Importance of male fertility control in family planning.

The world population, currently estimated to be almost seven billion, is expected to double in less than four decades. The projected population growth will cause severe competition for existing resources, not to mention the issue of overcrowding of the planet and additional greenhouse gases that will have an adverse effect on the ecological health of the planet. A recent survey conducted by the United Nations Population Control Division shows that the majority of today's young men in many countries are willing to participate in family planning by taking full control of their fertility, an important global health issue. However, the contraceptive needs of tens of millions of men/couples go unmet every single day and results in millions of unwanted pregnancies. Ever since the approval of the birth control pill by the Food and Drug Administration (FDA) in 1960, scientists have been hoping for a male equivalent. It has, however, been a difficult road, in part because of the complicated science of the male reproductive system. It is easier to control a monthly event of ovulation in women than to regulate the production of millions of fertile spermatozoa every day in men. Thus, the contraceptive options for men have not changed in decades and are still limited to the use of condoms, a timely withdrawal/pulling out (coitus interruptus) or vasectomy, a minor surgical procedure in which the vas deferens is occluded to prevent the release of spermatozoa during ejaculation. The first two approaches have a relatively higher failure rate, whereas the last approach is largely irreversible and not suitable for younger men. In this article, we will discuss various approaches currently available for men to take control of their fertility. Our intention is to discuss the details of three similar approaches that will provide safe, affordable and reversible contraception for men and are close to being approved for use by millions of men around the globe. The availability of safe, reversible and reliable male contraceptives will allow men and women to take full control of their fertility in family planning.

Biological Processes that Prepare Mammalian Spermatozoa to Interact with an Egg and Fertilize It.

In the mouse and other mammals studied, including man, ejaculated spermatozoa cannot immediately fertilize an egg. They require a certain period of residence in the female genital tract to become functionally competent cells. As spermatozoa traverse through the female genital tract, they undergo multiple biochemical and physiological changes collectively referred to as capacitation. Only capacitated spermatozoa interact with the extracellular egg coat, the zona pellucida. The tight irreversible binding of the opposite gametes triggers a Ca(2+)-dependent signal transduction cascade. The net result is the fusion of the sperm plasma membrane and the underlying outer acrosomal membrane at multiple sites that causes the release of acrosomal contents at the site of sperm-egg adhesion. The hydrolytic action of the acrosomal enzymes released, along with the hyperactivated beat pattern of the bound spermatozoon, is important factor that directs the sperm to penetrate the egg coat and fertilize the egg. The sperm capacitation and the induction of the acrosomal reaction are Ca(2+)-dependent signaling events that have been of wide interest to reproductive biologists for over half a century. In this paper, we intend to discuss data from this and other laboratories that highlight the biological processes which prepare spermatozoa to interact with an egg and fertilize it.

How close are we in achieving safe, affordable and reversible male contraceptives?

The world population, currently estimated to be over six billions, is expected to double in the next forty years. The projected growth will cause severe over crowding that will have an adverse effect on the ecological health of the planet. A recent survey by the United Nations found that a majority of men in many countries are willing to participate in family planning by taking full control of their fertility. However, the available contraceptives for men have either higher failure rates or they are irreversible. Thus, the contraceptive needs of tens of millions of men go unmet every day resulting in millions of unwanted pregnancies, and hundreds of thousands of abortions. Since the introduction of oral contraceptive (pill) for women over five decades ago, there have been numerous collaborative efforts by scientists and pharmaceutical companies to improve the effectiveness and delivery of contraceptives to women who wish to safely regulate their reproductive physiology. However, the contraceptive options available to men have not changed in several decades and are still limited to the use of condoms and timely withdrawal (coitus interruptus) or under going a minor surgical procedure (vasectomy) that prevents the release of spermatozoa during ejaculation. The first two methods have relatively higher typical-use failure rates, whereas the last approach is largely irreversible and not suitable for younger men. Despite non-stop efforts worldwide, we may still be several years away from providing safe, effective and affordable male contraceptives which will allow both men and women to participate fully in family planning. In this article, we will discuss various contraceptives currently available to regulate male fertility. In addition, we will summarize potentially new contraceptives for men that are at various stages of research and development. Finally, our intention is to discuss details of two safe, reversible and affordable male contraceptive approaches that are inching closure to being approved for use by the masses in India and China, the world's two most populous nations.

