Effect of various chemicals on the aldehyde dehydrogenase activity of the rat liver cytosol

Hepatic drug metabolizing profile of Flinders Sensitive Line rat model of depression

The Flinders Sensitive Line (FSL) rat model of depression exhibits some behavioral, neurochemical, and pharmacological features that have been reported in depressed patients and has been very effective in screening antidepressants. Major factor that determines the effectiveness and toxicity of a drug is the drug metabolizing capacity of the liver. Therefore, in order to discriminate possible differentiation in the hepatic drug metabolism between FSL rats and Sprague-Dawley (SD) controls, their hepatic metabolic profile was investigated in this study. The data showed decreased glutathione (GSH) content and glutathione S-transferase (GST) activity and lower expression of certain major CYP enzymes, including the CYP2B1, CYP2C11 and CYP2D1 in FSL rats compared to SD controls. In contrast, p-nitrophenol hydroxylase (PNP), 7-ethoxyresorufin-O-dealkylase (EROD) and 16alpha-testosterone hydroxylase activities were higher in FSL rats. Interestingly, the wide spread environmental pollutant benzo(alpha)pyrene (B(alpha)P) induced CYP1A1, CYP1A2, CYP2B1/2 and ALDH3c at a lesser extend in FSL than in SD rats, whereas the antidepressant mirtazapine (MIRT) up-regulated CYP1A1/2, CYP2C11, CYP2D1, CYP2E1 and CYP3A1/2, mainly, in FSL rats. The drug also further increased ALDH3c whereas suppressed GSH content in B(alpha)P-exposed FSL rats. In conclusion, several key enzymes of the hepatic biotransformation machinery are differentially expressed in FSL than in SD rats, a condition that may influence the outcome of drug therapy. The MIRT-induced up-regulation of several drug-metabolizing enzymes indicates the critical role of antidepressant treatment that should be always taken into account in the designing of treatment and interpretation of insufficient pharmacotherapy or drug toxicity.

Tissue distribution, ontogeny, and regulation of aldehyde dehydrogenase (Aldh) enzymes mRNA by prototypical microsomal enzyme inducers in mice

Aldehyde dehydrogenases (Aldhs) are a group of nicotinamide adenine dinucleotide phosphate-dependent enzymes that catalyze the oxidation of a wide spectrum of aldehydes to carboxylic acids. Tissue distribution and developmental changes in the expression of the messenger RNA (mRNA) of 15 Aldh enzymes were quantified in male and female mice tissues using the branched DNA signal amplification assay. Furthermore, the regulation of the mRNA expression of Aldhs by 15 typical microsomal enzyme inducers (MEIs) was studied. Aldh1a1 mRNA expression was highest in ovary; 1a2 in testis; 1a3 in placenta; 1a7 in lung; 1b1 in small intestine; 2 in liver; 3a1 in stomach; 3a2 and 3b1 expression was ubiquitous; 4a1, 6a1, 7a1, and 8a1 in liver and kidney; 9a1 in liver, kidney, and small intestine; and 18a1 in ovary and small intestine. mRNAs of different Aldh enzymes were detected at lower levels in fetuses than adult mice and gradually increased after birth to reach adult levels between 15 and 45 days of age, when the gender difference began to appear. Aromatic hydrocarbon receptor (AhR) ligands induced the liver mRNA expression of Aldh1a7, 1b1, and 3a1, constitutive androstane receptor (CAR) activators induced Aldh1a1 and 1a7, whereas pregnane X receptor (PXR) ligands and NF-E2 related factor 2 (Nrf2) activators induced Aldh1a1, 1a7, and 1b1. Peroxisome proliferator activator receptor alpha (PPAR alpha) ligands induced the mRNA expression in liver of almost all Aldhs. The Aldh organ-specific distribution may be important in elucidating their role in metabolism, elimination, and organ-specific toxicity of xenobiotics. Finally, in contrast to other phase-I metabolic enzymes such as CYP450 enzymes, Aldh mRNA expression seems to be generally insensitive to typical microsomal inducers except PPAR alpha ligands.

