Molecular cloning and characterization of Plasmodium falciparum transketolase

The pentose phosphate pathway (PPP) is an important metabolic pathway for yielding reducing power in the form of NADPH and production of pentose sugar needed for nucleic acid synthesis. Transketolase, the key enzyme of non-oxidative arm of PPP, plays a vital role in the survival/replication of the malarial parasite. This enzyme in Plasmodium falciparum is a novel drug target as it has least homology with the human host. In the present study, the P. falciparum transketolase (PfTk) was expressed, localized and biochemically characterized. The recombinant PfTk harboring transketolase activity catalyzed the oxidation of donor substrates, fructose-6-phosphate (F6P) and hydroxypyruvate (HP), with K(m)(app) values of 2.25 and 4.78 mM, respectively. p-Hydroxyphenylpyruvate (HPP) was a potent inhibitor of PfTk, when hydroxypyruvate was used as a substrate, exhibiting a K(i) value of 305 microM. At the same time, noncompetitive inhibition was observed with F6P. The native PfTk is a hexamer with subunit molecular weight of 70kDa, which on treatment with low concentrations of guanidine hydrochloride (GdmCl) dissociated into functionally active dimers. This protein was localized in the cytosol and nucleus of the parasite as studied by confocal microscopy. A model structure of PfTk was constructed based on the crystal structure of the transketolases of Saccharomyces cerevisae, Leishmania mexicana and Escherichia coli to assess the structural homology. Consistent with the homology modeling predictions, CD analysis indicated that PfTk is composed of 39% alpha-helices and 26% beta-sheets. The availability of a structural model of PfTk and the observed differences in its kinetic properties compared to the host enzyme may facilitate designing of novel inhibitors of PfTk with potential anti-malarial activity.     

Characterization of a PRL protein tyrosine phosphatase from Plasmodium falciparum

Isoprenylated proteins have important functions in cell growth and differentiation of eukaryotic cells. Inhibitors of protein prenylation in malaria have recently shown strong promise as effective antimalarials. In studying protein prenylation in the malaria protozoan parasite Plasmodium falciparum, we have shown earlier that the incubation of P. falciparum cells with (3)H-prenol precursors resulted in various size classes of labeled proteins. To understand the physiological function of prenylated proteins of malaria parasites, that are targets of prenyltransferase inhibitors, we searched the PlasmoDB database for proteins containing the C-terminus prenylation motif. We have identified, among other potentially prenylated proteins, an orthologue of a PRL (protein of regenerating liver) subgroup protein tyrosine phosphatases, termed PfPRL. Here, we show that PfPRL is expressed in the parasite's intraerythrocytic stages, where it partially associates with endoplasmic reticulum and within a subcompartment of the food vacuole. Additionally, PfPRL targeting parallels that of apical membrane antigen-1 in developing merozoites. Recombinant PfPRL shows phosphatase activity that is preferentially inhibited by a tyrosine phosphatase inhibitor suggesting that PfPRL functions as a tyrosine phosphatase. Recombinant PfPRL can also be farnesylated in vitro. Inhibition of malarial farnesyltransferase activity can be achieved with the heptapetide RKCHFM, which corresponds to the C-terminus of PfPRL. This study provides the first evidence for expression of enzymatically active PRL-related protein tyrosine phosphatases in malarial parasites, and demonstrates the potential of peptides derived from Plasmodium prenylated proteins as malarial farnesyltransferase inhibitors.     

Mesangioproliferative glomerulonephritis: an important glomerulonephritis in nephrotic syndrome of young adult

Mesangioproliferative glomerulonephritis (MesPGN) consists 10% of the total renal biopsy of glomerulonephritis. Aim of the present study was to find out clinicopathological changes in MesPGN and differences between diffuse and focal variety. MesPGN was seen mostly in young adults with mean age of 28.63 years for males and 26.3 years for females. Male predominance was noted (M:F ratio - 1.4:1). About 70.83% patient presented with edema feet, followed by hypertension (29.19%), fever (16.66%), oliguria, nausea and vomiting (10.41%). Urine analysis in 50 patients revealed that 70% patients presented with nephrotic-range proteinuria, 36% patients with microscopic hematuria and 56% patients with leukocyturia. Statistically, no significant difference was found in clinical features of diffuse and focal MesPGN. Microscopic comparison between diffuse and focal variety showed that significant increase of focal glomerular basement membrane thickening, focal endothelial cell proliferation, focal smooth muscle hyperplasia, hyaline sclerosis and vasculitis was more common in diffuse variety. In focal variety, Capillary loop congestion, periglomerulitis, cloudy swelling and vacuolar degeneration in tubules were significantly more as compared to diffuse variety. Details of the clinical features, special laboratory tests and histological details revealed that diffuse variety had systemic diseases, which included Wegner's granulomatosis, microscopic polyangitis, Henoch's schonlein purpura, systemic lupus erythematosus (two cases) and one case each of Kimura's disease, pyelonephritis and tuberculosis. Only one case of focal MesPGN showed tuberculosis. Thus, our study concludes that MesPGN is an important cause of nephrotic syndrome among young adults. Secondly, search for some other diseases should be made and thirdly, if biopsy shows focal mesangial cell proliferations in minimal change glomerulonephritis (MCGN), it should be diagnosed as focal MesPGN rather than MCGN because these cases show recurrences.     

