Stimulatory effects of ethanol on amino acid transport by rat fetal hepatocytes

Fetal alcohol spectrum disorders model alters the functionality of glutamatergic neurotransmission in adult zebrafish

Fetal alcohol spectrum disorders (FASD) describe a wide range of ethanol-induced developmental disabilities, including craniofacial dysmorphology, and neurochemical and behavioral impairments. Zebrafish has become a popular animal model to evaluate the long-lasting effects of, both, severe and milder forms of FASD, including alterations to neurotransmission. Glutamate is one of the most affected neurotransmitter systems in ethanol-induced developmental disabilities. Therefore, the aim of the present study was to evaluate the functionality of the glutamatergic neurotransmitter system in an adult zebrafish FASD model. Zebrafish larvae (24 h post-fertilization) were exposed to ethanol (0.1 %, 0.25 %, 0.5 %, and 1%) for 2 h. After 4 months, the animals were euthanized and their brains were removed. The following variables were measured: glutamate uptake, glutamate binding, glutamine synthetase activity, Na+/K + ATPase activity, and high-resolution respirometry. Embryonic ethanol exposure reduced Na+-dependent glutamate uptake in the zebrafish brain. This reduction was positively modulated by ceftriaxone treatment, a beta-lactam antibiotic that promotes the expression of the glutamate transporter EAAT2. Moreover, the 0.5 % and 1% ethanol groups demonstrated reduced glutamate binding to brain membranes and decreased Na+/K + ATPase activity in adulthood. In addition, ethanol reduced glutamine synthetase activity in the 1% EtOH group. Embryonic ethanol exposure did not alter the immunocontent of the glutamate vesicular transporter VGLUT2 and the mitochondrial energetic metabolism of the brain in adulthood. Our results suggest that embryonic ethanol exposure may cause significant alterations in glutamatergic neurotransmission in the adult zebrafish brain.

The assessment of an in-vitro model for evaluating the role of PARP in ethanol-mediated hepatotoxicity

This investigation aims to assess whether the hepatocellular carcinoma cell line, HepG2, is an appropriate model to assess the role of poly (ADP-ribose) polymerase (PARP) during acute ethanol toxicosis. HepG2 cells were dosed with graded concentrations of ethanol, ranging from 100 mM to 800 mM, for 6 hours to assess PARP activity induction, while another parallel experiment examined cellular damage via medium aspartate aminotransferase activity and cellular viability via MTT reduction. Aspartate aminotransferase activity was significantly elevated at 600 mM ethanol (FOLD; P < 0.01), with further increases at the 800 mM dose (1.43 fold; P < 0.001), compared to controls. Cellular viability was not significantly decreased compared to controls among all dose groups. PARP activity measured in total cell lysates showed a significant decreasing trend with respect to ethanol dose, reaching statistical significance at the 100 mM dose group (P < 0.05). Paradoxically, exposure to 50 μM etoposide (Positive apoptosis-inducing control) did not demonstrate significant PARP activity ablation. When analyzing PARP activity observation temporally, a significant correlation (R(2) =0.5314) was observed between activity and assay sequence. Overall, a clear HepG2 insensitivity to ethanol was observed.

Glutathione content as a potential mediator of the vulnerability of cultured fetal cortical neurons to ethanol-induced apoptosis

