Expression of modified human cytochrome P450 1A2 in Escherichia coli: stabilization, purification, spectral characterization, and catalytic activities of the enzyme

A full-length human cytochrome P450 (P450) 1A2 cDNA clone and four derivatives in which the 5'-terminus was modified were inserted into the pCW vector and used to transform Escherichia coli cells. Low levels of expression were seen with most of the constructs but high expression levels (245 nmol membrane-bound P450 recovered per liter culture) were achieved when the N-terminus was MALLLAVFL, as reported earlier by Fisher et al. (C. W. Fisher, D. L. Caudle, C. Martin-Wixtrom, L. C. Quattrochi, R. H. Tukey, M. R. Waterman, and R. W. Estabrook, 1992, FASEB J. 6, 759-764). The expressed human P450 1A2 in bacterial membranes was rapidly denatured to cytochrome P420 in the presence of detergents. This denaturation was blocked by the inhibitory ligand alpha-naphthoflavone (alpha NF, 7,8-benzoflavone). Human P450 1A2 was solubilized using high concentrations of sodium cholate and Triton N-101 and could be purified to near homogeneity in high yield in two steps. alpha NF was included in the buffer in the first step and then removed in the second chromatography step along with the detergent. The purified human P450 1A2 was found to be almost completely in the high spin iron configuration, in contrast to P450 1A2 enzymes isolated from rats and rabbits. The enzyme was catalytically active toward the known substrates 7-ethoxyresorufin and phenacetin. The N-terminal appears to be blocked, as is the case for other P450s we have expressed that contain the sequence MALLLAVFL in E. coli. Previously this human P450 has only been available in limited amounts; the methods presented here should facilitate further biochemical and practical studies on this interesting enzyme.

Expression of modified cytochrome P450 2C10 (2C9) in Escherichia coli, purification, and reconstitution of catalytic activity

The human cytochrome P450 (P450) 2C gene family is complex and heterologous expression methods are needed to facilitate the isolation of individual P450 proteins and the elucidation of their catalytic specificities. We prepared a series of constructs of P450 2C10 in the plasmid vector pCW, with modification of the 5' end of the coding sequence of the cDNA. Some were not expressed at all in Escherichia coli; two were expressed at levels of 5-20 nmol membrane-bound P450 (liter culture)-1--one (2C1028) with original codons 2-7 altered by substitution of the 5'-terminal sequence described by Barnes et al. (Barnes, H. J., Arlotto, M. P., and Waterman, M. R., Proc., Natl. Acad. Sci. USA 88, 5597-5601, 1991) and one (2C1029) with original codon 2 modified, codons 3-20 deleted, and alteration of the immediate downstream codons. In both cases the P450 2C10 proteins were found essentially only in the bacterial membranes. These proteins could be purified to a high degree by solubilization and a single DEAE chromatography step. Typical P450 Fe2+.CO absorption spectra were observed in the bacterial membranes and the purified preparations. The P450 2C1029 protein was found to have its N-terminal Met removed and the expected residues 2 (Ala)-24 were identified by amino acid sequence analysis. However, the other P450 (2C1028) was apparently blocked at the N-terminus. Three native P450 2C9/10 preparations isolated from human liver showed the expected sequences (beginning with Met) for at least the first 17 residues. The blocked N-terminus in the P450 2C1028 protein may be the result of the MALLLAVF sequence, which was also used in the expression of P450 3A4 and resulted in a blocked protein. Catalytic activities of P450 2C1028 and P450 2C1029 for tolbutamide hydroxylation were similar to those measured with purified liver P450 C29/10 in the presence of cytochrome b5, although the effect of cytochrome b5 did not always show the same pattern as with the isolated liver enzyme. The recombinant P450 2C10 enzymes did not catalyze (S)-mephenytoin 4'-hydroxylation.

In-vitro metabolism of celecoxib, a cyclooxygenase-2 inhibitor, by allelic variant forms of human liver microsomal cytochrome P450 2C9: correlation with CYP2C9 genotype and in-vivo pharmacokinetics