Laboratory and field evaluation of the fungus Chrysosporium lobatum against the larvae of the mosquito Culex quinquefasciatus

Eleven fungal species in three genera were isolated from the soil at Agra, India by the feather-baiting technique. Out of the 11 species, Chrysosporium lobatum Scharapov, a deuteromycetous (Moniliales: Moniliaceae) fungus, caused high mortality of Culex quinquefasciatus Say (Diptera: Culicidae) larvae in the laboratory. Laboratory and field trials were carried out to study the efficacy of C. lobatum against various instars of C. quinquefasciatus. In the laboratory bioassays, first, second and third instar larvae were assessed separately. Conidia of C. lobatum that were 15 days old were used both in laboratory and field bioassays. Six different concentrations were used in the laboratory bioassays (10, 10³, 10⁴, 5 × 10⁴, 10⁵ and 10⁶ conidia/mL), and one concentration was tested in the field trials (10⁶ conidia/mL). The LC₅₀ values with 95% fiducial limits and probit equations were calculated by the probit analysis. Significant (analysis o.f variance (ANOVA): P < 0.0001) mortality difference between the instars of C. quinquefasciatus was observed after 72 h of exposure to conidia of C. lobatum. The third instar C. quinquefasciatus were 319- and 25-fold more susceptible to C. lobatum (0.47 × 10³ conidia/mL) than the first and second instars, respectively. The cuticle of the abdominal region and anal papillae were densely covered by the C. lobatum conidia. In the field trials, populations had declined significantly (t test, P = 0.003) 15 days after inoculation in the four test pools. Significantly (t test, P = 0.03) higher mortality was observed in the pools with water quality that was lower in total dissolved solids, hardness, chemical oxygen demand and conductivity. Based on the performance and survival in the trial, C. lobatum may be considered as a bio-control agent of mosquitoes.     

Aberrant splicing of the PTPRD gene mimics microdeletions identified at this locus in neuroblastomas

Neuroblastoma (NBL), a pediatric tumor arising from precursor cells of the sympathetic nervous system, is characterized by numerous recurrent large-scale chromosomal imbalances. High resolution oligonucleotide array CGH analysis of NBL has previously identified microdeletions that are confined to the 5' UTR of the protein tyrosine phosphatase receptor D (PTPRD) gene, implicating this gene in the pathogenesis of these tumors. Here, we demonstrate that the 5' UTR of this gene, consisting of 11 noncoding exons, is also aberrantly spliced in >50% of NBL primary tumors and cell lines. The loss of exons from the 5' UTR region through aberrant splicing results in aberrant mRNA isoforms that are similar to those generated through microdeletions. The aberrant splicing or microdeletion of 5' UTR exons in such a high proportion of tumors indicates that loss of these exons dys-regulates the mRNA sequence. To further validate the role of PTPRD in NBL, we have examined the expression of this gene in normal fetal adrenal neuroblasts (the cell of origin of NBL) and in tumors from patients with either low stage or high stage disease. This gene is expressed at lower levels in high stage NBL tumors, particularly those with amplification of MYCN, relative to low stage tumors or normal fetal adrenal neuroblasts, consistent with the possibility that loss of the 5' UTR exons have destabilized the mRNA.     

Unusual associations of pachydermoperiostosis: a case report

Primary hypertrophic osteoarthropathy (HOA), or pachydermoperiostosis, is a rare benign disorder of unknown etiology. It is characterized by clubbing, periosteal reaction, and thickening of the skin. Disease usually progresses slowly, and natural arrest may occur. Reported herein is the case of a 28-year-old male patient with progressively increasing swelling of large joints of lower limbs with severe anemia. He was diagnosed as a case of pachydermoperiostosis with myelofibrosis, which is a rare association. The development of myelofibrosis makes primary HOA a disease with unfavorable outcome.     

