Acetazolamide-induced increase in blood flow to rabbit organs is confirmed using colored microspheres

Sulfonamides and their isosters as carbonic anhydrase inhibitors

Molecules containing the sulfonamide group (R-SO2NH2) as well as its structurally related isosters, sulfamido (R-NH-SO2NH2) and sulfamato (R-O-SO2NH2), constitute the most important class of inhibitors acting on the metalloenzyme carbonic anhydrase (EC 4.2.1.1). Despite their presence in the literature, in general the reports lack of a clear and organic overview linking the main structural features of the clinically used inhibitors with the therapeutic aspects. The current review is intended to highlight the structural basis of the interactions of sulfonamide-like groups within the active site of the carbonic anhydrases and will summarize the clinical use of the most interesting molecules for the treatment of relevant pathologies, such as glaucoma, obesity, cancer and CNS-affecting diseases.

Diuretics with carbonic anhydrase inhibitory action: a patent and literature review (2005 - 2013)

INTRODUCTION

The benzothiadiazines and high ceiling diuretics (hydrochlorothiazide, hydroflumethiazide, quinethazone, metolazone, chlorthalidone, indapamide, furosemide and bumetanide) contain primary sulfamoyl moieties acting as zinc-binding groups in the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). These drugs are widely used clinically and were recently shown to weakly inhibit isoforms CA I and II, but to possess stronger activity against isoforms involved in other important pathologies, for example, obesity, cancer, epilepsy and hypertension.

AREAS COVERED

The class of clinically used diuretics, with CA inhibitory properties, is the main topic of the review. A patent literature review covering the period from 2005 to 2013 is presented.

EXPERT OPINION

This section presents an overview of the patent literature in the sulfonamide diuretic field. Most of the patents deal with the combination of diuretic sulfonamide CA inhibitors with other agents useful in the management of cardiovascular diseases and obesity. Such combinations exert a better therapeutic activity compared to similar diuretics that do not inhibit CAs, raising the question of the polypharmacological and drug repositioning effects of these old drugs. These effects seem to be due to the potent inhibition of such drugs against CA isoforms present in kidneys and blood vessels, which explain both the blood pressure lowering effects as well as organ-protective activity of the drugs. An explanation of these data is provided by the fact that inhibition of the renal CAs leads to a large increase of the nitrite excretion in urine, suggesting that renal CAs are involved in nitrite reabsorption in humans. Important lessons for the drug design of sulfonamide CA inhibitors (CAIs) can be drawn from these data.

A comparison of sodium bicarbonate infusion versus normal saline infusion and its combination with oral acetazolamide for prevention of contrast-induced nephropathy: a randomized, double-blind trial

BACKGROUND

Contrast-induced nephropathy (CIN) is commonly encountered. Because the therapy of choice for prevention of CIN is controversial, in this study we compared the preventive efficacy of bicarbonate (Bi) infusion in dextrose water versus normal saline (NLS) infusion alone or in combination with oral acetazolamide (AZ).

METHODS

In a double-blind and randomized clinical trial, all patients undergoing coronary angiography or percutaneous coronary intervention received NLS (NLS group), its combination with AZ (AZ group) or infusion of Bi (Bi group) before the procedures. RIFLE (risk of renal failure, injury to the kidney, failure of kidney function, loss of kidney function, and end-stage renal disease) criteria were used to define CIN-associated acute kidney injury (AKI).

RESULTS

The risk of AKI in CIN was significantly lower in the Bi and AZ groups than in the NLS group (P <or= 0.04). Comparing pre-treatment and post-treatment values in each group the following results were obtained: serum creatinine (Scr) increased and eGFR decreased significantly in the NLS group (P = 0.04) and in all patients (P = 0.001, P = 0.02, respectively). In addition, serum potassium decreased significantly in the Bi and NLS groups (P <or= 0.02). Also, serum Bi increased significantly in the Bi group (P = 0.001) whereas it decreased significantly in the AZ group (P = 0.001). Urinary pH also increased in all groups (P <or= 0.04) except the NLS group (P > 0.05).

CONCLUSIONS

It seems that both Bi and AZ reduce the risk of CIN-related AKI, and close monitoring of serum potassium is needed during bicarbonate infusion.

Regulation of hemoglobin affinity for oxygen by carbonic anhydrase

We studied the effect on hemoglobin (Hb)-oxygen affinity induced by changes in carbonic anhydrase (CA) activity. Oxygen partial pressure at the 50% saturation of Hb (P(50)) in human blood was measured as CA activity was inhibited to varying degrees with acetazolamide (AZ; 100 and 200 microg/mL). Transient but significant change in P(50) was observed when AZ was administered and the CO(2) concentration was changed from 10% to 5%. Finally, the differences induced with AZ were attenuated when the blood sample was subjected to 4 hours of tonometry. The findings in this study could be accounted for by reduced velocity of pH changes caused by the inhibition of CA by AZ. We conclude that CA can change Hb's affinity for oxygen by controlling the movement of CO(2) gas between air and liquid compartments.

