GnRH Analogs
Hormone Analogs

Author: Gianpiero Pescarmona
Date: 15/06/2008

2012-02-20T21:42:21 - Pietro Zeppa

Androgen deprivation therapy

Testosterone play a prominent role in the development, maintenance and progression of prostate cancer. The introduction of androgen deprivation therapies into the treatment paradigm for prostate cancer patients has resulted in a wide variety of benefits ranging from a survival advantage for those with clinically localized or locally advanced disease, to improvements in symptom control for patients with advanced disease. ADT refers to any intervention which results in the androgen receptor of target cells not being activated via either a reduction in the production of testosterone or blockade of the androgen receptor. (Use of androgen deprivation therapy in prostate cancer: indications and prevalence, 2012)
Androgen deprivation is often achieved by suppression of the release of luteinizing hormone from the anterior pituitary. Gonadotropin-releasing hormone (GnRH) is a decapeptide hormone synthesized in the hypothalamus. When GnRH is released in a pulsatile fashion, it induces the anterior pituitary gland to release luteinizing hormone (Figure 1). Luteinizing hormone induces Leydig cells in the testes to produce testosterone. GnRH agonists mimic GnRH and shuts down luteinizing hormone production by continuous pituitary stimulation, overcoming the endogenous pulsatile GnRH release. GnRH agonists are the most commonly used medications for ADT in the treatment of prostate cancer patients. When GnRH agonists are given, there can be an initial rise in the level of testosterone (known as the “flare”). Such an increase can stimulate prostate cancer cells to grow and cause patients to have worsening symptoms. For instance, patients with bone metastases could have worsening of their pain. Therefore, a nonsteroidal androgen receptor antagonist is often given before the GnRH agonist to block the effect of the rise in testosterone. (Efficacy and safety of gonadotropin-releasing hormone agonists used in the treatment of prostate cancer, 2011)

Although GnRH agonist therapy has significant benefits for patients with prostate cancer, it has also been shown to have significant side effects as recently emphasized by the FDA: FDA Drug Safety Communication: Update to Ongoing Safety Review of GnRH Agonists and Notification to Manufacturers of GnRH Agonists to Add New Safety Information to Labeling Regarding Increased Risk of Diabetes and Certain Cardiovascular Diseases

2012-02-20T21:40:47 - Pietro Zeppa

Does androgen deprivation therapy increase risk of stroke?

Some evidence indicates that androgen-deprivation therapy (ADT) increases the risk of diabetes and cardiovascular disease. To date, few studies have investigated whether this therapy also increases the risk of cerebrovascular events. ADT is not an innocuous therapy. Beyond the quality-of-life side effects, the suppression of testosterone levels has been associated with several adverse effects often called the androgen-deprivation syndrome. This hypogonadal condition is characterized by metabolic changes such as dyslipidemia, insulin resistance, and modification of body composition towards an increase of fat mass. All these metabolic changes put patients at an increased risk of cerebrovascular events, such as ischaemic strokes and transient ischaemic attacks (TIAs). Nevertheless evidence for these potential adverse events is limited and conflicting. (Hormone therapy for prostate cancer and the risk of stroke: a 5-year follow-up study, 2011; Lower Testosterone Levels Predict Incident Stroke and Transient Ischemic Attack in Older Men, 2009)
Recently a large population-based cohort study (Androgen-Deprivation Therapy and the Risk of Stroke inPatients With Prostate Cancer, 2011) was conducted within the GPRD population, consisting of all male patients, at least 40 years of age, diagnosed for the first time with prostate cancer between January 1, 1988, and December 31, 2008, with follow-up until December 31, 2009 (patients with a history of stroke/TIA at any time before cohort entry were excluded). This study provides additional evidence that ADT may increase the risk of stroke/TIA, though some of the associations are at limit of statistical significance.
Interestingly the strongest association was found in the under 65 year subpopulation, this can be explained with a physiological decline testosterone level that reduces the difference between treated and control group.

Population-based study seems to indicate an association between ADT end cerebrovascular events, but there is some physiological evidence of an androgen action on blood vessels?

Testosterone seems to have both a direct physiological role in maintaining cardiovascular health, independent of common risk factors as well as an indirect role by modulating cardiac risk factors such as those implicated in the metabolic syndrome.

