β-keto amyrin isolated from Cryptostegia grandiflora R. br. inhibits inflammation caused by Daboia russellii viper venom: Direct binding of β-keto amyrin to phospholipase A2

The search for mechanism-based anti-inflammatory therapies is of fundamental importance to avoid undesired off-target effects. Phospholipase A2 (PLA2) activity is a potential molecular target for anti-inflammatory drugs because it fuels arachidonic acid needed to synthesize inflammation mediators, such as prostaglandins. Herein, we aim to investigate the molecular mechanism by which β-keto amyrin isolated from a methanolic extract of Cryptostegia grandiflora R. Br. Leaves can inhibit inflammation caused by Daboia russellii viper (DR) venom that mainly contains PLA2. We found that β-keto amyrin neutralizes DR venom-induced paw-edema in a mouse model. Molecular docking of PLA2 with β-keto amyrin complex resulted in a higher binding energy score of -8.86 kcal/mol and an inhibition constant of 611.7 nM. Diclofenac had a binding energy of -7.04 kcal/mol and an IC50 value of 620 nM, which predicts a poorer binding interaction than β-keto amyrin. The higher conformational stability of β-keto amyrin interaction compared to diclofenac is confirmed by molecular dynamics simulation. β-keto amyrin isolated from C. grandiflora inhibits the PLA2 activity contained in Daboia russellii viper venom. The anti-inflammatory property of β-keto amyrin is due to its direct binding into the active site of PLA2, thus inhibiting its enzyme activity.

Antiophidic potential of chlorogenic acid and rosmarinic acid against Bothrops leucurus snake venom

Bothrops leucurus is responsible for most cases of snakebite in Northeast Brazil; however, this species is not included in the pool of venoms used in antivenom production in Brazil. The serotherapy has logistical and effectiveness limitations, which stimulates the search for therapeutic alternatives. Chlorogenic acid and rosmarinic acid present several biological activities, but their antiophidic potential has been poorly explored. Thus, the aim of this approach was to evaluate the potential inhibitory effects of these compounds on B. leucurus venom. Initially, the enzymatic inhibition of toxins was evaluated in vitro. Then, anti-hemorrhagic, anti-myotoxic, and anti-edematogenic assays were performed in vivo, as well analysis of several biochemical markers and hemostatic parameters. In addition, the interaction of inhibitors with SVMP and PLA2 was investigated by docking analysis. Results revealed that compounds inhibited in vitro the enzymatic activities and venom-induced edema, with a decrease in both myeloperoxidase and interleukin quantification. The inhibitors also attenuated the hemorrhagic and myotoxic actions and mitigated changes in serum biochemical and hemostatic markers, as well as decreased lipid peroxidation in liver and kidney tissues. Docking analysis revealed attractive interactions of both inhibitors with the zinc-binding site of SVMP and, in the case of PLA2, chlorogenic acid showed a similar inhibition mechanism to that described for rosmarinic acid. The results evidenced the antiophidic potential of both compounds, which showed higher efficiency than antivenom serum. Thus, both inhibitors are promising candidates for future adjuvants to be used to complement antivenom serotherapy.

Bee venom phospholipase A2 alleviates collagen-induced polyarthritis by inducing Foxp3+ regulatory T cell polarization in mice

The mechanism underlying bee venom (BV) therapy is still controversial, with opinions ranging from constituent-based pharmacological action to homeopathic-like activity. The purpose of this study was to examine whether BV phospholipase A2 (bvPLA2), an enzymatic component of BV, is a novel anti-inflammatory and anti-arthritic mediator capable of stimulating CD25+ Foxp3+ regulatory T cell (Treg) polarization in a mouse model of human rheumatoid arthritis (RA). An experimental model of RA was established in male DBA/1 mouse by 2-week-interval injections of 100 μg type II collagen emulsified in complete (first injection) or incomplete Freund's adjuvant (second injection) at the base of the tail. During arthritis development, bvPLA2 (0.1, 0.5, 1.0 mg/kg) and/or Treg inhibitors such as anti-CD25 antibodies and peptide 60 (P60) were injected intraperitoneally for 5 weeks. Arthritic symptoms and the expansion of Tregs were then assessed by behavioral assessments, histological and micro-CT imaging, and flow cytometry. bvPLA2 injections significantly alleviated arthritic behaviors such as squeaking and joint swelling, consistent with changes seen on both histological and micro-CT images. The anti-arthritic effects of bvPLA2 were blocked by intraperitoneal injections of 0.25 mg/kg anti-CD25 antibody and 10 μg/kg P60, as determined by behavioral assessments. Flow cytometric analysis of dendritic cells, B cells, and major T cell subsets from spleens revealed a significant depletion of Tregs following anti-CD25 antibody, but not P60, treatment. bvPLA2 treatment exerted significant anti-inflammatory and anti-arthritic activities in a mouse model of RA via the induction of Tregs.

