Structure-activity relationship, molecular docking, and molecular dynamic studies of diterpenes from marine natural products with anti-HIV activity.

HIV-1 infection is a global epidemic whose treatment is limited majorly by viral resistance and adverse effects. Natural products from algae have been studied for many years, including antiviral, being an alternative to anti-HIV drug design. Since the isolation of natural products can be a hurdle, molecular modeling is an important tool to study these compounds. Herein, structure-activity relationship, molecular docking, and molecular dynamic studies were performed to direct the studies of ten marine natural products with anti-HIV activity. In the structure-activity relationship, descriptors were identified associating the anti-HIV activity of five diterpenes with possible action on the reverse transcriptase allosteric site. These diterpenes were evaluated by molecular docking, and it was identified that only dolabelladienetriol interacted in the allosteric site. Molecular dynamics suggested that the dolabelladienetriol might interfere with the viral RNA binding to HIV-1 RT by inducing a conformational change of the enzyme. Also, in silico ADMET simulations predicts that the dolabelladienetriol present a high potential to be successfully developed as a drug. Thus, applying in silico approaches was possible to suggest potential anti-HIV compounds derived from marine natural products.Communicated by Ramaswamy H. Sarma.

A rhamnose-binding lectin from Rhodnius prolixus and the impact of its silencing on gut bacterial microbiota and Trypanosoma cruzi.

Lectins are ubiquitous proteins involved in the immune defenses of different organisms and mainly responsible for non-self-recognition and agglutination reactions. This work describes molecular and biological characterization of a rhamnose-binding lectin (RBL) from Rhodnius prolixus, which possesses a 21 amino acid signal peptide and a mature protein of 34.6 kDa. The in-silico analysis of the primary and secondary structures of RpLec revealed a lectin domain fully conserved among previous insects studied. The three-dimensional homology model of RpLec was similar to other RBL-lectins. Docking predictions with the monosaccharides showed rhamnose and galactose-binding sites comparable to Latrophilin-1 and N-Acetylgalactosamine-binding in a different site. The effects of RpLec gene silencing on levels of infecting Trypanosoma cruzi Dm 28c and intestinal bacterial populations in the R. prolixus midgut were studied by injecting RpLec dsRNA into the R. prolixus hemocoel. Whereas T. cruzi numbers remained unchanged compared with the controls, numbers of bacteria increased significantly. The silencing also induced the up regulation of the R. prolixus defC (defensin) expression gene. These results with RpLec reveal the potential importance of this little studied molecule in the insect vector immune response and homeostasis of the gut bacterial microbiota.

1,4-Naphthoquinones potently inhibiting P2X7 receptor activity.

P2X7 receptor (P2X7R) is an ATP-gated ion-channel with potential therapeutic applications. In this study, we prepared and searched a series of 1,4-naphthoquinones derivatives to evaluate their antagonistic effect on both human and murine P2X7 receptors. We explored the structure-activity relationship and binding mode of the most active compounds using a molecular modeling approach. Biological analysis of this series (eight analogues and two compounds) revealed significant in vitro inhibition against both human and murine P2X7R. Further characterization revealed that AN-03 and AN-04 had greater potency than BBG and A740003 in inhibiting dye uptake, IL-1ß release, and carrageenan-induced paw edema in vivo. Moreover, we used electrophysiology and molecular docking analysis for characterizing AN-03 and AN-04 action mechanism. These results suggest 1,4-napthoquinones, mainly AN-04, as potential leads to design new P2X7R blockers and anti-inflammatory drugs.

Searching for a potential antibacterial lead structure against bacterial biofilms among new naphthoquinone compounds.