In-vitro studies were conducted to assess the impact of CYP2C9 genotype on the metabolism (methyl hydroxylation) and pharmacokinetics of celecoxib, a novel cyclooxygenase-2 inhibitor and CYP2C9 substrate. When compared to cDNA-expressed wild-type CYP2C9 (CYP2C9*1), the Vmax/Km ratio for celecoxib methyl hydroxylation was reduced by 34% and 90% in the presence of recombinant CYP2C9*2 and CYP2C9*3, respectively. These data indicated that the amino acid substitution at position 359 (Ile to Leu) elicited a more pronounced effect on the metabolism of celecoxib than did a substitution at position 144 (Arg to Cys). The Vmax/Km ratio was also decreased in microsomes of livers genotyped CYP2C9*1/*2 (47% decrease, mean of two livers), or CYP2C9*1/*3 (59% decrease, one liver). In all cases, these changes were largely reflective of a decrease in Vmax, with a minimal change in Km. Based on simulations of the in-vitro data obtained with the recombinant CYP2C9 proteins, it was anticipated that the pharmacokinetics of celecoxib (as a much as a five-fold increase in plasma AUC) would be altered (versus CYP2C9*1/*1 subjects) in subjects genotyped heterozygous or homozygous for the CYP2C9*2 (Cys144) or CYP2C9*3 (Leu359) allele. In a subsequent clinical study, the AUC of celecoxib was increased (versus CYP2C9*1/*1 subjects) approximately 2.2-fold (range, 1.6-3-fold) in two CYP2C9*1/*3 subjects and one CYP2C9*3/*3 subject receiving a single oral dose (200 mg) of the drug. In contrast, there was no significant change in celecoxib AUC in two subjects genotyped CYP2C9*1/*2.

Activation of procarcinogens by human cytochrome P450 enzymes expressed in Escherichia coli. Simplified bacterial systems for genotoxicity assays

Bacterial assays were used to examine the activation of 14 known procarcinogens by cytochrome P450 (P450) enzymes. Human P450s 1A1, 1A2 and 3A4 were expressed in Escherichia coli with slight modification of their N-terminal sequences. Genotoxicity was measured by the induction of the SOS response in Salmonella typhimurium NM2009 (TA1535/pSK1002/pNM12), which contains a umuC regulatory sequence attached to the lacZ reporter gene. Conditions for analysis were examined using E. coli membranes and purified enzymes. Membrane fractions, fortified with NADPH-P450 reductase, were found to be useful preparations for measuring activation of the procarcinogens. Conditions of linearity were established for these assays and the systems were applied to several particular problems related to bioactivation of procarcinogens by P450s. The patterns of activation of the 14 individual chemicals were consistent with the literature developed using human liver microsomes, purified liver P450s and other approaches. The P450s expressed in bacterial membranes could be inhibited by antibodies. 7,8-Benzoflavone inhibited P450s 1A1 and 1A2 and stimulated P450 3A4 in the membranes. The contributions of P450s 1A1 and 1A2 were distinguished with some of the arylamines and 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene. Recombinant P450 3A4 was found to be more active than P450 1A2 in the activation of aflatoxin B1 at all substrate concentrations examined.

Bacterial mutagenesis and hepatocyte unscheduled DNA synthesis induced by chrysoidine azo-dye components

5 azo dye components of Gurr chrysoidine 'Y' have been separated, synthesised and identified. Dyes with a methyl substitution (particularly between the two amino groups) were more mutagenic in Salmonella typhimurium strain TA100 with control rat liver S9 than the non-methylated counterpart (range 66-1992 revertants at 50 micrograms/plate). Mutagenicity was also catalysed by human-liver S9 and pre-treatment of rats with either phenobarbitone or beta-naphthoflavone enhanced the activation ability of S9 by greater than 4-fold. Using the most potent promutagenic component (2,4-diamino-3-methylazobenzene), the use of inhibitors of cytochrome P450 (metyrapone: 1.0 mM; alpha-naphthoflavone: 0.075 mM; DPEA: 0.125 mM) and of the flavin monooxygenase (methimazole: 0.75 mM) suggested a major role for cytochrome P448 in the activation of chrysoidine to mutagens. The ability of chrysoidine components to induce unscheduled DNA synthesis in rat hepatocytes in vitro was demonstrated and ranged between 11.92 and 23.5 net nuclear grains at a dose level of 2.5 micrograms/incubation. Since each dye was equi-potent, methyl substitution had little influence on genetic toxicity in hepatocytes.

Expression of human cytochrome P450 enzymes in yeast and bacteria and relevance to studies on catalytic specificity

Heterologous expression systems can be utilized to great advantage in the study of cytochrome P450 (P450) and other enzymes involved in the biotransformation of drugs and other xenobiotics. The list of studies made possible with the technology includes discernment of catalytic specificity, elucidation of structure-activity relationships, and various biophysical measurements. There are advantages and disadvantages to each of the vector systems and choices must be made on the basis of needs. Yeast expression systems were used to establish that different P450 2C enzymes are involved in the hydroxylations of tolbutamide and (S)-mephenytion. P450 3A4 was also expressed in yeast and its very broad catalytic specificity was confirmed. Recently, it has been possible to express P450 3A4 as well as other human and animal P450s in bacteria after slight modification of their 5'-coding sequences.

