Identification of the highly polymorphic S-mephenytoin hydroxylase in humans.
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Aryl Hydrocarbon Hydroxylases↗
Biomedical subjects
P Soucek
Publications and source records attributed to P Soucek.
The role of CYP2E1 and 2B1 in metabolic activation of benzene derivatives.
CYP2B1 and 2E1 oxidized toluene, aniline and monochlorobenzene (MCB) to water-soluble metabolites and to products covalently binding to microsomal proteins from male Wistar rats at high efficiency. Oxidation of benzene to covalently binding metabolites was catalysed by CYP2B1 and 2E1 more effectively than the formation of water-soluble metabolites, especially at low benzene levels. Thus, the formation of covalently binding products was inversely related but formation of soluble metabolites was proportional to benzene concentration. 1,4-Benzoquinone was responsible for the majority of covalent binding to microsomal proteins, being suppressed by ascorbate; 1,4-semiquinone was not important, since alpha-tocopherol did not inhibit the covalent binding and ESR showed its rapid decay, if NADPH was available. Specific antibodies and inhibitors confirmed the role of CYP2B1 and 2E1 induction. Covalent binding of benzene to DNA was largely due to benzene oxide; approximately 50% was due to N-7 guanine adduct. CYP2E1 oxidizing benzene via phenol to 1,4-hydroquinone appeared to mediate its further oxidation to 1,4-benzoquinone, which also occurred spontaneously, but was reversed in a reducing environment of microsomes with NADPH. Production of OH radicals in microsomes with NADPH was greatly stimulated by HQ and less by BQ, especially in CYP2E1 induced microsomes, although the quinones themselves failed to produce OH radicals. The quinones could act by simulation of the CYP futile cycle. Therefore, CYP2B1 and 2E1 in rats appeared essential for metabolic activation of benzene derivatives to potentially genotoxic products; BQ dominated the covalent binding of benzene to proteins, whereas DNA adducts were largely due to benzene oxide.
Animals↗
Cytochromes P450 in benzene metabolism and involvement of their metabolites and reactive oxygen species in toxicity.
Cytochrome P450 (CYP) 2E1 was the most efficient CYP enzyme that oxidized benzene to soluble and covalently bound metabolites in rat and human liver microsomes. The covalent binding was due mostly to the formation of benzoquinone (BQ), the oxidation product of hydroquinone (HQ), and was inversely related to the formation of soluble metabolites. In rats, inhalation of benzene (4 mg/liter of air) caused a rapid destruction of CYP2B1 previously induced by phenobarbital. The ability of benzene metabolites to destroy liver microsomal CYP in vitro decreased in the order BQ > HQ > catechol > phenol. The destruction was reversed by ascorbate and diminished by alpha-tocopherol, suggesting that HQ was not toxic, whereas BQ and semiquinone radical (SQ) caused the effect. In the presence of nicotinamide adenine dinucleotide phosphate, reduced (NADPH) the microsomes did not oxidize HQ to BQ, while the formation of superoxide anion radical from both HQ and BQ was markedly quenched. Destruction of CYP in vitro caused by HQ or BQ was not mediated by hydroxyl radical formation or by lipid peroxidation. On the contrary, HQ and BQ inhibited NADPH-mediated lipid peroxidation. Ascorbate induced high levels of hydroxyl radical formation and lipid peroxidation, which were differentially affected by quinones, indicating different mechanisms. Despite reducing the toxicity of HQ and BQ, ascorbate appeared to induce its own toxicity, reflected in high levels of lipid peroxidation. Iron redox cycling played a significant role in the NADPH-induced hydroxyl radical formation but not in that caused by ascorbate; however, lipid peroxidation induced by NADPH or ascorbate was suppressed by ethylenediaminetraacetate, indicating a crucial role of iron. Thus, the data indicate that the quinones destroyed CYP directly and not via oxygen activation or lipid peroxidation.
Animals↗
Identification of a common cytochrome P450 epitope near the conserved heme-binding petide with antibodies raised against recombinant cytochrome P450 family 2 proteins.
The cytochrome P450 (P450) proteins constitute a superfamily of enzymes involved in various oxidations and related activities. Polyclonal antibodies raised against bacterial recombinant human P450s varied in specificity, depending upon the individual rabbits used. Several of the antisera raised against P450s 2C10 and 2E1 recognized a number of P450 family 1, 2, and 3 proteins, and two of the less selective antibodies were used to identify cross-reactive epitopes. P450 2C10 peptides reacting with anti-P450 2E1 and P450 2E1 peptides reacting with anti-P450 2C10 were isolated after electrophoresis/immunoblotting and analyzed by Edman degradation. Several of these were in a region near the highly conserved Cys that is a putative axial ligand to the heme. Peptides corresponding to the most conserved regions in this area were synthesized. Anti-P450 2C10 sera did not recognize 14-mer peptides corresponding to the heme-binding region (2C10 410-423 or 2E1 409-422) or the 14-mer peptides immediately C-terminal to these (2C10 425-438 or 2E1 424-437), but anti-P450 2E1 sera showed weak reaction with the latter two synthetic peptides. A longer peptide (29-mer) of P450 2E1 containing parts of both regions (412-440) reacted with both anti-P450 2C10 and anti-P450 2E1 antisera. Antibodies raised against a conjugate of the 29-mer peptide (with hemocyanin) recognized this antigen, the more C-terminal 14-mer peptides (2C10 425-438 and 2E1 424-437), P450s 2C10 and 2E1, and P450s 1A1, 11A1, and 17A. The 29-mer peptide showed considerable alpha-helix structure as judged by CD spectroscopy, in contrast to any of the 14-mers.(ABSTRACT TRUNCATED AT 250 WORDS)
Amino Acid Sequence↗
[Retinal detachment in pseudophakia].
