Biomedical subjects

Michael W Devereaux

Publications and source records attributed to Michael W Devereaux.

11 recordsLinked to original sources

PubMed2006

Alpha-tocopherol regulation of hepatic cytochrome P450s and ABC transporters in rats.

To test the hypothesis that supra-elevated hepatic alpha-tocopherol concentrations would up-regulate mechanisms that result in increased hepatic alpha-tocopherol metabolism and excretion, rats received daily subcutaneous alpha-tocopherol injections (10 mg/100 g body wt) and then were sacrificed on Day 0 or 12 h following their previous injection on Days 3, 6, 9, 12, 15, and 18. Liver alpha-tocopherol concentrations increased from 12 +/- 1 nmol/g (mean +/- SE) to 819 +/- 74 (Day 3), decreased at Day 9 (486 +/- 67), and continued to decrease through Day 18 (338 +/- 37). alpha-Tocopherol metabolites and their intermediates increased and decreased similarly to alpha-tocopherol albeit at lower concentrations. There were no changes in known vitamin E regulatory proteins, i.e., hepatic alpha-tocopherol transfer protein or cytochrome P450 (CYP) 4F. In contrast, both CYP3A and CYP2B, key xenobiotic metabolizing enzymes, doubled by Day 6 and remained elevated, while P450 reductase increased more slowly. Consistent with the decrease in liver alpha-tocopherol concentrations, a protein involved in biliary xenobiotic excretion, p-glycoprotein, increased at Day 9, doubling by Day 15. Thus hepatic alpha-tocopherol concentrations altered hepatic proteins involved in metabolism and disposition of xenobiotic agents.

ATP-Binding Cassette Transporters↗

PubMed2005

Quantitation of rat liver vitamin E metabolites by LC-MS during high-dose vitamin E administration.

To evaluate vitamin E metabolism, a method was developed to quantitate liver alpha- and gamma-tocopherol metabolites, alpha-carboxyethyl hydroxychroman [alpha-CEHC; 2,5,7,8-tetramethyl-2-(2'-carboxyethyl)-6-hydroxychroman] and gamma-CEHC [2,7,8-trimethyl-2-(2'-carboxyethyl)-6-hydroxychroman], respectively. Vitamin E supraenriched livers were obtained from rats that were injected with vitamin E daily for 18 days. Liver samples (approximately 50 mg) were homogenized, homogenate CEHC-conjugates were hydrolyzed, CEHCs were extracted with ethyl ether, and then CEHCs were quantitated using liquid chromatography-mass spectrometry (LC-MS). Precision, based on intersample variability, ranged from 1% to 3%. Recovery of alpha- and gamma-CEHCs added to liver homogenates ranged from 77% to 87%. Detection limits of alpha- and gamma-CEHC were 20 fmol, with a linear detector response from 0.025 to 20 pmol injected. Corresponding with an increase in liver alpha-tocopherol, the MS peak for liver alpha-CEHC (mass-to-charge ratio 277.8) increased 80-fold (0.18 +/- 0.01 to 15 +/- 2 nmol/g). Liver alpha-CEHC concentrations were correlated with serum alpha-CEHC, liver alpha-tocopherol, and serum alpha-tocopherol (P < 0.001 for each comparison). alpha-CEHC represented 0.5-1% of the liver alpha-tocopherol concentration. Thus, LC-MS can be successfully used to quantitate alpha- and gamma-CEHC in liver samples. These data suggest that in times of excess liver alpha-tocopherol, increased metabolism of alpha-tocopherol to alpha-CEHC occurs.

Animals↗

PubMed2005

Licorice compounds glycyrrhizin and 18beta-glycyrrhetinic acid are potent modulators of bile acid-induced cytotoxicity in rat hepatocytes.

The accumulation of hydrophobic bile acids results in cholestatic liver injury by increasing oxidative stress, mitochondrial dysfunction, and activation of cell signaling pathways. Licorice root and its constituents have been utilized as antihepatotoxic agents. The purpose of this study was to evaluate the potential modulation by a primary component of licorice root, glycyrrhizin (GL), and its metabolite, 18beta-glycyrrhetinic acid (GA), in a hepatocyte model of cholestatic liver injury. Preincubation of fresh rat hepatocyte suspensions with GL or GA reduced glycochenodeoxycholic acid (GCDC)-dependent reactive oxygen species generation, with GA more potent than GL. Interestingly, GL and GA had opposing effects toward GCDC-induced cytotoxicity; GA prevented both necrosis and apoptosis, whereas GL enhanced apoptosis. GCDC promoted activation of caspase 10, caspase 3, and PARP; all were inhibited by GA but not GL. Induction of apoptosis by GCDC was also associated with activation of JNK, which was prevented by GA. Activation of caspase 9 and dissipation of mitochondrial membrane potential were prevented by GA but not GL. In liver mitochondrial studies, GL and GA were both potent inhibitors of the mitochondrial permeability transition, reactive oxygen species generation, and cytochrome c release at submicromolar concentrations. Results from this study suggest that GL exhibits pro-apoptotic properties, whereas GA is a potent inhibitor of bile acid-induced apoptosis and necrosis in a manner consistent with its antioxidative effect.

