The subcellular distribution and properties of aldehyde dehydrogenases in rat liver

Increased Brain Serotonin Rather Than Increased Blood Acetaldehyde as a Common Denominator Behind Alleged Disulfiram-Like Reactions

Several pharmaceutical agents are known to produce ethanol intolerance, which is often depicted as disulfiram-like reaction. As in the case with disulfiram, the underlying mechanism is believed to be the accumulation of acetaldehyde in the blood, due to inhibition of the hepatic aldehyde dehydrogenases, albeit this has not been confirmed in all cases by blood acetaldehyde measurements. Herein, cefamandole, cotrimoxazole, griseofulvin, procarbazine, and propranolol, which are reported to produce a disulfiram-like reaction, as well as disulfiram, were administered to Wistar rats and the hepatic activities of ethanol metabolizing enzymes along with the levels of brain monoamines were determined. Blood acetaldehyde was also evaluated after ethanol administration in rats pretreated with the abovementioned pharmaceutical products. Disulfiram, cefamandole, and procarbazine significantly increased blood acetaldehyde levels after ethanol administration, while on the contrary, cotrimoxazole, griseofulvin, and propranolol had no effect on blood acetaldehyde. Interestingly, all substances used, except disulfiram, increased the levels of brain serotonin. According to our findings, cotrimoxazole, griseofulvin, and propranolol do not produce a typical disulfiram-like reaction, because they do not increase blood acetaldehyde when given together with ethanol. On the other hand, all tested agents share the common property to enhance brain serotonin, whereas a respective effect of ethanol is well established. Hence, the ethanol intolerance produced by these agents, whether blood acetaldehyde concentration is elevated or not, could be the result of a “toxic serotonin syndrome,” as in the case of the concomitant use of serotonin-active medications that provoke clinical manifestations similar to those of a disulfiram reaction.

Can Lipoic Acid Attenuate Cardiovascular Disturbances Induced by Ethanol and Disulfiram Administration Separately or Jointly in Rats?

The exogenous lipoic acid (LA) is successfully used as a drug in the treatment of many diseases. It is assumed that after administration, LA is transported to the intracellular compartments and reduced to dihydrolipoic acid (DHLA) which is catalyzed by NAD(P)H-dependent enzymes. The purpose of this study was to investigate whether LA can attenuate cardiovascular disturbances induced by ethanol (EtOH) and disulfiram (DSF) administration separately or jointly in rats. For this purpose, we measured systolic and diastolic blood pressure, recorded electrocardiogram (ECG), and estimated mortality of rats. We also studied the activity of aldehyde dehydrogenase (ALDH) in the rat liver. It was shown for the first time that LA partially attenuated the cardiac arrhythmia (extrasystoles and atrioventricular blocks) induced by EtOH and reduced the EtOH-induced mortality of animals, which suggests that LA may have a potential for use in cardiac disturbance in conditions of acute EtOH intoxication. The administration of EtOH, LA, and DSF separately or jointly affected the ALDH activity in the rat liver since a significant decrease in the activity of the enzyme was observed in all treatment groups. The results indicating that LA is an inhibitor of ALDH activity are very surprising.

Inactivation of Aldehyde Dehydrogenase by Disulfiram in the Presence and Absence of Lipoic Acid or Dihydrolipoic Acid: An in Vitro Study

The inhibition of aldehyde dehydrogenase (ALDH) by disulfiram (DSF) in vitro can be prevented and/or reversed by dithiothreitol (DTT), which is a well-known low molecular weight non-physiological redox reagent commonly used in laboratory experiments. These observations inspired us to ask the question whether the inhibition of ALDH by DSF can be preserved or abolished also by dihydrolipoic acid (DHLA), which is the only currently known low molecular weight physiological dithiol in the body of humans and other animals. It can even be metaphorized that DHLA is an "endogenous DTT". Lipoic acid (LA) is the oxidized form of DHLA. We investigated the inactivation of ALDH derived from yeast and rat liver by DSF in the presence or absence of LA or DHLA. The results clearly show that DHLA is able both to restore and protect ALDH activity blocked by DSF. The proposed mechanism is discussed.

The use of liver slices from the Cape vulture (Gyps coprotheres) to better understand the role of liver toxicity of non-steroidal anti-inflammatory drugs (NSAIDs) in vultures

Diclofenac, a non-steroidal anti-inflammatory drug (NSAID) was responsible for the death of millions of vultures on the Asian subcontinent, following the consumption of diclofenac contaminated carcasses. The aim of this research was to establish if liver slices could serve as an alternate means of predicting the toxicity of NSAIDs in Gyps vultures. The Cape vulture liver slices was prepared and incubated with four NSAIDs for 6 h. A percent clearance of 1.0 ± 0.253, 0.58 ± 0.153, 0.961 ± 0.312 and 1.242 ± 0.406 (%/h*g) was attained for diclofenac, carprofen, ketoprofen and meloxicam respectively. Both meloxicam and diclofenac exerted toxic effects on the hepatic cells. Protein content indicated that the vulture tissue had lower enzyme levels than expected for an animal of its size. The poor distinction between the ex vivo hepatic percent clearance of meloxicam and diclofenac indicates that liver slices is not an ideal model to investigate NSAIDs toxicity in Cape vulture.

The Effects of Different Garlic-Derived Allyl Sulfides on Anaerobic Sulfur Metabolism in the Mouse Kidney

Diallyl sulfide (DAS), diallyl disulfide (DADS) and diallyl trisulfide (DATS) are major oil-soluble organosulfur compounds of garlic responsible for most of its pharmacological effects. The present study investigated the influence of repeated intraperitoneally (ip) administration of DAS, DADS and DATS on the total level of sulfane sulfur, bound sulfur (S-sulfhydration) and hydrogen sulfide (H₂S) and on the activity of enzymes, which catalyze sulfane sulfur formation and transfer from a donor to an acceptor in the normal mouse kidney, i.e., γ-cystathionase (CSE) and rhodanese (TST). The activity of aldehyde dehydrogenase (ALDH), which is a redox-sensitive protein, containing an –SH group in its catalytic center, was also determined. The obtained results indicated that all tested compounds significantly increased the activity of TST. Moreover, DADS and DATS increased the total sulfane sulfur level and CSE activity in the normal mouse kidney. ALDH activity was inhibited in the kidney after DATS administration. The results indicated also that none of the studied allyl sulfides affected the level of bound sulfur or H₂S. Thus, it can be concluded that garlic-derived DADS and DATS can be a source of sulfane sulfur for renal cells but they are not connected with persulfide formation.

Pharmaceutical Agents Known to Produce Disulfiram-Like Reaction: Effects on Hepatic Ethanol Metabolism and Brain Monoamines

Several pharmaceutical agents produce ethanol intolerance, which is often depicted as disulfiram-like reaction. As in the case with disulfiram, the underlying mechanism is believed to be the accumulation of acetaldehyde in the blood, due to inhibition of the hepatic aldehyde dehydrogenases. In the present study, chloramphenicol, furazolidone, metronidazole, and quinacrine, which are reported to produce a disulfiram-like reaction, as well as disulfiram, were administered to Wistar rats and the hepatic activities of alcohol and aldehyde dehydrogenases (1A1 and 2) were determined. The expression of aldehyde dehydrogenase 2 was further assessed by Western blot analysis, while the levels of brain monoamines were also analyzed. Finally, blood acetaldehyde was evaluated after ethanol administration in rats pretreated with disulfiram, chloramphenicol, or quinacrine. The activity of aldehyde dehydrogenase 2 was inhibited by disulfiram, chloramphenicol, and furazolidone, but not by metronidazole or quinacrine. In addition, although well known for metronidazole, quinacrine also did not increase blood acetaldehyde after ethanol administration. The protein expression of aldehyde dehydrogenase 2 was not affected at all. Interestingly, all substances used, except disulfiram, increased the levels of brain serotonin. According to our findings, metronidazole and quinacrine do not produce a typical disulfiram-like reaction, because they do not inhibit hepatic aldehyde dehydrogenase nor increase blood acetaldehyde. Moreover, all tested agents share the common property to enhance brain serotonin, whereas a respective effect of ethanol is well established. Therefore, the ethanol intolerance produced by these agents, either aldehyde dehydrogenase is inhibited or not, could be the result of a “toxic serotonin syndrome,” as in the case of the concomitant use of serotonin-active medications.

