Takeshi Haseba

Histological distribution of class III alcohol dehydrogenase in human brain.

The distributions of class III alcohol dehydrogenase (ADH), a glutathione-dependent formaldehyde dehydrogenase, and class I ADH in the human brain were examined immunohistochemically. The most intense immunostaining of class III ADH was observed in the dendrites and cytoplasm of cerebellar Purkinje cells. Scattered cerebral cortical neurons in layers IV and V, and some hippocampal pyramidal neurons were also immunopositive. The neuronal distribution of class III ADH resembled that of the vulnerable neurons in patients with hypoxic encephalopathy, which in view of the intense staining in the Purkinje cells, raises the possibility that this enzyme contributes to the hypoxia and cerebellar degeneration suffered by chronic alcoholics. Perivascular and subependymal astrocytes, which contribute to the maintenance of the cerebral cellular milieu and isolate the brain from the systemic circulation and cerebrospinal fluid, were also class III ADH positive. As the substrates of this enzyme include intrinsic toxic formaldehyde, inflammatory intermediate of 20-hydroxy-leukoteiene B4, and possibly ethanol, the distribution of class III ADH immunostaining indicates this enzyme contributes to the defence of the brain against degenerative processes. The finding that, unlike ependymal cells, subependymal astrocytes were class III ADH positive, suggests this enzyme may be useful for differentiating astrocytes and ependymal cells.

Alcohol dehydrogenase III exacerbates liver fibrosis by enhancing stellate cell activation and suppressing natural killer cells in mice

The important roles of retinols and their metabolites have recently been emphasized in the interactions between hepatic stellate cells (HSCs) and natural killer (NK) cells. Nevertheless, the expression and role of retinol metabolizing enzyme in both cell types have yet to be clarified. Thus, we investigated the expression of retinol metabolizing enzyme and its role in liver fibrosis. Among several retinol metabolizing enzymes, only alcohol dehydrogenase (ADH) 3 expression was detected in isolated HSCs and NK cells, whereas hepatocytes express all of them. In vitro treatment with 4‐methylpyrazole (4‐MP), a broad ADH inhibitor, or depletion of the ADH3 gene down‐regulated collagen and transforming growth factor‐β1 (TGF‐β1) gene expression, but did not affect α‐smooth muscle actin gene expression in cultured HSCs. Additionally, in vitro, treatments with retinol suppressed NK cell activities, whereas inhibition of ADH3 enhanced interferon‐γ (IFN‐γ) production and cytotoxicity of NK cells against HSCs. In vivo, genetic depletion of the ADH3 gene ameliorated bile duct ligation‐ and carbon tetrachloride‐induced liver fibrosis, in which a higher number of apoptotic HSCs and an enhanced activation of NK cells were detected. Freshly isolated HSCs from ADH3‐deficient mice showed reduced expression of collagen and TGF‐β1, but enhanced expression of IFN‐γ was detected in NK cells from these mice compared with those of control mice. Using reciprocal bone marrow transplantation of wild‐type and ADH3‐deficient mice, we demonstrated that ADH3 deficiency in both HSCs and NK cells contributed to the suppressed liver fibrosis. Conclusion: ADH3 plays important roles in promoting liver fibrosis by enhancing HSC activation and inhibiting NK cell activity, and could be used as a potential therapeutic target for the treatment of liver fibrosis. (Hepatology 2014;60:1044–1053)

A new view of alcohol metabolism and alcoholism--role of the high-Km Class III alcohol dehydrogenase (ADH3).

