Evaluation of the OECD 421 reproductive toxicity screening test protocol using butyl benzyl phthalate

Evaluation of reproductive toxicity in rats caused by organic extracts of Jialing River water of Chongqing, China

OECD 421 screening test protocol was used to evaluate the reproductive toxicity of organic extracts of river water. These extracts, at doses of 0, 2, 16, or 80 equivalent L/kgbody weight(bw), were administered to rats daily by oral gavage. Vacuole degeneration of seminiferous epithelium was observed in the dosed groups. The caudal sperm counts/epididymis weight and the percentages of sperm with abnormal heads were increased in the group dosed with 80L/kgbw/day compared to the control group. Exposure of rats to organic extracts at the high dose resulted in a decrease in testosterone levels. The serum level of follicle-stimulating hormone increased in the groups dosed with 16 or 80L/kgbw/day compared to the control group. The number of apoptotic spermatid increased in the dosed groups. The results suggest that the extracts cause pathological damage to testicular tissue and disruption of spermatogenesis.

Strengths and limitations of using repeat-dose toxicity studies to predict effects on fertility

The upcoming European chemicals legislation REACH (Registration, Evaluation, and Authorisation of Chemicals) will require the risk assessment of many thousands of chemicals. It is therefore necessary to develop intelligent testing strategies to ensure that chemicals of concern are identified whilst minimising the testing of chemicals using animals. Xenobiotics may perturb the reproductive cycle, and for this reason several reproductive studies are recommended under REACH. One of the endpoints assessed in this battery of tests is mating performance and fertility. Animal tests that address this endpoint use a relatively large number of animals and are also costly in terms of resource, time, and money. If it can be shown that data from non-reproductive studies such as in-vitro or repeat-dose toxicity tests are capable of generating reliable alerts for effects on fertility then some animal testing may be avoided. Available rat sub-chronic and fertility data for 44 chemicals that have been classified by the European Union as toxic to fertility were therefore analysed for concordance of effects. Because it was considered appropriate to read across data for some chemicals these data sets were considered relevant for 73 of the 102 chemicals currently classified as toxic to reproduction (fertility) under this system. For all but 5 of these chemicals it was considered that a well-performed sub-chronic toxicity study would have detected pathology in the male, and in some cases, the female reproductive tract. Three showed evidence of direct interaction with oestrogen or androgen receptors (linuron, nonylphenol, and fenarimol). The remaining chemicals (quinomethionate and azafenidin) act by modes of action that do not require direct interaction with steroid receptors. However, both these materials caused in-utero deaths in pre-natal developmental toxicity studies, and the relatively low NOAELs and the nature of the hazard identified in the sub-chronic tests provides an alert for possible effects on fertility (or early embryonic development), the biological significance of which can be ascertained in a littering (e.g. 2-generation) study. From the chemicals reviewed it would appear that where there are no alerts from a repeat-dose toxicity study, a pre-natal developmental toxicity study and sex steroid receptor binding assays, there exists a low priority for animal studies to address the fertility endpoint. The ability for these types of tests to provide alerts for effects on fertility is clearly dependent on the mode of action of the toxicant in question. Further work should therefore be performed to determine the 'failure rate' of this type of approach when applied to a larger group of chemicals with diverse modes of action.

A TWO-GENERATION REPRODUCTIVE TOXICITY STUDY OF BUTYL BENZYL PHTHALATE IN RATS

A two-generation reproductive toxicity study with extra parameters was performed for Butyl benzyl phthalate (BBP). The compound was administered orally by gavage with the doses of 0, 100, 200, or 400 mg/kg/day to groups of 24 Crj:CD (SD)IGS rats of both sexes to confirm the utility of the protocol for identification of non-steroid chemicals with endocrine activity by ssessing effects on parental animals and offspring. Softening of the testes, diffuse atrophy of testicular seminiferous tubules, decreased spermatozoa and/or residual germ cells in the epididymal lumina were observed in the F1generation after doses more than 100 mg/kg, lowering of the F1 epididymal weights at doses more than 200 mg/kg, along with low F0 epididymal weights, Leydig cell hyperplasia, residual germ cells in the epidimymal lumina, and low seminal vesicle weights, small testes and epididymes, partial aplasia or aplasia of the epididymes, and Leydig cell hyperplasia in the F1 generation with 400 mg/kg. With regard to effects on the reproductive capacity, F1 parents at the dose of 400mg/kg showed a reduced fertility index and delayed preputial separation of the penis. In the offspring, lowered body weights in the F1 case, and change in anogenital distance in the F1 females and F2 males were observed at doses more than 100 mg/kg, with low splenic weights at 400 mg/kg in both generations. Thus, the utility of this protocol was confirmed. In the parental animals, the no observed effect level (NOEL) and the no observed adverse effect level (NOAEL) were less than 100 mg/kg/day, and no serious effects on the reproductive capacity were induced at doses less than 200 mg/kg/day. The NOEL and NOAEL for the growth and development of offspring were concluded to be less than 100 mg/kg/day.

Postexposure effects of DDE and butylbenzylphthalate on feeding behavior in threespine stickleback

In a laboratory experiment we documented effects of sublethal concentrations of p,p'-2,2-bis(p-chlorophenyl)-1,1-dichloroethylene (DDE) and butylbenzylphthalate (BBP) on feeding behavior in threespine stickleback Gasterosteus aculeatus. The fish were exposed for 31 days to either BBP (10 or 100 microg/L) or DDE (5 or 50 microg/L) or to a mixture of BBP and DDE in the corresponding concentrations. Five weeks after exposure termination, we showed that fish that had been exposed to the higher concentrations of DDE and/or BBP initiated feeding more often than control fish. The latency time to feeding (ranging from 0.25 to 5.0 min) differed between control fish and fish exposed to mixtures of DDE and BBP. This experiment shows that feeding behavior may be used as a suitable behavioral variable in the detection of effects of pollutants even long time after the termination of exposure.