Ethanol ingestion during pregnancy elicits damage to the developing brain, some of which appears to result from enhanced apoptotic death of neurons. A consistent characteristic of this phenomenon is a highly differing sensitivity to ethanol within specific neuron populations. One possible explanation for this "selective vulnerability" could be cellular variations in glutathione (GSH) homeostasis. Prior studies have illustrated that ethanol elicits apoptotic death of neurons in the developing brain, that oxidative stress may be an underlying mechanism, and that GSH can be neuroprotective. In the present study, both multiphoton microscopy and flow cytometry demonstrate a striking heterogeneity in GSH content within cortical neuron populations. Ethanol differentially elicits apoptotic death and oxidative stress in these neurons. When neuron GSH content is reduced by treatment with butathione sulfoxamine, the ethanol-mediated enhancement of reactive oxygen species is exacerbated. Sorting of cells into high- and low-GSH populations further exemplifies ethanol-mediated oxidative stress whereby apoptotic indices are preferentially elevated in the low-GSH population. Western blot analysis of the low-GSH subpopulations shows higher ethanol-mediated expression of active caspase 3 and 24-kDa PARP-1 fragments compared with the high-GSH subpopulation. In addition, neuronal content of 4-hydroxynonenal adducts is higher in low-GSH neurons in response to ethanol. These studies suggest that GSH content is an important predictor of neuronal sensitivity to ethanol-mediated oxidative stress and subsequent cell death. The data support the proposition that the differences in proapoptotic responses to ethanol within specific neuron populations reflect a heterogeneity of neuron GSH content.

Astrocyte control of fetal cortical neuron glutathione homeostasis: up-regulation by ethanol

Ethanol increases apoptotic neuron death in the developing brain and at least part of this may be mediated by oxidative stress. In cultured fetal rat cortical neurons, Ethanol increases levels of reactive oxygen species (ROS) within minutes of exposure and reduces total cellular glutathione (GSH) shortly thereafter. This is followed by onset of apoptotic cell death. These responses to Ethanol can be blocked by elevating neuron GSH with N-acetylcysteine or by co-culturing neurons with neonatal cortical astrocytes. We describe here mechanisms by which the astrocyte-neuron gamma-glutamyl cycle is up-regulated by Ethanol, enhancing control of neuron GSH in response to the pro-oxidant, Ethanol. Up to 6 days of Ethanol exposure had no consistent effects on activities of gamma-glutamyl cysteine ligase or glutathione synthetase, and GSH content remained unchanged (p < 0.05). However, glutathione reductase was increased with 1 and 2 day Ethanol exposures, 25% and 39% for 2.5 and 4.0 mg/mL Ethanol by 1 day, and 11% and 16% for 2.5 and 4.0 mg/mL at 2 days, respectively (p < 0.05). A 24 h exposure to 4.0 mg/mL Ethanol increased GSH efflux from astrocyte up to 517% (p < 0.05). Ethanol increased both gamma-glutamyl transpeptidase expression and activity on astrocyte within 24 h of exposure (40%, p = 0.05 with 4.0 mg/mL) and this continued for at least 4 days of Ethanol treatment. Aminopeptidase N activity on neurons increased by 62% and 55% within 1 h of Ethanol for 2.5 and 4.0 mg/mL concentration, respectively (p < 0.05), remaining elevated for 24 h of treatment. Thus, there are at least three key points of the gamma-glutamyl cycle that are up-regulated by Ethanol, the net effect being to enhance neuron GSH homeostasis, thereby protecting neurons from Ethanol-mediated oxidative stress and apoptotic death.

Astrocytes protect neurons from ethanol-induced oxidative stress and apoptotic death

