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S Schenker

Publications and source records attributed to S Schenker.

At least 37 records · Page 2Linked to original sources
PubMed1998

Histochemical method for localization of hydrogen peroxide and oxygen radicals in the intact neonatal brain.

The generation of reactive oxygen species has been implicated in the pathogenesis of a wide variety of diseases of the central nervous system. Often these pathological conditions involve damage to specific cell types within selected areas of the brain. Thus, there is a marked need for a method which allows microscopic visualization/detection of these oxygen radicals in discrete brain areas. We are reporting a method to histochemically localize, with single cell resolution, hydrogen peroxide (H2O2) and oxygen radicals in the neonatal brain in vivo. This method expands on the technique developed to visualize H2O2 and the superoxide anion radical (O2-) in isolated perfused organs (e.g., lung, heart) (Bobbs, 1994). With our technique, the intact brain is perfused intracardially with warm oxygenated saline to remove blood, followed by perfusion with buffers containing either iron and diethylenetriaminepentaacetate for the detection of H2O2 or manganese for the detection of oxygen radicals. The free radical oxidizes its respective metal, which in turn oxidizes diaminobenzidine (DAB) to form a brown reaction product which can be visualized using light microscopy.

Animals↗
PubMed1997

4-hydroxynonenal levels are enhanced in fetal liver mitochondria by in utero ethanol exposure.

Lipid peroxidation has been implicated in ethanol-induced liver injury and observed in fetal liver and brain after maternal ethanol consumption with mitochondria being the target organelles. This process generates a highly reactive and toxic product, 4-hydroxynonenal (HNE). In the present study, HNE levels and metabolism were assessed in mitochondria of fetal and maternal liver after in vivo ethanol exposure. Female Sprague-Dawley rats received five doses of ethanol (4 g/kg orally at 12-hour intervals) and were killed on day 19 of gestation. The results showed that HNE levels were enhanced in hepatic mitochondria of fetal rats exposed to ethanol, far in excess of that in adult liver mitochondria. Measurement of HNE metabolism showed that fetal mitochondria had a lower capacity for HNE catabolism than adult mitochondria. In adult mitochondria, HNE could be metabolized by nicotine adenine dinucleotide-dependent oxidation, reduced glutathione conjugation, and reduced nicotine adenine dinucleotide-dependent reduction, whereas in fetal liver only the former two pathways were active, but to a lesser degree than in adult mitochondria. On the other hand, mitochondria from fetal liver showed a higher production of HNE when oxidative stress was induced with t-butyl hydroperoxide. Prior in vivo ethanol exposure further potentiated HNE formation in t-butyl hydroperoxide-stimulated fetal liver mitochondria, but not in adult mitochondria. These findings indicate that increased levels of HNE in fetal liver mitochondria after maternal ethanol consumption reflect a higher susceptibility to HNE formation in addition to a lesser capacity to metabolize it. The enhanced accumulation of this toxic aldehyde may contribute to oxidative damage observed in fetal tissues after in utero ethanol exposure.

Aldehydes↗
PubMed1997

Portal systemic encephalopathy.

The goal of this article is to update the status of Portal systemic encephalopathy (PSE) in the light of new data. First, PSE is the context of other types of hepatic encephalopathy. Subsequently, current views of the pathogenesis of the disorder are discussed, followed by an analysis of therapeutic options. Diagnosis will not be considered, as no major new developments have recently been documented in this area.

Ammonia↗
PubMed1997

Activity and tolerance of a continuous subcutaneous infusion of interferon-alpha2b in patients with chronic hepatitis C.

We administered interferon-alpha2b (IFN-alpha2b) by continuous subcutaneous infusion (60,000 IU/h, or 10 million IU/week) over 3 months to 7 patients with chronic hepatitis C. All had previously responded, as assessed by normalization of transaminases to the same dose of IFN administered by intermittent injection over 6 months, but had relapsed after cessation of therapy. The continuous infusion was tolerated well at the site of infusion, and the systemic side effects were similar in type but were lesser in intensity than with intermittent dosage. Four of 7 subjects had normalization of transaminase at the end of week 12 of therapy. Serum HCV RNA and HCV by PCR decreased with treatment, and there was a prompt and sustained increase in serum beta2-microglobulin and of 2', 5' OAS activity. The level of the latter appeared to correlate with response of the transaminase. Serum IFN concentrations were low but detectable throughout therapy. After stopping IFN administration, the transaminases in responders increased again to pretreatment levels.

Administration, Cutaneous↗
PubMed1997

Catalase mediates acetaldehyde formation from ethanol in fetal and neonatal rat brain.

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.

Acetaldehyde↗
PubMed1996

Mechanism of clearance and transfer of dipeptides by perfused human placenta.

Glycylglutamine (Gly-Gln) is stable source of glutamine for parenteral nutrition. In the present study we have investigated whether this dipeptide is transferred intact across the human placenta. Although after 90 min of placental perfusion there was almost complete disappearance of Gly-Gln (100 microM) from the maternal compartment, only a small concentration of this dipeptide (< 6 microM) appeared in the fetal compartment. To investigate whether this transfer was due to transcellular transport, brush-border membrane vesicles of the human placenta were probed with [3H]Gly-Gln, which showed no uptake. To investigate whether hydrolysis was the mechanism of disappearance of Gly-Gln, the perfusion study was repeated with glycylsarcosine (Gly-Sar), which is resistant to hydrolysis. In sharp contrast to Gly-Gln, after 90 min of perfusion nearly 80% of Gly-Sar remained in the perfusate (half-life of 24 vs. 235 min). The rest of the Gly-Sar was recovered intact in the fetal compartment. The addition of Gly-Gln to the maternal compartment increased the accumulation of glycine, but not glutamine, in both the maternal and fetal compartments. In conclusion, our data suggest that 1) the mechanism of clearance of Gly-Gln by perfused human placenta is largely hydrolysis, whereas that of Gly-Sar is largely passive diffusion, and 2) the placenta has a greater preference for glutamine than for glycine.

