DNA fragmentation during exposure of rat cerebella to ethanol under hypoxia imposed in vitro

Differential effects of ethanol on bid, tBid, and Bax:tBid interactions in postnatal day 4 and postnatal day 7 rat cerebellum

BACKGROUND

Exposure to ethanol (EtOH) during central nervous system (CNS) development can lead to a wide array of neuroanatomical, behavioral, and cognitive abnormalities, broadly subsumed under the fetal alcohol spectrum disorder classification. One mode of EtOH-induced interference in the normal developmental program appears to be through induction of apoptotic processes mediated by the Bcl-2 family of survival-regulatory proteins. The present series of studies investigated the role of the Bcl-2-related, pro-apoptotic Bid protein, and its truncated, apoptotically active fragment, tBid, in developmental EtOH neurotoxicity.

METHODS

Protein analyses were made via enzyme-linked immunosorbent assays (ELISA) in neonatal rat cerebellum, of basal Bid, and of Bid and tBid, following EtOH exposure via vapor inhalation, at an age of peak EtOH sensitivity in this region (postnatal day 4 [P4]) and a later age of relative resistance (P7). ELISA analyses were also made of Bax:tBid heterodimers, a process which activates Bax, essential for its apoptotic functioning. Finally, in vitro assessments of the importance of tBid to EtOH neurotoxicity were made in cultured cerebellar granule cells, using a specific tBid inhibitor.

RESULTS

Basal levels of Bid were higher at P4 compared to P7, possibly contributing to the differential sensitivity. EtOH exposure elicited further increases in cytosolic Bid and mitochondrial tBid when administration was at P4, but not at P7. Bax:tBid heterodimers were markedly increased by EtOH exposure on P4, an increase which persisted even 2 hours after termination of treatment. Similar effects were not seen at P7. The in vitro analyses revealed that tBid inhibition provided complete protection against EtOH-induced cell death and depressed EtOH-mediated cytochrome-c release.

CONCLUSIONS

These results suggest that Bid/tBid may be important elements in EtOH-mediated neurotoxicity during CNS development. The molecular processes and interactions revealed may represent critical points which can be targeted in studies concerned with designing possible therapeutic strategies for minimizing these devastative effects.

Ethanol influences on Bax associations with mitochondrial membrane proteins in neonatal rat cerebellum

These studies investigated interactions taking place at the mitochondrial membrane in neonatal rat cerebellum following ethanol exposure and focused on interactions between proapoptotic Bax and proteins of the permeability transition pore (PTP), voltage-dependent anion channel (VDAC) and adenine nucleotide translocator (ANT) of the outer and inner mitochondrial membranes, respectively. Cultured cerebellar granule cells were used to assess the role of these interactions in ethanol neurotoxicity. Analyses were made at the age of maximal cerebellar ethanol vulnerability (P4), compared to the later age of relative resistance (P7), to determine whether differential ethanol sensitivity was mirrored by differences in these molecular interactions. We found that, following ethanol exposure, Bax proapoptotic associations with both VDAC and ANT were increased, particularly at the age of greater ethanol sensitivity, and these interactions were sustained at this age for at least 2 h postexposure. Since Bax:VDAC interactions disrupt protective VDAC interactions with mitochondrial hexokinase (HXK), we also assessed VDAC:HXK associations following ethanol treatment and found such interactions were altered by ethanol treatment, but only at 2 h postexposure and only in the P4, ethanol-sensitive cerebellum. Ethanol neurotoxicity in cultured neuronal preparations was abolished by pharmacological inhibition of both VDAC and ANT interactions with Bax but not by a Bax channel blocker. Therefore, we conclude that, at this age, within the constraints of our experimental model, a primary mode of Bax-induced initiation of the apoptosis cascade following ethanol insult involves interactions with proteins of the PTP complex and not channel formation independent of PTP constituents.

