Role of physiological factors in prognosis of the risk of oncological diseases development on the basis of xenobiotic metabolism enzyme system polymorphism

Summarised data about polymorphism of xenobiotic metabolism enzyme system (XMES) have been presented. Metabolic molecular mechanisms and the role of genetic polymorphism in metabolic transformation of different xenobiotics are reviewed. Significance of X-transport proteins and nuclear receptors in regulation of XMES-activity are discussed. Possible connection of XMES polymorphism with the development of cancer was examined. Experimental modeling of different levels of epoxide syntase and epoxide hydratase activites has revealed their connection with cancer development. Physiological factors should be considered when evaluation of risk extent for cancer development is carried out.     

Role of physiological factors in predicting the risk of oncological diseases on the basis of the polymorphism of the xenobiotic metabolism enzyme system

Summarized recent data on the polymorphism of the xenobiotic metabolism and detoxification enzyme (XMDE) system in humans are presented. The current notions on the molecular mechanisms of metabolic processes and the role of genetic polymorphism are reviewed. The roles of transport proteins and nuclear receptors in the regulation of the activity of the XMDE system are shown. The possibilities of using the polymorphism of the XMDE system as the basis for predicting the risk of oncological diseases are considered. Experimental modeling of different levels of the epoxide synthetase and epoxide hydratase activities revealed their close relationship with the toxic, mutagenic, and carcinogenic actions of polycyclic aromatic hydrocarbons. The data indicating the necessity of considering the physiological factors that could influence xenobiotic metabolism and the development of pathological changes are given.     

The role of enzymes of xenobiotic metabolism in the resistance of insects to insecticides

The activity of three enzymatic systems of xenobiotic metabolism (cytochrome P-450-dependent monooxygenases, non-specific esterases and glutathione S-transferases) was studied in sensitive (S) and resistant to tetrametrin (Rtetr.), permetrin (Rperm.), mecarbenyl (Rmec.) and chlorophos (Rchlor.) strains of the housefly M. domestica L. In Rtetr. and Rmec., the activity of microsomal monooxygenases was increased 2.7- and 2.3-fold, respectively, as compared to S. The position of maxima of CO-difference spectra of cytochrome P-450 in all resistant strains (with the exception of Rchlor.) were shifted towards the short-wave region by 1-2 nm. The activity of glutathione S-transferase in Rtetr. was increased as compared to S. Analysis of the total esterase activity and electrophoresis in starch gel revealed quantitative and qualitative differences between the strains under study. In all resistant strains, except for Rmec., additional bands corresponding to the esterase activity were observed. The experimental results are discussed in terms of resistance of insects to insecticides.     

Changes in the activity of enzyme systems of xenobiotic metabolism at different stages of insect development

The cytochrome P-450 content, activity of microsomal monooxygenases, nonspecific esterases and glutathione S-transferases were studied at different stages of development of the Colorado beetle, cotton bollworm, cabbage butterfly, wax moth from the laboratory and natural populations. The data obtained demonstrate significant species, sexual and age differences in the activity of enzyme systems of insecticide detoxication. The toxic efficiency of insecticides at certain developmental stages depends on the level of activity of the enzyme systems involved in their metabolism. These data are discussed with respect to the problem of insects' sensitivity to insecticides at different developmental stages.     

The effect of perfluordecaline on the activity of phase III xenobiotic transformation enzymes

Injection of perfluorodecaline to rats caused an increase of the phase II xenobiotic biotransformation enzyme activities followed by cytochrome P-450 induction. The activities of liver microsomal UDP-glucuronosyl transferase and glutathione transferase increased by 130 and 40%, respectively, against the control level. The increase of the cytosolic glutathione transferase activity was insignificant In contrast, the activity of sulfotransferase decreased about 2-fold. The role of modification of xenobiotic biotransformation enzymes in the biological effect of perfluorodecaline is discussed.     

Human matrix metalloproteinases: an ubiquitarian class of enzymes involved in several pathological processes

Human matrix metalloproteinases (MMPs) belong to the M10 family of the MA clan of endopeptidases. They are ubiquitarian enzymes, structurally characterized by an active site where a Zn(2+) atom, coordinated by three histidines, plays the catalytic role, assisted by a glutamic acid as a general base. Various MMPs display different domain composition, which is very important for macromolecular substrates recognition. Substrate specificity is very different among MMPs, being often associated to their cellular compartmentalization and/or cellular type where they are expressed. An extensive review of the different MMPs structural and functional features is integrated with their pathological role in several types of diseases, spanning from cancer to cardiovascular diseases and to neurodegeneration. It emerges a very complex and crucial role played by these enzymes in many physiological and pathological processes.     