AIMS: The aims of this study were to design, synthesize and to evaluate 2-hydroxy-3-phenylsulfanylmethyl-[1,4]-naphthoquinones against Gram-negative and Gram-positive bacterial strains, including methicillin-resistant Staphylococcus aureus (MRSA) and its biofilm, to probe for potential lead structures. METHODS AND RESULTS: Thirty-six new analogues were prepared with good yields using a simple, fast, operational three-procedure reaction and a thiol addition to an ο-quinone methide using microwave irradiation. All compounds were tested against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Proteus mirabilis ATCC 15290, Serratia marcescens ATCC 14756, Klebsiella pneumoniae ATCC 4352, Enterobacter cloacae ATCC 23355, Enterococcus faecalis ATCC 29212, S. aureus ATCC 25923, Staphylococcus simulans ATCC 27851, Staphylococcus epidermidis ATCC 12228 and a hospital strain of MRSA. Their antibacterial activity was determined using the disc diffusion method, revealing the activity of 19 compounds, mainly against Gram-positive strains. Interestingly, the minimal inhibitory concentration ranges detected for the hit molecules (32-128 µg ml-1 ) were within Clinical and Laboratory Standards Institute levels. Promisingly, compound 15 affected the MRSA strain, with a reduction of up to 50% in biofilm formation, which is better than vancomycin as biofilm forms a barrier against the antibiotic that avoids its action. CONCLUSIONS: After probing 36 naphthoquinones for a potential antibacterial lead structure against the bacterial biofilm, we found that compound 15 should be explored further and also should be structurally modified in the near future to test against Gram-negative strains. SIGNIFICANCE AND IMPACT OF THE STUDY: Since vancomycin is one of the last treatment options currently available, and it is unable to inhibit biofilm, the research of new antimicrobials is urgent. In this context, 2-hydroxy-3-phenylsulfanylmethyl-[1,4]-naphthoquinones proved to be a promising lead structure against MRSA and bacterial biofilm.

Controle fitopatológico do Fusarium subglutinans pelo óleo essencial do capim-citronela (Cymbopogon nardus L. ) e do composto citronelal / Fungitoxic activity of essential oil of citronella grass (Cymbopogon nardus L. ) and compound citronellal

Este trabalho teve como objetivo avaliar o efeito fungitóxico do óleo essencial de capim-citronela e do seu constituinte majoritário citronelal sobre a inibição micelial do fitopatógeno Fusarium subglutinans, agente causal da fusariose da cultura do abacaxi (Ananas comosus). Para avaliar o efeito do óleo essencial no crescimento micelial do fungo, foram utilizadas seis alíquotas (0, 5, 10, 15, 20 e 25 ìL) do óleo e do citronelal que foram distribuídas na superfície do meio BDA (batata-dextrose-ágar) antes da repicagem do fungo. O crescimento micelial foi medido após 48 h de instalação do experimento e em cinco épocas de avaliação (2, 4, 6, 8 e 10 dias após repicagem). Os resultados indicaram que o óleo essencial do capim-citronela demonstrou maior efeito inibitório do crescimento micelial do fungo F. subglutinans do que o composto citronelal. Em todas as alíquotas utilizadas o óleo essencial proporcionou menor taxa de crescimento micelial do que o citronelal.

This study aimed to evaluate the fungitoxic effect of the essential oil of citronella grass and its major constituent citronellal on the inhibition of mycelial pathogen Fusarium subglutinans, the causal agent of Fusarium culture of pineapple (Ananas comosus). To evaluate the effect of essential oil in the mycelial growth of the fungus were used six rates (0, 5, 10, 15, 20 and 25 mL) of oil that were distributed on the surface of PDA medium (potato dextrose agar) before subculturing of the fungus. Mycelial growth was measured after 48 h of the experiment and five times of assessment (2, 4, 6, 8 and 10 days after subculturing). The results indicated that the essential oil of citronella grass showed higher inhibitory effect of mycelial growth of the fungus F. subglutinans than compound citronellal. In all rates used of the essential oil gave lower growth rate than the mycelial citronellal.

Antiplatelet activity and structure-activity relationship study of Pyrazolopyridine Derivatives as potential series for treating thrombotic diseases.

