An investigation into the effects of ketoconazole on testicular function in Wistar rats

A time-course analysis of effects of the steroidogenesis inhibitor ketoconazole on components of the hypothalamic-pituitary-gonadal axis of fathead minnows

The objective of this study was to evaluate temporal effects of the model steroidogenesis inhibitor ketoconazole (KTC) on aspects of reproductive endocrine function controlled by the hypothalamic-pituitary-gonadal (HPG) axis in the fathead minnow (Pimephales promelas). Ketoconazole inhibits the activity of two cytochrome P450s (CYPs) key to sex steroid production in vertebrates, CYP11a (cholesterol side chain cleavage) and CYP17 (c17α-hydroxylase/17, 20-lyase). Sexually mature fish were exposed to water-borne KTC (30 or 300 μg/L) in a flow-through system for up to 8d, following which animals were allowed to recover in clean water. Fish were sampled after 1, 4 and 8d of exposure, and after 1, 8 and 16d of recovery. A shorter-term time-course experiment also was conducted in which females were sampled on seven occasions during a 12h KTC exposure. Ketoconazole consistently depressed ex vivo gonadal synthesis of testosterone (T) in both sexes, and 17β-estradiol (E2) in females during both exposure and recovery phases of the time-course studies. Effects on ex vivo steroidogenesis in females occurred within as little as 1h of exposure. Plasma concentrations of T in males and E2 in females also were depressed by exposure to KTC, but these decreases did not persist to the same degree as observed for the ex vivo effects. In females, after decreases within 12h, plasma E2 concentrations were similar to (or greater than) controls at 24h of exposure, while in males, plasma T returned to levels comparable to controls within 1d of cessation of KTC exposure. The discrepancy between the ex vivo and in vivo data at later stages in the test is consistent with some type of compensatory response to KTC in fish. However, we were unable to ascertain the mechanistic basis for such a response. For example, although a number of genes related to steroid synthesis (e.g., cyp11a, cyp17) were up-regulated in the gonads of both males and females during the exposure and early recovery phases of the experiment, this did not seem to account for the resurgence in plasma steroid concentrations in KTC-exposed fish. Further studies focused on metabolism and clearance of steroids might lend insights as to the effects of KTC on plasma steroid concentrations. Overall, our results demonstrate the complex, temporally dynamic nature of the vertebrate HPG system in response to chemical stressors.

Steroidogenesis in the fetal testis and its susceptibility to disruption by exogenous compounds

Masculinization depends on adequate production of testosterone by the fetal testis within a specific "masculinization programming window." Disorders resulting from subtle deficiencies in this process are common in humans, and environmental exposures/lifestyle could contribute causally because common therapeutic and environmental compounds can affect steroidogenesis. This evidence derives mainly from rodent studies, but because there are major species differences in regulation of steroidogenesis in the fetal testis, this may not always be a guide to potential effects in the human. In addition to direct study of the effects of compounds on steroidogenesis, information also derives from study of masculinization disorders that result from mutations in genes in pathways regulating steroidogenesis. This review addresses this issue by critically reviewing the comparative timing of production and regulation of steroidogenesis in the fetal testis of humans and of rodents and its susceptibility to disruption; where there is limited information for the fetus, evidence from effects on steroidogenesis in the adult testis is considered. There are a number of fundamental regulatory differences between the human and rodent fetal testis, most notably in the importance of paracrine vs. endocrine drives during masculinization such that inactivating LH receptor mutations block masculinization in humans but not in rodents. Other large differences involve the steroidogenic response to estrogens and GnRH analogs and possibly phthalates, whereas for other compounds there may be differences in sensitivity to disruption (ketoconazole). This comparison identifies steroidogenic targets that are either vulnerable (mitochondrial cholesterol transport, CYP11A, CYP17) or not (cholesterol uptake) to chemical interference.

