Loop diuretics are open-channel blockers of the cystic fibrosis transmembrane conductance regulator with distinct kinetics.

BACKGROUND AND PURPOSE: Loop diuretics are widely used to inhibit the Na(+), K(+), 2Cl(-) co-transporter, but they also inhibit the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel. Here, we investigated the mechanism of CFTR inhibition by loop diuretics and explored the effects of chemical structure on channel blockade. EXPERIMENTAL APPROACH: Using the patch-clamp technique, we tested the effects of bumetanide, furosemide, piretanide and xipamide on recombinant wild-type human CFTR. KEY RESULTS: When added to the intracellular solution, loop diuretics inhibited CFTR Cl(-) currents with potency approaching that of glibenclamide, a widely used CFTR blocker with some structural similarity to loop diuretics. To begin to study the kinetics of channel blockade, we examined the time dependence of macroscopic current inhibition following a hyperpolarizing voltage step. Like glibenclamide, piretanide blockade of CFTR was time and voltage dependent. By contrast, furosemide blockade was voltage dependent, but time independent. Consistent with these data, furosemide blocked individual CFTR Cl(-) channels with 'very fast' speed and drug-induced blocking events overlapped brief channel closures, whereas piretanide inhibited individual channels with 'intermediate' speed and drug-induced blocking events were distinct from channel closures. CONCLUSIONS AND IMPLICATIONS: Structure-activity analysis of the loop diuretics suggests that the phenoxy group present in bumetanide and piretanide, but absent in furosemide and xipamide, might account for the different kinetics of channel block by locking loop diuretics within the intracellular vestibule of the CFTR pore. We conclude that loop diuretics are open-channel blockers of CFTR with distinct kinetics, affected by molecular dimensions and lipophilicity.

[Mechanism of action of xipamide and its classification as a "low ceiling diuretic". Pharmacodynamic-pharmacokinetic studies in healthy volunteers and in kidney and liver patients]. / Zur Wirkungsweise von Xipamid und seiner Klassifizierung als "Low-ceiling- Diuretikum". Pharmakodynamische und pharmakokinetische Untersuchungen an gesunden Probanden sowie bei Nieren- und Leberkranken.

Xipamide (CAS 14293-44-8) shows structural features comparable with the thiazide- as well as the class of loop diuretics. According to earlier findings this diuretic, in contrast to the thiazides, should not decrease the glomerular filtration rate (GFR) and be effective even in patients with advanced renal failure. Therefore recently the question, which class of diuretics xipamide should be related to, has been increasingly discussed. In order to solve this issue, the diuretic effect of xipamide was assessed in healthy volunteers once without and once under strict water and salt restriction. Additionally, changes in GFR were monitored by means of measurement of the creatinine clearance. Kinetic parameters were determined in plasma and urine; further, in patients with liver cirrhosis, renal elimination kinetics of the diuretic were correlated with the concentration of direct plasma bilirubin, as a marker of cholestasis, at the beginning of a treatment with xipamide, 40 mg qd. The investigations proved that xipamide, like a typical thiazide diuretic, gives rise to a temporary decrease in GFR of about 30 %, provided the renin-angiotensin-aldosterone system of the volunteer is activated by previous salt and water restriction. Xipamide leads to an increase of K+ and Mg2+ excretion, but to a decrease of Ca2+ excretion in urine, a charactaristical feature of the thiazide-like diuretics. The correlation between Na+ excretion and drug excreted in urine over time showed a functional graph that is characteristic for a "low ceiling" thiazide diuretic. In patients with renal failure FE(Na) was increased when related to the GFR-adjusted drug excretion rate, whereas it was diminished in conditions with decreased effective circulating volume like in liver cirrhosis with ascites. It could be shown that the elimination kinetics of xipamide are determined by renal drug clearance, which proportionally decreases with GFR. In patients with liver failure, a decrease of non-renal drug clearance went along with an increase in urinary drug excretion. The amount of drug excreted in urine (Ae) proportionally increased with the concentration of the patients' direct plasma bilirubin. Thus, from a pharmacological as well as clinical point of view xipamide acts like a thiazide diuretic. As could be shown for other thiazides some time ago, xipamide is effective not only in patients with cardiovascular diseases, but also in those with advanced renal failure.