Influence of starvation on the induction of xenobiotic metabolism by polychlorinated biphenyls

The administration of a commercial polychlorinated biphenyl mixture, Aroclor 1254, at a dose of 10 mg/kg/day po for 14 days to rats resulted in increases in EPN detoxification, p-nitroanisole demethylation, NADPH cytochrome $\text{c}$ reductase and cytochrome P-450 which persisted for up to four to five months. Starvation for four days prior to making these determinations caused an enhancement of this induction. This interaction may be due to mobilization of PCBs from storage sites in adipose tissue.     

Activity of enzymes participating in xenobiotic metabolism and the condition of microsomal membranes of rat liver in vitamin K deficiency

Alimentary deficiency or vitamin K (vitamin K-poor diet) as well as the vitamin deficiency resulting from sinkumar administration are accompanied by a decreased activity of microsomal demethylases, hydroxylase, NADH- and nNADPH-reductases of dichlorophenolindophenol and neotrazolium. The activity of cytosolic enzymes (only glutathione-S-transferases, aryl- and allyl esterases) is diminished in a lesser degree. Vitamin K deficiency does not significantly interfere with the effect of the xenobiotic metabolism enzyme inducer (phenobarbital) or the cytochrome P-450 inhibitor (cobalt chloride). The changes in the enzyme activity result in a decrease of acetanilide biotransformation. A possible reason for the observed changes in the activity of microsomal enzymes is the weakening of hydrophobic and polar interactions in microsomal membranes. This hypothesis was confirmed by experiments with the use of membrane perturbants as well as by solubilization of membrane-bound enzymes.     

Genetic polymorphism of enzymes of alcohol metabolism and susceptibility to alcoholic liver disease

Differences in the pharmacokinetics of alcohol absorption and elimination are, in part, genetically determined. There are polymorphic variants of the two main enzymes responsible for ethanol oxidation in liver, alcohol dehydrogenase and aldehyde dehydrogenase. The frequency of occurrence of these variants, which have been shown to display strikingly different catalytic properties, differs among different racial populations. Since the activity of alcohol dehydrogenase in liver is a rate-limiting factor for ethanol metabolism in experimental animals, it is likely that the type and content of the polymorphic isoenzyme subunit encoded at ADH2, beta-subunit, and at ADH3, the gamma-subunit, are contributing factors to the genetic variability in ethanol elimination rate. The recent development of methods for genotyping individuals at these loci using white cell DNA will allow us to test this hypothesis as well as any relationship between ADH genotype and the susceptibility to alcoholism or alcohol-related pathology. A polymorphic variant of human liver mitochondrial aldehyde dehydrogenase, ADLH2, which has little or no acetaldehyde oxidizing activity has been identified. Individuals with the deficient ALDH2 phenotype do not have altered ethanol elimination rates but they do exhibit high blood acetaldehyde levels and dysphoric symptoms such as facial flushing, nausea and tachycardia, after drinking alcohol. Because acetaldehyde is so reactive, it binds to free amino groups of proteins including a 37 kilodalton hepatic protein-acetaldehyde adduct and may elicit an antibody response. We would predict that individuals who have low ALDH2 activity because of liver disease or because they have the inactive ALDH2 variant isoenzyme might form more protein-acetaldehyde adducts and elicit a greater immune response. These adducts may represent good biological markers of alcohol abuse and may also play a role in liver injury due to chronic alcohol consumption.     

Liver enzymes of serine metabolism during neonatal development of the rat.

The developmental patterns of L-serine hydroxymethyltransferase, L-phosphoserine aminotransferase, L-serine aminotransferase and L-serine dehydratase were determined in rat liver. The results point to an increased capacity for serine biosynthesis de novo in the perinatal period. It is suggested that serine at this time, and also at weaning, may serve as a precursor, via the serine hydroxymethyltransferase reaction, for nucleotide biosynthesis to support the rapid phases of liver growth. The role of the alternative pathways of serine metabolism during neonatal development is discussed.     

