Use of primary cultures of human hepatocytes in toxicology studies.

Often results from toxicological studies using rodent models cannot be directly extrapolated to probable effects in human beings. In order to examine the genotoxic potential of chemicals in human liver cells, a human hepatocyte DNA repair assay has been defined. Procedures were optimized to prepare primary cultures of human hepatocytes from discarded surgical material. On eight different occasions human hepatocyte cultures of sufficient viability to measure DNA repair were successfully prepared by collagenase perfusion techniques. The cells were allowed to attach to plastic or collagen substrata for periods of 1.5 to 24 h and subsequently incubated with [3H]thymidine and test chemicals for periods of 18 to 24 h. Chemically induced DNA repair, measured as unscheduled DNA synthesis, was quantitated autoradiographically. The following compounds were tested: 2-acetylaminofluorene, aflatoxin B1, 2-aminobenzyl alcohol, aniline, benzo(a)pyrene, carbon tetrachloride, chloroform, 2,4-diaminotoluene, 2,6-diaminotoluene, di(2-ethylhexyl)phthalate, dimethylnitrosamine, 1,6-dinitropyrene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, methyl chloride, 5-methylchrysene, mono(2-ethylhexyl)phthalate, 2-methyl-2-P-(1,2,3,4-tetrahydro-1-naphthyl)phenoxypropionic acid (nafenopin), beta-naphthylamine, nitrobenzene, 2-nitrobenzyl alcohol, 2-nitrotoluene, 2,3,7,8-tetrachlorodibenzo-p-dioxin, unleaded gasoline, and 4-chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic acid (Wy-14,643). In only one of eight cases did some of the chemicals generally regarded as genotoxic fail to give a positive response. For purposes of comparison, all test chemicals were evaluated in the in vitro rat hepatocyte DNA repair assay. Individual-to-individual variation in the DNA repair response was far greater for the human cultures than for cultures derived from rats. For only three chemicals was there a qualitative difference in the response between the rodent and the human cells; beta-naphthylamine was positive in the rat but in none of the human cultures examined, whereas the opposite was seen for 2,6-diaminotoluene and 5-methylchrysene. Clofibric acid, mono(2-ethylhexyl)phthalate, and Wy-14,643 induced enzymes indicative of peroxisomal proliferation in primary rat hepatocyte cultures, but not in two human hepatocyte cultures. These results indicate that, in general, the in vitro rat hepatocyte DNA repair assay is a valid model for predicting potential genotoxic effects in human beings. However, rodent hepatocytes may not be appropriate for assessing the potential of chemicals to elicit nongenotoxic effects in human beings such as the induction of hepatocyte peroxisomal proliferation.

Doxorubicin entrapped in sterically stabilized liposomes: effects on bacterial blood clearance capacity of the mononuclear phagocyte system.

The introduction of long-circulating liposomes sterically stabilized by surface coating with polyethylene glycol has expanded the potential for drug targeting to tumors. In recent clinical studies, evidence of significant antitumor activity has been obtained with the industrially prepared formulation of long-circulating polyethylene glycol-coated liposomes containing doxorubicin, referred to as DOXIL. Previous studies performed in rats showed that doxorubicin-containing liposomes can exert major toxic effects on the liver macrophage population for a considerable period of time; a strong impairment of phagocytic function and even a substantial depletion of the liver macrophage populations were observed. In the present study, the phagocytic function of the mononuclear phagocyte system (MPS) after administration of DOXIL at a clinically relevant dosage schedule was evaluated in rats. Phagocytic function of the MPS was assessed by determining bacterial blood clearance capacity. The observations reported herein show that DOXIL is fairly well tolerated regarding bacterial blood clearance capacity of the MPS when administered in a regimen that resembles the clinical setting closely. This outcome has important implications with regard to the clinical utility of the liposomal drug, especially in the restricted context of immunocompromised cancer patients who easily develop systemic infections and should not be confronted with a therapy-induced reduction of the bacterial blood clearance capacity of the MPS.

Encapsulation of the topoisomerase I inhibitor GL147211C in pegylated (STEALTH) liposomes: pharmacokinetics and antitumor activity in HT29 colon tumor xenografts.