Can xipamide or tacrolimus inhibit the glucuronidation of mycophenolic acid in rat liver slices?

The objective of this study was to investigate the effect of tacrolimus (Tac) and xipamide (X) on mycophenolic acid (MPA) glucuronidation in precision-cut rat liver slices. To assess a possible effect of these two drugs, the influence of the anti-inflammatory drug niflumic acid (NA)--a well-known inhibitor for MPA glucuronidation in human liver microsomes--was used as a standard. MPA and its main metabolite mycophenolic acid glucuronide (MPAG) were determined by means of high-performance liquid chromatography. MPA glucuronidation rate showed a significant linear correlation (p = 0.012) with MPA concentrations from 15.61 up to 124.88 microM in the medium. That means, the enzyme(s) responsible for the glucuronidation of MPA worked far below Km-value. With all MPA concentrations tested, neither the addition of Tac (31.30 nM) nor of X (28.25 nM) influenced the glucuronidation of MPA. In comparison, NA at a concentration of 70.92 nM showed a marked inhibitory effect (by 72%). The present pilot-study indicates that precision-cut rat liver slices are a suitable in vitro model to characterize the glucuronidation of MPA to its primary metabolite MPAG and interferences with other substances.

Inhibition by xipamide of amiloride-induced acidification in cultured rat cardiocytes.

The diuretic drug xipamide improves myocardial relaxation in hypertensive patients with left ventricular hypertrophy, but its mechanism of action is unknown. Here, xipamide was tested in cultured rat heart myogenic H9c2 cells and newborn cardiomyocytes for its effects on cell acidification (and Ca2+ mobilization). In H9c2 cells, blocking Na+/H+ exchange with amiloride (2 mM) provoked cell acidification with rate = 0.82 +/- 0.17 pH units/h (n = 6). Xipamide 1 microM maximally inhibited 50 +/- 7% (n = 9) of cell acidification. The action of xipamide required the presence of HCO3- and was antagonized by the HCO3(-)-transport blocker DIDS (4,4'-diisothiocyanostilbene-2.2'-disulfonic acid). Conversely, the carbonic anhydrase (EC 4.2.1.1) inhibitor acetazolamide failed to prevent xipamide action. Finally, xipamide was without significant effect on the Ca2+ signals induced by endothelin-1, vasopressin or the Ca2+ ionophore ionomycin. In newborn rat cardiomyocytes, xipamide reduced amiloride-induced cell acidification at similar concentrations as in H9c2 cardiocytes, but with a slightly higher extent of maximal inhibition (70-80%). In conclusion, xipamide reduced amiloride-dependent cell acidification in the rat heart myogenic H9c2 cell line and in newborn rat cultured cardiomyocytes. This action of xipamide seems to be related to a complex interaction with DIDS-sensitive HCO3- movements. Prevention of cell acidification by xipamide could be involved in the beneficial effects of this compound in myocardial relaxation and left ventricle filling in hypertensive patients with left ventricular hypertrophy.

[Effect of 3 hypertensive++ agents on ventricular geometry and function]. / Efecto de tres antihipertensivos sobre la geometría y función ventriculares.

