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Waly M.I.,Sultan Qaboos University | Kharbanda K.K.,Liver Study Unit | Deth R.C.,Northeastern University
Alcoholism: Clinical and Experimental Research | Year: 2011

Background: Methionine synthase (MS) is a ubiquitous enzyme that requires vitamin B12 (cobalamin) and 5-methyl-tetrahydrofolate for the methylation of homocysteine to methionine. Previous studies have shown that acute or chronic ethanol (ETOH) administration results in the inhibition of MS and depletion of glutathione (GSH), and it has been proposed that GSH is required for the synthesis of methylcobalamin (MeCbl). Methods: We measured GSH levels and investigated the ability of different cobalamin cofactors [cyano- (CNCbl), glutathionyl- (GSCbl), hydroxo- (OHCbl), and MeCbl] to support MS activity in liver and brain cortex from control and ETOH-treated rats. Results: In control animals, MS activity was higher in liver than in cortex for all cobalamins and MeCbl-based activity was higher than for other cofactors. S-adenosylmethionine (SAM) was required for OHCbl, CNCbl, and GSCbl-based activity, but not for MeCbl. Feeding an ETOH-containing diet for four weeks caused a significant decrease in liver MS activity, in a cobalamin-dependent manner (OHCbl≥CNCbl>GSCbl>MeCbl). In brain cortex, OHCbl, CNCbl, and GSCbl-based activity was reduced by ETOH treatment, but MeCbl-based activity was unaffected. GSH levels were reduced by ETOH treatment in both liver and cortex homogenates, and addition of GSH restored OHCbl-based MS activity to control levels. Betaine administration had no significant effect on GSH levels or MS activity in either control or ETOH-fed groups. Conclusions: The ETOH-induced decrease in OHCbl-based MS activity is secondary to decreased GSH levels and a decreased ability to synthesize MeCbl. The ability of MeCbl to completely offset ETOH inhibition in brain cortex, but not liver, suggests tissue-specific differences in the GSH-dependent regulation of MS activity. © 2010 by the Research Society on Alcoholism. Source

We investigated the hypothesis that postconditioning by FTY720 (FTY) in isolated perfused mouse hearts is independent of the sphingosine 1-phosphate (S1P) pathway. Ex vivo hearts were exposed to postconditioning (POST) by either ischemia or FTY720. Protection against ischemia/reperfusion (IR) injury was measured by recovery of left ventricular developed pressure (LVDP) and infarct size. FTY effectively postconditioned (POST) ex vivo hearts against ischemia/reperfusion (IR) injury as measured by recovery of LVDP and a low infarct size. FTY protection, unlike S1P but like sphingosine (Sph), was insensitive to inhibition of S1P G-Protein Coupled Receptors (GPCRs) or inhibition of PI3 kinase. Protection by FTY and Sph was however blocked by inhibitors of PKA and PKG. Thus, FTY follows the same cardioprotective pathway as Sph. This was further supported by studies of FTY POST in knockout (KO) mice lacking the SphK2 form of Sph kinase that is needed for phosphorylation of FTY to an S1P analog. In the absence of SphK2, FTY (and Sph) POST was still cardioprotective. This differed from the effect of SphK2 KO on protection by ischemic POST (IPOST). IPOST was not effective in KO hearts. To see if the GPCR signaling pathway to protection is normal in KO hearts, we looked at POST by GPCR agonists S1P and adenosine. Both provided effective protection even in KO hearts suggesting that the problem with IPOST in KO hearts is a low level of S1P available for release during IPOST. Thus, pharmacologic POST with FTY or Sph, like adenosine and S1P, is unaffected in the KO. FTY720 administered in vivo might behave in a dual manner showing both S1P-like effects and sphingosine-like effects. It appears that the latter may have been overlooked and may be the more important in aging hearts. Source

Rasineni K.,University of Nebraska Medical Center | Casey C.A.,University of Nebraska Medical Center | Casey C.A.,Liver Study Unit
Indian Journal of Pharmacology | Year: 2012