Ethanol induces oxidative stress in cultured fetal rat cortical neurons and this is followed by apoptotic death, which can be prevented by normalization of cell content of reduced glutathione (GSH). Because astrocytes can play a central role in maintenance of neuron GSH homeostasis, the following experiments utilized cocultures of neonatal rat cortical astrocytes and fetal cortical neurons to determine if astrocytes could protect neurons from ethanol-mediated apoptotic death via this mechanism. In cortical neurons cultured in the absence of astrocytes, ethanol (2.5 and 4 mg/ml; 6-, 12-, and 24-hr exposures) decreased trypan blue exclusion and the MTT viability measures by up to 45% (P < 0.05), increased levels of reactive oxygen species (ROS) by up to 81% (P < 0.05), and decreased GSH within 1 hr of treatment by 49 and 51% for 2.5 and 4 mg/ml, respectively (P < 0.05). This was followed by onset of apoptotic cell death as determined by increased Annexin V binding and DNA fragmentation by 12 hr of ethanol exposure. Coculturing neurons with astrocytes prevented GSH depletion by 2.5 mg/ml ethanol, whereas GSH content was increased over controls in neurons exposed to 4 mg/ml ethanol (by up to 341%; P < 0.05). Ethanol generated increases in neuron ROS and apoptosis; decreases in viability were also prevented by coculture. Astrocytes were largely insensitive to ethanol, using the same measures. Only exposure to 4.0 mg/ml ethanol decreased GSH content in astrocytes, concomitant with a 204% increase in GSH efflux (P < 0.05). These studies illustrate that astrocytes can protect neurons from ethanol-mediated apoptotic death and that this may be related to maintenance of neuron GSH.

Selective antiproliferative and apoptotic effects of flavonoids purified from Rhus verniciflua Stokes on normal versus transformed hepatic cell lines

Considerable attention is being concentrated on dietary flavonoids in developing novel cancer-preventive approaches due to their potential ability to induce selective apoptosis of cancer cells. In this study, we prepared a flavonoid-containing fraction from a crude acetone extract of Rhus verniciflua Stokes (RVS), traditionally used as a food additive and as an herbal medicine, and named RVS chloroform-methanol fraction (RCMF). We evaluated the effects of RCMF on proliferation and apoptosis using mouse embryonic primary hepatic cells (MPHC), embryonic normal hepatic cell line (BNL CL.2), and its SV40-mediated transformed cell line (BNL SV A.8). We also investigated the effects of RCMF on the antioxidant defense system in those cells. This study demonstrated that RCMF exhibited a selective growth inhibition and apoptosis induction on transformed cells. BNL SV A.8 cells were more sensitive to RCMF-mediated cytotoxicity than were MPHC or BNL CL.2. RCMF-mediated reduction of MnSOD activity and glutathione (GSH) content in BNL SV A.8 cells is thought to be associated with RCMF-induced apoptosis. Our findings suggest that RCMF is an agent which may be capable of inducing growth inhibition and apoptosis of hepatic tumor cells.

Ethanol-induced oxidative stress and enzymatic defenses in cultured fetal rat hepatocytes

Previously, we have documented an ethanol (E)-induced oxidative stress (OS) in cultured fetal rat hepatocytes (FRH). The cause of this is uncertain, but an inhibition of key antioxidant enzymes could be a/the factor. OS was also observed in fetal liver (FL) during in utero E exposure, but not in maternal liver, a difference that might be related to selectively lower enzymatic defenses in the fetus. Here, we record effects of E on activities of catalase (Cat), superoxide dismutase (Cu, Zn SOD and Mn SOD), glutathione peroxidase (GPX), and glutathione-S-transferase (GST) in FRH isolated from 20-day-old fetuses and exposed to E (2 mg/ml) for up to 24 h and we compare these to adult rat liver data. E treatment decreased fetal liver reduced glutathione (GSH) pools by 23% (p < 0.05) and increased malondialdehyde (MDA) by 14% (p < 0.05) within 24 h of E exposure. E caused an increase in fetal liver Cat by 18%, 32%, and 47% by 3, 6, and 24 h of E, respectively (p < 0.05). A 24-h E exposure increased Cu, Zn SOD by 22% (p < 0.05) and Mn SOD by 21% (p < 0.05). A 24 h E treatment increased GPX by 18% (p < 0.05) and GST by 17% (p < 0.05). Cat in whole FL was 26% of adult (p < 0.05) whereas Cu, Zn SOD and Mn SOD in whole FL were 12% and 11% of adult levels (p < 0.05). GPX and GST in FL were 11% and 28% of adult values (p < 0.05). It is concluded that in FRH, E-induced OS is not caused by impaired activities of these enzymes, but their low basal activities (vs. adult) may predispose the fetus to OS.

