.8% of men in the USA, with the lower end of the range representing the strictest criteria for diagnosis. Men with a diagnosis of hypogonadism consume $14 118 in direct and indirect costs to the payer. Over the last 2 decades, TRT prescriptions have increased between 1.8- and 4-fold. After 1 yr, 80-85% of men discontinue TRT. There is an association between direct-to-consumer advertising and testosterone testing, TRT prescriptions, and TRT without testosterone testing. There is a high prevalence of misinformation on Internet advertising.

CONCLUSIONS

Off-label indications have driven the dramatic expansion of TRT prescriptions over the last 2 decades. Direct-to-consumer advertising poses a unique challenge in the USA. Overtreatment can be avoided by applying strict diagnostic criteria for hypogonadism, which limits the addressable market for TRT.

PATIENT SUMMARY

In this report, we reviewed the relationship between marketing and testosterone therapy in the USA. We found that many patients are prescribed testosterone without an appropriate diagnosis of hypogonadism, which may be related to the marketing efforts for off-label prescribing.

Testosterone Replacement Therapy and the Cardiovascular System

As testosterone replacement therapy (TRT) has emerged as a commonly prescribed therapy for symptomatic low testosterone, conflicting data have been reported in terms of both its efficacy and potential adverse outcomes. One of the most controversial associations has been that of TRT and cardiovascular morbidity and mortality. This review briefly provides background on the history of TRT, the indications for TRT, and the data behind TRT for symptomatic low testosterone. It then specifically delves into the rather limited data for cardiovascular outcomes of those with low endogenous testosterone and those who receive TRT. The available body of literature strongly suggests that more work, by way of clinical trials, needs to be done to better understand the impact of testosterone and TRT on the cardiovascular system.

Reactive oxygen species: players in the cardiovascular effects of testosterone

Androgens are essential for the development and maintenance of male reproductive tissues and sexual function and for overall health and well being. Testosterone, the predominant and most important androgen, not only affects the male reproductive system, but also influences the activity of many other organs. In the cardiovascular system, the actions of testosterone are still controversial, its effects ranging from protective to deleterious. While early studies showed that testosterone replacement therapy exerted beneficial effects on cardiovascular disease, some recent safety studies point to a positive association between endogenous and supraphysiological levels of androgens/testosterone and cardiovascular disease risk. Among the possible mechanisms involved in the actions of testosterone on the cardiovascular system, indirect actions (changes in the lipid profile, insulin sensitivity, and hemostatic mechanisms, modulation of the sympathetic nervous system and renin-angiotensin-aldosterone system), as well as direct actions (modulatory effects on proinflammatory enzymes, on the generation of reactive oxygen species, nitric oxide bioavailability, and on vasoconstrictor signaling pathways) have been reported. This mini-review focuses on evidence indicating that testosterone has prooxidative actions that may contribute to its deleterious actions in the cardiovascular system. The controversial effects of testosterone on ROS generation and oxidant status, both prooxidant and antioxidant, in the cardiovascular system and in cells and tissues of other systems are reviewed.

Testosterone Deficiency Syndrome: an overview with emphasis on the diagnostic conundrum

OBJECTIVES

To review the controversial issues of the Testosterone Deficiency Syndrome (TDS) with an emphasis on the concerns about the diagnosis.

DESIGN AND METHODS

The relevant literature was reviewed with particular attention to matters related to the clinical manifestations of the syndrome, the need for biochemical assessment and questions of biological and analytical variation that have to be taken into account. Therapeutic options were also appraised.

RESULTS

There are numerous difficulties with the clinical diagnosis of TDS due to the lack of specificity and subtlety of the manifestations when the degree of deficiency is not severe. Confirmation of the clinical impression requires laboratory evaluation but the choice of assays remains an unsettled issue although there is a general consensus that both free testosterone and bioavailable testosterone best reflect the degree of androgenicity. The laboratory diagnosis enjoys a great deal of credibility among clinicians but shortcomings in the interpretation of the assays need to be reiterated and the need for close collaboration between the clinician and the clinical biochemist is important for diagnostic accuracy. Even when the clinical picture is convincing, the laboratory may produce inconclusive results. The option of a therapeutic trial should be contemplated in this situation. Treatment options should be decided between the physician and the patient considering issues of availability, tolerance, efficacy and cost.

CONCLUSIONS

TDS is a prevalent condition but a matter of persistent controversy due to the vagaries of the clinical and laboratory diagnosis. Symptomatic men with documented T deficiency deserve treatment to improve their quality of life.