Understanding the Role and Mechanism of Carbonic Anhydrase V in Obesity and its Therapeutic Implications.

Obesity is a metabolic syndrome leading to several health problems such as hypertension, heart attack, type II diabetes, and even cancer. Carbonic anhydrase VA (CAVA) is a mitochondrial enzyme which is directly associated with the glucose homeostasis and considered as a promising target for obesity and other associated diseases in humans. So far, numerous inhibitors have been designed to inhibit the catalytic activity of CAVA with an assumption for its possible therapeutic uses against type II diabetes and other metabolic diseases. Among these, sulphonamide inhibitors and various non-classical inhibitors are extensively used. The focus of this review is to understand the mechanism and role CAVA in glucose homeostasis to ascertain as a potential drug target of obesity. We have further highlighted different types of inhibitors and their mode of binding and possible consequences with an aim to investigate possible therapeutic used for the treatment of obesity and associated diseases. Along with classical inhibitors, various non-classical inhibitors have proved to be potential inhibitors of CAV which may be employed to combat obesity. Certain phytochemicals are utilized as therapeutic molecules to fight obesity. These phytochemicals have been discussed in detail here.

Effect of sulfonamides as carbonic anhydrase VA and VB inhibitors on mitochondrial metabolic energy conversion.

Obesity is quickly becoming an increasing problem in the developed world. One of the major fundamental causes of obesity and diabetes is mitochondria dysfunction due to faulty metabolic pathways which alter the metabolic substrate flux resulting in the development of these diseases. This paper examines the role of mitochondrial carbonic anhydrase (CA) isozymes in the metabolism of pyruvate, acetate, and succinate when specific isozyme inhibitors are present. Using a sensitive electrochemical approach of wired mitochondria to analytically measure metabolic energy conversion, we determine the resulting metabolic difference after addition of an inhibitory compound. We found that certain sulfonamide analogues displayed broad spectrum inhibition of metabolism, where others only had significant effect on some metabolic pathways. Pyruvate metabolism always displayed the most dramatically affected metabolism by the sulfonamides followed by fatty acid metabolism, and then finally succinate metabolism. This allows for the possibility of using designed sulfonamide analogues to target specific mitochondrial CA isozymes in order to subtly shift metabolism and glucogenesis flux to treat obesity and diabetes.

Topiramate treatment protects blood-brain barrier pericytes from hyperglycemia-induced oxidative damage in diabetic mice.

Diabetes mellitus causes cerebral microvasculature deterioration and cognitive decline. The specialized endothelial cells of cerebral microvasculature comprise the blood-brain barrier, and the pericytes (PC) that are in immediate contact with these endothelial cells are vital for blood-brain barrier integrity. In diabetes, increased mitochondrial oxidative stress is implicated as a mechanism for hyperglycemia-induced PC loss as a prerequisite leading to blood-brain barrier disruption. Mitochondrial carbonic anhydrases (CA) regulate the oxidative metabolism of glucose and thus play an important role in the generation of reactive oxygen species and oxidative stress. We hypothesize that the inhibition of mitochondrial CA would reduce mitochondrial oxidative stress, rescue cerebral PC loss caused by diabetes-induced oxidative stress, and preserve blood-brain barrier integrity. We studied the effects of pharmacological inhibition of mitochondrial CA activity on streptozotocin-diabetes-induced oxidative stress and PC loss in the mouse brain. At 3 wk of diabetes, there was significant oxidative stress; the levels of reduced glutathione were lower and those of 3-nitrotyrosine, 4-hydroxy-2-trans-nonenal, and superoxide dismutase were higher. Treatment of diabetic mice with topiramate, a potent mitochondrial CA inhibitor, prevented the oxidative stress caused by 3 wk of diabetes. A significant decline in cerebral PC numbers, at 12 wk of diabetes, was also rescued by topiramate treatment. These results provide the first evidence that inhibition of mitochondrial CA activity reduces diabetes-induced oxidative stress in the mouse brain and rescues cerebral PC dropout. Thus, mitochondrial CA may provide a new therapeutic target for oxidative stress related illnesses of the central nervous system.

