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M W Devereaux

Publications and source records attributed to M W Devereaux.

At least 19 recordsLinked to original sources
PubMed2001

Bile acid-induced rat hepatocyte apoptosis is inhibited by antioxidants and blockers of the mitochondrial permeability transition.

The accumulation of hydrophobic bile acids plays a role in the induction of apoptosis and necrosis of hepatocytes during cholestasis. The aim of this study was to determine in freshly isolated rat hepatocytes the roles of oxidant stress and the mitochondrial permeability transition (MPT) in bile acid-induced apoptosis. Hepatocytes isolated from adult male Sprague-Dawley rats were incubated for 4 hours in buffer containing the hydrophobic bile acid, glycochenodeoxycholic acid (GCDC, 0-500 micromol/L) or the hydrophilic bile acid, glycocholic acid (GCA), and either the antioxidants, alpha tocopherol, ebselen, or idebenone (a coenzyme Q analogue); or the MPT blockers, cyclosporin A, or bongkrekic acid, or a caspase-8 inhibitor. Apoptosis was assessed hourly by nuclear morphologic changes of fixed cells by DAPI fluorescence microscopy and reactive oxygen species (ROS) generation by dichlorofluorescein fluorescence of hepatocytes. The percent of cells undergoing apoptosis increased in a time- and concentration-dependent manner in cells exposed to GCDC, and to a much lesser extent to GCA. ROS generation preceded the onset of apoptosis. MPT blockers, caspase-8 inhibition, and antioxidants prevented apoptosis and reduced ROS generation by hepatocytes. Flow cytometry analysis showed that MPT occurred within 1 hour of exposure of cells to 100 micromol/L GCDC, prior to onset of significant apoptosis. In conclusion, ROS generation, MPT induction, and cytochrome c release are critical steps in the induction of apoptosis by bile acids. Antioxidants may reduce liver injury caused by low levels of bile acids by preventing the generation of oxidant stress and subsequent stimulation of the MPT and release of cytochrome c from mitochondria.

Animals↗
PubMed2001

Role of oxidant stress in the permeability transition induced in rat hepatic mitochondria by hydrophobic bile acids.

Hydrophobic bile acids may cause hepatocellular necrosis and apoptosis during cholestatic liver diseases. The mechanism for this injury may involve mitochondrial dysfunction and the generation of oxidant stress. The purpose of this study was to determine the relationship of oxidant stress and the mitochondrial membrane permeability transition (MMPT) in hepatocyte necrosis induced by bile acids. The MMPT was measured spectrophotometrically and morphologically in rat liver mitochondria exposed to glycochenodeoxycholic acid (GCDC). Freshly isolated rat hepatocytes were exposed to GCDC and hepatocellular necrosis was assessed by lactate dehydrogenase release, hydroperoxide generation by dichlorofluorescein fluorescence, and the MMPT in cells by JC1 and tetramethylrhodamine methylester fluorescence on flow cytometry. GCDC induced the MMPT in a dose- and Ca(2+)-dependent manner. Antioxidants significantly inhibited the GCDC-induced MMPT and the generation of hydroperoxides in isolated mitochondria. Other detergents failed to induce the MMPT and a calpain-like protease inhibitor had no effect on the GCDC-induced MMPT. In isolated rat hepatocytes, GCDC induced the MMPT, which was inhibited by antioxidants. Blocking the MMPT in hepatocytes reduced hepatocyte necrosis and oxidant stress caused by GCDC. Oxidant stress, and not detergent effects or the stimulation of calpain-like proteases, mediates the GCDC-induced MMPT in hepatocytes. We propose that reducing mitochondrial generation of reactive oxygen species or preventing increases in mitochondrial Ca(2+) may protect the hepatocyte against bile acid-induced necrosis.

Animals↗
PubMed2000

Glutathione status of isolated rat hepatocytes affects bile acid-induced cellular necrosis but not apoptosis.