The topoisomerase I inhibitor GL147211C [7-[(4-methylpiperazino)methyl]-10,11-(ethylenedioxy)-(20S)-campto thecin trifluoroacetate], a camptothecin analogue, has significant activity in tumor cell cytotoxicity assays in vitro and antitumor activity in both animal tumor models and human patients. Its toxicity is significant, however, effectively limiting the amount of drug that can be administered and its clinical utility. To determine whether the therapeutic index of GL147211C could be improved, the drug was encapsulated in long-circulating, pegylated (STEALTH) liposomes (SPI-355). The pharmacokinetics and antitumor activity of SPI-355 were compared to those of nonliposomal GL147211C. The plasma pharmacokinetics of SPI-355 in rats were typical of those of other pegylated liposomal formulations, with significantly increased blood circulation time; the dose-corrected area under the curve and Cmax of SPI-355 (10 mg/kg) were 1250- and 35-fold higher, respectively, than those of nonliposomal GL14711C (8.72 mg/kg). The comparative antitumor activity of SPI-355 and nonliposomal GL1472211C was evaluated in nude mice implanted with HT29 colon carcinoma xenografts. SPI-355 was 20-fold more effective than GL147211C in inhibiting tumor growth (1 mg/kg SPI-355 and 20 mg/kg GL147211C) and produced durable complete remissions of tumors at well-tolerated dose levels that were >5-fold lower than the maximally tolerated dose of GL147211C, which induced no durable complete responses. Signs of toxicity were similar between the two drugs, but liposome encapsulation increased the toxicity of drug approximately 4-fold, with increased weight loss and several deaths with SPI-355 (5 mg/kg SPI-355 versus 20 mg/kg GL147211C). Despite the increased toxicity seen with SPI-355, the therapeutic index of the liposomal formulation was increased approximately 5-fold over that of nonliposomal GL147211C, suggesting that such a pegylated liposomal formulation could demonstrate increased therapeutic index in human patients.

Male reproductive toxicology: comparison of the human to animal models.

The human male is of relatively low fertility and thus may be at greater risk from reproductive toxicants than are males of the common laboratory animal model species. Lack of knowledge of the physiological differences that contribute to interspecies variation between man and animals can prevent the effective application of animal data to the assessment of human reproductive risk. Evaluation of spermatogenesis from testicular histology, while uncommon, can provide valuable information about human reproductive risk. The measurement of sperm count or concentration has long been the most feasible approach for human semen evaluation, but may be an insensitive indicator of reproductive function because of high sample-to-sample variability. Interspecies extrapolation factors can be calculated by comparing the reduction in sperm count in humans and test species after exposure to drugs or chemicals. These factors can provide a realistic assessment of relative risk, provided that the sperm are counted at the appropriate time after exposure. However, the degree to which extrapolation factors derived for one agent, and only from sperm counts, can be generalized is not known. Monitoring of sperm motility and morphology parameters is also a common means of evaluating human semen quality, but these techniques are also hampered by the relatively high interindividual and intersample variability. Computer-assisted and morphometric approaches show promise of decreasing the subjective nature of these evaluations and increasing their value in risk assessment procedures. Improvements in predicting human reproductive risk can be expected to come from increased knowledge about reproductive mechanisms in man and animals, together with the utilization of objective measures of cellular indicators of male reproductive function.

Sterically stabilized liposomes in cancer therapy and gene delivery.

The introduction of colloidally stable liposomes with low drug leakage rates resulted in a renaissance in liposome applications in cancer therapy. Furthermore, a platform of sterically stabilized liposomes also allows the construction of new generations of drug delivery vehicles. These include targeted liposomes and targeted nucleic acid delivery vehicles, based either on cationic sterically stabilized liposomes or pre-condensed DNA encapsulated in neutral or negatively charged liposomes.

TAURINE AND HYPOTAURINE: THEIR EFFECTS ON MOTILITY, CAPACITATION AND THE ACROSOME REACTION OF HAMSTER SPERM IN VITRO AND THEIR PRESENCE IN SPERM AND REPRODUCTIVE TRACT FLUIDS OF SEVERAL MAMMALS.