In utero ethanol exposure elicits oxidative stress in the rat fetus

Prior studies in our laboratory have shown that exposure of cultured fetal rat hepatocytes to ethanol (E) blocks epidermal growth factor-dependent replication and that this is paralleled by cell membrane damage, mitochondrial dysfunction, membrane lipid peroxidation (LP), and enhanced generation of reactive oxygen species. These measures of E-mediated oxidative stress (OS) were mitigated by treatment with antioxidants, and cell replication could be normalized by maintaining cell glutathione (GSH) pools. We have now extended these studies to an in vivo model. Rats were administered E (4 g/kg, po) at 12-hr intervals on days 17 and 18 of gestation and killed on day 19, 1 hr following a final dose of E (a total of 5 doses). Fetal and maternal brain and liver were assayed for signs of OS. The 2-day in utero E exposure increased membrane LP in fetal brain as evidenced by increased malondialdehyde (MDA) levels from 1.76 +/- 0.12 SE (nMol/mg protein) to 2.00 +/- 0.08 (p < 0.05) and conjugated dienes from 0.230 +/- 0.006 SE (OD223/mg lipid) to 0.282 +/- 0.006 (p < 0.05). In fetal liver, MDA levels increased from 2.39 +/- 0.08 SE (nMol/mg protein) to 2.87 +/- 0.08 (p < 0.05), whereas dienes differed significantly only between ad libitum controls and the E and pair-fed control groups (p < 0.05). E decreased GSH levels in fetal brain by 19%, from 19.88 +/- 0.72 to 16.13 +/- 1.06 (nMol/mg protein) (p < 0.05). A 10% decrease in GSH was seen in fetal liver (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Ganciclovir transfer by human placenta and its effects on rat fetal cells

Cytomegalovirus is a common cause of intrauterine infection. Ganciclovir is an accepted therapeutic agent for this infection, but is proscribed in pregnancy, except when there is a life-threatening maternal infection, because of its known teratogenic and embryotoxic effects in experimental animals. There are no such data in humans and the human transplacental transfer of this drug has not been studied. This study defines the rate and mechanism of human-placental ganciclovir transport using maternal-facing syncytiotrophoblast vesicles and the perfused, isolated single-cotyledon system and determines further the effects of ganciclovir on fetal tissue, using cultured rat fetal hepatocytes. Ganciclovir was taken up by the maternal-facing placental membrane by a carrier-dependent, Na-independent system inhibited by adenine, guanine, and acyclovir, but not by cytosine and thymine or thymidine and uridine. By contrast, the overall transfer of the drug by the placenta was passive and without drug metabolism. Therefore, the drug is concentrated initially at the maternal placental surface and then crosses passively into the fetal compartment, with the latter process being rate-limiting. There was little or no toxic effect of high concentrations of ganciclovir on cultured fetal-rat hepatocytes.

Development of primary culture of ovine fetal hepatocytes for studies of amino acid metabolism and insulinlike growth factors

We report the development and characterization of a system of primary culture of ovine fetal hepatocytes to aid in the understanding of the cellular regulation of fetal growth and metabolism with emphasis on amino acid metabolism and insulinlike growth factor gene expression and to allow comparison to in vivo studies. Hepatocytes were isolated from late gestation fetal lambs by in situ perfusion and collagenase digestion utilizing occlusion of the ductus venosus to limit intrahepatic shunting. Hepatocytes were cultured in media modified to mimic fetal concentrations of glucose, lactate, and amino acids. Ovine fetal hepatocytes in primary culture maintain the pattern of fetal amino acid production and utilization seen across the fetal liver in vivo. Specifically, there is a net production of serine and a net utilization of glycine. Cultured ovine fetal hepatocytes specifically increase tritiated thymidine incorporation in response to insulin and insulinlike growth factor II (IGF-II). IGF-II mRNA abundance is high and IGF-I mRNA is low in cultured ovine fetal hepatocytes as in the fetal sheep liver in vivo. These data demonstrate the successful isolation of ovine fetal hepatocytes that retain some of the characteristics of the ovine fetal liver while maintained in short-term culture.