An accumulation of hydrophobic bile acids is implicated in the pathogenesis of cholestatic liver diseases. In the present study, we determined if hydrophobic bile acid-induced cellular injury compromised hepatocyte glutathione (GSH) status, and if modulating intracellular GSH levels prevented or facilitated bile acid-induced cellular cytotoxicities. Freshly isolated rat hepatocytes incubated with >/=125 microM of the hydrophobic bile acid, glycochenodeoxycholic acid (GCDC), underwent a time- and dose-dependent decrease of intracellular GSH levels by 4-h incubation. This loss of intracellular GSH was not associated with an increase of intracellular GSH disulfide (GSSG). Rather, GCDC stimulated the dose-dependent accumulation of extracellular GSSG. The mechanism for extracellular GSSG accumulation by GCDC was through increased efflux of reduced GSH from hepatocytes into the media, where it subsequently oxidized to GSSG. Treatment of hepatocytes with GCDC (0-750 microM) did not directly alter GSH-dependent enzyme activities. The reduction of intracellular GSH with 125 microM GCDC correlated with extensive apoptosis at this concentration as determined by fluorescence microscopy of DAPI (4, 6-diamindino-2-phenylindole hydrochloride)-stained nuclei. Higher concentrations of GCDC (>/=500 microM) favored cellular necrosis and lipid peroxidation. Depleting GSH by treating hepatocytes with 1-bromoheptane increased their sensitivity toward GCDC-induced cellular necrosis, but not apoptosis. However, enhancing the hepatocyte GSH content by supplementation with GSH-ethylester (GSH-EE) failed to protect hepatocytes against either mode of cellular death. In conclusion, while GCDC-induced cytotoxicities were associated with an increased efflux of GSH from rat hepatocytes, GSH status modulated GCDC-induced necrosis, but not apoptosis.

Animals↗
PubMed2000

The neuro-ophthalmologic complications of cervical manipulation.

Cervical manipulation, specifically chiropractic manipulation, is an important cause of vertebrobasilar and occasionally carotid distribution strokes. Neuro-ophthalmologic findings are a common and at times relatively isolated feature of cervical manipulation-induced stroke. A case of chiropractic-induced occipital lobe infarction with homonymous hemianopsia is reported, and the literature regarding neuro-ophthalmologic findings is reviewed.

Adult↗
PubMed1998

Vitamin E reduces oxidant injury to mitochondria and the hepatotoxicity of taurochenodeoxycholic acid in the rat.

BACKGROUND & AIMS: Hydrophobic bile acids have been implicated in the pathogenesis of cholestatic liver injury. The hypothesis that hydrophobic bile acid toxicity is mediated by oxidant stress in an in vivo rat model was tested in this study. METHODS: A dose-response study of bolus intravenous (i.v.) taurochenodeoxycholic acid (TCDC) in rats was conducted. Rats were then pretreated with parenteral alpha-tocopherol, and its effect on i.v. TCDC toxicity was evaluated by liver blood tests and by assessing mitochondrial lipid peroxidation. RESULTS: Four hours after an i.v. bolus of TCDC (10 mumol/100 g weight), serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels peaked, hepatic mitochondria showed evidence of increased lipid peroxidation, and serum bile acid analysis was consistent with a cholestatic injury. Liver histology at 4 hours showed hepatocellular necrosis and swelling and mild portal tract inflammation. Treatment with parenteral alpha-tocopherol was associated with a 60%-70% reduction in AST and ALT levels, improved histology, and a 60% reduction in mitochondrial lipid peroxidation in rats receiving TCDC. CONCLUSIONS: These data show that hepatocyte injury and oxidant damage to mitochondria caused by i.v. TCDC can be significantly reduced by pretreatment with the antioxidant vitamin E. These in vivo findings support the role for oxidant stress in the pathogenesis of bile acid hepatic toxicity.

Animals↗
PubMed1998

The effect of idebenone, a coenzyme Q analogue, on hydrophobic bile acid toxicity to isolated rat hepatocytes and hepatic mitochondria.

Oxidant stress induced by hydrophobic bile acids has been implicated in the pathogenesis of liver injury in cholestatic liver disorders. We evaluated the effect of idebenone, a coenzyme Q analogue, on taurochenodeoxycholic acid (TCDC)-induced cell injury and oxidant stress in isolated rat hepatocytes and on glycochenodeoxycholic acid (GCDC)-induced generation of hydroperoxides in fresh hepatic mitochondria. Isolated rat hepatocytes in suspension under 9% oxygen atmosphere were preincubated with 0, 50, and 100 micromol/l idebenone for 30 min and then exposed to 1000 micromol/l TCDC for 4 h. LDH release (cell injury) and thiobarbituric acid reactive substances (measure of lipid peroxidation) increased after TCDC exposure but were markedly suppressed by idebenone pretreatment. In a second set of experiments, the addition of 100 micromol/l idebenone up to 3 h after hepatocytes were exposed to 1000 micromol/l TCDC resulted in abrogation of subsequent cell injury and markedly reduced oxidant damage to hepatocytes. Chenodeoxycholic acid concentrations increased to 5.15 nmol/10(6) cells after 2 h and to 7.05 after 4 h of incubation of hepatocytes with 1000 micromol/l TCDC, and did not differ in the presence of idebenone. In freshly isolated rat hepatic mitochondria, when respiration was stimulated by succinate, 10 micromol/l idebenone abrogated the generation of hydroperoxides during a 90-minute exposure to 400 micromol/l GCDC. These data demonstrate that idebenone functions as a potent protective hepatocyte antioxidant during hydrophobic bile acid toxicity, perhaps by reducing generation of oxygen free radicals in mitochondria.

