Regulation of ABC transporters by sex steroids may explain differences in drug resistance between sexes

Drug efficacy is dependent on the pharmacokinetics and pharmacodynamics of therapeutic agents. Tight junctions, detoxification enzymes, and drug transporters, due to their localization on epithelial barriers, modulate the absorption, distribution, and the elimination of a drug. The epithelial barriers which control the pharmacokinetic processes are sex steroid hormone targets, and in this way, sex hormones may also control the drug transport across these barriers. Thus, sex steroids contribute to sex differences in drug resistance and have a relevant impact on the sex-related efficacy of many therapeutic drugs. As a consequence, for the further development and optimization of therapeutic strategies, the sex of the individuals must be taken into consideration. Here, we gather and discuss the evidence about the regulation of ATP-binding cassette transporters by sex steroids, and we also describe the signaling pathways by which sex steroids modulate ATP-binding cassette transporters expression, with a focus in the most important ATP-binding cassette transporters involved in multidrug resistance. (AU)

Regulation of ABC transporters by sex steroids may explain differences in drug resistance between sexes.

Drug efficacy is dependent on the pharmacokinetics and pharmacodynamics of therapeutic agents. Tight junctions, detoxification enzymes, and drug transporters, due to their localization on epithelial barriers, modulate the absorption, distribution, and the elimination of a drug. The epithelial barriers which control the pharmacokinetic processes are sex steroid hormone targets, and in this way, sex hormones may also control the drug transport across these barriers. Thus, sex steroids contribute to sex differences in drug resistance and have a relevant impact on the sex-related efficacy of many therapeutic drugs. As a consequence, for the further development and optimization of therapeutic strategies, the sex of the individuals must be taken into consideration. Here, we gather and discuss the evidence about the regulation of ATP-binding cassette transporters by sex steroids, and we also describe the signaling pathways by which sex steroids modulate ATP-binding cassette transporters expression, with a focus in the most important ATP-binding cassette transporters involved in multidrug resistance.

The Crosstalk between Melatonin and Sex Steroid Hormones.

Melatonin, an indolamine mainly released from the pineal gland, is associated with many biological functions, namely, the modulation of circadian and seasonal rhythms, sleep inducer, regulator of energy metabolism, antioxidant, and anticarcinogenic. Although several pieces of evidence also recognize the influence of melatonin in the reproductive physiology, the crosstalk between melatonin and sex hormones is not clear. Here, we review the effects of sex differences in the circulating levels of melatonin and update the current knowledge on the link between sex hormones and melatonin. Furthermore, we explore the effects of melatonin on gonadal steroidogenesis and hormonal control in females. The literature review shows that despite the strong evidence that sex differences impact on the circadian profiles of melatonin, reports are still considerably ambiguous, and these differences may arise from several factors, like the use of contraceptive pills, hormonal status, and sleep deprivation. Furthermore, there has been an inconclusive debate about the characteristics of the reciprocal relationship between melatonin and reproductive hormones. In this regard, there is evidence for the role of melatonin in gonadal steroidogenesis brought about by research that shows that melatonin affects multiple transduction pathways that modulate Sertoli cell physiology and consequently spermatogenesis, and also estrogen and progesterone production. From the outcome of our research, it is possible to conclude that understanding the correlation between melatonin and reproductive hormones is crucial for the correction of several complications occurring during pregnancy, like preeclampsia, and for the control of climacteric symptoms.

Regucalcin, a calcium-binding protein with a role in male reproduction?

Regucalcin (RGN) is a calcium (Ca(2+))-binding protein which plays an important role in the regulation of Ca(2+) homeostasis and has been shown to catalyse an important step in L-ascorbic acid biosynthesis. It is encoded by an X-linked gene and differs from other Ca(2+)-binding proteins by lacking the typical EF-hand Ca(2+)-binding domain. RGN controls intracellular Ca(2+) concentration by regulating the activity of membrane Ca(2+) pumps. Moreover, RGN has been indicated to regulate the activity of numerous enzymes and to act in the regulation of cell proliferation and apoptosis. The importance of Ca(2+) homeostasis in spermatogenesis has been demonstrated by several studies, and its disruption has been shown to cause reversible male infertility. Recently, the expression of RGN in male reproductive tissues has been described and its localization in all testicular cell types was demonstrated. In addition, RGN expression is regulated by androgens, a class of steroid hormones recognized as male germ cell survival factors and of uttermost importance for spermatogenesis. Altogether, available information suggests the hypothesis that RGN might play a role in spermatogenesis, directly or as a mediator of androgen action. This review discusses this hypothesis presenting novel data about RGN expression in human testis.

Apoptosis-inhibitor Aven is downregulated in defective spermatogenesis and a novel estrogen target gene in mammalian testis.

OBJECTIVE: To study the expression and localization of Aven in rat and human testis from azoospermic patients with different etiologies and its regulation by estrogens. DESIGN: Experimental study. SETTING: University research center and private IVF clinic. PATIENT(S): Six men with obstructive azoospermia, five with hypospermatogenesis, and six with Sertoli cell-only syndrome; male Wistar rats. INTERVENTION(S): Testicular biopsies and rat seminiferous tubules (SeT) cultured in the presence or absence of 17ß-estradiol (E(2)). MAIN OUTCOME MEASURE(S): Testicular cell localization of Aven protein was analyzed by immunohistochemistry. Expression levels of Aven in testicular biopsies and cultured SeT, in the presence or absence of 17ß-estradiol, were determined by quantitative reverse transcription-polymerase chain reaction and Western blot. RESULT(S): Aven is expressed in Sertoli cells, spermatocytes, and spermatogonia of both rat and human testis. Aven is underexpressed in the testis of men with nonobstructive azoospermia, and its expression levels correlate with severity of spermatogenic status. Aven expression is regulated by E(2) in rat SeT cultured ex vivo. CONCLUSION(S): The results suggest that deregulation of the expression of the apoptosis inhibitor Aven may be related to male factor infertility. Moreover, Aven is an estrogen target gene and may be involved in the mechanism of testicular apoptosis control by estrogens.

Estrogen receptors alpha and beta in human testis: both isoforms are expressed.

Currently, clinical and experimental evidence point to an essential role of estrogens and estrogen receptors in male fertility. The expression of estrogen receptor alpha (ERalpha) and beta (ERbeta) in human testis has been described. However, some studies were unable to detect ERalpha, while others report the expression of both isoforms, with ERbeta presenting a wide distribution within somatic and germinal testicular cells. This has suggested that estrogens may exert their testicular effects exclusively through ERbeta. The present work aims to study the expression of ERalpha and ERbeta in testicular biopsies of men with conserved and disrupted spermatogenesis, in order to better clarify the positive cell populations. Human testicular tissue was obtained from 10 men undergoing testicular biopsy for infertility relief due to azoospermia: two patients had secondary obstructive azoospermia with conserved spermatogenesis, five had Sertoli cell-only syndrome, two had hypospermatogenesis and one had meiotic arrest. Reverse-transcription polymerase chain reaction (RT-PCR) allowed the detection of both ERalpha and ERbeta mRNAs in all samples. Immunohistochemistry revealed that ERalpha was present in Leydig cells, Sertoli cells, spermatogonia, spermatocytes, round spermatids and elongated spermatids/spermatozoa, while ERbeta was present in the same cell types except spermatogonia and Sertoli cells. This study demonstrates ERalpha mRNA expression in human testis and describes its localization in somatic and germ cell subtypes. These findings suggest that both ER isoforms are involved in the control of testicular function.