Benzo[a]pyrene, an active component of tobacco smoke and automobile exhaust can cause increased hyperactivation and premature acrosome reaction in human spermatozoa.
AMRI Medical Center06 May 2009
Benzo[a]pyrene significantly affected sperm functional competence as evidenced by increased hyperactivation as well as premature acrosomal reaction in vitro- according to a collaborative study published in Fertility & Sterility done by Institute of Reproductive Health & Toxicology, University of Calcutta and IVF Div, AMRI Medical center, Kolkata, India.
Content: The polycyclic aromatic hydrocarbon benzo[a]pyrene is one of the most harmful components of tobacco and its other environmental sources are automobile exhausts and coal tar.
Present study has shown that Benzo[a]pyrene significantly affected sperm functional competence as evidenced by increased hyperactivation as well as premature acrosomal reaction in vitro. A person who smokes a pack of 20 tobacco cigarettes per day is expected to inhale anything from 0.067 mg to 0.568 mg of benzo [a] pyrene per day.
According to Dr. Dyutiman Mukhopadhyaya, a scientist in the team who did the present study, hyperactivation of human spermatozoa is characterized by high amplitude and asymmetrical flagellar bending. Computer assisted semen analyzers can be used to identify hyperactivated sperm by setting minimum thresholds for curvilinear velocity and lateral head movement and a maximum threshold for linearity of path. One of the important parameters of the CASA-based study is the hyperactivation module in recent CASA system in the market whereby one can analyze the percentage of hyperactivated spermatozoa. Mammalian sperm hyperactivation is calcium dependent and is typified by a change in normal motility parameters during capaciation.
It is worth mentioning here that epidemiologic surveys on smoking have revealed that the seminograms of smokers differ considerably from those of nonsmokers, and that the parameters affected include spermmotility andmorphology
According to Dr. Alex Varghese, Scientific Director, AMRI IVF and a co-author of the paper, in a previous study by our group we noted that heavy smokers (more than 20 tobacco cigarettes per day) showed an increased percentage of hyperactivated spermatozoa compared with nonsmokers.
Earlier studies have shown that polycyclic aromatic hydrocarbons can alter intracellular calcium homeostasis. The Ca rise is coupled with increased tyrosine phosphorylation, and it has also been shown that benzo[a]pyrene and especially its metabolites can increase intracellular Ca with an increase in tyrosine phosphorylation activity. Recently, Harvard researchers have zeroed in on a protein called CatSper1-, which appears to hold a key to this whole process. In a paper published in the journal Nature, the researchers showed that the protein plays a key role in the flow of calcium ions into the sperm cell. Studies on Ion-channel complexes in germ cells exposed to environmental toxicants hence may throw light on molecular defects associated with increasing cases of male infertility. According to Dr. Varghese, although the sperm hyperactivation assay using modern CASA systems, an important test in the functional as well as fertilization potential of spermatozoa population, pre!
sence of higher proportion of hyperactivated sperm fraction in neat semen may indicate functional incompetence of germ cells.