Evaluation of the effects of α-cypermethrin on fetal rat testicular steroidogenesis

Determination of biochemical and histopathological changes on testicular and epididymis tissues induced by exposure to insecticide Imidacloprid during postnatal development in rats

BACKGROUND

Imidacloprid is a neonicotinoid insecticide belonging to the chloronicotinyl nitroguanidine chemical family. Toxicity of IMD for mammals in scientific studies has shown high mutagenic, immunotoxic, teratogenic and neurotoxic effects. The present study was designed to assess the toxic effects of imidacloprid (IMD) on the testicular and epididymis tissues as well as testosterone levels of neonatal male rats.

METHODS

Neonatal male rats from postnatal day (PND) 1 to PND 26 were consecutively administered with different concentrations of IMD (1, 5 and 10 mg/kg) subcutaneously. The effect of IMD on body and organ weight, lipid profile, histopathological alterations, oxidative stress and altered testosterone levels were assessed in the testis and plasma.

RESULTS

The results of body weight gain showed a significant difference in group 4 (10 mg/kg) animals as compared to the control. A significant increase in total cholesterol and triglycerides, while a decrease in high-density lipoprotein concentrations was evident. Similarly, a significant decrease in concentrations of antioxidant enzymes (CAT and SOD) among all the IMD-treated groups was evident, when compared to the control. Increased production of ROS was also noticed in the highest-dose treatment group. Further, we observed that IMD-treated rats indicated histopathological changes in the testis and epididymis along with a significant decrease in the plasma testosterone concentrations among IMI-treated groups in contrast to the control. Histological examination of the testis of IMD-treated neonatal male rats also showed decreased spermatogenesis in the treated groups when compared to the control. Furthermore, an increase in lumen diameter and a decrease in epithelial height of seminiferous tubules were also observed in IMD-treated rats in comparison with the control.

CONCLUSION

It is concluded that sub-chronic exposure to IMD in neonatal male rats may induce histopathological changes in reproductive tissues and damage normal testicular functions via inducing oxidative stress, decrease in body weight, disturbing normal blood lipid profile and testosterone concentration. IMD exposure can induce pathophysiological effects calls for further evaluation of this widely used insecticide.

The toxicity of microplastics and their leachates to embryonic development of the sea cucumber Apostichopus japonicus

Microplastic pollution has been widely detected across the global ocean, posing a major threat to a wide variety of marine biota. To date, the deleterious impacts of microplastics have predominantly been linked to their direct exposure, while the potential risks posed by the leachates emanating from microplastics have received comparatively less attention. Here, the toxicity of virgin plasticized polyvinyl chloride (PVC) microspheres and their leachates were evaluated on the embryo-larval development of sea cucumber Apostichopus japonicus using an in-vitro assay. Results showed that a significant toxic effect of both PVC microspheres and their leachates on the embryo development and larval growth of sea cucumbers follows a dose-dependent and time-dependent pattern. Nonetheless, the toxicity of PVC leachates surpasses that of the microspheres themselves. Abnormal developmental phenotypes, such as aberrant gastrulation, misaligned mesenchymal cells, and delayed arm development, were also observed in embryos and larvae treated with PVC. Further chemical analyses of PVC microspheres and leachates revealed the existence of five distinct phthalate esters (PAEs), with DIBP (diisobutyl phthalate) and DBP (dibutyl phthalate) exhibiting higher concentrations in the PVC leachates. This finding suggests that the elevated toxicity of plastic leachate may be attributed to the leaching of phthalate additives from the plastic particles.

Cypermethrin inhibits Leydig cell development and function in pubertal rats

Cypermethrin is a broad-spectrum pyrethroid insecticide that is widely used. It may induce adverse endocrine-disrupting effects on the male reproductive system. Whether cypermethrin can disrupt Leydig cell development and function in the late puberty remains elusive. The objective of this study was to explore the effect of cypermethrin exposure to male rats on the development and function of Leydig cells in late puberty and explore the underlying mechanism. Thirty-six male Sprague-Dawley rats (age of 35 days) were gavaged with cypermethrin (0, 12.5, 25, and 50 mg/kg/day) from postnatal day 35-49. Cypermethrin significantly lowered serum testosterone level while elevating serum luteinizing hormone level at a dose of 50 mg/kg, without altering serum follicle-stimulating hormone level. Cypermethrin markedly decreased CYP11A1-positive Leydig cell number at 50 mg/kg without affecting SOX9-positive Sertoli cell number. It significantly down-regulated the expression of Leydig cell genes, Lhcgr, Star, Cyp11a1, and Cyp17a1 and their proteins, while up-regulating the expression of Sertoli cell genes, Dhh and Amh, and their proteins, at doses of 12.5-50 mg/kg. In addition, cypermethrin significantly increased malondialdehyde level while lowering the expression of Sod1 and Sod2 and their proteins at 50 mg/kg. Cypermethrin markedly induced reactive oxidative species at a concentration of 200 μM and reduced mitochondrial membrane potential at 25 μM and higher concentrations after 24 h of treatment to primary Leydig cells in vitro. In conclusion, cypermethrin inhibits the development and function of Leydig cells in male rats in late puberty.

