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P Ljubuncic

Publications and source records attributed to P Ljubuncic.

9 recordsLinked to original sources
PubMed2004

Dopamine toxicity involves mitochondrial complex I inhibition: implications to dopamine-related neuropsychiatric disorders.

Dopamine, which is suggested as a prominent etiological factor in several neuropsychiatric disorders such as Parkinson's disease and schizophrenia, demonstrates neurotoxic properties. In such dopamine-related diseases mitochondrial dysfunction has been reported. Dopamine oxidized metabolites were shown to inhibit the mitochondrial respiratory system both in vivo and in vitro. In the present study, we suggest an additional mechanism for dopamine toxicity, which involves mitochondrial complex I inhibition by dopamine. In human neuroblastoma SH-SY5Y cells dopamine induced a reduction in ATP concentrations, which was negatively correlated to intracellular dopamine levels (r = - 0.96, P = 0.012), and was already evident at non-toxic dopamine doses. In disrupted mitochondria dopamine inhibited complex I activity with IC50 = 11.87 +/- 1.45 microm or 8.12 +/- 0.75 microM in the presence of CoQ or ferricyanide, respectively, with no effect on complexes IV and V activities. The catechol moiety, but not the amine group, of dopamine is essential for complex I inhibition, as is indicated by comparing the inhibitory potential of functionally and structurally dopamine-related compounds. In line with the latter is the finding that chelatable FeCl2 prevented dopamine-induced inhibition of complex I. Monoamine oxidase A and B inhibitors, as well as the antioxidant butylated hydroxytoluene (BHT), did not prevent dopamine-induced inhibition, suggesting that dopamine oxidation was not involved in this process. The present study suggests that dopamine toxicity involves, or is initiated by, its interaction with the mitochondrial oxidative phosphorylation system. We further hypothesize that this interaction between dopamine and mitochondria is associated with mitochondrial dysfunction observed in dopamine-related neuropsychiatric disorders, such as schizophrenia and Parkinson's disease.

Adenosine Triphosphatases↗
PubMed2001

Oxidative stress and vascular smooth muscle cell function in liver disease.

Reactive oxygen species and reactive nitroxy species are now being recognized as regulatory molecules in signaling pathways influencing contractile and noncontractile functions of healthy vascular smooth muscle cells. In liver disease, oxidative stress is a systemic phenomenon, whose extent correlates with the severity of disease. A role for oxidative stress in the development of the hyperdynamic circulation in portal hypertension has been proposed. Evaluation of the limited available data indicates that it is premature to conclude that oxidative stress per se impacts on vascular smooth muscle cell function in liver disease.

Animals↗
PubMed2001

Ursodeoxycholic acid and in vitro vasoactivity of hydrophobic bile acids.

Lipophilic bile acids, such as deoxycholic acid (DCA), are nonspecific endothelium-independent vasorelaxants whose underlying basis is complex, involving membrane calcium channels blockade and receptor antagonism. The vasorelaxant action of these acids has also been linked to the generation of reactive oxygen species and an increased extent of lipid peroxidation. Ursodeoxycholic acid (UDCA) is a naturally occurring tertiary dihydroxy hydrophilic acid whose mechanism of action has been attributed to minimizing the effects of lipophilic bile acids. Hence, we considered UDCA might be a useful pharmacological tool to delineate the role of enhanced lipid peroxidation in lipophilic bile acid-induced vasorelaxation. UDCA abrogates in vitro DCA-induced vasorelaxation in rat aortic rings and can suppress DCA-initiated lipid peroxidation in vascular smooth muscle microsomal membrane fractions prepared from the rat aortae. Three different studies were performed. In study 1, the ability of UDCA to restore the DCA-blunted contractile response to the alpha1-adrenoceptor, phenylephrine in rat aortic rings, was evaluated. In study 2, the ability of UDCA to restore DCA-induced vasorelaxation in precontracted rat aortic rings was assessed. In study 3, the ability of UDCA to suppress the increased extent of lipid peroxidation effected by DCA in vascular smooth muscle microsomal membrane fractions prepared from rat aortae was measured using the thiobarbituric acid reactive substance (TBARS) assay. UDCA, at a concentration equivalent to that seen in the plasma of patients with cholestatic liver disease treated with the bile acid, partially restored DCA-induced impaired contractility, prevented DCA-induced vasorelaxation, and abolished DCA-induced increases in the extent of lipid peroxidation. In conclusion, these data suggest that DCA-induced vasorelaxation is mediated by increasing the extent of lipid peroxidation in vascular tissue.

Animals↗
PubMed2000

The effects of bile acids on beta-adrenoceptors, fluidity, and the extent of lipid peroxidation in rat cardiac membranes.

