No abstract

No abstract

Fetal ethanol (E) exposure has well documented deleterious effects on brain development, yet it is uncertain if the neurotoxicity of maternal E consumption is generated by E itself, by its primary metabolite acetaldehyde (AcHO), or both. The current studies present evidence that homogenates of immature rat brains can generate AcHO via a catalase (CAT)-mediated reaction and that AcHO may be produced in vivo by this system. Homogenates of day 19 fetal rat brain were incubated with E (50 mM). When incubated with CAT inhibitors (sodium azide or 3-aminotriazole), AcHO formation was blocked, whereas neither the alcohol dehydrogenase inhibitor, 4-methylpyrazole, nor P-450 inhibitors decreased AcHO production. Three hours after one oral dose of E (4 g/kg) to a pregnant dam (gestation day 19), AcHO levels in fetal brain increased to 14.28 +/- 1.82 nM/g tissue. Baseline CAT activity in day 19 fetal brains was 4.5 times adult values (p < 0.05). Western blot analysis determined that CAT protein level in the day 19 fetal brain exceeded that in adult brain by 2.5 times. One hour after a single dose of E, CAT activity in day 19 fetal brain increased by 8.2 units/mg protein. In 5-day-old neonatal brains during the "third trimester" brain growth spurt, baseline CAT activity was twice the adult values (p < 0.05) and a 2-day in vivo E regimen increased AcHO levels to four times the control values, with a concomitant 1.7-fold increase in CAT activity. This was prevented by administration of a CAT inhibitor (3-amino-1,2,4-triazole). Immunohistochemical staining of neonatal brains exposed to E illustrated the presence of acetaldehyde-protein adducts. We conclude that AcHO is likely produced in rat fetal and neonatal brain via CAT-mediated oxidation of E. This phenomenon may be an important factor in the neurotoxic effects of in utero E exposure.

Fetal ethanol (E) exposure has well documented deleterious effects on brain development, yet it is uncertain if the neurotoxicity of maternal E consumption is generated by E itself, by its primary metabolite acetaldehyde (AcHO), or both. The current studies present evidence that homogenates of immature rat brains can generate AcHO via a catalase (CAT)-mediated reaction and that AcHO may be produced in vivo by this system. Homogenates of day 19 fetal rat brain were incubated with E (50 mM). When incubated with CAT inhibitors (sodium azide or 3-aminotriazole), AcHO formation was blocked, whereas neither the alcohol dehydrogenase inhibitor, 4-methylpyrazole, nor P-450 inhibitors decreased AcHO production. Three hours after one oral dose of E (4 g/kg) to a pregnant dam (gestation day 19), AcHO levels in fetal brain increased to 14.28 +/- 1.82 nM/g tissue. Baseline CAT activity in day 19 fetal brains was 4.5 times adult values (p < 0.05). Western blot analysis determined that CAT protein level in the day 19 fetal brain exceeded that in adult brain by 2.5 times. One hour after a single dose of E, CAT activity in day 19 fetal brain increased by 8.2 units/mg protein. In 5-day-old neonatal brains during the "third trimester" brain growth spurt, baseline CAT activity was twice the adult values (p < 0.05) and a 2-day in vivo E regimen increased AcHO levels to four times the control values, with a concomitant 1.7-fold increase in CAT activity. This was prevented by administration of a CAT inhibitor (3-amino-1,2,4-triazole). Immunohistochemical staining of neonatal brains exposed to E illustrated the presence of acetaldehyde-protein adducts. We conclude that AcHO is likely produced in rat fetal and neonatal brain via CAT-mediated oxidation of E. This phenomenon may be an important factor in the neurotoxic effects of in utero E exposure.

Studies in many laboratories show that ethanol can induce Lipid peroxidation has been implicated in ethanol-inoxidative stress in adult tissues and that this may be associduced liver injury and observed in fetal liver and brain ated with subsequent ethanol-related damage. 3,4 Likewise, after maternal ethanol consumption with mitochondria lipid peroxidation resulting from oxidative stress has been being the target organelles. This process generates a shown to increase in tissues/cells after in vivo and in vitro highly reactive and toxic product, 4-hydroxynonenal ethanol exposure and could be an important factor in the (HNE). In the present study, HNE levels and metabolism pathogenesis of alcoholic liver disease. 5,6 There is compelling were assessed in mitochondria of fetal and maternal evidence that a key target organelle for ethanol-related oxidaliver after in vivo ethanol exposure. Female Spraguetive stress is the mitochondrion. 3,7 Long-term administration Dawley rats received five doses of ethanol (4 g/kg orally at 12-hour intervals) and were killed on day 19 of gesta-of ethanol to rats has been shown to increase production of tion. The results showed that HNE levels were enhanced malondialdehyde, conjugated dienes, and 4-hydroxynonenal in hepatic mitochondria of fetal rats exposed to ethanol, (HNE) in mitochondria.8 Moreover, ethanol may selectively far in excess of that in adult liver mitochondria. Mea-deplete hepatic mitochondrial glutathione, and this may be surement of HNE metabolism showed that fetal mito-connected to its impairment of key mitochondrial functions. chondria had a lower capacity for HNE catabolism thanThe role of oxidative stress in the fetotoxicity of ethanol is adult mitochondria. In adult mitochondria, HNE could much less studied and is under investigation in our laborabe metabolized by nicotine adenine dinucleotide-tory. We have recently documented ethanol-associated oxidadependent oxidation, reduced glutathione conjugation, tive stress in fetal brain and liver after in utero ethanol expoand reduced nicotine adenine dinucleotide-dependent sure and in cultured fetal hepatocytes, neonatal astrocytes, reduction, whereas in fetal liver only the former two and cardiac myocytes. 10,11 In both settings, ethanol increased pathways were active, but to a lesser degree than in membrane lipid peroxidation. The ethanol-mediated blockadult mitochondria. On the other hand, mitochondria ade of fetal hepatocyte replication could be reversed by augfrom fetal liver showed a higher production of HNE mentation of cellular antioxidant defenses, as could inhibiwhen oxidative stress was induced with t-butyl hydro-tory effects of ethanol on mitochondrial respiration.10,11 Thus, peroxide. Prior in vivo ethanol exposure further potenti-oxidative stress may play an important mechanistic role in ated HNE formation in t-butyl hydroperoxide-stimu-the fetotoxic effects of ethanol, yet the specific means by lated fetal liver mitochondria, but not in adult which this occurs remain unclear. mitochondria. These findi...