Induction of CYP1A by carbofuran in primary culture of fish hepatocytes

In vitro effects of diosmin, naringenin, quercetin and indole-3-carbinol on fish hepatic CYP1A1 in the presence of clotrimazole and dexamethasone

Phytochemicals are widely present in fruits, vegetables and other plants and have great health benefits owing to their antioxidant properties. They are naturally found in the aquatic environment as well as discharged from sewage treatment plants after their large consumption. Little is known about their impact on fish; particularly in light of their interactions with pharmaceuticals. Therefore, this study was designed to determine the effects of diosmin, naringenin, quercetin and idole-3-carbinol on CYP1A-dependent 7-ethoxyresorufin-O-deethylase (EROD) activity on rainbow trout hepatic microsomes in the presence of two pharmaceuticals: clotrimazole and dexamethasone. The interactions between the phytochemicals and pharmaceuticals used in this study were determined using a combination index. Hepatic microsomes were exposed to two concentrations (1-or 50 μM) of phytochemicals and pharmaceuticals separately and in combinations. Singly, clotrimazole inhibited EROD activity 40% and 90% of control, while dexamethasone did not. Naringenin and diosmin inhibited EROD activity alone up to 90% and 55% respectively, but activities were further inhibited in the presence of either pharmaceutical. The preliminary study of combinations of clotrimazole with phytochemicals primarily showed synergistic effects. While EROD activity was not inhibited in the presence of quercetin or indole-3-carbinol, significant and synergistic inhibition was detected when either of these was combined with clotrimazole or dexamethasone.

Inducible headkidney cytochrome P450 contributes to endosulfan immunotoxicity in walking catfish Clarias gariepinus

The effect of endosulfan metabolites on fish immune system is not well known. It is also not clear whether endosulfan accumulates in fish immune organs and undergoes metabolic biotransformation in situ. In the present study we investigated the role of headkidney (HK), an important fish immune organ on endosulfan metabolism and the long term effects of endosulfan metabolites on the fish immune system. C. gariepinus (walking catfish) were exposed to 2.884ppb of endosulfan (1/10th LC50) for 30d followed by their maintenance in endosulfan-free water for 30d for recovery. Endosulfan induced time-dependent reduction in the HK somatic index and histo-pathological changes in renal and hemopoietic components of the organ. At cellular level, exposure to endosulfan led to death of HK leucocytes. Gas-liquid-chromatography documented the presence of both α- and β-isomers of endosulfan along with the toxic metabolite endosulfan sulfate (ESS) in the HK of exposed fishes. We report that β-endosulfan accumulates more readily in the HK. Depuration studies suggested the persistence of ESS in the HK. Enzyme-immunoassay and qPCR results demonstrated direct relationship between cytochrome P450 1A (CYP1A) expression and ESS levels in the HK. Pre-treatment of HKL with CYP1A specific inhibitor α-Naphthoflavone (ANF) led to reduction in CYP1A mRNA, protein levels, and inhibited ESS formation together implicating the role of CYP1A on endosulfan metabolism. When the exposed fish were transferred to endosulfan-free water ('recovered fish') it was observed that after 30d of recovery period the concentration of endosulfan and its metabolite in the HK were significantly reduced, compared to 30-d exposed fish. We also observed improvement in HK histo-architecture but no significant recovery in HKL number and viability. Collectively, our findings suggest that HK plays an important role in endosulfan metabolism. We propose that endosulfan induces the activation of CYP1A in HK which led to the generation of persistent metabolite, ESS, resulting in immunotoxicity.

