Effects of chloride channel inhibitors on H(2)O(2)-induced renal epithelial cell injury

The role of glycine in regulated cell death

The cytoprotective effects of glycine against cell death have been recognized for over 28 years. They are expressed in multiple cell types and injury settings that lead to necrosis, but are still not widely appreciated or considered in the conceptualization of cell death pathways. In this paper, we review the available data on the expression of this phenomenon, its relationship to major pathophysiologic pathways that lead to cell death and immunomodulatory effects, the hypothesis that it involves suppression by glycine of the development of a hydrophilic death channel of molecular dimensions in the plasma membrane, and evidence for its impact on disease processes in vivo.

Effects of different concentrations of artemisinin and artemisinin-iron combination treatment on Madin Darby Canine Kidney (MDCK) cells

Artemisinin is a sesquitrepenelactone with an endoperoxide bridge. It is a naturally occurring substance from Artemisia species plants. Artemisia species have been used in oriental medicine for centuries to treat malaria, gastrointestinal helminthosia, diarrhea, and as an antipyretic and sedative agent. Antileishmanial activity of the plants has been announced a few years ago. Dogs are the most important reservoir of leishmaniasis in some parts of the world. To use it as an antileishmanial drug in dogs, its side effects on different organs, among them the kidney as the organ of elimination have to be elucidated. Artemisinin with different concentrations (0.15, 0.3, 0.6 and 1.2 μg/ml) was added to the culture of MDCK (Madin darby canine kidney) cells with and without iron (86 μg/dl). All the changes were controlled and photographed every 12 hours using an invert microscope. After 60 hours, supernatants and cell extracts were examined for LDH (lactate dehydrogenase) concentration and total protein. Also TBARS (thiobarbituric acid reactive substances) test was performed on cell extracts. Some microscopic slides were prepared from the cells and stained with hematoxylin-eosin for microscopic exams. Biochemical parameters showed cellular reaction and injury in a concentration dependent manner. Cell injury was more severe in the iron-added groups. Microscopic exams showed cell and nuclear swelling, granular degeneration, vacuole and vesicle formation, cellular detachment, piknosis, karyorrhexis, cellular necrosis and inhibition of new mitosis. On using the drug for leishmaniasis treatment in the dog, it should be done with caution and supervision.

Hydroxytyrosol glucuronides protect renal tubular epithelial cells against H(2)O(2) induced oxidative damage

Hydroxytyrosol (2-(3',4'-dihydroxyphenyl)ethanol; HT), the most active ortho-diphenolic compound, present either in free or esterified form in extravirgin olive oil, is extensively metabolized in vivo mainly to O-methylated, O-sulfated and glucuronide metabolites. We investigated the capacity of three glucuronide metabolites of HT, 3'-O-β-d-glucuronide and 4'-O-β-d-glucuronide derivatives and 2-(3',4'-dihydroxyphenyl)ethanol-1-O-β-d-glucuronide, in comparison with the parent compound, to inhibit H(2)O(2) induced oxidative damage and cell death in LLC-PK1 cells, a porcine kidney epithelial cell line. H(2)O(2) treatment exerted a toxic effect inducing cell death, interacting selectively within the pro-death extracellular-signal relate kinase (ERK 1/2) and the pro-survival Akt/PKB signaling pathways. It also produced direct oxidative damage initiating the membrane lipid peroxidation process. None of the tested glucuronides exhibited any protection against the loss in renal cell viability. They also failed to prevent the changes in the phosphorylation states of ERK and Akt, probably reflecting their inability to enter the cells, while HT was highly effective. Notably, pretreatment with glucuronides exerted a protective effect at the highest concentration tested against membrane oxidative damage, comparable to that of HT: the formation of malondialdehyde, fatty acid hydroperoxides and 7-ketocholesterol was significantly inhibited.