Signal transduction pathways that regulate sperm capacitation and the acrosome reaction.

Ejaculated spermatozoa must undergo physiological priming as they traverse the female reproductive tract before they can bind to the egg's extracellular coat, the zona pellucida (ZP), undergo the acrosome reaction, and fertilize the egg. The preparatory changes are the net result of a series of biochemical and functional modifications collectively referred to as capacitation. Accumulated evidence suggests that the event that initiates capacitation is the efflux of cholesterol from the sperm plasma membrane (PM). The efflux increases permeability and fluidity of the sperm PM and causes influx of Ca(2+) ions that starts a signaling cascade and result in sperm capacitation. The binding of capacitated spermatozoa to ZP further elevates intrasperm Ca(2+) and starts a new signaling cascade which open up Ca(2+) channels in the sperm PM and outer acrosomal membrane (OAM) and cause the sperm to undergo acrosomal exocytosis. The hydrolytic action of the acrosomal enzymes released at the site of sperm-egg (zona) binding, along with the hyperactivated beat pattern of the bound spermatozoon, are important factors in directing the sperm to penetrate the ZP and fertilize the egg. The role of Ca(2+)-signaling in sperm capacitation and induction of the acrosome reaction (acrosomal exocytosis) has been of wide interest. However, the precise mechanism(s) of its action remains elusive. In this article, we intend to highlight data from this and other laboratories on Ca(2+) signaling cascades that regulate sperm functions.

Male contraception: an overview of the potential target events.

The contraceptive options available to men have not changed in several decades and are still limited to the non-surgical methods of the use of a condom, a timely withdrawal, or a surgical procedure that removes a segment of the vas deferens (vasectomy). The first two approaches have relatively higher failure rates whereas the last approach is largely irreversible and may not be suitable for younger men. Thus, providing a safe, effective and readily available contraception for men has remained an unfulfilled goal. In this article, we intend to review the current status of the research and development on male contraceptives. It is apparent that the scientific community in the past few decades has witnessed impressive progress in understanding the basics of male physiology, the knowledge necessary for developing new contraceptive methods for men. We will highlight various new and improved strategies for the regulation of fertility in males. The diverse approaches that are at various stages of development and/or in clinical trials include: 1) administration of hormones, herbal extracts or chemicals to suppress/arrest sperm production in the testes (spermatogenesis); 2) interference with the delivery of spermatozoa during ejaculation by targeted blockage of vas deferens with plugs or chemicals (polymers) that prevent flow of sperm through the vas duct; 3) active or passive immunization of males with well characterized antigens/antibodies which are intended to block sperm function; and 4) administration of site-directed antagonists to block specific sperm function(s) necessary for normal fertilization. All these approaches do not involve surgery and are reversible. Our intention is to discuss the current status of various approaches which show promising results in clinical trials, particularly in China and India, the world's most populous nations.

Biology of sperm capacitation: evidence for multiple signalling pathways.

The endpoint of in vitro/in vivo capacitation is the ability of sperm surface receptors to bind to their complementary ligands on zona pellucida, the extracellular glycocalyx that surrounds the egg, and undergo the Ca2+-dependent signal transduction. The net result is the fenestration and fusion of the sperm plasma membrane and the underlying outer acrosomal membrane at multiple sites and exocytosis of acrosomal contents. The hydrolytic action of glycohydrolases and proteinases, released at the site of sperm-zona binding, along with the enhanced thrust generated by the hyperactivated flagellar motility of the bound spermatozoon, are important factors that regulate the fertilization process. This report discusses the physiological significance of calmodulin, a 17 kDa Ca2+ sensor protein, in sperm function. The in vitro experimental approaches described in this article provide evidence strongly suggesting that calmodulin plays an important role in the priming (that is, capacitation) of mouse spermatozoa as well as in the agonist-induced acrosome reaction. In addition, we have used several calmodulin antagonists in an attempt to characterize further the morphological and biochemical changes associated with sperm capacitation. Data presented in this report suggest that calmodulin antagonists prevent capacitation by interfering with multiple regulatory pathways and do so either with or without adverse effects on sperm motility and protein tyrosine phosphorylation of sperm components.