BACKGROUND: To assess the prevalence of left ventricular hypertrophy in hypertensive patients referred to an outpatient cardiology unit, and to assess its evolution under antihypertensive treatment. METHODS: One hundred and seven mild to moderate hypertensive patients were randomized to receive either xipamide, verapamil or atenolol. Cross-sectional echocardiography was performed in order to assess left ventricular mass and function. RESULTS: Mean age was 56 years, with a 4:1 female/male ratio. Mean follow-up was 120 days. Left ventricular hypertrophy was very common (65%) and decreased to 54% under antihypertensive treatment. Left ventricular mass decreased from 134.3 g/m2 to 118.1 g/m2 (p < 0.001). Concentric hypertrophy was the most common geometric pattern (42%), decreasing to 30% with treatment. Xipamide decreased ventricular mass by decreasing left ventricular diameters, while verapamil and atenolol decreased left ventricular thickness, mainly in septal wall. Systolic function was not modified during the treatment period. Diastolic function was not modified by xipamide and verapamil, and improved with atenolol. CONCLUSIONS: Left ventricular hypertrophy is very frequent when determined by echocardiography and all three drugs produced regression of left ventricular hypertrophy in a different way with respect to left ventricle geometry, an effect which could have potential therapeutic implications.

Clinicopharmacological reappraisal of the potency of diuretics.

From a clinicopharmacological standpoint, the urinary excretory potency of diuretics should be assessed comparatively on the basis of the changes in 24-hour natriuresis, with respect to 24-hour natriuresis after placebo, caused by single oral doses administered to healthy adult subjects who are in habitual and steady-state external sodium balance. The potency of various formulations of loop (e.g., furosemide), of early distal tubular (e.g., the thiazides), and of potassium-retaining diuretics, as well as of several combinations of diuretics, has been evaluated in a series of studies. Two formulations of loop diuretics (muzolimine 20 mg and torasemide 2.5 mg) are definitely nondiuretic. The majority of the other formulations of loop diuretics studied are, in general, comparatively less potent than most of the common formulations of early distal tubular diuretics studied. As a general rule, most common formulations of early distal tubular diuretics are at least not less potent than the majority of common formulations of loop diuretics. Hydrochlorothiazide 25 mg and furosemide 80 mg have similar potencies. Loop diuretics increase mean renal sodium output strikingly within the first few (0-6) hours after dosing, but this forced excretion is followed by a rebound with respect to postplacebo mean urinary sodium flow; the rebound usually takes place between 6 and 24 hours after dosing. However, no rebound in mean urinary sodium flow occurs during the 24 hours following a single dose of a distal tubular diuretic; these substances increase urinary sodium excretion with lower maximal intensity but more protractedly than loop diuretics.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum lipoprotein profile under different antihypertensive therapy.

Serum lipids of 80 patients with moderately severe essential hypertension under four different antihypertensive therapies were compared to ten matched hypertensives on a placebo, after eight weeks of therapy. The results in the serum lipid parameters measured after therapy showed with enalapril a significant increase in high-density lipoprotein cholesterol (HDL-C) and a decrease in the total cholesterol/HDL-C ratio. With benazepril a significant decrease in the total cholesterol/HDL-C ratio was obtained. With the diuretic combination Epitens the effect on serum sodium and potassium was minimal. No significant changes were found in the lipoprotein profile following the administration of the placebo. Both angiotensin converting enzyme inhibitors (enalapril and benazapril) induced a significant improvement in the atherogenic ratio; as well as the calcium antagonist (isradipine), though to a less extent. The diuretic Epitens induced an insignificant deterioration of the atherogenic ratio.

Hormonal effects of the diuretic xipamide in healthy men.

The effect of xipamide on plasma alpha-atrial natriuretic peptide and the renin-aldosterone-kallikrein system have been studied in 12 healthy men, using a double-blind cross-over design. After a run-in period on placebo of 1 week, the subjects were treated with either placebo (n = 6) or xipamide 20 mg once daily (n = 6) for 16 weeks and were then switched to the alternative medication for another 16 weeks. The plasma concentration of alpha-atrial natriuretic peptide fell after 1 week of xipamide administration and increased during prolonged xipamide administration but remained reduced. The changes in plasma alpha-ANP observed after 1 week of xipamide were negatively correlated with the changes in hematocrit and hemoglobin. Plasma renin activity (PRA), aldosterone concentration (PAC), and urinary excretion of aldosterone and kallikrein increased after 1 week of xipamide administration, levelled off during the second and fourth weeks, but remained elevated during further prolonged xipamide administration for 16 weeks. The xipamide-induced changes in PRA and PAC were positively correlated with the changes in the hematocrit and hemoglobin. The changes in plasma renin, aldosterone, and alpha-atrial natriuretic peptide during xipamide administration may be related to diuretic-induced volume contraction.