Animals↗

PubMed2005

Increased susceptibility of fat-laden Zucker-rat hepatocytes to bile acid-induced oncotic necrosis: an in vitro model of steatocholestasis.

UNLABELLED: Metabolic liver disorders cause chronic liver disease and liver failure in childhood. Many of these disorders share the histologic features of steatosis and cholestasis, or steatocholestasis. In this study we sought to (1) develop an in vitro model of steatocholestasis, (2) determine the mechanisms of cell death in this model, and (3) determine the role of mitochondrial disturbances in this model. METHODS: Hepatocytes were isolated from 8-week-old obese (fa/fa) and lean Zucker rats. Cell suspensions were treated with glycochenodeoxycholic acid (GCDC), after which reactive oxygen species (ROS) generation, oncotic necrosis, apoptosis, and ATP content were assessed. Isolated liver mitochondria were exposed to GCDC and analyzed for ROS generation, mitochondrial membrane-permeability transition (MPT), and cytochrome c release. Oncotic necrosis was significantly increased and apoptosis reduced in fa/fa hepatocytes exposed to GCDC compared with that in lean hepatocytes. Necrosis occurred by way of an ROS- and MPT-dependent pathway. Basal and dynamic ATP content did not differ between fa/fa and lean hepatocytes. GCDC stimulated ROS generation, MPT, and cytochrome c release to a similar extent in purified mitochondria from both fa/fa and lean rats. These findings suggest that fat-laden hepatocytes favor a necrotic rather than an apoptotic cell death when exposed to low concentrations of bile acids. The protective effects of antioxidants and MPT blockers suggest novel therapeutic strategies for the treatment of steatocholestatic metabolic liver diseases.

Adenosine Triphosphate↗

PubMed2005

Human hepatic mitochondria generate reactive oxygen species and undergo the permeability transition in response to hydrophobic bile acids.

OBJECTIVES: Hydrophobic bile acids accumulate in the liver during cholestasis and are believed to cause hepatocellular necrosis and apoptosis in part through induction of the mitochondrial permeability transition (MPT) and the mitochondrial generation of oxidative stress. The purpose of this study was to determine if human hepatic mitochondria respond to bile acids in this manner. METHODS: The MPT was measured spectrophotometrically and morphologically in normal human liver mitochondria exposed to glycochenodeoxycholic acid (GCDC) with and without cyclosporin A, an inhibitor of the MPT, antioxidants, and tauroursodeoxycholic acid (TUDC). Hydroperoxide generation was measured by dichlorofluorescein fluorescence. Cytochrome c and apoptosis-inducing factor were assessed by immunoblotting. RESULTS: GCDC induced the MPT in a dose-dependent manner, which was inhibited by cyclosporin A, alpha-tocopherol, beta-carotene, idebenone, and TUDC. GCDC stimulated reactive oxygen species generation and release of cytochrome c and apoptosis-inducing factor, which were significantly inhibited by the antioxidants, cyclosporin A, and TUDC. CONCLUSIONS: Mitochondrial pathways of cell death are stimulated in human hepatic mitochondria exposed to GCDC consistent with the role of mitochondrial dysfunction in the pathogenesis of cholestatic liver injury. These results parallel those reported in rodents, supporting the extrapolation of mechanistic studies of bile acid toxicity from rodent to humans.

Antioxidants↗

PubMed2004

Enrichment of rat hepatic organelles by vitamin E administered subcutaneously.

Novel modes of administering antioxidants to improve delivery to targeted tissues or cells may be advantageous in preventing oxidant-induced pathologies. Vitamin E (alpha-tocopherol) has been shown to be protective in several models of liver injury. The objectives of this study were: (1) to determine if subcutaneously (s.q.) administered emulsified vitamin E enriched liver and hepatic subcellular fractions with the antioxidant and (2) to carry out a time-dependent analysis of serum and tissue vitamin E in rats receiving daily s.q. vitamin E. In the first experiment rats injected daily s.q. with emulsified vitamin E for 9 d increased serum, total liver, liver mitochondria, and liver microsomes by 8-, 16-, 30-, and 29-fold, respectively, compared with placebo injections. Similar enrichment was observed after intramuscular injections. In the second experiment, daily doses of s.q. vitamin E increased liver concentrations 40-fold by 9 d, which decreased to 22-fold by 18 d, whereas serum adjusted vitamin E levels maximized with a 24-fold increase by day 3 and plateaued thereafter. In conclusion, s.q. administration of emulsified vitamin E to rats resulted in substantially elevated serum and liver concentrations of alpha-tocopherol compared with levels achievable by dietary supplementation. The s.q. route of administration is a potentially effective parenteral mode of delivery of vitamin E for conditions in which hepatic oxidative stress is present.

