Christiane Van den Branden

HDAC inhibitors in experimental liver and kidney fibrosis

Histone deacetylase (HDAC) inhibitors have been extensively studied in experimental models of cancer, where their inhibition of deacetylation has been proven to regulate cell survival, proliferation, differentiation and apoptosis. This in turn has led to the use of a variety of HDAC inhibitors in clinical trials. In recent years the applicability of HDAC inhibitors in other areas of disease has been explored, including the treatment of fibrotic disorders. Impaired wound healing involves the continuous deposition and cross-linking of extracellular matrix governed by myofibroblasts leading to diseases such as liver and kidney fibrosis; both diseases have high unmet medical needs which are a burden on health budgets worldwide. We provide an overview of the potential use of HDAC inhibitors against liver and kidney fibrosis using the current understanding of these inhibitors in experimental animal models and in vitro models of fibrosis.

Valproic Acid Attenuates Proteinuria and Kidney Injury

Inhibitors of histone deacetylase (HDAC) have anti-inflammatory and antifibrotic effects in several organs and tissues, but their effect on the progression of renal disease is unknown. Here, we studied the effect of valproic acid in adriamycin-induced nephropathy in mice. Administration of valproic acid before kidney injury prevented the development of proteinuria and the onset of glomerulosclerosis. Even after postponing treatment until the peak of adriamycin-induced proteinuria, valproic acid rapidly decreased the quantity of proteinuria and attenuated the progression of renal disease. Valproic acid abrogated the decrease in glomerular acetylation observed during adriamycin-induced nephropathy. Furthermore, valproic acid attenuated the significant upregulation of profibrotic and proinflammatory genes, the deposition of collagen, and the infiltration of macrophages into the kidney. Valproic acid decreased glomerular apoptosis and proliferation induced by adriamycin. Ultrastructural studies further supported the protective effect of valproic acid on podocytes in this model. Taken together, these data suggest that HDACs contribute to the pathogenesis of renal disease and that HDAC inhibitors may have therapeutic potential in CKD.

Effect of various n − 3/n − 6 fatty acid ratio contents of high fat diets on rat liver and heart peroxisomal and mitochondrial β-oxidation

The present work extends tissue investigations previously performed in rat gastric mucosa on lipid metabolism alterations caused by n-3 and n-6 fatty acid-enriched diets. Liver and heart tissues are here studied and demonstrated to undergo, upon exposure to high fat diets with various n-3/n-6 fatty acid ratio contents, biochemical and morphological changes which may be enumerated as follows: (1) Rat liver peroxisomal prostaglandin E2, fatty acid but not bile acid beta-oxidation rates are enhanced, especially upon the diet with the higher n-3/n-6 fatty acid ratio. Mitochondrial beta-oxidation rates are little or not affected by the high fat diets. (2) Rat liver carnitine acyltransferases are stimulated by the high fat diets, the more rich the n-3 fatty acid content, the more pronounced the stimulatory effect. (3) Rat heart peroxisomal and mitochondrial beta-oxidation rates were increased in animals receiving the n-3 fatty acid-enriched diet. At a low n-3/n-6 fatty acid ratio content of the diet, these oxidizing rate values were in control range. The carnitine acyltransferase activities were increased in rat heart to different extents, depending on the n-3/n-6 fatty acid ratio content of the diet. (4) Ultrastructural examination and morphometric determinations on hepatocytes from rats receiving the diets with the lowest and the highest n-3/n-6 fatty acid ratio contents disclose that in the latter case the numbers and fractional volumes of peroxisomes and mitochondria are significantly higher than in the former case.