Acetaldehyde as an underestimated risk factor for cancer development: role of genetics in ethanol metabolism

Chronic ethanol consumption is a strong risk factor for the development of certain types of cancer including those of the upper aerodigestive tract, the liver, the large intestine and the female breast. Multiple mechanisms are involved in alcohol-mediated carcinogenesis. Among those the action of acetaldehyde (AA), the first metabolite of ethanol oxidation is of particular interest. AA is toxic, mutagenic and carcinogenic in animal experiments. AA binds to DNA and forms carcinogenic adducts. Direct evidence of the role of AA in alcohol-associated carcinogenesis derived from genetic linkage studies in alcoholics. Polymorphisms or mutations of genes coding for AA generation or detoxifying enzymes resulting in elevated AA concentrations are associated with increased cancer risk. Approximately 40% of Japanese, Koreans or Chinese carry the AA dehydrogenase 2*2 (ALDH2*2) allele in its heterozygous form. This allele codes for an ALDH2 enzyme with little activity leading to high AA concentrations after the consumption of even small amounts of alcohol. When individuals with this allele consume ethanol chronically, a significant increased risk for upper alimentary tract and colorectal cancer is noted. In Caucasians, alcohol dehydrogenase 1C*1 (ADH1C*1) allele encodes for an ADH isoenzyme which produces 2.5 times more AA than the corresponding allele ADH1C*2. In studies with moderate to high alcohol intake, ADH1C*1 allele frequency and rate of homozygosity was found to be significantly associated with an increased risk for cancer of the upper aerodigestive tract, the liver, the colon and the female breast. These studies underline the important role of acetaldehyde in ethanol-mediated carcinogenesis.     

Effect of perfluorodecalin on activities of hepatic phase II xenobiotic biotransformation enzymes.

The activity of the hepatic phase II enzymes of xenobiotic biotransformation after intravenous administration of perfluorodecalin emulsion to rats was measured. Perfluorodecalin was found to increase the microsomal glutathione S-transferase and UDP-glucuronosyltransferase activities 1.4- and 2.3-fold, respectively. The activity of sulphotransferase was decreased 2-fold. These results show that perfluorodecalin is an inducer of both the enzymes of cytochrome P-450-dependent monooxygenase system [Mishin V. et al (1989) Chem.-Biol. Interactions, 72, 143-155.] and those catalyzing conjugation reactions: microsomal glutathione S-transferase and UDP-glucuronosyltransferase.     

Combined effects of cadmium and nickel on testicular xenobiotic metabolizing enzymes in rats

When male rats were given a single dose of cadmium (Cd) (3.58 mg CdCl₂·H₂O/kg, ip) 72 hr prior to sacrifice, the testicular 7-ethoxyresorufin O-deethylase (EROD) and glutathione S-transferase (GST) activities toward the substrates 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB), ethacrynic acid (EAA), 1,2-epoxy-3-(p-nitrophenoxy)-propane (EPNP), and cumene hydroperoxide (CHPx) decreased significantly as compared to controls. Cd also inhibited reduced glutathione (GSH) level while increasing the lipid peroxidation (LP) level significantly. When the animals were given a single dose of nickel (Ni) (59.5 mg NiCl₂·6H₂O/kg, ip) 16 hr prior to sacrifice, significant decreases were observed in EROD and GST activities toward CDNB, EAA, EPNP, and CHPx, and GSH level. No significant alterations were noted in DCNB GST activity and LP level by Ni. For the combined treatment, rats received the single dose of Ni 56 hr after the single dose of Cd and were killed 16 hr later. In these animals, lesser depressions were observed on EROD activity and LP level than those of Cd alone. The combination of metals significantly inhibited GST activities and GSH level but not to a greater degree than noted by Cd or Ni alone. Plasma testosterone levels of Cd-, Ni-, and combination-treated rats decreased significantly compared to controls. The strongest depression was achieved by Cd alone. Cd, both alone and in combination with Ni, increased the tissue Ni uptake significantly. Ni, however, did not produce such an effect on the tissue uptake of Cd in either case. Cd treatment caused interstitial edema and coagulation necrosis in seminiferous tubules and also caused fibrinoidal necrosis in vascular endothelium. Ni treatment did not produce any pathological testicular alterations compared to controls. Combined treatment produced fewer pathological alterations (i.e., only interstitial edema) than that of Cd treatment. These results reveal that the combination of Cd and Ni does not have a synergistic effect on testicular xenobiotic metabolizing enzymes, and in contrast, Ni has an ameliorating effect on pathological disturbances caused by Cd alone in the rat testis.     

