Molecular pathology of drug-disease interactions in chronic autoimmune inflammatory diseases

Involvement of Cytochrome P450 in Reactive Oxygen Species Formation and Cancer

This review examines the involvement of cytochrome P450 (CYP) enzymes in the formation of reactive oxygen species in biological systems and discusses the possible involvement of reactive oxygen species and CYP enzymes in cancer. Reactive oxygen species are formed in biological systems as byproducts of the reduction of molecular oxygen and include the superoxide radical anion (∙O2-), hydrogen peroxide (H2O2), hydroxyl radical (∙OH), hydroperoxyl radical (HOO∙), singlet oxygen ((1)O2), and peroxyl radical (ROO∙). Two endogenous sources of reactive oxygen species are the mammalian CYP-dependent microsomal electron transport system and the mitochondrial electron transport chain. CYP enzymes catalyze the oxygenation of an organic substrate and the simultaneous reduction of molecular oxygen. If the transfer of oxygen to a substrate is not tightly controlled, uncoupling occurs and leads to the formation of reactive oxygen species. Reactive oxygen species are capable of causing oxidative damage to cellular membranes and macromolecules that can lead to the development of human diseases such as cancer. In normal cells, intracellular levels of reactive oxygen species are maintained in balance with intracellular biochemical antioxidants to prevent cellular damage. Oxidative stress occurs when this critical balance is disrupted. Topics covered in this review include the role of reactive oxygen species in intracellular cell signaling and the relationship between CYP enzymes and cancer. Outlines of CYP expression in neoplastic tissues, CYP enzyme polymorphism and cancer risk, CYP enzymes in cancer therapy and the metabolic activation of chemical procarcinogens by CYP enzymes are also provided.

Apolipoprotein A-I-dependent cholesterol esterification in patients with rheumatoid arthritis

Growing evidence suggests that atherogenesis is associated with inflammation or defective removal of cholesterol excess from peripheral cells. Apolipoprotein A-I [ApoA-I] activates the enzyme Lecithin-Cholesterol Acyl-Transferase to esterify cell cholesterol for transport to liver. Haptoglobin [Hpt] was previously found able to bind ApoA-I, and suggested to reduce the enzyme activation. The aim of this study was to demonstrate that enhanced levels of Hpt, as present during inflammation, are associated with low enzyme activity and increased thickness of the arterial wall. Enzyme activity and Hpt concentration were analysed in patients with rheumatoid arthritis having the same plasma levels of antioxidants (ascorbate, urate, alpha-tocopherol, retinol) or oxidation markers (nitrotyrosine, lipoperoxide) of healthy subjects. Cholesterol esterification, determined as ratio of cholesteryl esters with cholesterol in high-density lipoproteins, was lower in patients than in controls, and negatively correlated with the intima-media wall thickness of the common carotid. The ratio of Hpt with ApoA-I was negatively correlated with the enzyme activity, while positively correlated with intima-media wall thickness. The results suggest that high Hpt levels might severely impair the enzyme activity, thus contributing to cholesterol accumulation in vascular cells, and lesion formation in the endothelium.

Quantitative structure-activity relationships (QSARs) within the cytochrome P450 system: QSARs describing substrate binding, inhibition and induction of P450s

Quantitative structure-activity relationships (QSARs) within substrates, inducers and inhibitors of cytochromes P450 involved in xenobiotic metabolism are reported, together with QSARs associated with induction, inhibition and metabolic rate. The importance of frontier orbitals and shape descriptors, such as planarity (estimated by the area/depth(2) parameter) and rectangularity (estimated by the length/width parameter) is discussed, particularly in the context of the COMPACT system which discriminates between several P450 families associated with the activation and detoxication of xenobiotics. The use of parameters, particularly those derived from homology modelling of mammalian (especially human) P450s that are involved in exogenous metabolism, in generating QSARs for P450 substrates is discussed in the context of explaining differences in the binding affinities of human P450 substrates which are pharmacologically active.

Rheumatologic manifestations of gastrointestinal diseases

One of the most significant extraintestinal manifestations of gastrointestinal diseases is rheumatologic disorders. The gastrointestinal diseases with rheumatologic manifestations can be divided into two major categories: intestinal disorders and disorders of the liver, biliary tree, and pancreas. The cause of diseases in each of these categories is different. Although intestinal permeability and immune responsiveness are frequently implicated in disorders of the intestine, diseases of the liver, biliary tree, and pancreas usually involve the production of autoantibodies, cytokines, or enzymes. Treatment of rheumatologic complications frequently involves therapy directed at the underlying gastrointestinal disease.