Differential effects of ethanol on c-jun N-terminal kinase, 14-3-3 proteins, and Bax in postnatal day 4 and postnatal day 7 rat cerebellum

These studies investigated ethanol effects on upstream cellular elements and interactions which contribute to Bax-related apoptosis in neonatal rat cerebellum at ages of peak ethanol sensitivity (postnatal day 4 [P4]), compared to later ages of relative resistance (P7). Analyses were made of basal levels of the pro-apoptotic c-jun N-terminal kinase (JNK), Bax, and the 14-3-3 anchoring proteins, as well as the responsiveness of these substances to ethanol at P4 versus P7. Dimerization of Bax with 14-3-3 was also investigated at the two ages following ethanol treatment, a process which sequesters Bax in the cytosol, thus inhibiting its mitochondrial translocation and disruption of the mitochondrial membrane potential. Cultured cerebellar granule cells were used to examine the protective potential of JNK inhibition on ethanol-mediated cell death. Basal levels of JNK were significantly higher at P4 than P7, but no differences in the other proteins were found. Activated JNK, and cytosolic and mitochondrially-translocated Bax were increased in P4 but not P7 animals following ethanol exposure, while protective 14-3-3 proteins were increased only at P7. Ethanol treatment resulted in decreases in Bax:14-3-3 heterodimers at P4, but not at P7. Inhibition of JNK activity in vitro provided partial protection against ethanol neurotoxicity. Thus, differential temporal vulnerability to ethanol in this CNS region correlates with differences in both levels of apoptosis-related substances (e.g., JNK), and differential cellular responsiveness, favoring apoptosis at the most sensitive age and survival at the resistant age. The upstream elements contributing to this vulnerability can be targets for future therapeutic strategies.

Biopathology of the dentate-olivary complex in sudden unexplained perinatal death and sudden infant death syndrome related to maternal cigarette smoking

OBJECTIVES

The present study was aimed to evaluate the possible presence of cytohistologic and/or biologic modifications of the human dentate-olivary complex in sudden unexplained perinatal and infant deaths.

METHODS

We investigated the histologic morphology of the dentate and inferior olivary nuclei, the glial index, the c-fos and apoptotic immunopositivity, as well as the possible effects elicited by maternal cigarette smoking, in 44 cases of perinatal and infant death victims, aged from the 26th gestational week to 10 months of life.

RESULTS

We observed subtle alterations of both the medullary inferior olivary nucleus and of the cerebellar dentate nucleus, represented by a significant increase in the reactive astrocyte density and in the neuronal c-fos and apoptotic expression in unexplained death victims, compared with age-matched controls. These alterations were closely related to a maternal cigarette smoking habit.

DISCUSSION

We postulate that maternal smoking, besides inducing the previously demonstrated morpho-functional alterations of the autonomic central nervous system, could also exert an adverse influence on the dentate-olivary complex, leading to sudden death in vulnerable periods of perinatal development or early infancy.

Effects of Acute Ethanol Exposure on Regulatory Mechanisms of Bcl-2-Associated Apoptosis Promoter, Bad, in Neonatal Rat Cerebellum: Differential Effects During Vulnerable and Resistant Developmental Periods

BACKGROUND

Prenatal alcohol exposure produces anatomical and behavioral abnormalities associated with fetal alcohol syndrome (FAS). Animal FAS models have demonstrated temporal windows of vulnerability in the developing cerebellum, with substantial ethanol (EtOH)-mediated apoptotic activation during these periods. In rodents, the cerebellum is most sensitive to EtOH on postnatal days 4 to 6 (P4 to P6). At slightly later ages (P7 and later), this region is less vulnerable to EtOH. The present study investigated EtOH effects on mechanisms related to activities of Bad, a proapoptotic member of the Bcl-2 gene family, to further characterize processes underlying these disparate EtOH sensitivities. In healthy cells, Bad is retained in the cytosol by association with 14-3-3, a primarily cytosolic protein. Bad promotes apoptosis by disassociating from 14-3-3 and sequestering Bcl-xL through heterodimerization. This dimerization prevents the neutralizing association of Bcl-xL with Bax, freeing Bax to perform in a prodeath manner. Caspase-dependent cleavage of Bad to a 15-kDa fragment increases its proapoptogenic capacity.

METHODS

Two hours following EtOH exposure of P4 and P7 animals via inhalation, we determined how exposure affects intracellular localization and proteolytic cleavage of Bad and expression of cerebellar 14-3-3, using subcellular fractionation and Western blot techniques. Ethanol effects on interactions between Bad and 14-3-3 or Bcl-xL at the more vulnerable and less vulnerable ages were determined using an enzyme-linked immunosorbent assay-based technique to detect native protein-protein interactions.