QSARs on human carbonic anhydrase VA and VB inhibitors of some new not yet synthesized, substituted aromatic/heterocyclic sulphonamides as anti-obesity agent.

This paper presents result of quantitative structure-activity relationships (QSAR) study realized with the PRECLAV, omega, brood and MOPAC software. The dependent property is the inhibitory activity against human carbonic anhydrase mitochondrial isoforms VA and VB. The calibration set includes 17 aromatic/heterocyclic sulphonamides incorporating phenacetyl, pyridylacetyl and thienylacetyl tails with three clinically used CA inhibitors namely AZA, TPM and ZNS molecules. The prediction set contains 24 others not yet synthesized substituted aromatic/heterocyclic sulphonamides having unknown observed values of activity. In the presence of prediction set, the predictive quality of QSAR of hCA VA (r(2) = 0.9789, F = 418.115, r(2)(CV) = 0.9689) and hCA VB (r(2) = 0.9768; F = 379.717; r(2)(CV) = 0.9637) is large. The obtained models suggest a slightly different inhibition mechanism for the two isoforms. Large percentage, in weight, of CONH molecular fragments seems to be favourable to inhibitory activity of both VA and VB.

Inhibition of human mitochondrial carbonic anhydrases VA and VB with para-(4-phenyltriazole-1-yl)-benzenesulfonamide derivatives.

A library of 10 novel benzenesulfonamides containing triazole-tethered phenyl 'tail' moieties were synthesized by a Cu(I) catalyzed 1,3-dipolar cycloaddition reaction (DCR) (i.e., click chemistry) between 4-azido benzenesulfonamide and a panel of variously substituted phenyl acetylenes. These compounds were very effective inhibitors (low nanomolar) of the human mitochondrial carbonic anhydrase isozymes VA and VB. Mitochondrial carbonic anhydrases are potential targets for anti-obesity therapies, acting to reduce lipogenesis through a novel mechanism of action. The inhibitors reported here should prove valuable as lead compounds to further investigate the potential of CA inhibition for this novel therapeutic application.

Carbonic anhydrase inhibitors: inhibition of the human isozymes I, II, VA, and IX with a library of substituted difluoromethanesulfonamides.

An inhibition study of the human cytosolic isozymes I, and II, the mitochondrial isoform VA, and the tumor-associated, transmembrane isozyme IX of carbonic anhydrase (CA, EC 4.2.1.1) with a library of aromatic/heteroaromatic/polycyclic difluoromethanesulfonamides is reported. Most of the inhibitors were derivatives of benzenedifluoromethanesulfonamide incorporating substituted-phenyl moieties, or were methylsulfonamide and difluoromethyl-sulfonamide derivatives of the sulfamates COUMATE and EMATE, respectively. Except for the methylsulfonamide-COUMATE derivative which behaved as a potent CA II inhibitor (K(I) of 32nM), these sulfonamides were moderate inhibitors of all isozymes, with inhibition constants in the range of 96-5200nM against hCA I, of 80-670nM against hCA II, and of 195-9280nM against hCA IX, respectively. Remarkably, some derivatives, such as 3-bromophenyl-difluoromethanesulfonamide, showed a trend to selectively inhibit the mitochondrial isoform CA VA, showing selectivity ratios for inhibiting CA VA over CA II of 3.53; over CA I of 6.84 and over CA IX of 9.34, respectively, although it is a moderate inhibitor (K(I) of 160nM). Some of these derivatives may be considered as leads for the design of isozyme selective CA inhibitors targeting the mitochondrial isozyme CA VA, with potential use as anti-obesity agents.

Carbonic anhydrase inhibitors. Inhibition of isozymes I, II, IV, V and IX with complex fluorides, chlorides and cyanides.