AIM: Platelets plays a central role in hemostatic processes and consequently are similarly involved in pathological processes, such as arterial thrombosis and atherosclerosis. Herein we described the synthesis, antiplatelet profile and structure-activity relationship (SAR) of a new series of N'-substitutedphenylmethylene-1H-pyrazolo[3,4-b]pyridine-carbohydrazide derivatives (3a-3k). METHODS: These compounds were synthesized in good yield and tested in platelet aggregation assays using collagen, ADP and arachidonic acid as agonists. We also performed a SAR studies using SPARTAN' 08 program, in silico ADMET screening and the Lipinski " rule of five " using Osiris Property Explorer and molinspiration on-line programs. RESULTS: Interestingly, the new compounds were active against collagen and arachidonic acid (AA) with the two most actives compounds (3a and 3c - IC(50)=61 microM and 68 microM respectively) almost 5-fold more potent than aspirin (IC(50)=300 microM). These derivatives showed low theoretical toxicity risks in in silico ADMET screening and fulfilled the Lipinski rule of five, suggesting good oral biodisponibility. CONCLUSION: This work showed carbohydrazide group as potential for designing new antiplatelets. On that purpose, 3a and 3c may act as prototypes to generate more efficient and safe molecules for treating thrombotic diseases.

Trypanosoma cruzi: in vitro activity of Epoxy-alpha-Lap, a derivative of alpha-lapachone, on trypomastigote and amastigote forms.

Chagas disease is an endemic parasitic infection caused by Trypanosomacruzi that affects 18-20 million people in Central and South America. Recently we described the Epoxy-alpha-Lap, an oxyran derivative of alpha-lapachone, which presents a low toxicity profile and a high inhibitory activity against T.cruzi epimastigotes forms, the non-infective form of this parasite. In this work we described the trypanocidal effects of Epoxy-alpha-Lap on extracellular (trypomastigote) and intracellular (amastigote) infective forms of two T. cruzi strains (Y and Colombian) known by their different infective profile. Our results showed that Epoxy-alpha-Lap is lethal to trypomastigote Y and Colombian strains (97% and 84%, respectively). Interestingly, Epoxy-alpha-Lap also showed a trypanocidal effect in human macrophage infected with T. cruzi Y (85.6%) and Colombian (71.9%) strains amastigote forms. Similar effects were observed on T. cruzi amastigote infected Vero cells (96.4% and 95.0%, respectively). Our results pointed Epoxy-alpha-Lap as a potential candidate for Chagas disease chemotherapy since it presents trypanocidal activity on all T. cruzi forms with low) toxicity profile.

Expression of B7-1 costimulatory molecules in patients with multibacillary leprosy and reactional states.

BACKGROUND: The expression of B7 as a costimulatory molecule on the surface of antigen-presenting cells such as macrophages and on dendritic cells characterizes the efficiency of the cell-mediated immune response. AIMS: Our purpose was to evaluate B7-1 expression in peripheral blood mononuclear cells (PBMCs) immediately after cell isolation ('spontaneous' B7 expression), and in inflammatory cells from cutaneous lesions of patients with multibacillary leprosy (MB-L) without and during the reactional states of erythema nodosum leprosum (ENL) or reversal reaction (RR). METHODS: Peripheral blood samples and skin biopsies of eight patients without (MB-L) and with reactional episodes (ENL and RR) were studied using antibodies against B7-1, CD1b, DR and CD14 in flow-cytometry and immunohistochemistry experiments. RESULTS: The flow-cytometry studies (mean +/- SD% of fluorescent cells) revealed significant B7-1 expression on PBMCs isolated from patients with ENL (8.0 +/- 0.6%) and RR (15.0 +/- 1.4%) compared with that observed for patients with MB-L (0.4 +/- 0.2%). Similar results were observed for cutaneous lesions of these patients by immunohistochemical assays. One patient studied before and during ENL revealed weak B7 expression before the reactional episode (0.3% of cells) compared with the marked level of B7-expressing cells detected during ENL (8.5% fluorescent cells). Interestingly, an even higher B7 expression (15% of cells) was observed in patients with RR. CONCLUSIONS: Our results strongly suggest that B7 expression precedes reactional episodes in MB-L, which could be related to the acquisition of effective immunity to Mycobacterium leprae during reactional episodes in leprosy. We propose B7 expression as a marker of CMI response in reactional episodes in leprosy.

HIV-1 reverse transcriptase: a therapeutical target in the spotlight.

Human Immunodeficiency Virus type 1 Reverse Transcriptase (HIV-1 RT) is one of the most important targets for treatment of Acquired Immune Deficiency Syndrome (AIDS). It catalyzes the reverse transcription of HIV-RNA into a double stranded DNA, and the knowledge of its substrate specificity and catalytic mechanism has guided the development of several inhibitors widely used on current HIV/AIDS therapy. However, mutations in HIV-1 RT structure can lead to the emergence of drug-resistant virus strains. The goal of this review is to summarize relevant structural features of HIV-1 RT and its inhibitors in such a way that this cost-effective target in the development of new antiretroviral drugs is particularly highlighted.