Animals↗

PubMed2004

Beta-carotene prevents bile acid-induced cytotoxicity in the rat hepatocyte: Evidence for an antioxidant and anti-apoptotic role of beta-carotene in vitro.

Hydrophobic bile acids are implicated in the pathogenesis of cholestatic liver disorders through mechanisms involving oxidative stress and mitochondrial dysfunction. Antioxidants ameliorate bile acid-induced cytotoxicity in rat hepatocyte suspensions. The purpose of the current study was to evaluate the potential protective role of beta-carotene (betaC), a putative fat-soluble antioxidant that is reduced in patients with cholestasis, against bile acid-induced hepatotoxicity. In freshly isolated rat hepatocyte suspensions that were exposed to the toxic hydrophobic bile acid glycochenodeoxycholic acid (100 or 500 microM), betaC (100 microM) decreased generation of reactive oxygen species by >50%, similar to the inhibition afforded by alpha-tocopherol. Commensurate with this antioxidant effect, 100 microM betaC also protected hepatocytes against both glycochenodeoxycholic acid-induced cellular necrosis and apoptosis, which was associated with reduction in caspase 3 activation, inhibition of mitochondrial cytochrome c release in rat hepatocytes, and prevention of the mitochondrial permeability transition in both liver mitochondria and rat hepatocytes. A lower concentration of betaC (50 microM) produced similar antioxidant and anti-apoptotic protection but with less inhibition against cell necrosis, suggesting that the higher concentration of betaC may have conferred additional cytoprotection not directly related to its antioxidant function. These results demonstrate that the antioxidant effects of betaC may provide hepatoprotection against cholestatic liver injury by preventing bile acid-induced oxidative stress and mitochondrial perturbations.

Animals↗

PubMed2004

Neck pain.

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Diagnosis, Differential↗

PubMed2004

Low back pain.

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Humans↗

PubMed2003

Neck and low back pain.

These cases represent a sample of conditions that impact the spine and paraspinous structures. Central to establishing a correct diagnosis and the cost-effective application of neurodiagnostic tests is a careful history and physical examination. The primary care physician is often the only physician to have a perception of the whole patient. The primary care physician is in an excellent position to initiate the evaluation of patients with spine symptoms and, where appropriate, monitor the treatment plans of consulting physicians.

Adult↗

PubMed2002

Nitric oxide ameliorates hydrophobic bile acid-induced apoptosis in isolated rat hepatocytes by non-mitochondrial pathways.

Hydrophobic bile acids are toxic to isolated rat hepatocytes by mechanisms involving mitochondrial dysfunction and oxidative stress. In the current study we examined the role of nitric oxide (NO), a potential mediator of apoptosis, during bile acid-induced apoptosis. Freshly isolated rat hepatocytes and hepatic mitochondria generated NO and peroxynitrite (ONOO(-)) in a concentration- and time-dependent manner when exposed to the toxic bile salt glycochenodeoxycholate (GCDC) (25-500 microm), which was prevented by the nitric-oxide synthase (NOS) inhibitors N(G)-monomethyl-N-arginine monoacetate (l-NMMA) and 1400W. Relationships between hepatocyte NO production and apoptosis were examined by comparing the effects of NOS inhibitors with other inhibitors of GCDC-induced apoptosis. Inhibitors of caspases 8 and 9, the mitochondrial permeability transition blocker cyclosporin A, and the antioxidant idebenone reduced NO generation and apoptosis in GCDC-treated hepatocytes. In contrast, NOS inhibitors had no effect on GCDC-induced apoptosis despite marked reduction of NO and ONOO(-). However, treatment with the NO donors S-nitroso-N-acetylpenicillamine and spermine NONOate [N-(-aminoethyl)N-(2-hydroxy-2-nitrohydrazino)-1,2-ethylenediamine) inhibited apoptosis and caspase 3 activity while significantly elevating NO levels above GCDC-stimulated levels. Neither NO donors nor NOS inhibitors affected GCDC-induced mitochondrial permeability transition or cytochrome c release from liver mitochondria or GCDC-induced mitochondrial depolarization from isolated hepatocytes, suggesting that NO inhibits bile acid-induced hepatocyte apoptosis by a non-mitochondrial-dependent pathway. In conclusion, whereas NO produced from GCDC-treated hepatocytes neither mediates nor protects against bile acid-induced apoptosis, higher levels of NO inhibit GCDC-induced hepatocyte apoptosis by caspase-dependent pathways.

Animals↗