Anikó Berkó

The involvement of heme oxygenase-1 activity in the therapeutic actions of 5-aminosalicylic acid in rat colitis

The mechanism of action of 5-aminosalicylic acid (5-ASA), the active therapeutic moiety of a number of clinically used anti-colitic agents, is unclear. The present study investigates whether the beneficial effects in vivo could involve induction of the heat shock protein, heme oxygenase-1 (HO-1), known to provide endogenous anti-oxidant and anti-inflammatory moieties which can modulate colonic inflammation. The effects of 5-ASA on the colonic expression and activity of HO-1 along with its effect on the inflammatory damage have been evaluated in the colitis provoked by instillation of trinitrobenzene sulphonic acid (TNBS) over 48 h in the rat. Intracolonic administration of 5-ASA (8, 25 and 75 mg/kg/day) dose-dependently reduced the TNBS-provoked macroscopic colonic inflammatory injury, myeloperoxidase (MPO) activity and TNF-alpha levels, while also dose-dependently increasing colonic heme oxygenase enzyme activity. Colonic HO-1 protein expression, determined by Western blot analysis in this colitis model, was likewise further induced by 5-ASA. Intracolonic administration of 5-ASA alone under unchallenged conditions also induced colonic HO-1 protein expression and stimulated heme oxygenase enzyme activity. Administration of zinc protoporphyrin (50 micromol/kg/day, s.c.), which prevented the increase in colonic heme oxygenase activity, abolished the anti-colitic effect of 5-ASA. These results suggest that 5-ASA may exert its colonic anti-oxidant and anti-inflammatory effects in vivo in part through the up-regulation of HO-1 enzyme expression and activity.

Attenuation of inflammation and cytokine production in rat colitis by a novel selective inhibitor of leukotriene A4 hydrolase

Leukotriene B4 (LTB4), formed by the sequential actions of the 5‐lipoxygenase (5‐LO) and leukotriene A4 hydrolase (LTA4H), is a pro‐inflammatory mediator implicated in the pathogenesis of inflammatory bowel disease. However, inhibitors of 5‐LO have not proved to be consistent in their therapeutic efficacy in colitis. Another approach to inhibiting LTB4 synthesis is through the use of inhibitors of LTA4H, such as the novel, potent and selective compound, JNJ 26993135.

Zerumbone exerts a beneficial effect on inflammatory parameters of cholecystokinin octapeptide-induced experimental pancreatitis but fails to improve histology.

Objective: Our experiments were designed to investigate the effects of zerumbone pretreatment on cholecystokinin octapeptide (CCK-8)-induced acute pancreatitis in rats. Methods: Male Wistar rats weighing 240 to 280 g were divided into a control group, a group treated with CCK-8, a group receiving 20 mg/kg zerumbone before CCK-8 administration, and a group treated with zerumbone only. Results: The serum amylase and lipase activities and the pancreatic weight-body weight ratio were significantly reduced by zerumbone pretreatment, but the drug failed to influence the histological parameters of pancreatitis. The anti-inflammatory effects of the drug were manifested in decreases in the cytosolic interleukin 6 and tumor necrosis factor &agr; concentrations and an elevation in the I-&kgr;B concentration, whereas the antioxidant ability of zerumbone was demonstrated by reductions in inducible nitric oxide synthase, Mn- and Cu/Zn-superoxide dismutase activities in the zerumbone-treated rats. Conclusion: Zerumbone ameliorated the changes of several parameters of acute pancreatitis probably by interfering with I-&kgr;B degradation, but in the applied dose, it failed to influence the histology of the disease.Abbreviations: CCK-8 - cholecystokinin octapeptide, DMSO - dimethyl sulfoxide, iNOS - inducible nitric oxide synthase, cNOS - constitutive nitric oxide synthase, TNF, tumor necrosis factor, IL-6 - interleukin 6, NF-&kgr;B - nuclear factor &kgr;B, SOD - superoxide dismutase, ASAT - aspartate aminotransferase

Raloxifene, an oestrogen–receptor modulator, prevents decreased constitutive nitric oxide and vasoconstriction in ovariectomized rats

Administration of graded doses of [Arg(8)]vasopressin (0.06-0.18 microg kg(-1), i.v.) induced a dose-dependent increase in arterial blood pressure in the catecholamine-depleted (phentolamine; 10 mg kg(-1), i.p.) intact and ovariectomized female rat, with the elevation of blood pressure more marked following ovariectomy. In addition, ovariectomy caused the down-regulation of aortic Ca(2+)-dependent constitutive nitric oxide synthase (assessed by the citrulline assay). The down-regulation of the Ca(2+)-dependent constitutive nitric oxide synthase and augmentation of vasopressin-induced blood pressure responses were prevented by the therapy (1 month, p.o.) with the selective oestrogen receptor modulator, raloxifene (0.3-1.0 mg kg(-1) day(-1)), or with 17beta-oestradiol (0.3 mg kg(-1) day(-1)) in ovariectomized rats. Thus, oestrogen deficiency down-regulates vascular constitutive nitric oxide synthase, which appears to be involved in the increased sensitivity of the vasculature to vasopressin, since both effects can be reversed by the exogenous administration of the natural oestrogen 17beta-oestradiol or the selective oestrogen-receptor modulator raloxifene.