Effect of long-term treatment with a mixture of pyrethroids on the expression of genes that govern male germ cell production in rats

Humans are exposed to pyrethroid-based pesticides through agricultural produce. In this study, male Wistar rats were orally treated for 9 to 12 months with a mixture of pyrethroids that is equivalent to one-fifth (high dose; HD) or one-twenty fifth (low dose; LD) of the amount of pyrethroids present in the cereals and rice consumed by an average Indian. In rats treated for 9 months, the spermatogenesis-associated genes Abp, Ar, Cd9, Dax1, Dazap1, Ddx3y, Gdnf, Gfra1, Grth, Inhb, Ovol1, P1, Plzf, Pygo2, Scf, Tgfb1, Tp1, Tp2, and Vim1 were downregulated in both LD and HD groups. In rats treated for 12 months Gdnf, Hsf2, Inhb, Tgfb1, Thy1, and Ybx2 expression was downregulated in both LD and HD groups. Steroidogenesis-associated genes 17-β-Hsd, Gata4, Hmgcr, Hmgcs1, Pde4b, and Tspo gene expression were reduced in both LD- and HD-treated groups treated for 9 months. In 12-month-treated rats, Creb1 expression decreased in both LD and HD groups. The epigenetic reprogramming-associated genes, Dnmt1, Dnmt3a, Dnmt3b, Hdac10, Hp1bp3, Kat3a Kat3b, Mch2ta, Ncoa7, and Sirt1 were downregulated in both HD and LD groups of 9-months-treated rats. In rats treated for 12 months, Hdac10, Mch2ta, Ncoa7, and Sirt1 messenger RNA levels decreased in both the HD and LD groups. Thus, we demonstrate that long-term exposure to a mixture of pyrethroids caused aberrations in the transcriptome of factors involved in sperm production and development.

Hazards of diisobutyl phthalate (DIBP) exposure: A systematic review of animal toxicology studies

BACKGROUND

Biomonitoring studies indicate a trend towards increased human exposure to diisobutyl phthalate (DIBP), a replacement for dibutyl phthalate (DBP). Recent reviews have found DIBP to be a male reproductive toxicant, but have not evaluated other hazards of DIBP exposure.

OBJECTIVE

To inform chemical risk assessment, we performed a systematic review to identify and characterize outcomes within six broad hazard categories (male reproductive, female reproductive, developmental, liver, kidney, and cancer) following exposure of nonhuman mammalian animals to DIBP or the primary metabolite, monoisobutyl phthalate (MIBP).

METHODS

A literature search was conducted in four online scientific databases [PubMed, Web of Science, Toxline, and Toxic Substances Control Act Test Submissions 2.0 (TSCATS2)], and augmented by review of regulatory sources as well as forward and backward searches. Studies were identified for inclusion based on defined PECO (Population, Exposure, Comparator, Outcome) criteria. Studies were evaluated using criteria defined a priori for reporting quality, risk of bias, and sensitivity using a domain-based approach. Evidence was synthesized by outcome and life stage of exposure, and strength of evidence was summarized into categories of robust, moderate, slight, indeterminate, or compelling evidence of no effect, using a structured framework.

RESULTS

Nineteen toxicological studies in rats or mice met the inclusion criteria. There was robust evidence that DIBP causes male reproductive toxicity. Male rats and mice exposed to DIBP during gestation had decreased testosterone and adverse effects on sperm or testicular histology, with additional phthalate syndrome effects observed in male rats. There was also evidence of androgen-dependent and -independent male reproductive effects in rats and mice following peripubertal or young adult exposure to DIBP or MIBP, but confidence was reduced because of concerns over risk of bias and sensitivity in the available studies. There was also robust evidence that DIBP causes developmental toxicity; specifically, increased post-implantation loss and decreased pre- and postnatal growth. For other hazards, evidence was limited by the small number of studies, experimental designs that were suboptimal for evaluating outcomes, and study evaluation concerns such as incomplete reporting of methods and results. There was slight evidence for female reproductive toxicity and effects on liver, and indeterminate evidence for effects on kidney and cancer.

