Biomedical subjects

Guillermo León

Publications and source records attributed to Guillermo León.

6 recordsLinked to original sources

PubMed2006

Efficacy and safety of two whole IgG polyvalent antivenoms, refined by caprylic acid fractionation with or without beta-propiolactone, in the treatment of Bothrops asper bites in Colombia.

The efficacy and safety of two whole IgG polyvalent antivenoms (A and B) were compared in a randomised, blinded clinical trial in 67 patients systemically envenomed by Bothrops asper in Colombia. Both antivenoms were fractionated by caprylic acid precipitation and had similar neutralising potencies, protein concentrations and aggregate contents. Antivenom B was additionally treated with beta-propiolactone to lower its anticomplementary activity. Analysing all treatment regimens together, there were no significant differences between the two antivenoms (A=34 patients; B=33 patients) in the time taken to reverse venom-induced bleeding and coagulopathy, to restore physiological fibrinogen concentrations and to clear serum venom antigenaemia. Blood coagulability was restored within 6-24 h in 97% of patients, all of whom had normal coagulation and plasma fibrinogen levels 48 h after the start of antivenom treatment. Two patients (3.0%) had recurrent coagulopathy and eight patients suffered recurrence of antigenaemia within 72 h of treatment. None of the dosage regimens of either antivenom used guaranteed resolution of venom-induced coagulopathy within 6 h, nor did they prevent recurrences. A further dose of antivenom at 6 h also did not guarantee resolution of coagulopathy within 12-24 h in all patients. The incidence of early adverse reactions (all mild) was similar for both antivenoms (15% and 24%; P>0.05).

Adolescent↗

PubMed2006

Anti-human erythrocyte antibodies in horse-derived antivenoms used in the treatment of snakebite envenomations.

This work examined the presence of antibodies reacting with human erythrocytes in horse-derived antivenoms used in the treatment of snakebite envenomations, and assessed the efficacy of various fractionation protocols in the elimination of agglutinating antibodies. A number of antivenoms produced by various fractionation protocols were tested for direct agglutination of human erythrocytes. Reactions were observed visually and microscopically, and an indirect anti-equine globulin test was also used. In addition, rabbits and mice were injected intravenously with antivenoms to observe possible intravascular hemolysis and erythrocyte sequestration. All tested antivenoms agglutinated human erythrocytes, albeit to different extent, and also gave a positive anti-globulin test. Agglutination was due to IgG(T) subclass of antibodies. Pepsin digestion of horse IgG, to obtain F(ab')(2) fragments, reduced the direct agglutination, but not the indirect anti-globulin test. Ion-exchange chromatography of IgG in a strongly basic quaternary ammonium cellulose membrane abrogated direct agglutination and reduced the indirect anti-globulin test. Binding of antivenom antibodies to erythrocytes in vivo was demonstrated in rabbits, although there was no evidence of intravascular hemolysis or erythrocyte sequestration in rabbits and mice. It is concluded that anti-human erythrocyte antibodies are present in horse-derived antivenoms, and that fractionation of horse plasma by pepsin digestion, and especially by anion-exchange chromatography, reduces the titer of these antibodies. Our in vivo experimental results do not support a role for these antibodies in early adverse reactions occurring after antivenom administration.

Animals↗

PubMed2005

Factors associated with adverse reactions induced by caprylic acid-fractionated whole IgG preparations: comparison between horse, sheep and camel IgGs.

Caprylic acid purification of IgG, currently used in the manufacture of horse-derived antivenoms, was successfully adapted for the preparation of sheep and camel IgG. Sheep IgG had a molecular mass of approximately 150 kDa, whereas camel IgG presented two bands of molecular masses of approximately 160 and 100 kDa, the latter corresponding to heavy-chain IgG, which is devoid of light chains. Horse, sheep and camel IgGs were compared by several parameters aiming at predicting their potential for induction of early and late adverse reactions. Horse and sheep IgGs showed a higher anticomplementary activity than camel IgG, and also elicited a higher anti-IgG response than camel IgG, when injected in mice. Horse IgG agglutinated human type O+ erythrocytes, whereas no such reactivity was observed in sheep and camel IgG preparations. A novel procedure was used for the detection of antibodies in human serum against animal IgGs. It was found that a pool of human sera collected in Costa Rica had a higher titer of antibodies directed against horse and sheep IgGs than against camel IgG. Overall, camel IgG showed the lowest potential for the induction of adverse reactions among the three IgGs tested.

Animals↗

PubMed2005

Anticomplementary activity of equine whole IgG antivenoms: comparison of three fractionation protocols.

