RESUMO
Two synthetic magainins A and G are shown to have spermicidal activity. Transmission electron microscopic micrographs show that both magainins alter the plasma membranes of sperm and that these actions are rapid. Further studies will better delineate the contraceptive potential of synthetic magainins.
PIP: 2 synthetic magainins--A and G-- have been shown, through transmission electron microscopy, to have spermicidal activity. Magainins, a class of peptides isolated from the skin of the African clawed frog. I have been demonstrated to have wide spectrum in vitro antimicrobial activity. In this study, semen sample collected from 7 healthy volunteers were diluted with magainins A and G and then examined for spermiostatic activity. Sperm diluted only with saline were used as a control. Sperm assays indicated the potency of magainin A to be significantly greater than that of magainin G. Magainin A demonstrated spermiostatic activity at concentrations of 0.024-0.095 mg/mL compared to concentrations of 0.095-0.380 mg/mL for magainin G. A similar pattern was identified in the concentration of peptide required to inhibit sperm motility. Magainin A inhibited sperm motility when diluted in seminal plasma at concentrations of 0.77-1.54 mg/mL, while 1.54-3.08 mg/mL of magainin G were required to produce this effect. In the transmission electron microscopic studies, magainin-treated sperm cells incubated with either peptide consistently demonstrated denudation of the outer plasma membrane and partial disappearance of the acrosome, while sperm incubated in saline remained unaltered. It is hypothesized that magainins exert their spermicidal activity by disrupting the outer plasma membrane. The contraceptive potential of synthetic magainins should be explored through animal studies that measure the in vivo effects of seminal fluid and vaginal secretions on magainin activity and the effects of these agents on vaginal and cervical mucosa.