Impact of different partitioned solvents on chemical composition and bioavailability of Sasa quelpaertensis Nakai leaf extract

The leaves of Sasa quelpaertensis Nakai were extracted with 80% ethanol and further partitioned with n-hexane, chloroform, ethyl acetate, n-butanol, and aqueous fractions to evaluate the biological activity through assessment via various in vitro assays, including total phenol content; 1,1-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis-(3-ethylbenzothiazothiazoline-6-sulfornic acid (ABTS) radical scavenging; reducing power; α-glucosidase and tyrosinase inhibitory; and alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) activity assays. The highest activity was found in the ethyl acetate fraction for all assays and showed stronger DPPH radical scavenging, reducing power, and tyrosinase inhibitory activity than the positive controls (butylated hydroxytoluene, α-tocopherol, and arbutin, respectively). When compared to the ethyl acetate fraction, the n-butanol fraction had lower rates, but it still demonstrated relatively high activity. The activity of the n-hexane fraction was high for DPPH and ABTS radical scavenging activity and contained significant amounts of phenol content, whereas the chloroform fraction possessed the highest reducing power, tyrosinase inhibitory, and ADH and ALDH activity, despite having the lowest phenol content when compared to the other fractions. These findings clearly indicate that S. quelpaertensis Nakai leaves can be a good natural source of antioxidants and tyrosinase inhibitors, as well as ADH and ALDH activity inducers, suggesting that may have potential for treating various diseases and improving human health.

The Comparative Analysis of Antioxidant and Biological Activity for the Dendropanax morbifera LEV. Leaves Extracted by Different Ethanol Concentrations

The different concentrations of ethanol (20-100%) and distilled water extract for Dendropanax morbifera LEV. leaves were evaluated to induce antioxidant and biological activity employed by variety of assays. The 20%, 80%, and 100% ethanol extract demonstrated the relatively higher activity, whereas distilled water, 40%, and 60% ethanol extracts exhibited the lower antioxidant and biological activity. Especially, 80% ethanol extract showed the remarkably higher radical scavenging activity, reducing power, total phenol and flavonoid content, α-glucosidase, and tyrosinase inhibitory activity, and alcohol dehydrogenases (ADH) and aldehyde dehydrogenase (ALDH) activity. Also, 100% ethanol extract exhibited relatively greater activity, but there did not show significant radical scavenging activity. Furthermore, there were 50% and 30% promotion effect for ADH activity assay and 80% and 40% promotion effect for ALDH activity assay in 80% and 100% ethanol extract, respectively. In addition, in the minimum inhibitory concentration (MIC), all extracts except for distilled water extract inhibited Bacillus cereus, Staphylococcus aureus subsp. aureus, Escherichia coli. For Pichia jadinii, whole extracts effectively inhibited yeast multiplication at concentration of 125 μg/mL for 100% ethanol extract and 250 μg/mL for the rest of extract. These result indicated that D. morbifera LEV. leaves extracted by 80% ethanol would be the ideal extracting solution to maximize inherent antioxidant and biological activity agent.

Probucol attenuates ethanol-induced liver fibrosis in rats by inhibiting oxidative stress, extracellular matrix protein accumulation and cytokine production

1. Liver fibrosis is characterized by excessive accumulation of extracellular matrix (ECM) proteins in the liver. Probucol, a lipid-lowering drug, was found to prevent liver injury in rats treated with carbon tetrachloride (CCl4 ). In the present study, we investigated whether probucol has protective effect against liver fibrosis in rats treated with ethanol and CCl4 . 2. Thirty rats were randomly divided into five groups. Groups I and II served as the normal control and the model of liver fibrosis, respectively. Groups III-V were treated with probucol at a doses of 250, 500 and 1000 mg/kg, respectively. Rats in Group II were fed a complex diet that includes alcohol, corn oil and pyrazole, and were injected intraperitoneally with CCl4 to induce hepatic fibrosis. Blood was obtained to assess markers of liver function. Liver samples were collected to evaluate mRNA and protein expression, histological changes and oxidative stress. 3. Probucol significantly attenuated the histological changes induced by ethanol + CCl4 and improved liver function. Expression levels of α-smooth muscle actin and collagen I was decreased in the probucol-treated groups. Moreover, probucol markedly suppressed increases in oxidative stress, ECM protein accumulation and cytokine production induced by ethanol + CCl4 . Finally, probucol inhibited activation of the extracellular signal-regulated kinase signalling pathway induced by ethanol + CCl4 . 4. Our findings reveal that probucol attenuates ethanol + CCl4 -induced liver fibrosis by inhibiting oxidative stress, ECM protein accumulation and cytokine production. These data suggest that probucol may be useful for the prevention and treatment of hepatic fibrosis.

Role of the lipid peroxidation product, 4-hydroxynonenal, in the development of nitrate tolerance

Tolerance to nitrates such as nitroglycerin (GTN) is associated with oxidative stress, inactivation of aldehyde dehydrogenase 2 (ALDH2), and decreased GTN-induced cGMP accumulation and vasodilation. We hypothesized that GTN-induced inactivation of ALDH2 results in increased 4-hydroxy-2-nonenal (HNE) adduct formation of key proteins involved in GTN bioactivation, and, consequently, an attenuated vasodilator response to GTN (i.e., tolerance). We used an in vivo GTN tolerance model, a cell culture model of nitrate action, and Aldh2(-/-) mice to assess whether GTN exposure resulted in HNE adduct formation, and whether exogenous HNE affected GTN-induced relaxation and cGMP accumulation. Immunoblot analysis indicated a marked increase in HNE adduct formation in GTN-tolerant porcine kidney epithelial cells (PK1) and in aortae from GTN-tolerant rats and untreated Aldh2(-/-) mice. Preincubation of PK1 cells with HNE resulted in a dose-dependent decrease in GTN-induced cGMP accumulation, and pretreatment of isolated rat aorta with HNE resulted in dose-dependent decreases in the vasodilator response to GTN, thus mimicking GTN-tolerance. Pretreatment of aortae from Aldh2(-/-) mice with 10 μM HNE resulted in a desensitized vasodilator response to GTN. In the in vivo rat tolerance model, changes in HNE adduct formation correlated well with the onset of GTN tolerance and tolerance reversal. Furthermore, coadministration of an HNE scavenger during the tolerance induction protocol completely prevented HNE adduct formation and GTN tolerance but did not prevent the inactivation of ALDH2. The data are consistent with a novel mechanism of GTN tolerance suggesting a primary role of HNE adduct formation in the development of GTN tolerance.

The thiocarbamate disulphide drug, disulfiram induces osteopenia in rats by inhibition of osteoblast function due to suppression of acetaldehyde dehydrogenase activity

Dithiocarbamates (DTC), a sulfhydryl group containing compounds, are extensively used by humans that include metam and thiram due to their pesticide properties, and disulfiram (DSF) as an alcohol deterrent. We screened these DTC in an osteoblast viability assay. DSF exhibited the highest cytotoxicity (IC50 488nM). Loss in osteoblast viability and proliferation was due to induction of apoptosis via G1 arrest. DSF treatment to osteoblasts reduced glutathione (GSH) levels and exogenous addition of GSH prevented DSF-induced reactive oxygen species generation and osteoblast apoptosis. DSF also inhibited osteoblast differentiation in vitro and in vivo, and the effect was associated with inhibition of aldehyde dehydrogenase (ALDH) activity. Out of various ALDH isozymes, osteoblasts expressed only ALDH2 and DSF downregulated its transcript as well as activity. Alda-1, a specific activator of ALDH2, stimulated osteoblast differentiation. Subcutaneous injection of DSF over the calvarium of new born rats reduced the differentiation phenotype of calvarial osteoblasts but increased the mRNA levels of Runx-2 and osteocalcin. DSF treatment at a human-equivalent dose of 30 mg/kg p.o. to adult Sprague Dawley rats caused trabecular osteopenia and suppressed the formation of mineralized nodule by bone marrow stromal cells. Moreover, DSF diminished bone regeneration at the fracture site. In growing rats, DSF diminished growth plate height, primary and secondary spongiosa, mineralized osteoid and trabecular strength. Substantial decreased bone formation was also observed in the cortical site of these rats. We conclude that DSF has a strong osteopenia inducing effect by impairing osteoblast survival and differentiation due to the inhibition of ALDH2 function.

