Current Medicinal Chemistry (v.19, #10)

Although the parasitology belongs to one of the longest established disciplines, the recent methodical advances led to the substantial broadening of the possibilities for the detection and treatment of parasitic diseases. However, the exact mechanisms involved in the parasite establishment and survival are frequently unclear and only recently uncovered. At the cellular level, the emerging mechanisms, discussed in this journal issue, include the newly recognized role of mast cells in the host defense against bacterial pathogens, and the role of granulocytes in the host defense against helminths. At the protein level, we discuss here the emerging role of protein tyrosine phosphatases as both targets and tools of nonmetazoan pathogens and viruses. At the level of small signaling molecules, we attempt here to highlight the role of reactive oxygen species as molecules involved both in the host defense, but also produced by some human pathogens and commensals. Scientometric analysis of the fields covered by this journal issue is provided.

Respiratory syncytial virus (RSV; Family Paramyxoviridae, Genus Pneumovirus) is a major respiratory pathogen of infants and children and an emerging pathogen of the elderly. Current management of RSV disease includes monoclonal antibody prophylaxis for infants identified as high risk and supportive care for those with active infection; there is no vaccine, although several are under study. In this manuscript, we review published findings from human autopsy studies, as well as experiments that focus on human clinical samples and mouse models of acute pneumovirus infection that elucidate basic principles of disease pathogenesis. Consideration of these data suggests that the inflammatory responses to RSV and related pneumoviral pathogens can be strong, persistent, and beyond the control of conventional antiviral and anti-inflammatory therapies, and can have profound negative consequences to the host. From this perspective, we consider the case for specific immunomodulatory strategies that may have the potential to alleviate some of the more serious sequelae of this disease.

Mast cells are best known as central effector cells in IgE-mediated type I allergic diseases including asthma and hay fever. An increasing amount of evidence, however, has demonstrated that mast cells are sentinel cells playing a critical role in host defense against invading microbes. Mast cells are located immediately beneath the epithelial surfaces exposed to the outer environment, such as genitourinary and gastrointestinal tracts, skin, and airways. This review discusses recent studies on the critical roles of mast cells in host defense against Gram-negative bacterial infection. Mast cells are equipped with multiple receptors detecting the invading Gram-negative bacteria in both direct (opsonin-independent) and indirect (opsonin-dependent) mechanisms. The former includes Toll-like receptors (TLRs), CD48, and nucleotide-binding oligomerization (NOD) proteins, while the latter includes Fcγ receptors (FcγRs) and complement receptors. In addition to the detecting systems, mast cells are also armed with versatile tools to combat and kill Gram-negative bacteria. In response to the recognition of the Gram-negative bacterial infection, mast cells secrete various types of mediators which either regulate host immune system or directly attack the bacteria. Mast cells can also phagocytize and subsequently display the bacterial antigens on their cell surfaces. Moreover, recent findings have revealed the formation of extra-cellular traps by mast cells. Finally this review will especially focus on recent findings on LPS signaling in mast cells, both the functional outcome and the molecular mechanisms.

Leishmaniasis remains a public health problem worldwide, affecting approximately 12 million people in 88 countries; 50 000 die of it each year. The disease is caused by Leishmania, obligate intracellular vector-borne parasites. In spite of its huge health impact on the populations in vast areas, leishmaniasis is one of the most neglected diseases. No safe and effective vaccine currently exists against any form of human leishmaniasis. The spectrum and efficacy of available antileishmanial drugs are also limited. First part of this review discusses the approaches used for the vaccination against leishmaniasis that are based on the pathogen and includes virulent or attenuated parasites, parasites of related nonpathogenic species, whole killed parasites, parasites

Malaria imposes a serious threat to human and becomes more prevalent due to the emergence of drug resistant parasite. Understanding of the underlying mechanism of drug resistance and identification of novel drug targets are key effective processes for the management of malaria. Malaria parasite is highly susceptible to oxidative stress but lives in a pro-oxidant rich environment containing oxygen and iron, which produce a large amount of reactive oxygen species. Management of oxidative stress in malaria parasite is tightly regulated through active redox and antioxidant defense systems. The elevation of oxidative stress as a result of inhibition of any component of this defense system leads to redox imbalance and ultimately parasite death. Therefore, redox system plays an indispensable role for the survival of parasite within the host. Identification of key molecules, which disrupt parasite redox balance by altering key redox reactions and promote oxidative stress in parasites, would be an effective approach to develop novel antimalarial drugs. During the last few decades, contributions by researchers around the globe provide even better understanding of redox biology of malaria parasite. Here, in this review, we are highlighting the knowledge gathered so far regarding the essential redox-active processes and their components in malaria parasite to overcome elevated oxidative insults. We have also given maximum efforts to enlist currently used redox-active antimalarials, their mode of action and pharmacotherapeutic implications.

