Testosterone Replacement in Older Men and Atherosclerosis Progression

Overview

As men grow older, their testosterone levels decrease with age. One-third of men, 70 years of age or older, have low testosterone levels. It is known that short-term testosterone replacement is safe, and can increase muscle strength and physical function, but the risks of long-term testosterone replacement in older men with low testosterone levels are incompletely understood. Atherosclerosis is characterized by thickening of the artery walls, and the narrowing of the blood vessels as cholesterol is deposited in the lining of the arteries. It is the major cause of cardiovascular disease including ischemic heart disease (heart attacks) and stroke. Although, historically, there has been a widespread perception that higher levels of testosterone might increase the risk of atherosclerosis, the evidence from research does not support this. In observational studies, higher testosterone levels have been correlated with more favorable cardiovascular risk factors, and supplementation with testosterone to bring older men into the normal range for healthy younger men appears to improve several cardiovascular risk factors, and may slow the progression of atherosclerosis. The primary purpose of this study is to look at the effects of testosterone replacement on the progression of atherosclerosis in older men. This study is also being done to find out whether replacement with testosterone in older men with low testosterone levels improves their health-related quality of life.

Although short-term administration of testosterone in replacement doses is relatively safe, the risks of long-term testosterone administration in older men remain poorly understood. The two major areas of concern include the potential for increased risk of atherosclerotic heart disease and exacerbation of a pre-existing, subclinical prostate cancer. There is a widespread perception that testosterone supplementation adversely affects plasma lipoprotein profile and increases the risk of atherosclerotic heart disease; this premise is not supported by data. Thus, the long-term consequences of testosterone supplementation on the risk of atherosclerosis progression remain unknown. While supraphysiological doses of testosterone and non-aromatizable androgens frequently employed by body-builders undoubtedly decrease plasma high density lipoprotein (HDL)-cholesterol levels, physiologic testosterone replacement in older men has been associated with only a modest or no decrease in plasma HDL-cholesterol. Cross-sectional studies of middle-aged men find a direct, rather than an inverse, relationship between serum testosterone levels and plasma HDL-cholesterol concentrations as well as an inverse correlation between serum testosterone levels and visceral fat volume. Testosterone supplementation of middle-aged men with truncal obesity is associated with a reduction in visceral fat volume, serum glucose concentration, blood pressure, and an improvement in insulin sensitivity. All of these changes are associated with lower risk for atherosclerosis. These data suggest that serum testosterone levels in the range that is mid-normal for healthy young men are consistent with an optimal cardiovascular risk profile at any age, and that testosterone concentrations either above or below the physiologic male range may increase the risk of atherosclerotic heart disease. Studies in a low density lipoprotein (LDL)-receptor deficient mice provide compelling evidence that testosterone retards early atherogenesis, and that testosterone effects on atherogenesis are mediated through its conversion to estradiol by the action of aromatase enzyme that is expressed in the vessel wall. The effects of testosterone replacement on cardiovascular risk in humans have never been directly examined. Therefore, the primary objective of this study is to examine directly the effects of testosterone replacement on atherosclerosis progression in men by measuring common carotid artery intima-media thickness (CCA IMT) and coronary artery calcification (CAC) by multidetector computed tomography (MDCT), two independent measurements of generalized atherosclerosis. The second objective of this study is to determine whether physiologic testosterone replacement of older men with low testosterone levels improves health-related quality of life. Aging-associated decline in physical, sexual, and cognitive functions contributes to diminished quality of life in older men. Although the pathophysiology of impairment in each of these subdomains of health-related quality of life is complex and multifactorial, one correctable cause of the diminished quality of life in older men is the decrease in serum testosterone concentrations. Total and free testosterone (T) levels decline with advancing age in normal men, with a significant number of men meeting usual criteria for hypogonadism by the sixth to seventh decades. Spontaneous and experimentally-induced androgen-deficiency in young men is associated with decreased muscle mass and strength and impaired sexual function. Because loss of muscle mass and function contributes to diminished health-related quality of life (HRQOL) in older men, anabolic therapies such as testosterone that increase muscle mass and strength, would be expected to improve physical function. In older men with low testosterone levels, testosterone might also improve sexual function and marital interaction. A growing body of literature suggests that testosterone impacts neuronal functioning and may affect cognitive performance. Because physical, sexual, and cognitive functions are important determinants of health-related quality of life, testosterone replacement of older men with low testosterone levels would be expected to improve general health perceptions. The aging of humans is a recent evolutionary event. Of the thousand generations of men and women who have lived on this planet, only the humans of the last two generations could have hoped to live past the age of 50. The population is getting proportionally older. The number of people 85 years of age and older today is substantially greater than at the beginning of the 20th century. Advancing age is associated with decreased muscle mass and strength, and impairment of physical, sexual, and cognitive functions. Diminished muscle mass and strength increases the risk of falls, disability and poor quality of life. Age-related impairment of sexual and cognitive functions also contributes to overall reduction in quality of life. Testosterone replacement, by improving some aspects of physical, sexual and cognitive functions, would be expected to improve health-related quality of life. Previous studies have established that testosterone replacement in older men with low testosterone levels increases muscle mass and strength. However, lack of information in two areas has prevented formulation of general recommendations about wider use of testosterone replacement in older men. First, the effectiveness of testosterone in improving physical function, quality of life, and other health-related outcomes has not been demonstrated. Second, while there is agreement that short-term administration of testosterone in replacement doses is safe, the long-term risks of testosterone supplementation in older men remain unknown. The areas of major concern are the risks of prostate cancer and heart disease. Because of the high prevalence, even small increases in the incidence rates of atherosclerotic heart disease associated with testosterone supplementation will have significant impact on overall morbidity and mortality, and health care costs. The study will evaluate one important aspect of the long-term safety of testosterone administration by directly examining its effects on the rate of progression of atherosclerosis. If the study demonstrates that testosterone retards atherosclerosis progression, then that would provide one additional reason for testosterone supplementation of older men with low testosterone levels. If the study demonstrates a neutral effect of testosterone on atherosclerosis progression, that information would also be reassuring and useful to regulatory agencies. This study will establish the efficacy of testosterone replacement in improving physical, sexual and cognitive functions that are major determinants of health-related quality of life in older men. In spite of the paucity of efficacy and safety data, the sales of testosterone and other androgenic products have witnessed explosive growth because of increased media attention and public interest. During the summer of 2000, testosterone-related stories were on the cover of Time, Newsweek, New York Times, and Los Angeles Times. The prescription sales of testosterone that had been growing at 25-30% annual rate since 1993, almost doubled in the year 2000, and have cumulatively increased 500% since 1993 (Source: IMS Sales Data, provided by Reed Selby, Marketing Director for ALZA Corporation). The growing testosterone use in older men, without a clear understanding of its benefits or long-term risks, has raised concern among regulatory agencies. The proposed study by providing definitive information on the effects of testosterone replacement on several measures of efficacy and safety in older men would facilitate an analysis of its risk:benefit ratio.