The inhibition of five human carbonic anhydrase (hCA, EC 4.2.1.1) isozymes, the cytosolic hCA I and II, the membrane-bound hCA IV, the mitochondrial hCA V and the tumour associated, transmembrane hCA IX, with complex anions incorporating fluoride, chloride and cyanide, as well as B(III), Si(IV), P(V), As(V), Al(III), Fe(II), Fe(III), Pd(II), Pt(II), Pt(IV), Cu(I), Ag(I), Au(I) and Nb(V) species has been investigated. Apparently, the most important factors influencing activity of these complexes are the nature of the central metal ion/element, and its charge. Geometry of these compounds appears to be less important, since both linear, tetrahedral, octahedral as well as pentagonal bipyramidal derivatives led to effective inhibitors. However, the five isozymes showed very different affinities for these anion inhibitors. The best hCA I inhibitors were cyanide, dicyanocuprate and dicyanoaurate (K(I)s in the range of 0.5-7.7 microM), whereas the least effective were fluoride and hexafluoroarsenate. The best hCA II inhibitors were cyanide, hexafluoroferrate and tetrachloroplatinate (K(I)s in the range of 0.02-0.51 mM), whereas the most ineffective ones were fluoride, hexafluoroaluminate and chloride. The best hCA IV inhibitors were dicyanocuprate (K(I) of 9.8 microM) and hexacyanoferrate(II) (K(I) of 10.0 microM), whereas the worst ones were tetrafluoroborate and hexafluoroaluminate (K(I)s in the range of 124-126 mM). The most effective hCA V inhibitors were cyanide, heptafluoroniobate and dicyanocuprate (K(I)s in the range of 0.015-0.79 mM), whereas the most ineffective ones were fluoride, chloride and tetrafluoroborate (K(I)s in the range of 143-241 mM). The best hCA IX inhibitors were on the other hand cyanide, heptafluoroniobate and dicyanoargentate (K(I)s in the range of 4 microM-0.33 mM), whereas the worst ones were hexacyanoferrate(III) and hexacyanoferrate(II).

Carbonic anhydrase inhibitors. Inhibition of isozymes I, II, IV, V, and IX with anions isosteric and isoelectronic with sulfate, nitrate, and carbonate.

The inhibition of five human carbonic anhydrase (hCA, EC 4.2.1.1) isozymes; the cytosolic hCA I and II, the membrane-bound hCA IV, the mitochondrial hCA V, and the tumor-associated, transmembrane hCA IX, with anions isosteric and isoelectronic with sulfate, nitrate, and carbonate; such as chlorate, perchlorate, bromate, iodate, periodate, silicate, bismuthate, vanadate, molybdate, and wolframate is reported. Apparently, the geometry of the inhibitor (tetrahedral or trigonal) does not influence its binding to the Zn(II) ion of the enzyme active site, but the nature of the central element is the most important factor influencing potency. Isozymes hCA I and II are best inhibited by chlorate, perchlorate, and silicate, together with the anions structurally related to sulfate, sulfamate, and sulfamidate, but sulfate itself is a weak inhibitor (inhibition constant of 74 mM against hCA I and 183 mM against hCA II). Molybdate is a very weak hCA I inhibitor (K(I) of 914 mM) but it interacts with hCA II (K(I) of 27.5mM). Isozyme IV is well inhibited by sulfate (K(I) of 9 mM), sulfamate, and sulfamidate (in the low micromolar range), but not by perchlorate (K(I) of 767 mM). The mitochondrial isozyme V has the lowest affinity for sulfate (K(I) of 680 mM) and carbonate (K(I) of 95 mM) among all the investigated isozymes, suggesting on one hand its possible participation in metabolon(s) with sulfate anion exchanger(s), and on the other hand an evolutionary adaptation to working at higher pH values (around 8.5 in mitochondria) where rather high amounts of carbonate in equilibrium with bicarbonate may be present. Metasilicate, isosteric to carbonate, is also about a 10 times weaker inhibitor of this isozyme as compared to other CAs investigated here (K(I) of 28.2 mM). Surprisingly, the tumor-associated isozyme IX is resistant to sulfate inhibition (K(I) of 154 mM) but has affinity in the low micromolar range for carbonate, sulfamate, and sulfamidate (K(I) in the range of 8.6-9.6 microM). This constitutes another proof that this isozyme best works at acidic pH values present in tumors, being inhibited substantially at higher pH values when more carbonate may be present. Bromate and chlorate are quite weak CA IX inhibitors (K(I) s of 147-274 mM).

