Polyclonal amanitin-specific antibodies: production and cytoprotective properties in vitro

Toxic Effects of Amanitins: Repurposing Toxicities toward New Therapeutics

The consumption of mushrooms has become increasingly popular, partly due to their nutritional and medicinal properties. This has increased the risk of confusion during picking, and thus of intoxication. In France, about 1300 cases of intoxication are observed each year, with deaths being mostly attributed to Amanita phalloides poisoning. Among amatoxins, α- and β-amanitins are the most widely studied toxins. Hepatotoxicity is the hallmark of these compounds, leading to hepatocellular failure within three days of ingestion. The toxic mechanisms of action mainly include RNA polymerase II inhibition and oxidative stress generation, leading to hepatic cell apoptosis or necrosis depending on the doses ingested. Currently, there is no international consensus concerning Amanita phalloides poisoning management. However, antidotes with antioxidant properties remain the most effective therapeutics to date suggesting the predominant role of oxidative stress in the pathophysiology. The partially elucidated mechanisms of action may reveal a suitable target for the development of an antidote. The aim of this review is to present an overview of the knowledge on amanitins, including the latest advances that could allow the proposal of new innovative and effective therapeutics.

Treatment of amatoxin poisoning: 20-year retrospective analysis

BACKGROUND

Amatoxin poisoning is a medical emergency characterized by a long incubation time lag, gastrointestinal and hepatotoxic phases, coma, and death. This mushroom intoxication is ascribed to 35 amatoxin-containing species belonging to three genera: Amanita, Galerina, and Lepiota. The major amatoxins, the alpha-, beta-, and gamma-amanitins, are bicyclic octapeptide derivatives that damage the liver and kidney via irreversible binding to RNA polymerase II.

METHODS

The mycology and clinical syndrome of amatoxin poisoning are reviewed. Clinical data from 2108 hospitalized amatoxin poisoning exposures as reported in the medical literature from North America and Europe over the last 20 years were compiled. Preliminary medical care, supportive measures, specific treatments used singly or in combination, and liver transplantation were characterized. Specific treatments consisted of detoxication procedures (e.g., toxin removal from bile and urine, and extracorporeal purification) and administration of drugs. Chemotherapy included benzylpenicillin or other beta-lactam antibiotics, silymarin complex, thioctic acid, antioxidant drugs, hormones and steroids administered singly, or more usually, in combination. Supportive measures alone and 10 specific treatment regimens were analyzed relative to mortality.

RESULTS

Benzylpenicillin (Penicillin G) alone and in association was the mostfrequently utilized chemotherapy but showed little efficacy. No benefit was found for the use of thioctic acid or steroids. Chi-square statistical comparison of survivors and dead vs. treated individuals supported silybin, administered either as mono-chemotherapy or in drug combination and N-acetylcysteine as mono-chemotherapy as the most effective therapeutic modes. Future clinical research should focus on confirming the efficacy of silybin, N-acetylcysteine, and detoxication procedures.

Poisoning and drug overdose

Poisoning is a common cause for intensive care unit admission for both children and adults, and most poisoning victims are effectively treated using standard decontamination measures and supportive care. For a small number of poisons, acceleration of toxin removal with hemodialysis or hemofiltration is indicated. Similarly, specific antidotes are indicated in a few selected circumstances. Rarely, patients may benefit from more aggressive supportive techniques such as cardiopulmonary bypass.

Reduction of desipramine cardiotoxicity and prolongation of survival in rats with the use of polyclonal drug-specific antibody Fab fragments

STUDY OBJECTIVE

Tricyclic antidepressants (TCAs) are a leading cause of death from intentional drug overdose. Available therapies are often unsatisfactory. In this study we evaluated the use of a high-affinity drug-specific polyclonal Fab fragment (TFab) as an antidote to desipramine toxicity.

DESIGN

We gave anaesthetized rats under mechanical ventilation IV desipramine so that we might study the effect of TFab on survival or IP desipramine to facilitate study of the interaction of TFab and hypertonic sodium bicarbonate (NaHCO3), the standard clinical treatment for TCA overdose.

INTERVENTIONS

For the study of the effects of TFab and NaHCO3 on survival, each rat was given a constant IV infusion of desipramine until it died, together with TFab 2 g/kg, bovine serum albumin, or .9% NaCl starting 5 minutes after the desipramine infusion. In the study of the interaction of TFab and NaHCO3, each rat received 30 mg/kg IP desipramine followed by TFab (molar TFab:desipramine ratio, .11), NaHCO3, TFab+NaHCO3, or NaCl at the time of maximal toxicity (15 minutes).

RESULTS

In the survival protocol, QRS-interval duration, systolic blood pressure, and heart rate were significantly improved by TFab, and survival was prolonged by 58% compared with that in the albumin and NaCl groups (P < .001). The molar ratio of TFab to administered desipramine was .21. The unbound fraction of desipramine in serum at the time of death was reduced by TFab, but the unbound desipramine concentration was not, suggesting that TFab prolonged survival by delaying the increase in the unbound serum desipramine concentration. In the interaction protocol, neither TFab nor NaHCO3 was effective alone, but the combination significantly reduced QRS-interval prolongation (P = .001).

CONCLUSION

These data demonstrate the efficacy of TFab in reducing desipramine-induced cardiovascular toxicity and prolonging survival. The pharmacokinetic effects of TFab in rats with severe desipramine toxicity were similar to those observed in sublethal desipramine toxicity. Therapeutic benefit is enhanced by the concurrent use of NaHCO3 and may be achieved despite binding only a fraction of the desipramine dose.

Toxicity of high doses of polyclonal drug-specific antibody Fab fragments

Drug-specific antibody Fab fragments have been used as a treatment for acute drug overdose. For some drugs, the required Fab dose may be very high (up to several g/kg) and may have adverse effects of its own. The current study evaluated the potential toxicity of an affinity purified sheep polyclonal Fab (TFab) directed at the two antidepressants desipramine (DMI) and nortriptyline. TFab 4 g/kg was administered to anesthetized rats i.v. over 10, 25 or 60 min, with or without a toxic dose of DMI. This high dose of TFab, which is in excess of that needed to reduce DMI toxicity, was used in order to exaggerate any adverse effects. In the absence of DMI, TFab produced minimal changes in the electrocardiographic QRS duration, systolic blood pressure and heart rate compared with control animals and was well tolerated. In the presence of DMI, groups receiving TFab as a 10 or 25 min infusion showed a therapeutic effect (lessening of DMI toxicity) over the first 60 min compared with the control group, but one of six animals in each of the TFab groups died prior to the end of the 180 min experiment. No control animals died, but progressive QRS prolongation and decreasing blood pressure toward the end of the experiment suggested that DMI toxicity was increasing over time. These data suggest that, when administered alone, very high doses of rapidly infused TFab are well tolerated. When administered with DMI, TFab is effective in initially reducing DMI toxicity. However, this dose of TFab may later aggravate DMI toxicity and/or the effects of prolonged anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)