Monensin for lactating dairy cows grazing mixed-alfalfa pasture and supplemented with partial mixed ration.

The effect of monensin on milk production was evaluated in 58 lactating Holstein cows (48 multiparous; 10 primiparous) grazing a mixed-alfalfa pasture and supplemented with a partial mixed ration in a completely randomized design with repeated measurements. Cows were paired by calving date, lactation number, previous lactation milk production, body weight, and body condition score and were assigned to one of 2 treatments: control or monensin. Cows on the monensin treatment received 2 monensin controlled-release capsules (335 mg/d for 90 d), one 30 d before the expecting calving date and the other 60 d after calving. Short-term (0 to 150 d in milk) and long-term (305-d adjusted lactation) effects of monensin were evaluated. Pasture (measured by difference between pre- and postgrazing pasture mass), supplements, and total dry matter intake did not differ between treatments and averaged 8.7, 14.1, and 22.9 kg/d, respectively. In the short-term, monensin increased milk production (27.7 vs. 26.6 kg/d) and milk protein yield (0.890 vs. 0.860 kg/d); milk fat yield was not affected (0.959 kg/d). Monensin decreased milk fat content (3.51 vs. 3.60%) with no changes in milk protein content (3.25%). In the long term, milk production and milk protein yield were also increased by monensin: 214 and 7 kg, respectively. Monensin reduced the loss of body condition score and increased percentage of pregnancy at first service (44.8 vs. 20.7%). Monensin improves production and reproduction performance of dairy cows grazing a mixed-alfalfa pasture and supplemented with a partial mixed ration.

Snake venom thrombin-like enzymes: from reptilase to now.

The snake venom thrombin-like enzymes (SVTLEs) comprise a number of serine proteases functionally and structurally related to thrombin. Until recently, only nine complete sequences of this subgroup of the serine protease family were known. Over the past 5 years, the primary structure of several SVTLEs has been characterized, and now this family includes several members. Of particular interest is their possible use in pathologies such as thrombosis. The aim of the present review is to summarize the state of the art concerning the evolutionary, structural and biological features of the SVTLEs.

Comparative evaluation of immunological and structural similarities of snake venom C-type lectin proteins.

Antibodies raised against denatured and native forms of bothrojaracin were used to analyze the immunological similarities compared to the structural and biological features of five C-type lectin proteins from snake venom (bothrojaracin, botrocetin, Factor IX/X binding protein (FIX/Xbp), convulxin and Bothrops jararaca lectin). Anti-denatured-bothrojaracin antibodies, which recognize mainly linear epitopes, cross-reacted with botrocetin, FIX/Xbp and convulxin, as expected for homologous proteins. On the other hand, anti-native-bothrojaracin antibodies, which mostly interact with conformational epitopes, exhibited a higher degree of selectivity. These results show that differences exist at the surface of these proteins and that they should be related to their different biological activities, while they share a common and similar scaffold.

Hydrogenated fish fat for grazing dairy cows in summer.

Thirty-two multiparous Holando argentino cows in mid lactation were randomly assigned to two treatments: control or HFF (hydrogenated fish fat) at Rafaela, 31 degrees 11' South, during summer 1997/1998, to evaluate the effect of using HFF as a supplement under grazing conditions. Animals in both treatments grazed an alfalfa pasture, and were confined from 1000 hours to 1700 hours daily in a shaded pen where water was provided ad libitum. During each milking, animals in the control group received 3.73 kg dry matter per cow each day (DM cow(-1) day(-1)) concentrate (15% crude protein; 8.69 MJ energy for location/kg DM). Cows in the HFF group received 3.25 kg DM cow(-1) day(-1) concentrate, plus 0.200 kg DM cow(-1) day(-1) HFF. Both diets presented similar energy, protein and neutral detergent fibre contents. The trial was performed during a strong "El Niño" event, which resulted in a total rainfall of 396.3 mm (80% higher than normal). The mean temperature was 23.7 (SD 3.2) degrees C and the mean temperature humidity index was 72.9 (SD 4.96). Production data were analysed using a completely randomised design with analysis of covariance. Supplementation with HFF produced an increase in daily milk production (26.4 (SD 2.46) l/cow compared to 23.9 (SD 2.68) l/cow for the controls; P<0.05). Milk fat production was higher for HFF (P<0.05): 941 (SD 96) g cow(-1) day(-1) as compared to controls, which yielded 846 (SD 95) g cow(-1) day(-1). Milk protein yields also differed significantly (P<0.05), the respective values for HFF and controls being 795 (SD 72) g cow(-1) day(-1) and 715 (SD 83) g cow(-1) day(-1). It was concluded that hydrogenated fish fat could be a good ingredient to sustain high yields and elevated maintenance requirements in a grazing system during hot conditions.