The author evaluates the prevalence and results of surgical treatment of retinal detachment (RD) after implantation of intraocular lenses in a group of 10,185 eyes operated at the First and Second Ophthalmological Clinic from 1988 to the end of 1993. Retinal detachment was observed in 0.4% of artephakic eyes. A striking risk factor for the development of RD was in particular loss of the vitreous body during cataract operation, a previous injury, myopia and YAG capsulotomy. The presence of an intraocular lens did not influence in a substantial way the selection of the surgical procedure. In cases with a complicated finding in the anterior segment and the retina the authors selected more frequently pars plana vitrectomy (PPV) with internal tamponade with an expansive gas or silicone oil (in 44.3% eyes). The retina became attached in 90.4% of the eyes, while in patients operated by cryosurgery anatomical success was achieved in 82.1% of the eyes and in the group operated by PPV with internal tamponade in 100% of the eyes. Functional improvement, as compared with the condition before surgery of RD, was achieved in 48.9% of successfully operated eyes. In the PPV group the authors observed, however, substantially poorer functional results as compared with cryosurgery. In complicated artephakic RD PPV with internal tamponade contributed to a striking improvement of anatomical results but the poorer functional results after PPV in complicated RD provide evidence of a poorer prognosis of artephakic RD, as compared with aphakic ones.
Adult↗
Cytochrome P450 destruction and radical scavenging by benzene and its metabolites. Evidence for the key role of quinones.
Exposure to benzene was reported to lower the cytochrome P450 (CYP; EC 1.14.14.1) content in phenobarbital-pretreated (PB) rats in vivo (Gut I, Zbl Pharm 122: 1139-1161, 1983). In this paper we followed the ability of benzene and its metabolites, phenol, catechol, hydroquinone and benzoquinone to destroy CYP in liver microsomes from PB rats in vitro. The spectrophotometric determinations of the total CYP content, 7-pentoxyresorufin O-depentylase and aniline hydroxylase activities, electrophoresis and western blot analysis after incubation of PB-microsomes with benzene or its metabolites revealed that: (1) benzene is metabolically activated to intermediates causing CYP destruction; phenol is not responsible for this effect. (2) Quinonic metabolites of benzene cause CYP destruction with different potency (30% CYP was destroyed by 3 mM catechol, 0.3 mM hydroquinone and 0.03 mM benzoquinone). (3) Low concentrations of quinones are capable of protecting CYP against reactive oxygen species produced in the CYP futile cycle. (4) Ascorbate effectively protects CYP against quinones, apparently by maintaining them in the reduced state. (5) Quinones attack both heme and protein of CYP. (6) CYP activities differ in the sensitivity to quinone-mediated destruction. In conclusion, we suggest that quinones may be responsible for CYP destruction by benzene in vivo.
Animals↗
[Relaxing retinectomy: anatomic and functional results].
The author analyzed the results of relaxing retinectomy (RR) combined with internal tamponade of the retina by silicone oil in 50 patients. The causes of tractional detachment and shortening of the retina were: proliferative vitretinopathy complicating idiopathic rhegmatogenic detachment of the retina in 25 eyes, proliferative diabetic retinopathy in 12 eyes, post-traumatic proliferation in seven eyes, intraocular inflammation in four eyes and the cicatricial stage of retinopathy of the premature in two eyes. During an observation period of 6-75 months, mean 17 months, the authors recorded complete adherence of the retina in 60%, partial anatomical success with defined retinal detachment and adherent macula in 24% and functional success with visual acuity of 0.02 or better in 66%. The poorest functional results were obtained in proliferative diabetic retinopathy (success in 30%). Functional success declined with the observation period from 66% 6 months after RR to 38% after 36 months following RR. The extent of RR did not have a substantial effect on the anatomical and functional results. Sufficiently extensive RR with internal tamponade of the retina with silicone oil is the operation of choice in complicated retinal detachment where radical membranectomy does not release the retinal traction. Reproliferation after RR were the frequent causes of relapses of retinal detachment and an impediment for removal of silicone oil from the eye.
Adolescent↗
[Artephakic retinal detachment].