Hemodynamic Effects of Arteriovenous Fistula in End‐Stage Renal Failure

Hemodynamic parameters using Swan Ganz catheter were studied in 17 patients with end stage renal disease. The acute effects of radiocephalic AV fistula on the hemodynamic parameters were studied at 24 hours of surgery. The chronic effects were studied in 8 of these patients at 6 weeks of arteriovenous (AV) fistula. The AV fistula matured in 3 to 4 weeks time and blood flow was sufficient for hemodialysis (400 mL/min). Patients with chronic renal failure had normal or high normal hemodynamic parameters. Six weeks after the AV fistula, the cardiac index and the stroke volume index slightly increased along with a significant increase in systolic and mean systemic arterial pressure. None of the patients had significant increase in cardiac filling pressures. Although there was some fall in systemic vascular resistance index and rise in cardiac index and stroke volume index, these changes were physically small and unlikely to put any extra hemodynamic load. Thus, AV fistula in dialysis patients is not an appreciable cause of circulatory or pulmonary congestion.

Plasma Homocysteine and Insulin in Diabetic Nephropathy: Relationship to Body Mass Index

The data on plasma homocysteine and endogenous insulin in type 2 diabetes mellitus with nephropathy and relationship to body mass index (BMI) is particularly from the Indian subcontinent. A prospective study was carried out in 50 patients of type 2 diabetes mellitus with overt nephropathy (Group A). The results were compared with 25 diabetics without nephropathy (Group B), and 25 age and sex matched healthy controls (Group C). Microenzyme immunoassay and ELISA estimated the plasma homocysteine and insulin, respectively. The mean values of plasma homocysteine were significantly elevated in diabetic nephropathy (21.3+/-7.2 micromol/L) and diabetics without nephropathy (19.4+/-7.1) when compared to healthy control (11.5+/-2.3). The insulin levels and BMI were significantly higher in diabetics as compared to controls. There was no correlation between homocysteine and insulin, homocysteine and BMI, and homocysteine with the degree of renal failure.

Non-traumatic rhabdomyolysis with acute renal failure

A clinical profile of non-traumatic rhabdomyolysis with acute renal failure is presented. Myoglobinuric renal failure is treatable and hence a high index of suspicion is warranted in the etiologies discussed.

A postal survey to assess the views of community pharmacists on the deregulation of emergency hormonal contraception

Focal points

Evaluation of NR-LU-10 with the Neoprobe gamma detector in a mouse model

The Neoprobe Model 1000 hand-held gamma detector, in combination with the murine monoclonal antibody (MAb) B72.3 can successfully intraoperatively target both primary and recurrent colorectal cancer. Because of the shortcomings of this system (length of time needed to clear unbound MAb and heterogeneous staining of cancer cells), new MAbs are under investigation. NR-LU-10 IgG and its FAB fragment were evaluated with the Neoprobe gamma detector in a nude mouse model. NR-LU-10 is a pancarcinoma IgG2b antibody that recognizes an oncofetal glycoprotein antigen that is expressed by most carcinomas. Animals were injected intraperitoneally with 125I-labeled IgG, 125I, or technetium 99m (99mTc)-labeled Fab fragment. The Neoprobe gamma detector and standard gamma well counts provided biodistribution and pharmacokinetic data. The Fab fragment achieved a 5:1 tumor to blood-pool background (BPB) ratio in only 66 hr, whereas the whole MAb required 14 days. Technetium did not appear to be an adequate isotope for this system because of its short half-life. Autoradiographs performed for both the 125I-labeled NR-LU-10 IgG and its 125I-labeled Fab fragment (but not 99mTc-labeled Fab) localized well in this model and gave adequate tumor to BPB and tissue ratios. Use of the 125I-labeled Fab significantly decreased the time required for clearance of the MAb radionuclide complex from the blood and tissue background, thus providing earlier tumor localization in the Radioimmunoguided Surgery (RIGS) system.

Global Metabolome of Palmer Amaranth (Amaranthus palmeri) Populations Highlights the Specificity and Inducibility of Phytochemical Responses to Abiotic Stress

Commonalities in adaptive responses to abiotic stressors could contribute to the development of cross-resistance in weeds. The degree to which herbicide-induced changes in weeds parallel those induced by other abiotic stress remains unknown. We investigated the specificity of metabolic perturbations induced by glyphosate and drought across three glyphosate-resistant (GR) and two glyphosate-susceptible (GS) biotypes of Palmer amaranth (Amaranthus palmeri) using global metabolomics approaches. Compared to GS-biotypes, in the absence of stress, the GR-biotypes had a higher abundance of primary metabolites, including sugars, nonaromatic amino acids, and organic acids. However, despite having a higher 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene copy number that could upregulate the phenylpropanoid metabolism, the nonstressed GR-biotypes were less abundant in specialized (secondary) metabolites. Under glyphosate stress, 80% of metabolites, including shikimate, that accumulated in GS-biotypes also increased in the GR-biotypes. However, glyphosate triggered the preferential accumulation of glycosides of dihydroxylated and methoxylated flavanols with higher antioxidant potential, and ferulic acid derivatives, specifically in GR-biotypes. The disruption of the shikimate pathway and the accumulation of phenylpropanoids upon glyphosate exposure suggest that the stress response of GR-biotypes could be partly induced. This differential response was less evident in other phytochemical classes and under drought, highlighting that the phytochemical responses are stress-specific rather than biotype-specific.