[Beneficial effects of xipamide on pH and Ca2+ ions of cardiac cells]. / Effets bénéfiques du xipamide sur le pH et le Ca2+ des cardiocytes.

We have shown that xipamide is the only antihypertensive agent able to selectively inhibit the anion exchanger (AE), a transport system translocating (i) chloride and bicarbonate (thus participating to internal pH), but also (ii) Na+ as NaCO3-(which could explain the natriuretic effect of xipamide). On the other hand, Ollivier (Val de Grâce, Paris) has shown that xipamide exerts a beneficial action on heart by favoring left ventricular relaxation in essential hypertensive patients exhibiting cardiac hypertrophy. In order to understand this clinical effect, we have studied the effect of xipamide on pH and cytosolic free calcium in cultured Rat cardiocytes (H9c2 line). pHi was measured at equilibrium using 14C-DMO and cytosolic free calcium was measured spectrofluorimetrically with Fura2 (Shimadzu RF 5000). 1) The presence of bicarbonate induced a 0.39 +/- 0.14 (mean +/- SD; n = 3) alkalinization; final pHi was 7.08 +/- 0.15 (n = 8). Nor 20 microM DIDS (specific AE inhibitor), neither 50 microM xipamide were able to modify this result. This suggests that the alkalinization is not due to the anion exchanger. 2) After preincubation in the presence of 0.5 microM DIDS, we observed a 0.35 +/- 0.21 acidification (n = 4). Conversely, 0.5 microM xipamide induced a 0.22 +/- 0.16 alkalinization (n = 4). 3) Xipamide (0.5-500 microM) increased the internal K/Na ratio (at 0.5 microM, delta = 3.1 +/- 0.2; n = 3); this was mainly due to internal K+ increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocyte sodium and potassium transport systems during longterm administration of the diuretic xipamide in men.

The effects of xipamide on the intracellular concentration and transmembrane fluxes of Na+ and K+ were studied in twenty-four normal sodium-replete or -deplete male subjects, using a double-blind study design. After a run-in period on placebo for 1 week on their regular diet, subjects were treated on their regular diet or on a low-sodium diet with either placebo or xipamide 20 mg once a day for 16 weeks. Intra-erythrocyte Na+ concentration was increased during xipamide administration in sodium-replete and deplete subjects, while intra-erythrocyte K+ and total intraleukocyte Ca2+ concentrations were decreased. Red cell Na+, K+-cotransport activity was lower in xipamide-treated subjects, while Na+, Li-countertransport activity was increased. No significant effect of xipamide could be demonstrated on ouabain-sensitive 86Rb-uptake or on maximal [3H]-ouabain binding in erythrocytes.

Plasma atrial natriuretic peptide and the renin-aldosterone system during long-term administration of the diuretic xipamide in man.

