Posttranscriptional elevation of cytochrome P450 3A expression

Approaches to optimizing animal cell culture process: substrate metabolism regulation and protein expression improvement

Some high value proteins and vaccines for medical and veterinary applications by animal cell culture have an increasing market in China. In order to meet the demands of large-scale productions of proteins and vaccines, animal cell culture technology has been widely developed. In general, an animal cell culture process can be divided into two stages in a batch culture. In cell growth stage a high specific growth rate is expected to achieve a high cell density. In production stage a high specific production rate is stressed for the expression and secretion of qualified protein or replication of virus. It is always critical to maintain high cell viability in fed-batch and perfusion cultures. More concern has been focused on two points by the researchers in China. First, the cell metabolism of substrates is analyzed and the accumulation of toxic by-products is decreased through regulating cell metabolism in the culture process. Second, some important factors effecting protein expression are understood at the molecular level and the production ability of protein is improved. In pace with the rapid development of large-scale cell culture for the production of vaccines, antibodies and other recombinant proteins in China, the medium design and process optimization based on cell metabolism regulation and protein expression improvement will play an important role. The chapter outlines the main advances in metabolic regulation of cell and expression improvement of protein in animal cell culture in recent years.

Efficient replication of primary or culture hepatitis C virus isolates in human liver slices: a relevant ex vivo model of liver infection

The development of human cultured hepatitis C virus (HCV) replication-permissive hepatocarcinoma cell lines has provided important new virological tools to study the mechanisms of HCV infection; however, this experimental model remains distantly related to physiological and pathological conditions. Here, we report the development of a new ex vivo model using human adult liver slices culture, demonstrating, for the first time, the ability of primary isolates to undergo de novo viral replication with the production of high-titer infectious virus as well as Japanese fulminant hepatitis type 1, H77/C3, and Con1/C3. This experimental model was employed to demonstrate HCV neutralization or HCV inhibition, in a dose-dependent manner, either by cluster of differentiation 81 or envelope protein 2-specific antibodies or convalescent serum from a recovered HCV patient or by antiviral drugs.

CONCLUSION

This new ex vivo model represents a powerful tool for studying the viral life cycle and dynamics of virus spread in native tissue and also allows one to evaluate the efficacy of new antiviral drugs.

Cytochrome P450 levels are altered in patients with esophageal squamous-cell carcinoma

AIM: To investigate the role of cytochrome P450 (CYP) in the carcinogenesis of squamous-cell carcinoma (SCC) in human esophagus by determining expression patterns and protein levels of representative CYPs in esophageal tissue of patients with SCC and controls.

METHODS: mRNA expression of CYP2E1, CYP2C, CYP3A4, and CYP3A5 was determined using RT-PCR in both normal and malignant esophageal tissues of patients with untreated esophageal SCC (n = 21) and in controls (n = 10). Protein levels of CYP2E1, CYP2C8, CYP3A4, and CYP3A5 were measured by Western blot.

RESULTS: Within the group of SCC patients, mRNA expression of CYP 3A4 and CYP2C was significantly lower in malignant tissue (-39% and -74%, respectively, P < 0.05) than in normal tissue. Similar results were found in CYP3A4 protein levels. Between groups, CYP3A4, CYP3A5, and CYP2C8 protein concentration was significantly higher in non-malignant tissue of SCC patients (4.8-, 2.9-, and 1.9-fold elevation, P < 0.05) than in controls. In contrast, CYP2E1 protein levels were significantly higher in controls than in SCC patients (+46%, P < 0.05).

CONCLUSION: Significant differences exist in protein levels of certain CYPs in non-malignant esophageal tissue (e.g. CYP2C8, CYP3A4, CYP3A5, and CYP2E1) between SCC patients and healthy subjects and may contribute to the development of SCC in the esophagus.

