The Oral NOAEL of Flurochloridone in Male Wistar Rats in Ninety-Day Subchronic Toxicity Test Was 3mg/kg/day

Flurochloridone induced abnormal spermatogenesis by damaging testicular Sertoli cells in mice

BACKGROUND

Flurochloridone (FLC), a selective herbicide used on a global scale, has been reported to have male reproductive toxicity whose evidence is limited, but its mechanism remains unclear. The present study was conducted to systematically explore the male reproductive toxicity of FLC, including sperm quality, spermatogenesis, toxicity targets, and potential mechanisms.

METHODS

Male C57BL/6 mice aged 6-7 weeks received gavage administration of FLC (365/730 mg/kg/day) for 28 consecutive days. Then, the tissue and sperm of mice were collected for analysis. We measured the gonadosomatic index and analyzed sperm concentration, motility, malformation rate, and mitochondrial membrane potential (MMP). Spermatocyte immunofluorescence staining was performed to analyze meiosis. We also performed pathological staining on the testis and epididymis tissue and TUNEL staining, immunohistochemical analysis, and ultrastructural observation on the testicular tissue.

RESULTS

Results showed that FLC caused testicular weight reduction, dysfunction, and architectural damage in mice, but no significant adverse effect was found in the epididymis. The exposure interfered with spermatogonial proliferation and meiosis, affecting sperm concentration, motility, kinematic parameters, morphology, and MMP, decreasing sperm quality. Furthermore, mitochondrial damage and apoptosis of testicular Sertoli cells were observed in mice treated with FLC.

CONCLUSION

We found that FLC has significant adverse effects on spermatogonial proliferation and meiosis. Meanwhile, apoptosis and mitochondrial damage may be the potential mechanism of Sertoli cell damage. Our study demonstrated that FLC could induce testicular Sertoli cell damage, leading to abnormal spermatogenesis, which decreased sperm quality. The data provided references for the toxicity risk and research methods of FLC application in the environment.

Flurochloridone Induced Cell Apoptosis via ER Stress and eIF2α-ATF4/ATF6-CHOP-Bim/Bax Signaling Pathways in Mouse TM4 Sertoli Cells

Flurochloridone (FLC), as a novel herbicide, has been widely used in many countries since 1980s. Current studies have shown that FLC has toxic effects on male reproduction and its target organ is testis, while the underlying mechanism is still unknown. Mouse testis Sertoli cell line TM4 cells were used as an in vitro model and treated with FLC at different doses (40, 80, 160 μM) for different times (6, 12, 24 h). Cell viability, cytotoxicity and apoptotic cells were detected by CCK-8 assay, LDH leakage assay and flow cytometry. The protein levels of GRP78, phosphorylated-eIF2α, ATF4, ATF6, CHOP, Bim and Bax were observed by Western Blot and Immunofluorescence staining. FLC inhibited cell viability and induced cytotoxicity in dose-dependent way in TM4 cells. The percentage of apoptotic cells were 6.2% ± 0.6%, 7.3% ± 0.3%, 9.8% ± 0.4%, 13.2% ± 0.2%, respectively. The expression levels of ER stress and UPR related proteins were activated over dose. Meanwhile, the pro-apoptotic proteins (Bim and Bax) were also up-regulated in dose-dependent. After pretreated with ISRIB, the inhibitor of eIF2α phosphorylation, the elevated expression of GRP78, phosphorylated-eIF2α, ATF4, ATF6, CHOP and Bim was down to normal level accordingly. In conclusion, FLC induced apoptosis in TM4 cells mediated by UPR signaling pathways.

Effects of prepubertal exposure to forchlorfenuron through prenatal and postnatal gavage administration in developing Sprague-Dawley rats