ALDH1A1 and ALDH3A1 expression in lung cancers: correlation with histologic type and potential precursors

We hypothesize that aldehyde dehydrogenase (ALDH) isozymes may be upregulated in lung tissue as a result of exposure to carcinogenic aldehydes found in cigarette smoke. To investigate this hypothesis, we studied the expression of two ALDH isozymes in lung cancer from patient samples and its relationship to the history of cigarette smoking. Immunohistochemical staining for ALDH1A1 and ALDH3A1 was performed on archival specimens from control patients without lung cancer, and patients with one of the primary lung cancers: squamous cell cancer (SCCA), adenocarcinoma (AdenoCA), and small cell lung cancer (SCLC). An overall score was obtained for each sample based upon multiplying the staining intensity (0-3) and the extensiveness (0-100%). Mean+/-S.E.M. for each experimental group was calculated and compared. Our results indicate a significantly higher level of expression of ALDH1A1 and ALDH3A1 in SCCA (155+/-19 and 162+/-17, respectively) and AdenoCA (116+/-12 and 107+/-10) than SCLC (39+/-11 and 42+/-12) (P<0.01). Atypical pneumocytes demonstrated significantly higher levels of expression of ALDH1A1 and ALDH3A1 than normal pneumocytes (a normal counterpart of AdenoCA), which is suggestive of up regulation during malignant transformation to AdenoCA. A subset analysis of all samples studied revealed increased expression of ALDH1A1 (P=0.055) and ALDH3A1 (P=0.0093) in normal pneumocytes of smokers (n=32) in comparison to those of non-smokers (n=17). Non-small cell lung cancer (NSCLC) express very high levels of ALDH1A1 and ALDH3A1 in comparison with SCLC, elevated expression of both enzymes may be associated with malignant transformation to AdenoCA, and cigarette smoking seems to result in increased expression of these enzymes in normal pneumocytes.

Effects of 3-methylcholanthrene and aspirin co-administration on ALDH3A1 in HepG2 cells

The effects of two different protocols of 3-methylcholanthrene (3MC) and aspirin co-administration were studied in a well-established human hepatoma cell line (HepG2). During this work, we have performed toxicity tests for cell viability/cell proliferation as well as studies on the expression of ALDH3A1 after exposure of HepG2 cells to 3MC or/and aspirin. For the evaluation of toxic concentrations of 3MC and aspirin, the WST-1 test was used. WST-1 is a reliable cytotoxicity test which is based on the cleavage of the tetrazolium salt WST-1 to formazan by mitochondrial enzymes of living cells. A broad range of drug concentrations for either 3MC (0.25-50.0 microM) or aspirin (0.05-10.0 mM) were used for cell exposure, in several periods of time. The expression of ALDH3A1 in HepG2 cells showed typical time- and dose-response curves of induction after application of 3MC (1-5 days, 1.5-5.0 microM, respectively). When cells were firstly exposed to 3MC (2.5 and 5.0 microM) and then to aspirin (0.25 mM), the induced ALDH3A1 activity was further enhanced in a statistically significant way (P<0.05). On the contrary, when aspirin application was preceded 3MC exposuring a statistically significant decrease in ALDH3A1 inducibility was observed, as compared with the application of 3MC alone.

Stress modulates the enzymatic inducibility by benzo[alpha]pyrene in the rat liver

The role of stress on the inducibility by benzo[alpha]pyrene (B[alpha]P), a representative polycyclic aromatic hydrocarbon, of several drug-metabolizing enzymes was investigated in rats, using restraint stress and mild unpredictable stress as models of psychological stress. Restraint stress was found to significantly suppress basal ethoxyresorufin 7-dealkylase (EROD) and pentoxyresorufin 7-dealkylase (PROD) activities (two-fold). In contrast, mild unpredictable stress markedly increased basal EROD activity, while PROD activity was not affected. In addition, both types of stress resulted in a significant reduction of basal p -nitrophenol hydroxylation (PNP). It is worth noting that restraint stress greatly enhanced the inducibility of EROD, methoxyresorufin 7-dealkylase (MROD) and to a lesser extent PROD activities by B[alpha]P, while mild unpredictable stress had no, or only a mild effect on the inducibility of cytochrome P450s (CYPs) by B[alpha]P. In conclusion, psychological stress may modulate different enzymatic systems which are vital elements of the detoxification mechanisms of the body. The two distinct types of psychological stress used in this study appear to affect the enzymatic systems under investigation in a stress-specific manner at the basal level and at the induced state by B[alpha]P.

