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

Combining fibril-induced alpha-synuclein aggregation and 6-hydroxydopamine in a mouse model of Parkinson's disease and the effect of cerebral dopamine neurotrophic factor on the induced neurodegeneration

The existent pre-clinical models of Parkinson's disease do not simultaneously recapitulate severe degeneration of dopamine neurons and the occurrence of alpha-synuclein (aSyn) aggregation in one study system. In this study, we injected aSyn pre-formed fibrils (PFF) and 6-hydroxydopamine (6-OHDA) unilaterally into the striatum of C57BL/6 wild-type male mice at an interval of 2 weeks to induce aggregation of aSyn protein and trigger the loss of dopamine neurons simultaneously in one model and studied the behavioural effects of the combination in these mice. 6-OHDA was tested at three different doses, and 2 μg of 6-OHDA combined with PFF-induced aSyn aggregation was found to produce the most optimal disease phenotype. At 14 weeks timepoint, mice injected with a combination of PFF and 6-OHDA sustained significant damage to the nigrostriatal pathway and exhibited aSyn-positive aggregation. Our data suggest that the neurons that formed large aSyn aggregates were particularly vulnerable to 6-OHDA-induced degeneration. We also demonstrate the manifestation of a relatively aggressive pathology in 2- to 4-month-old mice, as compared to younger 7- to 9-week-old ones. Furthermore, cerebral dopamine neurotrophic factor (CDNF) administered intrastriatally rescued dopamine neurons and motor behaviour of the animals to some extent from 6-OHDA toxicity. However, no such effect could be seen in the novel 6-OHDA + PFFs combination model. For the first time, we demonstrate the combined effect of PFF and 6-OHDA simultaneously in one model. We further discuss the scope for further optimizing this combination model to develop it as a promising pre-clinical platform for drug screening and development.

A pilot pharmacokinetic study of tricyclic antidepressant ovine Fab for TCA poisoning in children

CONTEXT

A pilot study of tricyclic antidepressant (TCA)-specific antibody fragments (TCA Fab) in TCA-intoxicated adults showed a marked increase in serum total TCA concentrations following TCA Fab infusion with no worsening signs of TCA toxicity. TCA Fab pharmacokinetics (PK) was not described in this adult study. The objective of this study was to evaluate the PK of TCA Fab in children with TCA poisoning.

METHODS

This was an open-label, single-center, dose escalation pilot trial of three patients. Inclusion criteria were documented TCA ingestion with at least one serious complication (QRS prolongation, dysrhythmia, hypotension, seizure, or coma). Patients were assigned to either a low-dose intravenous TCA Fab regimen (15, 30, and 60 mg/kg) or a high-dose regimen (30, 60, and 120 mg/kg) as needed to reverse TCA toxicity. Following the administration of TCA Fab, samples of blood and urine were obtained for PK evaluations. The outcomes of interest were serum and urine TCA concentrations (free and total), serum and urine Fab concentrations, improvement or worsening of TCA toxicity, and adverse effects.

RESULTS

Three study patients were 11, 11, and 14 years of age. Two patients received 15 mg/kg of TCA Fab and one patient received a total of 90 mg/kg of TCA Fab (30 + 60 mg/kg). Serum-bound TCA increased significantly following TCA Fab administration with concomitant enhanced urinary elimination. Serum-free TCA concentrations were minimal to undetectable. Fab data were available for two patients. The serum TCA Fab area under the curve was 306.12 mg/L/h for the 15 mg/kg dose and 2,198.10 mg/L/h for the 90 mg/kg dose of TCA Fab. Maximum Fab concentrations correlated with maximum bound TCA in serum. The volume of distribution (V(D)) of TCA Fab was 0.2-0.3 L/kg. The clearance was 0.036-0.05 L/kg/h and the elimination half-life was 4 h. No adverse effects were observed.

