Methotrexate Promotes Platelet Apoptosis via JNK-Mediated Mitochondrial Damage: Alleviation by N-Acetylcysteine and N-Acetylcysteine Amide

Thrombocytopenia in methotrexate (MTX)-treated cancer and rheumatoid arthritis (RA) patients connotes the interference of MTX with platelets. Hence, it seemed appealing to appraise the effect of MTX on platelets. Thereby, the mechanism of action of MTX on platelets was dissected. MTX (10 μM) induced activation of pro-apoptotic proteins Bid, Bax and Bad through JNK phosphorylation leading to ΔΨm dissipation, cytochrome c release and caspase activation, culminating in apoptosis. The use of specific inhibitor for JNK abrogates the MTX-induced activation of pro-apoptotic proteins and downstream events confirming JNK phosphorylation by MTX as a key event. We also demonstrate that platelet mitochondria as prime sources of ROS which plays a central role in MTX-induced apoptosis. Further, MTX induces oxidative stress by altering the levels of ROS and glutathione cycle. In parallel, the clinically approved thiol antioxidant N-acetylcysteine (NAC) and its derivative N-acetylcysteine amide (NACA) proficiently alleviate MTX-induced platelet apoptosis and oxidative damage. These findings underpin the dearth of research on interference of therapeutic drugs with platelets, despite their importance in human health and disease. Therefore, the use of antioxidants as supplementary therapy seems to be a safe bet in pathologies associated with altered platelet functions.     

An overview on genus garcinia: phytochemical and therapeutical aspects

The genus Garcinia belongs to the family Clusiaceae and has been involved in ayurvedic preparations to medicate various pathophysiological disorders. The bioactive molecules like hydroxycitric acid (HCA), flavonoids, terpenes, polysaccharides, procyanidines and polyisoprenylated benzophenone derivatives like garcinol, xanthochymol and guttiferone isoforms have been isolated from the genus Garcinia. The genus has received the attention of pharmaceutical industries due to their immense remedial qualities. The HCA has been known for its hypolipidemic property. The polyisoprenylated benzophenone and xanthone derivatives are known for their antioxidant, apoptotic, anti-cancer, anti-inflammatory, anti-bacterial, anti-viral, anti-fungal, anti-ulcer, anti-protozoal, and HAT inhibiting properties. Future studies on the synthesis of therapeutically important products and their analogs and evaluation of their safety and efficacy would be of great interest. Though the genus includes more than 300 species, we have made an effort to conceive the curative qualities of bioactive compounds of selected plants to the best of our knowledge.     

EMILIN2 Regulates Platelet Activation,Thrombus Formation,and Clot Retraction

Thrombosis, like other cardiovascular diseases, has a strong genetic component, with largely unknown determinants. EMILIN2, Elastin Microfibril Interface Located Protein2, was identified as a candidate gene for thrombosis in mouse and human quantitative trait loci studies. EMILIN2 is expressed during cardiovascular development, on cardiac stem cells, and in heart tissue in animal models of heart disease. In humans, the EMILIN2 gene is located on the short arm of Chromosome 18, and patients with partial and complete deletion of this chromosome region have cardiac malformations. To understand the basis for the thrombotic risk associated with EMILIN2, EMILIN2 deficient mice were generated. The findings of this study indicate that EMILIN2 influences platelet aggregation induced by adenosine diphosphate, collagen, and thrombin with both EMILIN2-deficient platelets and EMILIN2-deficient plasma contributing to the impaired aggregation response. Purified EMILIN2 added to platelets accelerated platelet aggregation and reduced clotting time when added to EMILIN2-deficient mouse and human plasma. Carotid occlusion time was 2-fold longer in mice with platelet-specific EMILIN2 deficiency, but stability of the clot was reduced in mice with both global EMILIN2 deficiency and with platelet-specific EMILIN2 deficiency. In vitro clot retraction was markedly decreased in EMILIN2 deficient mice, indicating that platelet outside-in signaling was dependent on EMILIN2. EMILIN1 deficient mice and EMILIN2:EMILIN1 double deficient mice had suppressed platelet aggregation and delayed clot retraction similar to EMILIN2 mice, but EMILIN2 and EMILIN1 had opposing affects on clot retraction, suggesting that EMILIN1 may attenuate the effects of EMILIN2 on platelet aggregation and thrombosis. In conclusion, these studies identify multiple influences of EMILIN2 in pathophysiology and suggest that its role as a prothrombotic risk factor may arise from its effects on platelet aggregation and platelet mediated clot retraction.     

Expression of Functional Plasmodium falciparum Enzymes Using a Wheat Germ Cell-Free System

One decade after the sequencing of the Plasmodium falciparum genome, 95% of malaria proteins in the genome cannot be expressed in traditional cell-based expression systems, and the targets of the best new leads for antimalarial drug discovery are either not known or not available in functional form. For a disease that kills up to 1 million people per year, routine expression of recombinant malaria proteins in functional form is needed both for the discovery of new therapeutics and for identification of targets of new drugs. We tested the general utility of cell-free systems for expressing malaria enzymes. Thirteen test enzyme sequences were reverse amplified from total RNA, cloned into a plant-like expression vector, and subjected to cell-free expression in a wheat germ system. Protein electrophoresis and autoradiography confirmed the synthesis of products of expected molecular masses. In rare problematic cases, truncated products were avoided by using synthetic genes carrying wheat codons. Scaled-up production generated 39 to 354 μg of soluble protein per 10 mg of translation lysate. Compared to rare proteins where cell-based systems do produce functional proteins, the cell-free yields are comparable or better. All 13 test products were enzymatically active, without failure. This general path to produce functional malaria proteins should now allow the community to access new tools, such as biologically active protein arrays, and lead to the discovery of new chemical functions, structures, and inhibitors of previously inaccessible malaria gene products.     