Anti-inflammatory agents and inducibility of hepatic drug metabolism

Two rat liver cytosolic aldehyde dehydrogenases, ALDH1 and ALDH3c, are of particular interest because they are inducible by different classes of xenobiotics. ALDHI is mainly increased by phenobarbital-type inducers; polycyclic aromatic hydrocarbons (PAHs), such as 3- methylcholanthrene (3MC), increase ALDH3c enzyme activity in all rat species currently tested. In addition, ALDH3c has been found to reflect the subfamily CYPIA of cytochrome P-450, as well as other enzymes functionally related to the aryl hydrocarbon receptor (the "Ah-receptor enzyme battery"), which is activated by the same type of inducers. In the present study we investigated whether the induction of ALDH3c might be connected with a chemically produced aseptic inflammation of the hepatocyte. To answer this question, we examined the relationship between the induction of ALDH3c by 3MC and the arachidonic acid cascade. Different non-steroid anti-inflammatory drugs (NSAIDs) were tested in combination with 3MC and in post-treatment. The 3MC-induced ALDH3c activity was significantly diminished by the co-administered anti-inflammatory agents. Two microsomal enzyme activities (ethoxyresorufin-O-deethylase, EROD; aryl-hydrocarbon-hydroxylase, AHH) were also decreased. Similar results were obtained with NSAIDs administered to animals pre- treated with 3MC, as far as the ALDH3c activity was concerned, but not for the microsomal enzyme activity (EROD and AHH). In conclusion, the induction of ALDH3c, after PAH treatment, may be related to an aseptic inflammation of the hepatocytes. This effect is reduced by commonly used steroid and non-steroid anti- inflammatory drugs, and although the mechanism of inhibition has not yet been elucidated, it appears likely that ALDH3c and CYP1A activities are associated with the "acute phase" response.

Zoxazolamine-induced paralysis in two rat substrains: differences in hepatic drug metabolism

Aldehyde dehydrogenase (ALDH) is involved in the metabolism of endogenous and exogenous aldehydes originating from biogenic amines, lipids, food and drugs. Rat liver contains at least two cytosolic ALDHs that can be stimulated by inducers of drug metabolism. Phenobarbital- type inducers increase ALDH1 activity while polycyclic aromatic hydrocarbons (such as benzo[alpha]pyrene) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) increase ALDH3c isoenzyme activity. Two rat substrains were isolated according to a different induction of hepatic ALDH after treatment with phenobarbital (PB). Animals that responded to treatment (RR) and those that did not respond (rr) were inbred and divided into two homogenous groups. These animals constituted an ideal experimental model due to their common origin. Apart from the dramatic induction of cytosolic ALDH1 and ALDH3c, the effects of PB on pentoxy-, ethoxy- and methoxy-resorufin-O-dealkylase (P-, E-, and MROD) between the two substrains were also studied. 3-Methylcholanthrene (3MC) greatly increased ALDH3c levels in both substrains, although it was slightly more pronounced in the rr rats, in which it was assessed either as ALDH3c or as total cytosolic ALDH. A similar trend was also noted in EROD, PROD and MROD activities. Dealkylation of the methoxy group was found to be statistically different between the two substrains (rr > RR). The relevance of the biochemical findings with the in vivo hepatic capacity for drug metabolism was investigated by measuring the duration of zoxazolamine paralysis. Both animal substrains were tested with zoxazolamine either without pretreatment or after administration of PB or 3MC: the paralysis produced by zoxazolamine lasted for a longer period in rr than in RR rats. After pretreatment with PB, the duration of paralysis was greatly reduced, but the differences between the two substrains remained. Pretreatment with various doses of 3MC produced differences in the duration of paralysis in RR and rr rats, although the time period was much shorter than that observed in control animals.

Ligands of four receptors in the nuclear steroid/thyroid hormone superfamily inhibit induction of rat cytosolic aldehyde dehydrogenase-3 (ALDH3c) by 3-methylcholanthrene

Using six ligands that bind to four different receptors in the nuclear steroid/thyroid hormone superfamily, we have examined the effects of these chemicals on induction of the cytosolic aldehyde dehydrogenase (ALDH3c) activity by 3-methylcholanthrene (3MC) in rat liver and uterus. In contrast to negligible activities in the untreated rat, ALDH3c enzyme activities are induced after a single dose of 3MC. Hepatic ALDH3c induction is decreased 60% to 90% when 3MC is administered together with any of the following ligands: estradiol, testosterone, progesterone, hydrocortisol, diethylstilbestrol, or tamoxifen. None of these same doses of chemicals, administered alone, affects ALDH3c enzyme activity. In addition, when these ligands are injected 2 days after 3MC, no changes are observed in liver or uterus ALDH3c induction. These results suggest that ligands that bind to different receptors in the nuclear steroid/thyroid hormone superfamily might inhibit the ALD3H3c induction process by polycyclic aromatic hydrocarbons; the molecular mechanism(s) of this inhibitory effect is not yet understood.