The conventional view is that alcohol metabolism is carried out by ADH1 (Class I) in the liver. However, it has been suggested that another pathway plays an important role in alcohol metabolism, especially when the level of blood ethanol is high or when drinking is chronic. Over the past three decades, vigorous attempts to identify the enzyme responsible for the non-ADH1 pathway have focused on the microsomal ethanol oxidizing system (MEOS) and catalase, but have failed to clarify their roles in systemic alcohol metabolism. Recently, using ADH3-null mutant mice, we demonstrated that ADH3 (Class III), which has a high Km and is a ubiquitous enzyme of ancient origin, contributes to systemic alcohol metabolism in a dose-dependent manner, thereby diminishing acute alcohol intoxication. Although the activity of ADH3 toward ethanol is usually low in vitro due to its very high Km, the catalytic efficiency (kcat/Km) is markedly enhanced when the solution hydrophobicity of the reaction medium increases. Activation of ADH3 by increasing hydrophobicity should also occur in liver cells; a cytoplasmic solution of mouse liver cells was shown to be much more hydrophobic than a buffer solution when using Nile red as a hydrophobicity probe. When various doses of ethanol are administered to mice, liver ADH3 activity is dynamically regulated through induction or kinetic activation, while ADH1 activity is markedly lower at high doses (3–5 g/kg). These data suggest that ADH3 plays a dynamic role in alcohol metabolism, either collaborating with ADH1 or compensating for the reduced role of ADH1. A complex two-ADH model that ascribes total liver ADH activity to both ADH1 and ADH3 explains the dose-dependent changes in the pharmacokinetic parameters (β, CLT, AUC) of blood ethanol very well, suggesting that alcohol metabolism in mice is primarily governed by these two ADHs. In patients with alcoholic liver disease, liver ADH3 activity increases, while ADH1 activity decreases, as alcohol intake increases. Furthermore, ADH3 is induced in damaged cells that have greater hydrophobicity, whereas ADH1 activity is lower when there is severe liver disease. These data suggest that chronic binge drinking and the resulting liver disease shifts the key enzyme in alcohol metabolism from low-Km ADH1 to high-Km ADH3, thereby reducing the rate of alcohol metabolism. The interdependent increase in the ADH3/ADH1 activity ratio and AUC may be a factor in the development of alcoholic liver disease. However, the adaptive increase in ADH3 sustains alcohol metabolism, even in patients with alcoholic liver cirrhosis, which makes it possible for them to drink themselves to death. Thus, the regulation of ADH3 activity may be important in preventing alcoholism development.

Dose and time changes in liver alcohol dehydrogenase (ADH) activity during acute alcohol intoxication involve not only class I but also class III ADH and govern elimination rate of blood ethanol

BACKGROUND The elimination rate of blood ethanol usually depends on the activity of liver alcohol dehydrogenase (ADH). During acute alcohol intoxication, however, it is unclear how liver ADH activity changes with dose and time and what the involvement is of the two major isozymes of liver ADH: the classically known class I ADH and the very high Km class III ADH. We investigated dose- and time-wise changes in liver ADH activity and the contents of both ADHs by administering ethanol to mice, and analyzed the relationship among these ADH parameters to assess the contributions of these ADHs to liver ADH activity and ethanol metabolism in vivo. METHODS Mice were given ethanol doses of 0, 1, 3 or 5 g/kg body weight and killed 0.5, 1, 2, 4, 8 or 12 h after administration. The elimination rate of blood ethanol was calculated from the regression line fitted to the blood ethanol curve. The liver ADH activity of crude extract was conventionally measured with 15 mM ethanol as a substrate. The liver class I and class III ADH contents were determined by enzyme immunoassay. These three ADH parameters were statistically analyzed. RESULTS The change in liver ADH activity depended on both dose and time (P<0.001 by two-way ANOVA, n=74), but the change in the class I content depended on dose alone (P<0.0001). The class III content depended on both dose and time (P<0.001) with a time course similar to that of liver ADH activity for each dose. The sum of the class I and class III contents exhibited a higher correlation with liver ADH activity (r=0.882, P<0.0001) than the class I content alone did (r=0.825). The mean liver ADH activity during ethanol metabolism for each dose correlated significantly with the elimination rate of blood ethanol (r=0.970, P<0.0001). CONCLUSION Liver ADH activity changes dose and time dependently during acute alcohol intoxication and governs the elimination rate of blood ethanol through the involvement not only of class I but also of class III ADH.

Dose-Dependent Change in Elimination Kinetics of Ethanol due to Shift of Dominant Metabolizing Enzyme from ADH 1 (Class I) to ADH 3 (Class III) in Mouse

ADH 1 and ADH 3 are major two ADH isozymes in the liver, which participate in systemic alcohol metabolism, mainly distributing in parenchymal and in sinusoidal endothelial cells of the liver, respectively. We investigated how these two ADHs contribute to the elimination kinetics of blood ethanol by administering ethanol to mice at various doses, and by measuring liver ADH activity and liver contents of both ADHs. The normalized AUC (AUC/dose) showed a concave increase with an increase in ethanol dose, inversely correlating with β. CLT (dose/AUC) linearly correlated with liver ADH activity and also with both the ADH-1 and -3 contents (mg/kg B.W.). When ADH-1 activity was calculated by multiplying ADH-1 content by its V max⁡/mg (4.0) and normalized by the ratio of liver ADH activity of each ethanol dose to that of the control, the theoretical ADH-1 activity decreased dose-dependently, correlating with β. On the other hand, the theoretical ADH-3 activity, which was calculated by subtracting ADH-1 activity from liver ADH activity and normalized, increased dose-dependently, correlating with the normalized AUC. These results suggested that the elimination kinetics of blood ethanol in mice was dose-dependently changed, accompanied by a shift of the dominant metabolizing enzyme from ADH 1 to ADH 3.