Combined genetic polymorphism and risk for development of lung cancer

Susceptibility to lung cancer has been shown to be modulated by host specific factors. Inheritance of different polymorphic cytochrome P450s (CYPs) and the glutathione S-transferases (GSTs) which affect metabolism of environmental toxicants may play a key role in individual susceptibility. Although individual polymorphic genes have been reported to be associated with development of lung cancer, little is known about the combined effects of several genes in carcinogenesis. From our study of 54 lung cancer patients and 50 matched controls, we observed that a combination of several versions of ‘unfavorable' metabolizing genes (CYP2D6, CYP2E1, GSTM1 and GSTT1) is strongly associated with lung cancer. The relative risk for the different combinations of these genotypes ranged between 1.3 and 14, with higher risk involving the activating genes. The duration and intensity of heavy smoking (expressed in pack-years) are the most important determinant for the development of lung cancer. For example, the estimated risk for development of lung cancer associated with smoking >30 pack-years is represented by an odds ratio=6.65; 95% CL=2.3–19.9 irrespective of an individual's genotype, whereas for smoking between >30 and <50 pack-years, odds ratio=4.5; 95% CL=1.37–15; and for smoking >50 pack-years, odds ratio=30; 95% CL=5.7–114. On the other hand, smoking of less than 30 pack-years is associated with an increased risk in the presence of the polymorphic genes (odds ratio=2.5; 95% CL=0.32–54). The results of our study indicate that the inheritance of multiple ‘unfavorable' genotypes, especially activating genes, is a crucial predisposing factor for the development of lung cancer from cigarette smoking. In addition, the genes may cause moderate smokers who would normally outlive the deleterious effects of smoking to develop lung cancer. The information can therefore be used to target individuals for prevention of health problems.     

The relevance of xenobiotic metabolism in the interindividual susceptibility to chemicals

Biotransformation enzymes may catalyze either detoxication or bioactivation reactions; indeed, many xenobiotics exert their toxic effects after metabolic activation to electrophilic chemicals, interacting with nucleophilic sites on cellular macromolecules. On the other hand, by increasing xenobiotic hydrophilicity, the drug-metabolizing enzymes favors excretion of lipophilic chemicals, not allowing their bioaccumulation up to toxic levels. The expression of the enzymes of the drug-metabolizing system is modulated by genetic, pathological, developmental, environmental and dietary factors. Genetic polymorphism resulting in interindividual and interethnic variation in xenobiotic metabolism is responsible for differences in the susceptibility to chemical-induced toxicity and carcinogenicity, allowing the identification of people at increased risk. Moreover, differences in drug metabolism may correspond to variability in drug response during pharmacological therapy, which can be manifest either as adverse reactions or as a lack of benefit.     

Modulatory influence of Adhatoda vesica (Justicia adhatoda) leaf extract on the enzymes of xenobiotic metabolism,antioxidant status and lipid peroxidation in mice

The effect of two different doses (50 and 100 mg/kg body wt/day for 14 days) of 80% ethanolic extract of the leaves of Adhatoda vesica were examined on drug metabolizing phase I and phase II enzymes, antioxidant enzymes, glutathione content, lactate dehydrogenase and lipid peroxidation in the liver of 8 weeks old Swiss albino mice. The modulatory effect of the extract was also examined on extra-hepatic organs viz. lung, kidney and forestomach for the activities of glutathione S-transferase, DT-diaphorase, superoxide dismutase and catalase. Significant increase in the activities of acid soluble sulfhydryl (-SH) content, cytochrome P450, NADPH-cytochrome P450 reductase, cytochrome b₅, NADH-cytochrome b₅ reductase, glutathione S-transferase (GST), DT-diaphorase (DTD), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR) were observed in the liver at both dose levels of treatments. Adhatoda vesica acted as bifunctional inducer since it induced both phase I and phase II enzyme systems. Both the treated groups showed significant decrease in malondialdehyde (MDA) formation in liver, suggesting its role in protection against prooxidant induced membrane damage. The cytosolic protein was significantly inhibited at both the dose levels of treatment indicating the possibility of its involvement in the inhibition of protein synthesis. BHA has significantly induced the activities of GR and GSH in the present study. The extract was effective in inducing GST and DTD in lung and forestomach, and SOD and CAT in kidney. Thus, besides liver, other organs viz., lung, kidney and forestomach were also stimulated by Adhatoda, to increase the potential of the machinery associated with the detoxification of xenobiotic compounds. But, liver and lung showed a more consistent induction. Since the study of induction of the phase I and phase II enzymes is considered to be a reliable marker for evaluating the chemopreventive efficacy of a particular compound, these findings are suggestive of the possible chemopreventive role played by Adhatoda leaf extract.     

