The functional roles of cytochrome P-450 mediated systems: present knowledge and future areas of investigations

Genome-wide identification, molecular evolution and gene expression of P450 gene family in Cyrtotrachelus buqueti

BACKGROUND

Insect Cytochrome P450 monooxygenase (CYPs or P450s) plays an important role in detoxifying insecticides, causing insect populations to develop resistance. However, the molecular functions of P450 gene family in Cyrtotrachelus buqueti genome are still lacking.

RESULTS

In this study, 71 CbuP450 genes have been identified. The amino acids length of CbuP450 proteins was between 183 aa ~ 1041 aa. They are proteins with transmembrane domains. The main component of their secondary structure is α-helix and random coils. Phylogenetic analysis showed that C. buqueti and Rhynchophorus ferrugineus were the most closely related. This gene family has 29 high-frequency codons, which tend to use A/T bases and A/T ending codons. Gene expression analysis showed that CbuP450_23 in the female adult may play an important role on high temperature resistance, and CbuP450_17 in the larval may play an important role on low temperature tolerance. CbuP450_10, CbuP450_17, CbuP450_23, CbuP450_10, CbuP450_16, CbuP450_20, CbuP450_23 and CbuP450_ 29 may be related to the regulation of bamboo fiber degradation genes in C. buqueti. Protein interaction analysis indicates that most CbuP450 proteins are mainly divided into three aspects: encoding the biosynthesis of ecdysteroids, participating in the decomposition of synthetic insecticides, metabolizing insect hormones, and participating in the detoxification of compounds.

CONCLUSIONS

We systematically analyzed the gene and protein characteristics, gene expression, and protein interactions of CbuP450 gene family, revealing the key genes involved in the stress response of CbuP450 gene family in the resistance of C. buqueti to high or low temperature stress, and identified the key CbuP450 proteins involved in important life activity metabolism. These results provided a reference for further research on the function of P450 gene family in C. buqueti.

Role of efflux pumps and metabolising enzymes in drug delivery

The impact of efflux pumps and metabolic enzymes on the therapeutic activity of various drugs has been well established. The presence of efflux pumps on various tissues and tumours has been shown to regulate the intracellular concentration needed to achieve therapeutic activity. The notable members of efflux proteins include P-glycoprotein, multi-drug resistance protein and breast cancer resistance protein. These efflux pumps play a pivotal role not only in extruding xenobiotics but also in maintaining the body's homeostasis by their ubiquitous presence and ability to coordinate among themselves. In this review, the role of efflux pumps in drug delivery and the importance of their tissue distribution is discussed in detail. To improve pharmacokinetic parameters of substrates, various strategies that modulate the activity of efflux proteins are also described. Drug metabolising enzymes mainly include the cytochrome P450 family of enzymes. Extensive drug metabolism due to the this family of enzymes is the leading cause of therapeutic inactivity. Therefore, the role of metabolising enzymes in drug delivery and disposition is extensively discussed in this review. The synergistic relationship between metabolising enzymes and efflux proteins is also described in detail. In summary, this review emphasises the urgent need to make changes in drug discovery and drug delivery as efflux pumps and metabolising enzymes play an important role in drug delivery and disposition.

Biochemical changes associated with the potentiation of acetaminophen hepatotoxicity by brief anesthesia with diethyl ether

Acetaminophen hepatotoxicity in male CD-1 mice was enhanced markedly by brief anesthesia with diethyl ether (ether), and particularly so if acetaminophen was given several hours after ether. The present study was conducted to examine the possible biochemical mechanisms behind this delayed toxicologic synergism. In vitro biochemical studies indicated that ether anesthesia produced a delayed reduction in the activities of glucuronyl transferase and glutathione (GSH) S-transferase, and in the hepatic content of GSH. The hepatic content but not activity of the cytochromes P-450 was initially reduced by ether but recovered by the time of maximal toxicologic enhancement. In vivo studies showed that ether produced a small decrease in the plasma concentrations of glucuronide and sulfate conjugates of acetaminophen, with a concomitant, minor increase in the half-life of acetaminophen, and a major increase in the bioactivation of acetaminophen, as determined by an early, 2-fold increase in the plasma GSH and cysteine conjugates of acetaminophen, and a 3-fold increase in the covalent binding of acetaminophen to hepatocellular protein. Decreases produced by ether in the in vivo production of acetaminophen glucuronide correlated with increasing plasma concentrations of unmetabolised acetaminophen, decreasing hepatic GSH content and increasing covalent binding of acetaminophen to hepatocellular protein when these measurements were performed in the same animals. The biochemical mechanisms underlying the potentiation of acetaminophen hepatoxicity as measured by plasma glutamic pyruvic transaminase concentrations appeared to be due to delayed, complex effects of ether upon multiple enzymatic pathways of acetaminophen elimination and detoxification.

The effects of temperature on the cytochrome P-450 system of thermally acclimated bluegill

The effects of temperature acclimation at 10, 20 and 30 degrees C on the concentration and activity of the mixed function oxidase system in bluegill are as follows. Liver weight/body weight varied inversely with temperature. Significant (P less than 0.05) differences in concentration of cytochrome P-450 of hepatic microsomes were seen and varied inversely with temperature. Benzo(a)pyrene hydroxylase activity tested in vitro at incubation temperatures of 10, 20 and 30 degrees C showed significant differences in Km, but no differences in Vmax. SDS polyacrylamide gel electrophoresis revealed some quantitative differences in cytochrome P-450 isozymes between groups.

