A high-throughput turbidometric assay for screening inhibitors of Leishmania major protein disulfide isomerase

Drug Discovery for Cutaneous Leishmaniasis: A Review of Developments in the Past 15 Years

Leishmaniasis is a group of vector-borne, parasitic diseases caused by over 20 species of the protozoan Leishmania spp. The three major disease classifications, cutaneous, visceral, and mucocutaneous, have a range of clinical manifestations from self-healing skin lesions to hepatosplenomegaly and mucosal membrane damage to fatality. As a neglected tropical disease, leishmaniasis represents a major international health challenge, with nearly 350 million people living at risk of infection a year. The current chemotherapeutics used to treat leishmaniasis have harsh side effects, prolonged and costly treatment regimens, as well as emerging drug resistance, and are predominantly used for the treatment of visceral leishmaniasis. There is an undeniable need for the identification and development of novel chemotherapeutics targeting cutaneous leishmaniasis (CL), largely ignored by concerted drug development efforts. CL is mostly non-lethal and the most common presentation of this disease, with nearly 1 million new cases reported annually. Recognizing this unaddressed need, substantial yet fragmented progress in early drug discovery efforts for CL has occurred in the past 15 years and was outlined in this review. However, further work needs to be carried out to advance early discovery candidates towards the clinic. Importantly, there is a paucity of investment in the translation and development of therapies for CL, limiting the emergence of viable solutions to deal with this serious and complex international health problem.

The potential role of protein disulfide isomerases (PDIs) during parasitic infections: a focus on Leishmania spp

Leishmaniasis is a group of vector-borne diseases caused by intracellular protozoan parasites belonging to the genus Leishmania. Leishmania parasites can employ different and numerous sophisticated strategies, including modulating host proteins, cell signaling, and cell responses by parasite proteins, to change the infected host conditions to favor the parasite persistence and induce pathogenesis. In this sense, protein disulfide isomerases (PDIs) have been described as crucial proteins that can be modulated during leishmaniasis and affect the pathogenesis process. The effect of modulated PDIs can be investigated in both aspects, parasite PDIs and infected host cell PDIs, during infection. The information concerning PDIs is not sufficient in parasitology; however, this study aimed to provide data regarding the biological functions of such crucial proteins in parasites with a focus on Leishmania spp. and their relevant effects on the pathogenesis process. Although there are no clinical trial vaccines and therapeutic approaches, highlighting this information might be fruitful for the development of novel strategies based on PDIs for the management of parasitic diseases, especially leishmaniasis.

A computer-aided approach to identify novel Leishmania major protein disulfide isomerase inhibitors for treatment of leishmaniasis

Leishmaniasis is an infectious disease caused by parasites of the genus Leishmania and transmitted by the bite of a sand fly. To date, most available drugs for treatment are toxic and beyond the economic means of those affected by the disease. Protein disulfide isomerase (PDI) is a chaperone protein that plays a major role in the folding of newly synthesized proteins, specifically assisting in disulfide bond formation, breakage, or rearrangement in all non-native proteins. In previous work, we demonstrated that Leishmania major PDI (LmPDI) has an essential role in pathogen virulence. Furthermore, inhibition of LmPDI further blocked parasite infection in macrophages. In this study, we utilized a computer-aided approach to design a series of LmPDI inhibitors. Fragment-based virtual screening allowed for the understanding of the inhibitors' modes of action on LmPDI active sites. The generated compounds obtained after multiple rounds of virtual screening were synthesized and significantly inhibited target LmPDI reductase activity and were shown to decrease in vitro parasite growth in human monocyte-derived macrophages. This novel cheminformatics and synthetic approach led to the identification of a new series of compounds that might be optimized into novel drugs, likely more specific and less toxic for the treatment of leishmaniasis.

Identification and Characterization of a Novel Protein Disulfide Isomerase Gene (MgPDI2) from Meloidogyne graminicola

Protein disulfide isomerase (PDI) is a multifunctional enzyme that catalyzes rate-limiting reactions such as disulfide bond formation, isomerization, and reduction. There is some evidence that indicates that PDI is also involved in host-pathogen interactions in plants. In this study, we show that the rice root-knot nematode, Meloidogyne graminicola, has evolved a secreted effector, MgPDI2, which is expressed in the subventral esophageal glands and up-regulated during the early parasitic stage of M. graminicola. Purified recombinant MgPDI2 functions as an insulin disulfide reductase and protects plasmid DNA from nicking. As an effector, MgPDI2 contributes to nematode parasitism. Silencing of MgPDI2 by RNA interference in the pre-parasitic second-stage juveniles (J2s) reduced M. graminicola multiplication and also increased M. graminicola mortality under H2O2 stress. In addition, an Agrobacterium-mediated transient expression assay found that MgPDI2 caused noticeable cell death in Nicotiana benthamiana. An intact C-terminal region containing the first catalytic domain (a) with an active motif (Cys-Gly-His-Cys, CGHC) and the two non-active domains (b and b') is required for cell death induction in N. benthamiana. This research may provide a promising target for the development of new strategies to combat M. graminicola infections.