RESULTS

At P4, EtOH increased mitochondrial localization of Bad, expression of a 15-kDa fragment recognized by Bad antibody, and formation of Bad:Bcl-xL complexes. At that more vulnerable age, EtOH also decreased formation of Bad:14-3-3 complexes. At P7, EtOH increased Bad:14-3-3 complexes and reduced Bad:Bcl-xL complexes. Cytosolic 14-3-3 remained unchanged by EtOH at P4 and P7.

CONCLUSIONS

Ethanol-induced alterations of Bad-related mechanisms at P4 favor a prodeath response. EtOH does not influence these same mechanisms in a manner that promotes cell death at P7. Divergent Bad-related responses at these 2 developmental ages likely contribute to their differential EtOH vulnerability.

The medical complications of alcohol use: understanding mechanisms to improve management

The use of alcohol in a dependent or even a regular heavy pattern predisposes the drinker to a range of adverse consequences. These include a risk of direct harm from alcohol, including organ damage, mental health disorders and a range of social and legal problems associated with behaviours due to alcohol's effects. The range of organ damage associated with regular heavy alcohol consumption is well described. Much new information on the mechanisms by which damage occurs is available and is reviewed in this paper. New knowledge can assist in the development of more appropriate management strategies for those affected by the medical complications of alcohol use. Genetic susceptibility to tissue injury is explored and the reasons why many heavy drinkers do not appear to experience organ damage are considered. Approaches to the management of certain alcohol-related disorders are outlined.

Prevention of alcohol-induced developmental delays and learning abnormalities in a model of fetal alcohol syndrome

OBJECTIVE

Prenatal alcohol exposure results in fetal death and neurobehavioral complications including learning impairment. Previously synthetic peptides derived from activity-dependent neurotrophic factor have been shown to prevent aspects of alcohol-induced damage in pregnancy. The objective of this work was to evaluate whether activity-dependent neurotrophic factor-12 could prevent alcohol-induced damage in a model of fetal alcohol syndrome.

STUDY DESIGN

Using a well-characterized model, C57Bl6/J mice on gestational day 8 were treated with placebo, alcohol (30% volume/volume alcohol 0.03 mL/kg), alcohol plus activity-dependent neurotrophic factor-12 30 minutes prior to alcohol, or activity-dependent neurotrophic factor-12 alone. Fetal death was assessed on gestational day 18 (25 litters were evaluated: alcohol, n = 5; placebo, n = 9; alcohol plus activity-dependent neurotrophic factor-12, n = 11). Neonatal behavior tests were performed on postnatal days 1 through 21 with the offspring of 12 dams (alcohol, n = 16; placebo, n = 46; alcohol plus activity-dependent neurotrophic factor-12, n = 23; and activity-dependent neurotrophic factor-12, n = 35). Adult males were tested in the Morris water maze for learning assessment and with the hole punch activity test for exploratory activity. Statistical analysis included Kruskal-Wallis and analysis of variance.

RESULTS

Fetal death was greater in alcohol (67% +/- 13%) vs placebo (8.4% +/- 3%, P < .001). Pretreatment with activity-dependent neurotrophic factor-12 prevented the alcohol-induced fetal death (2.2% +/- 8.1%) with levels similar to control (P = .12). Alcohol exposure caused a delay in achieving developmental milestones, with alcohol achieving milestones later than all other groups (all P < .001). Pretreatment with activity-dependent neurotrophic factor-12 prevented the alcohol-induced milestone delays. In the Morris water maze, the placebo learned, decreasing their latency to find the hidden platform over 70% (P < .01). Alcohol plus activity-dependent neurotrophic factor-12 also significantly learned, with a learning curve not different from placebo (all P > .5) and significantly better than alcohol on days 4, 6, and 7 (all P < .05). Alcohol exposure resulted in significantly less time in hole punch activity (P < .02) than control. Activity-dependent neurotrophic factor-12 pretreatment prevented the alcohol-induced decline, with levels the same as control (P = .1).