Further evaluation of COMPACT, the molecular orbital approach for the prospective safety evaluation of chemicals

The molecular dimensions and electronic structures of the first group of 100 US NCI/NTP miscellaneous chemicals, evaluated for potential carcinogenicity by computer-optimized molecular parametric analysis for chemical toxicity (COMPACT) have been re-determined. Using improved criteria for cytochrome P450 (CYP) substrate specificity, re-defined for CYP1 as having a COMPACT radius [square root of (deltaE - 9.5)2 + (a/d(2) - 7.8)2] of < 6.5, and for CYP2E as having a collision diameter of 6.5 angstroms or less and deltaE < 15.5, the likely substrates of CYP1 and CYP2E, which are regarded as potential carcinogens, have been identified. In addition, log P values have been taken into account; those chemicals with log P < 0 are non-lipophilic substrates unlikely to reach the activating cytochrome enzymes, and have been regarded as non-carcinogens. The second group of 100 US NCI/NTP chemicals have also now been categorized by COMPACT into CYP1 and CYP2E substrates, and their potential carcinogenicities evaluated. Of the 203 chemicals in the 2 groups, those positive in the rodent two-species life-span carcinogenicity study (rodent assay) were 53%, those positive in the Ames test (mutagenicity) were 48%, and those positive in the COMPACT programme (carcinogenicity, mutagenicity, cytotoxicity) were 54%. Concordance between the COMPACT prediction of carcinogenicity/cytotoxicity and rodent two species life-span carcinogenicity data for the 203 chemicals is 69%, and correlation of COMPACT with Ames test data is 61%. The sensitivity of COMPACT for predicting rodent carcinogenicity is 72%, whereas the sensitivity of the Ames test for predicting carcinogenicity for the 203 chemicals was only 57%. The degree (severity) of rodent carcinogenicity also showed correlation with the COMPACT predictive evaluations of the chemicals.

Personal reflections on 50 years of study of benzene toxicology

The metabolism of benzene is reviewed, and the objectives of a quantitative balance study begun in 1945 are outlined; problems of toxicology and metabolism research of some 50 years ago are considered. The quantitative metabolism of 14C-benzene in the rabbit is annotated and compared with that of unlabeled benzene quantified by nonisotopic methods. The anomalies of phenylmercapturic acid and trans-trans-muconic acid as metabolites of benzene are examined in detail by isotopic and nonisotopic methods; these compounds are true but minor metabolites of benzene. Oxygen radicals are involved in both the metabolism of benzene and its toxicity; the roles of CYP2E1, the redox cycling of quinone metabolites, glutathione oxidation, and oxidative stress in the unique radiomimetic, hematopoietic toxicity of benzene are discussed. Differences between the toxicity of benzene and the halobenzenes are related to fundamental differences in their electronic structures and to the consequent pathways of metabolic activation and detoxication.

Pharmacokinetics of single oral doses of feprazone in patients with rheumatoid arthritis or with impaired renal clearance

1. The pharmacokinetics of feprazone have been studied in 10 patients with rheumatoid arthritis (RA), and in a further six patients with renal impairment (RI) who were not suffering from rheumatoid disease. 2. For RA patients, the mean elimination half-life (t1/2) of feprazone after a single oral dose was 21 +/- 5 h (SD), the mean apparent clearance (Cl) was 0.012 +/- 0.009 l/h per kg, and the mean apparent volume of distribution (Vd) was 0.33 +/- 0.17 l/kg. Corresponding values for RI patients were 25 +/- 13 h, 0.016 +/- 0.011 l/h per kg, and 0.46 +/- 0.24 l/kg, respectively. 3. These results show no impairment of the elimination of feprazone in RA or RI patients; Vd and Cl are greater than in healthy young volunteers or elderly subjects, the AUC values are lower, but t1/2 values are similar in all groups. 4. It is suggested that the greater Cl and Vd, and lower AUC, in RA and RI patients may be due to renal insufficiency and decreased plasma protein binding of feprazone and its metabolite, or to induction of glucuronyl transferase activity by the prior medication, thus enhancing the formation of the major metabolite, the C(4)-glucuronide, and increasing drug elimination.

Safety aspects of food preservatives

The use of food preservatives, such as benzoic acid, nitrites, and sulphites, as antimicrobials, and butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), ascorbic acid and tocopherols, as antioxidants, has probably changed food production patterns and eating habits more than has the use of any other class of food additive. These food preservative chemicals confer substantial benefits on man, not only by the preservation and increased palatability of food, but also by affording protection against the pathological effects of reactive oxygen species (ROS) which are associated with cancer, cardiovascular disease and aging. Nevertheless, although most preservatives are now considered to be without potential adverse effects and are classified as GRAS, there have been problems concerning the safety of some of these chemicals, including the possibility of allergies from benzoic acid and sulphites, the formation of carcinogenic nitrosamines from nitrites, and the possible rodent carcinogenicity of BHA and BHT. The mechanisms of this toxicity at high dosage, the roles of the cytochromes P450, and the generation and scavenging of ROS in the toxicity of these chemicals, are reviewed and discussed.

The sequence homologies of cytochromes P-450 and active-site geometries

The amino acid sequence alignment of 16 cytochrome P-450 proteins representative of the major families is reported. The sequence matching process has been carried out on the basis of maximum homology by residue type, retention of secondary structure and minimization of deletions/insertions except where additional loop regions exist. From the starting point of known reported sequence homology matching from the literature, a realignment on the basis of conserved residues involved in both structure and function gives rise to a self-consistent set of sequences which correlates with known mechanistic and structural data. Once fitted, these archetypal sequences form a straightforward template for the alignment of all P-450 subfamilies. Computer modelling of the active-site regions constructed from homology with the bacterial form of the enzyme (P-450CAM) evinces the correct substrate specificity. Furthermore, the construction of the macromolecular assembly of components of the cytochrome P-450 system on the microsomal endoplasmic reticular membrane is presented from the evidence of site-directed mutagenesis, analysis by molecular probes, X-ray crystallography and molecular modelling.