Bioassay-guided fractionation, phospholipase A2-inhibitory activity and structure elucidation of compounds from leaves of Schumanniophyton magnificum

CONTEXT

Schumanniophyton magnificum Harms (Rubiaceae) is used traditionally in Nigeria for the treatment of snake bites. Snake venom contains phospholipase A₂ (PLA₂) which plays a key role in causing inflammation and pain.

OBJECTIVE

To assess the anti-inflammatory effect of the methanol extract of Schumanniophyton magnificum (MESM) leaves through the inhibition of PLA₂ and investigate the compounds responsible for the effect.

MATERIALS AND METHODS

PLA₂-inhibitory activity of MESM was assessed at concentrations of 0.1-0.8 mg/mL using human red blood cells as substrate. Prednisolone was used as the standard control. MESM was subsequently partitioned using n-hexane, dichloromethane, ethyl acetate and aqueous-methanol (90:10 v/v), after which PLA₂-inhibitory activity of the partitions was determined. The best partition was subjected to chromatographic techniques and the fractions obtained were assessed for PLA₂ inhibition at 0.4 mg/mL. Compounds in the most active fraction were determined using Fourier-transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS).

RESULTS

MESM significantly inhibited PLA₂ activity at 0.8 mg/mL (44.253%) compared to prednisolone (35.207%). n-Hexane partition (SMP1) proved more active with inhibition of 55.870% observed at 0.1 mg/mL. Fraction 1 (SMF1) showed the highest PLA₂-inhibitory activity of 58.117%. FTIR studies revealed the presence of some functional groups in SMF1, and GC-MS confirmed the presence of 9 compounds which are first reported in this plant. Hexadecanoic acid, ethyl ester was identified as the major compound (24.906%).

DISCUSSION AND CONCLUSIONS

The PLA₂-inhibitory activity of MESM suggests that its compounds may be explored further in monitoring anti-inflammatory genes affected by the venoms.

Activity-Based Protein Profiling Identifies α-Ketoamides as Inhibitors for Phospholipase A2 Group XVI

Phospholipase A2, group XVI (PLA2G16) is a thiol hydrolase from the HRASLS family that regulates lipolysis in adipose tissue and has been identified as a host factor enabling the cellular entry of picornaviruses. Chemical tools are essential to visualize and control PLA2G16 activity, but they have not been reported to date. Here, we show that MB064, which is a fluorescent lipase probe, also labels recombinant and endogenously expressed PLA2G16. Competitive activity-based protein profiling (ABPP) using MB064 enabled the discovery of α-ketoamides as the first selective PLA2G16 inhibitors. LEI110 was identified as a potent PLA2G16 inhibitor ( Ki = 20 nM) that reduces cellular arachidonic acid levels and oleic acid-induced lipolysis in human HepG2 cells. Gel-based ABPP and chemical proteomics showed that LEI110 is a selective pan-inhibitor of the HRASLS family of thiol hydrolases (i.e., PLA2G16, HRASLS2, RARRES3 and iNAT). Molecular dynamic simulations of LEI110 in the reported crystal structure of PLA2G16 provided insight in the potential ligand-protein interactions to explain its binding mode. In conclusion, we have developed the first selective inhibitor that can be used to study the cellular role of PLA2G16.

