Mutagenicity of Ascaris chymotrypsin inhibitor in germ cells of mice

Abstract

Chymotrypsin inhibitor isolated from Ascaris suum (ACHI) was tested for the induction of dominant lethal mutations in male mice. Dominant lethal effects of ACHI for the main stages of germ cell development were analyzed by mating at specific time points after dosing. Two groups of adult BALB/c males received 24 or 40 mg per kilogram body weight (BW) per day intraperitoneal (IP) injection of ACHI in sterile phosphate-buffered saline (PBS) for five consecutive days (subacute exposure). Males from a third group were administered single IP injections of ACHI-60 mg/kg BW (acute exposure). The control group received concurrent injections of PBS for five successive days. After the last dose, each male was mated with two untreated females. For fractionated examination with regard to successive germ cell stages (spermatozoa, spermatids, spermatocytes, spermatogonia), every second week, two other untreated virgin females were placed with each male for mating. The uteri of the females were inspected on the 15th day of gestation, and preimplantation loss and postimplantation loss determined from dominant lethal parameters. Exposure of mice germ cells to ACHI did not impair mating activity of males. Fertility index was reduced (P < 0.05) only for females mated at the third week with males exposed to the highest dose of ACHI. In the females bred to ACHI-treated males, significant (P < 0.05) increase in preimplantation loss was observed at postinjection weeks 1 (reflecting exposure to spermatozoa after single treatment and to spermatozoa or late spermatids after subacute dosing) and 3 (reflecting exposure to mid and early spermatids for acute dosing and to mid and early spermatids or late spermatocytes following acute treatment), regardless of dose and length of exposure to the inhibitor. At the 60-mg/kg-BW group, a significant increase of this parameter was also noted at week 5 (reflecting exposure to early spermatocytes). During mating days 15-21, a significant (P < 0.05) increase in postimplantation loss and dominant lethal effects were observed for all doses of ACHI. Acute ACHI exposure 5 weeks prior to mating resulted in dominant lethal effects in early spermatocytes. These preliminary data suggest that ACHI induces dominant lethal mutations at postmeiotic and meiotic stages of spermatogenesis, but spermatids are the most sensitive cell stage to the effect of ACHI. These results show that ACHI may be one of the factors causing disturbances in spermatogenesis leading to a reduction of host reproductive success.