Effects of dimethylsulfoxide on metabolism and toxicity of acetaminophen in mice

Effects of dimethylsulfoxide (DMSO) on metabolism and toxicity of acetaminophen (APAP) were examined using male mice. A dose of DMSO (1 ml/kg, i.p.) inhibited the induction of APAP hepatotoxicity almost completely as indicated by changes in serum hepatotoxic parameters. Quantification of major APAP metabolites in plasma showed that APAP-glutathione (GSH), a conjugate generated via metabolic activation of APAP, was reduced significantly while APAP-sulfate and APAP-glucuronide, detoxified metabolites both produced directly from the parent drug, were increased in mice pretreated with DMSO. However, microsomal CYP2E1 activity measured with p-nitrophenol and p-nitroanisole as substrates was increased by DMSO treatment. Generation of APAP-GSH in microsomes from control mice was inhibited by DMSO in a dose-dependent manner. Lineweaver-Burk plot analysis indicated that the inhibition pattern produced by DMSO was competitive in nature. A 10000 g supernatant was reconstituted with the cytosolic fraction and microsomes from DMSO- or saline-treated animals. APAP-GSH production was increased significantly when the cytosolic fraction from saline-treated mice and/or microsomes from DMSO-treated mice were used. The results indicate that DMSO induces the enzyme activity responsible for oxidative metabolism of APAP, but its direct inhibitory effect on the enzymatic interaction with this drug decreases the overall production of a reactive metabolite, resulting in reduction of the hepatotoxicity. It is suggested that DMSO effects on metabolism of a xenobiotic would vary depending on its potential to inhibit the interaction of enzyme(s) and the xenobiotic.

Comparative effects of dimethylsulfoxide on metabolism and toxicity of carbon tetrachloride and dichloromethane

The effects of dimethylsulfoxide (DMSO) on the metabolism and toxicity of chlorinated methanes were examined. Male mice were treated with DMSO (1, 2.5 or 5 ml kg(-1), i.p.) prior to challenge with dichloromethane (CH(2)Cl(2)) or carbon tetrachloride (CCl(4)). Blood carboxyhemoglobin elevation resulting from metabolic conversion of CH(2)Cl(2) to carbon monoxide was inhibited dose-dependently by DMSO pretreatment. The elevation of serum aspartate aminotransferase, alanine aminotransferase and sorbitol dehydrogenase activities induced by CCl(4) (0.1 mmol kg(-1)) was not changed in mice pretreated with DMSO at 1 ml kg(-1), but depressed significantly at a greater dose of DMSO. However, DMSO failed to alter the hepatotoxicity of CCl(4) injected at a dose of 0.2 mmol kg(-1). DMSO induced the microsomal p-nitrophenol hydroxylase and p-nitroanisole O-demethylase activities as early as 2 h following the treatment. Microsomal disposition of CH(2)Cl(2) and CCl(4) was measured using a vial equilibration technique. The disappearance of CH(2)Cl(2) was inhibited competitively by addition of DMSO. But DMSO did not affect the metabolic degradation of CCl(4). The results indicate that DMSO has multiple effects on metabolism and toxicity of xenobiotics. DMSO induces the hepatic metabolizing activity mediated by CYP2E1, but the presence of this solvent in the enzyme site may inhibit directly the enzymatic interaction with a substrate. The toxicological significance of DMSO-induced effects on such an interaction may be variable depending on the properties of each substrate. The invulnerability of CCl(4) metabolism to the effects of DMSO appears to be related to its high affinity for the lipophilic CYP enzyme site.

Decreased expression of cytochrome P450 protein in non-malignant colonic tissue of patients with colonic adenoma

BACKGROUND

Cytochrome P450 (CYP) enzymes in epithelial cells lining the alimentary tract play an important role in both the elimination and activation of (pro-)carcinogens. To estimate the role of cytochrome P450 in carcinogenesis of the colon, expression patterns and protein levels of four representative CYPs (CYP2C, CYP2E1, CYP3A4 and CYP3A5) were determined in colon mucosa of normal and adenomatous colonic tissue of patients with adenomas and disease-free controls.

METHODS

Expression of CYP2C, CYP2E1, CYP3A4, and CYP3A5 in colon mucosa of normal and adenomatous colonic tissue of patients with adenoma and disease-free controls was determined by RT-PCR. Protein concentration of CYPs was determined using Western blot.