Anti-Inflammatory Effect of Recreational Exercise in TNBS-Induced Colitis in Rats: Role of NOS/HO/MPO System

There are opposite views in the available literature: Whether physical exercise has a protective effect or not on the onset of inflammatory bowel disease (IBD). Therefore, we investigated the effects of recreational physical exercise before the induction of colitis. After 6 weeks of voluntary physical activity (running wheel), male Wistar rats were treated with TNBS (10 mg). 72 hrs after trinitrobenzene sulphonic acid (TNBS) challenge we measured colonic gene (TNF-α, IL-1β, CXCL1 and IL-10) and protein (TNF-α) expressions of various inflammatory mediators and enzyme activities of heme oxygenase (HO), nitric oxide synthase (NOS), and myeloperoxidase (MPO) enzymes. Wheel running significantly increased the activities of HO, constitutive NOS (cNOS) isoform. Furthermore, 6 weeks of running significantly decreased TNBS-induced inflammatory markers, including extent of lesions, severity of mucosal damage, and gene expression of IL-1β, CXCL1, and MPO activity, while IL-10 gene expression and cNOS activity were increased. iNOS activity decreased and the activity of HO enzyme increased, but not significantly, compared to the sedentary TNBS-treated group. In conclusion, recreational physical exercise can play an anti-inflammatory role by downregulating the gene expression of proinflammatory mediators, inducing anti-inflammatory mediators, and modulating the activities of HO and NOS enzymes in a rat model of colitis.

Inhibitory effect of vasopressin receptor antagonist OPC-31260 on experimental brain oedema induced by global cerebral ischaemia

SummaryThe effects of the non-peptide vasopressin V2 receptor antagonist 5-dimethylamino-1-[4-(2-methylbenzoylamino)benzoyl]-2,3,4,5-tetrahydro-1H-benzazepine hydrochloride (OPC-31260) on the cerebral oedema induced by general cerebral hypoxia were studied in rats. The general cerebral hypoxia was produced by bilateral common carotid ligation in Sprague-Dawley rats of the CFY strain. By 6 h after the ligation, half of the rats had died, but the survival rate was significantly higher following OPC-31260 administration. Electron microscopic examinations revealed typical ischaemic changes after the carotid ligation. The carotid ligation increased the brain contents of water and Na+ and enhanced the plasma vasopressin level. The increased brain water and Na+ accumulation was prevented by OPC-31260 administration, but the plasma vasopressin level was further enhanced by OPC-31260. These results demonstrate the important role of vasopressin in the development of the disturbances in brain water and electrolyte balance in response to general cerebral hypoxia. The carotid ligation-induced cerebral oedema was significantly reduced following oral OPC-31260 administration. The protective mechanism exerted by OPC-31260 stems from its influence on the renal vasopressin V2 receptors. These observations might suggest an effective approach to the treatment of global hypoxia-induced cerebral oedema in humans.

Sexual dimorphism of cardiovascular ischemia susceptibility is mediated by heme oxygenase

We investigated the gender differences in heme-oxygenase (HO) enzyme, which produces endogenous vascular protective carbon monoxide (CO). We studied (1) the activity and expression of HO enzymes in the left ventricle (LV) and aorta, (2) basal increase in basal blood pressure provoked by arginine vasopressine (AVP) in vivo, (3) the heart perfusion induced by AVP, (4) the ST segment depression provoked by adrenaline and 30 seconds later phentolamine, and (5) the aorta ring contraction induced by AVP in female and male Wistar rats. We found that HO activity and the expression of HO-1 and HO-2 were increased in female rat aorta and LV. We demonstrated that the basal blood pressure and administration of AVP provoked blood pressure response are increased in the males; the female myocardium was less sensitive towards angina. Both differences could be aggravated by the inhibition of HO. The aorta rings were more susceptible towards vasoconstriction by AVP in males; isolated heart perfusion decrease was higher in males. The HO inhibition aggravated the heart perfusion in both sexes. In conclusion, the increased HO activity and expression in females might play a role in the sexual dimorphism of cardiovascular ischemia susceptibility during the reproductive age.