We have studied the effect of xipamide on plasma alpha-atrial natriuretic peptide and the renin-aldosterone-kallikrein system in twelve healthy men, using a double-blind cross-over design. After a run-in period on placebo for 1 week the subjects were treated with either placebo (n = 6) or xipamide 20 mg once daily (n = 6) for 16 weeks and were then switched to the alternative medication for another 16 weeks. The plasma concentration of alpha-atrial natriuretic peptide fell after 1 week of xipamide administration and increased during prolonged xipamide administration but remained suppressed. The changes in plasma alpha-ANP observed after 1 week of xipamide were negatively correlated with the changes in haematocrit and haemoglobin. Plasma renin activity (PRA), aldosterone concentration (PAC), and urinary excretion of aldosterone and kallikrein increased after 1 week of xipamide administration, levelled off during the second and fourth weeks, but remained elevated during further prolonged xipamide administration for 16 weeks. The xipamide-induced changes in PRA and PAC were positively correlated with the changes in the haematocrit and haemoglobin. Our data suggest that the changes in plasma renin, aldosterone, and alpha-atrial natriuretic peptide during xipamide administration may be related to diuretic-induced volume contraction.

In vitro effect of xipamide on sodium-potassium transport systems in human erythrocytes.

The in vitro effects of xipamide in a concentration range of 10(-8) to 10(-2) M were investigated on various Na+ and K+ transport systems in human red blood cells. Xipamide inhibited the anion carrier or DIDS-sensitive LiCO3- -influx starting from a concentration of 10(-5) M. However, a decrease in the Na+, K+-pump and the Na+, K+-cotransport activity and a rise in the passive permeability of the cell membrane was only observed starting from a concentration of 10(-4) M xipamide.

Inhibition of the Cl-/NaCO3- anion exchanger by xipamide in human red blood cells.

The mechanism of action of classical loop diuretics of the 2- or 3-amino-5-sulfamoylbenzoic acid and (aryloxy)acetic acid families involves competition with chloride for a common site on the (Na+, K+, 2Cl-) co-transport system. However this is not the mechanism of action of some high-ceiling diuretics like muzolimine, MK 473, xipamide, indapamide and clopamide, which are not carboxylic acids. We evaluated three of these latter diuretics (xipamide, muzolimine and clopamide) for their inhibitory effects on five ion transport systems in human red blood cells: (i) Cl(-)-dependent (Na+, K+) co-transport, (ii) (NaCO3-/Cl-) anion exchanger, (iii) (Cl-, K+) co-transport, (iv) Na+, K+ pump and (v) Na+: Li+ counter-transport; and on one ion channel the Ca2+-dependent, K+ channel. All erythrocyte transport pathways were resistant to the three diuretics studied (IC50 of 10(-3) M or higher) with one remarkable exception, the (NaCO3-/Cl-) anion exchanger. This transport system was inhibited by xipamide (IC50 of 2.5 +/- 0.4 X 10(-5) M, mean +/- S.D. of five experiments) and less potently by muzolimine (IC50 of 1.1 +/- 0.3 X 10(-4) M, mean +/- S.D. of three experiments). Clopamide only inhibited the anion exchanger at high concentrations (IC50 of about 10(-3) M). Xipamide, the most potent diuretic in this test, was at least one order of magnitude more active than furosemide, ethacrynic acid, hydrochlorothiazide and amiloride. Inhibition of the anion carrier could be involved in the diuretic action (inhibition of CO2-stimulated NaCl absorption in the TAL) and/or in the antihypertensive action (inhibition of net NaCO3- influx and secondarily of Ca2+ influx through Na+: Ca2+ exchange in vascular smooth muscle cells of xipamide).

Liver carbonic anhydrase and urea synthesis. The effect of diuretics.