Ethanol inhibits C6 cell growth: fetal alcohol syndrome model

Maternal consumption of ethanol produces a pattern of malformations, including nervous system abnormalities, in the developing fetus, a state called Fetal Alcohol Syndrome. We report the dose-dependent inhibition by ethanol of the growth of a glioma derived cell line, C6 cells; the effects occur at ethanol concentrations commonly encountered in the blood during human intoxication. The effects occur with different morphological subtypes of the cell line and do not occur when the cells are exposed to iso-osmolar concentrations of other chemicals. The results demonstrate that C6 cells are a model for the study of the effects of ethanol on nervous system cell growth.

Decreased glucose transporter 1 gene expression and glucose uptake in fetal brain exposed to ethanol

Using pregnant rats fed equicaloric liquid diets (AF, and libitum-fed controls; PF, pair-fed controls; EF, ethanol-fed), we have previously shown that maternal alcoholism produces a specific and significant decrease of glucose in the fetal brain, which is accompanied by growth retardation. To further define the mechanisms of ethanol-induced perturbations in fetal fuel supply, we have examined (i) the uptake of 2-deoxyglucose (2-DG) by dissociated brain cells from fetal rats that were exposed to ethanol in utero and (ii) the steady-state levels of the glucose transporter-1 (GT-1) mRNA. A 9% decrease in brain weight (P less than 0.001) and a 54.8% reduction in 2-DG uptake into brain cells (P less than 0.02) were found in offspring of EF mothers compared to the AF group. Brain weight correlated with the rate of 2-DG uptake (P less than 0.05). Northern blot analysis showed a 50% reduction of GT-1 mRNA in EF brain relative to that in the AF and PF groups. We conclude that glucose transport into the brain is an important parameter altered by maternal ethanol ingestion.

Interactive effects of ethanol and caffeine on rat fetal hepatocyte replication and EGF receptor expression

This study reports on the interactive effects of ethanol and caffeine on growth of rat fetal hepatocytes. Exposure of cultured rat fetal hepatocytes (RFH) to ethanol in concentrations above 1 mg/ml, causes a blockade of EGF-dependent cell replication along with an overexpression of surface EGF receptors (EGF-R). However, RFHs exposed for 24 hours to ethanol at a concentration of 1 mg/ml alone had little effect on cell replication. Caffeine, when combined with this concentration of alcohol, progressively impaired RFH growth by up to 100%. Caffeine alone up to 10 micrograms/ml, on the other hand, caused a progressive increase in RFH replication associated with a 69% enhancement of DNA synthesis. Caffeine concentrations in excess of 50 micrograms/ml had no effect on replicative capacity. Concomitant caffeine exposure had no effect on the ethanol-related increase in cell DNA content, yet it caused a further enhancement of the cell protein accural induced by ethanol alone. Caffeine (10 micrograms/ml) alone had no effect on EGF-R expression, while ethanol (2 mg/ml) increased it by almost 200%. Addition of caffeine to ethanol reduced this enhanced EGF binding by 45%. Scatchard analysis indicated that no treatment altered ligand affinity for the receptor, but that the alterations in binding caused by ethanol and the caffeine/ethanol combination reflected changes in binding capacity, in both low and high affinity components. It is concluded that (1) ethanol blocks EGF-mediated replication accompanied by a reduction in DNA synthesis, (2) caffeine alone at low concentrations has the opposite effect and can actually potentiate the EGF-mediated mitogenic response, (3) caffeine in combination with ethanol acts synergistically to reduce RFH replication.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrest of epidermal growth factor-dependent growth in fetal hepatocytes after ethanol exposure

