Evaluation of Leishmania infantum pyridoxal kinase protein for the diagnosis of human and canine visceral leishmaniasis

Recognition of Immunoreactive Proteins in Leishmania infantum Amastigote-Like and Promastigote Using Sera of Visceral Leishmaniasis Patients: a Preliminary Study

PURPOSE

Visceral leishmaniasis (VL) is a systemic and parasitic disease that is usually fatal if left untreated. VL is endemic in different parts of Iran and is caused mainly by Leishmania infantum. This study aimed to recognition immunoreactive proteins in amastigote-like and promastigote stages of L. infantum (Iranian strain) by antibodies present in the sera of VL patients.

METHODS

Total protein extract from amastigote-like and promastigote cells was separated by two-dimensional electrophoresis (2DE). To detect the immunoreactive proteins, 2DE immunoblotting method was performed using different pools of VL patients' sera.

RESULTS

Approximately 390 and 430 protein spots could be separated in 2DE profiles of L. infantum amastigote-like and promastigote stages, respectively. In immunoblotting method, approximately 295 and 135 immunoreactive proteins of amastigotes-like reacted with high antibody titer serum pool and low antibody titer serum pool, respectively. Approximately 120 and 85 immunoreactive proteins of promastigote extract were recognized using the high antibody titer sera pool and low antibody titer sera, respectively.

CONCLUSION

The present study has recognized a number of antigenic diversity proteins based on the molecular weight and pH in amastigote-like and promastigote stages of L. infantum. These results provide us a new concept for further analysis development in the field of diagnosis biomarkers and vaccine targets.

A systematic review of peptide-based serological tests for the diagnosis of leishmaniasis

Serological methods should meet the needs of leishmaniasis diagnosis due to their high sensitivity and specificity, economical and adaptable rapid diagnostic test format, and ease of use. Currently, the performances of serological diagnostic tests, despite improvements with recombinant proteins, vary greatly depending on the clinical form of leishmaniasis and the endemic area. Peptide-based serological tests are promising as they could compensate for antigenic variability and improve performance, independently of Leishmania species and subspecies circulating in the endemic areas. The objective of this systematic review was to inventory all studies published from 2002 to 2022 that evaluate synthetic peptides for serological diagnosis of human leishmaniases and also to highlight the performance (e.g., sensitivity and specificity) of each peptide reported in these studies. All clinical forms of leishmaniasis, visceral and tegumentary, and all Leishmania species responsible for these diseases were considered. Following PRISMA statement recommendations, 1,405 studies were identified but only 22 articles met the selection criteria and were included in this systematic review. These original research articles described 77 different peptides, of which several have promising performance for visceral or tegumentary leishmaniasis diagnosis. This review highlights the importance of and growing interest in synthetic peptides used for serological diagnosis of leishmaniases, and their performances compared to some widely used tests with recombinant proteins.

Development of Immunological Assays Based on Leishmania donovani Antigen for Diagnosis of Canine Visceral Leishmaniasis and Their Multicenter Evaluation in Brazil and Italy

Canine visceral leishmaniasis (CVL) due to Leishmania infantum infection is a zoonotic disease prevalent in the areas of South America and the Mediterranean. Infected dogs as reservoirs can contribute to disease transmission and can be a scourge to public health. Therefore, early diagnosis of infected dogs may play a pivotal role in circumscribing disease progression. Invasive tissue aspiration and insufficient serological methods impair a single assay for prompt CVL diagnosis. In the present study, we aimed to evaluate the potential of Leishmania donovani isolated membrane protein, LAg, for the diagnosis of CVL through immunological assays. Initially, enzyme-linked immunosorbent assay was done with Brazilian dog sera to evaluate the performance of LAg in diagnosing CVL and found sensitivity and specificity of 92.50% and 95%, respectively. The study further confirmed the diagnostic efficacy of LAg in a dipstick format. The dipstick test of canine sera from three centers in Brazil and one center in Italy collectively showed sensitivity values in the range of 53.33% to 100% in recognizing symptomatic dogs and specificity values between 75% and 100% to rule out healthy dogs. Moreover, a rapid immunochromatographic test was developed and optimized using LAg. This test was able to identify 94.73% of CVL of Brazilian origin with specificity of 97.29%. The current results highlight the reactive potential of the L. donovani antigen, LAg, for L. infantum CVL diagnosis and support our previous findings, which suggest the utility of LAg for the diagnosis of both L. donovani and L. infantum human VL in a variety of endemic regions. LAg as a diagnostic candidate may be employed to identify comprehensive CVL cases in epidemiological areas.