CONCLUSION

The novel peptide activity-dependent neurotrophic factor-12 prevents alcohol-induced fetal death and developmental and learning abnormalities in a model of fetal alcohol syndrome. This demonstrates that a single treatment with a peptide is efficacious and may be of value in the prevention of alcohol-induced damage.

Functional mechanisms of apoptosis-related proteins in neonatal rat cerebellum are differentially influenced by ethanol at postnatal days 4 and 7

Exposure of the developing nervous system to ethanol (EtOH) produces neurological aberrations associated with fetal alcohol syndrome. During a well-defined period, cerebellar neurons are highly susceptible to EtOH-induced death, primarily through apoptosis. Neonatal rodent cerebellum is exquisitely sensitive to EtOH on postnatal days 4-6 (P4-6); however, at slightly later developmental ages (P7 and later), EtOH effects are minimal. We have previously shown that EtOH differentially influences expression of apoptosis-related proteins of the Bcl-2 survival-regulatory gene family in P4 and P7 cerebellum. In the present study, the effects of EtOH on multiple functional mechanisms of Bcl-2, Bcl-xL, and Bax were investigated to characterize further the processes underlying these disparate EtOH sensitivities. For these analyses, we addressed the following questions, by using P4 and P7 cerebellar tissue following in vivo exposure: 1) Are there differential patterns of expression of antiapoptotic Bcl-2 or proapoptotic Bax in EtOH-vulnerable Purkinje cells that could contribute to the different degrees of temporal EtOH vulnerability? 2) How does EtOH affect intracellular localization of apoptosis-related proteins? 3) Does cleavage of Bax contribute to EtOH sensitivity? 4) Does EtOH differentially modulate cerebellar protein-protein interactions of Bcl-2, Bcl-xL, and Bax at the vulnerable vs. the resistant ages? Overall, we show that, at P4, the EtOH-mediated effects on Bcl-2, Bcl-xL, and Bax favor a prodeath response, whereas most of the intracellular responses to EtOH exposure at P7 promote survival. Such differential responsiveness likely plays a major role in the disparate ethanol vulnerability at these two postnatal ages.

Ethanol effects on neonatal rat cortex: comparative analyses of neurotrophic factors, apoptosis-related proteins, and oxidative processes during vulnerable and resistant periods

The developing central nervous system (CNS) is highly susceptible to ethanol, with acute or chronic exposure producing an array of anomalies and cell loss. Certain periods of vulnerability have been defined for various CNS regions, and are often followed by periods of relative ethanol resistance. In the present study, neonatal rats were acutely exposed to ethanol during a time when peak cell death is found in developing cerebral cortex (postnatal day 7; P7), and during a later neonatal period of ethanol resistance (P21). Comparisons at the two ages were made of basal levels of neurotrophic factors (NTFs), and in addition, ethanol-mediated changes in NTFs, apoptosis-related proteins, antioxidant activities, and generation of reactive oxygen species (ROS) were quantified at 0, 2, and 12 h following termination of exposure. It was found that at P21, basal levels of NTF nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) were considerably higher than at P7, possibly affording protection against ethanol neurotoxicity at this age. Following ethanol treatment at P7, approximately equal numbers of pro-apoptotic and pro-survival changes were produced, although most of the pro-apoptotic alterations occurred rapidly following termination of treatment, a critical period for initiation of apoptosis. At P21, however, the large majority of ethanol-mediated changes were adaptive, favoring survival. We speculate that the capacity of the older CNS to upregulate a number of protective elements within the cellular milieu serves to greatly mitigate ethanol neurotoxicity, while in younger animals, such adjustments are minimal, thus enhancing ethanol vulnerability within this developing region.

