Embryonic exposure to phenanthrene caused developmental defects of craniofacial cartilage in F1 larvae.

As a representative polycyclic aromatic hydrocarbon with low ring numbers, phenanthrene (Phe) is ubiquitously present in the environment. In this study, zebrafish embryos were exposed to Phe at 0.05, 0.5, 5 and 50 nmol/L for 96 h, and then cultured to adulthood in clean water, the developmental defects of craniofacial cartilage were observed in F1 larvae produced by adult males and females mated with untreated fish. Delayed development of craniofacial cartilage, including a shorter and wider Meckel's cartilage and mandibular arch were observed in F1 larvae from adult fish of both sexes. Maternal F1 larvae showed a greater impact on the lower jaw than paternal F1 larvae, this may be connected with greater downregulation of the transcription of genes related to the development of craniofacial cartilage such as runt-related transcription factor 2 (runx2), fibroblast growth factor 8 (fgf8), sonic hedgehog (shh), Indian hedgehog (ihh). Further results indicated that the modification DNA methylation levels in the promotors of gene runx2 and shh in maternal and paternal F1 larvae were inherited from embryonic F0 larvae, and might be linked with the toxicity of craniofacial cartilage in F1 larvae. This study illustrated that embryonic exposure to Phe could induce adverse effects on craniofacial development in F1 offspring, emphasizing the importance of transgenerational toxicology studies in risk assessment.

Maternal exposure to phenanthrene during gestation disturbs glucose homeostasis in adult mouse offspring.

Epidemiological studies have indicated that polycyclic aromatic hydrocarbons were related to diabetes and insulin resistance. However, studies in mammals on the development of diabetes caused by polycyclic aromatic hydrocarbons are lacking. Pregnant mice were orally exposed to phenanthrene (0, 60 and 600 µg kg-1 body weight) once every 3 days during gestation. In adult mouse offspring, in-utero phenanthrene exposure caused glucose intolerance and decreased insulin levels in females, while caused elevated fasting blood glucose and insulin levels in males. Serum resistin and interleukin-6 levels were elevated in offspring of both sexes. Serum adiponectin levels were decreased in females but increased in males. The insulin receptor signals were upregulated in the liver and downregulated in the skeletal muscle of F1 females, while they were inhibited in both tissues of F1 males. The visceral fat weight and body weight of the treated mice were not increased, suggesting that phenanthrene is not an obesogen, which is supported by the nonsignificant alteration in pparγ transcription in visceral adipose tissue. The transcription of retn in visceral adipose tissue was upregulated in both sexes, and that of adipoq was downregulated in females but upregulated in males, which were matched with the promoter methylation levels of these genes. The results indicated that phenanthrene exposure during gestation could disturb adipocytokine levels via epigenetic modification in adult offspring, and further influence glucose metabolism. These results might be helpful for understanding nonobesogenic pollutant-induced insulin resistance and preventing against diabetes without obesity.

Chronic Exposure to Environmental Level Phenanthrene Induces Non-Obesity-Dependent Insulin Resistance in Male Mice.

Epidemiological evidence shows that the body burden of polycyclic aromatic hydrocarbons (PAHs) is related to the disruption of glucose homeostasis. However, the contribution of PAHs to the development of diabetes remains poorly documented. In the current work, male Kunming mice received phenanthrene (Phe) (5, 50, and 500 ng/kg) by gavage administration once every 2 days for 28 weeks. The significant elevation of homeostasis model assessment-insulin resistance (HOMA-IR) and HOMA-ß cell, accompanied by hyperinsulinemia, indicated the occurrence of insulin resistance. The suppression of the insulin receptor signaling pathway in skeletal muscle might be responsible for glucose intolerance. Under the nonobese state, the serum levels of resistin, tumor necrosis factor-α, and interleukin-6 were elevated, whereas the levels of adiponectin were reduced. These changes in adipocytokine levels were consistent with their transcription in white adipose tissue. The promoter methylation levels of Retn (encoding resistin) and Adipoq (encoding adiponectin) were inversely correlated with their mRNA levels, indicating that Phe exposure could cause the disruption of adipocytokine secretion via epigenetic modification. The results would be helpful for understanding the pathogenesis in the development of T2DM caused by nonobesogenic pollutants.

Exposure to low-level metalaxyl impacts the cardiac development and function of zebrafish embryos.