Ethanol abuse and chronic ethanol consumption remains a major public health problem and is responsible for a high rate of morbidity. Alcohol-induced fatty liver generally begins as hepatic steatosis, and if the cause persists, this invariably progresses to steatohepatitis and cirrhosis. The original biochemical explanation for an alcoholic fatty liver centered on the ability of ethanol metabolism to shift the redox state of the liver and inhibit fatty acid oxidation. Subsequent studies found repression of fatty acid oxidation and that the induction of lipogenesis can occur in alcoholic conditions. Ethanol activates sterol regulatory element binding protein 1, inducing a battery of lipogenic enzymes. These effects may be due in part to inhibition of AMP-dependent protein kinase, reduction in plasma adiponectin or increased levels of TNF- the liver. They in turn activate lipogenic pathways and inhibit fatty acid oxidation. Besides the fatty acid synthesis and oxidation, ethanol also alters lipid droplet (LD, the storage form of triglycerides, TG) metabolism in hepatocytes and very low-density lipoprotein (VLDL) secretion from liver. Because steatosis is now regarded as a significant risk factor for advanced liver pathology, an understanding of the molecular mechanisms in its etiology provides new therapeutic targets to reverse the alcoholic fatty liver. Source

Czaja M.J.,Yeshiva University | Ding W.-X.,University of Kansas Medical Center | Donohue Jr. T.M.,Liver Study Unit | Friedman S.L.,The New School | And 11 more authors.
Autophagy | Year: 2013

Autophagy has emerged as a critical lysosomal pathway that maintains cell function and survival through the degradation of cellular components such as organelles and proteins. Investigations specifically employing the liver or hepatocytes as experimental models have contributed significantly to our current knowledge of autophagic regulation and function. The diverse cellular functions of autophagy, along with unique features of the liver and its principal cell type the hepatocyte, suggest that the liver is highly dependent on autophagy for both normal function and to prevent the development of disease states. However, instances have also been identified in which autophagy promotes pathological changes such as the development of hepatic fibrosis. Considerable evidence has accumulated that alterations in autophagy are an underlying mechanism of a number of common hepatic diseases including toxin-, drug- and ischemia/reperfusion-induced liver injury, fatty liver, viral hepatitis and hepatocellular carcinoma. This review summarizes recent advances in understanding the roles that autophagy plays in normal hepatic physiology and pathophysiology with the intent of furthering the development of autophagy-based therapies for human liver diseases. © 2013 Landes Bioscience. Source

Vessey D.A.,Liver Study Unit | Vessey D.A.,University of California at San Francisco | Li L.,Liver Study Unit | Kelley M.,Liver Study Unit
American Journal of Physiology - Heart and Circulatory Physiology | Year: 2011

Protection of the heart from ischemia-reperfusion injury can be achieved by ischemic preconditioning and ischemic postconditioning. Previous studies revealed that a complex of pannexin-1 with the P2X7 receptor forms a channel during ischemic preconditioning and ischemic postconditioning that results in the release of endogenous cardioprotectants. ATP binds to P2X7 receptors, inducing the formation of a channel in association with pannexin-1. We hypothesized that this channel would provide a pathway for the release of these same cardioprotectants. Preconditioning-isolated perfused rat hearts with 0.4 μM ATP preceding 40 min of ischemia minimized infarct size upon subsequent reperfusion (5% of risk area) and resulted in >80% recovery of left ventricular developed pressure. Postconditioning with ATP after ischemia during reperfusion was also protective (6% infarct and 72% recovery of left ventricular developed pressure). Antagonists of both pannexin-1 (carbenoxolone and mefloquine) and P2X7 receptors (brilliant blue G and A438079) blocked ATP pre-and postconditioning, indicating that ATP protection was elicited via the opening of a pannexin-1/P2X7 channel. An antagonist of binding of the endogenous cardioprotectant sphingosine 1-phosphate to its G protein-coupled receptor diminished protection by ATP, which is also consistent with an ATP-dependent release of cardioprotectants. Suramin, an antagonist of binding of ATP (and ADP) to P2Y receptors, was without effect on ATP protection. Benzoyl benzoyl-ATP, a more specific P2X7 agonist, was also a potent pre-and postconditioning agent and sensitive to blockade by pannexin-1/P2X7 channel antagonists. The data point out for the first time the potential of P2X7 agonists as cardioprotectants. © 2011 the American Physiological Society. Source

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