Brain alcohol dehydrogenase

CNS Viral Infections-What to Consider for Improving Drug Treatment: A Plea for Using Mathematical Modeling Approaches

Neurotropic viruses may cause meningitis, myelitis, encephalitis, or meningoencephalitis. These inflammatory conditions of the central nervous system (CNS) may have serious and devastating consequences if not treated adequately. In this review, we first summarize how neurotropic viruses can enter the CNS by (1) crossing the blood-brain barrier or blood-cerebrospinal fluid barrier; (2) invading the nose via the olfactory route; or (3) invading the peripheral nervous system. Neurotropic viruses may then enter the intracellular space of brain cells via endocytosis and/or membrane fusion. Antiviral drugs are currently used for different viral CNS infections, even though their use and dosing regimens within the CNS, with the exception of acyclovir, are minimally supported by clinical evidence. We therefore provide considerations to optimize drug treatment(s) for these neurotropic viruses. Antiviral drugs should cross the blood-brain barrier/blood cerebrospinal fluid barrier and pass the brain cellular membrane to inhibit these viruses inside the brain cells. Some antiviral drugs may also require intracellular conversion into their active metabolite(s). This illustrates the need to better understand these mechanisms because these processes dictate drug exposure within the CNS that ultimately determine the success of antiviral drugs for CNS infections. Finally, we discuss mathematical model-based approaches for optimizing antiviral treatments. Thereby emphasizing the potential of CNS physiologically based pharmacokinetic models because direct measurement of brain intracellular exposure in living humans faces ethical restrictions. Existing physiologically based pharmacokinetic models combined with in vitro pharmacokinetic/pharmacodynamic information can be used to predict drug exposure and evaluate efficacy of antiviral drugs within the CNS, to ultimately optimize the treatments of CNS viral infections.

Quantification of Neural Ethanol and Acetaldehyde Using Headspace GC-MS

BACKGROUND

There is controversy regarding the active agent responsible for alcohol addiction. The theory that ethanol (EtOH) itself was the agent in alcohol drinking behavior was widely accepted until acetaldehyde (AcH) was found in the brain. The importance of AcH formation in the brain is still subject to speculation due to the lack of a method to accurately assay the AcH levels directly. A highly sensitive gas chromatography mass spectrometry (GC-MS) method to reliably determine AcH concentration with certainty is needed to address whether neural AcH is indeed responsible for increased alcohol consumption.

METHODS

A headspace gas chromatograph coupled to selected-ion monitoring MS was utilized to develop a quantitative assay for AcH and EtOH. Our GC-MS approach was carried out using a Bruker Scion 436-GC SQ MS.

RESULTS

Our approach yields limits of detection of AcH in the nanomolar range and limits of quantification in the low micromolar range. Our linear calibration includes 5 concentrations with a least-square regression greater than 0.99 for both AcH and EtOH. Tissue analyses using this method revealed the capacity to quantify EtOH and AcH in blood, brain, and liver tissue from mice.

CONCLUSIONS

By allowing quantification of very low concentrations, this method may be used to examine the formation of EtOH metabolites, specifically AcH, in murine brain tissue in alcohol research.

Lack of effects of GHB precursors GBL and 1,4-BD following i.c.v. administration in rats

Gamma-hydroxybutyrate (GHB) is used therapeutically and recreationally worldwide. Since the scheduling of GHB by the USA and the United Nations in 2000-2001, the recreational use of GHB precursors has reportedly increased. The aim of this study was to examine if potency differences of GHB and GHB-like compounds are due to their blood-brain barrier permeability. The effects of peripheral and central administration of GHB, GHB precursors gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD), and the gamma-aminobutyric acid (GABA)(B) receptor agonist baclofen on schedule-controlled responding were examined in rats. GHB and baclofen were 276- and 253-fold more potent, respectively, after intracerebroventricular (i.c.v.) administration than after intraperitoneal (i.p.) administration, whereas GBL and 1,4-BD, up to a dose of 1780 microg were without effect after i.c.v. administration. These data suggest that GBL and 1,4-BD are not metabolically converted to GHB in the brain, that enhanced brain penetration cannot account for potency differences between compounds, and that baclofen, like GHB, can readily cross the blood-brain barrier.

