Jiayin Dai

Induction of time-dependent oxidative stress and related transcriptional effects of perfluorododecanoic acid in zebrafish liver.

The effects of acute perfluorododecanoic acid (PFDoA) exposure on the induction of oxidative stress and alteration of mitochondrial gene expression were studied in the livers of female zebrafish (Danio rerio). Female zebrafish were exposed to PFDoA via a single intraperitoneal injection (0, 20, 40, or 80 microg PFDoA/g body weight) and were then sacrificed 48 h, 96 h, or seven days post-PFDoA administration. PFDoA-treated fish exhibited histopathological liver damage, including swollen hepatocytes, vacuolar degeneration, and nuclei pycnosis. Glutathione (GSH) content and catalase (CAT) activity decreased significantly at 48 h post-injection while superoxide dismutase (SOD) activity was initially decreased at 48 h post-injection but was then elevated by seven days post-injection. The activity of glutathione peroxidase (GPx) increased at 48 h and seven days compared to control fish, although the increased level at seven days post-injection was decreased compared to the level at 48 h post-injection. Lipid peroxidation levels were increased at seven days post-injection, while no apparent induction was observed at 48 h or 96 h post-injection. The mRNA expression of medium-chain fatty acid dehydrogenase (MCAD) was induced, while the transcriptional expression of liver fatty acid binding protein (L-FABP), peroxisome proliferating activating receptor alpha (PPARalpha), carnitine palmitoyl-transferase I (CPT-I), uncoupling protein 2 (UCP-2), and Bcl-2 were significantly inhibited. Furthermore, the transcriptional expression of peroxisomal fatty acyl-CoA oxidase (ACOX), very long-chain acyl-CoA dehydrogenase (VLCAD), long-chain acyl-CoA dehydrogenase (LCAD) did not exhibit significant changes following PFDoA treatment. No significant changes were noted in the transcriptional expression of genes involved in mitochondrial respiratory chain and ATP synthesis, including cytochrome c oxidase subunit I (COXI), NADH dehydrogenase subunit I (NDI), and ATP synthase F0 subunit 6 (ATPo6). These results demonstrate that turbulence of fatty acid beta-oxidation and oxidative stress responses were involved in the PFDoA-induced hepatotoxicity.

Immunotoxic Effects of Perfluorononanoic Acid on BALB/c Mice

The effects of perfluorononanoic acid (PFNA) on the immune system and its mechanism of action in mice have not been elucidated. Thus, BALB/c mice were exposed to the PFNA (0, 1, 3, or 5 mg/kg/day) for fourteen days. Exposure to PFNA led to a decrease in body weight and in the weight of the lymphoid organs. Cell cycle arrest and apoptosis were observed in the spleen and thymus following PFNA exposure. In the thymus, PFNA mostly modulated CD4+CD8+ thymocytes, whereas the F4/80+, CD11c+, and CD49b+ cells were major targets in the spleen. Although concanavalin A-induced T lymphocyte blastogenesis was not altered by PFNA, production of interleukin (IL)-4 and interferon-gamma by splenic lymphocytes was remarkably impaired. The levels of cortisol and adrenocorticotrophic hormone in sera were increased; however, the expression of glucocorticoid receptor in the thymus was unchanged. In addition, expression of the peroxisome proliferator-activated receptors (PPAR-alpha and PPAR-gamma) and IL-1beta were upregulated significantly in the thymus at a dose of 1 mg PFNA/kg/day. No significant changes in expression of the inhibitory protein IkappaBalpha and IkappaBalpha kinase were observed. Together, these results suggest that PFNA exerts toxic effects on lymphoid organs and T cell and innate immune cell homeostasis in mice and that these effects may result from the activation of PPAR-alpha, PPAR-gamma, and the hypothalamic-pituitary-adrenal axis. Interestingly, at the transcriptional level, the nuclear factor-kappa B signaling pathway appears to be uninvolved in the immunotoxic potential of PFNA.