Structural features of a snake venom thrombin-like enzyme: thrombin and trypsin on a single catalytic platform?

The Lachesis muta thrombin-like enzyme (LM-TL) is a single chain serine protease that shares 38% sequence identity with the serine protease domain of thrombin and also displays similar fibrinogen-clotting activity. In addition, the 228 amino acid residue LM-TL is 52% identical to trypsin, and cleaves chromogenic substrates with similar specificity. Herein we report a three-dimensional (3D) model validated experimentally for LM-TL based on these two homologous proteins of known 3D structure. Spatial modeling of LM-TL reveals a serine protease with a chymotrypsin fold presenting a hydrophobic pocket on its surface, involved in substrate recognition, and an important 90's loop, involved in restricting the LM-TL catalytic site cleft. Docking analysis showed that LM-TL would not form a stable complex with basic pancreatic trypsin inhibitor and wild-type ecotin since its 90's loop would restrict the access to the catalytic site. LM-TL formed acceptable interactions with fibrinopeptide A and a variant of ecotin; ecotin-TSRR/R in which both the primary and secondary binding sites are mutated Val81Thr, Thr83Ser, Met84Arg, Met85Arg and Asp70Arg. Furthermore, analysis of the primary structures of LM-TL and of the seven snake venom thrombin-like enzymes (SVTLEs) family reveals a subgroup formed by LM-TL, crotalase, and bilineobin, both closely related to thrombin. Therefore, LM-TL provides an initial point to compare SVTLEs with their counterparts, e.g. the mammalian serine proteases, and a basis for the localization of important residues within the little known SVTLEs family.

Proteolytic action of Bothrops jararaca venom upon its own constituents.

Many of the components of Bothrops jararaca venom are proteolytic enzymes. In the present work, we investigated the proteolytic action of B. jararaca venom upon its own constituents. Crude venom was reconstituted and incubated at pH 5.0 or 8.5 for up to 48h at room temperature. Aliquots taken at 0, 24 and 48h of incubation were then tested for proteolytic activity and several biological activities, as well as electrophoretic migration pattern and antibody recognition. Rate of hydrolysis of azocasein by venom samples was not changed by the incubation, but hemagglutinating activity decreased by 93% after 24h of incubation at pH 8.5, with no detectable changes at pH 5.0. Incubation of venom samples caused a progressive increase in phospholipase A(2) and procoagulant activities that was more evident in samples incubated at pH 5.0. The electrophoretic migration pattern showed no significant change for venom samples incubated at pH 5.0, whereas in samples incubated at pH 8.5 bands in the region between 66 and 45kDa gradually disappeared. The addition of a mixture of protease inhibitors (EDTA, PMSF, PPACK and benzamidine) effectively protected against venom degradation at pH 8.5. The cocktail of inhibitors also reduced the changes in phospholipase A(2) activity found in venom samples incubated at pH 5.0. Recognition of venom samples by polyclonal antibodies raised against crude venom was progressively lost during incubation at both pH 5.0 and 8.5; again the addition of protease inhibitors protected against loss of antibody recognition. We conclude that prolonged manipulation of B. jararaca venom at an acidic or alkaline pH can produce significant changes in its biological properties.

Identification of bothrojaracin-like proteins in snake venoms from Bothrops species and Lachesis muta.