Glucose transporters and glucose utilization in rat brain after acute ethanol administration

In the normal adult brain, glucose provides 90% of the energy requirements as well as substrate for nucleic acid and lipid synthesis. In the present study, effects of ethanol on glucose transporters (GLUT) and glucose utilization were examined in rat brain. Male Sprague-Dawley rats weighing 250-300 gms were given either ethanol 3 gm/kg BW or saline i.p. 4 hrs prior to the animal sacrifice and removal of the cerebral cortical tissue. The cortical plasma membranes analyzed by cytochalasin B binding assay showed a decrease in GLUT number but not in GLUT affinity in the ethanol treated rats as compared to the control rats. The estimated Ro values were 70 +/- 8.9 Vs 91 +/- 8.9 pmoles/mg protein (p < 0.05 N=4) and the estimated Kd values were 0.37 +/- 0.03 and 0.28 +/- 0.05 microM (p: NS) in ethanol and control experiments respectively. Immunoblots of purified cerebral plasma membranes and low density microsomal fraction showed 17% and 71% decrease for GLUTI and 54% and 21% (p<0.05 or less; n=6) for GLUT3 respectively in ethanol treated rats than in control animals. Immunofluoresence studies also showed reduction of GLUT1 immunoreactively in choroid plexus and cortical microvessels of ethanol treated rats as compared to control rats. The effect of ethanol on regional cerebral metabolic rates for glucose (CMR(Glc)) was studied using [6-(14)C] glucose and showed statistically insignificant decrease in brain glucose utilization. These data suggest that ethanol in-vivo decrease GLUT number and protein content in rat cerebral cortex.

Ethanol metabolism in the brain

Acetaldehyde is suspected of being involved in the central mechanism of central nervous system depression and addiction to ethanol, but in contrast to ethanol, it can not penetrate easily from blood into the brain because of metabolic barriers. Therefore, the possibility of ethanol metabolism and acetaldehyde formation inside the brain has been one of the crucial questions in biomedical research of alcoholism. This article reviews the recent progress in this area and summarizes the evidence on the first stage of ethanol oxidation in the brain and the specific enzyme systems involved. The brain alcohol dehydrogenase and microsomal ethanol oxidizing systems, including cytochrome P450 II E1 and catalase are considered. Their physicochemical properties, the isoform composition, substrate specificity, the regional and subcellular distribution in CNS structures, their contribution to brain ethanol metabolism, induction under ethanol administration and the role in the neurochemical mechanisms of psychopharmacological and neurotoxic effects of ethanol are discussed. In addition, the nonoxidative pathway of ethanol metabolism with the formation of fatty acid ethyl esters and phosphatidylethanol in the brain is described.

Stress proteins and SH-groups in oxidant-induced cell damage after acute ethanol administration in rat

It is generally accepted that lipid peroxides play an important role in the pathogenesis of ethanol-induced cellular injury and that free sulfhydryl groups are vital in cellular defense against endogenous or exogenous oxidants. It has been observed that oxidative stress induces the synthesis of the 70-kDa family of heat-shock proteins (HSPs). Furthermore, induction of HSPs represents an essential and highly conserved cellular response to a variety of stressful stimuli. In the present study, we measured the intracellular levels of HSP 70 proteins after administration of mild intoxicating and grossly intoxicating doses of ethanol to rats. Our results demonstrate that elevated doses of ethanol induce HSP in various brain areas, namely, cerebellum, hippocampus, and to a lesser extent, striatum or liver. Induction of HSP 70 protein was correlated with a marked depletion of intracellular bound thiols and a decrease in lipid peroxidation measured as MDA formation. These studies support the hypothesis that a redox mechanism may be involved in the heat-shock signal pathway.