Bile acids have been proposed as a causative factor for the cardiomyopathy of cholestatic liver disease, since they cause negative inotropism and chronotropism and attenuate cardiac responsiveness to sympathetic stimulation. Bile acids can also modify membrane fluidity and generate reactive oxygen species (ROS). The effects of 10(-6)-10(-3) M deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA) and their taurine conjugates, TDCA and TCDCA, on (1) the binding characteristics of beta-adrenoceptors, (2) membrane fluidity, and (3) the extent of lipid peroxidation in rat cardiac membranes were assessed. The results were compared to the effects of the oxidant, 10(-4)-10(-3) M hydrogen peroxide (H(2)O(2)), and the membrane-fluidizing compound, 5 x 10(-5) M 2-(2-methoxyethoxy)ethyl 8-(cis-2-n-octylcyclopropyl)octanoate (A(2)C). Cardiac beta-adrenoceptor density alone was reduced at 10(-4) M bile acid concentration while, at 10(-3) M bile acids, reductions in both receptor density and affinity were seen. At 10(-4) M H(2)O(2), receptor number and affinity were reduced, whereas A(2)C increased receptor affinity without affecting receptor density. Bile acids (10(-3) M) and 10(-4) M H(2)O(2) reduced membrane fluidity. H(2)O(2) caused a concentration-dependent increase in the extent of lipid peroxidation, whereas the bile acids and A(2)C had no effect. Bile acids (10(-4) M) reduced beta-adrenoceptor density in the absence of variations in membrane fluidity and in the extent of membrane lipid peroxidation. This result suggests that bile acids, at concentrations equivalent to the plasma/serum total or estimated free bile acid concentration, may have a possible role in the etiology of cardiomyopathy of cholestatic liver disease. At 10(-3) M bile acid concentration, beta-adrenoceptor number and affinity were adversely affected, accompanied by a decrease in membrane fluidity but without any significant increase in the extent of membrane lipid peroxidation. Although cardiac beta-adrenoceptor density and affinity and membrane fluidity were adversely affected by bile acids, the relevance of these findings to our understanding of the etiological basis of hepatic cardiomyopathy is questionable, since such concentrations exceeded the highest concentrations seen in the plasma and/or tissues of patients with cholestatic liver disease.

Animals↗
PubMed2000

Ursodeoxycholic acid suppresses extent of lipid peroxidation in diseased liver in experimental cholestatic liver disease.

The therapeutic benefit of ursodeoxycholic acid (UDCA) in treating cholestatic liver disease is globally recognized. It is generally accepted that the mechanism of action of UDCA can be attributed to several diverse processes that appear to be uniformly targeted towards minimizing the deleterious actions of accumulated hydrophobic bile acids in the cholestatic liver. Since hydrophobic bile acids are prooxidants, emerging in vitro evidence suggests that UDCA may have an antioxidant mechanism of action. We hypothesize that UDCA suppresses the extent of lipid peroxidation in the cholestatic liver. This hypothesis was tested by assessing the extent of lipid peroxidation in livers harvested from chronic bile duct ligated (CBDL) rats dosed daily for 24 days with 5, 10, or 15 mg/kg UDCA. The extent of lipid peroxidation was evaluated by determining the hepatic content of conjugated dienes, lipid peroxides, and malondialdehyde. The data were compared with identical data collected from unoperated control and 24-day bile duct manipulated (SO) rats. In the two groups of control rats, UDCA has no effect on the serum indices of liver function. In CBDL rats, UDCA suppressed the increased extent of lipid peroxidation in the liver in a dose-dependent manner in the absence of improvement of laboratory parameters of liver function and hepatic architecture. In conclusion, UDCA suppresses the augmented extent of lipid peroxidation in the diseased liver of CBDL rats.

Animals↗
PubMed2000

On the in vitro vasoactivity of bile acids.

We compared the vasorelaxant action of nine different bile acids and correlated their vasorelaxant activity with their individual indices for hydrophobicity or lipophilicity. Vasorelaxant activity correlated with the relative lipid solubility of bile acids with lipophilic bile acids exhibiting the greatest vasorelaxant activity with modest to no vasorelaxant activity exhibited by hydrophilic bile acids. We also investigated whether bile acid-induced vasorelaxation is mediated by antagonism of a prototypal contractile receptor, the alpha(1)-adrenoceptor, by stimulation of a bile acid surface membrane receptor, by the release of endothelium-derived relaxant factors, by promoting the generation of reactive oxygen species and increasing the extent of lipid peroxidation, or by modifying membrane fluidity. Lipophilic bile acids induce vasorelaxation possibly by antagonizing alpha(1)-adrenoceptors, a phenomenon that manifests itself as a lowering of the affinity of vascular alpha(1)-adrenoceptors. Bile acid-induced vasorelaxation was not dependent upon stimulation of a bile acid surface membrane receptor or the release of endothelium-derived relaxant factors. Lipophilic bile acids can also increase the extent of lipid peroxidation with a subtle reduction in the fluidity of rat vascular smooth muscle membranes not associated with loss of membrane cholesterol or phospholipid. We have concluded that lipophilic bile acids are non-selective vasorelaxants whose mechanism of action is a multifaceted process involving antagonism of contractile surface membrane receptors possibly effected by an increased extent of lipid peroxidation and/or membrane fluidity but occurs independent of the release of endothelial-derived relaxant factors or stimulation of a surface membrane bile acid binding site.