Forchlorfenuron (CPPU), a plant growth regulator, is widely used in agriculture. However, its long-term exposure effects on humans, especially neonates, remain unclear. Therefore, we investigated the developmental toxicity of prenatal and postnatal gavage administration of CPPU in rats. Pregnant Sprague-Dawley rats were administered 300 mg/kg/day CPPU by gavage from day 6 of gestation to the cessation of nursing. During weaning, rat offspring were administered 0, 30, 100, or 300 mg/kg/day CPPU for 4 weeks, followed by a 4-week CPPU-free recovery period. There were no significant differences in clinical symptoms, body weight, development indicators, serum biochemical parameters, sex hormone levels, sperm motility, relative organ weights, and histopathological changes among the 0-100 mg/kg/day CPPU groups. In the 300 mg/kg/day CPPU group, female rats exhibited decreased body weight, earlier time of vaginal opening (VO) and first estrus time (FE), elevated estradiol and blood urea nitrogen (BUN) levels, and upregulation of estrogen receptor 1 gene expression, whereas male rats only exhibited increases in serum BUN, creatinine, and glucose levels. Most changes were reversed after the recovery period. Furthermore, the endometrial epithelial height was significantly increased in female rats despite the absence of significant changes in uterine wall thickness and endometrial glands. Thus, CPPU may promote estradiol secretion, resulting in altered VO and FE and adverse effects in prepubertal female rats. These findings may be applied for risk assessment following CPPU exposure in humans.

RNA-seq analysis of testes from flurochloridone-treated rats

Flurochloridone (FLC) is a widely used herbicide in developing countries. Although the testes are a target organ for FLC in rats, the adverse effects of FLC on testes have not been fully elucidated. To clarify them, we performed RNA-seq analysis using the testes of FLC-treated rats from our previous subchronic toxicity tests. Unilateral testes of three male rats from solvent control groupand three FLC-treated groups (3 mg/kg, 31.25 mg/kg and 125 mg/kg) were used for RNA extraction. A poly A selection protocol coupled with an Illumina TruSeq RNA-Seq library protocol was used to construct RNA-Seq libraries. Principal component analysis (PCA), differentially expressed gene (DEG) analysis, and hierarchical clustering analysis (HCA) were conducted using R. Gene Ontology (GO) term enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were performed to understand the biological characteristics of the DEGs using the Database for Annotation, Visualization and Integrated Discovery (DAVID). The results indicated that many up-regulated DEGs were enriched in pathways associated with testicular injury, such as mitogen-activated protein kinase (MAPK) signaling, lysosome and focal adhesion. Many down-regulated DEGs were enriched in pathways associated with testicular reproduction function, such as sexual reproduction, spermatogenesis and germ cell development. Moreover, we confirmed the oral no-observed-adverse-effect level (NOAEL) of 3 mg/kg in subchronic toxicity test, because the overall testicular gene expression in 3 mg/kg FLC-treated group was similar to that of the solvent control group. In 31.25 mg/kg and 125 mg/kg groups, DEGs revealed that testicular injury was related to oxidative stress.

Low dose of flurochloridone affected reproductive system of male rats but not fertility and early embryonic development

BACKGROUND

Fluorochloridone (FLC) is a widely used herbicide, and its target organs are testes and epididymides. The Globally Harmonized System of Classification and Labelling of Chemicals classified FLC as Level 2-possibly cause fertility or fetal damage (no relevant data support). The maximum residue levels of FLC in processed crops have been reviewed in the latest European Food Safety Authority (EFSA) report in 2018. However, the toxic effect of FLC on fertility and early embryonic development is limited, and the health risk assessment of FLC needs further consideration. This study investigated the potential effects of FLC on fertility and early embryonic development in rats.

METHODS

One hundred rats of each sex were divided into four groups including three FLC-treated groups at doses of 2 mg/kg, 5 mg/kg and 15 mg/kg, and a vehicle control group (0.5% (w/v) sodium carboxymethyl cellulose). Male and female rats were dosed for 9 and 2 consecutive weeks, intragastrically, prior to cohabitation and lasted throughout the mating period for males and continued until Gestation Day 7 (GD7) for females. Parameters such as weights and coefficients of reproductive organs, epididymal sperm number and motility, indexes of copulation, fecundity and fertility indexes, mating period, estrous cycle, corporalutea number, implantations, live, dead and resorbed fetuses, preimplantation loss rate, and postimplantation loss rate were observed in this study.

RESULTS

Obvious toxicity of male reproductive system was found at the dose of 15 mg/kg including decreases in testicular and epididymal weight, also in sperm motility rate. Whereas the increase in sperm abnormality rate was observed. However, no significant effects of FLC were found on lutea count, implantations count, fetuses count and weight, live fetuses count (rate), dead fetuses count (rate), resorbed fetuses count (rate), placentas weight, fetuses gender, preimplantation loss (rate) and postimplantation loss (rate). Furthermore, FLC had no adverse effects on fertility and early embryonic development in rats.

CONCLUSION

The no-observable-adverse-effect level (NOAEL) of FLC on fertility and early embryonic development in rats was considered to be 5 mg/kg/day.