Protective effects of ursodeoxycholic acid against 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced testicular damage in mice

Animal Toxicology Studies on the Male Reproductive Effects of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin: Data Analysis and Health Effects Evaluation

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a well-known environmental poison that exist in the environment for many years. However, its effect on the male reproductive system has not been clearly stated. We conducted a meta-analysis of the effect of TCDD on the male reproductive system of rodents about TCDD. Results showed that that TCDD exposure reduced the testis weight (weighted mean difference [WMD]: -0.035, 95% confidence interval [CI]: -0.046 to -0.025), sperm count (WMD: -35, 95% CI: -42.980 to -27.019), and blood testosterone concentration (WMD: -0.171, 95% CI: -0.269 to -0.073). According to our research results, TCDD can cause damage to the male reproductive system of rodents through direct or indirect exposure. In order to further explore the potential hazards of TCDD to humans, more human-related research needs to be carried out.

Aryl hydrocarbon receptor (AhR) mediated short-term effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on bile acid homeostasis in mice

The effects of the most potent aryl hydrocarbon receptor (AhR) agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on bile acid (BA) homeostasis was examined in male and female wild-type and AhR-null mice shortly after 4-day exposure, rather than at a later time when secondary non-AhR dependent effects are more likely to occur. TCDD had similar effects on BA homeostasis in male and female mice. TCDD decreased the concentration of total-(Σ) BAs in liver by approximately 50% (all major BA categories except for the non-6,12-OH BAs), without decreasing the expression of the rate limiting BA synthetic enzyme (Cyp7a1) or altering the major BA regulatory pathways (FXR) in liver and intestine. Even though the Σ-BAs in liver were markedly decreased, the Σ-BAs excreted into bile were not altered. TCDD decreased the relative amount of 12-OH BAs (TCA, TDCA, CA, DCA) in bile and increased the biliary excretion of TCDCA and its metabolites (TαMCA, TUDCA); this was likely due to the decreased Cyp8b1 (12α-hydroxylase) in liver. The concentration of Σ-BAs in serum was not altered by TCDD, indicating that serum BAs do not reflect BA status in liver. However, proportions of individual BAs in serum reflected the decreased expression of Cyp8b1. All these TCDD-induced changes in BA homeostasis were absent in AhR-null mice. In summary, through the AhR, TCDD markedly decreases BA concentrations in liver and reduces the 12α-hydroxylation of BAs without altering Cyp7a1 and FXR signaling. The TCDD-induced decrease in Σ-BAs in liver did not result in a decrease in biliary excretion or serum concentrations of Σ-BAs.

Ursodeoxycholic acid alleviates cholestasis-induced histophysiological alterations in the male reproductive system of bile duct-ligated rats

Ursodeoxycholic acid is the most widely used drug for treating cholestatic liver diseases. However, its effect on the male reproductive system alterations associated with cholestasis has never been studied. Thus, this study aimed to investigate the effect of ursodeoxycholic acid on cholestasis-induced alterations in the male reproductive system. Cholestasis was induced by bile duct ligation. Bile duct-ligated rats had higher cholestasis biomarkers and lower levels of testosterone, LH and FSH than did the Sham rats. They also had lower reproductive organs weights, and lower sperm motility, density and normal morphology than those of Sham rats. Histologically, these animals suffered from testicular tubular atrophy, interstitial edema, thickening of basement membranes, vacuolation, and depletion of germ cells. After ursodeoxycholic acid administration, cholestasis-induced structural and functional alterations were significantly ameliorated. In conclusion, ursodeoxycholic acid can ameliorate the reproductive complications of chronic cholestasis in male patients, which represents an additional benefit to this drug.

The PERK-eIF2α signaling pathway is involved in TCDD-induced ER stress in PC12 cells

Studies have shown that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces apoptotic cell death in neuronal cells. However, whether this is the result of endoplasmic reticulum (ER) stress-mediated apoptosis remains unknown. In this study, we determined whether ER stress plays a role in the TCDD-induced apoptosis of pheochromocytoma (PC12) cells and primary neurons. PC12 cells were exposed to different TCDD concentrations (1, 10, 100, 200, or 500nM) for varying lengths of time (1, 3, 6, 12, or 24h). TCDD concentrations much higher than 10nM (100, 200, or 500nM) markedly increased glucose-regulated protein (GRP78) and C/EBP homologous protein (CHOP) levels, which are hallmarks of ER stress. We also evaluated the effects of TCDD on ER morphology in PC12 cells and primary neurons that were treated with different TCDD concentrations (1, 10, 50, or 200nM) for 24h. Ultrastructural ER alterations were observed with transmission electron microscopy in PC12 cells and primary neurons treated with high concentrations of TCDD. Furthermore, TCDD-induced ER stress significantly promoted the activation of the PKR-like ER kinase (PERK), a sensor for the unfolded protein response (UPR), and its downstream target eukaryotic translation initiation factor 2 α (eIF2α); in contrast, TCDD did not appear to affect inositol-requiring enzyme 1 (IRE1) and activating transcription factor 6 (ATF6), two other UPR sensors. Importantly, TCDD significantly inhibited eIF2α phosphorylation and triggered apoptosis in PC12 cells after 6-24h of treatment. Salubrinal, which activates the PERK-eIF2α pathway, significantly enhanced eIF2α phosphorylation in PC12 cells and attenuated the TCDD-induced cell death. In contrast, knocking down eIF2α using small interfering RNA markedly enhanced TCDD-induced cell death. Together, these results indicate that the PERK-eIF2α pathway plays an important role in TCDD-induced ER stress and apoptosis in PC12 cells.