Babesiosis is a disease with a world-wide distribution affecting many species of mammals principally cattle and man. The major impact occurs in the cattle industry where bovine babesiosis has had a huge economic effect due to loss of meat and beef production of infected animals and death. Nowadays to those costs there must be added the high cost of tick control, disease detection, prevention and treatment. In almost a century and a quarter since the first report of the disease, the truth is: there is no a safe and efficient vaccine available, there are limited chemotherapeutic choices and few low-cost, reliable and fast detection methods. Detection and treatment of babesiosis are important tools to control babesiosis. Microscopy detection methods are still the cheapest and fastest methods used to identify Babesia parasites although their sensitivity and specificity are limited. Newer immunological methods are being developed and they offer faster, more sensitive and more specific options to conventional methods, although the direct immunological diagnoses of parasite antigens in host tissues are still missing. Detection methods based on nucleic acid identification and their amplification are the most sensitive and reliable techniques available today; importantly, most of those methodologies were developed before the genomics and bioinformatics era, which leaves ample room for optimization. For years, babesiosis treatment has been based on the use of very few drugs like imidocarb or diminazene aceturate. Recently, several pharmacological compounds were developed and evaluated, offering new options to control the disease. With the complete sequence of the Babesia bovis genome and the B. bigemina genome project in progress, the post-genomic era brings a new light on the development of diagnosis methods and new chemotherapy targets. In this review, we will present the current advances in detection and treatment of babesiosis in cattle and other animals, with additional reference to several apicomplexan parasites.

The resident prokaryotic microbiota of the mammalian intestine influences diverse homeostatic functions, including regulation of cellular growth, maintenance of barrier function, and modulation of immune responses. However, it is unknown how commensal prokaryotic organisms mechanistically influence eukaryotic signaling networks. Recent data has demonstrated that gut epithelia contacted by enteric commensal bacteria rapidly generate reactive oxygen species (ROS). While the induced generation of ROS via stimulation of formyl peptide receptors is a cardinal feature of the cellular response of phagocytes to pathogenic or commensal bacteria, evidence is accumulating that ROS are also similarly elicited in other cell types, including intestinal epithelia, in response to microbial signals. Additionally, ROS have been shown to serve as critical second messengers in multiple signal transduction pathways stimulated by proinflammatory cytokines and growth factors. This physiologically-generated ROS is known to participate in cellular signaling via the rapid and transient oxidative inactivation of a defined class of sensor proteins bearing oxidant-sensitive thiol groups. These proteins include tyrosine phosphatases that serve as regulators of MAP kinase pathways, cytoskeletal dynamics, as well as components involved in control of ubiquitination-mediated NF-κB activation. Consistently, microbial-elicited ROS has been shown to mediate increased cellular proliferation and motility and to modulate innate immune signaling. These results demonstrate how enteric microbiota influence regulatory networks of the mammalian intestinal epithelia. We hypothesize that many of the known effects of the normal microbiota on intestinal physiology, and potential beneficial effects of candidate probiotic bacteria, may be at least partially mediated by this ROSdependent mechanism.

Protein tyrosine phosphatases (PTPs) are increasingly recognized as important effectors of host-pathogen interactions. Since Guan and Dixon reported in 1990 that phosphatase YopH serves as an essential virulence determinant of Yersinia, the field shifted significantly forward, and dozens of PTPs were identified in various microorganisms and even in viruses. The discovery of extensive tyrosine signaling networks in non-metazoan organisms refuted the moth-eaten paradigm claiming that these organisms rely exclusively on phosphoserine/phosphothreonine signaling. Similarly to humans, phosphotyrosine signaling is thought to comprise a small fraction of total protein phosphorylation, but plays a disproportionately important role in cell-cycle control, differentiation, and invasiveness. Here we summarize the state-of-art knowledge on PTPs of important non-metazoan pathogens (Listeria monocytogenes, Staphylococcus aureus, Porphyromonas gingivalis, Caulobacter crescentus, Yersinia, Synechocystis, Leishmania, Plasmodium falciparum, Entamoeba histolytica, etc.), and focus also at the microbial proteins affecting directly or indirectly the PTPs of the host (Mycobacterium tuberculosis MTSA-10, Bacillus anthracis anthrax toxin, streptococcal β protein, Helicobacter pylori CagA and VacA, Leishmania GP63 and EF-1α, Plasmodium hemozoin, etc.). This is the first review summarizing the knowledge on biological activity and pharmacological inhibition of non-metazoan PTPs, with the emphasis of those important in host-pathogen interactions. Targeting of numerous non-metazoan PTPs is simplified by the fact that they act either as ectophosphatases or are secreted outside of the pathogen. Interfering with tyrosine phosphorylation represents a powerful pharmacologic approach, and even though the PTP inhibitors are difficult to develop, lifting the fog of phosphatase inhibition is of the great market potential and further clinical impact.

Helminths are parasitic organisms that can be broadly described as “worms” due to their elongated body plan, but which otherwise differ in shape, development, migratory routes and the predilection site of the adults and larvae. They are divided into three major groups: trematodes (flukes), which are leaf-shaped, hermaphroditic (except for blood flukes) flatworms with oral and ventral suckers; cestodes (tapeworms), which are segmented, hermaphroditic flatworms that inhabit the intestinal lumen; and nematodes (roundworms), which are dioecious, cylindrical parasites that inhabit intestinal and peripheral tissue sites. Helminths exhibit a sublime co-evolution with the host's immune system that has enabled them to successfully colonize almost all multicellular species present in every geographical environment, including over two billion humans. In the face of this challenge, the host immune system has evolved to strike a delicate balance between attempts to neutralize the infectious assault versus limitation of damage to host tissues. Among the most important cell types during helminthic invasion are granulocytes: eosinophils, neutrophils and basophils. Depending on the specific context, these leukocytes may have pivotal roles in host protection, immunopathology, or facilitation of helminth establishment. This review provides an overview of the function of granulocytes in helminthic infections.