Determination of aldehyde dehydrogenase isozyme activity in human liver

Acetaldehyde metabolism in different aldehyde dehydrogenase-2 genotypes

In order to clarify the relationships between acetaldehyde (Ac-CHO) metabolism and low Km (mitochondrial) aldehyde dehydrogenase (ALDH2) genotypes, hepatic ALDH2 activity was determined and serial changes of blood Ac-CHO levels after ethanol administration were analyzed in the individuals homozygous for the normal ALDH2 genes, heterozygous for the normal and mutant ALDH2 genes, and homozygous for the mutant ALDH2 genes. Genomic DNA was extracted from white blood cells and genotyping of ALDH2 was performed using the polymerase chain reaction technique and slot blot hybridization with synthesized oligonucleotide probes specific to the normal and mutant ALDH2 genes. ALDH2 activity was not detectable in the liver in two cases of the mutant homozygote. In four out of eight cases of the heterozygote, hepatic ALDH2 activity was measurable, although the activity was lower compared with that in the normal homozygote. Blood ethanol levels after alcohol administration were not different among the three different ALDH2 genotypes. Blood Ac-CHO levels after drinking of alcohol were significantly higher in the heterozygotes and the mutant homozygotes than in the normal homozygotes. The levels after a moderate amount of ethanol (0.8 g/kg of body weight) in a case of the mutant homozygote were not different from those of the heterozygotes. However, the levels after a small amount of ethanol (0.1 g/kg of body weight) were significantly higher in the mutant homozygotes than in the heterozygotes. These results indicate that hepatic ALDH2 activity is lacking completely, and metabolism of Ac-CHO in the liver is severely impaired in the homozygotes of the mutant ALDH2 genes.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol and acetaldehyde metabolism in cultured hepatocytes from chronic alcoholic rats

In this study the authors analyzed ethanol (Et-OH) and acetaldehyde (Ac-CHO) metabolism in cultured hepatocytes isolated from chronic alcoholic rats. Hepatocytes were isolated and cultured from two groups of rats, one was fed with a liquid diet containing Et-OH and another was pair-fed with a control diet for 4 weeks. After 48 hours of the primary culture, Et-OH was added to the culture medium at a final concentration of 5 mM with or without 2 mM 4-methyl pyrazole (Py). Serial changes of Et-OH and Ac-CHO levels in the medium for 48 hours were determined in 4 groups of the alcohol alone, alcohol-Py, control and control-Py groups. In the alcohol alone and control groups, Et-OH disappearance rates (EDR), which are roughly equivalent to Et-OH oxidation rates in the hepatocytes, were significantly higher than those in the corresponding Py treated groups. In the two alcoholic groups, the EDR was significantly higher than those in the corresponding control groups. In cultured hepatocytes, 75-80% of Ac-CHO produced from Et-OH was oxidized. The increasing rates of Ac-CHO (AcICR), a function of Ac-CHO production and oxidation rates in the hepatocytes, increased in parallel with the increase in the EDR. However, the AcICR/EDR rate, which is a parameter of the Ac-CHO oxidation rate in the hepatocytes, was not different among the 4 groups. These results indicate that the cultured cells maintain the characteristics of Et-OH metabolism in chronic alcoholic rats and may also be used for the study of Et-OH and Ac-CHO metabolism as an in vitro model.

Methodological aspects of aldehyde dehydrogenase assay by spectrophotometric technique

Aldehyde dehydrogenase (ALDH) activity was assayed spectrophotometrically by measuring the increase in delta A at 340 nm, as a criteria of NAD conversion to NADH in the presence of propionaldehyde. The effect of pH and substrate(s) concentration of nonenzymatic increase in absorbance at 340 nm was studied. Results indicate that the increase in absorbance at 340 nm is not entirely due to NAD conversion to NADH. It was observed that nonenzymatic interaction of NAD and aldehyde could as well result in increase in absorbance at 340 nm. The magnitude of the nonenzymatic contribution towards increase in absorbance at 340 nm is found to be pH, substrate(s) conc., and time dependent. Further, the observed nonenzymatic reaction product was found to be different from that of NADH as confirmed by u.v. spectral characteristics (lambda max. 346 nm) and its inability to activate NADH/NADPH-dependent glutathione reductase. Based on these findings, a final assay method comprising a substrate blank consisting of NAD and aldehyde, and the assay pH of 7.4 is recommended for measuring the ALDH activity. Further, under these experimental conditions the Km value of human RBC ALDH was found to be 0.59 mM for propionaldehyde substrate.