Animals↗
PubMed1998

Effect of oxypurinol, a xanthine oxidase inhibitor, on hepatic injury in the bile duct-ligated rat.

Oxidant stress has been implicated as playing a role in the pathogenesis of cholestatic liver injury. The objective of this study was to determine whether the xanthine oxidase/xanthine dehydrogenase enzyme system was involved in this oxidant stress. Adult Sprague-Dawley rats were treated with the xanthine oxidase inhibitor, oxypurinol, and randomized to bile duct ligation or sham surgery; vehicle-treated, sham-operated rats served as controls. After 5 d of bile duct ligation, serum aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and total and direct bilirubin concentrations were significantly elevated, and increased lipid peroxidation of hepatic mitochondria and microsomes was present. Treatment with oxypurinol reduced the aspartate aminotransferase, alanine aminotransferase, and bilirubin values by 26-47% but did not alter the increased lipid peroxidation of mitochondria and microsomes. Serum vitamin E:total lipids ratio was also reduced in both bile duct-ligated groups, consistent with oxidant injury. These data show that inhibition of xanthine oxidase reduces biochemical evidence of hepatocellular injury during bile duct ligation without affecting oxidant damage to intracellular hepatocyte organelles. Thus, in this model a component of cholestatic injury appears to have been caused by oxidant stress from a source outside of the hepatocyte.

Animals↗
PubMed1996

Hepatic oxidant injury and glutathione depletion during total parenteral nutrition in weanling rats.

Hepatobiliary dysfunction occurs commonly in infants on prolonged parenteral nutrition alimentation; however, the underlying mechanisms causing liver injury are poorly understood. We postulated that oxidant stress played a significant role in parenteral nutrition-induced liver abnormalities and tested this hypothesis in a rat model. Weanling male rats received 8 days of total parenteral nutrition (TPN) through a central venous catheter (TPN group), pair feeding of rat chow and placement of a central venous catheter (sham group), or ad libitum feedings of rat chow (control group). After 8 days of TPN, serum alanine aminotransferase and cholylglycine levels were elevated, hepatocellular steatosis was present, hepatic mitochondria had dilated intracristal spaces, and lipid peroxidation of mitochondria was increased compared with sham and control groups. Hepatic glutathione levels decreased to 16% of control values after 5 days of TPN; this was followed by mitochondrial lipid peroxidation and elevated serum cholylglycine levels after 8 days of TPN. Sham and control rats showed no evidence of mitochondrial lipid peroxidation or liver injury after 8 days. Removal of metabisulfate from TPN solutions and addition of cysteine HCl or choline had no major effect on these findings. Bacterial translocation was not increased in TPN rats. These data suggest that glutathione depletion and oxidant stress are important factors in the pathogenesis of TPN-induced liver abnormalities in the weanling rats.

Animals↗
PubMed1996

alpha-tocopherol ameliorates oxidant injury in isolated copper-overloaded rat hepatocytes.

The objective of this study was to determine the role of oxidant stress in cell injury produced by in vivo copper overload of isolated rat hepatocytes. Rats were maintained on diets with elevated or normal copper content, and hepatocytes were isolated and then incubated for 4 h in physiologic buffer at physiologic oxygen saturations. In hepatocytes from copper-overloaded rats, a significant loss of cell viability (trypan blue exclusion) over 4 h compared with control cells was associated with a significant increase in lipid peroxidation (thiobarbituric acid-reacting substances). Incubation of copper-overloaded hepatocytes with the copper chelator, 2,3,2-tetramine, had a partial protective effect. Incubation with D-alpha-tocopheryl succinate completely ameliorated the copper-induced changes in viability and lipid peroxidation. We conclude that antioxidants may protect the isolated hepatocyte from copper toxicity and should be explored as potential therapeutic agents in states of copper overload.

Alanine Transaminase↗
PubMed1995

Generation of hydroperoxides in isolated rat hepatocytes and hepatic mitochondria exposed to hydrophobic bile acids.