Bothrojaracin, a 27 kDa protein isolated from Bothrops jararaca venom, forms a non-covalent complex with thrombin, thus blocking its activity. We have previously identified a bothrojaracin-like protein in B. alternatus venom [Castro, H.C., Dutra, D.L.S., Oliveira-Carvalho, A.L., Zingali, R.B., 1998. Bothroalternin, an inhibitor of thrombin from the venom of Bothrops alternatus. Toxicon 36, 1903-1912]. In this report, we have examined snake venoms from six different Bothrops species (B. atrox, B. cotiara, B. jararacussu, B. moojeni and B. neuwiedi), from Lachesis muta and from Crotalus durissus terrificus for the presence of bothrojaracin-like proteins, which we define here as 27 kDa proteins that are immunologically related to bothrojaracin and that inhibit thrombin-induced platelet aggregation. The immunological analysis of these venoms by different techniques indicated the existence of at least one protein recognized by anti-bothrojaracin serum in all venoms tested. Bothrojaracin-like proteins were purified from all crude venoms, except for C. d. terrificus, by a single-step procedure using a thrombin affinity column (PPACK-thrombin-Sepharose). Retained material that inhibits thrombin-induced platelet aggregation was found in a different proportion in each species. Under non-reducing conditions, SDS-PAGE of this material revealed several bands between 20-60 kDa; only those bands corresponding to 27 kDa were recognized by anti-bothrojaracin serum. ELISA confirmed the greater bothrojaracin immunoreactivity of proteins present in B. atrox and B. cotiara as compared to other Bothrops species. Smaller amounts of proteins related to bothrojaracin were found in L. muta venom and were absent from the venom of C. d. terrificus. Our results thus suggest that bothrojaracin-like proteins are widely distributed among Bothrops genera.

Bothroalternin, a thrombin inhibitor from the venom of Bothrops alternatus.

Bothroalternin (MW 27 kDa), a new member of the family of C-type lectins is a thrombin inhibitor which was purified from pooled B. alternatus venom by affinity chromatography on PPACK-thrombin-Sepharose, followed by size exclusion and reverse-phase on HPLC columns. Material retained on the affinity column contained proteins with apparent molecular weights ranging from 20 to 60 kDa on SDS-PAGE and inhibited aggregation of rabbit platelets induced by alpha-thrombin (IC50 = 28 microg/ml). A single band of approximately 27 kDa was recognized in Western-blot assays using polyclonal antibodies raised against bothrojaracin, a thrombin inhibitor purified from B. jararaca venom (Zingali et al., 1993). The immunological similarity of this fraction to bothrojaracin was confirmed by ELISA and competitive ELISA. Further purification by size exclusion and reverse-phase on HPLC, produced a single homogenous peak called bothroalternin. This protein was highly homologous to bothrojaracin (95% in its N-terminal sequence-for residues 1 to 25) but displaying lower inhibitory effect on thrombin induced platelet aggregation (Ic50 = 0.19 microg/ml) compared to bothrojaracin (IC50 = 0.06). Altogether, bothroalternin is a new thrombin inhibitor isolated from Bothrops alternatus venom and has been characterized as a bothrojaracin-like protein.

Bothrops sp. snake venoms: comparison of some biochemical and physicochemical properties and interference in platelet functions.

