Anion inhibition studies of the α-carbonic anhydrase from the protozoan pathogen Trypanosoma cruzi, the causative agent of Chagas disease

Cloning, expression, and purification of an α-carbonic anhydrase from Toxoplasma gondii to unveil its kinetic parameters and anion inhibition profile

Toxoplasmosis, induced by the intracellular parasite Toxoplasma gondii, holds considerable implications for global health. While treatment options primarily focusing on folate pathway enzymes have notable limitations, current research endeavours concentrate on pinpointing specific metabolic pathways vital for parasite survival. Carbonic anhydrases (CAs, EC 4.2.1.1) have emerged as potential drug targets due to their role in fundamental reactions critical for various protozoan metabolic processes. Within T. gondii, the Carbonic Anhydrase-Related Protein (TgCA_RP) plays a pivotal role in rhoptry biogenesis. Notably, α-CA (TcCA) from another protozoan, Trypanosoma cruzi, exhibited considerable susceptibility to classical CA inhibitors (CAIs) such as anions, sulphonamides, thiols, and hydroxamates. Here, the recombinant DNA technology was employed to synthesise and clone the identified gene in the T. gondii genome, which encodes an α-CA protein (Tg_CA), with the purpose of heterologously overexpressing its corresponding protein. Tg_CA kinetic constants were determined, and its inhibition patterns explored with inorganic metal-complexing compounds, which are relevant for rational compound design. The significance of this study lies in the potential development of innovative therapeutic strategies that disrupt the vital metabolic pathways crucial for T. gondii survival and virulence. This research may lead to the development of targeted treatments, offering new approaches to manage toxoplasmosis.

From Benznidazole to New Drugs: Nanotechnology Contribution in Chagas Disease

Chagas disease is a neglected tropical disease caused by the protozoan Trypanosoma cruzi. Benznidazole and nifurtimox are the two approved drugs for their treatment, but both drugs present side effects and efficacy problems, especially in the chronic phase of this disease. Therefore, new molecules have been tested with promising results aiming for strategic targeting action against T. cruzi. Several studies involve in vitro screening, but a considerable number of in vivo studies describe drug bioavailability increment, drug stability, toxicity assessment, and mainly the efficacy of new drugs and formulations. In this context, new drug delivery systems, such as nanotechnology systems, have been developed for these purposes. Some nanocarriers are able to interact with the immune system of the vertebrate host, modulating the immune response to the elimination of pathogenic microorganisms. In this overview of nanotechnology-based delivery strategies for established and new antichagasic agents, different strategies, and limitations of a wide class of nanocarriers are explored, as new perspectives in the treatment and monitoring of Chagas disease.

A simple yet multifaceted 90 years old, evergreen enzyme: Carbonic anhydrase, its inhibition and activation

Advances in the carbonic anhydrase (CA, EC 4.2.1.1) research over the last three decades are presented, with an emphasis on the deciphering of the activation mechanism, the development of isoform-selective inhibitors/ activators by the tail approach and their applications in the management of obesity, hypoxic tumors, neurological conditions, and as antiinfectives.

Targeting Metalloenzymes: The "Achilles' Heel" of Viruses and Parasites

Metalloenzymes are central to the regulation of a wide range of essential viral and parasitic functions, including protein degradation, nucleic acid modification, and many others. Given the impact of infectious diseases on human health, inhibiting metalloenzymes offers an attractive approach to disease therapy. Metal-chelating agents have been expansively studied as antivirals and antiparasitics, resulting in important classes of metal-dependent enzyme inhibitors. This review provides the recent advances in targeting the metalloenzymes of viruses and parasites that impose a significant burden on global public health, including influenza A and B, hepatitis B and C, and human immunodeficiency viruses as well as Trypanosoma brucei and Trypanosoma cruzi.

Inhibition studies of the protozoan α-carbonic anhydrase from Trypanosoma cruzi with phenols

The α-class carbonic anhydrase (CA, EC 4.2.1.1) from the protozoan pathogen Trypanosoma cruzi, TcCA, was investigated earlier for its inhibition with anions, sulphonamides, thiols and hydroxamates, well-known classes of CA inhibitors (CAIs). Here we present the first inhibition study of this enzyme with phenols, which possess a diverse CA inhibition mechanism compared to the previously investigated compounds, which are all zinc binders. Indeed, phenols are known to anchor to the zinc coordinated water molecule within the enzyme active site. In a series of 22 diversely substituted phenols, the best inhibitors were simple phenol, pyrocatechol, salicylic acid, 3,5-difluorophenol, 3,4-dihydroxy-benzoic acid, 3,6- dihydroxy-benzoic acid, caffeic acid and its des-hydroxy analog, with K_Is of 1.8 - 7.3 µM. The least effective TcCA inhibitor was 3-chloro-4-amino-phenol (K_I of 47.9 µM). Although it is not yet clear whether TcCA can be considered as an anti-Chagas disease drug target, as no animal model for investigating the antiprotozoan effects is available so far, finding effective in vitro inhibitors may be a first relevant step towards new antiprotozoal agents.

Design, Synthesis and Biological Assessment of Rhodanine-Linked Benzenesulfonamide Derivatives as Selective and Potent Human Carbonic Anhydrase Inhibitors

A novel series of twenty-five rhodamine-linked benzenesulfonamide derivatives (7a-u and 9a-d) were synthesized and screened for their inhibitory action against four physiologically relevant human (h) carbonic anhydrase (CA) isoforms, namely hCA I, hCA II, hCA IX, and hCA XII. All the synthesized molecules showed good to excellent inhibition against all the tested isoforms in the nanomolar range due to the presence of the sulfonamide as a zinc binding group. The target compounds were developed from indol-3-ylchalcone-linked benzenesulfonamide where the indol-3-ylchalcone moiety was replaced with rhodanine-linked aldehydes or isatins to improve the inhibition. Interestingly, the molecules were slightly more selective towards hCA IX and XII compared to hCA I and II. The most potent and efficient ones against hCA I were 7h (K_I 22.4 nM) and 9d (K_I 35.8 nM) compared to the standard drug AAZ (K_I 250.0 nM), whereas in case of hCA II inhibition, the derivatives containing the isatin nucleus as a tail were preferred. Collectively, all compounds were endowed with better inhibition against hCA IX compared to AAZ (K_I 25.8 nM) as well as strong potency against hCA XII. Finally, these newly synthesized molecules could be taken as potential leads for the development of isoform selective hCA IX and XII inhibitors.

Discovery of novel drugs for Chagas disease: is carbonic anhydrase a target for antiprotozoal drugs?

INTRODUCTION

Carbonic anhydrase (CA) arose significant interest as a potential new target for Chagas disease since its discovery in Trypanosoma cruzi in 2013. Benznidazole and Nifurtimox have been used for Chagas disease treatment for 60 years despite all efforts done for obtaining more efficient treatments, acting in the acute and chronic phases of illness, with fewer side effects and resistance induction.

AREAS COVERED

We discuss the positive and negative aspects of T. cruzi CA (TcCA) studies as a target for developing new drugs. The current research discoveries and the classes of TcCA inhibitors are reviewed. The sulfonamides and their derivatives are the main inhibitor classes, but hydroxamates and the thiols, were investigated too. These compounds inhibited the growth of the evolutive forms of the parasite. A comparative analysis was done with CAs from other Trypanosomatids and protozoans.

EXPERT OPINION

The search for new targets and drugs is a significant challenge worldwide, and TcCA is a potential candidate for developing new drugs. Several studied inhibitors were active against Trypanosoma cruzi, but their penetration and toxicity problems emerged. New approaches are in progress to obtain inhibitors with desired properties, allowing further steps such as tests using an adequate animal model and subsequent developments for the preclinical testing.

Why hasn't there been more progress in new Chagas disease drug discovery?

Introduction: Chagas disease (CD) is a neglected disease caused by the protozoan parasite Trypanosoma cruzi. In terms of novel drug discovery, there has been no progress since the 1960s with the same two drugs, benznidazole and nifurtimox, still in use. The complex life cycle, genetic diversity of T. cruzi strains, different sensitivities to the available drugs, as well as little interest from pharmaceutical companies and inadequate methodologies for translating in vitro and in vivo findings to the discovery of new drugs have all contributed to the lack of progress.Areas covered: In this perspective, the authors give discussion to the relevant points connected to the lack of developments in CD drug discovery and provide their expert perspectives.Expert opinion: There are few drugs currently in the preclinical pipeline for the treatment of CD. Only three classes of compounds have been shown to achieve high cure rates in mouse models of infection: nitroimidazoles (fexinidazole), oxaborole DNDi-6148 and proteasome inhibitors (GNF6702). New biomarkers for Chagas' disease are urgently needed for the diagnosis and detection of cure/treatment efficacy. Efforts from academia and pharmaceutical companies are in progress and more intense interaction to accelerate the process of new drugs development is necessary.

Application of Dithiocarbamates as Potential New Antitrypanosomatids-Drugs: Approach Chemistry, Functional and Biological

Dithiocarbamates represent a class of compounds that were evaluated in different biomedical applications because of their chemical versatility. For this reason, several pharmacological activities have already been attributed to these compounds, such as antiparasitic, antiviral, antifungal activities, among others. Therefore, compounds that are based on dithiocarbamates have been evaluated in different in vivo and in vitro models as potential new antimicrobials. Thus, the purpose of this review is to present the possibilities of using dithiocarbamate compounds as potential new antitrypanosomatids-drugs, which could be used for the pharmacological control of Chagas disease, leishmaniasis, and African trypanosomiasis.

Appraisal of anti-protozoan activity of nitroaromatic benzenesulfonamides inhibiting carbonic anhydrases from Trypanosoma cruzi and Leishmania donovani

Chagas disease and leishmaniasis are neglected tropical disorders caused by the protozoans Trypanosoma cruzi and Leishmania spp. Carbonic anhydrases (CAs, EC 4.2.1.1) from these protozoans (α-TcCA and β-LdcCA) have been validated as promising targets for chemotherapic interventions. Many anti-protozoan agents, such as nitroimidazoles, nifurtimox, and benznidazole possess a nitro aromatic group in their structure which is crucial for their activity. As a continuation of our previous work on N-nitrosulfonamides as anti-protozoan agents, we investigated benzenesulfonamides bearing a nitro aromatic moiety against TcCA and LdcCA, observing selective inhibitions over human off-target CAs. Selected derivatives were assessed in vitro in different developmental stages of T. cruzi and Leishmania spp. A lack of significant growth inhibition has been found, which has been connected to the low permeability of this class of derivatives through cell membranes. Further strategies necessarily need to be designed for targeting Chagas disease and leishmaniasis with nitro-containing CA inhibitors.

N-Nitrosulfonamides as Carbonic Anhydrase Inhibitors: A Promising Chemotype for Targeting Chagas Disease and Leishmaniasis

Trypanosoma cruzi and Leishmania spp. are protozoa of the Trypanosomatidae family, respectively, responsible of the neglected tropical disorders (NTDs) Chagas disease and leishmaniasis. The present pharmacotherapy is often ineffective and exhibits serious side effects. The metalloenzyme carbonic anhydrases (CAs, EC 4.2.1.1) recently identified in these protozoans (α-TcCA and β-LdcCA) are novel promising targets for chemotherapeutic interventions. Herein, we report a series of N-nitrosulfonamides, as a novel chemotype to yield the target CA isoform selective inhibition over ubiquitous human isozymes. Two derivatives selected among the most active and selective ones for TcCA/LdcCA over off-target CAs were progressed as silver salts to in vitro studies with various developmental forms and spp of Trypanosoma cruzi and leishmania. Excellent values of parasites growth inhibition (IC₅₀) were observed, with some selectivity index (over cytotoxicity for macrophages and Vero cells) being comparable or better than reference drugs. These findings make N-nitrosulfonamides and their salts promising lead compounds for a rational optimization of innovative agents for the treatment of Chagas disease and leishmaniasis based on CA inhibition.

Antileishmanial activity of sulphonamide nanoemulsions targeting the β-carbonic anhydrase from Leishmania species

The β-carbonic anhydrase (CA, EC 4.2.1.1) from Leishmania spp. (LdcCA) is effectively inhibited by aromatic/heterocyclic sulphonamides, in the low nanomolar range, but no in vitro antileishmanial activity was detected for such compounds. We formulated some of these sulphonamides as nanoemulsions (NEs) in clove oil, and tested them in vitro against Leishmania infantum MHOM/BR/1974/PP75 and Leishmania amazonensis IFLA/BR/1967/PH8 strains. Interesting inhibitory concentrations IC50 were observed for some of the sulphonamides NEs, with IC50 as low as 3.90 µM (NE-3F) and 2.24 µM (NE-5B) for L. amazonensis and 3.47 µM (NE-5B) for L. infantum. Some of the investigated NEs displayed toxicity for macrophages beyond the parasites. For the same nonoemulsions, a selective index (SI) greater than for Amphotericin B. Haemolytic assay using human red blood cells indicate that the NEs were less cytotoxic than amphotericin B, a widely used antifungal agent. NEs demonstrated to be an excellent strategy for increasing the penetration of these hydrophilic drugs through membranes, with a huge increase of efficacy over the sulphonamide CA inhibitor (CAI) alone.

Nanoemulsions of sulfonamide carbonic anhydrase inhibitors strongly inhibit the growth of Trypanosoma cruzi

Sulfonamide carbonic anhydrase (CA, EC 4.2.1.1) inhibitors targeting the α-class enzyme from the protozoan pathogen Trypanosoma cruzi, responsible of Chagas disease, were recently reported. Although many such derivatives showed low nanomolar activity in vitro, they were inefficient anti-T. cruzi agents in vivo. Here, we show that by formulating such sulfonamides as nanoemulsions in clove (Eugenia caryophyllus) oil, highly efficient anti-protozoan effects are observed against two different strains of T. cruzi. These effects are probably due to an enhanced permeation of the enzyme inhibitor through the nanoemulsion formulation, interfering in this way with the life cycle of the pathogen either by inhibiting pH regulation or carboxylating reactions in which bicarbonate/CO2 are involved. This type of formulation of sulfonamides with T. cruzi CA inhibitory effects may lead to novel therapeutic approaches against this orphan disease.

Carbonic anhydrases from Trypanosoma cruzi and Leishmania donovani chagasi are inhibited by benzoxaboroles

A series of 6-substituted ureido- and thioureido-benzoxaboroles were investigated as inhibitors of carbonic anhydrases from Trypanosoma cruzi (TcCA), and Leishmania donovani chagasi (LdcCA). Both enzymes were inhibited by benzoxaboroles in the micromolar range. Preferential inhibitory potency against the β-CA LdcCA versus the α-CA TcCA was observed with submicromolar inhibitory activities. Some derivatives displayed excellent inhibitory and selectivity profile over the ubiquitous and physiological relevant human off-target hCA II. This study provides a convincing opportunity to study benzoxaborole scaffold for the design of antiprotozoan potential drugs targeting the pathogen's carbonic anhydrases.

Cloning, expression and purification of the complete domain of the η-carbonic anhydrase from Plasmodium falciparum

The antimalarial drugs are of fundamental importance in the control of malaria, especially for the lack of efficient treatments and acquired resistance to the existing drugs. For this reason, there is a continuous work in identifying novel, less toxic and effective chemotherapies as well as new therapeutic targets against the causative agents of malaria. In this context, a superfamily of metalloenzymes named carbonic anhydrases (CAs, EC 4.2.1.1) has aroused a great interest as druggable enzymes to limit the development of Plasmodium falciparum gametocytes. CAs catalyze a common reaction in all life domains, the carbon dioxide hydration to bicarbonate and protons (CO₂ + H₂O ⇔ HCO₃^- + H⁺). P. falciparum synthesizes pyrimidines de novo starting from HCO₃^-, which is generated from CO₂ through the action of the η-CA identified in the genome of the protozoan. Here, we propose a procedure for the preparation of a wider portion of the protozoan η-CA, named PfCAdom (358 amino acid residues), with respect to the truncated form prepared by Krungkrai et al. (PfCA1, 235 amino acid residues). The results evidenced that the recombinant PfCAdom, produced as a His-tag fusion protein, was 2.7 times more active with respect the truncated form PfCA1.

Cloning, expression, purification and sulfonamide inhibition profile of the complete domain of the η-carbonic anhydrase from Plasmodium falciparum

We report the cloning, purification and characterization of the full domain of carbonic anhydrase (CA, EC 4.2.1.1) from Plasmodium falciparum, which incorporates 358 amino acid residues (from 181 to 538, in the sequence of this 600 amino acid long protein), called PfCAdom. The enzyme, which belongs to the η-CA class showed the following kinetic parameters: kcat of 3.8×10(5)s(-1) and kcat/Km of 7.2×10(7)M(-1)×s(-1), being 13.3 times more effective as a catalyst compared to the truncated form PfCA. PfCAdom is more effective than the human (h) isoform hCA I, being around 50% less effective compared to hCA II, one of the most catalytically efficient enzymes known so far. Intriguingly, the sulfonamides CA inhibitors generally showed much weaker inhibitory activity against PfCAdom compared to PfCA, prompting us to hypothesize that the 69 amino acid residues insertion present in the active site of this η-CA is crucial for the active site architecture. The best sulfonamide inhibitors for PfCAdom were acetazolamide, methazolamide, metanilamide and sulfanilamide, with KIs in the range of 366-808nM.

New light on bacterial carbonic anhydrases phylogeny based on the analysis of signal peptide sequences

Among protein families, carbonic anhydrases (CAs, EC 4.2.1.1) are metalloenzymes characterized by a common reaction mechanism in all life domains: the carbon dioxide hydration to bicarbonate and protons (CO2+H2O ⇔ HCO3(-)+H(+)). Six genetically distinct CA families are known to date, the α-, β-, γ-, δ-, ζ- and η-CAs. The last CA class was recently discovered analyzing the amino acid sequences of CAs from Plasmodia. Bacteria encode for enzymes belonging to the α-, β-, and γ-CA classes and recently, phylogenetic analysis revealed an interesting relationship regarding the evolution of bacterial CA classes. This result evidenced that the three bacterial CA classes, in spite of the high level of the structural similarity, are evolutionarily distinct, but we noted that the primary structure of some β-CAs identified in the genome of Gram-negative bacteria present a pre-sequence of 18 or more amino acid residues at the N-terminal part. These observations and subsequent phylogenetic data presented here prompted us to propose that the β-CAs found in Gram-negative bacteria with a periplasmic space and characterized by the presence of a signal peptide might have a periplasmic localization and a role similar to that described previously for the α-CAs.

Inhibition of carbonic anhydrase from Trypanosoma cruzi for the management of Chagas disease: an underexplored therapeutic opportunity

An α-carbonic anhydrases (CAs, EC 4.2.1.1) was recently discovered, cloned and characterized in the genome of the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease, a neglected but widespread tropical disease. Inhibition of this α-CAs (TcCA) with anions, sulfonamides, sulfamates, thiols and hydroxamates has been investigated in detail, with several low nanomolar in vitro inhibitors. Although the sulfonamides were the best in vitro inhibitors, they showed no ex vivo anti-T. cruzi activity, due to poor penetration. However, some thiols and hydroxamates acting as low nanomolar TcCA inhibitors also showed significant antitrypanosomal ex vivo activity, making this enzyme an attractive yet underexplored drug target for the management of Chagas disease.

Anion inhibition studies of the β-carbonic anhydrase from the pathogenic bacterium Vibrio cholerae

The genome of the pathogenic bacterium Vibrio cholerae encodes for three carbonic anhydrases (CAs, EC 4.2.1.1) belonging to the α-, β- and γ-classes. Here we report and anion inhibition study of the β-CA, VchCAβ with anions and other small molecules which inhibit metalloenzymes. The best VchCAβ anion inhibitors were sulfamide, sulfamate, phenylboronic acid and phenylarsonic acid, which showed KIs in the range of 54-86μM. Diethyldithiocarbonate was also an effective VchCAβ inhibitor, with an inhibition constant of 0.73mM. The halides, cyanate, thiocyanate, cyanide, bicarbonate, carbonate, nitrate, nitrite, stannate, selenate, tellurate, divanadate, tetraborate, perrhenate, perruthenate, peroxydisulfate, selenocyanide, trithiocarbonate, and fluorosulfonate showed affinity in the low millimolar range, with KIs of 2.3-9.5mM. Identification of selective inhibitors of VchCAβ (over the human CA isoforms) may lead to pharmacological tools useful for understanding the physiological role(s) of this under-investigated enzyme.

Cloning, characterization and anion inhibition studies of a new γ-carbonic anhydrase from the Antarctic bacterium Pseudoalteromonas haloplanktis

A new γ-class carbonic anhydrase (CA, EC 4.2.1.1) was cloned, purified and characterized from the Antarctic bacterium Pseudoalteromonas haloplanktis, PhaCAγ. The enzyme has a medium-low catalytic activity for the physiologic reaction of CO2 hydration to bicarbonate and protons, with a kcat of 1.4×10(5)s(-1) and a kcat/Km of 1.9×10(6)M(-1)s(-1). An anion inhibition study of PhaCAγ with inorganic anions and small molecule inhibitors is also reported. Many anions present in sea water, such as chloride, fluoride, sulfate, iodide, but also others such as azide, perchlorate and tetrafluoroborate did not inhibit this enzyme. Pseudohalides such as cyanate, thiocyanate, cyanide, selenocyanide, and also bicarbonate, nitrate, nitrite and many complex inorganic anions showed inhibition in the millimolar range (KI in the range of 1.7-9.3mM). The best PhaCAγ inhibitors detected in this study were diethyldithiocarbamate (KI of 0.96 mM) as well as sulfamide, sulfamate, phenylboronic acid and phenylarsonic acid (KI in the range of 82-91 μM). Since γ-CAs are poorly understood at this moment, being present in carboxysomes and thus involved in photosynthesis, this study may be relevant for a better understanding of these processes in Antarctic bacteria/cyanobacteria.

Protonography, a powerful tool for analyzing the activity and the oligomeric state of the γ-carbonic anhydrase identified in the genome of Porphyromonas gingivalis

Carbonic anhydrases (CAs, EC 4.2.1.1) are metalloenzymes, mostly containing zinc within their active site, which catalyze a simple but physiologically relevant reaction in all life kingdoms, carbon dioxide hydration to bicarbonate and protons. Six CA classes (α, β, γ, δ, ζ and η) and multiple CA isoforms evolved in organisms all over the phylogenetic tree, for facing the need to efficiently convert high amounts of CO2 to its hydration products. These enzymes are thus involved in many physiologic processes, such as photosynthesis, respiration, CO2 transport, electrolyte secretion in many tissues/organs; biosynthetic reactions (gluconeogenesis, lipogenesis, ureagenesis), etc. Recently, our group reported a new technique to assay CA activity on SDS-PAGE gels, named 'protonography' due to its similarity to zymography. By using protonography, the conversion of CO2 into protons can be visualized as a yellow band on a polyacrylamide gel. By using this technique we demonstrated the possibility to detect activity of the α-CA from Vibrio cholerae as well as the β- and γ-CAs present in Escherichia coli extracts. Furthermore, the activity of the newly discovered η-class enzyme from Plasmodium falciparum has also been evidenced with protonography, illustrating its wide use. Here we show that protonography can be also useful to reveal the oligomeric state of the γ-CA identified in the genome of the bacterial parasite colonizing the oral cavity, Porphyromonas gingivalis, possibly allowing for a simple and efficient diagnostic method.

Sulfonamide inhibition studies of the γ-carbonic anhydrase from the Antarctic cyanobacterium Nostoc commune

A carbonic anhydrase (CA, EC 4.2.1.1) belonging to the γ-class has been cloned, purified and characterized from the Antarctic cyanobacterium Nostoc commune. The enzyme showed a good catalytic activity for the physiologic reaction (hydration of carbon dioxide to bicarbonate and a proton) with the following kinetic parameters, kcat of 9.5×10(5)s(-1) and kcat/KM of 8.3×10(7)M(-1)s(-1), being the γ-CA with the highest catalytic activity described so far. A range of aromatic/heterocyclic sulfonamides and one sulfamate were investigated as inhibitors of the new enzyme, denominated here NcoCA. The best NcoCA inhibitors were some sulfonylated sulfanilamide derivatives possessing elongated molecules, aminobenzolamide, acetazolamide, benzolamide, dorzolamide, brinzolamide and topiramate, which showed inhibition constants in the range of 40.3-92.3nM. As 1,5-bisphosphate carboxylase/oxygenase (RubisCO) and γ-CAs are closely associated in carboxysomes of cyanobacteria for enhancing the affinity of RubisCO for CO2 and the efficiency of photosynthesis, investigation of this new enzyme and its affinity for modulators of its activity may bring new insights in these crucial processes.

Protonography, a technique applicable for the analysis of η-carbonic anhydrase activity

Protonography, a sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) technique derived from zymography was recently reported by our group to be an effective, cheap and reproducible technique for evidencing catalytically active α-carbonic anhydrase (CA, EC 4.2.1.1) isoforms, such as the bovine red blood cell isoform bCA or the bacterial enzyme from Vibrio cholerae, VchCA. CA activity was also observed on the protonogram of a cellular extract of Escherichia coli, evidencing the presence of one or more β-class such enzymes. Here we show that protonography can also be applied to the recently discovered η-CA family using the Plasmodium falciparum enzyme PfCA as an example. The protonogram of PfCA clearly showed catalytically active η-CA with a specific band at 22.0 kDa, which was quite distinct from the band of the red blood cell bovine enzyme bCA, which was observed at 28.8 kDa. The different migration pattern of α- and η-CAs might be a useful tool to detect Plasmodium falciparum in infected human red blood cells by an easy, routine inexpensive technique.

Identification of metal dithiocarbamates as a novel class of antileishmanial agents

Dithiocarbamates have emerged as potent carbonic anhydrase (CA) inhibitors in recent years. Given that CAs are important players in cellular metabolism, the objective of this work was to exploit the CA-inhibitory property of dithiocarbamates as a chemotherapeutic weapon against the Leishmania parasite. We report here strong antileishmanial activity of three hitherto unexplored metal dithiocarbamates, maneb, zineb, and propineb. They inhibited CA activity in Leishmania major promastigotes at submicromolar concentrations and resulted in a dose-dependent inhibition of parasite growth. Treatment with maneb, zineb, and propineb caused morphological deformities of the parasite and Leishmania cell death with 50% lethal dose (LD50) values of 0.56 μM, 0.61 μM, and 0.27 μM, respectively. These compounds were even more effective against parasites growing in acidic medium, in which their LD50 values were severalfold lower. Intracellular acidosis leading to apoptotic and necrotic death of L. major promastigotes was found to be the basis of their leishmanicidal activity. Maneb, zineb, and propineb also efficiently reduced the intracellular parasite burden, suggesting that amastigote forms of the parasite are also susceptible to these metal dithiocarbamates. Interestingly, mammalian cells were unaffected by these compounds even at concentrations which are severalfold higher than their antileishmanial LD50s). Our data thus establish maneb, zineb, and propineb as a new class of antileishmanial compounds having broad therapeutic indices.

The η-class carbonic anhydrases as drug targets for antimalarial agents

INTRODUCTION

The η-class of carbonic anhydrases (CAs, EC 4.2.1.1) was recently discovered as the sixth genetic family of this metalloenzyme superfamily, and seems to be present only in various Plasmodium species, the malaria-provoking pathogens. The present review through detailed biochemical, kinetic and phylogenetic studies afford a clear view regarding the differences between η- and the other CA families.

AREAS COVERED

In this review, the authors underlined as the η-CAs, like α-, γ- and δ-class enzymes, have the Zn(II) ion coordinated by three histidine residues and a water molecule. They seem to be more closely related to the α-CAs, but there are notable differences between them, such as the lack of the proton shuttle residue (His64) and gatekeeper residues, Glu106 and Thr199 in the η-CAs, which are conserved in all α-CAs.

EXPERT OPINION

Plasmodium falciparum η-CA showed a moderate but significant activity for the CO2 hydration reaction, with a kcat of 1.4 × 10(5)s(-1) and a kcat/Km of 5.4 × 10(6) M(-1) × s(-1). Several inhibition studies with anions and sulfonamides/sulfamates, allowed the identification of interesting lead compounds. The discovery of η-CA-specific inhibitors may lead to novel such agents with a new mechanism of action.

A new class of quinazoline-sulfonamides acting as efficient inhibitors against the α-carbonic anhydrase from Trypanosoma cruzi

The protozoan parasite Trypanosoma cruzi is the agent responsible for trypanosomiasis (Chagas disease) in humans and other animals. It has been recently reported that this pathogen encodes for an α-class carbonic anhydrase (CA, EC 4.2.1.1), denominated TcCA, which was shown to be crucial for its life cycle. Inhibition studies of a class of 4-oxoquinazoline containing a benzensulfonamide moiety and their 4-thioxo bioisosteres against the protozoan enzyme TcCA are described here. Most of 4-oxoquinazoline sulfonamides showed nanomolar TcCA inhibition activity with K(I)s in the same order of magnitude of acetazolamide (AAZ), whereas their thioxo bioisosters showed moderate anti-Trypanosoma CA potency with K(I)s in the micromolar range. The discovery of compounds incorporating a 4-oxoquinazoline ring as a low-nanomolar TcCA inhibitor is quite promising and it may be useful for developing anti-Trypanosoma agents with a novel mechanism of action compared to the clinically used drugs (such as benznidazole, nifurtimox) for which significant resistance and serious adverse effects due to their high-toxicity appeared.

Discovery of a new family of carbonic anhydrases in the malaria pathogen Plasmodium falciparum--the η-carbonic anhydrases

The genome of the protozoan parasite Plasmodium falciparum, the causative agent of the most lethal type of human malaria, contains a single gene annotated as encoding a carbonic anhydrase (CAs, EC 4.2.1.1) thought to belong to the α-class, PfCA. Here we demonstrate the kinetic properties of PfCA for the CO2 hydration reaction, as well as an inhibition study of this enzyme with inorganic and complex anions and other molecules known to interact with zinc proteins, including sulfamide, sulfamic acid, and phenylboronic/arsonic acids, detecting several low micromolar inhibitors. A closer examination of the sequence of this and the CAs from other Plasmodium spp., as well as a phylogenetic analysis, revealed that these protozoa encode for a yet undisclosed, new genetic family of CAs termed the η-CA class. The main features of the η-CAs are described in this report.

Sulfonamide inhibition study of the carbonic anhydrases from the bacterial pathogen Porphyromonas gingivalis: the β-class (PgiCAb) versus the γ-class (PgiCA) enzymes

The oral pathogenic bacterium Porphyromonas gingivalis, encodes for two carbonic anhydrases (CAs, EC 4.2.1.1) one belonging to the γ-class (PgiCA) and another one to the β-class (PgiCAb). This last enzyme has been cloned and characterized here for its inhibition profile with the main class of CA inhibitors, the sulfonamides. Many of the clinically used sulfonamides as well as simple aromatic/heterocyclic sulfonamides were ineffective as PgiCAb inhibitors whereas better inhibition was observed with simple derivatives such as sulfanilamide, metanilamide, 4-aminoalkylbenzenesulfonamides (KIs of 364-475nM). The halogenosulfanilamides incorporating heavy halogens, 4-hydroxy- and 4-hydroxyalkyl-benzenesulfonamides, were also micromolar, ineffective PgiCAb inhibitors. The best inhibitors of the β-class enzyme were acetazolamide and ethoxzolamide, with KIs of 214-280nM. Interestingly, the γ-class enzyme was much more sensitive to sulfonamide inhibitors compared to the β-class one, PgiCAb. Identification of potent and possibly selective inhibitors of PgiCAb/PgiCA may lead to pharmacological tools useful for understanding the physiological role(s) of these enzymes, since this bacterium is the main causative agent of periodontitis and few treatment options are presently available.

Protonography, a new technique for the analysis of carbonic anhydrase activity

All proteolytic enzymes, which are able to renature and reacquire the proteolytic activity on a copolymerized substrate, can be analyzed by zymography upon removal of sodium dodecyl sulfate (SDS). Protonography, the new technique described in this study, unlike zymography, allows the detection of a different protein, not a protease, i.e. of the carbonic anhydrase (CA, EC 4.2.1.1) activity on a SDS polyacrylamide gel electrophoresis gel. CAs are zinc-containing enzymes that catalyze the reversible conversion of carbon dioxide to bicarbonate and protons. Hydrogen ions produced during the catalyzed reaction are responsible for the change of color that appears on the gel around the CA band. For this reason, we named the new technique "protonography". The following four salient features characterize this new technique: (a) on the basis of molecular weight markers, recombinant or native CAs with different molecular weights can be detected and quantified rapidly on a single gel; (b) the hydratase activity can be reversibly inhibited by SDS during electrophoresis and recovered by incubating the gel in aqueous Triton X-100; (c) it is possible to separate active oligomeric forms of CAs on the gel enabling their activities to be determined independently of one another. This feature is not possible when using solution assays; and (d) it can be a useful tool to establish if a putative or a newly identified CA in a genome is expressed and enzymatically active. This article outlines the general principles employed in protonography, providing an easy procedure to implement it in laboratories working with CAs. It also presents an overview of its development and current research applications through specific examples.

Sulfonamide inhibition studies of the γ-carbonic anhydrase from the oral pathogen Porphyromonas gingivalis

A carbonic anhydrase (CA, EC 4.2.1.1) denominated PgiCA, belonging to the γ-class, from the oral pathogenic bacteria Porphyromonas gingivalis, the main causative agent of periodontitis, was investigated for its inhibition profile with sulfonamides and one sulfamate. Dichlorophenamide, topiramate and many simple aromatic/heterocyclic sulfonamides were ineffective as PgiCA inhibitors whereas the best inhibition was observed with halogenosulfanilamides incorporating heavy halogens, 4-hydroxy- and 4-hydroxyalkyl-benzenesulfonamides, acetazolamide, methazolamide, zonisamide, indisulam, celecoxib, saccharin and hydrochlorothiazide (KIs in the range of 131-380nM). The inhibition profile of PgiCA was very different from that of CAM, hCA I and II or the β-CA from a protozoan parasite (Leishmania donovani chagasii). Identification of potent and possibly selective inhibitors of PgiCA may lead to pharmacological tools useful for understanding the physiological role(s) of this enzyme.