Effect of overexpression of human aldehyde dehydrogenase 2 in LLC-PK1 cells on glyceryl trinitrate biotransformation and cGMP accumulation

BACKGROUND AND PURPOSE

Recent studies suggest a primary role for aldehyde dehydrogenase 2 (ALDH2) in mediating the biotransformation of organic nitrates, such as glyceryl trinitrate (GTN), to the proximal activator of soluble guanylyl cyclase (sGC), resulting in increased cGMP accumulation and vasodilation. Our objective was to assess the role of ALDH2 in organic nitrate action using a cell culture model.

EXPERIMENTAL APPROACH

Porcine renal epithelial (LLC-PK1) cells possess an intact NO-sGC-cGMP signaling system, and can be used as a biochemical model of organic nitrate action. We used a pcDNA3.1-human ALDH2 expression vector to establish a stably transfected cell line (PK1(ALDH2)) that overexpressed ALDH2, or small interfering RNA (siRNA) to deplete endogenous ALDH2, and assessed GTN biotransformation and GTN-induced cGMP formation.

KEY RESULTS

ALDH2 activity in the stably transfected cells was approximately sevenfold higher than wild-type cells or cells stably transfected with empty vector (PK1(vector)); and protein expression, as assessed by immunoblot analysis, was markedly increased. In PK1(ALDH2), GTN biotransformation was significantly increased as a result of increased glyceryl-1,2-dinitrate formation compared to wild-type or PK1(vector). However, the incubation of PK1(ALDH2) with 1 or 10 μM GTN did not alter GTN-induced cGMP accumulation compared with wild-type or PK1(vector) cells. Furthermore, siRNA-mediated depletion of ALDH2 had no effect on GTN-induced cGMP formation.

CONCLUSIONS AND IMPLICATIONS

In an intact cell system, neither overexpression nor depletion of ALDH2 affects GTN-induced cGMP formation, indicating that ALDH2 does not mediate the mechanism-based biotransformation of GTN to an activator of sGC.

Aldehyde dehydrogenase inhibition as a pathogenic mechanism in Parkinson disease

Parkinson disease (PD) is a neurodegenerative disorder particularly characterized by the loss of dopaminergic neurons in the substantia nigra. Pesticide exposure has been associated with PD occurrence, and we previously reported that the fungicide benomyl interferes with several cellular processes potentially relevant to PD pathogenesis. Here we propose that benomyl, via its bioactivated thiocarbamate sulfoxide metabolite, inhibits aldehyde dehydrogenase (ALDH), leading to accumulation of the reactive dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL), preferential degeneration of dopaminergic neurons, and development of PD. This hypothesis is supported by multiple lines of evidence. (i) We previously showed in mice the metabolism of benomyl to S-methyl N-butylthiocarbamate sulfoxide, which inhibits ALDH at nanomolar levels. We report here that benomyl exposure in primary mesencephalic neurons (ii) inhibits ALDH and (iii) alters dopamine homeostasis. It induces selective dopaminergic neuronal damage (iv) in vitro in primary mesencephalic cultures and (v) in vivo in a zebrafish system. (vi) In vitro cell loss was attenuated by reducing DOPAL formation. (vii) In our epidemiology study, higher exposure to benomyl was associated with increased PD risk. This ALDH model for PD etiology may help explain the selective vulnerability of dopaminergic neurons in PD and provide a potential mechanism through which environmental toxicants contribute to PD pathogenesis.

Aldehyde-stress resulting from Aldh2 mutation promotes osteoporosis due to impaired osteoblastogenesis

Osteoporosis is a complex disease with various causes, such as estrogen loss, genetics, and aging. Here we show that a dominant-negative form of aldehyde dehydrogenase 2 (ALDH2) protein, ALDH2*2, which is produced by a single nucleotide polymorphism (rs671), promotes osteoporosis due to impaired osteoblastogenesis. Aldh2 plays a role in alcohol-detoxification by acetaldehyde-detoxification; however, transgenic mice expressing Aldh2*2 (Aldh2*2 Tg) exhibited severe osteoporosis with increased levels of blood acetaldehyde without alcohol consumption, indicating that Aldh2 regulates physiological bone homeostasis. Wild-type osteoblast differentiation was severely inhibited by exogenous acetaldehyde, and osteoblastic markers such as osteocalcin, runx2, and osterix expression, or phosphorylation of Smad1,5,8 induced by bone morphogenetic protein 2 (BMP2) was strongly altered by acetaldehyde. Acetaldehyde treatment also inhibits proliferation and induces apoptosis in osteoblasts. The Aldh2*2 transgene or acetaldehyde treatment induced accumulation of the lipid-oxidant 4-hydroxy-2-nonenal (4HNE) and expression of peroxisome proliferator-activated receptor gamma (PPARγ), a transcription factor that promotes adipogenesis and inhibits osteoblastogenesis. Antioxidant treatment inhibited acetaldehyde-induced proliferation-loss, apoptosis, and PPARγ expression and restored osteoblastogenesis inhibited by acetaldehyde. Treatment with a PPARγ inhibitor also restored acetaldehyde-mediated osteoblastogenesis inhibition. These results provide new insight into regulation of osteoporosis in a subset of individuals with ALDH2*2 and in alcoholic patients and suggest a novel strategy to promote bone formation in such osteopenic diseases.

Changes in aldehyde dehydrogenase 2 expression in rat blood vessels during glyceryl trinitrate tolerance development and reversal

BACKGROUND AND PURPOSE

Recent studies have suggested an essential role for aldehyde dehydrogenase 2 (ALDH2) in the bioactivation of organic nitrates such as glyceryl trinitrate (GTN). In the present study, we utilized an in vivo GTN tolerance model to further investigate the role of ALDH2 in GTN bioactivation and tolerance.

EXPERIMENTAL APPROACH

We assessed changes in aortic ALDH activity, and in ALDH2 protein expression in various rat blood vessels (aorta, vena cava, femoral artery and femoral vein) during continuous GTN exposure (0.4 mg·h⁻¹ for 6, 12, 24 or 48 h) or after a 1-, 3- or 5-day drug-free period following a 48 h exposure to GTN, in relation to changes in vasodilator responses to GTN and in vascular GTN biotransformation.

KEY RESULTS

A decrease was observed in both ALDH2 protein expression (80% in tolerant veins and 30% in tolerant arteries after 48 h exposure to GTN) and aortic ALDH activity, concomitant with decreased vasodilator responses to GTN and decreased aortic GTN biotransformation. However, after a 24 h drug-free period following 48 h of GTN exposure, vasodilator responses to GTN and aortic GTN biotransformation activity had returned to control values, whereas vascular ALDH2 expression and aortic ALDH activity were still significantly depressed, and remained so for 3-5 days following cessation of GTN exposure.

CONCLUSIONS AND IMPLICATIONS

The dissociation of reduced ALDH activity and ALDH2 expression from the duration of the impaired vasodilator and biotransformation responses to GTN in nitrate-tolerant blood vessels, suggests that factors other than changes in ALDH2-mediated GTN bioactivation contribute to nitrate tolerance.

Tryptophan in alcoholism treatment I: kynurenine metabolites inhibit the rat liver mitochondrial low Km aldehyde dehydrogenase activity, elevate blood acetaldehyde concentration and induce aversion to alcohol

AIMS

The aims were to provide proofs of mechanism and principle by establishing the ability of kynurenine metabolites to inhibit the liver mitochondrial low K(m) aldehyde dehydrogenase (ALDH) activity after administration and in vivo, and to induce aversion to alcohol.