BACKGROUND & AIMS: The mechanisms causing liver injury in cholestatic diseases are unclear. The hypothesis that accumulation of hydrophobic bile acids in hepatocytes during cholestasis leads to generation of oxygen free radicals and oxidative injury was tested. The aim of this study was to determine if hydrophobic bile acid toxicity is associated with increased hydroperoxide generation in isolated rat hepatocytes and mitochondria. METHODS: Hepatocytes were exposed to taurochenodeoxycholic acid (TCDC; 0-2000 mumol/L) or taurocholic acid (TC; 1000 mumol/L), and cellular injury, intracellular hydroperoxide generation, and thiobarbituric acid-reacting substances (TBARS) were measured. Isolated mitochondria were incubated with 400 mumol/L chenodeoxycholic acid or 400 mumol/L cholic acid, and hydroperoxide generation was measured fluorometrically. RESULTS: Hepatocyte injury, hydroperoxide generation, and TBARS increased over 4 hours on exposure to TCDC but not TC. Hydroperoxide generation preceded hepatocyte injury and accumulation of TBARS. Preincubation of hepatocytes with the antioxidant, d-alpha-tocopheryl succinate, completely abrogated cellular injury, hydroperoxide, and TBARS generation. Hydroperoxide generation was increased in mitochondria exposed to chenodeoxycholic acid. CONCLUSIONS: Intracellular generation of hydroperoxides by mitochondria appears to be an early event in hydrophobic bile acid-induced hepatocyte toxicity. Antioxidants may be of benefit in cholestasis.

Animals↗
PubMed1995

Developmental changes in newborn lamb brain mitochondrial activity and postasphyxial lipid peroxidation.

Previously, our laboratory has demonstrated inhibition of mitochondrial state 3 (ADP-dependent) respiration 5 min after resuscitation from an asphyxial insult in lambs less than 3 days of age. Older lambs were resistant to this transient mitochondrial dysfunction. This study was designed to examine if age-related differences in baseline state 3 mitochondrial respiration, electron transport chain activity, or susceptibility to oxygen free radical-mediated lipid peroxidation were related to the previously observed differences in postasphyxial mitochondrial respiration. Mitochondrial respiration was measured in 24 nonasphyxiated control lambs aged 1-10 days using four different substrates. Electron transport chain activity was assessed in 15 of these lambs, and lipid peroxidation measured as conjugated diene production was measured in 11 of these lambs. These lambs were all ventilated to maintain normal blood gases for a time period equal to the length of the hypoxic insult in asphyxiated lambs (see below), after which samples of brain were removed for isolation of mitochondria. A second group of 11 lambs (seven < or = 3 days of age and four > 3 days of age) were asphyxiated. The insult was a 75-to-90-min episode of hypoxia and hypercarbia that resulted in bradycardia and systemic hypotension over the final 15 min of the insult. At the end of asphyxia, the lambs were resuscitated and returned to control ventilator settings. Samples of brain were removed 5 min after resuscitation. Postasphyxia electron transport chain activity and lipid peroxidation were measured. All measurements described above were done in both nonsynaptic (primarily glial in origin) and synaptic mitochondria. State 3 mitochondrial respiration varied significantly with age, decreasing by an average of 41.2% +/- 11.1% (mean +/- SEM) from Day 2 to Day 5-6 and then increasing back to levels similar to Day 2 by Day 8-10 in nonsynaptic mitochondria. State 3 respiration in synaptic mitochondria decreased 60.6% +/- 5.2% from Day 2 to Day 5-6 before returning to levels similar to Day 2 by Day 8-10. Resting (nonADP-dependent) state 4 respiration demonstrated similar developmental patterns. Electron transport chain activities did not vary with age in the nonasphyxiated control animals. In addition, an asphyxial insult did not diminish electron transport chain activities in either lambs < or = 3 days old or those > 3 days of age.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenine Nucleotides↗
PubMed1994

Oxidant injury to hepatic mitochondria in patients with Wilson's disease and Bedlington terriers with copper toxicosis.