Low and moderate doses of ethanol produce distinct patterns of cerebral metabolic changes in rats

The quantitative autoradiographic 2-[14C]deoxyglucose method was used to measure the effects of the acute administration of ethanol on local rates of glucose utilization in male Sprague-Dawley rats. Rates of glucose utilization were measured 10 min after the intraperitoneal administration of 0.00, 0.25, 0.50, and 1.00 g/kg ethanol. The acute administration of the lowest dose of ethanol (0.25 g/kg) significantly increased rates of cerebral metabolism, as compared with vehicle-treated controls, in structures of the mesocorticolimbic and nigrostriatal dopaminergic systems. Among the affected regions were the nucleus accumbens, medial prefrontal cortex, olfactory tubercle, caudate, ventral tegmental area, and substantia nigra. Acute administration of 0.50 g/kg ethanol resulted in similar trends in increased functional activity; however, significant increases were limited to the somatosensory cortex, posterior nucleus accumbens, and the CA3 region of the hippocampus. In contrast, the administration of 1.00 g/kg ethanol produced widespread decreases in rates of glucose utilization in brain regions involved in processing of sensory and motor information, as well as in portions of the limbic system. These data indicate that the effects of acute ethanol administration on functional activity as reflected by rates of glucose utilization are dose-dependent. These cerebral metabolic effects parallel the dose-dependent effects of ethanol on motor behavior, with stimulatory effects generally observed at lower doses and depressive effects at higher doses. Moreover, each of the doses studied produced alterations in functional activity in a unique subset of structures. This suggests that different neuroanatomical circuits mediate the effects of each dose.

Metabolic changes in the rat brain after acute and chronic ethanol intoxication: a 31P NMR spectroscopy study

In this work, 31P phosphorus NMR (31P NMR) studies of the brain have been conducted in rats acutely and chronically intoxicated with ethanol. In both groups, changes in levels of high-energy phosphates were observed: increase of phosphocreatinine (PCr)/beta AaTP and PCr/inorganic phosphate (Pi) in acute and long-term ethanol exposure, and decrease of Pi/beta ATP after acute ethanol administration. These changes in high-energy phosphates, indicative of a reduction of adenosine triphosphate (ATP) and PCr consumption (PCr+ ADP+ H+ ATP+ Cr; ATP ADP+ Pi), suggest a reduction of cerebral metabolism both in acute and chronic ethanol exposure. In addition, in the group of rats chronically intoxicated with ethanol, there were variations in phosphodiester peak intensities (decrease of phosphomonoester (PME)/phosphodiester (PDE), increase of PDE/beta ATP), suggesting increased breakdown of membrane phospholipids. These changes could provide a metabolic explanation for the development of cerebral atrophy in chronic alcoholism.

Regional distribution of low-Km mitochondrial aldehyde dehydrogenase in the rat central nervous system

To clarify the regional capacity of the brain to oxidize biogenic aldehydes and ethanol-derived acetaldehyde, a quantitative immunohistochemical study of the microregional and cellular expression of low Km mitochondrial aldehyde dehydrogenase (mALDH; EC 1.2.1.3) in the rat central nervous system was undertaken, using antiserum raised in rabbit against low-Km aldehyde dehydrogenase purified from rat liver mitochondria. mALDH-specific immunoreactivity (IR) was observed to various extent in the majority of structures in all brain and spinal cord areas. Staining was strong in the extranuclear cytoplasm of neuronal and glial cell bodies but less pronounced in their processes and terminals, the conducting tracts, white matter and neuropile and in blood vessels. Immunostaining density was 2 to 3 times higher in neuronal perikarya as compared with neuropile. mALDH-positive neurons were found in all brain regions, being strongest in the inferior olive and hippocampus stratum pyramidale and weakest in substantia nigra. The percentage of morphologically identifiable ALDH-positive neurons ranged from 40% in the arcuate hypothalamic nucleus to 88% in the cerebellar Purkinje cells. A comparison of the heterogeneous expression of mALDH in various rat CNS regions and cells, as observed in the present study, with the corresponding previously published distributions of the potential acetaldehyde-producing enzymes ADH and cytochrome P450 2E1 indicates major differences, which may help in understanding potential acetaldehyde-mediated CNS effects of ethanol. Knowledge of the regional distribution of high-affinity aldehyde dehydrogenase should also throw light on the neurophysiological role of local regulation of the metabolism of biogenic aldehydes in the brain.