Evaluation of OECD screening tests 421 (reproduction/developmental toxicity screening test) and 422 (combined repeated dose toxicity study with the reproduction/developmental toxicity screening test)

The Advisory Committee on Existing Chemicals (BUA) of the Federal Republic of Germany convened a panel with expertise in reproductive and developmental toxicology to evaluate the OECD Screening Tests 421 (Reproduction/Developmental Toxicity Screening Test) and 422 (Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test) with respect to their ability to unmask any potential toxic effects on reproduction. The original assignment for that panel was to "validate" those screening tests. However, the panel members recognized beforehand that this was actually an impossible task because of lack of a sufficient database. Only five chemicals with known reproductive toxicity had been examined following the OECD Screening Test Guidelines 421 or 422. A comparison of these test results with those of the definitive OECD Test Guidelines 414, 415, 416, or additional investigations could, therefore, only have been made with this very limited number of chemicals that had also undergone evaluation by one of the test guidelines cited. In each case biological properties relevant to reproductive toxicity were also indicated by the OECD Screening Tests 421 or 422. This communication reviews the main differences in study design of OECD Screening Test Guidelines 421 and 422 compared to those definitive test guidelines of similar study design for reproduction or developmental toxicity (especially with the one-generation study, OECD Test Guideline 415). The very limited possibilities of detecting late postnatal and postlactational manifestations are emphasized, as is the low statistical power of the OECD Screening Tests 421 and 422. Furthermore, the very limited ability to unmask teratogenicity is delineated. The outcome of screening tests was evaluated based on the results of 57 studies conducted according to the OECD Test Guideline 421 or 422. The test results were categorized according to the incidence of toxic effects on reproduction in the parent animals or their offspring and related to general toxic effects. Based on the ranking of these results, recommendations regarding setting rational priorities for further evaluations of existing chemicals' reproductive hazards are made. In general, the reviewer panel supports the OECD position that the screening tests are useful for initial hazard assessment and can contribute to the decision-making process on setting priorities for further test requirements. The panel also agrees with the OECD statement that the OECD Screening Tests 421 and 422 are neither an alternative to definitive tests (i.e., OECD Test Guidelines 414, 415, and 416) nor are they intended as their replacement.

Developmental effects of plasticizer butyl benzyl phthalate after a single administration in rats

The objective of this study was to determine the susceptible day for the developmental toxicity of butyl benzyl phthalate (BBP) by a single administration on one of the days during organogenesis. Pregnant rats were given a single dose of BBP by gastric intubation at a dose of 1000 mg kg(-1) on one of days 13-15 of pregnancy and at 1500 mg kg(-1) on one of days 6-16 of pregnancy. Post-implantation embryolethality was found in pregnant rats given on one of days 6-16, except for day 7. Teratogenicity was noted after a single dosing of BBP on one of days 6, 7, 9, 10, 12, 14 and 15. Deformity of the cervical vertebrae frequently was observed after administration of BBP on day 7. Cleft palate and fusion of the sternebrae were found exclusively, after administration of BBP on day 15. It can be concluded that the manifestation of deviant development induced by BBP varies with the developmental stage at the time of administration and that BBP induces two discrete responses from embryos to teratogenicity during early and late organogenesis.

Reproductive effects of butyl benzyl phthalate in pregnant and pseudopregnant rats

In our previous studies, butyl benzyl phthalate (BBP) was found to be embryolethal and teratogenic in rats. In this study, the reproductive effects of BBP were investigated in pregnant and pseudopregnant rats. Rats were given BBP by gastric intubation at 0, 250, 500, 750, or 1000 mg/kg on Days 0 to 8 of pregnancy and the pregnancy outcome was determined on Day 20 of pregnancy. The same doses of BBP were given to pseudopregnant rats, with an induced decidual cell response on Days 0 to 8 of pseudopregnancy, and the uterine weight on Day 9 served as an index of the uterine decidualization. BBP caused significant increases in the incidences of preimplantation loss in females successfully mated at 1000 mg/kg and of postimplantation loss in females having implantations at 750 mg/kg and above. Uterine decidual growth in pseudopregnant rats was significantly decreased at 750 mg/kg and above. These findings suggest that early embryonic loss due to BBP may be mediated, at least in part, via the suppression of uterine decidualization, an impairment of uterine function.

Characterization of developmental toxicity of mono-n-benzyl phthalate in rats

The objective of this study was to characterize the developmental toxicity of mono-n-benzyl phthalate (MBeP), which is one of the major metabolites of n-butyl benzyl phthalate. Pregnant rats were given MBeP by gastric intubation at 250, 375, 500, or 625 mg/kg on days 7 to 9, 10 to 12, or 13 to 15 of pregnancy. A significantly increased incidence of postimplantation loss was found at 500 mg/kg and above regardless of the days of administration. While administration of MBeP on days 7 to 9 or 13 to 15 at 375 mg/kg and above was significantly teratogenic, no evidence of teratogenicity was detected when MBeP was given on days 10 to 12. Deformity of the vertebral column and ribs and dilation of the renal pelvis were frequently observed after administration on days 7 to 9. Cleft palate and fused sternebrae were exclusively found after administration on days 13 to 15. These findings indicate that the susceptibility and spectrum of the developmental toxicity of MBeP vary with the developmental stages at the time of administration.