Previous work from this laboratory has shown that the ß-amino acid taurine can support and stimulate hamster sperm motility during in vitro capacitation in the presence or absence of epinephrine. The present report describes in vitro results which demonstrate that hypotaurine, a precursor of taurine, can also support and stimulate motility under these conditions and that a higher number of acrosome reactions occur in the presence of taurine as compared to hypotaurine (both in the presence and absence of epinephrine). In all cases, the greates percentage of acrosome reactions occurs in the presence of epinephrine. Whether these ß-amino acids act independently of epinephrine of in a synergistic manner with it remains to be determined. In addition to these in vitro studies, we report that hypotaurine and taurine are present at high levels in bovine follicular fluid, rabbit uterine and ampullar oviductal fluid (11 hr after mating, i.e., 1 hr after ovulation), monkey oviductal fluid, bovine adrenal cortex "motility factor" preparation and human, guinea pig and hamster sperm preparations. Based on these results, we suggest the possibility that taurine and hypotaurine may have roles in vivo in the maintenance and stimulation of sperm motility and stimulation of capacitation and/or acrosome reactions.

Postheparin plasma lipase activities in obesity: failure to increase with adipose organ enlargement.

Published studies have shown that overproduction of very low density lipoproteins is a major factor leading to hypertiglyceridemia in obesity. Few systematic studies of triglyceride removal or postheparin lipoprotein lipase activity (LPLA) in obesity have appeared. We have examined heparin-released lipoprotein triglyceride hydrolase activities in 12 lean and 12 obese age- and sex-matched volunteers after overnight fasting. Heparin doses were calculated to compensate for the disproportionality between body mass and plasma volume in obesity. Triglyceride hydrolase activities of hepatic (HTGLA) and extrahepatic (LPLA) origin were distinguished by in vitro inhibition of LPLA with protamine sulfate. Incremental heparin doses were given to each subject to determine lipase activities under conditions of maximal release and to define sensitivity to heparin-facilitated lipase release. Maximal postheparin LPLA and HTGLA (u/ml plasma or u/total plasma vol) were similar in lean and obese individuals despite a nearly three-fold increase in calculated adipose tissue mass in the obese. Since adipose tissue LPLA has been reported to increase in proportion to adipocyte size, the lack of difference in maximal postheparin LPLA was expected. There was an inverse correlation between plasma triglyceride concentration and LPLA/kg adipose tissue. These empirical observations may reflect relatively decreased heparin-releaseable (functional) LPLA in relation to adipose organ mass in obese subjects. The mechanism of this relationship has not been established.

Heparin resistance and decreased hepatic triglyceride hydrolase release during long-term estrogen-progestin treatment.

These studies were undertaken to define the mechanism for the depression of post-heparin triglyceride hydrolase activity in women treated with estrogen-progestin oral contraceptives. Six treated and six control women were studied. Total, protamine-inhibited, and protamine-resistant triglyceride hydrolase activities were measured after six different intravenous doses of heparin in each subject in order to determine the dose-response relationships for lipase release. As has been reported during short-term treatment with estrogens, long-term treatment with oral contraceptive agents is accompanied by selective depression of protamine-resistant (hepatic) lipase activity. This depression can be partly reversed by the administration of large heparin doses, but maximally releasing heparin does fail to restore postheparin protamine-resistant activity to control values. These data are compatible with the idea that the releasable pool of hepatic triglyceride hydrolase activity is diminished in women who receive oral contraceptive agents and that the pharmacokinetics of its release are altered in such a way that only relatively high concentrations of heparin displace the enzyme from this pool.

Effect of short-term infusion of recombinant human relaxin on blood pressure in the late-pregnant rhesus macaque (Macaca mulatta).

OBJECTIVE: To test a recombinant human relaxin preparation, developed for potential therapeutic application, for possible hypotensive actions in near-term pregnant rhesus monkeys. METHODS: Groups of four females received 1-hour intravenous infusions of 0, 0.1, or 2.0 mg recombinant human relaxin/kg on gestation day 147 (term = 165 days). Maternal heart rate, electrocardiogram, and diastolic, systolic, and mean arterial pressure; and fetal heart rate were monitored before, during, and after the infusion. After spontaneous delivery, physical, neurobehavioral, and physiologic examinations were conducted on the newborn. RESULTS: No effects of recombinant human relaxin were detected by statistical analysis or examination of data records. CONCLUSION: Intravenous infusion of up to 2.0 mg recombinant human relaxin/kg in conscious pregnant rhesus monkeys had no effect on maternal cardiovascular indices or fetal heart rate.