Reactive oxygen species are related to ionic fluxes and volume decrease in apoptotic cerebellar granule neurons: role of NOX enzymes

Reactive oxygen species (ROS) are produced early during apoptosis of cerebellar granule neurons induced by low potassium (K5) and staurosporine (Sts). In addition, K5 and Sts activate NADPH oxidases (NOX). Recently, we described that K5 and Sts induce apoptotic volume decrease (AVD) at a time when ROS generation and NOX activity occur. In the present study, we evaluated the relationship between ROS generation and ionic fluxes during AVD. Here, we showed that K5- and Sts-induced AVD was inhibited by antioxidants and that direct ROS production induced AVD. Moreover, NOX inhibitors eliminated AVD induced by both K5 and Sts. Sts, but not K5, failed to induce AVD in cerebellar granule neurons from NOX2 knockout mice. These findings suggest that K5- and Sts-induced AVD is largely mediated by ROS produced by NOX. On the other hand, we also found that the blockage of ionic fluxes involved in AVD inhibited both ROS generation and NOX activity. These findings suggest that ROS generation and NOX activity are involved in ionic fluxes activation, which in turn could maintain ROS generation by activating NOX, leading to a self-amplifying cycle.

Tomato powder is more protective than lycopene supplement against lipid peroxidation in rats

The hypothesis that tomato powder (TP) is more protective than lycopene-beadlet (LB) treatment in rats fed with or without H(2)O(2) was tested by comparing their beneficial effects on serum and hepatic lipids, peroxidation product (malondialdehyde [MDA]), and serum lipoproteins. In groups receiving no H(2)O(2), TP and LB similarly lowered MDA, a major lipid peroxidation product, moderately in the serum but markedly in the liver, more than their respective controls. Hydrogen peroxide consumption elevated liver and serum MDA levels similarly among all treatments, but induced no increase in serum MDA for the TP group, which indicated a stronger protection against lipid peroxidation by TP than by LB treatment. Although the TP and LB diets provided equal amounts of lycopene, serum, and liver lycopene levels for treatments with or without H(2)O(2), they were markedly elevated in TP but still higher in LB group than controls. This indicated a greater lycopene bioavailability in LB than TP. Importantly, TP and LB treatments with or without H(2)O(2) consumption lowered serum total cholesterol and triglycerides by one fifth, as well as decreased serum low-density lipoprotein cholesterol by more than one third of their respective levels in controls. Similarly, liver total cholesterol was markedly lowered (>1/3) by TP or LB treatment, but liver triglycerides were lowered to one fourth by only TP treatment, of the levels in their respective controls. Thus, TP appeared to be more protective because of its additional ability to prevent the H(2)O(2)-induced rise in serum MDA and seemed to lower liver triglycerides more than LB treatment.

Protective effect of hydroxytyrosol and tyrosol against oxidative stress in kidney cells

Bioavailability studies in animals and humans fed with extravirgin olive oil demonstrated that hydroxytyrosol and tyrosol, the major simple phenolic compounds in extravirgin olive oil, are dose-dependently absorbed and excreted. Once absorbed, they undergo extensive metabolism; hydroxytyrosol and tyrosol concentrate mainly in the kidney, where they may exert an important role in the prevention of oxidative stress induced renal dysfunction. In this study we monitored the ability of hydroxytyrosol and tyrosol to protect renal cells (LLC-PK1) following oxidative damage induced by H2O2. Oxidative stress was evaluated by monitoring the changes of the membrane lipid fraction. Hydroxytyrosol exerted a significant antioxidant action, inhibiting the production of MDA, fatty acids hydroperoxides and 7-ketocholesterol, major oxidation products of unsaturated fatty acids and cholesterol, and thus protecting the cells from H2O2-induced damage. Tyrosol, instead, in this experimental model, did not exert any protective effect.

Volume-sensitive chloride channels (ICl,vol) mediate doxorubicin-induced apoptosis through apoptotic volume decrease in cardiomyocytes