Perfluorononanoic acid induces apoptosis involving the Fas death receptor signaling pathway in rat testis

Perfluorononanoic acid (PFNA, C9), a synthetic perfluorinated chemical containing nine carbons, accumulates and is biomagnified through food webs. This compound has been detected in the serum of humans and wildlife and has the potential for reproductive interference. Few studies, however, have reported the effects of PFNA exposure on male reproduction. To determine this, male rats were orally dosed for 1, 3 and 5mg/kgday PFNA or with vehicle for 14 days. In the present study, serum testosterone levels were decreased, while estradiol levels were increased dramatically in rats receiving 5mg PFNA/kgday. Spermatogenic cells from rats that received 5mg PFNA/kgday exhibited apoptotic features including crescent chromatin condensation and chromatin margination. Flow cytometric analysis and TUNEL assays revealed a dose-dependent increase of apoptotic cell numbers. In addition, expression of Fas and Bax mRNA levels were upregulated significantly, and Bcl-2 mRNA levels were downregulated markedly in the 3 and 5mg/kgday groups. A dose-dependent increase in levels of active caspase-8 and no significant changes of active caspase-9 were observed. Our results indicate that PFNA exposure can lead to cell apoptosis in rat testis, and this apoptosis was probably associated with the Fas death receptor-dependent apoptotic pathway.

Degradation of acetochlor by four microbial communities

Four microbial communities capable of degrading acetochlor, designated A, D, E, and J, were obtained from acetochlor-contaminated soil and sludge. Acetochlor at an initial concentration of 55mg/L was completely degraded by the four mixed cultures after 4 days. At 80 mg/L acetochlor, more than 99% degradation was observed with D, 84% with A and E, and 88% with J after 9 days. There are primary eight strains of bacteria in community A, three in community D, E, and J, respectively. No single isolate was able to degrade acetochlor efficiently. The acetochlor biodegradation products were identified by gas chromatography-mass spectrometry. The probable degradative pathways of acetochlor involved dechlorination, hydroxylation, deethoxymethylation, cyclization, carboxylation, and decarboxylation. Propachlor, alachlor, and metolachlor, which are also the main components of the chloroacetanilide herbicide, could be degraded by the four mixed cultures to some degree. Given the high degradation rates observed here, the four mixed cultures obtained may be useful in the degradation processes of acetochlor.

Alterations of Cytokines and MAPK Signaling Pathways are Related to the Immunotoxic Effect of Perfluorononanoic Acid

Perfluorononanoate (PFNA), a perfluorinated alkyl acid containing nine carbon chains, has been detected in abiotic and biotic matrices worldwide. Although a few studies have reported toxic effects of PFNA, little information of the mechanism has been offered. In this study, the effects of PFNA exposure on thymus and the related mechanisms were investigated. Male rats were orally dosed with 0, 1, 3, or 5 mg PFNA/kg/day for 14 days. A significant decrease of body weight and thymus weight were observed in the rats receiving 3 or 5 mg PFNA/kg/day. Histopathological examination revealed dose-dependent increases in thymocyte apoptosis. Rats receiving 3 or 5 mg PFNA/kg/day exhibited increased interleukin (IL)-1 and decreased IL-2 concentrations in sera, whereas elevated IL-4 and cortisol levels only occurred in the highest dose group. Quantitative real-time PCR indicated that expression of peroxisome proliferator-activated receptor alpha (PPAR-alpha) was increased in the thymi of all dosed rats, and a similar trend occurred for PPAR-gamma in the two highest dose groups. The mRNA levels of c-Jun NH(2)-terminal kinase (JNK), nuclear factor-kappa B, p65 subunit, and inhibitory protein IkappaBalpha were unchanged; however, increased and decreased mRNA levels of p38 kinase were found in rats exposed to 3 or 5 mg PFNA/kg/day, respectively. Decreased Bcl-2 mRNA levels were observed in rats receiving 5 mg PFNA/kg/day. A significant increase in protein levels of phospho-JNK was found in all PFNA-treated rats. Phospho-p38 was significantly enhanced in 1 and 3 mg PFNA/kg/day groups, whereas phospho-IkappaBalpha remained consistent in all rats studied. Together, these data suggested that apart from the activation of PPARs, PFNA exposure in rats lead to the alteration of serum cytokines, which subsequently activated mitogen-activated protein kinase signaling pathways and potentially modulated the immune system. Additionally, increased serum cortisol and decreased expression of Bcl-2 in thymus likely contributed to the PFNA-induced thymocyte apoptosis.