The authors investigated the incidence of retinal detachment from a total of 3,802 artephakic eyes in which between September 1988 and June 1993, an intraocular lens was implanted at the First Eye Clinic in Prague. Detachment of the retina occurred in 10 eyes, 9 patients (0.3%). Risk factors for detachment of the retina were loss of the vitreous body during extraction of the cataract, a previous injury, myopia and YAG capsulotomy. Cryosurgery was selected in 76.9%, pars plana vitrectomy with an internal tamponade using silicon oil in 15.4% of the eyes. The retina attached in 92.3%, the visual acuity improved, as compared with the condition before operation of the detached retina, in 58.4% of successfully operated patients. Extracapsular extraction of the lens with implantation of an intraocular lens significantly reduced the incidence of retinal detachment. The prognosis of artephakic retinal detachment is comparable with the prognosis of aphakic retinal detachment.
Cataract Extraction↗
[What is cytochrome P-450? Enzyme forms of cytochrome P-450--extent of knowledge].
The submitted review summarizes contemporary knowledge of the enzyme P 450, the importance of which in human metabolic processes has been beyond doubt for a long time. The existence of various forms of the enzyme (there is a number of enzymatic forms of this haemoprotein which does not differ only as regards the structure of the alipoprotein but also as regards some physical and chemical properties) was proved in many prokaryotic and eukaryotic organisms. It played a special role in herbivores. New forms were detected which can be induced e. g. by polycyclic hydrocarbons, barbiturates, steroids, ethanol (1), hypolipidaemic substances and some antibiotics. Also other regulating factors are known. The clinical use of P 450 is complicated so far by the great genetically conditioned multiplicity of its forms in man. However, a number of very promising and important applications are foreseen.
Animals↗
Exposure to various benzene derivatives differently induces cytochromes P450 2B1 and P450 2E1 in rat liver.
Benzene (B), toluene (T), ethylbenzene (EB), styrene (S) and xylene isomers (oX, mX, pX) are important environmental pollutants and B is a proved human carcinogen. Their inhalation by male Wistar rats (4 mg/l, 20 h/day, 4 days) caused cytochrome P450 (P450) induction. The degree of P450 2B1 induction increased and that of 2E1 decreased in the series B, T, EB, S, oX, mX and pX, as estimated by Western blots, while neither solvent was as effective for 2B1 induction as phenobarbital and B was more effective for 2E1 than ethanol. The levels of several other P450s decreased after exposure to these solvents, B being most effective. Exposure to these solvents increased in vitro hepatic microsomal oxidation of B and aniline (AN) (2E1 substrates) 3 to 6-fold, indicating induction of this P450. T oxidation was increased 2 to 4-fold and chlorobenzene (ClB) oxidation 3-fold. Sodium phenobarbital (PB, 80 mg/kg/day, 4 days, i.p.) did not increase ethylmorphine (EM) and benzphetamine (BZP) demethylation (2B1 substrates), neither of the B derivatives did so, and oX decreased it; however, pentoxyresorufin O-dealkylation was well related to the immunochemically detected 2B1 levels in control, PB and B microsomes. PB did not increase B, but increased T and ClB oxidation 2-4 and 3-fold, respectively, indicating possible 2B1 role in their oxidation. B oxidation after various inducers was related to immunochemical 2E1 levels, T and ClB oxidation to both 2B1 and 2E1 and AN oxidation to 2E1 and 1A2 levels.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Cytochromes P-450 in rats: structures, functions, properties and relevant human forms.
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Amino Acid Sequence↗
[Testing student knowledge of emergency care at the Charles University School of General Medicine and the processing of certain conditions in primary emergency care into computerized educational training models].
The objective expression of the state of knowledge of 6th year students of the Faculty of General Medicine in the field of emergency care is an important factor in the evaluation of their preparation for the medical profession, regardless of the specialty they choose. Knowledge of these data is essential for improvement of undergraduate teaching of emergency care. Suitable application of computer technique can supplement the possibilities how to achieve this. The application of so-called model situations on personal computers makes it possible to extend training of decision taking to all spheres of medical training.
Computer Simulation↗
Long-term results of pars plana vitrectomy and silicone oil for giant tears.
PURPOSE: To evaluate the long-term results of pars plana vitrectomy (PPV) and silicone oil implantation (SOI) for giant retinal tears (GT). METHODS: PPV with SOI was performed for GT in 50 eyes of 46 patients. Thirty-one eyes (62%) of 27 patients suffered from idiopathic GT. A direct injury of the eye preceded GT in 19 eyes (38%), a contusion in 14 and perforation of the sclera in five. The patients were followed up for 12 to 96 months, with a mean of 33 months. RESULTS: At the end of follow-up, anatomical success with a flat macula was achieved in 39 eyes (78%). Functional success with visual acuity 0.02 or better was obtained in 37 eyes (74%). The final functional results did not depend on the size of the GT, and were better in post-traumatic GT (success in 84%) than in idiopathic ones (success in 68%). The functional success rate by life table analysis decreased from 81% after one year and 79% after three years to 55% after five or more years. Silicone oil was removed from 22 eyes (44%). After removal, the retina redetached in seven eyes (30%), and the redetachment caused final failure in two (9%). CONCLUSIONS: PPV with SOI proved highly effective in GT. Proliferative vitreoretinopathy was the main cause of surgical failure and a frequent obstacle to silicone oil removal. The risks of redetachment have to be evaluated especially carefully when dealing with the only eye.
Adolescent↗