In isolated perfused rat liver, urea synthesis is rapid and reversibly inhibited not only by the well-known carbonic anhydrase inhibitors acetazolamide, methazolamide and ethoxzolamide, but also by diuretics, like xipamide, mefruside, chlortalidone, and chlorothiazide. Furosemide was without effect. Similar to findings with isolated perfused rat liver, acetazolamide inhibits urea synthesis from ammonium ions in normal and cirrhotic human liver slices. Inhibition of urea synthesis by xipamide and acetazolamide is accompanied by a 70% decrease of the cellular citrulline content and the tissue levels of 2-oxoglutarate and citrate, suggesting a block of urea synthesis at a step prior to citrulline formation. At a constant extracellular pH (7.4), inhibition of urea synthesis by xipamide, mefruside and acetazolamide was overcome by increasing the extracellular concentrations of HCO3- and CO2 to above twice the normal values. This shows that inhibition of urea synthesis by these diuretics is not due to an unspecific inhibition of one of the urea cycle enzymes but is due to an inhibition of mitochondrial carbonic anhydrase and therefore due to an impaired HCO3- provision for mitochondrial carbamoylphosphate synthesis. It is concluded that the activity of mitochondrial carbonic anhydrase is required for urea synthesis also in human liver and that several diuretics impair urea synthesis by inhibition of mitochondrial carbonic anhydrase. The pathophysiological significance of these data is discussed with respect to the development of diuretics-induced hyperammonemia and alkalosis in liver disease.

A Xipamida no tratamento da hipertensäo arterial moderada / Xipamide in the treatment of moderate arterial hypertension

Foram estudados 20 pacientes da raça branca, 11 mulheres e 9 homens, com média etária de 60,4 anos, portadores de hipertensäo arterial moderada (104 mmHg < pressäo diastólica <= 120 mmHg). Sem influência de medicaçäo prévia, receberam xipamida, na dose de 10 a 40 mg por dia, segundo resposta, por prazo médio de 14,45 + ou - 1,43 semanas. Obtiveram efeito anti-hipertensivo, estatisticamente significante ( < 0,05) 18 pacientes (90%), com reduçäo das cifras expressas pelos seguintes valores médios: pressäo sistólica 23%, de 181,40 + ou - 11,41 para 139,25 + ou - 10 mmHg; pressäo diastólica 20%, de 105,25 + ou - 5,84 para 84,75 + ou - 7,25 mmHg e pressäo arterial média 21%, de 130,45 + ou - 8,79 mmHg. A reduçäo mais acentuada ocorreu nas duas primeiras semanas e menor entre a segunda e a quarta semana (60% e 30% respectivamente, da variaçäo descendente total), estabilizando-se as cifras até o final do estudo. Notou-se hipotensäo postural, estatisticamente significante (p < 0,05), em 14 pacientes (70%), em termos médios de 15,05 mmHg. Näo foram registradas alteraçöes no eletrocardiograma. Embora existindo variaçöes individuais, näo se notaram alteraçöes significativas nos valores da glicemia, uricemia, natriemia, caliemía e creatininemia. Efeitos colaterais foram observados em três pacientes (15%) referidos como astenia, tontura, sensaçäo de desmaio, que cederam com a reduçäo da dose ou com a continuaçäo do tratamento, näo interrompido em nenhum caso

Xipamide. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic efficacy.

Xipamide is a diuretic derived from salicylic acid and has a structural resemblance to chlorthalidone. Its pharmacodynamic profile shows a diuretic efficacy is similar to that of frusemide (furosemide) at doses up to 40 mg, but the onset and duration of action are comparable to those of hydrochlorothiazide. Xipamide has been studied mostly in the treatment of mild to moderate essential hypertension, with few controlled studies of its use in oedematous states. The efficacy of xipamide 20 to 40 mg once daily in patients with mild to moderate hypertension is comparable to that of bendrofluazide 5 mg, bumetanide 1 mg or hydrochlorothiazide 50 mg when used alone in newly treated or previously treated patients. The addition of xipamide 20 to 40 mg daily to regimens containing beta-blockers, adrenergic neuron-blocking drugs and/or methyldopa has resulted in a further reduction in blood pressure. A few studies in oedematous states suggest that xipamide 40 to 80 mg is comparable in efficacy to equal doses of frusemide, and that the side effects of hypokalaemia, hyperuricaemia and increased blood glucose in diabetics or latent diabetics are similar to those of other diuretics. Thus, xipamide is a suitable alternative to other diuretics in the treatment of mild to moderate hypertension and combines the efficacy of frusemide with a less abrupt action in the treatment of oedema.