Phospholipase A2 is involved in galactosylsphingosine-induced astrocyte toxicity, neuronal damage and demyelination

Krabbe disease is a fatal rare inherited lipid storage disorder affecting 1:100,000 births. This illness is caused by mutations in the galc gene encoding for the enzyme galactosylceramidase (GALC). Dysfunction of GALC has been linked to the toxic build-up of the galactolipid, galactosylsphingosine (psychosine), which induces cell death of oligodendrocytes. Previous studies show that phospholipase A2 (PLA2) may play a role in psychosine induce cell death. Here, we demonstrate that non-selective inhibition of cPLA2/sPLA2 and selective inhibition of cPLA2, but not sPLA2, also attenuates psychosine-induced cell death of human astrocytes. This study shows that extracellular calcium is required for psychosine induced cell death, but intracellular calcium release, reactive oxygen species or release of soluble factors are not involved. These findings suggest a cell autonomous effect, at least in human astrocytes. Supporting a role for PLA2 in psychosine-induced cell death of oligodendrocytes and astrocytes, the results show inhibition of PLA2 attenuates psychosine-induced decrease in the expression of astrocyte marker vimentin as well as myelin basic protein (MBP), myelin oligodendrocyte glycoprotein (MOG) and the neuronal marker SMI-32 in organotypic slice cultures. These findings provide further mechanistic details of psychosine-induced death of glia and suggest a role for PLA2 in the process. This work also supports the proposal that novel drugs for Krabbe disease may require testing on astrocytes as well as oligodendrocytes for more holistic prediction of pre-clinical and clinical efficacy.

Lithium activates brain phospholipase A2 and improves memory in rats: implications for Alzheimer's disease

Phospholipase A2 (Pla2) is required for memory retrieval, and its inhibition in the hippocampus has been reported to impair memory acquisition in rats. Moreover, cognitive decline and memory deficits showed to be reduced in animal models after lithium treatment, prompting us to evaluate possible links between Pla2, lithium and memory. Here, we evaluated the possible modulation of Pla2 activity by a long-term treatment of rats with low doses of lithium and its impact in memory. Wistar rats were trained for the inhibitory avoidance task, treated with lithium for 100 days and tested for perdurability of long-term memory. Hippocampal samples were used for quantifying the expression of 19 brain-expressed Pla2 genes and for evaluating the enzymatic activity of Pla2 using group-specific radio-enzymatic assays. Our data pointed to a significant perdurability of long-term memory, which correlated with increased transcriptional and enzymatic activities of certain members of the Pla2 family (iPla2 and sPla2) after the chronic lithium treatment. Our data suggest new possible targets of lithium, add more information on its pharmacological activity and reinforce the possible use of low doses of lithium for the treatment of neurodegenerative conditions such as the Alzheimer's disease.

[In vitro lipid-lowering and fibrinolytic effects of regulatory leucine-containing glyprolines in human blood]

The lipid-lowering, fibrinolytic, and anticoagulant effects of leucine-containing glyprolines, Pro-Gly-Pro-Leu and Leu-Pro-Gly-Pro, were studied in vitro in the blood of patients with disorders of lipid metabolism. The lipid-lowering impact of glyprolines and their ability to reduce the polymerization and to increase the depolymerization of fibrin in human blood were found. Possible mechanisms of lipolytic action of peptides by means of modulation of the lipid-dependent phospholipase A2 were proposed.

Hyaluronidase, phospholipase A2 and protease inhibitory activity of plants used in traditional treatment of snakebite-induced tissue necrosis in Mali, DR Congo and South Africa

ETHNOPHARMACOLOGICAL RELEVANCE

Snakebite envenomation, every year, causes estimated 5-10,000 mortalities and results in more than 5-15,000 amputations in sub-Saharan Africa alone. Antiserum is not easily accessible in these regions or doctors are simply not available, thus more than 80% of all patients seek traditional practitioners as first-choice. Therefore it is important to investigate whether the plants used in traditional medicine systems contain compounds against the necrosis-inducing enzymes of snake venom.

MATERIALS AND METHODS

Extracts from traditionally used plants from DR Congo, Mali and South Africa were tested in hyaluronidase, phospholipase A2 and protease enzyme bioassays using Bitis arietans and Naja nigricollis as enzyme source.