Comparative intravenous toxicity of cisplatin solution and cisplatin encapsulated in long-circulating, pegylated liposomes in cynomolgus monkeys.

The toxicity of cisplatin encapsulated in pegylated, long-circulating liposomes (SPI-077) was compared with nonliposomal cisplatin in male and female cynomolgus monkeys (n = 2-4 per sex per group) treated with intravenous infusions of 2.5 or 25 mg/kg SPI-077, 2.5 mg/kg cisplatin, placebo liposomes, or saline once every 3 weeks for total of five treatments. All animals survived until scheduled necropsy at 3 days after the final treatment or after a treatment-free 4-week recovery period. Emesis occurred after each treatment in all cisplatin-treated monkeys, but only once in one monkey treated with high-dose SPI-077. Dose-related mild decreases in red blood cell (RBC) count, hemoglobin, and hematocrit to or slightly below low normal range occurred in the high-dose SPI-077 and placebo liposome treatment groups after each treatment, with partial to complete recovery between treatments and no signs of correlating bone marrow toxicity. Decreases were similar in cisplatin-treated monkeys, but resolved only slightly between treatments and after the end of treatment (continuing to decrease in females) and were accompanied by bone marrow hypocellularity. Indirect, but not direct, bilirubin levels were cyclically elevated in the high-dose SPI-077 and placebo-treated animals, but not in the other treatment groups. Levels had either fully resolved or were near baseline and/or saline group values prior to the next treatment. Serum cholesterol levels were cyclically increased in SPI-077- and placebo liposome-treated animals, and minimally increased numbers of foam cells were seen in the liver, spleen, kidney, and other organs; both were considered related to the lipid dose administered. Cisplatin-treated monkeys exhibited sensory polyneuropathy and moderate irreversible toxic tubular nephrosis, but no neuropathy or nephrotoxicity was seen in either SPI-077 treatment group. Microscopically, treatment-related cell death was seen in dorsal root ganglia (DRG), affecting 15% of the cells in cisplatin-treated animals, compared to 8 and 12% in the low- and high-dose SPI-077 treatment groups. Neither drug was ototoxic. In summary, repeated administration of SPI-077 produced minimal, reversible effects related to the lipid dose administered, mostly limited to the 25 mg/kg dose group. The most notable effects in this group were cyclical decreases in hematology parameters thought to be related to increased recycling of a small fraction of RBCs and limited cell death in the DRG in the absence of any neurophysiological changes. Animals treated with a 10-fold lower dose of cisplatin (2.5 mg/kg), in contrast, exhibited myelo-, nephro-, and neurotoxicity, including sensory neuropathy, and were emetic after every dose. The SPI-077 liposomal formulation of cisplatin may provide a less toxic alternative to standard cisplatin solution.

Comparative pharmacokinetics, tissue distribution, and therapeutic effectiveness of cisplatin encapsulated in long-circulating, pegylated liposomes (SPI-077) in tumor-bearing mice.

PURPOSE: The pharmacokinetics (PK), biodistribution and therapeutic efficacy of cisplatin encapsulated in long-circulating pegylated (Stealth) liposomes (SPI-077) were compared with those of nonliposomal cisplatin in two murine (C26 colon carcinoma and Lewis lung) tumor models. METHODS: In therapeutic effectiveness studies, mice bearing murine C26 or Lewis lung tumors received multiple intravenous doses of SPI-077 or cisplatin in a variety of treatment schedules and cumulative doses. In the PK and biodistribution study, mice received a single intravenous bolus injection of 3 mg/kg of either SPI-077 or cisplatin 14 days after inoculation with 10(6) C26 tumor cells. Plasma and tissues were analyzed for total platinum (Pt) content by graphite furnace (flameless) atomic absorption spectrophotometery (GF-AAS). RESULTS: Efficacy studies showed that SPI-077 had superior antitumor activity compared to the same cumulative dose of cisplatin. When lower doses of SPI-077 were compared to cisplatin at its maximally tolerated dose in Lewis lung tumors, equivalent SPI-077 antitumor activity was seen at only half the cisplatin dose. Higher cumulative doses of SPI-077 were well tolerated and had increased antitumor effect. SPI-077 PK were characterized by a one-compartment model with nonlinear (saturable) elimination, whereas cisplatin PK were described by a two-compartment model with linear elimination. SPI-077 had a 55-fold lower [corrected] volume of distribution, 3-fold higher peak plasma levels, and a 60-fold larger plasma AUC compared with cisplatin. In addition, SPI-077-treated animals displayed a 4-fold reduction in Pt delivered to the kidneys (primary target organ of toxicity) relative to cisplatin, but a 28-fold higher tumor AUC than cisplatin. CONCLUSIONS: Based on the results of our studies, encapsulation of cisplatin in long-circulating pegylated liposomes has overcome limitations experienced with other liposomal cisplatin formulations. SPI-077 has a prolonged circulation time and increased tumor Pt disposition, and its antitumor effect is significantly improved compared to cisplatin in murine colon and lung cancer models.