Ketoconazole in the fathead minnow (Pimephales promelas): reproductive toxicity and biological compensation

Ketoconazole (KTC) is a model pharmaceutical representing imidazole and triazole pesticides, which inhibit fungal growth through blocking a cytochrome P450 (CYP)-mediated step in ergosterol biosynthesis. Several of these fungicides have been shown to be reversible inhibitors of CYPs in vertebrates (primarily mammals), including CYP isoforms involved in the pathway that converts cholesterol to active sex steroids. In these studies, we assessed the effects of KTC on aspects of steroidogenesis and reproductive function in the fathead minnow (Pimephales promelas). Exposure of spawning adults to the fungicide for 21 d significantly decreased egg production at a water concentration as low as 25 microg/L. Despite evidence of reduced ex vivo testosterone production by gonads from KTC-exposed fathead minnows, circulating plasma concentrations of sex steroids (testosterone, 17beta-estradiol) were not affected. Exposure to KTC caused an increase in the gonadosomatic index in both sexes and, in males, the fungicide caused a marked proliferation of interstitial (Leydig) cells. In addition, mRNA transcripts for two key steroidogenic enzymes, cytochrome P450 side-chain cleavage (CYP11A) and cytochrome P450 c17alpha hydroxylase/17,20 lyase (CYP17), were elevated by exposure to KTC. Both the changes in transcript levels and proliferation of gonad tissue represent potential adaptive or compensatory responses to impaired steroidogenic capacity. Overall our data indicate that, although KTC does adversely affect steroidogenesis and reproduction in the fathead minnow, the fish can compensate to some degree to mitigate effects of the fungicide. This has important implications for the interpretation of data from tests with endocrine-active chemicals.

Differential Expression of 3.BETA.-Hydroxysteroid Dehydrogenase mRNA in Rat Testes Exposed to Endocrine Disruptors

Expression of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) is mainly found in the Leydig cells from which steroid hormones are biosynthesized in the testes. To investigate whether endocrine disruptors affect the microenvironment of the testes, the mRNA expression of 3beta-HSD as a molecular marker for androgen biosynthesis was analyzed in rat testes exposed to several endocrine disruptors using a reverse transcription-polymerase chain reaction technique. Testosterone [50, 200 and 1,000 microg/kg body weight (BW)], flutamide (1, 5 and 25 mg/kg BW), ketoconazole (0.2, 1, 5 and 25 mg/kg BW), diethylhexyl phthalate (10, 50 and 250 mg/kg BW), nonylphenol (10, 50, 100 and 250 mg/kg BW), octylphenol (10, 50 and 250 mg/kg BW), and diethylstilbestrol (10, 20 and 40 microg/kg BW) were orally administered to 4-week-old Sprague-Dawley rats for 3 weeks daily. Although testosterone at a low dose (50 microg/kg/day) increased the expression of 3beta-HSD mRNA, it was significantly decreased in the rats treated with 200 or 1,000 microg/kg/day testosterone compared with the control group (P<0.05). Furthermore, ketoconazole, diethylhexyl phthalate, nonylphenol, octylphenol and diethylstilbestrol caused significant downregulation of 3beta-HSD mRNA in the testes at all doses (P<0.05). However, flutamide remarkably increased the level of 3beta-HSD mRNA in the testes (P<0.05). These results suggest that endocrine disruptors may influence androgen biosynthesis in the testes by alteration of 3beta-HSD mRNA expression.

Repeated 28-day oral toxicity study of ketoconazole in rats based on the draft protocol for the “Enhanced OECD Test Guideline No. 407” to detect endocrine effects