METHODS

Kynurenic acid (KA), 3-hydroxykynurenine (3-HK) and 3-hydroxyanthranilic acid (3-HAA) were administered to normal male Wistar rats and ALDH activity was determined both in vitro in liver homogenates and in vivo (by measuring blood acetaldehyde following ethanol administration). Alcohol consumption was studied in an aversion model in rats and in alcohol-preferring C57 mice.

RESULTS

ALDH activity was significantly inhibited by all three metabolites by doses as small as 1 mg/kg body wt. Blood acetaldehyde accumulation after ethanol administration was strongly elevated by KA and 3-HK and to a lesser extent by 3-HAA. All three metabolites induced aversion to alcohol in rats and decreased alcohol preference in mice.

CONCLUSIONS

The above kynurenine metabolites of tryptophan induce aversion to alcohol by inhibiting ALDH activity. An intellectual property covering the use of 3-HK and 3-HAA and derivatives thereof in the treatment of alcoholism by aversion awaits further development.

Tryptophan in alcoholism treatment II: inhibition of the rat liver mitochondrial low Km aldehyde dehydrogenase activity, elevation of blood acetaldehyde concentration and induction of aversion to alcohol by combined administration of tryptophan and benserazide

AIMS

The aims were to provide proofs of mechanism and principle by establishing the ability of the amino acid L-tryptophan (Trp) combined with the kynureninase inhibitor benserazide (BSZ) to inhibit the liver mitochondrial low K(m) aldehyde dehydrogenase (ALDH) activity after administration and in vivo and to induce aversion to alcohol.

METHODS

Trp, BSZ or both were administered to male Wistar rats and ALDH activity was determined both in vitro in liver homogenates and in vivo (by measuring acetaldehyde accumulation in blood after ethanol administration). Alcohol consumption was studied in an aversion model in rats and in alcohol-preferring C57 mice.

RESULTS

Combined administration of Trp + BSZ, but neither compound alone, produced a strong inhibition of ALDH activity and an increase in blood acetaldehyde concentration after ethanol, and induced aversion to alcohol in rats and decreased preference in mice. Another kynureninase inhibitor, carbidopa, induced aversion to alcohol by itself, which was reversed by Trp co-administration.

CONCLUSIONS

The present results establish a prior art for the use of a combination of Trp plus BSZ in the treatment of alcoholism by aversion, which merits rapid clinical development.

Effect of catalase activators and inhibitors on ethanol pharmacokinetic parameteres and ethanol and aldehyde-metabolizing enzyme activities in the rat liver and brain

The effects of catalase regulators (aminotriazole, lead acetate, taurine, di-2-ethylhexylphthalate) on the preference for ethanol, its pharmacokinetics, and activities of rat liver and brain ethanol and acetaldehyde-metabolizing enzymes were studied.Lead acetate (100 mg/kg, i.p., 7 days), aminotriazole (1 g/kg, i.p., 7 days), and taurine (650 mg/kg, i.g., 14 days) decreased ethanol consumption under conditions of free choice (10% ethanol water), whereas di-2-ethylhexylphthalate (300 mg/kg, i.g., 7 days) did not exert any effect on this parameter.Taurine, lead acetate and di-2-ethylhexylphthalate significantly activated liver ADH, MEOS and catalase peroxidase activity. Aminotriazole also activated ADH and MEOS, but inhibited liver catalase. The activities of liver and brain AlDH as well as catalase were insignificantly changed by this treatment.The 7-day administration of lead acetate, di-2-ethylhexylphthalate and aminotriazole administrations significantly influenced the ethanol (2g/kg., i.p.) pharmacokinetic parameters: the area under the pharmacokinetic curve and the elimination half-life time were significantly reduced, whereas the elimination constant and clearance were increased. This unequivocally indicates accelerated ethanol elimination. The 14-day ingestion of taurine insignificantly changed the parameters of ethanol pharmacokinetics in rats.

Effects of chronic iron deficiency anaemia on myoglobin content, enzyme activity, and capillary density in the human skeletal muscle

The influence of chronic iron deficiency anaemia on myoglobin content, maximal enzyme activities and capillarization in the human skeletal muscle was investigated. Muscle samples from musculus vastus lateralis were screened in an Indonesian population. The causes of iron deficiency were chronic intestinal bleeding or repeated pregnancy combined with low iron intake. The maximal activities of iron-dependent and non-iron-dependent glycolytic and oxidative enzymes as well as myoglobin showed similar values in the iron-deficient group and the matched control group. The activities of the oxidative enzymes in both the iron-deficient group and the controls were lower, however, compared even to untrained Swedish subjects. The capillary density was essentially within a normal range in both groups. It is concluded that chronic iron deficiency anaemia of a moderate or severe degree, with Hb concentrations of about 80-100 g.1(-1), does not cause an impaired biochemical function of the human skeletal muscle.

The UChA and UChB rat lines: metabolic and genetic differences influencing ethanol intake

Ethanol non-drinker (UChA) and drinker (UChB) rat lines derived from an original Wistar colony have been selectively bred at the University of Chile for over 70 generations. Two main differences between these lines are clear. (1) Drinker rats display a markedly faster acute tolerance than non-drinker rats. In F2 UChA x UChB rats (in which all genes are 'shuffled'), a high acute tolerance of the offspring predicts higher drinking than a low acute tolerance. It is further shown that high-drinker animals 'learn' to drink, starting from consumption levels that are one half of the maximum consumptions reached after 1 month of unrestricted access to 10% ethanol and water. It is likely that acquired tolerance is at the basis of the increases in ethanol consumption over time. (2) Non-drinker rats carry a previously unreported allele of aldehyde dehydrogenase-2 (Aldh2) that encodes an enzyme with a low affinity for Nicotinamide-adenine-dinuclectide (NAD+) (Aldh2(2)), while drinker rats present two Aldh2 alleles (Aldh2(1) and Aldh2(3)) with four- to fivefold higher affinities for NAD+. Further, the ALDH2 encoded by Aldh2(1) also shows a 33% higher Vmax than those encoded by Aldh2(2) and Aldh2(3). Maximal voluntary ethanol intakes are the following: UChA Aldh2(2)/Aldh2(2) = 0.3-0.6 g/kg/day; UChB Aldh2(3)/Aldh2(3) = 4.5-5.0 g/kg/day; UChB Aldh2(1)/Aldh2(1) = 7.0-7.5 g/kg/day. In F2 offspring of UChA x UChB, the Aldh2(2)/Aldh2(2) genotype predicts a 40-60% of the alcohol consumption. Studies also show that the low alcohol consumption phenotype of Aldh2(2)/Aldh2(2) animals depends on the existence of a maternally derived low-activity mitochondrial reduced form of nicotinamide-adenine-dinucleotide (NADH)-ubiquinone complex I. The latter does not influence ethanol consumption of animals exhibiting an ALDH2 with a higher affinity for NAD+. An illuminating finding is the existence of an 'acetaldehyde burst' in animals with a low capacity to oxidize acetaldehyde, being fivefold higher in UChA than in UChB animals. We propose that such a burst results from a great generation of acetaldehyde by alcohol dehydrogenase in pre-steady-state conditions that is not met by the high rate of acetaldehyde oxidation in mitochondria. The acetaldehyde burst is seen despite the lack of differences between UChA and UChB rats in acetaldehyde levels or rates of alcohol metabolism in steady state. Inferences are drawn as to how these studies might explain the protection against alcoholism seen in humans that carry the high-activity alcohol dehydrogenase but metabolize ethanol at about normal rates.