Exposure of the fetal rat hepatocyte to ethanol in vitro blocks epidermal growth factor (EGF)-dependent cell replication. To define possible mechanisms for this growth arrest, we determined the effects of ethanol on EGF binding and EGF receptor (EGF-R) levels. During a 24-h exposure to ethanol (1.7 mg/ml, 31 mM), cell replication was completely blocked while EGF binding per cell doubled. This effect was no specific for EGF, with variable degrees of increased binding noted for insulin, transferrin, and glucagon. Significantly increased EGF binding was seen after 6 h of ethanol exposure, and both growth arrest and enhanced EGF binding were reversed within 12 h of ethanol withdrawal. Increases in both "high" and "low" affinity sites were seen, with no changes in the apparent Kd's. Total RNA, beta-actin mRNA, and EGF-R mRNA were increased 50-70% in ethanol exposed cells. However, direct measurements of EGF-R synthesis rates by [35S]methionine incorporation revealed no differences between control and ethanol exposed cells. Internalization of EGF-R was significantly altered by ethanol exposure. A 2-h incubation resulted in the internalization of 57% of the ligand in control cells, while only 31% of bound EGF was internalized in the ethanol exposed cells. Thus, the enhanced EGF binding may be due to decreased efficiency of internalization.

Ethanol effects on active Na+ and K+ transport in cultured fetal rat hepatocytes

To define further the influence of ethanol on membranes, its effects on Na+ pump function were studied in monolayer cultures of fetal rat hepatocytes. The effects of ethanol (2 and 4 mg/ml) on total K+ influx, ouabain-sensitive K+ influx, Na+ pump density (from specific [3H]ouabain binding), pump turnover rates and intracellular Na+ were measured following exposure of the cells to ethanol for 1-24 hr. In parallel studies, the effects of ethanol (2 mg/ml) on cell water content and membrane fluidity were measured. Ethanol had no immediate effect on K+ influx, but after 1 hr ethanol in concentrations of 2 and 4 mg/ml decreased the total K+ influx (mumol/10(11) cells/sec) from a control of 8.5 +/- 0.64 to 4.46 +/- 0.50 and 4.09 +/- 0.26 respectively (N = 6 for each experiment; P less than 0.001). This represented the maximum effect of ethanol since after 6 and 24 hr of ethanol treatment the K+ influx had increased towards control levels but remained significantly (P less than 0.01 for 2 mg/ml and P less than 0.001 for 4 mg/ml) below that in control cells even at 24 hr. The decrease in K+ influx reflected a decrease in mean ouabain-sensitive K+ influx from a control of 5.87 to 3.24 and 2.70 (mumol/10(11) cells/sec) after a 1-hr treatment with 2 and 4 mg ethanol/ml medium respectively. Ethanol (2 mg/ml) treatment for 1-hr decreased Na+ pump density (x 10(5) molecules ouabain per cell) from a control of 2.80 +/- 0.30 to 1.70 +/- 0.11 (P less than 0.001). At 6 and 24 hr [3H]ouabain binding showed a pattern similar to that seen with the K+ influx, tending to return to pretreatment levels. There was no change in individual pump turnover rates in the presence of ethanol. Following exposure to ethanol, cellular Na+ content steadily increased over the first 6 hr and then returned to control levels. When corrected for parallel changes in cell volume, however, intracellular Na+ concentration increased by 17% (P less than 0.01) after 1 hr and thereafter remained at this higher level throughout the 24-hr period. Measurements of membrane fluidity showed that it was increased markedly by ethanol at a concentration of 2 mg/ml and that the effect bore a close temporal relationship to the changes in active K+ influx and Na+ pump density. We conclude that ethanol has a depressant effect on hepatic Na+ pump function, resulting in an increase in intracellular Na+ and an eventual gain in cell water.(ABSTRACT TRUNCATED AT 400 WORDS)