Reprograming of gut microbiome energy metabolism by the FUT2 Crohn's disease risk polymorphism

Fucosyltransferase 2 (FUT2) is an enzyme that is responsible for the synthesis of the H antigen in body fluids and on the intestinal mucosa. The H antigen is an oligosaccharide moiety that acts as both an attachment site and carbon source for intestinal bacteria. Non-secretors, who are homozygous for the loss-of-function alleles of FUT2 gene (sese), have increased susceptibility to Crohn''s disease (CD). To characterize the effect of FUT2 polymorphism on the mucosal ecosystem, we profiled the microbiome, meta-proteome and meta-metabolome of 75 endoscopic lavage samples from the cecum and sigmoid of 39 healthy subjects (12 SeSe, 18 Sese and 9 sese). Imputed metagenomic analysis revealed perturbations of energy metabolism in the microbiome of non-secretor and heterozygote individuals, notably the enrichment of carbohydrate and lipid metabolism, cofactor and vitamin metabolism and glycan biosynthesis and metabolism-related pathways, and the depletion of amino-acid biosynthesis and metabolism. Similar changes were observed in mice bearing the FUT2^−/− genotype. Metabolomic analysis of human specimens revealed concordant as well as novel changes in the levels of several metabolites. Human metaproteomic analysis indicated that these functional changes were accompanied by sub-clinical levels of inflammation in the local intestinal mucosa. Therefore, the colonic microbiota of non-secretors is altered at both the compositional and functional levels, affecting the host mucosal state and potentially explaining the association of FUT2 genotype and CD susceptibility.     

Influence of aging and poly IC treatment on xenobiotic metabolism in mice

Cytochrome P-450-dependent and independent metabolism of xenobiotics in the liver of C57BL/10ScSn male mice was investigated in relation to age and the age-related differences in response to treatment with polyriboinosinic-polyribocytidylic acid (poly IC), an interferon inducing agent. Young (3 months), middle-aged (15 months) and old (27 months) animals were studied. Mean survival time of males of this strain is 30-33 months. Age-related changes in the metabolism of xenobiotics included significant decreases between middle and old age in activities of the microsomal P-450-dependent mixed function oxidases (MFO), aryl hydrocarbon hydroxylase (AHH) and p-nitroanisole (p-NA) O-demethylase, but not 7-ethoxycoumarin (7-Ec) O-deethylase. Analysis of P-450-independent enzymes revealed a significant decrease in the epoxide hydrolase activity in the microsomes and cytosol from old compared to middle-aged or young mice. Glutathione S-transferase activity towards 1-chloro-2,4-dinitrobenzene (CDNB) was lower in cytosols of middle-aged and old than young mice. Carboxylesterase activity was not altered by age. Hepatic microsomal protein content was significantly higher in middle-aged and old than in young mice. Intraperitoneal treatment with a single dose of 5 mg/kg poly IC 24 hours before sacrifice resulted, for mice of all age groups, in a marked inhibition of activities of all 3 microsomal cytochrome P-450-dependent enzymes, without any changes in activities of the P-450-independent enzymes. The inhibition of AHH by poly IC was much higher in old and middle-aged than in young mice, averaging 87.1%, 74.5%, and 41.9%, respectively, in the 3 age groups. Poly IC treatment increased lipid peroxidation in liver homogenates of all groups of mice. Body and liver weights were not altered in animals of the 3 age groups by poly IC treatment, but hepatic microsomal protein contents were significantly decreased.