RESULTS

With the exception of CYP3A5, expression of CYP mRNA was similar among groups and tissues (e.g. normal colon mucosa and adenoma). CYP3A5 mRNA expression was significantly higher in adenoma in comparison to normal tissue of patients with adenoma (approximately 48%). When comparing protein concentrations of CYPs measured in adenomas with neighboring normal colonic mucosa no differences were found. However, in normal tissue of patients with adenomas, protein levels of CYP2C8, CYP3A4 and CYP3A5, but not that of CYP2E1, were significantly lower than in biopsies obtained from disease-free controls. Specifically, in normal colonic mucosa of patients protein concentrations of CYP2C8, CYP3A4, and CYP3A5 were approximately 86%, approximately 69%, and approximately 54%, respectively, lower than in disease-free controls.

CONCLUSION

In conclusion, among other factors, the altered protein levels of certain CYPs (e.g. CYP2C8, CYP3A4 and CYP3A5) in colon mucosa might contribute to the development of neoplasia in the colon.

Distribution of cytochrome P450 2C, 2E1, 3A4, and 3A5 in human colon mucosa

Background

Despite the fact that the alimentary tract is part of the body's first line of defense against orally ingested xenobiotica, little is known about the distribution and expression of cytochrome P450 (CYP) enzymes in human colon. Therefore, expression and protein levels of four representative CYPs (CYP2C(8), CYP2E1, CYP3A4, and CYP3A5) were determined in human colon mucosa biopsies obtained from ascending, descending and sigmoid colon.

Methods

Expression of CYP2C, CYP2E1, CYP3A4, and CYP3A5 mRNA in colon mucosa was determined by RT-PCR. Protein concentration of CYPs was determined using Western blot methods.

Results

Extensive interindividual variability was found for the expression of most of the genes. However, expression of CYP2C mRNA levels were significantly higher in the ascending colon than in the sigmoid colon. In contrast, mRNA levels of CYP2E1 and CYP3A5 were significantly lower in the ascending colon in comparison to the descending and sigmoid colon. In sigmoid colon protein levels of CYP2C8 were significantly higher by ~73% than in the descending colon. In contrast, protein concentration of CYP2E1 was significantly lower by ~81% in the sigmoid colon in comparison to the descending colon.

Conclusion

The current data suggest that the expression of CYP2C, CYP2E1, and CYP3A5 varies in different parts of the colon.

Interactions of phospholipase D and cytochrome P450 protein stability

Previous studies have suggested a relationship between cytochrome P450 (P450) 3A (CYP3A) conformation and the phospholipid composition of the associated membrane. In this study, we utilized a novel microsomal incubation system that mimics many of the characteristics of CYP3A degradation pathway that have been observed in vivo and in cultured cells to study the effects of phospholipid composition on protein stability. We found that addition of phosphatidylcholine-specific phospholipase D (PLD) stabilized CYP3A in this system, but that phosphatidylinositol-specific phospholipase C (PLC) was without effect. Addition of phosphatidic acid also stabilized CYP3A protein in the microsomes. The use of 1,10-phenanthroline (phenanthroline), an inhibitor of PLD activity, decreased CYP3A stability in incubated microsomes. Similarly, 6-h treatment of primary cultures of rat hepatocytes with phenanthroline resulted in nearly complete loss of CYP3A protein. Treatment of rats with nicardipine or dimethylsulfoxide (DMSO), which have been shown to affect CYP3A stability, altered the phospholipid composition of hepatic microsomes. It did not appear, though, that the changes in phospholipid composition that resulted from these in vivo treatments accounted for the change in CYP3A stability observed in hepatic microsomes from these animals.

The paradoxical effect of acetaminophen on CYP3A4 activity and content in transfected HepG2 cells

HepG2 cell lines that constitutively and stably express human CYP3A4 were constructed in order to study enzyme interactions with CYP3A4 as the only P450 present. CYP3A4 activity and content were assessed by the metabolism of fentanyl, a CYP3A substrate, and Western blots. Northern blots were used to examine the effects of acetaminophen (APAP) on CYP3A4-mRNA. The HepG2 cell lines' CYP3A4 activity was stable over time. High concentrations of APAP inhibited CYP3A4 activity. At lower concentrations, APAP produced a dose-dependent increase in CYP3A4 activity and content. No increases in CYP3A4-mRNA were seen. Incubation with cycloheximide caused a decrease in fentanyl metabolism secondary to a decrease in P450 levels that was prevented by the coincubation with APAP. Additionally, human microsomal CYP3A4 was stabilized by APAP against cytosol-mediated degradation. In our models, APAP appears to increase CYP3A4 activity. This increase appears to be via substrate stabilization. This is the first report that APAP can increase CYP3A4 activity and content in transfected HepG2 cells.