Effect of testosterone on mediators of the atherosclerotic process

As reported in the side effects of ADT there are many evidence of a strong association between testosterone deficiency and general risk factors for atherosclerosis such as obesity, lipid alterations, metabolic syndrome and type 2 diabetes. (The effects of testosterone on risk factors for, and the mediators of, the atherosclerotic process, 2009)

Inflammatory cytokines
Evidence suggests that pro-inflammatory cytokines are involved in the early stages of atherosclerotic plaque formation. Under normal conditions, the endothelial cell layer is permeable to a number of molecules which readily pass between the circulating plasma and the sub-endothelial space. LDL-cholesterol is one such macromolecule, but on binding to proteoglycan molecules, is retained in the sub-endothelial space, a process exacerbated by increased circulating concentrations of LDL-cholesterol. The captured LDL-cholesterol becomes prone to oxidization, which triggers the expression of adhesion molecules on the endothelial cell surface. Monocytes are attracted to the adhesion molecules and pass into the sub-endothelial space where they differentiate into macrophages and produce inflammatory cytokines such as IL-6, IL-1β and TNF-α. This propagates the local inflammatory response, eventually resulting in the formation of a mature plaque, comprised of a lipid core retaining within a fibrous cap.
Continued expression of pro-inflammatory mediators such as IL- 6, IL-1β and TNF-α increases the instability of the plaque, making it prone to rupture. Evidence also suggests that TNF-α also plays a pathological role other vascular diseases suppressing nitric oxide synthase expression and contributing to the impaired endothelial function inherent to the condition. In vitro studies indicate that testosterone has immuno-modulatory capabilities, suppressing the expression of IL-6, IL-1β and TNF-α in human cell lines (Testosterone inhibits tumor necrosis factor-induced vascular cell adhesion molecule-1 expression in human aortic endothelial cells, 2002; Sex hormones modulate inflammatory mediators produced by macrophages, 1999; Androgens modulate interleukin-6 production by gingival fibroblasts in vitro,1999) and stimulating the production of anti-inflammatory IL-10. (Testosterone acts directly on CD4+ T lymphocytes to increase IL-10 production, 2001)
Evidence from several clinical studies investigating the association between testosterone levels and inflammatory cytokines highlights the potential benefits of testosterone therapy. In a detailed study of the relationship between serum testosterone and inflammatory cytokines in testosterone-deficient men with stable coronary artery disease, levels of IL-1β increased as serum testosterone decreased, and both IL-1β and IL-10 were implicated in disease pathogenesis. (Inverse relationship between serum levels of interleukin-1beta and testosterone in men with stable coronary artery disease, 2007)

C-reactive protein (CRP)
CRP is an acute phase protein produced primarily by hepatocytes in response to IL-6. The presence of CRP in plasma is indicative of acute inflammation and elevated levels of CRP bring an increased risk of metabolic syndrome, type 2 diabetes and CHD. (C-reactive protein and the prediction of cardiovascular events among those at intermediate risk: moving an inflammatory hypothesis toward consensus, 2007) However, it has been suggested that it can be the amount of LDL-cholesterol that determines CRP levels in CHD, rather than the presence of inflammatory mediators. CRP is used as a predictive indicator of myocardial infarction, ischaemic stroke and vascular death.
There appears to be an inverse correlation between CRP and testosterone levels in some reports (Study of androgen and atherosclerosis in old age male, 2005; The effect of testosterone replacement therapy on adipocytokines and C-reactive protein in hypogonadal men with type 2 diabetes, 2007), but not others. (Differential contribution of testosterone and estradiol in the determination of cholesterol and lipoprotein profile in healthy middle-aged men, 2003) However, androgen deprivation treatment was found to cause an undesirable increase in CRP levels over time in a retrospective study of diabetic prostate cancer patients. (Effects of androgen deprivation on glycaemic control and on cardiovascular biochemical risk factors in men with advanced prostate cancer with diabetes, 2007)

Haemostatic factors
The thrombotic process involves many factors, including tissue plasminogen activator (tPA) and tissue factor pathway inhibitor (TFPI), which act as anti-coagulant factors, and the pro-thrombotic plasminogen activator inhibitor-1 (PAI-1) and fibrinogen. Testosterone levels correlate negatively with fibrinogen and PAI-1 and positively with tPA. (Endogenous testosterone, fibrinolysis, and coronary heart disease risk in hyperlipidemic men,1993)