The role of retinoid X receptor alpha in regulating alcohol metabolism

There is substantial overlap in retinol and alcohol metabolism. Mice that lack retinoic acid (RA) receptor retinoid X receptor alpha (RXRalpha) expression in the liver are more susceptible to alcoholic liver disease. To investigate the interaction between RXRalpha and alcoholic liver disease, ethanol metabolism was studied in hepatocyte RXRalpha-deficient [RXRalpha knockout (KO)] mice. Hepatocyte RXRalpha deficiency resulted in a significant increase in hepatic alcohol dehydrogenase (ADH) activity, ADH1 protein, but not Adh1 mRNA. Polysomal distribution analysis indicated that more polysome-associated Adh1 mRNA was present in the mutant mouse livers, suggesting increased ADH1 protein synthesis in RXRalpha KO mice compared with wild-type mice. However, ADH2 and ADH3 enzyme activities were not affected by RXRalpha deficiency. Although ethanol clearance was increased, acetaldehyde elimination was reduced when RXRalpha was not expressed in the liver. Both mitochondrial aldehyde dehydrogenase (ALDH) 2 and cytosolic ALDH activities were reduced in the mutant mice compared with the wild type. Western blot analysis revealed that the levels of ALDH1A1 and ALDH1A2 were decreased in the mutant mice. Semiquantitative reverse transcriptase-polymerase chain reaction indicated that liver Aldh1a1 mRNA level was also reduced due to the lack of RXRalpha expression. Thus, RXRalpha differentially affects ADH and ALDH activity, leading to an increase in alcohol clearance, but a reduction in acetaldehyde elimination. In addition, CYP2E1 as well as mitochondrial and cytosolic glutathione S-transferase activities were significantly lower in RXRalpha KO mice than in wild-type mice. Our results reveal the central role of RXRalpha in ethanol metabolism.

Zinc supplementation prevents alcoholic liver injury in mice through attenuation of oxidative stress

Alcoholic liver disease is associated with zinc decrease in the liver. Therefore, we examined whether dietary zinc supplementation could provide protection from alcoholic liver injury. Metallothionein-knockout and wild-type 129/Sv mice were pair-fed an ethanol-containing liquid diet for 12 weeks, and the effects of zinc supplementation on ethanol-induced liver injury were analyzed. Zinc supplementation attenuated ethanol-induced hepatic zinc depletion and liver injury as measured by histopathological and ultrastructural changes, serum alanine transferase activity, and hepatic tumor necrosis factor-alpha in both metallothionein-knockout and wild-type mice, indicating a metallothionein-independent zinc protection. Zinc supplementation inhibited accumulation of reactive oxygen species, as indicated by dihydroethidium fluorescence, and the consequent oxidative damage, as assessed by immunohistochemical detection of 4-hydroxynonenal and nitrotyrosine and quantitative analysis of malondialdehyde and protein carbonyl in the liver. Zinc supplementation suppressed ethanol-elevated cytochrome P450 2E1 activity but increased the activity of alcohol dehydrogenase in the liver, without affecting the rate of blood ethanol elimination. Zinc supplementation also prevented ethanol-induced decreases in glutathione concentration and glutathione peroxidase activity and increased glutathione reductase activity in the liver. In conclusion, zinc supplementation prevents alcoholic liver injury in an metallothionein-independent manner by inhibiting the generation of reactive oxygen species (P450 2E1) and enhancing the activity of antioxidant pathways.

Characterization of S-(N,N-Dialkylaminocarbonyl)cysteine Adducts and Enzyme Inhibition Produced by Thiocarbamate Herbicides in the Rat

Thiocarbamates are a major class of herbicides used extensively in the agricultural industry. It has been shown that thiocarbamates can form reactive sulfoxide and sulfone intermediates, which may be involved in the toxicity of thiocarbamates through covalent modification of cysteine and serine active sites of enzymes. Molinate has been shown to generate an S-hexahydro-1H-azepine-1-carbonyl adduct on the Cys-125 residue of the beta2- and beta3-chains of rat globin analogous to that reported for disulfiram and to inhibit aldehyde dehydrogenase and nonspecific esterase activity. The present study examined whether other thiocarbamate herbicides produce similar covalent protein modifications and enzyme inhibition to that reported for molinate and whether S-(N,N-dialkylaminocarbonyl)cysteine adduct levels are correlated to enzyme inhibition or the structure of thiocarbamate herbicides. Additionally, the potential of molinate to act as a peripheral demyelinating agent similar to disulfiram was evaluated. To address these aims, rats were exposed ip to molinate, vernolate, ethiolate, EPTC, or butylate for 5 days after which hemogloblin was isolated and analyzed for protein adducts using HPLC and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. In addition, brain, liver, and testes mitochondrial and microsomal fractions were assayed for nonspecific esterase, low Km ALDH, or total ALDH activities, and S-(N,N-dialkylaminocarbonyl)cysteine adducts were measured by LC/MS/MS. For the neurotoxicity assessments, rats were administered molinate parenterally for subchronic periods and morphological evaluations performed on peripheral nerves. All of the thiocarbamates except butylate produced S-(N,N-dialkylaminocarbonyl)cysteine adducts on globin and the quantity of adducts detected decreased with increasing size of the nitrogen substituents. In contrast, a clear relationship between cysteine modification in mitochondrial and microsomal samples to nitrogen substituents was not evident, and although molinate produced relatively high levels of adducts and esterase inhibition and butylate low levels of adducts and esterase inhibition for most samples, in general, the level of S-(N,N-dialkylaminocarbonyl)cysteine adducts did not appear to be related to enzyme inhibition. Molinate did not produce segmental demyelination in peripheral nerve, suggesting that molinate and possibly other thiocarbamates do not share the neurotoxic potential of dithiocarbamates.

Brain mitochondrial aldehyde dehydrogenase: relation to acetaldehyde aversion in low-alcohol-drinking (UChA) and high-alcohol-drinking (UChB) rats

Previous reports indicate that the low-drinker (UChA) rats, when compared to high-drinker (UChB) rats, display lower mitochondrial aldehyde dehydrogenase (ALDH2) activity due to a mutation of the Aldh2 gene. Because a later study found line differences in sensitivity to the aversive effects of acetaldehyde (AcH) administered intraperitoneally (i.p.), which were not associated with the line difference detected in blood AcH levels, the present study examined the contribution of brain ALDH2 activity to AcH aversion in UChA and UChB rats. In experiment 1, we established the dose - response curves for AcH aversion (25, 50 or 100 mg/kg i.p.) in rats of both lines by using a conditioned taste aversion (CTA) paradigm. The results confirm our previous finding that UChA and UChB rats presented marked differences in their AcH aversion thresholds, which were not associated with the line differences detected in blood AcH levels. In experiment 2, the possibility that the inhibition of the brain ALDH2 would lower the AcH aversion threshold in both lines was studied by determining the effect of cyanamide (10 mg/kg i.p.) pretreatment, an inhibitor of ALDH, on AcH aversion, blood AcH levels and brain ALDH2 activity. The finding that blocking the brain ALDH2 (52%) by cyanamide can make a non-aversive dose of AcH (25 mg/kg) aversive to UChA and UChB rats at blood AcH levels comparable to those induced by a non-aversive dose of AcH (100 mg/kg) in control UChB rats indicates that the line difference in AcH aversion is associated more with brain ALDH2 activity than with liver ALDH2 activity.

Role of mitochondrial aldehyde dehydrogenase in nitrate tolerance

Glyceryl trinitrate (GTN) is used in the treatment of angina pectoris and cardiac failure, but the rapid onset of GTN tolerance limits its clinical utility. Research suggests that a principal cause of tolerance is inhibition of an enzyme responsible for the production of physiologically active concentrations of NO from GTN. This enzyme has not conclusively been identified. However, the mitochondrial aldehyde dehydrogenase (ALDH2) is inhibited in GTN-tolerant tissues and produces NO2- from GTN, which is proposed to be converted to NO within mitochondria. To investigate the role of this enzyme in GTN tolerance, cumulative GTN concentration-response curves were obtained for both GTN-tolerant and -nontolerant rat aortic rings treated with the ALDH inhibitor cyanamide or the ALDH substrate propionaldehyde. Tolerance to GTN was induced using both in vivo and in vitro protocols. The in vivo protocol resulted in almost complete inhibition of ALDH2 activity and GTN biotransformation in hepatic mitochondria, indicating that long-term GTN exposure results in inactivation of the enzyme. Treatment with cyanamide or propionaldehyde caused a dose-dependent increase in the EC50 value for GTN-induced relaxation of similar magnitude in both tolerant and nontolerant aorta, suggesting that although cyanamide and propionaldehyde inhibit GTN-induced vasodilation, these inhibitors do not affect the enzyme or system involved in tolerance development to GTN. Treatment with cyanamide or propionaldehyde did not significantly inhibit 1,1-diethyl-2-hydroxy-2-nitrosohydrazine-mediated vasodilation in tolerant or nontolerant aorta, indicating that these ALDH inhibitors do not affect the downstream effectors of NO-induced vasodilation. Immunoblot analysis indicated that the majority of vascular ALDH2 is present in the cytoplasm, suggesting that mitochondrial biotransformation of GTN by ALDH2 plays a minor role in the overall vascular biotransformation of GTN by this enzyme.