Adverse Outcomes Associated with Cigarette Smoke Radicals Related to Damage to Protein-disulfide Isomerase

Identification of factors contributing to the development of chronic obstructive pulmonary disease (COPD) is crucial for developing new treatments. An increase in the levels of protein-disulfide isomerase (PDI), a multifaceted endoplasmic reticulum resident chaperone, has been demonstrated in human smokers, presumably as a protective adaptation to cigarette smoke (CS) exposure. We found a similar increase in the levels of PDI in the murine model of COPD. We also found abnormally high levels (4-6 times) of oxidized and sulfenilated forms of PDI in the lungs of murine smokers compared with non-smokers. PDI oxidation progressively increases with age. We begin to delineate the possible role of an increased ratio of oxidized PDI in the age-related onset of COPD by investigating the impact of exposure to CS radicals, such as acrolein (AC), hydroxyquinones (HQ), peroxynitrites (PN), and hydrogen peroxide, on their ability to induce unfolded protein response (UPR) and their effects on the structure and function of PDIs. Exposure to AC, HQ, PN, and CS resulted in cysteine and tyrosine nitrosylation leading to an altered three-dimensional structure of the PDI due to a decrease in helical content and formation of a more random coil structure, resulting in protein unfolding, inhibition of PDI reductase and isomerase activity in vitro and in vivo, and subsequent induction of endoplasmic reticulum stress response. Addition of glutathione prevented the induction of UPR, and AC and HQ induced structural changes in PDI. Exposure to PN and glutathione resulted in conjugation of PDI possibly at active site tyrosine residues. The findings presented here propose a new role of PDI in the pathogenesis of COPD and its age-dependent onset.

Leishmania major protein disulfide isomerase as a drug target: enzymatic and functional characterization

Leishmaniasis is a major health problem worldwide and tools available for their control are limited. Effective vaccines are still lacking, drugs are toxic and expensive, and parasites develop resistance to chemotherapy. In this context, new antimicrobials are urgently needed to control the disease in both human and animal. Here, we report the enzymatic and functional characterization of a Leishmania virulence factor, Leishmania major Protein disulfide isomerase (LmPDI) that could constitute a potential drug target. LmPDI possesses domain structure organization similar to other PDI family members (a, a', b, b' and c domains), and it displays the three enzymatic and functional activities specific of PDI family members: isomerase, reductase and chaperone. These results suggest that LmPDI plays a key role in assisting Leishmania protein folding via its capacity to catalyze formation, breakage, and rearrangement of disulfide bonds in nascent polypeptides. Moreover, Bacitracin, a reductase activity inhibitor, and Ribostamycin, a chaperone activity inhibitor, were tested in LmPDI enzymatic assays and versus Leishmania promastigote in vitro cultures and Leishmania amastigote multiplication inside infected THP-1-derived macrophages. Bacitracin inhibited both isomerase and reductase activities, while Ribostamycin had no effect on the chaperone activity. Interestingly, Bacitracin blocked in vitro promastigote growth as well as amastigote multiplication inside macrophages with EC(50) values of 39 μM. These results suggest that LmPDI may constitute an interesting target for the development of new anti-Leishmania drugs.

Acid-denatured Green Fluorescent Protein (GFP) as model substrate to study the chaperone activity of protein disulfide isomerase

Green fluorescent protein (GFP) has been widely used in several molecular and cellular biology applications, since it is remarkably stable in vitro and in vivo. Interestingly, native GFP is resistant to the most common chemical denaturants; however, a low fluorescence signal has been observed after acid-induced denaturation. Furthermore, this acid-denatured GFP has been used as substrate in studies of the folding activity of some bacterial chaperones and other chaperone-like molecules. Protein disulfide isomerase enzymes, a family of eukaryotic oxidoreductases that catalyze the oxidation and isomerization of disulfide bonds in nascent polypeptides, play a key role in protein folding and it could display chaperone activity. However, contrasting results have been reported using different proteins as model substrates. Here, we report the further application of GFP as a model substrate to study the chaperone activity of protein disulfide isomerase (PDI) enzymes. Since refolding of acid-denatured GFP can be easily and directly monitored, a simple micro-assay was used to study the effect of the molecular participants in protein refolding assisted by PDI. Additionally, the effect of a well-known inhibitor of PDI chaperone activity was also analyzed. Because of the diversity their functional activities, PDI enzymes are potentially interesting drug targets. Since PDI may be implicated in the protection of cells against ER stress, including cancer cells, inhibitors of PDI might be able to enhance the efficacy of cancer chemotherapy; furthermore, it has been demonstrated that blocking the reductive cleavage of disulfide bonds of proteins associated with the cell surface markedly reduces the infectivity of the human immunodeficiency virus. Although several high-throughput screening (HTS) assays to test PDI reductase activity have been described, we report here a novel and simple micro-assay to test the chaperone activity of PDI enzymes, which is amenable for HTS of PDI inhibitors.