Early adverse reactions occur in a number of patients treated with heterologous antivenoms and have been associated with anticomplementary activity (ACA). In order to reduce the ACA of equine whole IgG antivenoms produced by caprylic acid fractionation, three different fractionation protocols were compared: (a) routine caprylic acid fractionation; (b) caprylic acid fractionation followed by beta-propiolactone treatment; and (c) caprylic acid fractionation followed by ion-exchange chromatography using a quaternary ammonium membrane. The three protocols yielded products with similar physicochemical characteristics and anti-Bothrops asper venom antibody titers, except that ion-exchange purified antivenom had a lower protein concentration. Antivenoms fractionated by using beta-propiolactone or filtration through quaternary ammonium membrane had a significantly reduced in vitro ACA. A preparation of caprylic acid-fractionated antivenom was heated in order to induce the formation of protein aggregates; however, its ACA was similar to non-heated antivenom. None of the antivenoms affected the hemolytic activity of serum complement in rabbits after a bolus intravenous administration. It is concluded that (a) beta-propiolactone and quaternary ammonium membranes significantly reduce in vitro ACA of caprylic acid-fractionated equine antivenom, and (b) the validity of in vitro ACA as a predictor of EAR needs to be reexamined in clinical and experimental studies, since it may not adequately predict in vivo complement activation by antivenoms.

Animals↗

PubMed2003

Pharmacokinetic-pharmacodynamic relationships of immunoglobulin therapy for envenomation.

Parenteral administration of horse- and sheep-derived antivenoms constitutes the cornerstone in the therapy of envenomations induced by animal bites and stings. Depending on the type of neutralising molecule, antivenoms are made of: (i) whole IgG molecules (150 kDa), (ii) F(ab')(2) immunoglobulin fragments (100 kDa) or (iii) Fab immunoglobulin fragments (50 kDa). Because of their variable molecular mass, these three types of antivenoms have different pharmacokinetic profiles. Fab fragments have the largest volume of distribution and readily reach extravascular compartments. They are catabolised mainly by the kidney, having a more rapid clearance than F(ab')(2) fragments and IgG. On the other hand, IgG molecules have a lower volume of distribution and a longer elimination half-life, showing the highest cycling through the interstitial spaces in the body. IgG elimination occurs mainly by extrarenal mechanisms. F(ab')(2) fragments display a pharmacokinetic profile intermediate between those of Fab fragments and IgG molecules. Such diverse pharmacokinetic properties have implications for the pharmacodynamics of these immunobiologicals, since a pronounced mismatch has been described between the pharmacokinetics of venoms and antivenoms. Some venoms, such as those of scorpions and elapid snakes, are rich in low-molecular-mass neurotoxins of high diffusibility and large volume of distribution that reach their tissue targets rapidly after injection. In contrast, venoms rich in high-molecular-mass toxins, such as those of viperid snakes, have a pharmacokinetic profile characterised by a rapid initial absorption followed by a slow absorption process from the site of venom injection. Such delayed absorption has been linked with recurrence of envenomation when antibody levels in blood decrease. This heterogeneity in pharmacokinetics and mechanism of action of venom components requires a detailed analysis of each venom-antivenom system in order to determine the most appropriate type of neutralising molecule for each particular venom. Besides having a high affinity for toxicologically relevant venom components, an ideal antivenom should possess a volume of distribution as similar as possible to that of the toxins being neutralised. Moreover, high levels of neutralising antibodies should remain in blood for a relatively prolonged time to assure neutralisation of toxins reaching the bloodstream later in the course of envenomation, and to promote redistribution of toxins from extravascular compartments to blood. Additional studies are required on different venoms and antivenoms in order to further understand the pharmacokinetic-pharmacodynamic relationships of antibodies and their fragments and to optimise the immunotherapy of envenomations.

Animals↗

PubMed2002

Effect of preservatives on IgG aggregation, complement-activating effect and hypotensive activity of horse polyvalent antivenom used in snakebite envenomation.

Intravenous administration of antivenoms is associated with early adverse reactions in a number of cases, but the causes of this phenomenon are still unclear. The effect of preservatives (phenol and thimerosal) on IgG aggregate and dimer formation, in vitro complement-activating effect and hypotensive activity of a whole IgG horse liquid polyvalent antivenom, produced by caprylic acid fractionation, was assessed. These parameters were studied since they have been associated with the development of early adverse reactions to the administration of antivenoms and human immunoglobulins. After a three-year storage period at 4 degrees C, antivenoms with preservatives had an increased content of IgG aggregates and dimers when compared with antivenom devoid of phenol and thimerosal. These observations correlate with a slight increment in the turbidity of preservative-containing antivenoms. The three antivenoms studied (formulation: no preservatives; with phenol and thimerosal; with thimerosal alone) activated human complement in vitro, with only minor quantitative differences among them. When antivenoms were administered as a bolus intravenous injection in rats, a rapid and prominent hypotension of short duration was observed after injection of phenol-containing antivenom, whereas such an effect was absent in antivenom free of preservative and in the one containing only thimerosal. Bolus injection of saline solution with phenol resulted in a similar hypotension, indicating that the effect is due to phenol. However, when phenol-containing antivenom was diluted 1:5 with saline solution before infusion, as occurs in the clinical use of this product, no hypotension was observed. Our results stress the need to evaluate the effects of preservatives on the physicochemical and pharmacological characteristics of antivenoms.

Animals↗