The effect of perfluorododecanonic acid on endocrine status, sex hormones and expression of steroidogenic genes in pubertal female rats.

Perfluorododecanoic acid (PFDoA), one of a number of commercially important perfluoroalkyl acids, has been detected in sera from humans and other animals; however, the effects of PFDoA on female reproduction remain unclear. To assess the impact of PFDoA on puberty and endocrine status, we exposed weaned pre-pubertal female rats to PFDoA, administered orally at doses of 0, 0.5, 1.5 and 3mg/kg-d for 28 days, and measured body weight, reproductive organ weight and morphology, pubertal indicators, endocrine hormones, total serum cholesterol levels and steroidogenic enzyme gene expression. At 3mg/kg-d, PFDoA significantly decreased body weight and serum estradiol levels, increased cholesterol levels (p<0.05), and altered ovarian expression of genes responsible for cholesterol transport and steroidogenesis, including steroidogenic acute regulatory protein, cholesterol side-chain cleavage enzyme and 17-beta-hydroxysteroid dehydrogenase (p<0.05). PFDoA at the highest dose also reduced estrogen receptor alpha and beta expression levels in the ovary (p<0.05), whereas a lower concentration of PFDoA (0.5mg/kg-d) decreased estrogen receptor beta mRNA levels in the uterus (p<0.05). PFDoA treatment did not affect serum follicle-stimulating hormone or luteinizing hormone (LH) levels at any concentration, although PFDoA at 3mg/kg-d reduced LH receptor mRNA levels. There were no marked changes in sexual organ weight, age and weight at vaginal opening or first estrous cycle, or ovarian/uterine histology at any PFDoA concentration. These data show that PFDoA does not affect the endocrine status of pubertal rats, but at higher doses it does impact estradiol production and the expression of some key genes responsible for estrogen synthesis.

Expression of a novel cytochrome P450 4T gene in rare minnow (Gobiocypris rarus) following perfluorooctanoic acid exposure

Cytochrome P450s play an important role in the biotransformation of endogenous substrates and xenobiotics; however, little is known about the function of the CYP4T subfamily in the transformation of environmental pollutants in fish. We isolated a full-length cDNA sequence (designated as CYP4T11) from rare minnow (Gobiocypris rarus) liver by rapid amplification of cDNA ends. The open reading frame encoded a 467-residue protein that exhibited 87% and 71% identity with zebrafish CYP4T8 and European sea bass CYP4T2, respectively. CYP4T11 was predominantly expressed in liver and intestine with lower expression in the gill and brain. To further examine the function of CYP4T11 in pollutant metabolism, the effects of perfluorooctanoic acid (PFOA) exposure on the transcriptional expression of CYP4T11 and two possible upstream regulators, peroxisome proliferator-activated receptor alpha (PPARalpha) and peroxisome proliferator-activated receptor gamma (PPARgamma), were determined in rare minnow gills and livers. PFOA induced a consistent significant upregulation of both PPARalpha and PPARgamma and a nonsignificant increase of CYP4T11 in the gill. In the liver, induced expression of PPARgamma was observed, although no obvious changes in PPARalpha expression were observed. Induction of CYP4T11 was only observed in males at the highest concentration of PFOA. These results suggest that the PPAR-CYP4T11 signaling pathway may be involved in PFOA-induced gill toxicity. Since the induced expression of CYP4T11 in liver was not consistent with the PPAR regulators, complex tissue-specific transcriptional regulation of CYP4T11 following PFOA exposure likely occurs.