Comparative assessment of metabolic enzyme levels in macrophage populations of the F344 rat

The immune system is a direct target for toxic insult by a number of drugs and other chemicals, many of which require activation to toxic metabolites by drug-metabolizing enzymes. We compared the induction of drug-metabolizing enzymes, including cytochrome P450 1A1 (CYP1A1) and aldehyde dehydrogenase (ALDH), which are differentially expressed in various macrophage populations following treatment of F344 rats with the inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Kupffer cells, alveolar macrophages and splenic macrophages from TCDD-treated animals expressed elevated levels of inducible CYP1A1 as compared to other macrophage subpopulations or cells from control rats. TCDD treatment also resulted in increased ethoxyresorufin-O-deethylase (EROD) activity and total cytochrome P450 content in tissue-derived macrophages. Immunoreactive protein and mRNA transcripts for CYP1A1 were not detectable in resident peritoneal macrophages or peripheral blood monocytes. Examination of aromatic hydrocarbon receptor (AhR) levels in macrophage populations suggests that the ability of TCDD to induce metabolic enzymes in specific cell types correlates well with AhR expression. In vivo activation of macrophages, using either Bacillus of Calmette and Guérin, Mycobacterium tuberculosis (BCG) or polyinosinic:polycytidylic acid (Poly I:C), caused no significant alteration in the levels of induction of CYP1A1. ALDH-3 induction was similar in all macrophage populations examined. These studies indicate that macrophages, particularly those from portals of entry, may be induced to produce increased levels of specific enzymes, and the induction is dependent upon their maturational stage rather than their activation state. The metabolism of xenobiotics to toxic intermediates by immune cells and its role in immunosuppression are discussed.

Lack of response of the rat liver "class 3" cytosolic aldehyde dehydrogenase to toxic chemicals, glutathione depletion, and other forms of stress

One of the rat liver "Class 3" cytosolic aldehyde dehydrogenases (EC 1.2.1.3), ALDH3c, is known to be markedly induced by polycyclic aromatic hydrocarbons and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin). In the present study we examined whether hepatic ALDH3c induction is a general response to toxicity. Treatment of Wistar rats for 4 days with known toxic doses of hepatotoxic agents--carbon tetrachloride, dimethylnitrosamine, diethylnitrosamine, aflatoxin B1, and D-ethionine--did not induce ALDH3c enzyme activity. Whereas dimethylaminoazobenzene at 100 mg/kg/day for 4 days did not increase ALDH3c, a 10-fold lower dose of dimethylaminoazobenzene for 4 days produced a 20-fold increase in ALDH3c activity. Treatment with phorone, diethylmaleate or L-buthionine-S,R-sulfoximine--which deplete reduced glutathione (GSH) by different mechanisms--did not affect ALDH3c activity. One dose of benzo[a]pyrene for 24 hr increased ALDH3c activity by 25-fold. Treatment with both the GSH-depleting chemicals and benzo[a]pyrene inhibited ALDH3c induction by 45% to 75%, suggesting a role for GSH during ALDH3c induction. After ALDH3c activity had already been induced by benzo[a]pyrene, however, the GSH-depleting chemicals did not affect ALDH3c activity. No changes in ALDH3c activity were seen 24 or 48 hr after partial hepatectomy, on the fifth day following surgical cholestasis, or after guanethidine-induced sympathectomy. These data indicate that hepatic ALDH3c inducibility in the rat is not a general or direct response to chemical toxicity, or to conditions of GSH depletion or other forms of stress.

The influence of vitamin E and selenium on lipid peroxidation and aldehyde dehydrogenase activity in rat liver and tissue

Malondialdehyde (MDA) production and cytosolic aldehyde dehydrogenase (ALDH) response were examined in rat liver tissues after feeding different levels of dietary vitamin E and/or selenium and polyunsaturated fat for 12-38 wk. MDA production was significantly increased by vitamin E deficiency or by high levels of polyunsaturated fat intake, but not by selenium deficiency. The activity of cytosolic ALDH increased upon increased production of MDA after 12-16 wk of feeding the lipid peroxidation-inducing diets. However, ALDH activity was suppressed after 38 wk of feeding the vitamin E-deficient diet. The results indicate that the hepatic cytosolic ALDH may be involved in the metabolism of MDA during a relatively short-term increase in in vivo lipid peroxidation, but that ALDH activity becomes suppressed after more severe in vivo lipid peroxidation has been produced. Hepatic and plasma alpha-tocopherol levels and lipid peroxidation products were measured for the various dietary groups.