Acetazolamide assisted Tc-99m MAG3 renography to assess renal blood flow reserve

OBJECTIVE

The present study examines whether or not baseline and acetazolamide (ACZ) Tc-99m MAG3 renography can assess renal blood flow reserve.

METHODS

Renography proceeded for 50 min after sequential injections of 370 MBq Tc-99m MAG3 for baseline renography and 10 min after a 1,000 mg injection of ACZ for ACZ renography. Effective renal plasma flow of renal cortex (cERPF) in each kidney and the percentage change in cERPF of those parameters (deltaERPF) were obtained before and after the administration of ACZ in 10 subjects without hypertension or diabetes (normal group), in 10 with essential hypertension (hypertensive group) and in 10 who had Type 2 diabetes with hypertension (diabetic group). A placebo test was performed in the 10 without hypertension or diabetes using distilled water instead of ACZ (placebo group).

RESULTS

The placebo test performed in the 10 without hypertension or diabetes using distilled water instead of ACZ indicated that the parameter variance between the two types of renogram was below 3.2%. The cERPF of baseline and ACZ Tc-99m MAG3 renography and deltaERPF in the normal, hypertensive and diabetic groups were 89 +/- 10 and 110 +/- 10 ml/min, 89 +/- 14 and 117 +/- 22 ml/min, 100 +/- 23 and 112 +/- 23 ml/min, respectively, and 24.5 +/- 13.5%, 26.0 +/- 9.7% and 12.3 +/- 11.1%, respectively. The difference in the cERPF value was significant in the normal and hypertensive groups whereas this did not change in the diabetic group before or after ACZ administration.

CONCLUSIONS

We suggested that the deltaERPF determined by baseline and ACZ Tc-99m MAG3 renography is a useful parameter for assessing renal blood flow reserve.

Carbonic anhydrase inhibitors: anticonvulsant sulfonamides incorporating valproyl and other lipophilic moieties

A series of aromatic/heterocyclic sulfonamides incorporating valproyl moieties were prepared to design antiepileptic compounds possessing in their structure two moieties known to induce such a pharmacological activity: valproic acid, one of the most widely used antiepileptic drugs, and the sulfonamide residue included in acetazolamide and topiramate, two carbonic anhydrase inhibitors with antiepileptic properties. Some of these derivatives showed very high inhibitory potency against three carbonic anhydrase (CA) isozymes, such as CA I, CA II, and CA IV, involved in important physiological processes. Topiramate, a recently developed antiepileptic drug possessing a sulfamate moiety, also shares this property, although earlier literature data reported this compound to be a weak-moderate CA I, II, and IV inhibitor. The valproyl derivative of acetazolamide (5-valproylamido-1,3,4-thiadiazole-2-sulfonamide, 6M) was one of the best hCA I and hCA II inhibitor in the series and exhibited very strong anticonvulsant properties in an MES test in mice. In consequence, other 1,3,4-thiadiazolesulfonamide derivatives possessing potent CA inhibitory properties and substituted with different alkyl/arylcarboxamido/sulfonamido/ureido moieties in the 5 position have been investigated for their anticonvulsant effects in the same animal model. It was observed that some lipophilic derivatives, such as 5-benzoylamido-, 5-toluenesulfonylamido-, 5-adamantylcarboxamido-, and 5-pivaloylamido-1,3,4-thiadiazole-2-sulfonamide, show promising in vivo anticonvulsant properties and that these compounds may be considered as interesting leads for developing anticonvulsant or selective cerebrovasodilator drugs.

Acetazolamide reduces hypoxic pulmonary vasoconstriction in isolated perfused rabbit lungs

Carbonic anhydrase (CA) may modulate regional blood flow by mediating changes in extra- and intracellular pH. We hypothesized that CA inhibition with acetazolamide would inhibit the kinetics and magnitude of hypoxic pulmonary vasoconstriction (HPV). Isolated rabbit lungs were ventilated and perfused in situ at constant flow, with buffer containing red blood cells. Preparations were sequentially challenged with hypoxic (FI(O(2)) 0.05) and/or hypercapnic (FI(CO(2)) 0.10) gas mixtures for 5 or 10 min. In the experimental groups, acetazolamide (33 microM) was added to the perfusate after establishing baseline responses, and gas challenges were repeated; control groups were studied without acetazolamide. Acetazolamide reduced the increase in pulmonary artery pressure (DeltaPAP) and the rate of pressure rise by approximately 30-50% during hypoxia and combined hypoxia/hypercapnia. The reduction in DeltaPAP occurred for both 5 and 10 min challenges. Acetazolamide did not affect expired nitric oxide concentrations. We conclude that acetazolamide reduces both the magnitude and kinetics of HPV by a mechanism that does not involve nitric oxide.