Modulation of intrasperm Ca2+: A possible maneuver for spermicidal activity

Chlormequat chloride induced activation of calmodulin mediated PI3K/AKT signaling pathway led to impaired sperm quality in pubertal mice

Chlormequat chloride (CCC), as a widely used plant growth regulator, can cause impaired sperm quality and decreased testosterone synthesis in pubertal rats, but the underlying mechanism remains unclear. The purpose of this study was to elucidate the toxicokinetics and tissue distribution of CCC, as well as the possible mechanism of CCC-induced impairment in sperm quality. The concentration of CCC reached its peak 1 h after a single dose (200 mg/kg·bw) administration in mice plasma, and a bimodal phenomenon appeared in the testes, liver, and epididymis. In vivo, 200 mg/kg CCC caused testicular damage and impaired sperm quality in pubertal mice, and the expression of p-tyrosine and GSK3α decreased in cauda epididymidis, sperm and testes. CCC also caused the down-regulation of AKAP4 and the up-regulation of calmodulin (CaM), and activated the PI3K/AKT signaling pathway in the testes. In vitro, CCC reduced the levels of p-tyrosine, AKAP4 and GSK3α, increased the level of CaM and activated the PI3K/AKT signaling pathway in GC-1 cells. CaM antagonist (W-7 hydrochloride) and PI3K inhibitor (LY294002) can effectively improve the expression of GSK3α and AKAP4 by suppressing the PI3K/AKT signaling pathway in GC-1 cells treated with CCC. It was indicated that CCC induced impairment in sperm quality might be partially related to the activation of PI3K/AKT signaling pathway mediated by CaM.

Zinc pyrithione induces immobilization of human spermatozoa and suppresses the response of the cAMP/PKA signaling pathway

Zinc pyrithione (ZPT), a zinc coordination complex, is used as an antimicrobial agent. This study investigated the molecular mechanisms underlying ZPT-induced spermatozoa immobilization by examining plasma membrane integrity, mitochondrial dysfunction, and the cAMP/PKA signaling pathway response. ZPT inhibited spermatozoa motility and movement patterns in a concentration-dependent manner. The 100% effective concentration (EC₁₀₀) and median effective concentration (EC₅₀) at which ZPT-induced spermatozoa immobilization at 20 s were 40 μmol/L and 16.19 μmol/L, respectively. ZPT did not significantly disrupt spermatozoa plasma membranes, but it exerted a strong and significant effect on the depolarization of mitochondria. In addition, ZPT exposure induced intracellular H⁺ accumulation and Ca²⁺ dissipation in spermatozoa, accompanied by suppression of the cAMP/PKA signaling pathway. Thus, ZPT induces spermatozoa immobilization without significant plasma membrane injury and so could be a candidate microbicidal spermicide.

Spermicidal activity of sulfonylureas and meglitinide analogues: role of intrasperm Ca2+ elevation

Intrasperm calcium concentration ([Ca2+]is) is known to play a vital role in regulating motility and viability of ejaculated spermatozoa. KATP channel blockers are reported to block KATP channels, leading to depolarization of the cell membrane. This activates the voltage-gated calcium channels, resulting in enhanced Ca2+ influx, which eventually elevates the intracellular [Ca2+] level. Hence, it can be hypothesized that drugs acting on KATP channels could possess the ability to elevate [Ca2+]is. Sulfonylureas such as glibenclamide or gliclazide, as well as meglitinide analogues such as repaglinide, produced a dose- and time-dependent decrease in viability, each requiring 7.5 mm, 10 mm and 6.5 mm, respectively, to produce death of all sperm cells immediately upon addition to ejaculated human semen samples. The reduction in sperm viability was accompanied by an elevation of [Ca2+]is and was affected by removal of extracellular Ca2+. Significantly (P < 0.05) less time was required to elevate [Ca2+]is and produce complete loss of sperm viability when any of these drugs were added to sperm cells simultaneously with selected agents affecting Ca2+ homeostasis. Thus, the spermicidal activity of these drugs attributed to elevation of [Ca2+]is and their synergism can be potentially exploited for developing contact spermicidal formulations.

Intrasperm Ca2+ modulation and human ejaculated sperm viability: influence of miconazole, clotrimazole and loperamide

Elevation of intrasperm Ca2+ is reported to influence viability of ejaculated spermatozoa. Human spermatozoa possess inositol triphosphate (IP3)-sensitive Ca2+ stores, which can be targeted for increasing intrasperm Ca2+ level. The influence of agents affecting Ca2+ homeostasis has been investigated. Miconazole nitrate, clotrimazole and loperamide hydrochloride produced a dose- and time-dependent decrease in viability, each requiring respectively 0.5, 1.0 and 1.0 mM for producing death of all sperm cells immediately upon addition to ejaculated human semen samples. The reduction in sperm viability was accompanied by elevation of intrasperm Ca2+ and was not affected by presence or absence of extracellular Ca2+. Significantly (P < 0.05) less time was required for producing complete loss of sperm viability and increasing intrasperm Ca2+ when any of these drugs was added to sperm cells previously treated with selected agents affecting Ca2+ homeostasis. This enhanced spermicidal activity of miconazole, clotrimazole and loperamide appeared to be due to further mobilization of Ca2+ from partially depleted intrasperm Ca2+ stores. Synergism of spermicidal activity and intrasperm Ca2+ elevation by miconazole or clotrimazole was observed when Ca2+ efflux from sperm cells was simultaneously inhibited by 2′,4′-dichlorobenzamil hydrochloride, a Na+-Ca2+ exchange inhibitor. The spermicidal activity of miconazole, clotrimazole or loperamide due to elevation of intrasperm Ca2+ and its synergism, therefore, has great potential for exploitation of these drugs as contact spermicides.

Calcium channel antagonists: clinical uses--past, present and future

The calcium channel antagonists are a mature group of drugs directed at cardiovascular diseases including hypertension, angina, peripheral vascular disorders and some arrhythmic conditions. Their sites and mechanisms of actions have been well explored over the past two decades and their interactions at the alpha(1) subunit of L-type channels (Ca(V)1.1-1.4) have made them valuable molecular tools for channel classification and localization. With the realization that other members of the voltage-gated calcium channel family exist--Ca(V)2.1-2.3 and Ca(V)3.1-3.3--considerable effort has been directed to drug discovery at these channel types where therapeutic prospects exist for a variety of disorders including pain, epilepsy, affective disorders, neurodegenerative disorders, etc. In contrast to the situation with the L-type channel antagonists success in developing small molecule antagonists of therapeutic utility for these other channel types has thus far been lacking. The reasons for this are explored and potential new directions are indicated including male fertility, bone growth, immune disorders, cancer and schistosomiasis.