Role of protein kinase C in estrogen protection against apoptotic cerebellar cell death in ethanol-withdrawn rats

Results of studies from our laboratory have shown that administration of 17beta-estradiol (E(2)) reduces cerebellar neuronal damage during ethanol withdrawal (EW). In the current study, we examined mechanisms underlying E(2) protection against EW-associated cerebellar damage by assessing apoptotic indicators: DNA fragmentation, caspase-3 activity, and protein kinase C (PKC) activity. Ovariectomized rats, implanted with E(2) or oil pellets, received ethanol [7.5% weight/volume (wt./vol.)] (EW/E(2) group and EW/Oil group, respectively) chronically (for 5 weeks) or control dextrin diet (Dextrin/Oil group). At day 14 of EW, cerebelli were collected for the terminal deoxynucleotidyltransferase (TdT)-mediated dUDP-biotin nick end labeling (TUNEL) assay to detect DNA fragmentation and for immunohistochemistry to detect caspase-3 activation. A separate group of rat cerebelli was prepared to assess for total PKC activity, as well as for activity of a specific PKC isozyme, epsilon (PKCepsilon), by using an in vitro [gamma-(32)P]ATP phosphorylation assay at days 1 and 14 of EW. Results indicated that rats in the EW/Oil group had more DNA fragments and caspase-3-positive neuronal cells than observed for control rats, and these effects were inhibited by E(2) treatment. For total PKC activity at day 1 of EW, rats in the EW/E(2) group had a lower cytosolic PKC activity than observed for either rats in the EW/Oil group or control rats. At day 14 of EW, both EW groups had a lower total PKC activity than observed for control rats. For PKCepsilon activity, rats in the EW/E(2) group had a lower cytosolic PKCepsilon activity than observed for rats in the EW/Oil group or for control rats at day 1, and they had a lower membrane PKCepsilon activity at day 14 of EW than observed for control rats. These findings support the suggestion that E(2) protects against cerebellar neuronal damage in ethanol-withdrawn rats by inhibition of DNA fragmentation and caspase-3 activation, and that reduced PKC activity may be involved in the protection.

Effects of ethanol on neurotrophic factors, apoptosis-related proteins, endogenous antioxidants, and reactive oxygen species in neonatal striatum: relationship to periods of vulnerability

The developing central nervous system is extremely sensitive to ethanol, with well-defined temporal periods of vulnerability. Many brain regions are particularly susceptible to ethanol during the early neonatal period, corresponding to the human third trimester, which represents a dynamic period of growth and differentiation. For this study, neonatal rats were acutely exposed to ethanol or control conditions at a neonatal age when the developing striatum has been shown to be vulnerable to ethanol (postnatal day 3 [P3]), and at a later age (P14), when this developing region is relatively ethanol-resistant. We then analyzed basal levels of neurotrophic factors (NTFs), and ethanol-mediated changes in NTFs, apoptosis-related proteins, antioxidants, and reactive oxygen species (ROS) generation, which may underlie this differential temporal vulnerability. Sequential analyses were made following ethanol exposure on these two postnatal days, with assessments of NTFs nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4); apoptosis-related proteins Bcl-2, Bcl-xl, Bax, Akt and c-jun N-terminal kinase (JNK); antioxidants superoxide dismutase, glutathione reductase and catalase; and ROS. The results indicated that basal levels of BDNF, and to some degree NGF, were greater at the older age, and that ethanol exposure at the earlier age elicited considerably more pro-apoptotic and fewer pro-survival changes than those produced at the later age. Thus, differential temporal vulnerability to ethanol in this CNS region appears to be related to differences in both differential levels of protective substances (e.g. NTFs), and differential cellular responsiveness which favors apoptosis at the most sensitive age and survival at the resistant age.

Ethanol-mediated generation of reactive oxygen species in developing rat cerebellum

The neonatal cerebellum undergoes an early period of ethanol sensitivity in which profound neuronal loss is seen following acute exposure, while slightly later exposure produces no such loss. This study was designed to determine whether this differential susceptibility is related to differences in ethanol-induced generation of reactive oxygen species (ROS). We found that ethanol treatment on postnatal day 4 (P4), the peak period of cerebellar vulnerability, resulted in ROS increases, but slightly later exposure (on P7) produced no immediate changes in ROS, but reductions were seen at 12 and 24 h following exposure. Exposure on P14 produced consistent decreases in ROS production. Thus, differential responsiveness in oxidative processes may play a major role in the differential temporal ethanol vulnerability of developing cerebellum.