Alcohol dehydrogenases in the brain of mice

Alcohol dehydrogenase (ADH) phenotypes were investigated in the brain of 15 different inbred mice by isoelectric focusing followed by staining of enzyme activities. The Class III ADH activity was detected in all the strains studied, whereas the Class II ADH activity was found only in few strains (including the alcohol-preferring strain--C57BL/6J) having the "a" allele (ADH-C2(2)) for this isozyme in stomach. The inbred strains having the "b" allele (ADH-C2(1)) for the Class II ADH in stomach (including the alcohol avoiding strains--BALB/c, CBA/H, C3H/He, DBA/2J, and SJL/J) demonstrated null variant for this phenotype in their brain. The Class I ADH activity was very low or absent in the brain extracts of all the strains studied. The ADH activities were confined to the cytosolic fractions of brain and were higher in the extracts of cerebral hemispheres than in cerebellum. The genetic linkage studies showed that the locus for the brain Class II ADH is closely linked to the "Adh gene complex" on chromosome 3 of mice.

Acute effects of ethanol on regional brain glucose metabolism and transport

To evaluate the effects of ethanol in the human brain, we tested six normal subjects and six alcoholics using positron emission tomography and 2-deoxy-2-[18F]-fluoro-D-glucose (FDG) under baseline conditions and 24 hours later after ethanol administration (1 g/kg). Ethanol inhibited cortical and cerebellar glucose metabolism with relative sparing of the basal ganglia and corpus callosum. This inhibition was more pronounced in the alcoholics than in the controls. Measurement of the constants for glucose transport and utilization showed that decreased glucose metabolism was due to a reduction in glucose phosphorylation and not to a change of glucose transport into the tissue. The pattern of regional metabolic inhibition by alcohol paralleled the distribution of benzodiazepine receptors in the human brain.

Immunocytochemistry of alcohol dehydrogenase in the rat central nervous system

A sensitive immunocytochemical method for the localization of alcohol dehydrogenase (ADH) in the rat brain is described. The method employs rat liver ADH isolated and purified with Cap-Gapp affinity chromatography. Antiserum to rat liver ADH is generated in rabbits, and used in the peroxidase-antiperoxidase immunocytochemical method. The method is compatible with both light and electron microscopic methods of tissue preparation. In the present report we describe the identification of ADH in neurons of the mammillary bodies, periaqueductal gray, and the cerebral and cerebellar cortices of normal adult rats. In all brain tissues examined, the enzyme is limited to neuronal cytoplasm, and only to some neurons. The restriction of the enzyme to a limited percentage of neurons in the central nervous system may help to account for the difficulty in demonstrating the enzyme in whole brain homogenates, as the dilution of enzyme-bearing cytoplasm with a large volume of enzymatically inactive tissue would reduce the specific activity of the enzyme to near the limit of detectability. In the cerebellar cortex, the enzyme is found only in Purkinje cell cytoplasm. In the other regions examined, we are unable to identify by other criteria a specific neuronal class that consistently displays ADH reactivity. The reactive cells seem to be generally midrange in size and bipolar or multipolar in configuration. The presence of ADH in certain neurons leads us to speculate that intraneuronal ethanol metabolism may lead to focal accumulation of acetaldehyde. The intracellular presence of this toxin may in turn help to account for brain dysfunction in acute ethanol intoxication, and the neuropathology of chronic alcohol abuse.

The effect of chronic ethanol consumption on [14C]deoxyglucose uptake in rat brain in vivo

The uptake of [14C]deoxyglucose by brains of rats that were given alcohol in drinking water for 7 months was investigated. There was a general, approximately 50%, increase in deoxyglucose uptake in brains of ethanol-treated rats with areas of the limbic system being particularly affected.

Influence of epinephrine on alcohol dehydrogenase activity in rat hepatocyte culture

The effects of epinephrine on alcohol dehydrogenase activity and on rates of ethanol elimination were determined in rat hepatocyte culture. Continuous exposure of the hepatocytes to epinephrine (10 microM) in combination with dexamethasone (0.1 microM) enhanced alcohol dehydrogenase activity on days 4-7 of culture, whereas neither hormone alone had an effect. The increased alcohol dehydrogenase activity was associated with an increased rate of ethanol elimination. Acute addition of 10 microM epinephrine to hepatocytes maintained in culture with 0.1 microM dexamethasone did not change alcohol dehydrogenase activity, but resulted in an immediate marked, but transitory, increase in ethanol elimination within the first 5 min after the addition of the hormone. Prazosin, an alpha 1-adrenergic blocker, and antimycin, an inhibitor of mitochondrial respiration, were powerful inhibitors of the transient increase in ethanol elimination, whereas 4-methylpyrazole was only partially inhibitory. These observations indicate that epinephrine has a chronic effect in increasing alcohol dehydrogenase activity and ethanol elimination and, also, an acute transient effect of increasing ethanol elimination which is not limited by alcohol dehydrogenase activity.

