Sperm Motility Is Lost In Vitro as a Consequence of Mitochondrial Free Radical Production and the Generation of Electrophilic Aldehydes but Can Be Significantly Rescued by the Presence of Nucleophilic Thiols1

Abstract

The prolonged incubation of human spermatozoa in vitro was found to induce a loss of motility associated with the activation of mitochondrial reactive oxygen species generation in the absence of any change in mitochondrial membrane potential. The increase in mitochondrial free radical production was paralleled by a loss of protein thiols and a concomitant rise in the formation of 4-hydroxynonenal, an electrophilic product of lipid peroxidation that was found to directly suppress sperm movement. These results prompted a search for nucleophiles that could counteract the action of such cytotoxic aldehydes, as a means of ensuring the long-term survival of spermatozoa in vitro. Four nucleophilic compounds were consequently assessed (penicillamine, homocysteine, N-acetylcysteine, and mercaptosuccinate) in three species (human, rat, and horse). The results of this analysis revealed drug and species specificity in the manner in which these compounds affected sperm function, with penicillamine conferring the most consistent, effective support. This prosurvival effect was achieved downstream of mitochondrial reactive oxygen species generation and was associated with the stabilization of 4-hydroxynonenal generation, the preservation of sperm thiols, and a reduction in 8-hydroxy-2'-deoxyguanosine formation. Theoretical calculations of Fe-S and Cu-S bond distances and corresponding binding energies suggested that the particular effectiveness of penicillamine may, in part, reflect the ability of this nucleophile to form stable complexes with transition metals that catalyze lipid peroxidation. The practical implications of these findings were indicated by the effective preservation of equine spermatozoa for 8 days at ambient temperature when the culture medium was supplemented with penicillamine.

Potential Risk of Senescence on Male fertility and Sperm DNA damage on Progeny

“…Studies in human and experimental animals have associated lipid peroxidation with abnormal sperm motility [61][62][63] . The prolongedexposure of human spermatozoa to ROS using xanthine oxidase as free radical generating system has shown that sperm motility is readily affected by oxidative attack and that hydrogen peroxide is the most cytotoxic oxygen specie [64][65][66][67][68].…”

Liquid storage of equine semen: Assessing the effect of d-penicillamine on longevity of ejaculated and epididymal stallion sperm

“…While storage at 5 • C for up to 72 h in an extender containing milk and/or egg yolk components generally yields acceptable pregnancy results, sperm motility, viability and fertilizing ability have all been shown to decline with storage time (Jasko et al, 1992;Aitken et al, 2012a;Pagl et al, 2006). The reduction in semen quality during liquid storage is partly attributable to the production of reactive oxygen species (ROS), as a result of oxidative phosphorylation by sperm mitochondria (Aitken et al, 2012b;Baumber et al, 2002;Ball, 2008).…”

“…Recently, attention has been directed to low molecular weight thiols [LMWTs] for their anti-oxidant properties (Aitken et al, 2012a;Wroblewski et al, 2003). These LWMTs are strong chelators of transition metals and act as free radical scavengers (Wadhwa and Mumper, 2013;Perret, 1977).…”

“…d-Penicillamine (3,3-dimethyl-d-cysteine) is a low molecular weight nucleophilic thiol and an ␣-amino acid metabolite of penicillin with anti-oxidant and metal chelating properties but no antibiotic properties (Perret, 1977;Shuxi Qiao et al, 2012). Moreover, during the storage of washed semen at both ambient and at body temperature, d-penicillamine has been reported to maintain higher percentages of motile stallion spermatozoa and to delay the decline in sperm velocity (Aitken et al, 2012a). Similar pro-survival effects of d-penicillamine have been reported for bull spermatozoa (Pavlok, 2000).…”

<b>Impacto da qualidade espermática sobre a fertilidade <i>in vivo</i> em bovinos:</b> contribuição de marcadores mitocondriais e subpopulações espermáticas

“…Os resultados deste estudo discordam desses achados, devido a que a peroxidação oxidativa teve correlação positiva com taxa de prenhez. Os dados sugerem que o dano peroxidativo marcado pelo BODIPY só é prejudicial para a fertilidade quando a produção de ROS na matriz mitocondrial supera as enzimas de defesa antioxidante intramitocondrial (SOD, GPx, Catalase) (KOPPERS et al, 2008 (AITKEN et al, 2012b).…”