The inner stratum corneum is likely to represent the location of the intact skin barrier, unperturbed by degradation processes. In our studies of the physical skin barrier a new high-performance liquid chromatography (HPLC)-based method was developed for the quantitative analysis of lipids of the inner stratum corneum. All main lipid classes were separated and quantitated by HPLC/light scattering detection (LSD) and the free fatty acid fraction was further analysed by gas-liquid chromatography (GLC). Mass spectrometry (MS) was used for peak identification and flame ionization detection (FID) for quantitation. Special attention was paid to the free fatty acid fraction since unsaturated free fatty acids may exert a key function in the regulation of the skin barrier properties by shifting the physical equilibrium of the multilamellar lipid bilayer system towards a noncrystalline state. Our results indicated that the endogenous free fatty acid fraction of the stratum corneum barrier lipids in essence exclusively consisted of saturated long-chain free fatty acids. This fraction was characterized as a very stable population (low interindividual peak variation) dominated by saturated lignoceric acid (C24:0, 39 molar%) and hexacosanoic acid (C26:0, 23 molar%). In addition, trace amounts of very long-chain (C32-C36) saturated and monounsaturated free fatty acids were detected in human forearm inner stratum corneum. Our analysis method gives highly accurate and precise quantitative information on the relative composition of all major lipid species present in the skin barrier. Such data will eventually permit skin barrier model systems to be created which will allow a more detailed analysis of the physical nature of the human skin barrier.

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Alcohols and aldehydes in the metabolic pathways of ethanol and serotonin are substrates for alcohol dehydrogenases (ADH) of class I and II. In addition to the reversible alcohol oxidation/aldehyde reduction, these enzymes catalyse aldehyde oxidation. Class-I gg ADH catalyses the dismutation of both acetaldehyde and 5-hydroxyindole-3-acetaldehyde (5-HIAL) into their corresponding alcohols and carboxylic acids. The turnover of acetaldehyde dismutation is high (k cat = 180 min 21 ) but saturation is reached first at high concentrations (K m = 30 mm) while dismutation of 5-HIAL is saturated at lower concentrations and is thereby more efficient (K m = 150 mm; k cat = 40 min 21 ). In a system where NAD + is regenerated, the oxidation of 5-hydroxytryptophol to 5-hydroxyindole-3-acetic acid proceeds with concentration levels of the intermediary 5-HIAL expected for a two-step oxidation. Butanal and 5-HIAL oxidation is also observed for class-I ADH in the presence of NADH. The class-II enzyme is less efficient in aldehyde oxidation, and the ethanol-oxidation activity of this enzyme is competitively inhibited by acetate (K i = 12 mm) and 5-hydroxyindole-3-acetic acid (K i = 2 mm).Reduction of 5-HIAL is efficiently catalysed by class-I gg ADH (k cat = 400 min 21 ; K m = 33 mm) in the presence of NADH. This indicates that the increased 5-hydroxytryptophol/5-hydroxyindole-3-acetic acid ratio observed after ethanol intake may be due to the increased NADH/NAD + ratio on the class-I ADH.Keywords: alcohol dehydrogenase; alcohol metabolism; aldehydes; sequential oxidation; serotonin metabolism.The alcohol dehydrogenase (ADH) family is the major enzyme system for metabolism of ingested ethanol [1,2]. In addition to ethanol, a range of substrates has been identified for these enzymes and a possible mechanism for ethanol-induced metabolic changes may be interference with other activities of ADH (Fig. 1). For example, ethanol affects human noradrenaline, dopamine and serotonin metabolism by increasing the relative formation of the alcohol products, 4-hydroxy-3-methoxyphenylglycol, 3,4-dihydroxyphenylethanol and 5-hydroxytryptophol (5-HTOL), while decreasing the formation of the carboxylic acid products, 4-hydroxy-3-methoxymandelic acid, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindole-3-acetic acid (5-HIAA) [3,4]. Clinical monitoring of recent drinking takes advantage of the elevated 5-HTOL/5-HIAA ratio which can be detected in urine for several hours after ethanol is no longer measurable [5,6]. The ADH activities for noradrenaline and dopamine metabolites have been characterized, and alcohols and aldehydes in these catabolic pathways serve as good substrates for ADH of both class I and class II [7,8]. It has also been shown that the serotonin metabolite 5-HTOL is an ADH substrate [9].In addition to reversible alcohol oxidation/aldehyde reduction, horse class-I and human class-I and class-II ADH catalyse aldehyde oxidation and thereby mimic the activity of aldehyde dehydrogenase (ALDH) [10±12]. Incubation of ADH with aldehyde and N...