Vascular and endothelial function

The relationship between androgen deficiency, endothelial dysfunction, and vascular disease is very complex, studies results are conflicting and often inconclusive. Surely testosterone action is dose dependent and findings can be made unclear by the local conversion in DHT or estradiol.
It is recognized that pharmacological (µmol) dose induce acute vasodilatation acting on the vascular smooth muscle. (Do androgens play a beneficial role in the regulation of vascular tone?, 2010)
There is increasing evidence that this rapid and direct action of testosterone is likely to be independent of the AR, aromatase (non-aromatizable DHT show the same action) and partially of vascular endothelium, but involves the inactivation of L-type calcium channels and/or the activation of potassium channels; however induced vasodilation was much higher in endothelium-intact than in endothelium-denuded vessels. Figure summarizes the possible nongenomic mechanisms of androgen action on the vascular wall. A variety of studies has demonstrated that the key mechanism underlying the vasorelaxing action of testosterone is associated with the modulation of vascular smooth muscle cell membrane ion channel function, particularly:
1) inactivation of L-type voltage-operated Ca2+ channels (VOCCs)
2) activation of K+ channels, particularly the voltage-operated K+ channel (Kv) and/or the large-conductance Ca2+ activated K+ channel (BKCa).
Testosterone at nanomolar concentrations is a powerful antagonist for L-type voltage–operated Ca2+ channels (L-VOCCs) too. The data showed that testosterone induced vasorelaxation involved concentration-dependent additional mechanisms involving L-VOCC antagonists at low concentrations and increasing [Ca2+]i and cAMP production at high concentrations. (Potassium channels are involved in testosterone-induced vasorelaxation of human umbilical artery, 2008)
However physiological doses of testosterone can increase vascular tone via endothelium-derived hyperpolarising factor modulation. (Testosterone suppresses endothelium dependent dilation of rat middle cerebral arteries, 2004)
These acute beneficial effects of testosterone on the vasculature would appear to be in direct conflict with the potential genomic effects caused by chronic exposure (pharmacological dose) of endothelial tissue to exogenous androgens that results from anabolic steroid use, which can lead to pro-hypertensive conditions over time. (Impaired vasoreactivity in bodybuilders using androgenic anabolic steroids, 2006)
The overall effects of testosterone on vascular endothelium and smooth muscle is complicated by the possibility of a local conversion to dihydrotestosterone or 17β-estradiol. Thus, in both males and females, the balance between estrogen and testosterone production through various life stages influences the function of both reproductive and nonreproductive organs.Gonzales et al. (Androgenic/estrogenic balance in the male rat cerebral circulation: metabolic enzymes and sex steroid receptors, 2007) demonstrated clearly that 5α-reductase and aromatase, enzymes that metabolize testosterone to active products, are both localized to cerebral blood vessels in males and that receptors for both steroids, AR and ERα, are present in cerebral blood vessels in males. Moreover protein levels of each receptor are increased by administration of androgens or estrogen, respectively.
These findings clearly suggest a potential physiological function for each receptor type in the cerebral circulation in males. Thus cerebral vessels are affected by circulating sex hormones as well as locally synthesized sex steroids.

Figure 2 don’t show the postulated non-genomic vasodilatatory effects of androgens.

Estrogen has a well-known vasodilatatory, anti-inflammatory and protective action on vessels. (Gender, sex hormones, and vascular tone, 2004)

Testosterone can also be locally converted to the 5-reduced dihydro-metabolites (5α and 5β reductions), which include 5α-DHT via the enzyme 5α-reductase type 1 and 2 and 5β-DHT via the enzyme 5β-reductase, a member of AKR superfamily. It is also important to recognize that the levels of 5α- and 5β-DHT in androgen target tissues that express 5-reductase are likely to be much higher than circulating plasma concentrations, which suggests that these metabolites act mainly as intracrine mediators in the androgen target tissues in which they are formed. For example, in the prostate gland, tissue 5α-DHT concentrations are 10-fold higher than in plasma. Thus the same may be true in the vascular wall. 5-reduced dihydro-metabolites, especially the 5β, could be more potent than testosterone in non-genomic vasodilatation. (Do androgens play a beneficial role in the regulation of vascular tone? Nongenomic vascular effects of testosterone metabolites, 2010)

The early stages of atherosclerosis are marked by endothelial dysfunction, which is characterized by a loss of sensitivity to vasodilators or an increase in vasoconstriction. Vasodilation occurs through endothelium-dependent mechanisms including the production of endothelium-derived relaxing factors (e.g. vasodilatory peptides, nitric oxide) and by the endothelium-independent activation or blockade of potassium and calcium channels in the vascular muscle cells.
Administration of testosterone to men and women suffering from angina was first shown to alleviate symptoms over 60 years ago. (Testosterone propionate therapy in one hundred cases of angina pectoris, 1946) Clinical and preclinical evidence exists linking endothelial dysfunction to androgen deficiency. (Low testosterone level is an independent determinant of endothelial dysfunction in men, 2007; Sex steroids and endothelial function: translating basic science to clinical practice, 2007)
Minamino et al. proposed that the senescence of endothelial cells is involved in endothelial dysfunction and atherogenesis. (Endothelial cell senescence in human atherosclerosis: role of telomere in endothelial dysfunction, 2002) Since that histological study of human atherosclerotic lesion has demonstrated the existence of vascular cells that exhibit the morphological features of senescence these changes have been suggested to results in increased risk of atherosclerotic disease in the elderly.