Time course and manner of Purkinje neuron death following a single ethanol exposure on postnatal day 4 in the developing rat

The present study was designed to evaluate the time course and manner of Purkinje cell death following a single ethanol dose delivered intragastrically on postnatal day (PN) 4 to rat pups. Analysis included immunolabeling of Purkinje cells with antibody specific for calbindin D28k and counting of Purkinje cells in each lobule of a mid-vermal slice. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling analysis and immunodetection for cleaved (activated) caspase-3 enzyme was used to identify apoptosis, with calbindin D28k co-immunolabeling to identify apoptotic Purkinje cells. Finally, immunodetection for cytochrome c, again with co-labeling using calbindin D28k antibody, identified intracellular release of cytochrome c from the mitochondria into the cytoplasm of Purkinje cells. The data demonstrate that a single dose of ethanol results in a significant and extensive, lobular dependent loss of Purkinje cells within 24 h after administration. Extensive loss in the early developing lobules (I-III, VIII-X) and less to no loss in the later developing lobules (IV-VII) is consistent with prior literature reports on the ethanol-induced effects on Purkinje cells at this age. Clear and consistent evidence of apoptotic Purkinje cells was identified and the pattern was transient in nature. Finally, cytochrome c is released from the mitochondria of Purkinje cells in a time course consistent with the activation of the mitochondrial pathway of apoptosis. These data support the hypothesis that ethanol-induced loss of Purkinje cells involves apoptotic mechanisms. Furthermore, the initiation of apoptosis by ethanol is consistent with ethanol-induced interruptions of Purkinje cell neurotrophic support leading to activation of the mitochondrial pathway of apoptosis.

Effect of hypoxia on DNA fragmentation in different brain regions of the newborn piglet

DNA fragmentation has been studied in different regions of the newborn piglet brain following different times of normobaric hypoxia (5% O(2), 95% N(2)). After 1 hr of hypoxia, fragmented DNA was observed in cerebellum, cortex, hippocampus, and striatum but not in hypothalamus. More fragmentation occurred in these areas of the brain when the animals were kept under hypoxia for times up to 8 hr 45 min. When the animals were submitted to hypoxia for two and a half hours, integrity of DNA was recovered respectively after 3 hr of exposure to the ambient atmosphere in hippocampus and striatum, but 4 hr of recovery were necessary for cerebellum and cortex. These results are discussed in terms of the consequences of neonatal hypoxia and apnea for newborn infants and economical impact for farm animals.

Ethanol potentiates dopamine release during acute hypoxia in rat striatum

We, and others, have previously demonstrated that N-methyl-D-aspartate (NMDA) receptor is involved in hypoxia or ischemia-mediated responses. We found that the NMDA antagonist ketamine attenuates cortical nitric oxide release during cerebroischemia. It has been reported that ethanol (EtOH) antagonizes NMDA-induced responses in various systems. In the present study, the interaction of EtOH and KCl-evoked striatal dopamine release in vivo during acute hypoxia was examined. High-speed chronoamperometric recording techniques, using Nafion-coated carbon fiber electrodes, were used to evaluate extracellular dopamine (DA) concentration in the striatum of urethane-anesthetized Sprague-Dawley rats. KCl was directly applied to the striatum to evoke release of DA. These anesthetized animals were paralyzed with d-tubocurarine and connected to a respirator to allow controlled respiration. Systemic concentrations of oxygen were altered by changing the rate of the respirator. We previously reported that lowering the respiratory rates from 90 to 20 times/min for 5 min decreased arterial PO(2) and facilitated KCl-induced DA release in the striatum. In this study, we found that application of NMDA antagonist MK801 attenuates hypoxic DA release, suggesting that NMDA receptor is involved in this hypoxic reaction. In contrast, EtOH dose dependently enhanced KCl-evoked DA release during hypoxia. To further examine the interactions of excitatory amino acid and EtOH on DA release, glutamate was locally applied to the striatum. Glutamate-induced DA release was not affected by the systemic application of EtOH. Taken together, these data suggest that EtOH enhances DA release in vivo during short-term hypoxia, possibly through mechanisms other than excitatory amino acid pathways.