Cell biology of cytochrome P-450 in the liver

Cytochromes P-450 (P-450) are members of a multigene superfamily of hemoproteins consisting the microsomal monooxygenase system with NADPH P-450 reductase (reductase) and/or reducing equivalents. Expression of many P-450 isoforms in hepatocytes is shown to be regulated at the level of transcription through interaction between cis-acting elements in the genes and DNA-binding (transacting) factors. Some isoforms of the CYP1A, 2B, 2E, and 3A subfamilies are regulated at the posttranscriptional level. For the topology of P-450 and reductase molecules in ER membrane of hepatocytes, models from stopped flow analysis and electron spin resonance are proposed. The densities of total P-450 and reductase molecules are revealed to be high enough to support the cluster model, suggesting that about ten P-450 molecules form an aggregate and surround one reductase molecule, and therefore the two enzymes form large micelles. ER proliferation after PB administration, which had been correlated with increase in P-450 level, is shown to be probably independent of the increase in P-450 level. There are considerable discrepancies among results reported on sublobular expression of various P-450 isoforms. Causes of the discrepancies are likely to be differences in experimental conditions of histochemical detection carried out and/or in species, strain, and/or sex.

Dexamethasone ameliorates oxidative DNA damage induced by benzene and LPS in mouse bone marrow

Mice were grouped to receive vehicle, dexamethasone (DEX), lipopolysaccharide (LPS), benzene (BZ, 200 mg/kg) and combinations: LPS + DEX, BZ + DEX, LPS + BZ, LPS + DEX + BZ. The DNA damage in bone marrow cells from BZ group was enhanced 2.8-fold measured by nuclear 8-hydroxy-2 '-deoxyguanosine (8-oxodG) and 1.4-fold measured by Comet score (index of DNA breaks) (p < 0.05). In the BZ + DEX group, 8-oxodG level and the Comet score were lowered to 65% and 76% respectively of that in the BZ group (p < 0.05). The BZ + LPS caused a 3.9-fold increase in 8-oxodG and a 1.6-fold increase in the Comet score (p < 0.05). The LPS + DEX + BZ lowered 8-oxodG level and the Comet score to 50% and 78% of the values in the LPS + BZ group, respectively (p < 0.05). Nitrate/nitrite levels in serum were higher after BZ + LPS treatment than after all other treatments. Both 8-oxodG level and the Comet scores were correlated to the serum nitrate/nitrite level across all the treatments (r = 0.55, p < 0.01 and r = 0.69, p < 0.01, respectively). In bone marrow cells the 8-oxodG correlated with the Comet scores (r = 0.80, p < 0.01). We conclude that DEX administration can reduce the DNA damage from BZ treatment and from the combination of BZ and LPS. The correlation of DNA damage with nitrate/nitrite indicates the possible involvement of reactive nitrogen species (RNS) in the interaction between BZ and the inflammatory reaction stimulated by LPS. The 8-oxodG determination is more sensitive than strand break analysis by the Comet assay in bone marrow in vivo in mice for measuring the BZ-induced DNA damage.