Carbonic anhydrase inhibitors. Interaction of isozymes I, II, IV, V, and IX with carboxylates.

A detailed inhibition study of five carbonic anhydrase (CA, EC 4.2.1.1) isozymes with carboxylates including aliphatic (formate, acetate), dicarboxylic (oxalate, malonate), hydroxy/keto acids (l-lactate, l-malate, pyruvate), tricarboxylic (citrate), or aromatic (benzoate, tetrafluorobenzoate) representatives, some of which are important intermediates in the Krebs cycle, is presented. The cytosolic isozyme hCA I was strongly activated by acetate, oxalate, pyruvate, l-lactate, and citrate (K(A) around 0.1 microM), whereas formate, malonate, malate, and benzoate were weaker activators (K(A) in the range 0.1-1mM). The cytosolic isozyme hCA II was weakly inhibited by all the investigated anions, with inhibition constants in the range of 0.03-24 mM. The membrane-associated isozyme hCA IV was the most sensitive to inhibition by carboxylates, showing a K(I) of 99 nM for citrate and oxalate, of 2.8 microM for malonate and of 14.5 microM for pyruvate among others. The mitochondrial isozyme hCA V was weakly inhibited by all these carboxylates (K(I)s in the range of 1.67-25.9 mM), with the best inhibitor being citrate (K(I) of 1.67 mM), whereas this is the most resistant CA isozyme to pyruvate inhibition (K(I) of 5.5mM), which may be another proof that CA V is the isozyme involved in the transfer of acetyl groups from the mitochondrion to the cytosol for the provision of substrate(s) for de novo lipogenesis. Furthermore, the relative resistance of CA V to inhibition by pyruvate may be an evolutionary adaptation of this mitochondrial isozyme to the presence of high concentrations of this anion within this organelle. The transmembrane, tumor-associated isozyme hCA IX was similar to isozyme II in its slight inhibition by all these anions (K(I) in the range of 1.12-7.42 mM), except acetate, lactate, and benzoate, which showed a K(I)>150 mM. The lactate insensitivity of CA IX also represents an interesting finding, since it is presumed that this isozyme evolved in such a way as to show a high catalytic activity in hypoxic tumors rich in lactate, and suggests a possible metabolon in which CA IX participates together with the monocarboxylate/H(+) co-transporter in dealing with the high amounts of lactate/H(+) present in tumors.

Carbonic anhydrase inhibitors. Interaction of isozymes I, II, IV, V, and IX with phosphates, carbamoyl phosphate, and the phosphonate antiviral drug foscarnet.

A detailed inhibition study of five carbonic anhydrase (CA, EC 4.2.1.1) isozymes with inorganic phosphates, carbamoyl phosphate, the antiviral phosphonate foscarnet as well as formate is reported. The cytosolic isozyme hCA I was weakly inhibited by neutral phosphate, strongly inhibited by carbamoyl phosphate (K(I) of 9.4 microM), and activated by hydrogen- and dihydrogenphosphate, foscarnet and formate (best activator foscarnet, K(A)=12 microM). The cytosolic isozyme hCA II was weakly inhibited by all the investigated anions, with carbamoyl phosphate showing a K(I) of 0.31 mM. The membrane-associated isozyme hCA IV was the most sensitive to inhibition by phosphates/phosphonates, showing a K(I) of 84 nM for PO(4)(3-), of 9.8 microM for HPO(4)(2-), and of 9.9 microM for carbamoyl phosphate. Foscarnet was the best inhibitor of this isozyme (K(I) of 0.82 mM) highly abundant in the kidneys, which may explain some of the renal side effects of the drug. The mitochondrial isozyme hCA V was weakly inhibited by all phosphates/phosphonates, except carbamoyl phosphate, which showed a K(I) of 8.5 microM. Thus, CA V cannot be the isozyme involved in the carbamoyl phosphate synthetase I biosynthetic reaction, as hypothesized earlier. Furthermore, the relative resistance of CA V to inhibition by inorganic phosphates suggests an evolutionary adaptation of this mitochondrial isozyme to the presence of high concentrations of such anions in these energy-converting organelles, where high amounts of ATP are produced by ATP synthetase, from ADP and inorganic phosphates. The transmembrane, tumor-associated isozyme hCA IX was on the other hand slightly inhibited by all these anions.