Ameliorative effect of supplementation with L-glutamine on oxidative stress, DNA damage, cell viability and hepatotoxicity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin in rat hepatocyte cultures

The most potent of the dioxins, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is a persistent and ubiquitous environmental contaminant. And the health impact of exposure to TCDD is of great concern to the general public. Recent data indicate that L-glutamine (Gln) has antioxidant properties and may influence hepatotoxicity. The objective of the present study was undertaken to explore the effectiveness of Gln in alleviating the hepatotoxicity of TCDD on primary cultured rat hepatocytes. Gln (0.5, 1 and 2 mM) was added to cultures alone or simultaneously with TCDD (0.005 and 0.01 mM). The hepatocytes were treated with TCDD and Gln for 48 h. Then cell viability was detected by [3-(4,5-dimethyl-thiazol-2-yl) 2,5-diphenyltetrazolium bromide] (MTT) assay and lactate dehydrogenase (LDH) release, while total antioxidant capacity (TAC), total glutathione (TGSH) and total oxidative stress (TOS) levels were determined to evaluate the oxidative injury. The DNA damage was also analyzed by liver micronucleus assay (MN) and 8-oxo-2-deoxyguanosine (8-OH-dG). The results of MTT and LDH assays showed that TCDD decreased cell viability but not L-glutamine. TCDD also increased TOS level in rat hepatocytes and significantly decreased TAC and TGSH levels. On the basis of increasing doses, the dioxin in a dose-dependent manner caused significant increases of micronucleated hepatocytes (MNHEPs) and 8-OH-dG as compared to control culture. Whereas, in cultures exposured with Gln alone, TOS levels were not changed and TAC and TGSH together were significantly increased in dose-dependent fashion. The presence of Gln with TCDD modulated the hepatotoxic effects of TCDD on primary hepatocytes cultures. Noteworthy, Gln has a protective effect against TCDD-mediated DNA damages. As conclusion, we reported here an increased potential therapeutic significance of L-glutamine in TCDD-mediated hepatic injury for the first time.

Quercetin prevents 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced testicular damage in rats

The protective effect of quercetin on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced testicular damage in rats was investigated. Twenty-two rats were equally divided into four groups; first group was kept as control and given corn oil as carrier. In second group, TCDD was orally administered at the dose of 2 μ (kg week)(-1) for 60 days. In third group, quercetin was orally administered at the dose of 20 mg (kg day)(-1) by gavages, and in fourth group TCDD and quercetin were given together at the same doses. Although TCDD increased the formation of thiobarbituric acid reactive substances (TBARS) significantly, it caused a significant decline in the levels of glutathione (GSH), catalase (CAT), GSH-Px and CuZn-Superoxide Dismutase (CuZn-SOD) in rats. In contrast, quercetin significantly increased the GSH, CAT, GSH-Px and CuZn-SOD levels but decreased the formation of TBARS. In addition, sperm motility, sperm concentration and serum testosterone levels were significantly decreased but abnormal sperm rate and testicular damage were increased with TCDD treatment. However, these effects of TCDD on sperm parameters, histological changes and hormone levels were eliminated by quercetin treatment. Our results show that administration of TCDD induces testicular damage (oxidative stress, testes tissue damage, serum hormone level and sperm parameters), and quercetin prevents TCDD-induced testicular damage in rats. Thus, quercetin may be useful for the prevention and treatment of TCDD-induced testicular damage.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) alters the mRNA expression of critical genes associated with cholesterol metabolism, bile acid biosynthesis, and bile transport in rat liver: a microarray study

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent hepatotoxin that exerts its toxicity through binding to the aryl hydrocarbon receptor (AhR) and the subsequent induction or repression of gene transcription. In order to further identify novel genes and pathways that may be associated with TCDD-induced hepatotoxicity, we investigated gene changes in rat liver following exposure to single oral doses of TCDD. Male Sprague-Dawley rats were administered single doses of 0.4 microg/kg bw or 40 microg/kg bw TCDD and killed at 6 h, 24 h, or 7 days, for global analyses of gene expression. In general, low-dose TCDD exposure resulted in greater than 2-fold induction of genes coding for a battery of phase I and phase II metabolizing enzymes including CYP1A1, CYP1A2, NADPH quinone oxidoreductase, UGT1A6/7, and metallothionein 1. However, 0.4 microg/kg bw TCDD also altered the expression of Gadd45a and Cyclin D1, suggesting that even low-dose TCDD exposure can alter the expression of genes indicative of cellular stress or DNA damage and associated with cell cycle control. At the high-dose, widespread changes were observed for genes encoding cellular signaling proteins, cellular adhesion, cytoskeletal and membrane transport proteins as well as transcripts coding for lipid, carbohydrate and nitrogen metabolism. In addition, decreased expression of cytochrome P450 7A1, short heterodimer partner (SHP; gene designation nr0b2), farnesyl X receptor (FXR), Ntcp, and Slc21a5 (oatp2) were observed and confirmed by RT-PCR analyses in independent rat liver samples. Altered expression of these genes implies major deregulation of cholesterol metabolism and bile acid synthesis and transport. We suggest that these early and novel changes have the potential to contribute significantly to TCDD induced hepatotoxicity and hypercholesterolemia.