Endothelial cells senescence
In S. cerevisiae, the Sir2 (silent information regulator-2) family of genes governs budding exhaustion and replicative life span (Sir2 links chromatin silencing, metabolism, and aging, 2000). Sir2 has been identified as an NAD+ -dependent histone deacetylase and is responsible for maintenance of chromatin silencing and genome stability. Mammalian sirtuin 1 (Sirt1), the closest homolog of Sir2, regulates the cell cycle, senescence, apoptosis and metabolism, by interacting with a number of molecules such as p53. Senescence of endothelial cells is involved in endothelial dysfunction and atherogenesis, and SIRT1 has been recognized as a key regulator of vascular endothelial homeostasis, controlling angiogenesis, endothelial senescence, and dysfunction. SIRT1 plays an important role in prevention of endothelial senescence induced by oxidative stress. (Sirt1 modulates premature senescence-like phenotype in human endothelial cells, 2007; MicroRNA 217 modulates endothelial cell senescence via silent information regulator 1, 2009)

Signaling pathways implicated in T- and DHT-stimulated NO release and eNOS activity
Ota et al. (Testosterone Deficiency Accelerates Neuronal and Vascular Aging of SAMP8 Mice: Protective Role of eNOS and SIRT1, 2012) observed that oxidative stress decreased eNOS and SIRT1 and increased PAI-1 expression, and DHT or testosterone treatment prevented these changes and increased the phosphorylation of eNOS at Ser1177. Overexpression of SIRT1 significantly inhibited oxidative stress induced senescence, and DHT accelerated the effect of SIRT1 through phosphorylation of eNOS at Ser1177. Phosphorylation on Ser1177 results in eNOS activation (Endothelial regulation of eNOS, PAI-1 and t-PA by testosterone and dihydrotestosterone in vitro and in vivo, 2010) and is targeted by a number of mediators of extra-nuclear signaling pathways recruited by sex steroid hormones, such as the phosphatidylinositol 3-OH kinase (PI3K)/Akt pathway or the extracellular-related protein kinase (ERK) 1/2 cascade (Activation of nitric oxide synthase in endothelial cells by Akt-dependent phosphorylation,1999; Interaction of oestrogen receptor with the regulatory subunit of phosphatidylinositol-3-OH kinase 2000). Human umbilical vein endothelial cells exposed rapidly (30 min) to testosterone or DHT displayed a quick recruitment of both pathways, with enhanced phosphorylation of ERK 1/2 as well as of Akt.
In addition, similar to what found for the longer-term actions of testosterone and DHT, the enhanced NO synthesis and eNOS activity linked to testosterone administration were in part abrogated by blocking both ER and AR, although the effect of DHT was only blocked by flutamide, confirming that even in this rapid time frame, some of the actions of T can be mediated by conversion to estrogens. Non-genomic action is primarily mediated by a steroid specific G protein coupled receptor mechanism tha activated eNOS.
To determine the role of endogenous SIRT1, DHT-treated endothelial cells were transfected with SIRT1 siRNA or treated with sirtinol, a chemical inhibitor of SIRT1. SIRT1 siRNA or sirtinol abrogated the effect of DHT.

Testosterone might improve parameters relating to CVD through mediation of endothelial progenitor cell activity.
Foresta et al. (Reduced number of circulating edothelial progenitor cells in hypogonadal men, 2006) investigated the effects of testosterone on the role that endothelial progenitor cells play in endothelial repair in 10 young idiopathic patients with hypogonadotrophic hypogonadism. They observed that the number of endothelial progenitor cells in hypogonadal men was fewer than the number in healthy control subjects. The authors further found that treating idiopathic hypogonadotropic hypogonadism with testosterone gel therapy, at 50 mg/d for 6 months, increased the number of circulating endothelial progenitor cells in these men. These findings point toward a decreased number of circulating endothelial progenitor cells as being apotential risk factor for CVD seen in patients with hypogonadism. Interestingly clinical data demonstrates that androgens can stimulate endothelial progenitor cells. Because all of the effects were abolished after flutamide (androgen receptor blocker) pretreatment, it was concluded that the effects were mediated via the androgen receptor. The levels of testosterone used in these studies were calculated to be in the normal physiological range. (Androgens stimulate endothelial progenitor cells through an androgen receptor-mediated pathway, 2008)

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