Negative regulation of the murine cytosolic aldehyde dehydrogenase-3 (Aldh-3c) gene by functional CYP1A1 and CYP1A2 proteins

We have examined enzyme activities and mRNA levels corresponding to aldehyde dehydrogenase-3 genes encoding cytosolic (ALDH3c) and microsomal (ALDH3m) forms. In contrast to negligible activities in the intact mouse liver, both ALDH3c and ALDH3m enzyme activities are inducible by benzo[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in mouse hepatoma Hepa-1c1c7 cell cultures. Constitutive mRNA levels of ALDH3c are virtually absent, whereas those of ALDH3m are substantial; using Hepa-1 mutant lines, we show that both ALDH3c and ALDH3m are TCDD-inducible by an Ah receptor-dependent mechanism. Basal mRNA levels of ALDH3c, but not those of ALDH3m, are strikingly elevated in untreated mutant cells lacking a functional CYP1A1 enzyme; low ALDH3c basal mRNA levels can be restored by introduction of a functional murine CYP1A1 or human CYP1A2 enzyme into these mutant cells. These data suggest that the TCDD induction process is distinct from the CYP1A1/CYP1A2 metabolism-dependent repression of constitutive gene expression; we suggest that this latter property classifies the Aldh-3c gene, but not the Aldh-3m gene, as a member of the murine [Ah] battery.

Induction of class 3 aldehyde dehydrogenase in the mouse hepatoma cell line Hepa-1 by various chemicals

The mouse hepatoma cell line Hepa-1 was shown to express an aldehyde dehydrogenase (ALDH) isozyme which was inducible by TCDD and carcinogenic polycyclic aromatic hydrocarbons. The induced activity could be detected with benzaldehyde as substrate and NADP as cofactor (B/NADP ALDH). As compared with rat liver and hepatoma cell lines, the response was moderate (maximally 5-fold). There was an apparent correlation between this specific form of ALDH and aryl hydrocarbon hydroxylase (AHH) in the Hepa-1 wild-type cell line--in terms of inducibility by several chemicals. However, the magnitude of the response was clearly smaller for ALDH than for AHH. Southern blot analysis showed that a homologous gene (class 3 ALDH) was present in the rat and mouse genome. The gene was also expressed in Hepa-1 and there was a good correlation between the increase of class 3 ALDH-specific mRNA and B/NADP ALDH enzyme activity after exposure of the Hepa-1 cells to TCDD. It is concluded that class 3 ALDH is inducible by certain chemicals in the mouse hepatoma cell line, although the respective enzyme is not inducible in mouse liver in vivo.

Aldehyde dehydrogenases and their role in carcinogenesis

Aldehydes are highly reactive molecules that may have a variety of effects on biological systems. They can be generated from a virtually limitless number of endogenous and exogenous sources. Although some aldehyde-mediated effects such as vision are beneficial, many effects are deleterious, including cytotoxicity, mutagenicity, and carcinogenicity. A variety of enzymes have evolved to metabolize aldehydes to less reactive forms. Among the most effective pathways for aldehyde metabolism is their oxidation to carboxylic acids by aldehyde dehydrogenases (ALDHs). ALDHs are a family of NADP-dependent enzymes with common structural and functional features that catalyze the oxidation of a broad spectrum of aliphatic and aromatic aldehydes. Based on primary sequence analysis, three major classes of mammalian ALDHs--1, 2, and 3--have been identified. Classes 1 and 3 contain both constitutively expressed and inducible cytosolic forms. Class 2 consists of constitutive mitochondrial enzymes. Each class appears to oxidize a variety of substrates that may be derived either from endogenous sources such as amino acid, biogenic amine, or lipid metabolism or from exogenous sources, including aldehydes derived from xenobiotic metabolism. Changes in ALDH activity have been observed during experimental liver and urinary bladder carcinogenesis and in a number of human tumors, including some liver, colon, and mammary cancers. Changes in ALDH define at least one population of preneoplastic cells having a high probability of progressing to overt neoplasms. The most common change is the appearance of class 3 ALDH dehydrogenase activity in tumors arising in tissues that normally do not express this form. The changes in enzyme activity occur early in tumorigenesis and are the result of permanent changes in ALDH gene expression. This review discusses several aspects of ALDH expression during carcinogenesis. A brief introduction examines the variety of sources of aldehydes. This is followed by a discussion of the mammalian ALDHs. Because the ALDHs are a relatively understudied family of enzymes, this section presents what is currently known about the general structural and functional properties of the enzymes and the interrelationships of the various forms. The remainder of the review discusses various aspects of the ALDHs in relation to tumorigenesis. The expression of ALDH during experimental carcinogenesis and what is known about the molecular mechanisms underlying those changes are discussed. This is followed by an extended discussion of the potential roles for ALDH in tumorigenesis. The role of ALDH in the metabolism of cyclophosphamidelike chemotherapeutic agents is described. This work suggests that modulation of ALDH activity may an important determinant of the effectiveness of certain chemotherapeutic agents.(ABSTRACT TRUNCATED AT 400 WORDS)