Is sperm capacitation analogous to early phases of Ca2+-triggered membrane fusion in somatic cells and viruses?

An important feature of male fertility is the physiological priming of spermatozoa by a multifaceted process collectively referred to as capacitation. The end point of this evasive process is the hyperactivated spermatozoa capable of binding to terminal sugar residues on the egg's extracellular coat, the zona pellucida (ZP), and undergoing acrosomal exocytosis (i.e., induction of the acrosome reaction). The hydrolytic action of acrosomal enzymes released at the site of zona binding, along with the enhanced thrust generated by the hyperactivated beat pattern of the bound spermatozoa, are important factors that regulate the penetration of ZP and fertilization of the egg. Despite many advances in identifying sperm components that promote capacitation, the mechanism underlying the calcium-triggered process remains elusive. The purpose of this review article is to focus on new advances that have enhanced our understanding of in vivo/in vitro capacitation, a prerequisite event resulting from a dramatic modification and reorganization of the sperm membrane molecules. Special emphasis has been laid on accumulating evidence suggesting potential similarities between the sperm capacitation and early phases of calcium-triggered membrane fusion (i.e., tethering and docking) during secretory and endocytotic pathways among eukaryotes.

Evidence for the capacitation-associated membrane priming of mouse spermatozoa.

An important feature of male fertility is the physiological priming of mammalian spermatozoa by a multifaceted process referred to as capacitation. It is a prerequisite event before spermatozoa can bind to the egg's extracellular coat, the zona pellucida, and undergo a signal transduction cascade. The net result is the fusion of the plasma membrane (PM) and underlying outer acrosomal membrane at multiple sites and the release of acrosomal contents (i.e., glycohydrolases, proteinases, etc.) at the site of sperm-zona binding. In this study, we have used an indirect immunofluorescence (IIF) assay and other staining approaches to examine capacitation-associated membrane priming of mouse spermatozoa. For IIF studies, we used affinity-purified antibodies against two glycohydrolases that cross-reacted with the acrosomal enzymes only when the uncapacitated spermatozoa were permeabilized. Incubation of spermatozoa in a medium that favors in vitro capacitation induced membrane priming that allowed the antibodies to cross-react with the acrosomal enzymes in capacitating acrosome-intact spermatozoa without permeabilization, as revealed by the appearance of several distinct fluorescent patterns, including an initial immunopositive lining over the acrosome cap to an intense immunopositive reaction throughout the acrosome. These early immunopositive patterns were followed by the appearance of intense fluorescent spots (droplets) that seem to establish contact with the PM in a time-dependent manner. Inclusion of calmodulin, a 17-kDa Ca(2+)-binding protein which promotes capacitation, in the incubation medium did not alter the overall rate of capacitation; however, its presence accelerated the initial stages of membrane priming. The potential similarities between sperm capacitation and early events of Ca(2+)-triggered membrane fusion among eukaryotes and among various stations of the secretory and endocytotic pathways are discussed.

Acid Glycohydrolases in Rat Spermatocytes, Spermatids and Spermatozoa: Enzyme Activities, Biosynthesis and Immunolocalization.

Mammalian sperm acrosome contains several glycohydrolases thought to aid in the dispersion and digestion of vestments surrounding the egg. In this study, we have used multiple approaches to examine the origin of acrosome-associated glycohdyrdolases. Mixed spermatogenic cells, prepared from rat testis, were separated by unit gravity sedimentation. The purified germ cells (spermatocytes [SP], round spermatids [RS], and elongated/condensed spermatids [E/CS]) contained several glycohydrolase activities. Metabolic labeling in the cell culture, immunoprecipitation, and autoradiographic approaches revealed that beta-D-galactosidase was synthesized in SP and RS in 88/90 kDa forms which undergo processing in a cell-specific manner. Immunohistochemical approaches demonstrated that the enzyme was localized in Golgi membranes/vesicles, and lysosome-like structures in SP and RS, and forming/formed acrosome of E/CS.