Membrane phospholipid augments cytochrome P4501a enzymatic activity by modulating structural conformation during detoxification of xenobiotics

Cytochrome P450 is a superfamily of membrane-bound hemoprotein that gets involved with the degradation of xenobiotics and internal metabolites. Accumulated body of evidence indicates that phospholipids play a crucial role in determining the enzymatic activity of cytochrome P450 in the microenvironment by modulating its structure during detoxification; however, the structure-function relationship of cytochrome P4501A, a family of enzymes responsible for degrading lipophilic aromatic hydrocarbons, is still not well defined. Inducibility of cytochrome P4501A in cultured catfish hepatocytes in response to carbofuran, a widely used pesticide around the world, was studied earlier in our laboratory. In this present investigation, we observed that treating catfish with carbofuran augmented total phospholipid in the liver. We examined the role of phospholipid on the of cytochrome P4501A-marker enzyme which is known as ethoxyresorufin-O-deethylase (EROD) in the context of structure and function. We purified the carbofuran-induced cytochrome P4501A protein from catfish liver. Subsequently, we examined the enzymatic activity of purified P4501A protein in the presence of phospholipid, and studied how the structure of purified protein was influenced in the phospholipid environment. Membrane phospholipid appeared to accelerate the enzymatic activity of EROD by changing its structural conformation and thus controlling the detoxification of xenobiotics. Our study revealed the missing link of how the cytochrome P450 restores its enzymatic activity by changing its structural conformation in the phospholipid microenvironment.

Detection of mutagens and BaPMO inducers in river water using the Blue Cotton adsorption technique

Induction of Mixed Function Oxidase (MFO) activity and bioactivation potential were measured in experimental carp and in native fish species from two rivers with different pollution level (Sava and Mrežnica). The experimental carp were intraperitoneally exposed to various water volume equivalents of Blue Cotton extracts from both rivers. The induction of MFO measured as a Benzo(a)pyrene monooxygenase (BaPMO) activity was increased up to 9.3-fold in experimental carp and up to 11.3-fold in native fish from Sava River, whereas the values from Mrežnica River showed only a slight increase when compared with the control (highest increase of 1.8-fold in nose carp). Accordingly, bioactivation potential using modified Ames test was higher in both experiments with Sava River. Both measured parameters in experimental carp increased in a dose-dependent manner in accordance to river volume equivalents. Different induction potential of native fish species comparable between two rivers confirmed the known possibility of their usage in biomonitoring studies. These results give qualitatively a new support to the idea of using Blue Cotton extraction technique combined with induction of MFO activity and Ames test in fish as a good biomarker for assessing risk of exposure to mutagens/carcinogens such as Polycyclic Aromatic Hydrocarbons (PAHs), especially due to the simplicity and cost-effectiveness of these methods.

Regulation of cytochrome P4501A by protein kinase C: the role of heat shock protein70

Carbofuran is a pesticide, which is used throughout the world as a nematicide and an acaricide. This pesticide integrates into living organisms through aquatic ecosystem. In earlier report, we had demonstrated that cytochrome P4501A was induced in cultured catfish hepatocytes in response to carbofuran, which might be responsible for the detoxification of this pesticide. As the underlying signaling mechanism associated with induction and regulation of cytochrome P4501A has not yet been well defined, we therefore in the present study have investigated to identify the regulatory network of cytochrome P4501A in catfish liver or cultured hepatocytes by targeting several key signaling molecules such as phosphatidyl inositol (PI) or protein kinase C (PKC), which are critical molecules for many important pathways. PKC and heat shock protein70 (HSP70) have been shown to be induced in response to carbofuran in catfish hepatocytes. Results also indicate that induction of CYP1A is modulated by HSP70 and PKC in fish hepatocytes. Thus our data shed light on the regulation of EROD activity, which has been used as a bio-monitoring tool for measuring aquatic pollution.

Hepatic monooxygenase (CYP1A and CYP3A) and UDPGT enzymatic activities as biomarkers for long-term carbofuran exposure in tench (Tinca tinca L)

The effect of a long-term exposure of tenchs to different concentrations (10 and 100 micro g/L) of the pesticide carbofuran has been evaluated. Microsomal hepatic cytochrome P450 subfamily 1A (CYP1A) and 3A (CYP3A) activities, as well as the phase II enzyme uridine diphospho-glucuronosyltransferase (UDPGT) activity were evaluated as adequate biomarkers of fish exposure to environmentally relevant concentrations of the pesticide carbofuran in freshwater ecosystems. A clear time-dependent inhibition of both CYP1A and UDPGT activities was observed in fish exposed to the highest dose of carbofuran with respect to controls, whereas in the case of CYP3A activity, values of exposed animals did not show a clear pattern of alteration during the experiment. The results of the present study demonstrated that hepatic CYP1A and UDPGT activities from tench could be considered as sensitive biomarkers for carbamate pesticides in polluted water, thus allowing future and ecologically relevant biomonitoring studies with this species.