Use of seminiferous tubule segments to study stage specificity of unscheduled DNA synthesis in rat spermatogenic cells.

DNA repair in spermatogenic cells at various stages of maturity was determined by quantitation of unscheduled DNA synthesis (UDS). Male F-344 rats were exposed (i.p.) to methyl methanesulfonate (MMS, 35 mg/kg); 1 hr later, segments of seminiferous tubules corresponding to spermatogenesis stages II, IV-V, VI, VII, VIII, IX-X, XII, and XIV were isolated with the transillumination pattern of the tubules as a guide. Intact tubule segments were cultured 24 hr in the presence of [3H]thymidine, and UDS was quantitated by autoradiography as net grains/nucleus (NG). In primary spermatocytes from treated rats, NG count increased with increasing maturity from leptotene primary spermatocytes (3.5 NG) up through stage VIII and IX-X pachytene spermatocytes (22 NG), after which NG decreased in stage-XII pachytene and diplotene spermatocytes (to 16 NG and 8 NG, respectively). Round spermatids of steps 2-8 of spermiogenesis all exhibited approximately the same UDS response (8 NG). Elongating spermatids as mature as step 14 underwent UDS after exposure to MMS, but step-15 and later-step spermatids did not. The DNA repair response of pachytene spermatocytes cultured within segments of seminiferous tubule corresponding to stages VIII and IX-X was 4 to 25 times greater, depending on the dose of MMS, than pachytene spermatocytes isolated by enzymatic digestion and cultured in suspension [Bentley and Working, Mutat Res 203:135-142, 1988]. Thus, the use of segments of seminiferous tubule both increased the sensitivity of UDS as an indicator of DNA damage in rat germ cells and enabled the study of UDS in spermatogenic cells at different stages of maturity.

Tissue-specific genotoxic effects of acrylamide and acrylonitrile.

Acrylamide (AA) has been reported to induce dominant lethal mutations in male rat germ cells and tumors in a variety of organs, including the scrotum, thyroid and mammary glands, but not the liver of rats. The structurally similar vinyl monomer acrylonitrile (ACN) does not induce dominant lethal mutations but does induce tumors of the brain, Zymbal gland, forestomach and mammary gland, but not the liver of rats. Several in vitro and/or in vivo unscheduled DNA synthesis (UDS) assays were employed to examine the potential tissue-specific genotoxic activity of these compounds. Neither AA nor ACN induced DNA repair in either the in vitro or in vivo hepatocyte DNA repair assays. Glycidamide (GA), a mutagenic metabolite of AA, induced DNA repair in the in vitro hepatocyte DNA repair assay. Cyanoethylene oxide (CEO), a mutagenic metabolite of ACN, did not yield a DNA repair response in the in vitro hepatocyte DNA repair assay, but was highly toxic and could not be tested at doses equivalent to GA. AA, but not ACN, produced a DNA repair response in the in vivo spermatocyte DNA repair assay. AA produced a slight response in the in vitro human mammary epithelial cell (HMEC) DNA repair assay in normal cells derived from discarded surgical samples from five different women. GA produced a strong UDS response in all cases in the same assay. CEO, but not its parent compound ACN, produced a response in the HMEC DNA repair assay. These results show a highly tissue-specific pattern of genotoxic activity for AA and ACN that correlates, to the extent that it has been examined, with the tissue-specific pattern of carcinogenic and dominant lethal activity. The induction of DNA repair by GA and CEO confirms the genotoxic potential of these metabolites. While the observation of genotoxic activity of AA in the HMEC DNA repair assay suggests that mammary cells might be a target for carcinogenic activity of this compound in humans, other factors such as pharmacokinetics and epidemiology must be evaluated to establish that effect.