Temperature compensation in the hepatic mixed-function oxidase system of bluegill

Bluegill (Lepomis macrochirus R.) were acclimated to 12, 22 or 32 degrees C for 5 or 14 days. Liver weight to body weight ratio and the rate of metabolism of benzo[alpha]pyrene by liver microsomes varied inversely with the acclimation temperature of the fish. Concentration of microsomal cytochrome P-450, as determined by CO-difference binding spectra, was not significantly affected by acclimation temperature. There were no qualitative or quantitative differences in the electrophoretic patterns of proteins with molecular weights similar to those reported for cytochrome P-450. There were no shifts in the temperature optima of the microsomal benzo[alpha]pyrene hydroxylase activity.

Cloxacillin absorption and disposition in cystic fibrosis

Because of reports of lowered antibiotic serum concentrations in patients with cystic fibrosis (CF), a bioavailability and pharmacokinetic study of cloxacillin was conducted in 12 control and 16 patients with CF after intravenously and orally administered doses of cloxacillin 25 mg/kg. The patients had mild to moderate CF and were in stable condition. Significantly lower serum concentrations in CF were a result of a 78% increase in total body clearance (P less than 0.005) and a 38% increase in the apparent volume of distribution (P less than 0.025). The bioavailability in CF (0.50) was not significantly different than in controls (0.38), but more variability was seen in the group with CF. After the intravenously given dose the fraction of cloxacillin excreted in the urine unchanged was similar in controls (0.644) and patients with CF (0.547). Compared with that in the control subjects, the mean renal clearance in patients with CF was 30% greater (P less than 0.10) and the nonrenal clearance was 144% greater (P less than 0.07). Enhanced nonrenal clearance explains most of the demonstrated difference between serum concentrations in controls and patients with CF after identical weight-adjusted doses. The data suggest enhanced cloxacillin biotransformation in CF.

Mixed-function oxidase studies in the redfish, Sciaenops ocellata, from Galveston Bay, Texas

The metabolism of parathion to para-nitrophenol (PNP) in redfish (Sciaenops ocellata) liver microsomes has been both identified and characterized. This mixed-function oxidase (MFO) reaction in redfish requires NADPH and is inhibited by carbon monoxide. It exhibits a temperature optimum of 25 degrees C but no clear pH optimum between 7.0-8.5. Redfish hepatic microsomal MFOs were not induced by 2.5 days after a single i.p. injection of 88 mg Aroclor 1254/kg body wt, but under the same dosage and time conditions male albino Swiss mice were significantly induced (p less than 0.05).

Carbon disulphide intrauterine sensitization

This study was designed to evaluate the effect of carbon disulphide (CS2) exposure during pregnancy in two subsequent generations. Albino rats (F1), which had been prenatally exposed by maternal inhalation to teratogenic (200 and 100 mg m-3) and subteratogenic (10 and 0.03 mg m-3) concentrations of CS2, were reared until maturity and mated to produce an F2 generation. During pregnancy the F1 females were again subjected to CS2 exposure at the same concentrations as the F0 females throughout gestation. Pre- and postnatal development of F1 and F2 generations, as well as the corresponding maternal effects, were studied. Embryonic lethality, weight, congenital malformations, indices of lipid and energy metabolism, DNA and some liver drug metabolizing enzymes in maternal and fetal tissues were studied at term. Postnatal viability, physical and behavioral development, and hexobarbital sleeping time of the progeny were evaluated. Comparisons of CS2 effect on F1 and F2 generations were performed. A marked increase in CS2-induced teratogenicity was found in the F2 generation, together with retarded development of MFO system and increased postnatal behavioral effects. The results point to intrauterine sensitization of progeny to CS2. This effect is discussed in the light of possible interference of the agent with the hormonal programming of intrauterine development.

Biotransformation of xenobiotics in Drosophila melanogaster and its relevance for mutagenicity testing

Biotransformation of lipophilic xenobiotics may lead to formation of reactive intermediates which can give rise to irreversible toxic events such as carcinogenesis, mutagenesis, teratogenesis, and tissue necrosis. In recent years considerable attention has been paid to the problem of testing for these effects. Short-term mutagenicity tests have been shown to have value for predicting the occurrence of delayed toxic effects in mammals following administration of indirectly acting harmful xenobiotics. In any test system the capacity to bioactivate the compound under test is a necessary prerequisite, and in most short-term test assays this is provided for by adding a metabolic activation system generally consisting of the 9,000 g supernatant fraction of a rat liver homogenate supplied with cofactors. The fruitfly Drosophila melanogaster constitutes an organism well-suited for mutagenicity testing, and it was shown that a number of precarcinogens evoke mutagenic effects in this species. Thus Drosophila is apparently able to metabolize xenobiotics to reactive intermediates, which in turn induce mutagenicity. However, knowledge about the presence and characteristics of the xenobiotic-metabolizing enzymes involved is lacking. Since knowledge of these enzymes contributes to the evaluation and interpretation of observed mutagenic events, this paper described studies concerning some important xenobiotic-metabolizing enzymes of Drosophila. Files were homogenized and subcellular fractions were investigated with respect to enzymatic activities. It was possible to demonstrate cytochrome P-450 and some related mixed-function oxidase activities. Cytochrome b5, epoxide hydrolase, and glutathione S-transferase are also present, while preliminary experiments suggest the presence of UDP-glucosyltransferase and phosphotransferase activities. The enzymes which have been found are discussed with respect to their similarities with rat liver enzymes and their relevance for mutagenicity testing with Drosophila melanogaster.