Cloning and Characterization of Pyridoxal Kinase from Geobacillus sp. H6a

Pyridoxal kinase encoded by pdxK gene, is the important key enzyme in the salvage pathway of vitamin B6 biosynthesis. The enzyme catalyzes the phosphorylation of the 5′ alcohol groups of free form vitamin B6 into their 5′-phosphate forms that requires metal ion and ATP. Pyridoxal kinase have been reported in many organisms except in the thermophilic bacterium. Therefore, this study aimed to clone, express and characterize pyridoxal kinase of Geobacillus sp. H6a isolated from the hot spring in the North of Thailand. The GhpdxK gene (810 base pairs) was inserted into pET28a(+) plasmids at restriction site of NdeI and BamHI and transformed into E.coli BL21(DE3). The expressed pyridoxal kinase of this bacterium exhibits a homodimer, in which each subunit had a molecular mass of about 32 kDa when examined by SDS-PAGE and gel filtration. The enzyme showed maximal activity at 70°C and at pH 8.0. The expressed enzyme obtained in this study was found to be more active (>50%) in the broad pH range (6.0 – 9.0) than those previously reported. This enzyme prefers Mg2+ and also accepts other cations to the less extent. Under optimal conditions, the expressed enzyme has higher affinity toward PN (20 ± 1.35 µM), while it showed the same affinity to pyridoxal (100 ± 0.76 µM) and pyridoxamine (100 ± 1.21 µM). The Km value for ATP and 4-amino-5-hydroxymethyl-2-methylpyridine were 8.99 ± 1.76 µM and 19 ± 0.85 µM, respectively. With high activity at high temperature and active in the broad pH range, it could be considered as a potential candidate for future application particularly bioconversion of vitamin B6.

Revealing a Novel Antigen Repressor of Differentiation Kinase 2 for Diagnosis of Human Visceral Leishmaniasis in India

Visceral leishmaniasis (VL) is one of the major global health concerns due to its association with morbidity and mortality. All available diagnostic tools have been, until now, unable to provide a very specific and cost-effective mode of detection for VL globally. Therefore, the design of robust, specific, and commercially translatable diagnostic tests is urgently required. Currently, we are attempting to identify and explore the diagnostic potential of a novel parasite antigen. Repressor of differentiation kinase 2 (RDK2), a serine/threonine kinase, has a versatile role in parasite life cycle progression. However, its role as a diagnostic candidate for VL has not been investigated. Herein, we cloned and over-expressed LdRDK2 and studied the recombinant RDK2 for the diagnosis of human VL using serum and urine samples. In silico analysis predicted that RDK2 is conserved among Leishmania species with the least conservation in humans. RDK2 developed immune-reactive bands with antibodies present in VL patients' sera, and it demonstrated no cross-reactivity with sera from healthy controls and other diseases. Additionally, RDK2 antigen demonstrated a significant reactivity with IgG antibodies of VL patients' sera, with 78% sensitivity and 86.67% specificity as compared to healthy controls and other diseases. Furthermore, we evaluated its utility for non-invasive diagnosis of VL using patients' urine samples and found 93.8% sensitivity and 85.7% specificity. RDK2 was found to have better sensitivity and treatment response in patients' urine compared to serum samples, indicating its role as a promising point of care (POC) antigen. In a nutshell, we explored the role of RDK2 as a potential diagnostic marker for VL in both invasive and non-invasive modes as well as its utility as a promising POC antigen for treatment response cases.

Antigens and their diagnostic performance for Canine Visceral Leishmaniasis: A critical review

Canine visceral leishmaniasis (CVL) is the most aggressive and lethal form of leishmaniasis manifesting in dogs and represents a major public health concern. Although there are sufficiently sensitive molecular tools for CVL diagnosis, they are not accessible at the main points of disease dissemination, in which context serodiagnosis has been used as an alternative tool on the epidemiological control. As an attempt to develop more accurate immunodiagnostic assays, many antigens have been tested over the years, on different platforms. This review aimed to access studies reporting new antigens that can be applied for CVL serodiagnosis. Articles published from January of 2016 to March of 2021 were retrieved from Google Scholar, Science Direct, and PubMed, using "Canine Visceral Leishmaniasis" and "Serodiagnosis" as keywords. In total, 1527 articles were identified, of which 42 were selected based on exclusion factors. Sensitivity, specificity, sample size, and sample quality data were extracted by manual curation and analyzed. Of the selected articles, 26 contemplated ELISA, which enabled a more thorough comparison and a critical review of these studies. Soluble Leishmania Antigens (SLA) and the A2 protein were used as controls in 53.8 and 46.15 % of these articles, respectively, and were evaluated separately; their frequent use was questioned. Subsequently, articles that evaluated other assay platforms, such as immunochromatography, immunosensors, and others, were also reported and evaluated. Finally, data relative to validation studies of commercial kits were briefly discussed. Our results show that there are several antigens with great potential for the development of accurate diagnostic tools, but further testing is required. The critical analysis also brings insights that can be useful for more assertive diagnostic development of more robust tools for CVL serodiagnosis.