Synthesis and reactivity of a potential carcinogenic metabolite of tamoxifen: 3,4-dihydroxytamoxifen-o-quinone

Although tamoxifen is approved for the treatment of hormone-dependent breast cancer as well as for the prevention of breast cancer in high-risk women, several studies in animal models have shown that tamoxifen is heptocarcinogenic, and in humans, tamoxifen has been associated with an increased risk of endometrial cancer. One potential mechanism of tamoxifen carcinogenesis could involve metabolism of tamoxifen to 3,4-dihydroxytamoxifen followed by oxidation to a highly reactive o-quinone which has the potential to alkylate and/or oxidize cellular macromolecules in vivo. In the study presented here, we synthesized the 3,4-dihydroxytamoxifen, prepared its o-quinone chemically and enzymatically, and studied the reactivity of the o-quinone with GSH and deoxynucleosides. The E (trans) and Z (cis) isomers of 3,4-dihydroxytamoxifen were synthesized using a concise synthetic pathway (four steps). This approach is based on the McMurry reaction between the key 4-(2-chloroethoxy)-3,4-methylenedioxybenzophenone and propiophenone, followed by selective removal of the methylenedioxy ring of (E, Z)-1-[4-[2-(N,N-dimethylamino)ethoxy]phenyl]-1-(3, 4-methylenedioxyphenyl)-2-phenyl-1-butene with BCl(3). Oxidation of 3,4-dihydroxytamoxifen by activated silver oxide or tyrosinase gave 3,4-dihydroxytamoxifen-o-quinone as a mixture of E and Z isomers. The resulting o-quinone has a half-life of approximately 80 min under physiological conditions. Reaction of the o-quinone with GSH gave two di-GSH conjugates and three mono GSH conjugates. Incubation of 3,4-dihydroxytamoxifen with GSH in the presence of microsomal P450 gave the same GSH conjugates which were also detected in incubations with human breast cancer cells (MCF-7). Reaction of 3, 4-dihydroxytamoxifen-o-quinone with deoxynucleosides gave only thymidine and deoxyguanosine adducts; neither deoxyadenosine nor deoxycytosine adducts were detected. Preliminary studies conducted with human breast cancer cell lines showed that 3, 4-dihydroxytamoxifen exhibited cytotoxic potency similar to that of 4-hydroxytamoxifen and tamoxifen in an estrogen receptor negative (ER(-)) cell line (MDA-MB-231); however, in the ER(+) cell line (MCF-7), the catechol metabolite was about half as toxic as the other two compounds. Finally, in the presence of microsomes and GSH, 4-hydroxytamoxifen gave predominantly quinone methide GSH conjugates as reported in the previous paper in this issue [Fan, P. W., et al. (2000) Chem. Res. Toxicol. 13, XX-XX]. However, in the presence of tyrosinase and GSH, 4-hydroxytamoxifen was primarily converted to o-quinone GSH conjugates. These results suggest that the catechol metabolite of tamoxifen has the potential to cause cytotoxicity in vivo through formation of 3,4-dihydroxytamoxifen-o-quinone.

Ethanol attenuates lactate production in hypoxic postnatal day 4 rat cerebella

Ethanol consumption during pregnancy may lead to a low oxygen supply to the brain of the developing fetus. Such a reduction in the oxygen supply will result in changes in intra- and extracellular lactate production, which subsequently may lead to cytoplasmic acidosis, changes in cerebral metabolism, and eventually, cell death. We used a novel application of gas chromatography to measure lactate changes, on a global level, in the cerebellar tissue of postnatal day (PD) 4 and PD 10 rat pups following in vitro exposure of either hypoxia or hypoxia plus ethanol (hypoxia/ethanol). The results showed hypoxia-induced increases in lactate concentrations as a function of treatment time in both PD 4 and PD 10 cerebellar tissue. However, there was a differential response to the additional ethanol treatment between the two age groups assessed, with an attenuation of the time-dependent increase of lactate production following hypoxia treatment in PD 4 cerebellar tissue. The results also indicated that PD 4 cerebellar tissue had increased oxygen utilization when compared with PD 10 tissue exposed to the same conditions. The ethanol-induced reduction in lactate is hypothesized as being due to limitations in glucose transport and utilization under ethanol/hypoxia exposure. It is believed that such limitations in cellular function may initiate a sequence of events that produce at least some of the cerebellar neuronal loss reported in the fetal alcohol literature.