Unscheduled DNA synthesis in the testis, a secondary test for the evaluation of chemical mutagens

Abstract

DNA damage induced by methylmethane sulfonate, cyclophosphamide, doxorubicin and procarbazine in male germ cells was assessed in rabbits by the demonstration of unscheduled DNA synthesis (UDS), in meiotic and postmeiotic phases of maturation. Immediately after treatment by the intravenous route tritiated thymidine was injected into both testicles. Subsequently, rabbits were ejaculated serially, sperm heads were isolated and assayed for radioactivity by liquid scintillation counting. Dose-dependent UDS was demonstrated in late spermatocytes and early spermatids. High doses of hycanthone also induced UDS, but isoniazid and metronidazole had no effect. The rabbit testis UDS test takes into account metabolic and pharmacokinetic aspects of the test substances and provides information about their penetration through the blood-testicular barrier. It is therefore useful for secondary evaluation of potential mutagens. UDS induced by procarbazine was abolished by simultaneous treatment with Ara-C. Thus, the test also recognizes substances that inhibit DNA repair synthesis.

Unscheduled DNA synthesis assay in mammalian spermatogenic cells: An update

“…3). Our results confirm the negative results obtained with the UDS assay in the rabbit [Zbinden, 1980]. However, these tests did not rule out the possibility that metronidazole may require metabolic activation to cause DNA damage.…”

“…UDS has not been detected in mature spermatids or sperm [Sega, 1974;Sotomayor et al, 1978Sotomayor et al, , 1979Tanaka and Katoh, 1979;Zbinden, 1980;Sega and Sotomayor, 1982;Working and Butterworth, 1984;Bentley and Working, 1988b]. Recently, UDS has been demonstrated in stem and early differentiating spermatogonia of mice after treatment with 1-ethyl-1-nitrosourea (ENU) and 1-methyl-1-nitrosourea (MNU) [Sotomayor et al, 1999a].…”

An assay to detect chemically induced DNA repair in rat spermatocytes

“…Similar results have been described in the mouse and rabbit [Sega, 1974;Sega et al, 1976;Schmid et al, 1978;Sotomayor et al, 19791. Rat spermatocytes, when exposed in vivo to the chemotherapeutic agent CPA, exhibited increased levels of UDS. CPA, an indirect alkylating agent, has also been shown to cause UDS in mouse and rabbit spermatids after in vivo exposure [Sotomayor et al, 1978;Zbinden, 1980;Schmid and Racine, 19821. Other compounds that require metabolic activation to be genotoxic-including DMN, AFBl , and 2-AAF,-did not cause UDS in rat pachytene spermatocytes, even when tested at dosages, times, and routes of exposure known to induce UDS in rat hepatocytes in the in vivo /in vitro hepatocyte DNA repair assay [Mirsalis et al, 19821. A similar UDS assay has been developed for mouse spermatogenic cells by Sega and co-workers [Sega, 1974;Sotomayor et al, 19791.…”

Reappraisal of the use of procarbazine in the treatment of lymphomas and brain tumors

“…Unscheduled DNA synthesis in the testes of rabbits has also been reported (Zbinden 1980). As might be expected with an agent that inhibits DNA, RNA, and/or protein synthesis, reduced fertility has been seen in male mice given procarbazine (Chryssanthou et al 1983).…”