Induction of apoptosis in the germ cells of adult male rats after exposure to cyclophosphamide

Treatment with cyclophosphamide, a commonly used anticancer drug, may result in oligozoospermia or azoospermia. The objective of this study was to determine whether exposure of male rats to cyclophosphamide induces apoptosis in male germ cells, and if so, when the peak of apoptosis occurs and at what specific stages of spermatogenesis. The presence of apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) detection in situ and by an increase in DNA fragmentation (DNA ladder). To determine the time course of drug-induced apoptosis, male Sprague-Dawley rats were treated with a single dose (70 mg/kg BW) of cyclophosphamide, and the testes were fixed 0, 4, 8, 12, 18, 24, and 48 h after treatment. To determine the dose response, rats were treated with doses of cyclophosphamide (0, 2, 7, 20, and 70 mg/kg), and the testes were fixed 12 h after treatment. A low spontaneous incidence of apoptosis was observed in controls, in particular in premeiotic germ cells of stages I-IV and XI-XIV of the seminiferous tubules. In cyclophosphamide-exposed rats, the incidence of apoptosis increased progressively at 4 h and 8 h, reached a peak at 12 h (about 3.5-fold above control), and then decreased rapidly to control levels by 48 h. A 70-mg/kg dose of cyclophosphamide induced a significant increase in apoptosis; lower doses did not. Although drug-induced apoptosis occurred in all stages of germ cells, it was most pronounced in spermatogonia and spermatocytes in stages I-IV and XI-XIV. Thus, apoptosis may be involved in the occurrence of oligozoospermia or azoospermia after cyclophosphamide treatment. Apoptosis of damaged premeiotic germ cells may serve a critical role in protecting subsequent generations from the diverse effects of toxicants.