Highly sensitive amperometric immunosensor for detection of Plasmodium falciparum histidine-rich protein 2 in serum of humans with malaria: comparison with a commercial kit

A disposable amperometric immunosensor was developed for the detection of Plasmodium falciparum histidine-rich protein 2 (PfHRP-2) in the sera of humans with P. falciparum malaria. For this purpose, disposable screen-printed electrodes (SPEs) were modified with multiwall carbon nanotubes (MWCNTs) and Au nanoparticles. The electrodes were characterized by cyclic voltammetry, scanning electron microscopy, and Raman spectroscopy. In order to study the immunosensing performances of modified electrodes, a rabbit anti-PfHRP-2 antibody (as the capturing antibody) was first immobilized on an electrode. Further, the electrode was exposed to a mouse anti-PfHRP-2 antibody from a serum sample (as the revealing antibody), followed by a rabbit anti-mouse immunoglobulin G-alkaline phosphatase conjugate. The immunosensing experiments were performed on bare SPEs, MWCNT-modified SPEs, and Au nanoparticle- and MWCNT-modified SPEs (Nano-Au/MWCNT/SPEs) for the amperometric detection of PfHRP-2 in a solution of 0.1 M diethanolamine buffer, pH 9.8, by applying a potential of 450 mV at the working electrode. Nano-Au/MWCNT/SPEs yielded the highest-level immunosensing performance among the electrodes, with a detection limit of 8 ng/ml. The analytical results of immunosensing experiments with human serum samples were compared with the results of a commercial Paracheck Pf test, as well as the results of microscopy. The specificities, sensitivities, and positive and negative predictive values of the Paracheck Pf and amperometric immunosensors were calculated by taking the microscopy results as the “gold standard.” The Paracheck Pf kit exhibited a sensitivity of 79% (detecting 34 of 43 positive samples; 95% confidence interval [CI], 75 to 86%) and a specificity of 81% (correctly identifying 57 of 70 negative samples; 95% CI, 76 to 92%), whereas the developed amperometric immunosensor showed a sensitivity of 96% (detecting 41 of 43 positive samples; 95% CI, 93 to 98%) and a specificity of 94% (correctly identifying 66 of 70 negative samples; 95% CI, 92 to 99%). The developed method is more sensitive and specific than the Paracheck Pf kit.     

Cerebral myogenic reactivity and blood flow in type 2 diabetic rats: role of peroxynitrite in hypoxia-mediated loss of myogenic tone

Dysregulation of cerebral vascular function and, ultimately, cerebral blood flow (CBF) may contribute to complications such as stroke and cognitive decline in diabetes. We hypothesized that 1) diabetes-mediated neurovascular and myogenic dysfunction impairs CBF and 2) under hypoxic conditions, cerebral vessels from diabetic rats lose myogenic properties because of peroxynitrite (ONOO(-))-mediated nitration of vascular smooth muscle (VSM) actin. Functional hyperemia, the ability of blood vessels to dilate upon neuronal stimulation, and myogenic tone of isolated middle cerebral arteries (MCAs) were assessed as indices of neurovascular and myogenic function, respectively, in 10- to 12-week control and type 2 diabetic Goto-Kakizaki rats. In addition, myogenic behavior of MCAs, nitrotyrosine (NY) levels, and VSM actin content were measured under normoxic and hypoxic [oxygen glucose deprivation (OGD)] conditions with and without the ONOO(-) decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl) prophyrinato iron (III), chloride (FeTPPs). The percentage of myogenic tone was higher in diabetes, and forced dilation occurred at higher pressures. Functional hyperemia was impaired. Consistent with these findings, baseline CBF was lower in diabetes. OGD reduced the percentage of myogenic tone in both groups, and FeTPPs restored it only in diabetes. OGD increased VSM NY in both groups, and although FeTPPs restored basal levels, it did not correct the reduced filamentous/globular (F/G) actin ratio. Acute alterations in VSM ONOO(-) levels may contribute to hypoxic myogenic dysfunction, but this cannot be solely explained by the decreased F/G actin ratio due to actin nitration, and mechanisms may differ between control and diabetic animals. Our findings also demonstrate that diabetes alters the ability of cerebral vessels to regulate CBF under basal and hypoxic conditions.