Phytophenols in whisky lower blood acetaldehyde level by depressing alcohol metabolism through inhibition of alcohol dehydrogenase 1 (class I) in mice

We recently reported that the maturation of whisky prolongs the exposure of the body to a given dose of alcohol by reducing the rate of alcohol metabolism and thus lowers the blood acetaldehyde level (Alcohol Clin Exp Res. 2007;31:77s-82s). In this study, administration of the nonvolatile fraction of whisky was found to lower the concentration of acetaldehyde in the blood of mice by depressing alcohol metabolism through the inhibition of liver alcohol dehydrogenase (ADH). Four of the 12 phenolic compounds detected in the nonvolatile fraction (caffeic acid, vanillin, syringaldehyde, ellagic acid), the amounts of which increase during the maturation of whisky, were found to strongly inhibit mouse ADH 1 (class I). Their inhibition constant values for ADH 1 were 0.08, 7.9, 15.6, and 22.0 mumol/L, respectively, whereas that for pyrazole, a well-known ADH inhibitor, was 5.1 mumol/L. The 2 phenolic aldehydes and ellagic acid exhibited a mixed type of inhibition, whereas caffeic acid showed the competitive type. When individually administered to mice together with ethanol, each of these phytophenols depressed the elimination of ethanol, thereby lowering the acetaldehyde concentration of blood. Thus, it was demonstrated that the enhanced inhibition of liver ADH 1 due to the increased amounts of these phytophenols in mature whisky caused the depression of alcohol metabolism and a consequent lowering of blood acetaldehyde level. These substances are commonly found in various food plants and act as antioxidants and/or anticarcinogens. Therefore, the intake of foods rich in them together with alcohol may not only diminish the metabolic toxicity of alcohol by reducing both the blood acetaldehyde level and oxidative stress, but also help limit the amount of alcohol a person drinks by depressing alcohol metabolism.

Direct and rapid PCR amplification using digested tissues for the diagnosis of drowning

We developed a direct and rapid method for the diagnosis of death by drowning by PCR amplification of phytoplankton DNA using human tissues. The primers were designed based on the DNA sequence of the 16S ribosomal RNA gene (16S rDNA) of Cyanobacterium. Samples of lung, liver and kidney tissues were collected from 53 autopsied individuals diagnosed as death by drowning. Without DNA extraction, the tissue fragments were incubated directly in a digest buffer developed in this study, for 20 min. Using 1 μL of the tissue digest solution in PCR, the 16S rDNA was successfully amplified. The specific 16S rDNA fragment was identified from the standard picoplankton Euglena gracilis, the tissues of bodies died from drowning and water samples from the drowning scenes. On the other hand, no PCR products were found in the tissues of individuals who died from causes other than drowning. Various quantities of tissue weighing 1, 5, 10, 20 and 30 mg were tested, and the PCR amplification detected the specific16S rDNA fragment from all the quantities of tissue tested. This method was found to be more reliable, sensitive, specific and rapid when compared to the conventional diagnosis of death by drowning using the diatom test by acid digestion method.

Alcohol dehydrogenase 3 contributes to the protection of liver from nonalcoholic steatohepatitis.