In vitro metabolism of the mammalian soluble epoxide hydrolase inhibitor, 1-cyclohexyl-3-dodecyl-urea

The metabolism of the soluble epoxide hydrolase (sEH) inhibitor, 1-cyclohexyl-3-dodecyl-urea (CDU), was studied in rat and human hepatic microsomes. The microsomal metabolism of CDU enhanced sEH inhibition potency of the reaction mixture and resulted in the formation of several metabolites. During the course of this study, a sensitive and specific high-performance liquid chromatography with tandem mass spectrometry analytical method was developed to investigate simultaneously the production of these metabolites. In both rat and human hepatic microsomes, CDU was ultimately transformed into the corresponding omega-carboxylate; however, the rodent tissue appeared to perform this transformation more rapidly. After a 60-min incubation in rat hepatic microsomes, the percentage of residual CDU, the omega-carboxylate, and the intermediary omega-hydroxyl were about 20%, 20%, and 50%, respectively. Carbon monoxide inhibited the metabolism of CDU by rat hepatic microsomes, suggesting that the initial step is catalyzed by cytochrome P450. Further metabolism was enhanced by the addition of NAD, suggesting that dehydrogenases are associated with intermediate metabolic steps. Regardless, the ultimate product of microsomal metabolism, 12-(3-cyclohexyl-ureido)-dodecanoic acid, is also an excellent sEH inhibitor with several hundred-fold higher solubility, supporting the hypothesis that CDU has prodrug characteristics. These findings will facilitate the rational design and optimization of sEH inhibitors with better physical properties and improved metabolic stability.

Comparative analysis of hepatic ethanol metabolism in Fawn-Hooded and Wistar-Kyoto rats

Results of a number of studies have supported the suggestion that a correlation exists between voluntary ethanol consumption and enhanced ethanol metabolism in some (but not all) rodent strains. However, as yet, the capacity for alcohol-preferring Fawn-Hooded (FH) rats to metabolize ethanol has not been investigated. Hence, the aim of the current study was to compare the activities of the major hepatic enzymes involved in ethanol metabolism--cytosolic alcohol dehydrogenase (ADH) and mitochondrial aldehyde dehydrogenase (ALDH)--in the FH rat and its alcohol-nonpreferring counterpart, the Wistar-Kyoto (WKY) rat. In addition, the effect of chronic (5 weeks in vivo) ethanol pretreatment on the activity of these enzymes was investigated. Alcohol-naive FH rats were found to have significantly higher ADH activity (+61%) and no significant change in ALDH activity when compared with findings for WKY rats. In addition, chronic ethanol self-administration produced a small increase in ADH activity (+14%) in WKY rats only. Taken as a whole, these findings are the first to demonstrate an increased in vitro hepatic ethanol metabolism in alcohol-preferring FH rats and further demonstrate an association between hepatic ethanol metabolism and voluntary ethanol self-administration in rodents.

Aversion to acetaldehyde: differences in low-alcohol-drinking (UChA) and high-alcohol-drinking (UChB) rats

We have previously found the existence of a relation between activity of the brain mitochondrial aldehyde dehydrogenase (ALDH2) and consumption of ethanol in rats of the low-alcohol-drinking (UChA) and the high-alcohol-drinking (UChB) strains. The aim of the present study was to determine whether UChA and UChB rats also differed in sensitivity to the aversive effects of acetaldehyde (AcH). Aversion to AcH was studied by using a conditioned taste aversion (CTA) paradigm. Ethanol naive UChA and UChB rats were administered AcH intraperitoneally (50, 100, or 150 mg/kg) or saline and exposed to a banana-flavored solution during five conditioning trials. A strong dose-dependent CTA to AcH was found in UChA rats, whereas UChB rats did not show a CTA to any dose of AcH. At equal doses of AcH, cerebral venous blood AcH levels in UChA rats were consistently higher than in UChB rats, a finding that may reflect the previously observed differences in the activity of ALDH2 between these strains. However, this observation is unlikely to explain fully the differences observed because aversion to AcH was developed in the UChA strain at blood levels of AcH that did not produce any aversion in the UChB strain. These results support the suggestion that, for the first time, differences in central or systemic effects of AcH per se may play a major role in determining the aversion to AcH in drinker and nondrinker animals.

Human kidney tubules detoxify chloroacetaldehyde, a presumed nephrotoxic metabolite of ifosfamide

The nephrotoxic effects of the antineoplastic drug ifosfamide have been attributed to its hepatic metabolite chloroacetaldehyde. The effects of chloroacetaldehyde on isolated human kidney cortex tubules metabolizing lactate (a physiologic substrate in human kidneys) were investigated. At concentrations of > or =0.5 mM, chloroacetaldehyde was toxic to the human kidney tubules, as demonstrated by a dramatic decrease in cellular ATP levels and a large increase in lactate dehydrogenase release; chloroacetaldehyde also stimulated pyruvate accumulation and inhibited lactate removal and glucose synthesis. These effects, which were associated with incomplete disappearance of chloroacetaldehyde and extensive depletion of the cellular CoA, acetyl-CoA, and glutathione contents, were prevented by the addition of thiol-protecting drugs (mesna and amifostine). Human kidney tubules were demonstrated to metabolize chloroacetaldehyde at high rates, presumably via aldehyde dehydrogenase, which is very active in human kidneys. Carbon-13 nuclear magnetic resonance spectroscopy measurements indicated that human kidney tubules converted [2-(13)C]chloroacetaldehyde to [2-(13)C]chloroacetate, the further metabolism of which was very limited. At equimolar concentrations, chloroacetate was much less toxic than chloroacetaldehyde, indicating that chloroacetate synthesis from chloroacetaldehyde by human kidney tubules represents a detoxification mechanism that could play a role in vivo in preventing or limiting the nephrotoxic effects observed during ifosfamide therapy.

Fatty aldehyde dehydrogenase: genomic structure, expression and mutation analysis in Sjögren-Larsson syndrome

Fatty aldehyde dehydrogenase (FALDH) is a microsomal enzyme that catalyzes the oxidation of medium- and long-chain aliphatic aldehydes derived from metabolism of fatty alcohol, phytanic acid, ether glycerolipids and leukotriene B4. The FALDH gene (ALDH3A2) in man and mouse consists of 11 exons and is closely linked to the gene for ALDH3. In both species, alternative splicing results in formation of a second minor protein, FALDHv, that has a unique carboxy-terminal end. The functional significance of this alternate protein is not known. In humans, mutations in the FALDH gene cause Sjögren-Larsson syndrome (SLS), which is characterized by ichthyosis, mental retardation and spasticity. Missense mutations involving 24 amino acid positions in FALDH have been identified. These amino acids are more highly conserved among related class 3 aldehyde dehydrogenase enzymes than expected, suggesting that they are critically important for protein folding, catalysis or stability. Studies of mutations in SLS should prove useful for understanding structure-function correlations in FALDH and other aldehyde dehydrogenase proteins.