Comparative effects of acute and chronic carbofuran exposure on oxidative stress and drug-metabolizing enzymes in liver

The current study has been designed to examine the comparative effects of acute and chronic carbofuran exposure on lipid peroxidation, glutathione levels, and drug-metabolizing enzymes in rat liver. Activity of acetylcholinesterase, a bona fide marker of carbofuran exposure, was markedly inhibited after acute carbofuran exposure, whereas the extent of inhibition was much less after chronic exposure. Lipid peroxidation was accentuated after chronic carbofuran exposure. However, acute exposure resulted in relatively less increase in lipid peroxidation levels than with chronic exposure. Glutathione levels were significantly increased in liver of animals chronically exposed to carbofuran; on the contrary, there was a drastic reduction in glutathione levels after acute exposure. Cytochrome P450 was significantly induced in liver of animals treated with acute as well as chronic carbofuran. The activity of glutathione-S-transferase was induced after both acute and chronic carbofuran exposure; the increase was much higher in chronically exposed animals as compared with animals exposed acutely. Based on the results, it is clear that acute and chronic carbofuran exposure have differential effects on oxidative stress and drug-metabolizing enzymes in liver.

Disruption of pituitary-ovarian axis by carbofuran in catfish, Heteropneustes fossilis (Bloch)

We investigated whether carbofuran (CF), a carbamate pesticide, at sub-lethal concentration had any adverse effects on reproductive function of the Indian catfish, Heteropneustes fossilis. 17beta-Estradiol content of serum and ovary of pre-spawning (P) and spawning (S) fish was reduced after sub-lethal concentration of carbofuran treatment (0.5-2 mg/ml, 30 days). After 30 days of CF treatment, the serum and ovarian vitellogenin levels of fish at the P stage were also reduced but remained unaltered in the S stage. The staining intensity of the pituitary gonadotrophs of the pre-spawning fish was significantly higher in CF-treated fish compared to controls suggesting the inability of the pituitary gonadotrophs to release gonadotropin following CF treatment. CF thus acts as an antiestrogenic, endocrine-disrupting agent in fish, possibly targeting the pituitary-gonad axis.

Impact of copper on biomonitoring enzyme ethoxyresorufin-o-deethylase in cultured catfish hepatocytes

The enzyme ethoxyresorufin-o-deethylase (EROD) of the cytochrome P4501A family (CYP1A) in fish liver is increasingly being used as a molecular marker for qualitative and quantitative estimation of aquatic pollution throughout the world. The regulation and expression of this enzyme protein is very important from the toxicological point of view. The regulation of gene expression for this enzyme is mediated by the aromatic hydrocarbon receptor. In addition, cellular glutathione status influences expression of CYP1A. In this study, we explored the relationships among glutathione, EROD, and copper in cultured hepatocytes from Indian catfish. EROD activity in cultured hepatocytes was induced by carbofuran (CF), a widely used agricultural pesticide, and by beta-napthoflavone (BNF), a known inducer of CYP1A. Addition of copper into the culture media of hepatocytes inhibited EROD activity significantly. The activity of EROD elevated by CF and BNF was inhibited in hepatocytes pretreated with CF and BNF exposed to CuSO4. This effect was reflected in the glutathione status of the cells. The level of glutathione was increased by 3.4 and 3.0 times in hepatocytes treated with CF and BNF, respectively. These levels were inhibited in hepatocytes exposed to CuSO(4). Thus, copper interactions with glutathione may play a role in regulating EROD in hepatocytes.