Differential inducibility of specific mRNA corresponding to five CYP3A isoforms in female rat liver by RU486 and food deprivation: comparison with protein abundance and enzymic activities

The induction of cytochrome P450 3A (CYP3A) protein and mRNA by RU486 [17beta-hydroxy-11beta-(4-dimethylaminophenyl)-17alpha-1-pro pyl-estra-4,9-dien-3-one] treatment and food deprivation in female rat liver was studied using Western blotting and competitive reverse transcription-polymerase chain reaction (RT-PCR). CYP3A apoprotein levels increased in response to food deprivation and to RU486 treatment, and the combination of RU486 treatment plus food deprivation had an apparent additive effect. Food deprivation and RU486 treatment also caused increases in CYP3A1, CYP3A18, and CYP3A23 mRNA, and the combined effects of these treatments on each of these mRNA forms were synergistic. CYP3A2 mRNA was not detected in any of the treatment groups, and there was a lack of concordance between CYP3A9 mRNA levels and the specific messages corresponding to the other CYP3A isoforms. CYP3A9 mRNA levels were highest in food-deprived animals, whereas RU486 inhibited CYP3A9 mRNA expression and suppressed the induction effect of food deprivation. Food deprivation and RU486 treatment each separately caused increased microsomal diazepam C3-hydroxylase activity, and the combined effects of these treatments on this monooxygenase were additive. In contrast, the [N-methyl-14C]erythromycin demethylase activity of the fasted, RU486-treated group of rats did not differ from that of the untreated group, and kinetic analyses revealed that both groups of animals exhibited similar Km and Vmax values. These results suggest that CYP3A9 may be primarily responsible for erythromycin N-demethylation and that the isoforms induced by the combination of fasting and RU486 administration are CYP3A1, CYP3A23, and, to a lesser extent, CYP3A18.

Tissue distributions of CYP2D1, 2D2, 2D3 and 2D4 mRNA in rats detected by RT-PCR

The tissue distributions of four isoforms (CYP2D1/5, 2D2, 2D3 and 2D4/18) in rat CYP2D subfamily were investigated. Twelve kinds of tissue (liver, kidney, brain, lung, heart, spleen, adrenal gland, small intestine mucosa, bladder, testis, ovary and gonecystis) were removed from Sprague-Dawley male and female rats. The expression of CYP2D mRNA in these tissues was detected by RT-PCR. Specific primers were designed to recognize the four isoforms individually. In liver, kidney and small intestine mucosa, the mRNA expression of all four CYP2D isoforms was detected as high-intensity PCR products. mRNA of CYP2D1/5 was expressed in all tissues used in this study except the brain, although the intensity of PCR products varied among tissues. mRNAs of CYP2D2 and CYP2D3 were mainly expressed in liver, kidney and small intestine mucosa, which were exposed to xenobiotics such as drugs, food components and environmental contaminations. mRNA of CYP2D4/18 was expressed in liver, kidney, small intestine mucosa and brain. In brain, only mRNA of CYP2D4/18 was expressed. CYP2D4/18 mRNA was also expressed in ovary, testis and gonecystis. The tissue distributions help to clarify the differences in physiological and pharmacological functions between CYP2D isoforms.

Posttranslational elevation of cytochrome P450 3A levels and activity by dimethyl sulfoxide

The molecular mechanisms by which dimethyl sulfoxide (DMSO) enhances CYP3A protein in phenobarbital-treated primary cultured rat hepatocytes were examined. DMSO treatment rapidly increased CYP3A protein levels in the absence of an increase in CYP3A mRNA levels or an increase in CYP2B protein or mRNA levels. CYP3A levels were increased approximately 3.7- and 9-fold following 0.1% DMSO treatment for 6 and 48 h, respectively. Analyses of the polysomal distribution of CYP3A mRNA suggested that DMSO treatment did not significantly alter the translational efficiency of the CYP3A mRNA. Comparative analyses of immunodetectable protein levels following treatment with cycloheximide showed that DMSO clearly decreased the rate of CYP3A protein turnover but not that of CYP2B. Examination of testosterone metabolism in hepatocyte cultures revealed that DMSO pretreatment increased CYP3A-catalyzed 2 beta- and 6 beta-testosterone hydroxylation. When DMSO was in the culture medium, no inhibitory affect on CYP3A-catalyzed testosterone metabolism was observed, although a slight (15-21%) inhibitory effect was noted for CYP2B-catalyzed 16 alpha- and 16 beta-testosterone hydroxylation. These data provide evidence that DMSO increased CYP3A protein levels as a result of decreased protein degradation. DMSO increased both immunodetectable CYP3A protein levels and catalytic activity, in contrast to compounds that have been reported to stabilize CYP3A protein and inhibit activity.