Max Hropot

S3226, a novel inhibitor of Na+/H+ exchanger subtype 3 in various cell types

Abstract Inhibition of Na+/H+ exchange (NHE) subtypes has been investigated in a study of the mouse fibroblast L cell line (LAP1) transfected with human (h) NHE1, rabbit (rb) NHE2, rat (rt) or human (h) NHE3 as well as an opossum kidney cell line (OK) and porcine renal brush-border membrane vesicles (BBMV). S3226 {3-[2-(3-guanidino-2-methyl-3-oxo-propenyl)-5-methyl-phenyl]-N-isopropylidene-2-methyl-acrylamide dihydro-chloride} was the most potent and specific NHE3 inhibitor with an IC50 value of 0.02 µmol/l for the human isoform, whereas its IC50 value for hNHE1 and rbNHE2 was 3.6 and @80 µmol/l, respectively. In contrast, amiloride is a weak NHE3 inhibitor (IC50>100 µmol/l) with a higher affinity to hNHE1 and rbNHE2. Cariporide (4-isopropyl-3-methylsulphonyl-benzoyl-guanidine methane-sulphonate), which has an IC50 for NHE3 of approximately 1 mmol/l, is a highly selective NHE1 inhibitor (0.08 µmol/l). Therefore, S3226 is a novel tool with which to investigate the physiological and pathophysiological roles of NHE3 in animal models.

The bradykinin B2 receptor antagonist Icatibant (HOE 140) corrects avid Na+ retention in rats with CCl4-induced liver cirrhosis: possible role of enhanced microvascular leakage

Avid Na+ retention is a hallmark of liver cirrhosis. The aim of this study was to investigate whether and how bradykinin is involved in Na+ retention in rats with CCl4-induced liver cirrhosis. To this end the bradykinin B2 receptor antagonist Icatibant (HOE 140) was used. On one hand, bradykinin has a renal natriuretic action. On the other hand, bradykinin is a potent mediator of both vasodilation and microvascular leakage. Both vascular mechanisms, which are reported for cirrhosis, could cause vascular underfilling and Na+ retention by activating the renin-angiotensin-aldosterone system. Icatibant normalised Na+ retention and reduced the hyperactivity of the renin-angiotensin-aldosterone system, suggesting a bradykinin-induced vascular disturbance. Icatibant had no significant effect on the mild hypotension which developed with CCl4 treatment. However, there was indirect evidence for enhanced microvascular leakage that was strongly inhibited by Icatibant. Our experimental results demonstrate that bradykinin is a key mediator of Na+ retention in liver cirrhosis and suggest that a bradykinin-induced increase in microvascular leakage is mainly responsible.

A Novel Screening Assay of the Na+-Dependent Cl-/HCO-3 Exchanger (NCBE) and Its Inhibitors

A mouse fibroblast L cell line defective in Na+/H+ antiport activity (LAP1) was used to develop a screening assay for the Na+-dependent Cl-/HCO–3

Pharmacological effects of 1,3,5-triazines and their excretion characteristics in the rat.

Hyperuricemia is a metabolic and/or excretory disorder of purines associated with humans only. Thus the availability of experimental animal models for the study of human hyperuricemia has been very limited. In most mammalian species uric acid is converted to allantoin by uricase. Uricase is lacking in man and the apes. In these species uric acid rather than water-soluble allantoin is the end-product of purine metabolism (Fanelli3). To obtain an animal model for studies on hyperuricemia, hepatic uricase must be blocked with a selective inhibitor. Recently, use of the rat as a hyperuricemic animal model was described and subsequently used in different areas of research. Fridovich4 and Johnson1 have shown that certain s-triazines are potent competitive inhibitors of uricase. Particularly oxonic acid and amide of oxonic acid have been described as effective inhibitors of uricase activity in vitro and in vivo. Since no studies have been carried out on their metabolism or excretion characteristics, the aim of this study was to examine the pharmacological effects and excretion characteristics of oxonic acid, amide of oxonic acid and of 5-azauracil in rats.

Uricostatic Effect of Allopurinol in the Allantoxanamide-Treated Rat: A New Method for Evaluating Antiuricopathic Drugs

In most mammals, uric acid is converted into allantoin by the enzyme uricase, which does not occur in man and apes. Thus, the urinary end product of purine metabolism in man and apes is uric acid, whereas it is allantoin in most mammals. An attempt to produce an animal model for research into hyperuricemia was made by Johnson1, who blocked the activity of hepatic uricase in rats by a selective enzyme inhibitor, oxonic acid (oxonate). Particularly the amide of oxonic acid (allantoxanamide) has been described as an effective inhibitor of uricase activity in vitro and in vivo. Hropot2 demonstrated that the prolonged duration of action of allantoxanamide as compared to oxonic acid is due to its elimination kinetics. Allantoxanamide was eliminated by the kidneys with a half-life of 25.4 min, which was double that of oxonate during the first 30 min after administration. The purpose of this study was to establish an appropriate screening method for evaluating antiuricopathic drugs in the allantoxanamide-treated rat.

The Excretion of 14C-Hypoxanthine and Its Metabolites in Rats Following Administration of Uricostatic Drugs

In vivo xanthine oxidase inhibition results in a reduction of uric acid (and allantoin) in urine and in an increase in the urinary excretion of hypoxanthine and xanthine as described by Elionl for allopurinol. The dose-dependence of the excreted amounts of hypoxanthine and xanthine is a relevant consideration when using these parameters to measure the action of uricostatics in the rat. The purpose of our studies was to obtain a simple and rapid method to detect the uricostatic quality of hypouricemic compounds.