Effect of exposure to a country liquor (Toddy) during gestation on lipid metabolism in rats

The objective of this study was to determine the effects of country liquor Toddy and its equivalent quantity of ethanol on lipid metabolism during gestation in rats. Female rats weighing an average of 125 g were exposed to Toddy (24.5 ml/body weight/day) and ethanol (0.52 ml/kg body weight/day) for 15 days before conception and throughout gestation. On the 19th day of gestation, altered liver function and hyperlipidemia was seen in both the treated groups. Altered liver function was evidenced by the increased activity of alcohol dehydrogenase, aldehyde dehydrogenase, glutamic oxaloacetic transaminase or aspartate amino transferase (GOT), glutamic pyruvic transaminase or alanine amino transferase (GPT) and gamma glutamyl transpeptidase (GGT). Hyperlipidemia was caused by increased biosynthesis and decreased degradation of lipids. The incorporation of 14C acetate in lipids and activities of HMG CoA reductase and lipogenic enzymes were elevated and activity of LPL and bile acids contents were decreased. Toddy treated rats were more severely affected than those receiving an equivalent quantity of ethanol. Toddy seemed to potentiate the toxicity induced by alcohol indicating the role of the nonethanolic portion. Hepatic functions were also affected.

Metabolism of retinaldehyde and other aldehydes in soluble extracts of human liver and kidney

Purification and characterization of enzymes metabolizing retinaldehyde, propionaldehyde, and octanaldehyde from four human livers and three kidneys were done to identify enzymes metabolizing retinaldehyde and their relationship to enzymes metabolizing other aldehydes. The tissue fractionation patterns from human liver and kidney were the same, indicating presence of the same enzymes in human liver and kidney. Moreover, in both organs the major NAD(+)-dependent retinaldehyde activity copurified with the propionaldehyde and octanaldehyde activities; in both organs the major NAD(+)-dependent retinaldehyde activity was associated with the E1 isozyme (coded for by aldh1 gene) of human aldehyde dehydrogenase. A small amount of NAD(+)-dependent retinaldehyde activity was associated with the E2 isozyme (product of aldh2 gene) of aldehyde dehydrogenase. Some NAD(+)-independent retinaldehyde activity in both organs was associated with aldehyde oxidase, which could be easily separated from dehydrogenases. Employing cellular retinoid-binding protein (CRBP), purified from human liver, demonstrated that E1 isozyme (but not E2 isozyme) could utilize CRBP-bound retinaldehyde as substrate, a feature thought to be specific to retinaldehyde dehydrogenases. This is the first report of CRBP-bound retinaldehyde functioning as substrate for aldehyde dehydrogenase of broad substrate specificity. Thus, it is concluded that in the human organism, retinaldehyde dehydrogenase (coded for by raldH1 gene) and broad substrate specificity E1 (a member of EC 1. 2.1.3 aldehyde dehydrogenase family) are the same enzyme. These results suggest that the E1 isozyme may be more important to alcoholism than the acetaldehyde-metabolizing enzyme, E2, because competition between acetaldehyde and retinaldehyde could result in abnormalities associated with vitamin A metabolism and alcoholism.

Trichloroethylene inhibits aldehyde dehydrogenase only for aliphatic aldehydes of short chains in rats

The effects of trichloroethylene (TCE) administration on aldehyde dehydrogenase (ALDH) and cytochrome P450 isozymes were studied in rats and compared with those of methanol. Intragastric administration of TCE to rats at 0.05 or 0.2 ml/kg for 1 week significantly inhibited ALDH activity for aliphatic aldehydes of short chains in the mitochondrial and cytosolic fractions of rat liver, respectively, but had no effect on the activity for long chain aliphatic aldehydes. ALDH activity catalyzing the metabolism of some aromatic aldehydes was even induced by TCE. Microsomal ALDH activity was not decreased by TCE treatment. A kinetic study showed that the low-Km isozyme of ALDH for propionaldehyde in mitochondrial and cytosolic fractions was inhibited by TCE treatment. Addition of TCE, trichloroethanol or trichloroacetic acid to the in vitro assay system did not affect the activity for acetaldehyde, but chloral hydrate at 0.02 mM decreased the activity by 42 and 35% in cytosol and the 700 x g supernatant, respectively. Methanol treatment, on the other hand, had no effect on any ALDH activity. Both TCE and methanol significantly induced CYP2E1 in rat liver. The combined effects of TCE on ALDH and cytochrome P450 may account for the degreasers' flush. Exposure to TCE and methanol may result in a change in the metabolism and toxicity of other chemicals.

Glutathione carbamoylation with S-methyl N,N-diethylthiolcarbamate sulfoxide and sulfone. Mitochondrial low Km aldehyde dehydrogenase inhibition and implications for its alcohol-deterrent action

S-Methyl N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO) and sulfone (DETC-MeSO2) both inhibit rat liver low Km aldehyde dehydrogenase (ALDH2) in vitro and in vivo (Nagendra et al., Biochem Pharmacol 47: 1465-1467, 1994). DETC-MeSO has been shown to be a metabolite of disulfiram, but DETC-MeSO2 has not. Studies were carried out to further investigate the inhibition of ALDH2 by DETC-MeSO and DETC-MeSO2. In an in vitro system containing hydrogen peroxide and horseradish peroxidase, the rate of DETC-MeSO oxidation corresponded to the rate of DETC-MeSO2 formation. Carbamoylation of GSH by both DETC-MeSO and DETC-MeSO2 was observed in a rat liver S9 fraction. Carbamoylation of GSH was not observed in the presence of N-methylmaleimide. In in vitro studies, DETC-MeSO and DETC-MeSO2 were equipotent ALDH2 inhibitors when solubilized mitochondria were used, but DETC-MeSO was approximately four times more potent than DETC-MeSO2 in intact mitochondria. In studies with rats, the dose (i.p. or oral) required to inhibit 50% ALDH2 (ED50) was 3.5 mg/kg for DETC-MeSO and approximately 35 mg/kg for DETC-MeSO2, approximately a 10-fold difference. Furthermore, maximum ALDH2 inhibition occurred 1 hr after DET(-MeSO administration, whereas maximal ALDH2 inhibition occurred 8 hr after DETC-MeSO2 dosing. DETC-MeSO is, therefore, not only a more potent ALDH2 inhibitor than DETC-MeSO2 in vivo, but also in vitro when intact mitochondria are utilized. The in vitro results thus support the in vivo findings. Since oxidation of DETC-MeSO can occur both enzymatically and non-enzymatically, it is possible that DETC-MeSO2 is formed in vivo. DETC-MeSO2, however, is not as effective as DETC-MeSO in inhibiting ALDH2, probably because it has difficulty penetrating the mitochondrial membrane. Thus, even if DETC-MeSO2 is formed in vivo from DETC-MeSO, it is the metabolite DETC-MeSO that is most likely responsible for the inhibition of ALDH2 after disulfiram administration.

Effect of in utero exposure of Toddy (coconut palm wine) on liver function and lipid metabolism in rat fetuses

The objective of this study was to determine the effects of a country liquor Toddy (Coconut palm wine) and an equivalent quantity of ethanol on liver function and lipid metabolism in utero. Female albino rats with an average weight of 125 +/- 5 g were exposed to Toddy from coconut palm (24.5 ml/kg body weight/day) and ethanol (0.52 ml/kg body weight/day) for 15 days before conception and during pregnancy. On day 13 and day 19 of gestation, altered liver function and hyperlipidemia were seen in the fetuses of both the treated groups. Altered liver function was evidenced by the increased activity of alcohol dehydrogenase, aldehyde dehydrogenase, glutamic oxaloacetic transaminase (aspartate amino transferase (GOT)), glutamic pyruvic transaminase (alanine amino transferase (GPT)). Hyperlipidemia was caused by increased biosynthesis since the incorporation of 14C acetate into lipids and activities of HMG CoA reductase and lipogenic enzymes were elevated. Toddy treated fetuses were more severely affected than those exposed to an equivalent quantity of ethanol. Toddy seemed to potentiate the toxicity induced by alcohol suggesting the role of non alcoholic components. Hepatic functions of the day 13 fetuses were effected to a lesser degree than those in the day 19 hepatic liver.