Computer-assisted semen analysis: results vary across technicians who prepare videotapes.

Automated semen analyses revealed differences of 21% to 30% in concentration-related parameters and 5% to 11% in motion-related parameters between means of groups of replicate specimens. Disparities among videotapes produced by two laboratory technicians accounted for the divergence in concentration-related parameters. This resulted partially from differences between the two technicians in propensity to dilute concentrated specimens. The causes of the greater portion of disparities between videotaping technicians, however, have not been identified. Differences in motion-related parameters could not be ascribed to technicians, but the basis for these differences is also unknown. The results suggest that values obtained from the CellSoft image analysis system may not be comparable between technicians or laboratories, despite use of identical computer parameter settings. Until effective quality control measures have been implemented, such comparisons must be made with caution.

Computerized videomicrographic analysis of rat sperm motility.

Quantitative methods for the determination of the concentration, percent motility and swimming speed of human and animal spermatozoa can assist in the objective analysis of sperm and semen quality. These parameters are among the most discriminating indicators for both clinical and toxicologic assessments of reproductive function. A computerized videomicrographic analysis system to measure sperm motility characteristics in the Fischer 344 rat was characterized and compared with both manual and semi-automated videomicrographic methods (Blazak et al, 1985). The system compares favorably, both in accuracy and sensitivity, to these more conventional methods. The most variable indicator of potential reproductive function in the Fischer 344 rat is the total sperm count from the cauda epididymidis (coefficient of variation [CV] = 24%), while parameters of sperm motility vary least. These include percentage of motile cells (CV = 15%), curvilinear velocity (CV = 9%) and linearity (CV = 10%), which is a ratio of straight-line to total distance traveled. It was concluded that the computerized system may be useful for routine assessment of changes in sperm quality that may occur in the rat after exposure to toxic drugs or chemicals.

Antitumor activity of Herceptin in combination with STEALTH liposomal cisplatin or nonliposomal cisplatin in a HER2 positive human breast cancer model.

Single agent antitumor activity of Herceptin, a humanized monoclonal antibody directed against HER2, has been demonstrated in numerous preclinical and clinical studies. Additionally, combination therapy with Herceptin and chemotherapy (CRx) has demonstrated additive antitumor activity in both preclinical models and early clinical trials. STEALTH (pegylated) liposomal (PL) cisplatin, also known as SPI-077, is currently in clinical trials for a variety of solid tumors. The three studies reported here discuss the antitumor activity of the combination of Herceptin and nonliposomal cisplatin or PL-cisplatin in two xenograft tumor models, initiated from the cell lines, BT474 and MDA453, that overexpress the oncogene, HER2. Herceptin alone had significant antitumor activity in all three experiments (p < 0.0001). Nonliposomal cisplatin and PL-cisplatin were both effective antitumor agents but, at tolerable dose levels, PL-cisplatin was superior to nonliposomal cisplatin (p < 0.0003). The effect of combining Herceptin with the chemotherapeutic cisplatin or PL-cisplatin, was most significant at moderate doses of H (0.5 mg/kg, p < 0.0001), but tended to be greater than either agent alone in all experiments. The combination of PL-cisplatin with Herceptin had statistically similar antitumor activity to that of nonliposomal cisplatin with Herceptin in all experiments. We conclude that combination therapy with PL-cisplatin and Herceptin results in significant antitumor activity with the potential for reducing toxicity in metastatic breast cancer patients.

Twelve-month evaluation of rhesus monkey dams and infants after relaxin (hRlx-2) infusion in late pregnancy.

Pregnant rhesus monkeys received daily i.v. infusions of chemically synthesized human relaxin (hRlx-2) (0.1 mg/kg/day N = 6, 2.0 mg/kg/day N = 6, vehicle control N = 7) from the onset of cervical softening to delivery (0 to 14 infusions) to simulate potential therapeutic use of this agent for cervical ripening. Reproductive fitness of dams was evaluated during the next breeding season, and infants were studied through 12 months of age. Birth weight and size, neonatal heart rate and body temperature and neurobehavioral status were not influenced by intrauterine relaxin exposure. Neonatal muscle tone was greater and responsiveness was lower in the hRlx-2 treated infants than in controls. No group differences were seen in infant postnatal growth, maturation or incidence of health problems. Maternal endpoints including uterine involution, resumption of menses, conception rate, and pregnancy outcome were similar across groups. Systemic exposure of rhesus monkeys to relatively high levels of hRlx-2 in late pregnancy did not have apparent long term effects for the measures evaluated under conditions of the experiment. Conclusions concerning adverse effects are limited by the small sample size.