Nutritional steatohepatitis is closely associated with dysregulation of lipid metabolism and oxidative stress control. ADH3 is a highly conserved bifunctional enzyme involved in formaldehyde detoxification and termination of nitric oxide signaling. Formaldehyde and nitric oxide are nonenzymatically conjugated with glutathione, which is regenerated after ADH3 metabolizes the conjugates. To clarify roles of ADH3 in nutritional liver diseases, we placed Adh3‐null mice on a methionine‐ and choline‐deficient (MCD) diet. The Adh3‐null mice developed steatohepatitis more rapidly than wild‐type mice, indicating that ADH3 protects liver from nutritional steatohepatitis. NRF2, which is a key regulator of cytoprotective genes against oxidative stress, was activated in the Adh3‐null mice with liver damage. In the absence of NRF2, the Adh3 disruption caused severe steatohepatitis by the MCD diet feeding accompanied by significant decrease in glutathione, suggesting cooperative function between ADH3 and NRF2 in the maintenance of cellular glutathione level for cytoprotection. Conversely, with enhanced NRF2 activity, the Adh3 disruption did not cause steatohepatitis but induced steatosis, suggesting that perturbation of lipid metabolism in ADH3‐deficiency is not compensated by NRF2. Thus, ADH3 protects liver from steatosis by supporting normal lipid metabolism and prevents progression of steatosis into steatohepatitis by maintaining the cellular glutathione level.

Alcohol dehydrogenase (ADH) isozymes in the AdhN/AdhN strain ofPeromyscus maniculatus (ADH− deermouse) and a possible role of class III ADH in alcohol metabolism

Although the AdhN/AdhN strain ofPeromyscus maniculatus (so-called ADH− deermouse) has been previously considered to be deficient in ADH, we found ADH isozymes of Classes II and III but not Class I in the liver of this strain. On the other hand, the AdhF/AdhF strain (so-called ADH+ deermouse), which has liver ADH activity, had Class I and III but not Class II ADH in the liver. In the stomach, Class III and IV ADHs were detected in both deermouse strains, as well as in the ddY mouse, which has the normal mammalian ADH system with four classes of ADH. These ADH isozymes were identified as electrophoretic phenotypes on the basis of their substrate specificity, pyrazole sensitivity, and immunoreactivity. Liver ADH activity of the ADH− strain was barely detectable in a conventional ADH assay using 15 mM ethanol as substrate; however, it increased markedly with high concentrations of ethanol (up to 3M) or hexenol (7 mM). Furthermore, in a hydrophobic reaction medium containing 1.0M t-butanol, liver ADH activity of this strain at low concentrations of ethanol (<100 mM) greatly increased (about sevenfold), to more than 50% that of ADH+ deermouse. These results were attributable to the presence of Class III ADH and the absence of Class I ADH in the liver of ADH− deermouse. It was also found that even the ADH+ strain has low liver ADH activity (<40% that of the ddY mouse) with 15 mM ethanol as substrate, probably due to low activity in Class I ADH. Consequently, liver ADH activity of this strain was lower than its stomach ADH activity, in contrast with the ddY mouse, whose ADH activity was much higher in the liver than in the stomach, as well as other mammals. Thus, the ADH systems in both ADH− and ADH+ deermouse were different not only from each other but also from that in the ddY mouse; the ADH− strain was deficient in only Class I ADH, and the ADH+ strain was deficient in Class II ADH and down-regulated in Class I ADH activity. Therefore, Class III ADH, which was found in both strains and activated allosterically, may participate in alcohol metabolism in deermouse, especially in the ADH− strain.

Real-time PCR assay for the detection of picoplankton DNA distribution in the tissues of drowned rabbits

The detection of plankton DNA is one of the important methods for the diagnosis of drowning from postmortem tissues. This study investigated the quantities of picoplankton (Cyanobacteria) DNA in the lung, liver, kidney tissues and blood of drowned and non-drowned rabbits, and the sensitivity of detection of picoplankton DNA by polymerase chain reaction (PCR) detect for the diagnosis of death from drowning. For this purpose, the DNA of the 16S ribosomal RNA gene of picoplankton was quantitatively assayed from the tissues of drowned and non-drowned rabbits immersed in water after death. Each of the liver, kidney and lung tissues and blood were obtained from drowned and non-drowned rabbits. Picoplankton DNA in the tissues was extracted using the DNeasy® Blood & Tissue kit to determine the yield of picoplankton DNA from each tissue. TaqMan real-time PCR was performed for quantitative analysis of picoplankton DNA. Target DNA was detected in the liver, kidney and lung samples obtained from the drowned rabbits, while no picoplankton DNA was detected in the non-drowned rabbit tissues (except in lung samples). The results verified that direct PCR for the detection of picoplankton DNA is useful for the diagnosis of drowning. Although we observed seasonal changes in the quantity of picoplankton in river water, we were able to detect DNA from various organs of drowned bodies during the season when picoplankton were not the most abundant.