Propensity of crocin to offset Vipera russelli venom induced oxidative stress mediated neutrophil apoptosis: a biochemical insight

Viper envenomation results in inflammation at the bitten site as well as target organs. Neutrophils and other polymorphonuclear leukocytes execute inflammation resolving mechanism and will undergo apoptosis after completing the task. However, the target specific toxins induce neutrophil apoptosis at the bitten site and in circulation prior to their function, thus reducing their number. Circulating activated neutrophils are major source of inflammatory cytokines and leakage of reactive oxygen species (ROS)/other toxic intermediates resulting in aggravation of inflammatory response at the bitten/target site. Therefore, neutralization of venom induced neutrophil apoptosis reduces inflammation besides increasing the functional neutrophil population. Therefore, the present study investigates the venom induced perturbances in isolated human neutrophils and its neutralization by crocin (Crocus sativus) a potent antioxidant carotenoid. Human neutrophils on treatment with venom resulted in altered ROS generation, intracellular Ca²⁺ mobilization, mitochondrial membrane depolarization, cyt-c translocation, caspase activation, phosphatidylserine externalization and DNA damage. On the other hand significant protection against oxidative stress and apoptosis were evidenced in crocin pre-treated groups. In conclusion the viper venom induces neutrophil apoptosis and results in aggravation of inflammation and tissue damage. The present study demands the necessity of an auxiliary therapy in addition to antivenin therapy to treat secondary/overlooked complications of envenomation.     

The Crystal Structure and Activity of a Putative Trypanosomal Nucleoside Phosphorylase Reveal It to be a Homodimeric Uridine Phosphorylase

Purine nucleoside phosphorylases (PNPs) and uridine phosphorylases (UPs) are closely related enzymes involved in purine and pyrimidine salvage, respectively, which catalyze the removal of the ribosyl moiety from nucleosides so that the nucleotide base may be recycled. Parasitic protozoa generally are incapable of de novo purine biosynthesis; hence, the purine salvage pathway is of potential therapeutic interest. Information about pyrimidine biosynthesis in these organisms is much more limited. Though all seem to carry at least a subset of enzymes from each pathway, the dependency on de novo pyrimidine synthesis versus salvage varies from organism to organism and even from one growth stage to another. We have structurally and biochemically characterized a putative nucleoside phosphorylase (NP) from the pathogenic protozoan Trypanosoma brucei and find that it is a homodimeric UP. This is the first characterization of a UP from a trypanosomal source despite this activity being observed decades ago. Although this gene was broadly annotated as a putative NP, it was widely inferred to be a purine nucleoside phosphorylase. Our characterization of this trypanosomal enzyme shows that it is possible to distinguish between PNP and UP activity at the sequence level based on the absence or presence of a characteristic UP-specificity insert. We suggest that this recognizable feature may aid in proper annotation of the substrate specificity of enzymes in the NP family.     

Thermal inactivation of glucose oxidase. Mechanism and stabilization using additives

Thermal inactivation of glucose oxidase (GOD; beta-d-glucose: oxygen oxidoreductase), from Aspergillus niger, followed first order kinetics both in the absence and presence of additives. Additives such as lysozyme, NaCl, and K2SO4 increased the half-life of the enzyme by 3.5-, 33.4-, and 23.7-fold respectively, from its initial value at 60 degrees C. The activation energy increased from 60.3 kcal mol-1 to 72.9, 76.1, and 88.3 kcal mol-1, whereas the entropy of activation increased from 104 to 141, 147, and 184 cal x mol-1 x deg-1 in the presence of 7.1 x 10-5 m lysozyme, 1 m NaCl, and 0.2 m K2SO4, respectively. The thermal unfolding of GOD in the temperature range of 25-90 degrees C was studied using circular dichroism measurements at 222, 274, and 375 nm. Size exclusion chromatography was employed to follow the state of association of enzyme and dissociation of FAD from GOD. The midpoint for thermal inactivation of residual activity and the dissociation of FAD was 59 degrees C, whereas the corresponding midpoint for loss of secondary and tertiary structure was 62 degrees C. Dissociation of FAD from the holoenzyme was responsible for the thermal inactivation of GOD. The irreversible nature of inactivation was caused by a change in the state of association of apoenzyme. The dissociation of FAD resulted in the loss of secondary and tertiary structure, leading to the unfolding and nonspecific aggregation of the enzyme molecule because of hydrophobic interactions of side chains. This confirmed the critical role of FAD in structure and activity. Cysteine oxidation did not contribute to the nonspecific aggregation. The stabilization of enzyme by NaCl and lysozyme was primarily the result of charge neutralization. K2SO4 enhanced the thermal stability by primarily strengthening the hydrophobic interactions and made the holoenzyme a more compact dimeric structure.