Hypothalamic and serum catecholamines in ethanol and acetaldehyde treated guinea-pigs. Relation to moderate short-term cold exposure

Adult guinea-pigs were treated with ethanol (2.5 g/kg, IP) or acetaldehyde (100 mg/kg, IP) and exposed to moderate cold (+4 degrees C) for 50 minutes. Controls were given 0.9% NaCl solution. The hypothalamic catecholamines norepinephrine (NE) and dopamine (DA) and also norepinephrine and epinephrine (E) in the serum were analyzed by high-performance liquid chromatography with an electrochemical detector. Blood glucose, free fatty acids and glycogen in the liver and skeletal muscle were also measured. Acetaldehyde caused a similar drop in colon temperature as did ethanol, but neither could prevent cold-induced vasoconstriction in the ear lobe. Ethanol significantly reduced the concentration of NE in the hypothalamus compared to the controls. Acetaldehyde had a tendency to lower hypothalamic NE. There was no significant difference between drug-treated groups in NE concentration. Neither ethanol nor acetaldehyde had any effect on hypothalamic DA. In the ethanol group serum E and glucose were significantly elevated compared to the acetaldehyde group. Serum glucose was also higher compared to the controls, and the difference in serum E concentration near the level of significance. No significant differences were found between the groups in serum NE, FFA or skeletal muscle and liver glycogen concentration. The results point to a possible central effect of ethanol during a short-term moderate cold exposure. The effects of acetaldehyde on neuronal tissue remain speculative, but a possible effect on noradrenergic neurons cannot be ruled out. Although the hypothermic effect of acetaldehyde corresponded that of ethanol, further experiments are required to elucidate the role of acetaldehyde in ethanol-induced hypothermia.

Biochemical basis of alcoholism: statements and hypotheses of present research

Experimental results and theoretical considerations on the biology of alcoholism are devoted to the following topics: genetically determined differences in metabolic tolerance; participation of the alternative alcohol metabolizing systems in chronic alcohol intake; genetically determined differences in functional tolerance of the CNS to the hypnotic effect of alcohol; cross tolerance between alcohol and centrally active drugs; dissociation of tolerance and cross tolerance from physical dependence; permanent effect of uncontrolled drinking behavior induced by alkaloid metabolites in the CNS; genetically determined alterations in the function of opiate receptors; and genetic predisposition to addiction due to innate endorphin deficiency. For the purpose of introducing the most important research teams and their main work, statements from selected publications of individual groups have been classified as to subject matter and summarized. Although the number for summary-quotations had to be restricted, the criterion for selection was the relevance to the etiology of alcoholism rather than consequences of alcohol drinking.

Prolyl endopeptidase: inhibition in vivo by N-benzyloxycarbonyl-prolyl-prolinal

The activity of prolyl endopeptidase in homogenates of mouse tissues was determined 30 min after intraperitoneal injection of N-benzyloxycarbonyl-prolyl-prolinal (1.25 mg/kg), a potent transition state analog inhibitor (K1 = 14 nM) of prolyl endopeptidase (EC 3.4.21.26). A more than 85% decrease of enzyme activity was obtained in all tissues. The in vivo degradation of potential prolyl endopeptidase substrates was studied by following the release of sulfamethoxazole from N-benzyloxycarbonylglycyl-prolyl-sulfamethoxazole, a model synthetic substrate of the enzyme. When this substrate was given intraperitoneally, its enzymatic degradation was blocked after administration of the inhibitor in a dose- and time-dependent manner, indicating inhibition of the enzyme in vivo. Of interest is the long duration of the inhibition. After a relatively low inhibitor dose (5 mg/kg) significant inhibition was seen in most tissues even after 6 h. The brain was particularly sensitive to the effect of the inhibitor. Since prolyl endopeptidase readily degrades many proline-containing neuropeptides, the inhibitor should be of value in studies on the role of the enzyme in neuropeptide metabolism.