RESULTS

A total of 226 extracts from 94 different plant species from the three countries, Mali, Democratic Republic of Congo and South Africa were tested in phospholipase A2, proteases and hyaluronidase enzyme assays. Forty plant species showed more than 90% inhibition in one or more assay. Fabaceae, Anacardiaceae and Malvaceae were the families with the highest number of active species, and the active compounds were distributed in different plant parts depending on plant species. Polyphenols were removed in the search for specific enzyme inhibitors against hyaluronidase, phospholipase A2 or proteases from extracts with IC50 values below 100µg/ml. Water extracts of Pupalia lappacea, Combretum molle, Strychnos innocua and Grewia mollis and ethanol extract of Lannea acida and Bauhinia thonningii still showed IC50 values below 100µg/ml in either the hyaluronidase or protease bioassay after removal of polyphenols.

CONCLUSION

As four of the active plants are widely distributed in the areas where the snake species Bitis arietans and Naja nigricollis occur a potential inhibitor of the necrotic enzymes is accessible for many people in sub-Saharan Africa.

Roles of BN52021 in platelet-activating factor pathway in inflammatory MS1 cells

AIM: To determine the effects of BN52021 on platelet-activating factor receptor (PAFR) signaling molecules under lipopolysaccharide (LPS)-induced inflammatory conditions in MS1 cells.

METHODS: MS1 cells (a mouse pancreatic islet endothelial cell line) were grown in Dulbecco’s modified Eagle’s medium supplemented with 10% fetal bovine serum, 2 mmol/L glutamine and 100 μg/mL penicillin/streptomycin in 5% CO₂ at 37 °C. After growth to confluency in media, the cells were processed for subsequent studies. The MS1 cells received 0, 0.1, 1 and 10 μg/mL LPS in this experiment. The viability/proliferation of the cells induced by LPS was observed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric assay. Apoptosis and necrosis of the cells under the inflammatory condition described previously were observed using Hoechst 33342-propidium iodide staining. Adenylate cyclase (AC), phospholipase A₂ (PLA₂), phospholipase Cβ (PLCβ), protein tyrosine kinase (PTK), G protein-coupled receptor kinases (GRK) and p38-mitogen-activated protein kinase (p38 MAPK) mRNA in the PAFR signaling pathway were measured by real-time polymerase chain reaction. The protein expression level of phosphorylated AC (p-AC), phosphorylated PLA₂ (p-PLA₂), phosphorylated PTK (p-PTK), phosphorylated p38 MAPK (p-p38 MAPK), PLCβ and GRK was measured using Western blotting analysis.

RESULTS: The activity of MS1 cells incubated with different concentrations of LPS for 6 h decreased significantly in the 1 μg/mL LPS group (0.49 ± 0.10 vs 0.67 ± 0.13, P < 0.05) and 10 μg/mL LPS group (0.44 ± 0.10 vs 0.67 ± 0.13, P < 0.001), but not in 0.1 μg/mL group. When the incubation time was extended to 12 h (0.33 ± 0.05, 0.32 ± 0.03 and 0.25 ± 0.03 vs 0.69 ± 0.01) and 24 h (0.31 ± 0.01, 0.29 ± 0.03 and 0.25 ± 0.01 vs 0.63 ± 0.01), MS1 cell activity decreased in all LPS concentration groups compared with the blank control (P < 0.001). BN52021 significantly improved the cell activity when its concentration reached 50 μmol/L compared with the group that received LPS treatment alone, which was consistent with the results obtained from fluorescence staining. The mRNAs levels of AC (4.02 ± 0.14 vs 1.00 ± 0.13), GRK (2.63 ± 0.03 vs 1.00 ± 0.12), p38 MAPK (3.87 ± 0.07 vs 1.00 ± 0.17), PLA₂ (3.31 ± 0.12 vs 1.00 ± 0.12), PLCβ (2.09 ± 0.08 vs 1.00 ± 0.06) and PTK (1.85 ± 0.07 vs 1.00 ± 0.11) were up-regulated after LPS stimulation as compared with the blank control (P < 0.05). The up-regulated mRNAs including AC (2.35 ± 0.13 vs 3.87 ± 0.08), GRK (1.17 ± 0.14 vs 2.65 ± 0.12), p38 MAPK (1.48 ± 0.18 vs 4.30 ± 0.07), PLCβ (1.69 ± 0.10 vs 2.41 ± 0.13) and PLA₂ (1.87 ± 0.11 vs 2.96 ± 0.08) were significantly suppressed by BN52021 except for that of PTK. The level of p-AC (1.11 ± 0.12 vs 0.65 ± 0.08), GRK (0.83 ± 0.07 vs 0.50 ± 0.03), PLCβ (0.83 ± 0.16 vs 0.50 ± 0.10) and p-p38 MAPK (0.74 ± 0.10 vs 0.38 ± 0.05) was up-regulated after LPS stimulation as compared with the blank control (P < 0.05). The up-regulated proteins, including p-AC (0.65 ± 0.15 vs 1.06 ± 0.14), GRK (0.47 ± 0.10 vs 0.80 ± 0.06), PLCβ (0.47 ± 0.04 vs 0.80 ± 0.19) and p-p38 MAPK (0.30 ± 0.10 vs 0.97 ± 0.05), was significantly suppressed by BN52021, but p-PLA₂ and p-PTK protein level were not suppressed.

CONCLUSION: BN52021 could effectively inhibit LPS-induced inflammation by down-regulating the mRNA and protein levels of AC, GRK, p38 MAPK, PLA₂ and PLCβ in the PAFR signaling pathway.

Effect of guggulsterone and cembranoids of Commiphora mukul on pancreatic phospholipase A(2): role in hypocholesterolemia

Guggulsterone (7) and cembranoids (8-12) from Commiphora mukul stem bark resin guggul were shown to be specific modulators of two independent sites that are also modulated by bile salts (1-6) to control cholesterol absorption and catabolism. Guggulsterone (7) antagonized the chenodeoxycholic acid (3)-activated nuclear farnesoid X receptor (FXR), which regulates cholesterol metabolism in the liver. The cembranoids did not show a noticeable effect on FXR, but lowered the cholate (1)-activated rate of human pancreatic IB phospholipase A2 (hPLA2), which controls gastrointestinal absorption of fat and cholesterol. Analysis of the data using a kinetic model has suggested an allosteric mechanism for the rate increase of hPLA2 by cholate and also for the rate-lowering effect by certain bile salts or cembranoids on the cholate-activated hPLA2 hydrolysis of phosphatidylcholine vesicles. The allosteric inhibition of PLA2 by certain bile salts and cembranoids showed some structural specificity. Biophysical studies also showed specific interaction of the bile salts with the interface-bound cholate-activated PLA2. Since cholesterol homeostasis in mammals is regulated by FXR in the liver for metabolism and by PLA2 in the intestine for absorption, modulation of PLA2 and FXR by bile acids and selected guggul components suggests novel possibilities for hypolipidemic and hypocholesterolemic therapies.

Up-regulation of cPLA(2) gene expression in astrocytes by all three conventional anti-bipolar drugs is drug-specific and enzyme-specific

RATIONALE

Common biological effects by all three conventional anti-bipolar drugs, the lithium ion (Li(+)), carbamazepine, and valproic acid, are important because identical effects may provide information about the pathophysiology of affective disorders. It has been reported that chronic treatment with either drug in vivo down-regulates the turnover of arachidonic acid in brain. This reaction is catalyzed by Ca(2+)-dependent phospholipase A(2) (cPLA(2)), the expression of which was down-regulated by Li(+) or carbamazepine but not by valproic acid; expression of two other PLA subtypes, iPLA(2) and sPLA(2) was unaffected. cPLA(2) is amply expressed in astrocytes, and in the present study, effects of 1-4 weeks of treatment with clinically relevant concentrations of each of the three anti-bipolar drugs on cPLA(2), iPLA(2), and sPLA(2) mRNA and protein expression were determined in primary cultures of mouse astrocytes by reverse transcription polymerase chain reaction (RT-PCR) and immunoblotting.

RESULTS

Two or more weeks treatment with Li(+) concentrations below 2 mM, carbamazepine or valproic acid up-regulated mRNA and protein expression of cPLA(2), but had no effect on iPLA(2) and sPLA(2), showing enzyme specificity. The effect occurred more rapidly at higher than lower concentrations but also tended to end after 4 weeks at the higher concentrations. Two millimolar Li(+) caused an initial increase of cPLA(2) followed by a decrease after 3 and 4 weeks. Topiramate had no effect, indicating specificity for anti-bipolar drugs.

CONCLUSIONS

Both up- and down-regulation of cPLA(2) gene expression are involved in the mechanisms of action of anti-bipolar drugs; astrocytes are a target for these drugs.