Nonpeptide tachykinin receptor antagonists. II. Pharmacological and pharmacokinetic profile of SB-222200, a central nervous system penetrant, potent and selective NK-3 receptor antagonist

The pharmacological and pharmacokinetic profile of SB-222200 [(S)-(-)-N-(alpha-ethylbenzyl)-3-methyl-2-phenylquinoline-4-car boxami de], a human NK-3 receptor (hNK-3R) antagonist, was determined. SB-222200 inhibited (125)I-[MePhe(7)]neurokinin B (NKB) binding to Chinese hamster ovary (CHO) cell membranes stably expressing the hNK-3 receptor (CHO-hNK-3R) with a K(i) = 4.4 nM and antagonized NKB-induced Ca(2+) mobilization in HEK 293 cells stably expressing the hNK-3 receptor (HEK 293-hNK-3R) with an IC(50) = 18.4 nM. SB-222200 was selective for hNK-3 receptors compared with hNK-1 (K(i) > 100,000 nM) and hNK-2 receptors (K(i) = 250 nM). In HEK 293 cells transiently expressing murine NK-3 receptors (HEK 293-mNK-3R), SB-222200 inhibited binding of (125)I-[MePhe(7)]NKB (K(i) = 174 nM) and antagonized NKB (1 nM)-induced calcium mobilization (IC(50) = 265 nM). In mice oral administration of SB-222200 produced dose-dependent inhibition of behavioral responses induced by i.p. or intracerebral ventricular administration of the NK-3 receptor-selective agonist, senktide, with ED(50) values of approximately 5 mg/kg. SB-222200 effectively crossed the blood-brain barrier in the mouse and rat. The inhibitory effect of SB-222200 against senktide-induced behavioral responses in the mouse correlated significantly with brain, but not plasma, concentrations of the compound. Pharmacokinetic evaluation of SB-222200 in rat after oral administration (8 mg/kg) indicated sustained plasma concentrations (C(max) = about 400 ng/ml) and bioavailability of 46%. The preclinical profile of SB-222200, demonstrating high affinity, selectivity, reversibility, oral activity, and central nervous system penetration, suggests that it will be a useful tool compound to define the physiological and pathophysiological roles of NK-3 receptors, in particular in the central nervous system.

Giant cavernous hemangiomas of liver mimicking metastasis

Most hepatic hemangiomas are small and symptomless. These are now being increasingly diagnosed with the greater use of scanning procedures. Hemangiomas can occasionally grow to a large size and become manifest to the patient and the clinician. Giant hemangiomas can produce symptoms including awareness of abdominal mass, pain due to thrombosis, and very rarely, rupture. Though ultrasound is known to be quite suggestive of the diagnosis, large hemangiomas may be mistaken for liver metastases due to their enormous size and variegated picture on the scanning procedure. Dynamic CT scan and at times MRI may be required for confirmation of the diagnosis. Needle biopsy is contraindicated if the diagnosis is suspected.

Lack of release from hepatocytes in vitro or excretion in vivo of mutagenic chrysoidine metabolites

Rat liver postmitochondrial supernatant (S9) converted the azo dyes chrysoidine Y and R to products that were mutagenic towards Salmonella typhimurium strain TA100. No such release of mutagens was demonstrated using intact rat hepatocytes as an activation system despite the fact that chrysoidine dyes cause unscheduled DNA synthesis in these cells. It appears that genotoxic products produced within hepatocytes either react within the cell or are detoxified prior to release. Following intraperitoneal administration of chrysoidine Y to rats (100 mg/kg i.p.) there was also no evidence of mutagenic or por-mutagenic products excreted in bile or urine. The S9-derived mutagens appear to be largely independent of bacterial acetylation since they were active in the acetylation-deficient strain TA98/1,8-DNP6 in addition to strain TA98. The ultimate mutagenic form(s) are therefore unlikely to be acetoxyarylamines.

Sonographic evaluation of renal allograft

Sonography has become an integral part of the care of renal allograft recipients. It is a simple, inexpensive and readily available non-invasive imaging modality. It is indicated as the initial investigation in patients presenting with decreased urine output, pain, infection and hematuria and for doing a percutaneous allograft biopsy. While sonography confirms the diagnosis of obstructive nephropathy and perinephric fluid collections, Doppler is an effective screening modality for the detection of post-transplant vascular complications.