Role of testicular versus epididymal toxicity in the induction of cytotoxic damage in Fischer-344 rat sperm by methyl chloride.

Exposure of male Fischer-344 (F-344) rats to methyl chloride (MeCl) results in testicular and epididymal toxicity and the induction of both pre- and postimplantation embryonic loss; the preimplantation loss is caused by cytotoxic damage to sperm that leads to failure of fertilization (Toxicol Appl Pharmacol 1986; 86:124-130). The present study examined whether the cytotoxicity of MeCl to sperm is due to the testicular or epididymal toxicity of MeCl. Groups of 18 males were exposed to 3000 ppm MeCl 6 h/day for 5 days, with and without concurrent treatment with the anti-inflammatory agent 3-amino-1-[m-(trifluoromethyl)phenyl]-2-pyrazoline (BW755C; 10 mg/kg, i.p. 1 h pre- and postexposure); BW755C was used to inhibit the epididymal toxicity of MeCl. Control groups were untreated or injected as described above with BW755C. Six males from each group were killed weekly for 3 weeks. Toxic effects of MeCl on the testis were demonstrated by decreased relative organ weight (week 3), testicular histopathology (weeks 1-3) and decreased daily sperm production (weeks 1-3); these effects were not prevented by BW755C. In both the MeCl and the MeCl + BW755C treatment groups, tubules devoid of sperm were observed in regions 4 and 5 of the epididymis at week 2, and in regions 6A and 6B at week 3. Sperm were present in the vas deferens of both groups at week 3 in decreased numbers and had decreased motility and more frequent morphologic abnormalities compared to untreated controls. In conjunction with known epididymal transit times for F-344 rat sperm, these data indicate that the induction of preimplantation loss by MeCl at weeks 2 and 3 postexposure is likely to result from cytotoxic effects on sperm located in the testes at the time of exposure.

Assessment of unscheduled DNA synthesis in Fischer 344 rat pachytene spermatocytes exposed to caprolactam or benzoin in vivo.

Male Fischer 344 rats were treated with the non-carcinogenic chemicals CAP and ZOIN. The spermatogenic cells were isolated at selected times post-exposure for assessment of chemically-induced DNA damage by quantitative autoradiography of unscheduled DNA synthesis (UDS). Neither chemical (750 mg/kg administered by gavage) induced UDS in pachytene spermatocytes isolated 12, 24 or 48 h after treatment.

Activity of germ-cell mutagens and nonmutagens in the rat spermatocyte UDS assay.

The ability of 13 chemicals of known germ-cell mutagenicity to induce unscheduled DNA synthesis (UDS) in rat spermatocytes was examined. At selected times following i.p. injection of test compounds, spermatocytes were isolated from Fischer 344 rats by enzymatic digestion of the seminiferous tubules and cultured for 24 h in the presence of [3H]thymidine. 7 compounds, methyl methanesulfonate, triethylenemelamine, cyclophosphamide, methylnitrosourea, ethylnitrosourea, procarbazine, and dibromochloropropane produced positive UDS responses in spermatocytes. These chemicals are also positive for specific locus mutations, heritable translocations, or dominant lethal mutations when administered to male rodents. Mitomycin C, which produces DNA interstrand crosslinks and induces heritable mutations and translocations in male germ cells, failed to stimulate UDS in rat spermatocytes. Germ-cell nonmutagens N-methyl-N'-nitro-N-nitrosoguanidine, dimethylnitrosamine, 4-nitroquinoline 1-oxide, and ethylene dibromide were negative in the rat spermatocyte UDS assay. Correlation of these results with those of other assays for heritable mutations in germ cells indicates that the in vivo/in vitro spermatocyte DNA repair assay is useful in predicting the mutagenic potential of chemicals in male germ cells.