Endogenous Estrogen-Mediated Heme Oxygenase Regulation in Experimental Menopause

Estrogen deficiency is one of the main causes of age-associated diseases in the cardiovascular system. Female Wistar rats were divided into four experimental groups: pharmacologically ovariectomized, surgically ovariectomized, and 24-month-old intact aging animals were compared with a control group. The activity and expression of heme oxygenases (HO) in the cardiac left ventricle, the concentrations of cardiac interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), the myeloperoxidase (MPO) activity in the cardiac left ventricle, and the effects of heme oxygenase blockade (by 24-hour and 1-hour pretreatment with tin-protoporphyrin IX, SnPP) on the epinephrine and phentolamine-induced electrocardiogram ST segment changes in vivo were investigated. The cardiac HO activity and the expression of HO-1 and HO-2 were significantly decreased in the aged rats and after ovariectomy. Estrogen depletion was accompanied by significant increases in the expression of IL-6 and TNF-α. The aged and ovariectomized animals exhibited a significantly elevated MPO activity and a significant ST segment depression. After pretreatment with SnPP augmented ST segment changes were determined. These findings demonstrate that the sensitivity to cardiac ischemia in estrogen depletion models is associated with suppression of the activity and expression of the HO system and increases in the secretion of proinflammatory cytokines and biomarkers.

Prevention of hypoxic brain oedema by the administration of vasopressin receptor antagonist OPC-31260

The numerous situations which can result in cerebral hypoxic damage occur in newborn infants and in the elderly. In research aimed at more effective therapeutic intervention in ischaemic disorders of the brain, the animal model used and the principles of the causal therapy should be better outlined. The effects of the non-peptide AVPR (V2) antagonist 5-dimethylamino-1-[4-(2-methylbenzoylamino) benzoyl]-2,3,4,5-tetrahydro-1H-benzazepine hydrochloride (OPC-31260) on the cerebral oedema induced by general cerebral hypoxia were studied in rats. The general cerebral hypoxia was produced by bilateral common carotid ligation in Sprague-Dawley rats of the CFY strain. By 6h after the ligation, half of the rats had died, but the survival rate was significantly higher following OPC-31260 administration. Electron microscopic examinations revealed typical ischaemic changes after the carotid ligation, and OPC-31260 treatment did not significantly reduce the hypoxic signs in the brain cortex; only a certain decrease in the pericapillary oedema was observed. The carotid ligation increased the brain contents of water and Na(+) and enhanced the plasma AVP level. The increased brain water and Na(+) accumulation was prevented by OPC-31260 administration, but the plasma AVP level was further enhanced by OPC-31260. These results demonstrate the important role of AVP in the development of the disturbances in brain water and electrolyte balance in response to general cerebral hypoxia. The carotid ligation-induced cerebral oedema was significantly reduced following oral OPC-31260 administration. The protective mechanism exerted by OPC-31260 stems from its influence on the renal AVPR (V2). These observations might suggest an effective approach to the treatment of global hypoxia-induced cerebral oedema in humans.

Astrocytic and neuronal localization of kynurenine aminotransferase-2 in the adult mouse brain.

During catabolism of tryptophan through the kynurenine (KYN) pathway, several endogenous metabolites with neuromodulatory properties are produced, of which kynurenic acid (KYNA) is one of the highest significance. The causal role of altered KYNA production has been described in several neurodegenerative and neuropsychiatric disorders (e.g., Parkinson’s disease, Huntington’s disease, schizophrenia) and therefore kynurenergic manipulation with the aim of therapy has recently been proposed. Conventionally, KYNA is produced from its precursor l-KYN with the aid of the astrocytic kynurenine aminotransferase-2 (KAT-2) in the murine brain. Although the mouse is a standard therapeutic research organism, the presence of KAT-2 in mice has not been described in detail. This study demonstrates the presence of kat-2 mRNA and protein throughout the adult C57Bl6 mouse brain. In addition to the former expression data from the rat, we found prominent KAT-2 expression not only in the astrocyte, but also in neurons in several brain regions (e.g., hippocampus, substantia nigra, striatum, and prefrontal cortex). A significant number of the KAT-2 positive neurons were positive for GAD67; the presence of the KAT-2 enzyme we could also demonstrate in mice brain homogenate and in cells overexpressing recombinant mouse KAT-2 protein. This new finding attributes a new role to interneuron-derived KYNA in neuronal network operation. Furthermore, our results suggest that the thorough investigation of the spatio-temporal expression pattern of the relevant enzymes of the KYN pathway is a prerequisite for developing and understanding the pharmacological and transgenic murine models of kynurenergic manipulation.