Apoptosis is associated with early changes in cell volume through a mechanism called apoptotic volume decrease (AVD). As volume-sensitive chloride channels (I(Cl,vol)) are known to play a key role in the regulation of cell volume, this study investigated the role of I(Cl,vol) and AVD in doxorubicin-induced apoptotic cell death in adult rabbit ventricular cardiomyocytes. Exposure of cardiomyocytes to 1 microm doxorubicin induced a rapid and significant reduction in cell volume of cardiomyocytes (average of 15%), i.e. AVD as well as increases in the early markers of apoptosis, annexin V labeling and caspase-3 activity. Doxorubicin also induced the activation of a current characterized as I(Cl,vol) on the basis of the external chloride sensitivity and pharmacological properties with the patch clamp technique. Doxorubicin-induced AVD and apoptosis were both abolished when cardiomyocytes were exposed to the I(Cl,vol) inhibitors 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) (0.1 mM) or indanyloxyacetic acid 94 (IAA-94) (10 microM). The crucial role of I(Cl,vol) during AVD and apoptosis was confirmed using C(2)-ceramide, another pro-apoptotic compound. These results demonstrate that activation of I(Cl,vol) plays a major role in the mechanism leading to cell shrinkage and apoptosis-induced AVD by agents such as doxorubicin or C(2)-ceramide in adult cardiomyocytes.

Oxidant and antioxidant modulation of chloride channels expressed in human retinal pigment epithelium

Retinal pigment epithelium (RPE) possesses regulated chloride channels that are crucial for transepithelial fluid and ion transport. At present, little is known about the molecular nature of chloride channels in human adult RPE (haRPE) or the effects of oxidative stress on membrane conductance properties. In the present study, we assessed ClC channel and cystic fibrosis transmembrane conductance regulator (CFTR) expression and membrane chloride conductance properties in haRPE cells. ClC-5, ClC-3, ClC-2, and CFTR mRNA expression was confirmed with RT-PCR analysis, and protein expression was detected with Western blot analysis and immunofluorescence microscopy. Whole cell recordings of primary cultures of haRPE showed an outwardly rectifying chloride current that was inhibited by the oxidant H(2)O(2). The inhibitory effects of H(2)O(2) were reduced in cultured human RPE cells that were incubated with precursors of glutathione synthesis or that were stably transfected to overexpress glutathione S-transferase. These findings indicate a possible role for ClC channels in haRPE cells and suggest possible redox modulation of human RPE chloride conductances.

VIP stimulation of cAMP production in corneal endothelial cells in tissue and organ cultures

PURPOSE

To demonstrate that vasoactive intestinal peptide (VIP), an immunosuppressive factor found in the aqueous humor, is a modulator of the corneal endothelium (CE) stimulating its intracellular cAMP production.

METHODS

Rabbit CE cells in cell culture and CE cells in cornea cup organ cultures established from bovine and human donor eyes were treated with VIP at varying concentrations (0, 10(-11)-10(-6) mol/L) for a constant time (4 minutes) or varying times (1, 3.25, 10, 15 minutes) at a constant concentration (1 x 10(-6) mol/L). Intracellular cAMP was extracted and its concentrations were determined by radioimmunoassay. Agonists that are known to modulate the intracellular cAMP concentrations of target cells were allowed to react with cultured rabbit CE cells at 1 x 10(-6) mol/L for 4 minutes.

RESULTS

Vasoactive intestinal peptide stimulated the intracellular cAMP production in CE cells in a dose- and time-dependent manner. At concentrations lower than 10(-9) mol/L, VIP showed little effect. Treatment with 10(-8), 10(-7), and 10(-6) mol/L VIP for 4 minutes, however, increased the intracellular cAMP by 5.7-, 12.3-, and 9.5-fold, respectively, compared with the basal level in rabbit CE cell cultures, and by 19.5-, 38.7-, and 23.3-fold, respectively, in CE cells in bovine cornea cups. The effect of VIP was confirmed in two pairs of donor human corneas in which an average of 2.7-fold stimulation by 5 x 10(-7) mol/L was observed. Treatment of rabbit CE cells with 1 x 10(-6) mol//L VIP for 1 to 15 minutes elevated the intracellular cAMP level by six- to 69-fold. Among the agonists tested, alpha-melanocyte-stimulating hormone and glucagon were not effective, whereas l-isoproterenol and prostaglandin E1 were capable of stimulating the intracellular cAMP levels in rabbit CE cells.

CONCLUSIONS

The current study demonstrated that VIP stimulated cAMP production in CE cells, similar to that shown previously in trabecular meshwork and nonpigmented ciliary epithelial cells. Tissues bathed in the aqueous humor are thus responsive to VIP modulation.