CONCLUSION

The limited PK data from this study are consistent with binding of TCA to TCA Fab and redistribution of TCA from the tissue to serum with subsequent enhanced urinary excretion of TCA. No toxic effects were observed with increased total TCA concentrations and no adverse effects were observed following TCA Fab administration. The small number of patients in this pilot study does not allow for safety or efficacy conclusions.

Current and Emerging Detoxification Therapies for Critical Care

Toxicity resulting from prescription drugs such as tricyclic antidepressants and cardioactive steroids, as well as drugs of abuse and exposure to environmental chemicals, represents a major need for detoxification treatments. Particles and colloids, antibody fragments (Fab), and indirect treatment methods such as macroemulsions, are currently being developed or employed as detoxification therapies. Colloids, particles, and protein fragments typically mitigate toxicity by binding to the toxin and reducing its concentration in vital organs. Indirect methods such as macroemulsions and sodium bicarbonate act directly on the affected organs, rather than the toxin. In this review, key design parameters (i.e. binding affinity, biocompatibility, pharmacokinetics) are discussed for each type of detoxification treatment. In addition, some of the latest research in each area is reviewed.

A Preliminary Study of Tricyclic Antidepressant (TCA) Ovine FAB for TCA Toxicity

BACKGROUND

Animal studies suggest that tricyclic antidepressant antibody fragments (TCA Fab) may be a useful therapy for tricyclic antidepressant poisoning. The objective of this study is to determine if TCA Fab increases total serum TCA levels without raising free serum TCA levels in human overdose patients, indicating that TCA Fab effectively binds TCA.

METHODS

This was a prospective, dose escalation study of patients with mild to moderate TCA poisoning. Patients were treated with an escalating intravenous infusion totaling 7 or 14 gm of TCA Fab. The outcomes of interest were serum TCA levels (total and free), worsening of TCA toxicity, and adverse effects.

RESULTS

Seven patients were treated with Fab. Infusion of TCA Fab was associated with a dramatic increase in total serum TCA levels, while free TCA levels fell in both dosing groups. There were no significant changes in QRS duration, heart rate or mean arterial pressure associated with the Fab Infusion. Worsening of TCA toxicity did not occur despite marked elevation of total serum TCA concentrations. The two patients with the greatest prolongation of QRS showed a prompt shortening in their QRS duration temporally associated with the Fab infusion. Mild wheezing was observed in one asthmatic patient.

CONCLUSIONS

1) TCA Fab raises total serum TCA levels while lowering free levels in TCA poisoned patients; 2) no toxic effects were associated with the increase in TCA levels and no severe adverse effects were observed during the hospital course following Fab infusion.

Fab antibody fragments: some applications in clinical toxicology

This review provides current information on the use of antigen-binding fragments (Fab) from cleaved antibodies to treat poisoning with digoxin and other potent, low formula mass poisons, such as colchicine and tricyclic antidepressants. Anti-digoxin Fab fragments have been used successfully for many years in the management of severe poisoning with digoxin, digitoxin, and a range of other structurally related compounds, including cardiotoxins from Nerium and Thevetia sp. (oleander) and Bufo sp. (toads). However, their main use remains treating digoxin poisoning. Equimolar doses of anti-digoxin Fab fragments completely bind digoxin in vivo. The approximate dose of Fab fragments (mg) is 80 times the digoxin body burden (mg). If neither the dose ingested nor the plasma digoxin/digitoxin concentration is known, in an adult 380 mg of anti-digoxin Fab fragments should be given. The dose for elderly patients or those with renal impairment should be similar to that for those with normal renal function. Fab fragments have a plasma half-life of 12-20 hours, but this can be prolonged in patients with renal impairment. Analysis of serum ultrafiltrate using an immunoassay shown not to have matrix bias remains the most accurate approach to measuring free digoxin in the presence of anti-digoxin Fab fragments. The antibody fragments are given intravenously over 15-30 minutes after dilution to at least 250 mL with plasma protein solution, 0.9% (w/v) sodium chloride, or deionised water, except in infants where the volume infused can be reduced. Factors limiting the efficacy of Fab fragments are the dose, the duration of the infusion and any delay in administration. