Current Enzyme Inhibition - Volume 7, Issue 1, 2011

The purpose of this second special issue on the theme “Enzyme inhibitors as new drugs for microbial disease control” is to present some of the latest research carried out in this area and the important developments in this field. This supplement focuses on the fungal aspartic peptidases, bacterial zinc peptidases, and peptidases from Leishmania and Trypanosome cruzi and their inhibitors. Peptidases are an important target for the development of new antimicrobial agents because they play a major role in the parasite-host -cell interaction and participate in numerous processes in the microbial physiology. In the last few years much progress has been made in the design and in clinical applications of peptidase inhibitors. In this context potential peptidase inhibitors have been developed for parasitic diseases. In addition, bacterial peptidases have been evidenced in the pathogenesis of microbial infections, and currently these are a target for disease control. The first review in this special issue, written by Dr. Supuran and Mastrolorenzo concerns the generation of inhibitors of Bacterial zinc peptidases. Zinc peptidases are present in many bacterial species, some of which cause serious disease such as Listeria, Vibrio, Pseudomonas aeruginosa, Legionella pneumophila, Clostridium spp and Enterococcus spp. Recently many peptidomimetic and non-peptide inhibitors have been discovered for these enzymes and some are being evaluated for pharmacological development. The second review by Dr. Almeida Rodrigues et al. presents an overview that focuses on the phytochemicals which are able to inhibit specific Trypanosoma spp. and Leishmania spp. enzymes. The next review by Dr. Bauerova et al. discusses the possibility of using vacuolar or GPI-anchored aspartic peptidase inhibitors against the genus Candida spp. that represents a serious threat to immunocompromised Individuals. In the last manuscript Dr. Soares has reviewed the peptidase inhibitors with antileishmanial activity covering the recent findings in the literature. Current chemotherapy of leishmaniases has limited efficiency, toxic side effects and presents drug resistance. As guest editor, I am grateful to the authors for providing their reviews on this important matter. We thank the reviewers for their useful comments on the manuscripts submitted to this issue.

There is a wealth of new data regarding zinc proteases present in many bacterial species, many of which cause serious disease, such as Listeria spp, Vibrio spp., Pseudomonas aeruginosa, Legionella pneumophila, Streptomyces spp., Clostridium spp., Enterococcus spp., etc. Many of these pathogens developed resistance to the clinically used antibiotics, which normally target bacterial cell wall biosynthesis or affect protein synthesis on ribosomes. Zinc-containing proteases play critical functions in these organisms, related to colonization and evasion of host immune defenses, acquisition of nutrients for growth and proliferation, facilitation of dissemination, or tissue damage during infection. However, only in the last decade such targets started to be investigated in detail. Thus, there are a lot of data available regarding the cloning, purification and biochemical characterization of many such zinc proteases, from both gram-positive as well as gram-negative pathogens. But for the moment, few potent and specific inhibitors for bacterial such proteases have been reported except for Clostridium histolyticum collagenase, botulinum and tetanus neurotoxin and anthrax lethal factor. No inhibitors of the critically important and ubiquitous IgA-specific metallopeptidases or AAA proteases have been reported to date, although such compounds would presumably constitute a new class of highly effective antibiotics. The clostridial neurotoxins, tetanus neurotoxin (TeNT) and botulinum neurotoxin (BoNT, of which seven distinct serotypes are known, BoNT/A-G), together with the anthrax lethal factor (LF) are zinc proteases and among the most toxic compounds known in Nature. The substrate of TeNT is a 120-residue protein anchored to the membrane of cell vesicles, which has been termed VAMP, whereas BoNTs/B, D, F and G cleave specifically VAMP at different single peptide bonds. BoNTs also possess two other intracellular targets in addition to VAMP: SNAP-25 (25 kDa synaptosomal-associated protein) and syntaxin, both of which are cleaved between Gln#Arg (by BoNT/A), Lys#Ala (by BoNT/C), Arg#Ala (by BoNT/C) or Gln#Lys (different neurotoxins) residues. The three proteases contain a Zn(II) ion coordinated by two His and a Glu residue, similarly to many other zinc proteases. Many different peptidomimetic and non-peptide inhibitors were discovered for the three enzymes, after the report of their X-ray crystal structures, alone or complexed to substrates/inhibitors. Such compounds, presently in clinical development, may be effective in case of terroristic attacks in which such toxins are used or to treat diseases provoked by these bacteria which are widespread in nature. Furthermore, BoNT A has many applications in medicine, for the management of dystonias, strabismus, facial wrinkling, brow position, as well as palmar and axillary hyperhidrosis. More recently, BoNT A was also shown to be useful in the symptomatic therapy of pain, together with disorders in which muscular hyperactivity plays a prominent role, such as for example glandular hypersecretion, lower urinary tract dysfunction, prostatic disorders and vaginismus in women suffering with pelvic floor muscle tension.

Proteases make up the largest class of enzymes, with more than 1600 proteases identified from over 1700 organisms. These proteases participate in numerous physiological and pathological processes. In Leishmania, these enzymes play important roles during their life cycle, and in different steps of the microorganism-host interplay. They have become important targets for the rational development of drugs. Proteolytic enzyme activity is closely regulated in many ways, including substrate selectivity, specific cellular location, and it can also be regulated by specific synthetic inhibitors. Protease inhibitor interactions are involved in the regulation of processes such as protein digestion, various physiological and pathological processes and microbial diseases. There are pathological conditions in which uncontrolled proteolytic activity of exogenous proteases derived from infectious agents such as protozoa play a role in the onset and perpetuation of infection, making protease inhibitors potentially applicable as therapeutic agents in the battle against these diseases. Current chemotherapy of leishmaniasis still relies on drugs, which have limited efficiency, toxic side effects and now the emergence of drug resistance. Here in this work some aspects of the relation between antileishmanial and protease inhibitor activities are discussed.

Chagas disease and leishmaniasis are important parasitic diseases afflicting the poorest countries in the world. The number and efficacy of drugs available for the treatment of human trypanosomiasis and leishmaniasis is limited and are not ideal, as they are often associated with severe side effects. The emerging resistance to the available drugs against these diseases represents an additional problem. However, some headway has been made in identifying factors that are keys to parasite virulence and the pathogenesis of the diseases they produce. Parasite-derived proteases have been widely studied in connection to parasite virulence and disease pathogenesis. Studies focused on plant-derived compounds active against species of Trypanosoma and Leishmania have reveled promising results, which highlights natural products as a valuable source of drug candidates. This review focuses on phytochemicals able to target specific Trypanosoma spp. and Leishmania spp. enzymes showing a modern approach to the development of new drugs against trypanosomiasis and leishmaniasis.

The renin-angiotensin system (RAS) plays a major role in regulating the cardiovascular, renal, respiratory and central nervous systems. Angiotensin-converting enzyme (ACE) and a newly identified homologue of ACE, angiotensinconverting enzyme 2 (ACE2), are regulators of the RAS. These enzymes, however, have distinct substrate specificity and physiological roles. There is evidence that a balance between ACE and ACE2 expression and activities plays an important role in maintaining normal organ physiology and also in the pathogenesis of various diseases. Thus understanding regulation of the two enzymes could have therapeutic implications. Both ACE and ACE2 are type I transmembrane glycoproteins in which the catalytic domains are located in their ectodomains. These ectoenzymes undergo proteolytic cleavage from the cell surface and this cellular process is known as ectodomain shedding. Ectodomain shedding results in release of the enzymatically active segments into the interstitial space and circulation. Both ACE and ACE2 also function as cell surface receptors that initiate intracellular signaling that can influence gene expression. Thus ectodomain shedding could influence various functions of ACE and ACE2. Recent evidence indicates that ectodomain shedding of these proteins is a highly regulated and versatile process. This review focuses on ectodomain shedding of ACE and ACE2 and summarizes what is known about the molecular and cellular mechanisms, the related clinical findings and potential therapeutic implications.

It is well known that NO has significant physiological effects including regulation of smooth muscle tonus, tissues differentiation, resistance to stress, inhibition of platelet aggregation and some gene expression. However, the practical application of scientific research on NO production and its metabolism is still mainly lacking. This can be explained by the insufficient knowledge of NO metabolism in physiological and pathological processes. The difficulty of quantitative determination of NO metabolites in biological objects is the main reason that limits the possibility of such studies. Modern methods are not able to determine the composition and concentration of these compounds in biological objects quickly and correctly. Application of enzymes to evaluate the NO metabolites is very promising due to their high specificity in physiological conditions. This review analyzes the various methods of nitro- and nitroso-compounds determination in biological objects. It is shown that methods enzyme-based assays are suitable for the correct, fast, cheap and high sensitive estimation of basic NO metabolites in biological objects. This makes possible to establish the NO metabolite content in biological objects, and particularly, the content of physiological NO donors and its variations in physiological and pathological processes. This data can be used for diagnostic in medicine and agriculture and also for testing of NO donors.