Paired helical filaments in rat spinal ganglia following chronic alcohol administration: an electron microscopic investigation

Young Wistar rats were given a 15% (v/v) ethanol solution ad libitum for at least 6 months, spinal ganglia (C6-7 and L1-2) in some of the experimental animals showed paired helical filaments. These curvilinear profiles consisted of 10 nm filaments with the twist every 35nm. There was also an increase in granular material and in nematosomes. Whether these features may be caused by an impaired cerebral protein biosynthesis is discussed.

Intraventricular self-administration of acetaldehyde, but not ethanol, in naive laboratory rats

For 11 consecutive days, naive rats were maintained in operant chambers where they were given the opportunity to self-administer acetaldehyde (1,2, or 5% v/v), ethanol (2 or 10% v/v), or pH control solutions directly into the cerebral ventricles. Only the animals that had access to the 2 and 5% acetaldehyde solutions showed rates of lever pressing significantly higher than controls. It is suggested that acetaldehyde rather than ethanol itself may mediate the positive reinforcing effects of ethanol in the brain.

Identiy of brain alcohol dehydrogenase with liver alcohol dehydrogenase

A method for obtaining electrophoretically homogeneous rat liver alcohol dehydrogenase (EC 1.1.1.1) at a specific activity of 2-2.5 mumol/min per mg of protein is presented. Anti-sera prepared against the purified enzyme inhibit alcohol dehydrogenase by up to 75% and cause precipitation of virtually all the enzyme. The antisera were shown by immunoelectrophoresis of a partially purified liver homogenate to be specifically directed against alcohol dehydrogenase and were used to demonstrate that the alcohol dehydrogenases of rat brain and liver share common antigens. The total activity of alcohol dehydrogenase in rat brain homogenates is normally quite low, with as much as 10% of the total activity attributable to the activity in the blood contained within the brain; in cases of severe liver damage (induced experimentally with carbon tetrachloride) this contribution may rise to as much as 60%.

Effects of ethanol on brain metabolism

The influence of acute or chronic ethanol administration on the biochemical processes in brain and cerebral metabolic pathways has been discussed. Ethanol seems to affect cerebral carbohydrate metabolism mainly through increased glycogenolysis, although the possibility of decreased cerebral glucose utilization remains eminent. Ethanol affects the consumption of oxygen by the brain tissue presumably through alterations in the brain cell membranes. Inhibition of Na+-K+-ATP-ase observed during ethanol intoxication is suspected to result in alterations in the membranes of the nerve cells. Isotope studies in addition to total respiratory carbon dioxide production strongly suggest the inhibition of citric acid cycle function during ethanol metabolism. Although synthetic pathways for lipids do not seem to be affected by ethanol, lipid oxidation in the cerebral tissue is significantly inhibited. In addition to above mentioned alterations in the cerebral metabolic processes, ethanol also affects ionic transport processes, adenine nucleotides, and amino acid and protein metabolism. The metabolic consequences of such effects of ethanol have been discussed.

Ethanol oxidation: effect on the redox state of brain in mouse

Administration of a single large dose of ethanol to mice results in increases, for concentrations in the brain, of ratios of lactate to pyruvate, of aglycerophosphate to dihydroxyacetone phosphate, of malate to oxaloacetate, and of glutamate to the product of alpha-ketoglutarate and ammonium ion. These changes are noticed as early as 5 minutes after the single dose is given. Ethanol administration for 30 days also produces these changes in metabolite concentrations in the brain. However, in contrast to the single alcohol dose, long-term alcohol administration results in a marked decrease in the concentration of adenosine triphosphate in brain and increases in those of adenosine diphosphate and adenosine monophosphate. Pyrazole, an inhibitor of alcohol dehydrogenase, prevents the effects of ethanol on the concentration of brain metabolites. These results may provide new insight into the biochemical and pharmacological effects of alcohol on brain metabolism and the importance of alcohol dehydrogenase activity in the brain.