Procoagulant, proteolytic, phospholipase and platelet pro-aggregating and inhibiting activities were screened for pooled venoms of seven Bothrops species as well as Crotalus durissus terrificus and Lachesis muta snakes typical of the Brazilian territory. As reported by other authors, we also found that examination of the electrophoretic and gel filtration patterns of Bothrops snakes venoms could not be used for identification of the species of a given venom because of the lack of marked interspecific differences within the same genus. Our data indicated that B. cotiara, B. alternatus and B. atrox possess no platelet pro-aggregating activity, low inhibitory effect on platelet aggregation and very low or intermediate levels for the other activities. B. moojeni, B. neuwiedi and B. jararacussu whose venoms possess high procoagulant, platelet pro-aggregating and phospholipase activities are low in both proteolytic and platelet inhibitory activities. B. jararaca venom showed the highest inhibitory effect on platelet aggregation and very low platelet pro-aggregating activity. Compared with the Bothrops venoms studied, L. muta venom showed that highest proteolytic activity while C. d. terrificus venom presented remarkable high platelet pro-aggregating and phospholipase activities. In all venoms, proteolytic activity could be completely inhibited by EDTA (2 mM) alone. In contrast, the presence of phenylmethylsulfonyl fluoride (5 mM) inhibited partially the caseinolytic activity of all venoms, except that L. muta venom, which was almost completely blocked by this reagent. Altogether, these data confirm the presence of high levels of metalloproteinases in the venoms of Crotalinae snakes. Most of these enzymes are dependent of the availability of Ca2+, being much less the same concerning the presence of serine residues in their active sites. The data indicated that the presence and levels of procoagulant, azocaseinolytic and phospholipase A2 activities alone could not differentiated the species of the Bothrops venoms studied, particularly in the cases of B. jararaca, B. moojeni and B. atrox. However, the platelet inhibiting property of low doses of B. jararaca venom can be useful to differentiate it from B. moojeni venom. In the same way, the platelet pro-aggregating activity of high doses of B. jararaca venom may be used to distinguish it from B. atrox crude venom, otherwise very similar but incapable to activate platelets. In conclusion, our comparative screening of biological properties has indicated that platelet studies may serve as a tool to distinguish among venoms that otherwise behave biochemically in a very similar way. Although promising, the general applicability of platelet activation studies by snake venoms for classification or taxanomical purposes has yet to be extended to other family of snakes to be proven useful.

Molecular cloning and expression of bothrojaracin, a potent thrombin inhibitor from snake venom.

Bothrojaracin is a potent and selective thrombin inhibitor that has been isolated from the venom of Bothrops jararaca. It does not interact with the catalytic site of the enzyme but binds to both anion-binding exosites 1 and 2 resulting in a potent inhibition of thrombin activity towards fibrinogen and platelets [Zingali, R. B., Jandrot-Perrus, M., Guillin, M. C. & Bon, C. (1993) Biochemistry 32, 10794-108021. Bothrojaracin is a 27-kDa protein composed of two disulfide-linked polypeptide chains, A and B, of 15 kDa and 13 kDa, respectively. The sequences of A and B chains determined by molecular cloning exhibit a high degree of identity with other snake venom lectin-like proteins. In contrast to other ligands that interact with thrombin exosite 1, the amino acid sequence of bothrojaracin does not contain an acidic sequence similar to the C-terminal tail of hirudin. Expression of functional bothrojaracin was achieved in COS cells upon transfection with two pcDNA3 vectors containing the complete cDNAs. Recombinant bothrojaracin, which was secreted into the medium, was able to bind to and inhibit thrombin. When expressed alone, the B chain formed inactive dimers that were secreted into the culture medium. In contrast, no bothrojaracin-related protein was detected in conditioned media from cells transfected with the A chain.

Interactions between local inflammatory and systemic haematological effects of PAF-acether in the rat.

Intraplantar injections of PAF-acether into the rat paw (0.025-16 micrograms/paw) were followed by a bell-shaped dose-response curve for oedema. In parallel to the ascending phase (0.25-2 micrograms/paw) a significant leukopenia was observed whereas thrombocytopenia, haemoconcentration and leukocytosis were seen during the descending phase (4-16 micrograms/paw) as was also observed after the i.v. injection of PAF-acether. I.v. injections of PAF-acether inhibited dose dependently the oedema induced by PAF-acether itself but were inactive against serotonin. Dexamethasone (0.1 mg/kg) inhibited the PAF-acether-induced thrombocytopenia and haemoconcentration but failed to modify the leukocytosis whereas aspirin (100 mg/kg) and indomethacin (1.0 mg/kg) inhibited only the haemoconcentration. The PAF-acether antagonist 48740 RP blocked the systemic haematological alterations and restored the auto-reduced oedema induced by a high dose of PAF-acether (16 micrograms/paw) but was unable to inhibit the paw oedema induced by PAF-acether. It is suggested that haemoconcentration, thrombocytopenia and leukocytosis are independent phenomena associated with the presence of PAF-acether in the bloodstream, these haematological changes and the local oedema induced by PAF-acether involve distinct mechanisms and the auto-inhibitory property of PAF-acether is not restricted to in vitro situations, but extends to local inflammation.