Inhibition of human mitochondrial aldehyde dehydrogenase by the disulfiram metabolite S-methyl-N,N-diethylthiocarbamoyl sulfoxide: structural characterization of the enzyme adduct by HPLC-tandem mass spectrometry

S-Methyl-N,N-diethylthiocarbamoyl sulfoxide (MeDTC-SO) is a known metabolite of the aversion therapy drug disulfiram (DSF). MeDTC-SO is also a potent inhibitor of human mitochondrial aldehyde dehydrogenase (hmALDH) with an IC50 of 1.5 microM. Inhibition of the enzyme by MeDTC-SO resulted in the addition of approximately 100 Da to the molecular mass of the intact protein, as determined by on-line HPLC-electrospray ionization MS (LC-MS). Dialysis of the inhibited protein did not reverse the inhibition, and the molecular mass of 54,533 Da (+/- 0.01%) remained unchanged, indicating that a covalent modification of the protein had occurred. Proteolytic digestion of hmALDH under basic conditions using trypsin at pH 7.8 revealed that the adduct was base labile. However, treating the adducted protein with endopeptidase-Glu-C at pH 3.7 produced a peptide adduct at MH+ = 4924, tentatively attributable to a carbamoylated peptide. This peptide contains three adjacent cysteines, one of which has been implicated as a key amino acid in the highly conserved active site region of ALDH. A pepsin digestion of hmALDH carried out at pH 3.7 and subsequent LC-MS analysis revealed an ion at MH2(2+) = 501.5, corresponding to the carbamoylated peptide FNQGQC1C2C3. This peptide contains the same adjacent active site cysteines. This latter peptide was subjected to LC-MS/MS, which enabled us to determine that the site of carbamoylation was at Cys2. The MS/MS product ion data also confirmed the presence of a carbamoyl group as the adduct species.

Polyenylphosphatidylcholine attenuates alcohol-induced fatty liver and hyperlipemia in rats

Chronic administration of a soybean-derived polyenylphosphatidylcholine (PPC) extract prevents the development of cirrhosis in alcohol-fed baboons. To assess whether this phospholipid also affects earlier changes induced by alcohol consumption (such as fatty liver and hyperlipemia), 28 male rat littermates were pair-fed liquid diets containing 36% of energy either as ethanol or as additional carbohydrate for 21 d, and killed 90 min after intragastric administration of the corresponding diets. Half of the rats were given PPC (3 g/l), whereas the other half received the same amount of linoleate (as safflower oil) and choline (as bitartrate salt). PPC did not affect diet or alcohol consumption [15.4 +/- 0.5 G/(kg.d)], but the ethanol-induced hepatomegaly and the hepatic accumulation of lipids (principally triglycerides and cholesterol esters) and proteins were about half those in rats not given PPC. The ethanol-induced postprandial hyperlipemia was lower with PPC than without, despite an enhanced fat absorption and no difference in the level of plasma free fatty acids. The attenuation of fatty liver and hyperlipemia was associated with correction of the ethanol-induced inhibition of mitochondrial oxidation of palmitoyl-1-carnitine and the depression of cytochrome oxidase activity, as well as the increases in activity of serum glutamate dehydrogenase and aminotransferases. Thus, PPC attenuates early manifestations of alcohol toxicity, at least in part, by improving mitochondrial injury. These beneficial effects of PPC at the initial stages of alcoholic liver injury may prevent or delay the progression to more advanced forms of alcoholic liver disease.

Cloning of a cDNA encoding a constitutively expressed rat liver cytosolic aldehyde dehydrogenase

The presence of a constitutively expressed aldehyde dehydrogenase (ALDH) in the rat liver cytosol is controversial (Tottmar et al., 1973; Lindahl and Evces, 1984; Berger and Weiner, 1977; Tank et al., 1981; Truesdale-Mahoney et al., 1981; Cao et al., 1989). A cDNA encoding a constitutively expressed rat liver cytosolic class 1 ALDH was cloned using a PCR-based strategy. The open reading frame consisted of 1503 nucleotides which encoded a protein of 501 amino acids. In order to compare the rat and human nucleotide sequences, we sequenced the entire open reading frame of a human liver cytosolic ALDH cDNA clone (Zheng et al., 1993). Rat liver constitutively expressed cytosolic ALDH was 99.7, 91.8, 89.0, and 83.8% identical to rat kidney, mouse liver, rat liver phenobarbital-inducible, and human liver cytosolic class 1 ALDH cDNAs, respectively. Northern blot analysis indicated that constitutively expressed rat cytosolic ALDH mRNA is expressed in lung, kidney, liver, skeletal muscle, and testis, with weak expression in heart and brain. These results strongly suggest that a constitutively expressed ALDH is present in rat liver cytosol.

S-methyl-N,N-diethylthiocarbamate sulfoxide and S-methyl-N,N-diethylthiocarbamate sulfone, two candidates for the active metabolite of disulfiram

The mechanism of action of disulfiram involves inhibition of hepatic aldehyde dehydrogenase (ALDH). Although disulfiram inhibits ALDH in vitro, it is believed that the drug is too short-lived in vivo to inhibit the enzyme directly. The ultimate inhibitor is thought to be a metabolite of disulfiram. In this study, we examined the effects of S-methyl-N,N-diethylthiocarbamate (MeDTC) sulfoxide and S-methyl-N,N-diethylthiocarbamate sulfone (confirmed and proposed metabolites of disulfiram, respectively) on rat liver mitochondrial low K(m) ALDH. MeDTC sulfoxide and MeDTC sulfone, in 10-min incubations with detergent-solubilized mitochondria, inhibited ALDH activity with an IC50 (mean +/- SD) of 0.93 +/- 0.04 and 0.53 +/- 0.11 microM, respectively, compared with 7.4 +/- 1.0 microM for the parent drug disulfiram. Inhibition by MeDTC sulfone and MeDTC sulfoxide, both at 0.6 microM, was time-dependent, following apparent pseudo-first-order kinetics with a t1/2 of inactivation of 3.5 and 8.8 min, respectively. Dilution of ALDH inhibited by either sulfoxide or sulfone did not restore activity, an indication of irreversible inhibition. Addition of glutathione (50 to 1000 microM) to ALDH before the inhibitors did not alter the inhibition by MeDTC sulfoxide. In contrast, the inhibition by MeDTC sulfone was decreased > 10-fold (IC50 = 6.3 microM) by 50 microM of glutathione and almost completely abolished by 500 microM of glutathione. The cofactor NAD, in a concentration-dependent manner, protected ALDH from inhibition by MeDTC sulfoxide and MeDTC sulfone. In incubations with intact mitochondria, the potency of the two compounds was reversed (IC50 of 9.2 +/- 3.6 and 0.95 +/- 0.30 microM for the MeDTC sulfone and sulfoxide, respectively). Our results suggest that MeDTC sulfone is highly reactive with normal cellular constituents (e.g., glutathione), which may protect ALDH from inhibition, unless this inhibitor is formed very near the target enzyme. In contrast, MeDTC sulfoxide is a better candidate for the ultimate active metabolite of disulfiram, because it is more likely to be sufficiently stable to diffuse from a distant site of formation, such as the endoplasmic reticulum, penetrate the mitochondria, and react with ALDH located in the mitochondrial matrix.

Molecular mechanism of null expression of aldehyde dehydrogenase-1 in rat liver

In isozyme systems in general, the pattern of tissue-dependent expression of a given type of isozyme is uniform in various mammalian species. In contrast, a major cytosolic aldehyde dehydrogenase isozyme, termed ALDH1, which is strongly expressed in the livers of humans and other mammals, is hardly detectable in rat liver. Thirteen nucleotides existing in the 5'-promoter region of human, marmoset, and mouse ALDH1 genes are absent in the four rat strains examined. When the 13 nucleotides were deleted from a chloramphenicol acetyltransferase expression construct, which contained the 5'-promoter region of the human ALDH1 gene and a low-background promoterless chloramphenicol acetyltransferase expression vector, the expression activity was severely diminished in human hepatic cells. Thus, deletion of the 13 nucleotides in the promoter region of the gene can account for the lack of ALDH1 expression in rat liver.