Adrenergic alpha-1 Receptor Agonists↗
PubMed2000

Evidence of a systemic phenomenon for oxidative stress in cholestatic liver disease.

BACKGROUND: There is considerable evidence indicating that the severity of hepatic damage in individuals with cholestatic liver disease is causally associated with the extent of intrahepatic oxidative stress. Increased levels or accelerated generation of reactive oxygen species and toxic degradative products of lipid peroxidation have been reported in the plasma of individuals with chronic liver disease and animal models of liver disease. Hence, by virtue of their increased presence in the circulation, it is not unreasonable to suppose that they may account for extrahepatic tissue damage in chronic liver disease. MATERIALS AND METHODS: This hypothesis was tested by determining plasma levels of the ubiquitous antioxidant glutathione (GSH) and lipid peroxides (LP), together with assessment of the extent of lipid peroxidation in the kidney, brain, and heart, in 24 day chronically bile duct ligated (CBDL) rats. The extent of lipid peroxidation in tissues was based on measurement of conjugated dienes, lipid peroxides, and malondialdehyde (MDA) content. Data were compared with identical data collected from unoperated control, pair fed, 24 day bile duct manipulated (sham operated), and pair fed sham operated rats. RESULTS: In CBDL rats, total and reduced plasma GSH levels were almost half those determined in all control rats. Plasma, kidney, and heart LP levels were significantly increased in CBDL rats compared with controls. MDA levels were significantly higher in the kidney, brain, and heart homogenates prepared from CBDL rats compared with MDA content measured in tissue homogenates prepared from the four groups of control rats. CONCLUSIONS: Our data show that experimental cholestatic liver disease is associated with increased lipid peroxidation in the kidney, brain, and heart. Hence we have concluded that the oxidative stress in cholestatic liver disease is a systemic phenomenon probably encompassing all tissues and organs, even those separated by the blood-brain barrier.

Animals↗
PubMed1996

Effect of deoxycholic acid and ursodeoxycholic acid on lipid peroxidation in cultured macrophages.

BACKGROUND: Kupffer cells are essential for normal hepatic homeostasis and when stimulated, they secrete reactive oxygen species, nitric oxide, eicosanoids, and cytokines. Some of these products are cytotoxic and attack nucleic acids, thiol proteins, or membrane lipids causing lipid peroxidation. Hydrophobic bile acids, such as deoxycholic acid (DCA), can damage hepatocytes by solubilising membranes and impairing mitochondrial function, as well as increasing the generation of reactive oxygen species. OBJECTIVES: The hypothesis that hydrophobic bile acids could stimulate Kupffer cells to increase their capacity to generate reactive oxygen species by measuring cellular lipid peroxidation was tested. Because the hydrophilic bile acid, ursodeoxycholic acid (UDCA) can block hydrophobic bile acid induced cellular phenomena, it was also hypothesised that UDCA could antagonise macrophage activation by hydrophobic bile acids to blunt their capacity to generate reactive oxygen species. METHODS: J-774A.1 murine macrophages were incubated for 24 hours with either 10(-5) M and 10(-4) M (final concentration) DCA alone, or 10(-4) M UDCA alone, or a mixture of 10(-4) M 1:1 molar ratio of DCA and UDCA. At the end of the incubation period, the culture medium was collected for determination of cellular lipid peroxidation by measuring the malondialdehyde (MDA) content in the medium with the thiobarbituric acid reactive substances assay. RESULTS: 10(-5) M and 10(-4) M DCA increased MDA generation by cultured macrophages. 10(-4) M UDCA alone did not increase MDA generation but blocked the peroxidative actions of DCA. CONCLUSIONS: Hydrophobic bile acids, after their hepatic retention, can oxidatively activate Kupffer cells to generate reactive oxygen species. Because UDCA can block this action, the beneficial effect of UDCA is, in part, related to its ability to act as an antioxidant.

Animals↗