Comparison of trichostatin A and valproic acid treatment regimens in a mouse model of kidney fibrosis

Histone deacetylase (HDAC) inhibitors are promising new compounds for the therapy of fibrotic diseases. In this study we compared the effect of two HDAC inhibitors, trichostatin A and valproic acid, in an experimental model of kidney fibrosis. In mice, doxorubicin (adriamycin) can cause nephropathy characterized by chronic proteinuria, glomerular damage and interstitial inflammation and fibrosis, as seen in human focal segmental glomerulosclerosis. Two treatment regimens were applied, treatment was either started prior to the doxorubicin insult or delayed until a significant degree of proteinuria and fibrosis was present. Pre-treatment of trichostatin A significantly hampered glomerulosclerosis and tubulointerstitial fibrosis, as did the pre-treatment with valproic acid. In contrast, the development of proteinuria was only completely inhibited in the pre-treated valproic acid group, and not in the pre-treated trichostatin A animals. In the postponed treatment with valproic acid, a complete resolution of established doxorubicin-induced proteinuria was achieved within three days, whereas trichostatin A could not correct proteinuria in such a treatment regimen. However, both postponed regimens have comparable efficacy in maintaining the kidney fibrosis to the level reached at the start of the treatments. Moreover, not only the process of fibrosis, but also renal inflammation was attenuated by both HDAC inhibitors. Our data confirm a role for HDACs in renal fibrogenesis and point towards a therapeutic potential for HDAC inhibitors. The effect on renal disease progression and manifestation can however be different for individual HDAC inhibitors.

Effect of Vitamin E on Antioxidant Enzymes, Lipid Peroxidation Products and Glomerulosclerosis in the Rat Remnant Kidney

In rats with five-sixth nephrectomy (remnant kidney), glomerulosclerosis was significantly reduced by dietary administration of vitamin E (alpha-tocopherol) during 11 and 16 weeks after reduction of nephron number. The activity of catalase and the production of H2O2 in remnant kidney cortex homogenate were not influenced by the vitamin E diet; however, the activities of glutathione peroxidase and superoxide dismutase were significantly increased (up to 140 and 180%, respectively, after 16 weeks). Lipid peroxidation, evaluated by malonaldehyde and 4-hydroxynonenal concentrations, was decreased in cortex homogenates and in urine. Though the extent of the effect of vitamin E on antioxidant enzyme levels and lipid peroxidation is small, the important reduction of glomerulosclerosis is in favor of dietary supplementation with vitamin E.

Cytochrome P-450-dependent H2O2 production demonstrated in vivo: Influence of phenobarbital and allylisopropylacetamide

By administration of allylisopropylacetamide, an inhibitor of cytochrome P‐450, we demonstrated that cytochrome P‐450 is involved in the production of H2O2 during aminopyrine metabolism and phenobarbital induction in both the unanaesthetized guinea pig and rat. In the guinea pig we also found evidence for the existence of a basal cytochrome P‐450‐dependent H2O2 production, i.e. in the absence of exogenous substrate. Catalase participates in the decomposition of H2O2 produced in the endoplasmic reticulum where cytochrome P‐450 is localized.By administration of allylisopropylacetamide, an inhibitor of cytochrome P-450, we demonstrated that cytochrome P-450 is involved in the production of H2O2 during aminopyrine metabolism and phenobarbital induction in both the unanaesthetized guinea pig and rat. In the guinea pig we also found evidence for the existence of a basal cytochrome P-450-dependent H2O2 production, i.e. in the absence of exogenous substrate. Catalase participates in the decomposition of H2O2 produced in the endoplasmic reticulum where cytochrome P-450 is localized.

Thioridazine: a selective inhibitor of peroxisomal β-oxidation in vivo

In vivo administration of the phenothiazine drug, thioridazine, inhibits hepatic peroxisomal β‐oxidation in mice. In starving animals, 3‐hydroxybutyrate concentration is not decreased by thioridazine treatment. These results provide the first demonstration of thioridazine as a selective inhibitor of peroxisomal β‐oxidation in intact animals. Thioridazine might supply a tool for simulation of pathological conditions in which peroxisomal β‐oxidation is impaired.