Hepatic aldehyde dehydrogenase activity in liver diseases, with particular emphasis on alcoholic liver disease

Hepatic aldehyde dehydrogenase isozyme activity was measured in 51 patients with various types of liver diseases, including 24 patients with alcoholic liver disease, to elucidate the relationship between hepatic aldehyde dehydrogenase activity and liver disease, especially alcoholic liver disease. The levels of low-Km and total aldehyde dehydrogenase activity in the liver decreased both in alcoholic and nonalcoholic liver disease patients, who showed an isoelectric focusing pattern of the usual type. There was no significant difference in the aldehyde dehydrogenase activity between alcoholic and nonalcoholic liver disease. In alcoholic liver disease, the decrease in the activity was significantly correlated with the progression of liver histology. The activity in liver cirrhosis was significantly lower than that in the other types of alcoholic liver disease. In nonalcoholic liver disease patients, the unusual type of hepatic aldehyde dehydrogenase activity observed was not different from the unusual type observed in nonhepatobiliary disease patients. These results indicate that the reduction of hepatic low-Km aldehyde dehydrogenase activity is a change that occurs subsequent to liver damage. Genetic abnormality in aldehyde dehydrogenase may not be important in the pathogenesis of alcoholic liver injury.

Subcellular localization of aldehyde dehydrogenase isozymes in human liver

The subcellular distribution of aldehyde dehydrogenase (ALDH) isozymes in human liver was studied by isoelectric focusing and biochemical procedures in biopsied liver specimens obtained during surgical procedures. Four types of ALDH isozymes (ALDH I, II, III and IV) were identified in human liver by isoelectric focusing. In 6 of the 13 livers examined, ALDH I was not detected, indicating that about half of the Japanese people may be classified as the unusual type. ALDH I, which exhibits a low Km with respect to acetaldehyde (Ac-CHO), was located mainly in the mitochondrial and cytosolic fractions. ALDH II (high Km for Ac-CHO) was found to be localized mainly in the microsomal and cytosolic fractions. ALDH III and IV (very high Km for Ac-CHO) were localized in all fractions, except for ALDH III in the microsomal fraction. Biochemical analysis indicates that low Km ALDH activity was localized in the mitochondrial and cytosolic fractions, while high Km and whole ALDH activities were detected in all 3 fractions. More than 80% of the low Km, high Km and whole ALDH activity was found in the cytosolic fraction. These distribution patterns were quite different from those in rats. These results indicate that the results obtained in animal experiments cannot be directly applied to humans and that the main site of Ac-CHO oxidation in the human liver is in the cytosol.

Hepatic aldehyde dehydrogenase isoenzymes: differences with respect to species

Although changes in the acetaldehyde (Ac-CHO) oxidizing system in the liver are important for understanding the pathogenesis of alcoholic liver injury, interspecies differences of hepatic aldehyde dehydrogenase (ALDH: 1.2.1.3) isozymes have not yet been sufficiently studied. In the present study, the character and subcellular distribution of hepatic ALDH isozymes in male animals such as the Rhesus monkey, domestic cow, albino rabbit and Wistar strain rat were analyzed and compared with those in humans. The optimal pH for ALDH isozymes in human liver was 9.5, while those of monkey, cow, rabbit and rat were 9.0, 9.0, 8.5 and 8.5, respectively. In human liver, low Km ALDH activity was distributed mainly in the cytosol, while the corresponding activity was selectively distributed in the mitochondria in rat liver. The distribution patterns of low Km ALDH in the other animals were similar to those of the rat. In microsomes, low Km ALDH activity was very low or almost negligible in the livers of all species. These results indicate that Ac-CHO degrades mainly in the cytosol in the human liver, whereas, in the other species, it occurs in the mitochondria. This suggests that results obtained with experimental animals cannot be applied directly to humans. It is also suggested that degradation of the Ac-CHO produced in the microsomes may be slow in all species.