BACKGROUND/AIMS: Copper overload leads to liver injury in humans with Wilson's disease and in Bedlington terriers with copper toxicosis; however, the mechanisms of liver injury are poorly understood. This study was undertaken to determine if oxidant (free radical) damage to hepatic mitochondria is involved in naturally occurring copper toxicosis. METHODS: Fresh liver samples were obtained at the time of liver transplantation from 3 patients with Wilson's disease, 8 with cholestatic liver disease, and 5 with noncholestatic liver disease and from 8 control livers. Fresh liver was also obtained by open liver biopsy from 4 copper-overloaded and 4 normal Bedlington terriers and from 8 control dogs. Hepatic mitochondria and microsomes (humans only) were isolated, and lipid peroxidation was measured by lipid-conjugated dienes and thiobarbituric acid-reacting substances. In humans, liver alpha-tocopherol content was measured. RESULTS: Lipid peroxidation and copper content were significantly increased (P < 0.05) in mitochondria from patients with Wilson's disease and copper-overloaded Bedlington terriers. More modest increases in lipid peroxidation were present in microsomes from patients with Wilson's disease. Mitochondrial copper concentrations correlated strongly with the severity of mitochondrial lipid peroxidation. Hepatic alpha-tocopherol content was decreased significantly in Wilson's disease liver. CONCLUSIONS: These data suggest that the hepatic mitochondrion is an important target in hepatic copper toxicity and that oxidant damage to the liver may be involved in the pathogenesis of copper-induced injury.

Adolescent↗
PubMed1993

Abnormal hepatic mitochondrial respiration and cytochrome C oxidase activity in rats with long-term copper overload.

BACKGROUND: Dietary copper overload in the rat is associated with morphological abnormalities and lipid peroxidation of hepatic mitochondria. This study was designed to determine if copper hepatotoxicity was associated with functional alterations in mitochondrial respiration in conjunction with lipid peroxidation. METHODS: Weanling male rats were pair-fed for 8 weeks on diets containing normal or high levels of copper in combination with sufficient vitamin E. Serum and liver samples were obtained, and hepatic mitochondria were isolated by differential centrifugation. RESULTS: Oxidant injury (decreased levels of hepatic glutathione and alpha tocopherol and increased levels of mitochondrial thiobarbituric acid-reacting substances) was present in the copper-overloaded rats. Serum aminotransferase levels correlated with concentrations of mitochondrial copper and thiobarbituric acid-reacting substances. Copper overload caused a decrease in state 3 respiration and the respiratory control ratio in hepatic mitochondria when several electron donors were used. Analysis of the oxidoreductase activities of the four mitochondrial electron transport protein complexes showed that complex IV (cytochrome C oxidase) activity was reduced by 60% in copper overload. CONCLUSIONS: Functional abnormalities of mitochondria accompany lipid peroxidation and the morphological alterations caused by copper overload, supporting the hypothesis that the mitochondrion is one of the major intracellular targets in copper hepatotoxicity.

Animals↗
PubMed1990

Effect of vitamin E on transport processes in isolated rat hepatocytes.

Vitamin E deficiency is a common consequence of chronic cholestatic liver disorders. Inasmuch as vitamin E content of cellular membranes alters membrane properties such as fluidity and molecular order, we postulated that vitamin E status could affect hepatocyte transport processes dependent on membrane integrity. Hepatocytes were isolated from rats maintained on diets containing deficient, sufficient, or excess vitamin E. Cell viability and oxygen consumption were maintained in all groups of hepatocytes. Hepatocyte uptake of taurocholic acid and ouabain and Na+,K(+)-ATPase activity estimated by rubidium-86 influx did not differ with vitamin E status. Vitamin-E-deficient hepatocytes had increased generation of lipid peroxide products. We conclude that deficient or excess vitamin E status had little effect on selected transport processes in normal hepatocytes.

Animals↗
PubMed1989

Copper toxicity and lipid peroxidation in isolated rat hepatocytes: effect of vitamin E.

We investigated the role of lipid peroxidation as the mechanism mediating copper toxicity in isolated rat hepatocytes and the modulating effect of vitamin E. Hepatocytes, isolated from rats fed diets containing deficient (E-), sufficient (E+), and excess (E++) amounts of vitamin E, were incubated with CuCl2 (0-2400 microM) for 150 min. Dose and time-dependent decreases in hepatocyte viability (determined by trypan blue exclusion and lactate dehydrogenase release) due to copper toxicity correlated with production of malonyldialdehyde in E- and E+ hepatocytes. However, malonyldialdehyde generation did not accompany copper toxicity in E++ cells. Copper toxicity was enhanced in E- compared to E+ and E++ hepatocytes as assessed by cell viability studies and ultrastructural plasma membrane bleb formation. In vitro vitamin E repletion of E- hepatocytes restored resistance to copper and decreased malonyldialdehyde production proportionately. Thus vitamin E deficiency appeared to increase the susceptibility of hepatocytes to copper toxicity. We conclude that lipid peroxidation may not be the mechanism by which copper is toxic to isolated hepatocytes but that the site of injury may be thiol-rich cellular proteins.

Animals↗