We performed a 28-day repeated-dose toxicity study of ketoconazole, a widely used an antimycotic drug, based on the draft protocol of the "Enhanced OECD Test Guideline 407" (Enhanced TG407) to investigate whether ketoconazole has endocrine-mediated properties according to this assay. Seven-week-old SD rats were administered with ketoconazole daily by oral gavage at doses of 0, 6.25, 25 or 100 mg kg(-1) day(-1) for at least 28 days. The ketoconazole-treated male rats showed reduction of epididymis and accessory sex organ weights, spermatid retention in the seminiferous tubules, decrease of testosterone and increases of estradiol, luteinizing hormone (LH) and follicular stimulating hormone (FSH). A prolongation of the estrous cycle and increases of estradiol, LH and FSH were observed in the treated female rats. Thyroxin and triiodothyronine were decreased and thyroid-stimulating hormone was increased in both sexes; however, there were no compound-related microscopic lesions in the thyroid gland or changes in the thyroid weight. The endocrine-related effects of ketoconazole could be detected by the parameters examined in the present study based on the Organization for Economic Cooperation and Development (OECD) protocol, suggesting that the Enhanced TG407 protocol should be a suitable screening test for detection of endocrine-mediated effects of chemicals.

Pharmacokinetic and pharmacodynamic studies of the effect of ketoconazole on reproductive function in male rats

A single oral dose (300 mg kg-1) of ketoconazole induced reversible immobilization of rat epididymal spermatozoa at 8-24 h after dosing. This occurred when the drug concentrations in cauda epididymal fluid and seminal plasma were at their peak (18.0 +/- 7.3 and 13.5 +/- 3.0 micrograms ml-1, respectively), and which was preceded by a peak plasma concentration (Cmax) of 64.82 +/- 2.47 micrograms ml-1 at 5.15 +/- 0.68 h (Tmax). In contrast, rete testis fluid collected from the same animals contained only minute amounts of ketoconazole (0.47 +/- 0.34 micrograms ml-1). Plasma testosterone concentration showed a sharp decline within 4 h of dosing, followed by a recovery from suppression, even after administration of a low dose (100 mg kg-1) which did not affect sperm motility. These findings suggest that ketoconazole gains access to the post-testicular sex organs and affects the mature spermatozoa therein much more readily than it affects testicular spermatogenesis. Synthesis and screening of compounds with a related molecular structure but which exhibit more pronounced spermicidal and less pronounced anti-androgenic effects are thus suggested in the hope that rapidly acting and reversible male contraceptives might be identified and developed.

The effects of dietary protein deficiency on rat testicular function

Diets containing 0%, 5% and 10% protein were used for treatment periods of 30, 50, and 90 days respectively. Control rats were fed a diet containing 20% protein. Protein deficient rats failed to gain weight during the experiment. In addition, the weights of the testis, epididymis, prostate and seminal vesicle also decreased, with the 10% group less affected than the 0% and 5% groups. Testicular histology indicated retarded germ cell maturation in the 0% and 5% groups only. Overall testicular cell number and size were reduced in treated rats and there was a reduction in the diameter of the seminiferous tubule in these groups. Epididymal epithelial height was also reduced in protein deficient rats with a concomitant increase in the number of epididymal duct cross sections devoid of sperm. Protein deficiency caused significant reductions in testicular DNA, RNA and protein content. The proportion of motile epididymal sperm decreased in the 0% and 5% groups by 90% and 35% respectively. Epididymal sperm number decreased in both the 0% and 5% groups by 90% while the proportion of abnormal sperm increased by 65% and 61% respectively. Circulating androgen levels were also lowered by more than 50% on average in protein deficient animals.

Comparative effects of ketoconazole on rat, dog and human testicular steroidogenesis

Ketoconazole is an antifungal azole derivative which also inhibits the cytochrome P-450(17)alpha, catalyzing the conversion of progestins into androgens. The effects of ketoconazole on human, dog and rat testosterone biosynthesis were compared using short term incubations of dispersed testicular cells. The results showed that ketoconazole inhibited androgen biosynthesis at lower concentrations in dispersed human testicular cells (IC50: 0.08 mumol/l) than in canine (IC50: 0.1 mumol/l) and rat cells (IC50 greater than or equal to 0.2 mumol/l). Furthermore, they demonstrated that ketoconazole first inhibited the 17,20-lyase activity and then the 17-hydroxylation in rat and dog cells whereas only the 17-hydroxylation was affected in human cells.