CONCLUSION

Results support DIBP as a children's health concern and indicate that male reproductive and developmental toxicities are hazards of DIBP exposure, with some evidence for female reproductive and liver toxicity. Data gaps include the need for more studies on male reproductive effects following postnatal and adult exposure, and studies to characterize potential hormonal mechanisms in females.

Anogenital distance as a toxicological or clinical marker for fetal androgen action and risk for reproductive disorders

Male reproductive development is intricately dependent on fetal androgen action. Consequently, disrupted androgen action during fetal life can interfere with the development of the reproductive system resulting in adverse effects on reproductive function later in life. One biomarker used to evaluate fetal androgen action is the anogenital distance (AGD), the distance between the anus and the external genitalia. A short male AGD is strongly associated with genital malformations at birth and reproductive disorders in adulthood. AGD is therefore used as an effect readout in rodent toxicity studies aimed at testing compounds for endocrine activity and anti-androgenic properties, and in human epidemiological studies to correlate fetal exposure to endocrine disrupting chemicals to feminization of new-born boys. In this review, we have synthesized current data related to intrauterine exposure to xenobiotics and AGD measurements. We discuss the utility of AGD as a retrospective marker of in utero anti-androgenicity and as a predictive marker for male reproductive disorders, both with respect to human health and rodent toxicity studies. Finally, we highlight four areas that need addressing to fully evaluate AGD as a biomarker in both a regulatory and clinical setting.

The pyrethroid insecticides permethrin and esfenvalerate do not disrupt testicular steroidogenesis in the rat fetus

The present study investigated the effects of maternal exposure to the widely used pyrethroid insecticides, permethrin and esfenvalerate, on fetal testicular steroidogenesis. Pregnant Sprague-Dawley rats were administered permethrin at doses of 1, 10, 50, or 100 mg/kg/day, or esfenvalerate at 0.1, 1, 7.5 or 15 mg/kg/day, by gavage, from gestation day (GD) 13 to 19. Testicular testosterone production and the expression of several key genes necessary for cholesterol and androgen synthesis and transport were assessed in GD 19 male fetuses. Dams treated with 100 mg/kg/day of permethrin or 15 mg/kg/day of esfenvalerate showed clinical signs of neurotoxicity. The highest dose of esfenvalerate also resulted in reduced maternal body weight gain throughout the treatment period. In the fetal testes, mRNA expressions of HMG-CoA synthase and reductase, SR-B1, StAR, P450scc, 3βHSD, P450 17A1, and 17βHSD were not affected by exposure to either pyrethroid. No significant change was observed in ex vivo testosterone production. In conclusion, in utero exposure to permethrin or esfenvalerate has no effect on the testosterone biosynthesis pathway in the fetal rat testis up to maternal toxic doses.

Influence of lactic acid bacteria on stereoselective degradation of theta-cypermethrin

The purpose of this study was to investigate the influence of four kinds of Lactic acid bacteria (LAB) on stereoselective degradation of theta-cypermethrin (CYP), including Lactobacillus plantarum, Lactobacillus casei, Lactobacillus delbrueckii, and Streptococcus thermophilus. An effective analytical method for (±)-theta-CYP in medium was developed by high-performance liquid chromatography with cellulose tris-(3,5-dimethylphenylcarbamate) chiral stationary phase. theta-Cypermethrin was spiked to LAB medium with different inoculation rates and sampled at 0, 2, 8, 24, 36, 48, 72, 120, 168, and 240 hours. The results showed that LAB influenced the half-lives and enantiomer fractions of theta-CYP enantiomers, which lead a closer degradation rate between the 2 stereoisomers, and no obvious difference was found among 4 LABs. Besides, the stereoselective degradation of theta-CYP was closely related to pH. The lower the pH (pH of 3, 5, 7, and 9), the lower the enantiomer fraction (from 4.88 to 6.69). At pH of 3, 7, and 9, significant differences of half-lives between enantiomers were observed. (-)-theta-Cypermethrin decreased faster than (+)-theta-CYP under pH of 3, while opposite results were indicated under pH of 7 and 9. Moreover, the acidic condition contributed to the higher chiral configuration stability of (±)-theta-CYP. (+)-Enantiomer was influenced by pH in a greater degree than (-)-enantiomer.