Dipeptides↗
PubMed1995

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)

Animals↗
PubMed1995

Sumatriptan (Imitrex) transport by the human placenta.

Sumatriptan (Imitrex), a selective 5-hydroxytryptamine receptor agonist, has been found to be of therapeutic benefit in the acute management of migraine. There is no information on the transfer of this agent across the human placenta. Accordingly, the current study assessed the transport of this drug across the normal term human placenta, using the isolated perfused single cotyledon technique. We found that only about 15% of a single dose of the agent placed in the maternal reservoir crossed into the fetal compartment over 4 hr. Given the average elimination half-life of 2 hr for sumatriptan, it is evident that only very small amounts of the agent will cross from mother to fetus after single doses of Imitrex. Only the parent drug entered the fetal compartment. Metabolites were not detected in the perfusates, but there was evidence of some metabolism of sumatriptan in the placenta. The nature of the metabolites has not been determined. The mechanism of transfer of the drug across the placenta is passive (i.e., the clearance is similar to L-glucose which is passively transported), the rate of transfer is equal in both directions (maternal to fetal and in the reverse), and the drug does not cross into the fetus against a concentration gradient. This passive transport of sumatriptan across the placenta is consistent with its molecular weight, its water solubility, and its slow penetration across the blood-brain barrier in experimental animals.

Biological Transport↗
PubMed1995

Maternal-to-fetal transfer of 5-methyltetrahydrofolate by the perfused human placental cotyledon: evidence for a concentrative role by placental folate receptors in fetal folate delivery.

Folates play a vital role in cellular processes that are essential for fetal growth and viability. Thus the human placenta, which contains high-affinity membrane-associated placental folate receptors (PFRs), maintains a concentrative maternal-to-fetal flux of the vitamin under conditions of minimal dependence on variations of maternal dietary intake. To define transplacental folate transport and the role of PFRs in this mechanism, we utilized the isolated perfused human placental cotyledon. In closed system perfusions with 10 nmol/L 5-methyltetrahydrofolate, placental binding was rapid and extensive (47%), with a gradual maternal-to-fetal transfer of 5-methyltetrahydrofolate. Although hydrophilic PFRs were released into the fetal perfusate, PFR-bound folates constituted only a fraction of net transplacental folate transport. Transfer was bidirectional, not saturable, not inhibited by anion channel blockers, and dependent on perfusate levels. Placental binding far exceeded transfer, and pulsing the maternal circuit with tritiated 5-methyltetrahydrofolate, followed by washout of unbound radiolabel and rechallenge with unlabeled 5-methyltetrahydrofolate or folate, led to release of bound tritiated 5-methyltetrahydrofolate, illustrating reversible binding. Perfusion with the N-hydroxysuccinimide ester of folic acid eliminated essentially all 5-methyltetrahydrofolate binding to PFRs, while increasing net maternal-to-fetal transfer of the vitamin. Finally, because it has been suggested that impaired placental transport of folate may be linked to the fetotoxic effects of ethanol, the effect of this compound on the above processes was examined. An acute 6-hour exposure to ethanol (2.5 to 3.1 mg/ml) had no effect (p > 0.05) on net maternal-to-fetal transfer of 5-methyltetrahydrofolate. These studies suggest that net maternal-to-fetal transfer is a process consisting of two steps. First is the concentrative component in which circulating 5-methyltetrahydrofolate is bound to (captured by) PFRs on the maternally facing chorionic surface. Although kinetics favor binding, there is a dynamic state wherein a gradual release of 5-methyltetrahydrofolate from this pool can add to incoming circulating folates to generate an intervillous blood level approximately 3 times that in the maternal blood. In the second step, folates are passively transferred to the fetal circulation along a downhill concentration gradient. This unique mechanism for transplacental folate transport may be applicable to other small relative molecular mass ligand nutrients that bind to high-affinity placental receptors.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1994

Comparative placental transport of oral hypoglycemic agents in humans: a model of human placental drug transfer.

OBJECTIVE: This study compares the human placental transport of glyburide, glipizide, chlorpropamide, and tolbutamide. STUDY DESIGN: The recirculating single cotyledon human placenta model tested maternal-to-fetal transport in term placentas perfused immediately after delivery. Drug levels were measured by high-performance liquid chromatography and liquid scintillation spectrometry, and transport rates were calculated by comparing maternal and fetal concentrations. RESULTS: The transport of these substances differed significantly over a tenfold range (analysis of variance, p < 0.0008). A significant association exists by multiple linear regression between drug transfer and molecular weight, dissociation constant, and the octanol-water partition coefficient (R2 = 0.91, p < 0.0001). CONCLUSIONS: There is significant variability in human placental transfer rates of the oral hypoglycemics, which strongly correlates with molecular properties. These data suggest that less fetal exposure may occur with second-generation sulfonylureas and anticipate that regression models may be useful in selecting agents that minimize placental transport to the fetus.

Administration, Oral↗