Vitamin E Protects Renal Antioxidant Enzymes and Attenuates Glomerulosclerosis in Adriamycin-Treated Rats

Background/Aims: In the rat Adriamycin model of chronic renal failure, the development of glomerulosclerosis and tubulointerstitial lesions is accompanied by decreased activities and mRNA levels of the antioxidant enzymes. In this study, we investigated the effect of oral vitamin E supplementation on antioxidant enzyme activities in both the cortex and isolated glomeruli from Adriamycin-treated rats. Methods: Glomerulosclerosis, tubulointerstitial lesions and ferric iron deposits were evaluated by histochemical staining methods, and antioxidant enzyme activities were measured by spectrophotometry. Results: Vitamin E supplementation of the normal diet attenuates Adriamycin-induced glomerulosclerosis and tubulointerstitial lesions, but not proteinuria and serum total cholesterol, low-density lipoprotein cholesterol, triglycerides and total protein concentrations. In the cortex, vitamin E completely prevented a decrease in enzyme activity for Cu/Zn superoxide dismutase and catalase, and partly for Mn superoxide dismutase and glutathione peroxidase. In the glomeruli, vitamin E completely prevented a decrease in activity for Cu/Zn superoxide dismutase, catalase and glutathione peroxidase, and partly for Mn superoxide dismutase. Conclusion: Dietary supplementation of vitamin E protects the activities of antioxidant enzymes in the kidney cortex and glomeruli, and attenuates the evolution towards terminal renal failure in rats treated with Adriamycin.

Renal antioxidant enzymes and fibrosis-related markers in the rat adriamycin model

Excessive generation of reactive oxygen intermediates can induce changes in the cellular antioxidant defence system. In this study we examine the antioxidant enzyme status and the expression of fibrosis-related marker proteins in the Adriamycin model of chronic renal failure in the rat. Twenty weeks after Adriamycin treatment, rats have overt nephrotic syndrome and renal failure with development of tubulo-interstitial fibrosis and glomerulosclerosis. Lipids accumulate in blood and in both glomeruli and tubulo-interstitial tissue. Desmin and α-smooth muscle actin expression increases in glomeruli and in the tubulo-interstitial area. Renal cortex antioxidant enzyme activities are decreased 20 weeks after Adriamycin injection (to 41% for catalase, to 56% for total superoxide dismutase and to 69% for glutathione peroxidase). The mRNA levels of catalase, Cu/Zn-superoxide dismutase and glutathione peroxidase-1 evaluated by Northern blot are decreased by more than 50% for catalase, Cu/Zn-superoxide dismutase and glutathione peroxidase-1. We conclude that in the rat Adriamycin-induced model of chronic renal failure with fibrosis, the combination of decreased antioxidant enzyme status in renal cortex with high concentrations of lipids in blood and renal tissue facilitates oxidative damage. Development of fibrosis is paralleled by increased expression of desmin and α-smooth muscle actin.

Enalapril Increases Antioxidant Enzyme Activity in Renal Cortical Tissue of Five-Sixths- Nephrectomized Rats

In rats with five-sixths nephrectomy (remnant kidney), blood pressure, glomerulosclerosis, and proteinuria are significantly reduced by administration of the angiotensin-converting enzyme inhibitor enalapril, during 16 weeks after reduction of the nephron number. The activity of catalase in remnant-kidney cortex homogenate is not influenced by enalapril treatment; the activities of superoxide dismutase and glutathione peroxidase are significantly increased. Elevated lipid peroxidation in cortex homogenates, evaluated by malondialdehyde and 4-hydroxynonenal concentrations, is not changed by treatment. Supplementation of dietary vitamin E to enalapril treatment does not alter antioxidant enzyme activities when compared to enalapril monotherapy. These results show that enalapril improves the balance between reactive oxygen intermediates and antioxidant enzymes in the remnant-kidney cortex of the rat. This finding may in part explain the protective effect of angiotensin-converting enzyme inhibitors on the progression of glomerulosclerosis.