Carbonic anhydrase inhibitors: inhibition of human cytosolic isozyme II and mitochondrial isozyme V with a series of benzene sulfonamide derivatives.

Among the 14 human isozymes of carbonic anhydrase (CA, EC 4.2.1.1) presently known, the cytosolic hCA II is the most active and plays a host of physiological functions, whereas the mitochondrial hCA V is unique due to its role in several biosynthetic reactions. An inhibition study of these isozymes with a series of sulfonamides is reported here, with the scope to detect lead molecules for the design of isozyme-specific CA inhibitors (CAIs) targeting the mitochondrial isoform. Indeed, recently it has been shown that CA V is a novel target for the drug design of anti-obesity agents among others. Compounds included in this study were mainly ortho-, meta-, and para-substituted-benzenesulfonamides, together with several halogeno-substituted sulfanilamides and disubstituted-benzene-1,3-disulfonamide derivatives. Isozyme V showed an inhibition profile with these sulfonamides different of that of hCA II. Thus, IC(50) values in the range of 80 nM to 74 microM against hCA II, and 0.78-63.7 microM against hCA V with these derivatives have been obtained. Only one compound, 2-carboxymethyl-benzenesulfonamide, was more active against hCA V over hCA II (selectivity ratio of 1.39), whereas all other derivatives investigated here were much better hCA II inhibitors (selectivity ratios CA II/CA V in the range of 0.0008-0.73) than hCA V inhibitors.

Carbonic anhydrase inhibitors. Inhibition of mitochondrial isozyme V with aromatic and heterocyclic sulfonamides.

The first inhibition study of the mitochondrial isozyme carbonic anhydrase (CA) V (of murine origin) with a series of aromatic and heterocyclic sulfonamides is reported. Inhibition data of the cytosolic isozymes CA I and CA II and the membrane-bound isozyme CA IV with these inhibitors are also provided for comparison. Several low nanomolar CA V inhibitors were detected (KI values in the range of 4-15 nM), most of them belonging to the acylated sulfanilamide, ureido-benzenesulfonamide, 1,3,4-thiadiazole-2-sulfonamide, and aminobenzolamide type of compounds. The clinically used inhibitors acetazolamide, methazolamide, ethoxzolamide, dorzolamide, brinzolamide, and topiramate on the other hand were less effective CA V inhibitors, showing inhibition constants in the range of 47-63 nM. Some of the investigated sulfonamides, such as the ureido-benzenesulfonamides and the acylated sulfanilamides showed higher affinity for CA V than for the other isozymes, CA II included, which is a remarkable result, since most compounds investigated up to now inhibited the cytosolic isozyme CA II better. These results prompt us to hypothesize that the selective inhibition of CA V, or the dual inhibition of CA II and CA V, may lead to the development of novel pharmacological applications for such sulfonamides, for example in the treatment or prevention of obesity, by inhibiting CA-mediated lipogenetic processes.

Carbonic anhydrase inhibitors: inhibition of human and murine mitochondrial isozymes V with anions.

In addition to sulfonamides, metal complexing anions represent the second class of inhibitors of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1). The first inhibition study of the mitochondrial isozyme CA V (of murine and human origin) with anions is reported here. Inhibition data of the cytosolic isozymes CA I and CA II as well as the membrane-bound isozyme CA IV with a large number of anionic species such as halides, pseudohalides, bicarbonate, nitrate, hydrosulfide, arsenate, sulfamate, and sulfamidate and so on, are also provided for comparison. Isozyme V has an inhibition profile by anions completely different to those of CA I and IV, but similar to that of hCA II, which may have interesting physiological consequences. Similarly to hCA II, the mitochondrial isozymes show micro-nanomolar affinity for sulfonamides such as sulfanilamide and acetazolamide.