Metalaxyl is an anilide pesticide that is widely used to control plant diseases caused by Peronosporales species. In order to study the toxic effects, zebrafish embryos were exposed to metalaxyl at nominal concentrations of 5, 50 and 500 ng/L for 72 hr, and the cardiac development and functioning of larvae were observed. The results showed that metalaxyl exposure resulted in increased rates of pericardial edema, heart hemorrhage and cardiac malformation. The distance between the sinus venosus and bulbus arteriosus, stroke volume, cardiac output and heart rate were significantly increased in larvae exposed to 50 and 500 ng/L metalaxyl compared to solvent control larvae. Significant upregulation in the transcription of tbx5, gata4 and myh6 was observed in the 50 and 500 ng/L treatments, and that of nkx2.5 and myl7 was observed in the 5, 50 and 500 ng/L groups. These disturbances may be related to cardiac developmental and functional defects in the larvae. The activity of Na+/K+-ATPase and Ca2+-ATPase was significantly increased in zebrafish embryos exposed to 500 ng/L metalaxyl, and the mRNA levels of genes related to ATPase (atp2a11, atp1b2b, and atp1a3b) (in the 50 and 500 ng/L groups) and calcium channels (cacna1ab) (in the 500 ng/L group) were significantly downregulated; these changes might be associated with heart arrhythmia and functional failure.

Exposure to Aroclor 1254 persistently suppresses the functions of pancreatic ß-cells and deteriorates glucose homeostasis in male mice.

Polychlorinated biphenyls (PCBs) are a class of persistent organic pollutants that have been shown to be related to the occurrence of type 2 diabetes mellitus (T2DM). Nevertheless, it is necessary to further explore the development of T2DM caused by PCBs and its underlying mechanisms. In the present study, 21-day-old C57BL/6 male mice were orally treated with Aroclor 1254 (0.5, 5, 50 or 500 µg kg-1) once every three days. After exposure for 66 d, the mice showed impaired glucose tolerance, 13% and 14% increased fasting serum insulin levels (FSIL), and 63% and 69% increases of the pancreatic ß-cell mass in the 50 and 500 µg kg-1 groups, respectively. After stopping exposure for 90 d, treated mice returned to normoglycemia and normal FSIL. After re-exposure of these recovered mice to Aroclor 1254 for 30 d, fasting plasma glucose showed 15%, 28% and 16% increase in the 5, 50 and 500 µg kg-1 treatments, FSIL exhibited 35%, 27%, 30% and 32% decrease in the 0.5, 5, 50 or 500 µg kg-1 groups respectively, and there was no change in pancreatic ß-cell mass. Transcription of the pancreatic insulin gene (Ins2) was significantly down-regulated in the 50 and 500 µg kg-1 groups, while DNA-methylation levels were simultaneously increased in the Ins2 promoter during the course of exposure, recovery and re-exposure. Reduced insulin levels were initially rescued by a compensative increase in ß-cell mass. However, ß-cell mass eventually failed to make sufficient levels of insulin, resulting in significant increases in fasting blood glucose, and indicating the development of T2DM.

Exogenous leptin promotes the recovery of regressed ovary in fasted ducks.

The present study was undertaken to examine the effect of administered recombinant mouse leptin on the recovery of regressed ovary in fasted ducks. Twenty-eight ducks were divided into five groups: fed ad libitum (control; n=5), fasted control (FC; n=5), fasted+low dose of leptin (F+L; n=5), fasted+medium dose of leptin (F+M; n=5) and fasted+high dose of leptin (F+H; n=3). All four fasted groups were fasted for 2 days and then ad libitum and the ducks were treated with leptin at doses of 0 (control and FC), 50 (F+L), 250 (F+M) and 1000 (F+H) microg/kg body weight/day on day 3-5. Results showed that a moderate dose of leptin (250 microg/kg body weight/day) injected during the re-feeding period: (i) promoted the recovery of the regressed ovary as evidenced by an increase in ovary weight and recovery of yellow hierarchical follicles; (ii) elevated the plasma 17beta-estradiol (E(2)) level; (iii) increased the mRNA levels of ovary follicle-stimulating hormone receptor (FSHR), luteinizing hormone receptor (LHR) and estrogen receptor-beta (ER-beta). Furthermore, the results also showed that a high dose of leptin (1000 microg/kg body weight/day) may have a negative effect on the recovery of the regressed ovary. In conclusion, this study indicates that, in ducks, leptin may be involved in the recovery of the regressed ovary caused by 2 days of fasting. This effect may be related to increased plasma E(2) levels and stimulation of the mRNA levels of ovarian FSHR, LHR and especially ER-beta.