The oxidation of 5~-cholestane-3a,7a,l2a-triol by different subcellular fractions of rat liver homogenate was studied. The most efficient oxidation was observed with the microsomal fraction fortified with the 100000 x g supernatant fluid. Efficient oxidation occurred also with the microsoma1 fraction fortified with NADPH. The main products were identified as a number of cholestanetetrols. 5~-Cholestane-3a,7a,l2a,25-tetrol and 5p-cholestane-3a,7a, 12a,26-tetrol accounted for about 60 of the cholestanetetrols. The oxidation of 5~-cholestane-3a,7a,l2a-triol by the microsomal fraction fortified with NADPH was stimulated about five-fold by administration of phenobarbital. Phenobarbital treatment stimulated hydroxylations a t C-23, C-24 and C-25 to a much greater extent than that a t (2-26. Carbon monoxide inhibited all the side-chain hydroxylations and the most marked inhibition was observed for the 26-hydroxylation.5,4-Cholestane-3a,7a,l2a,26-tetrol was found to be a much more efficient precursor of cholic acid than either 5~-cholestane-3a,7a,l2a,25-tetrol or the two C-24 epimers of 5p-cholestane3a,7a,lZa,24-tetrol.5~-Cholestane-3a,7a,l2~-triol has been shown to be an intermediate in the formation of cholic acid from cholesterol in liver [l]. The initial reaction in the conversion of 5~-cholestane-3a,7a,12n-triol into cholic acid involves predominantly hydroxylation in the 26-position [l]. Early investigations showed that the mitochondria1 fraction of rat liver homogenate was able to carry out 26-hydroxylation of 5~-cholestane-3a,7a,l2a-triol [2,3]. The possibility that the microsomal fraction might be able to carry out the same reaction was not examined in detail in these investigations. A series of investigations during recent years has shown that the microsomal fraction of liver homogenate fortified with NADPH and in the presence of molecular oxygen catalyzes hydroxylations of many different compounds including o-hydroxylation of fatty acids and aliphatic hydrocarbons [4]. I n view of these findings and those reported recently from this laboratory concerning hydroxylations in the biosynthesis and metabolism of bile acids [5,6], it appeared of interest to reexamine the metabolism of 5~-cholestane-3~w,7a,l2a-triol in different subcellular fractions of liver homogenate with special emphasis on the metabolism in the presence of the microsomal fraction. The present communication describes the results of such a study. While this work was in progress, Okuda and Hoshita EXPERIMENTAL PROCEDURE Materials 5~-[7~-~H]Cho1estane-3a7+7a,12a-trio1 (specific radioactivity, 20 pC/mg) was prepared by reduction with tritium-labeled sodium borohydride (Radiochemical Centre, Amersham, England) of 3a,12a-dihydroxy-5~-cholestan-7-one, prepared from 58-cholestane-3a,7a,l2a-triol by oxidation with N-bromosuccinimide [S]. 5,!?-[7p-3H]Cholestane-3a,7a,12a-trio1 was purified by repeated thin-layer chromatography with ethyl acetate as solvent and by reversedphase partition chromatography with phase system F2 [9]. The purified material had m....

The incorporation of deuterium into bile acids and cholesterol in rata with a bile fistula given [ l-2H2]ethanol was studied by gas chromatography-mass spectrometry. Deuterium-labelling of cholic and chenodeoxycholic acids was observed with 0.03 g [i-2H2]ethanol per kg body weight. The 5j3 position in both bile acids reached a deuterium excess of about 7 atoms per cent with 1 g [l-2H2]ethanol per kg body weight. With this ethanol dose, the deuterium excess in the 3j3 position was 15 atoms per cent in chenodeoxycholic acid, and 9 atoms per cent in cholic acid. The deuterium excess in the 3j3 position of metabolites of 3-keto-5j3-cholanoic acid was about 13 atoms per cent. In the endogenous bile acids, several positions other than 38 and 5j3 were labelled, and the number of di-and trideuterated molecules relative to that of monodeuterated ones increased during the first 2 h after ethanol injection. Cholesterol in bile was also labelled in several positions, and the proportion of labelled molecules increased slowly to reach 8-i4O/, 2-3 h after the injection of 1 g [l-2H,]ethanol per kg body weight. The deuterium-labelling of bile acids in positions other than 38 and 5j3 was greater than that of cholesterol. Fasting for 48 h, and fasting followed by glucose feeding had little influence on the deuterium incorporation into bile acids, whereas pyrazole prevented it almost completely.The results indicate that deuterium is transferred from ethanol via NADH to the NADPH that is utilized in the biosynthesis of cholesterol and bile acids. The higher and more variable labelling of the 3j3 than the 5j3 position may be explained by isotope effects or by the ability of the 3a-hydroxysteroid dehydrogenase, involved in the reduction of the intermediary 3-keto steroids, to utilize NADH. The difference between biliary cholesterol and bile acids with respect to labelling in positions other than 3j3 and 51 indicates that these compounds do not originate from the same cholesterol pool.All metabolites of 3-keto-5j3-cholanoic acid carried a bhydroxy group. This indicates that the 3B-hydroxy-5j3-steroid dehydrogenase isoenzyme of alcohol dehydrogenase has no function in the reductive metabolism of bile acids. Furthermore, the increased production of NADH during ethanol metabolism did not induce a formation of 3/?-hydroxycholanoic acids.When [l.2H2]ethanol is oxidized in the liver, deuterium is incorporated into the i7a-position of certain 17j3-hydroxysteroids as these are formed from the corresponding 17-ketosteroids. This has been shown both in man in vivo [i] and in guinea pig in vitro in liver slices [2]. At the same time the ratio between the concentrations in plasma of i7j3-hydroxysteroids and 17-ketosteroids increases. These findings can be explained by a transfer of deuterium via r4ystematio Names and U n d Abbreviations. Cholic acid, 3a,7a,12a-trihydroxyy-5~-cholanoic acid; chenodeoxycholic acid, 3a,7a-dihydroxy-5~-cholanoic acid; lithocholio acid, 3a-hydroxy-5~-cholanoic acid ; a-muricholic acid, 3a,6~,7a-trihydroxy-5~-cholanoic...