Heterologous Expression and Immunogenic Potential of the Most Abundant Phospholipase A2 from Coral Snake Micrurus dumerilii to Develop Antivenoms

Micrurus dumerilii is a coral snake of clinic interest in Colombia. Its venom is mainly composed of phospholipases A₂ being MdumPLA₂ the most abundant protein. Nevertheless, Micrurus species produce a low quantity of venom, which makes it difficult to produce anticoral antivenoms. Therefore, in this work, we present the recombinant expression of MdumPLA₂ to evaluate its biological activities and its immunogenic potential to produce antivenoms. For this, a genetic construct rMdumPLA₂ was cloned into the pET28a vector and expressed heterologously in bacteria. His-rMdumPLA₂ was extracted from inclusion bodies, refolded in vitro, and isolated using affinity and RP-HPLC chromatography. His-rMdumPLA₂ was shown to have phospholipase A₂ activity, a weak anticoagulant effect, and induced myonecrosis and edema. The anti-His-rMdumPLA₂ antibodies produced in rabbits recognized native PLA₂, the complete venom of M. dumerilii, and a phospholipase from another species of the Micrurus genus. Antibodies neutralized 100% of the in vitro phospholipase activity of the recombinant toxin and a moderate percentage of the myotoxic activity of M. dumerilii venom in mice. These results indicate that His-rMdumPLA₂ could be used as an immunogen to improve anticoral antivenoms development. This work is the first report of an M. dumerilii functional recombinant PLA₂.

Protein composition and biochemical characterization of venom from Sonoran Coral Snakes (Micruroides euryxanthus)

The elapid genus, Micruroides, is considered the sister clade of all New World coral snakes (Genus Micrurus), is monotypic, and is represented by Sonoran Coral Snakes, Micruroides euryxanthus. Coral snakes of the genus Micrurus have been reported to have venoms that are predominantly composed of phospholipases A₂ (PLA₂) or three finger toxins (3FTx), but the venoms of the genus Micruroides are almost completely unstudied. Here, we present the first description of the venom of M. euryxanthus including identification of some proteins as well as transcriptomic, and biological activity assays. The most abundant components within M. euryxanthus venom are 3FTxs (62.3%) and there was relatively low proportion of PLA₂s (14.2%). The venom phenotype supports the hypothesis that the common ancestor of Micrurus and Micruroides had a 3FTx-dominated venom. Within the venom, there were two nearly identical α-neurotoxins (α-Ntx), one of which was designated Eurytoxin, that account for approximately 60% of the venom's lethality to mice. Eurytoxin was cloned, expressed in a soluble and active form, and used to produce rabbit hyperimmune serum. This allowed the analysis of its immunochemical properties, showing them to be different from the recombinant αNTx D.H., present in the venoms of some species of Micrurus. Finally, we observed that the commercial antivenom produced in Mexico for coral snake envenomation is unable to neutralize the lethality from M. euryxanthus venom. This work allowed the classification of Micruroides venom into the 3FTx-predominant group and identified the main components responsible for toxicity to mice.

What about COVID-19 and arachidonic acid pathway?

Background and objective

COVID-19 is a highly contagious viral disease. In this study, we tried to define and discuss all the findings on the potential association between arachidonic acid (AA) pathway and COVID-19 pathophysiology.

Methods

A literature search across PubMed, Scopus, Embase, and Cochrane database was conducted. A total of 25 studies were identified.

Results

The data elucidated that COX-2 and prostaglandins (PGs), particularly PGE₂, have pro-inflammatory action in COVID-19 pathophysiology. Arachidonic acid can act as endogenous antiviral compound. A deficiency in AA can make humans more susceptible to COVID-19. Targeting these pro-inflammatory mediators may help in decreasing the mortality and morbidity rate in COVID-19 patients.

Conclusions

PGE₂ levels and other PGs levels should be measured in patients with COVID-19. Lowering the PGE₂ levels through inhibition of human microsomal prostaglandin E synthase-1 (mPGES-1) can enhance the host immune response against COVID-19. In addition, the hybrid compounds, such as COX-2 inhibitors/TP antagonists, can be an innovative treatment to control the overall balance between AA mediators in patients with COVID-19.

Mucosal expression of defensin-5, soluble phospholipase A2 and lysozyme in the intestine in a rat model of acute liver failure and its relationship to intestinal bacterial translocation

INTRODUCTION

To study the expression of defensin-5 (RD-5), soluble phospholipase A2 (sPLA2) and lysozyme in the intestine in a rat model of acute liver failure and its relationship with intestinal bacterial translocation (BT).

PATIENTS AND METHODS

Sprague-Dawley (SD) rats were divided into two groups. The experimental group was divided into five subgroups according to the lapsing time after the model was established, which were designated accordingly as 8h, 16h, 24h, 48h, and 72h groups. Acute liver failure (ALF) model was induced by intraperitoneal injection of 10% d-galactosamine. The homogenates of mesenteric lymph nodes (MLNs), liver and spleen from each group were cultured in agar to determine the bacterial outgrowth. The mRNA expression of RD-5, sPLA2, lysozyme and the protein expression of sPLA2, lysozyme were determined.

RESULTS

No bacteria grew in the organ cultures from the control group while experimental groups had positive cultures. Expression of the RD-5 and sPLA2 mRNA in the experimental groups gradually increased at early time points and peaked 16h after induction of ALF, then progressively decreased. The mRNA expression of lysozyme in the experimental group peaked at 8h after ALF induction, then progressively decreased. Similar results were obtained with Western blot and immunohistochemical staining.

DISCUSSION

The immune barrier function of the ileal mucosa in the rat model of acute liver failure was compromised as demonstrated by the decreased expression of RD-5, sPLA2 and lysozyme in Paneth cells along with increased intestinal bacterial translocation.

Venoms of Iranian Scorpions (Arachnida, Scorpiones) and Their Potential for Drug Discovery

Scorpions, a characteristic group of arthropods, are among the earliest diverging arachnids, dating back almost 440 million years. One of the many interesting aspects of scorpions is that they have venom arsenals for capturing prey and defending against predators, which may play a critical role in their evolutionary success. Unfortunately, however, scorpion envenomation represents a serious health problem in several countries, including Iran. Iran is acknowledged as an area with a high richness of scorpion species and families. The diversity of the scorpion fauna in Iran is the subject of this review, in which we report a total of 78 species and subspecies in 19 genera and four families. We also list some of the toxins or genes studied from five species, including Androctonus crassicauda, Hottentotta zagrosensis, Mesobuthus phillipsi, Odontobuthus doriae, and Hemiscorpius lepturus, in the Buthidae and Hemiscorpiidae families. Lastly, we review the diverse functions of typical toxins from the Iranian scorpion species, including their medical applications.

Corticotropin-releasing hormone receptors mediate apoptosis via cytosolic calcium-dependent phospholipase A₂ and migration in prostate cancer cell RM-1

Peripheral corticotropin-releasing hormone receptors (CRHRs) are G protein-coupled receptors that play different roles depending on tissue types. Previously, we discovered the mechanism of CRHR-mediated apoptosis of mouse prostate cancer cell line (RM-1) to be a change of Bcl-2:Bax ratio, and CRH was found to inhibit transforming growth factor β migration of breast cancer cells via CRHRs. In the present study, we investigated cytosolic calcium-dependent phospholipase A2 (cPLA2) bridging CRHR activations and Bcl-2:Bax ratio and the effect of CRHR activation on cell migration. Silencing of cPLA2 attenuated a CRHR1 agonist, CRH-induced apoptosis, and the decrease of the Bcl-2:Bax ratio, whereas silencing of cPLA2 aggravated CRHR2 agonist, Urocortin 2 (Ucn2)-inhibited apoptosis, and the increase of the Bcl-2:Bax ratio. CRH in a time- and concentration-dependent manner increased cPLA2 expression mainly through interleukin 1β (IL1β) upregulation. Ucn2 decreased cPLA2 expression through neither tumor necrosis factor α nor IL1β. CRH-suppressed decay of cPLA2 mRNA and Ucn2 merely suppressed its production. Overexpression of CRHR1 or CRHR2 in HEK293 cells correspondingly upregulated or downregulated cPLA2 expression after CRH or Ucn2 stimulation respectively. In addition, both CRH and Ucn2 induced migration of RM-1 cells. Our observation not only established a relationship between CRHRs and cell migration but also for the first time, to our knowledge, demonstrated that cPLA2 participates in CRHR1-induced apoptosis and CRHR2-inhibited apoptosis.

Rickettsia typhi possesses phospholipase A2 enzymes that are involved in infection of host cells

The long-standing proposal that phospholipase A2 (PLA2) enzymes are involved in rickettsial infection of host cells has been given support by the recent characterization of a patatin phospholipase (Pat2) with PLA2 activity from the pathogens Rickettsia prowazekii and R. typhi. However, pat2 is not encoded in all Rickettsia genomes; yet another uncharacterized patatin (Pat1) is indeed ubiquitous. Here, evolutionary analysis of both patatins across 46 Rickettsia genomes revealed 1) pat1 and pat2 loci are syntenic across all genomes, 2) both Pat1 and Pat2 do not contain predicted Sec-dependent signal sequences, 3) pat2 has been pseudogenized multiple times in rickettsial evolution, and 4) ubiquitous pat1 forms two divergent groups (pat1A and pat1B) with strong evidence for recombination between pat1B and plasmid-encoded homologs. In light of these findings, we extended the characterization of R. typhi Pat1 and Pat2 proteins and determined their role in the infection process. As previously demonstrated for Pat2, we determined that 1) Pat1 is expressed and secreted into the host cytoplasm during R. typhi infection, 2) expression of recombinant Pat1 is cytotoxic to yeast cells, 3) recombinant Pat1 possesses PLA2 activity that requires a host cofactor, and 4) both Pat1 cytotoxicity and PLA2 activity were reduced by PLA2 inhibitors and abolished by site-directed mutagenesis of catalytic Ser/Asp residues. To ascertain the role of Pat1 and Pat2 in R. typhi infection, antibodies to both proteins were used to pretreat rickettsiae. Subsequent invasion and plaque assays both indicated a significant decrease in R. typhi infection compared to that by pre-immune IgG. Furthermore, antibody-pretreatment of R. typhi blocked/delayed phagosomal escapes. Together, these data suggest both enzymes are involved early in the infection process. Collectively, our study suggests that R. typhi utilizes two evolutionary divergent patatin phospholipases to support its intracellular life cycle, a mechanism distinguishing it from other rickettsial species.

Hippocampal gene network analysis in an experimental model of posttraumatic epilepsy

In the present study, we performed comprehensive gene expression and gene network analyses using a DNA microarray to elucidate the molecular events responsible for the pathology of posttraumatic epilepsy at the partial seizure stage. We used an experimental posttraumatic epilepsy model of amygdalar focal FeCl(3)-injected rats and compared gene expression profiles in the hippocampus at the partial seizure stage (less than stage 3 on Racine's convulsion scale) and that of sham-operated animals. At the partial seizure stage, upregulation of phospholipase A2 (PLA2) and lipid metabolism were observed, which have been reported to be caused by brain injury and seizures in previous studies. Furthermore, significant upregulation of genes related to inflammation and the immune system was observed. These molecular changes in PLA2 and lipid metabolism may be related to seizure propagation.

Increased expression and activation of cytosolic phospholipase A2 in the spinal cord of patients with sporadic amyotrophic lateral sclerosis

Compelling evidence identifies a link between cytotoxic effects of cytosolic phospholipase A2 (cPLA2) activity and neuron death in cell cultures. cPLA2 catalyzes the hydrolysis of membrane phospholipids to produce and release arachidonate, leading to plasma membrane injury, inflammatory response and subsequent cell death. To assess a role for cPLA2 in the pathomechanism of amyotrophic lateral sclerosis (ALS), we performed immunohistochemical, immunoblot, and densitometric analyses of cPLA2 and its active form phosphorylated at S505 (p-cPLA2) on spinal cords obtained at autopsy from ten sporadic ALS patients and ten age-matched controls. On sections, immunoreactivities for cPLA2 and p-cPLA2 were distinct and localized in almost all of the motor neurons, reactive astrocytes, and activated microglia in the ALS cases, while immunoreactivities were only weak or not at all observed in neurons and glia in the control cases. On immunoblots, both the cPLA2/β-actin density ratio and the p-cPLA2/cPLA2 density ratio were significantly increased in the ALS group compared to the control group. There was no significant link between the densitometric data and the clinical phenotypes, age at death or disease duration of the ALS patients. These results provide in vivo evidence for increased expression and activation of cPLA2 in motor neurons, reactive astrocytes, and activated microglia in ALS, suggesting occurrence of arachidonate cascade-induced motor neuron death via cell-autonomous and/or non-cell-autonomous mechanisms.

Expression of a mutated phospholipase A2 in transgenic Aedes fluviatilis mosquitoes impacts Plasmodium gallinaceum development

The genetic manipulation of mosquito vectors is an alternative strategy in the fight against malaria. It was previously shown that bee venom phospholipase A2 (PLA2) inhibits ookinete invasion of the mosquito midgut although mosquito fitness was reduced. To maintain the PLA2 blocking ability without compromising mosquito biology, we mutated the protein-coding sequence to inactivate the enzyme while maintaining the protein's structure. DNA encoding the mutated PLA2 (mPLA2) was placed downstream of a mosquito midgut-specific promoter (Anopheles gambiae peritrophin protein 1 promoter, AgPer1) and this construct used to transform Aedes fluviatilis mosquitoes. Four different transgenic lines were obtained and characterized and all lines significantly inhibited Plasmodium gallinaceum oocyst development (up to 68% fewer oocysts). No fitness cost was observed when this mosquito species expressed the mPLA2.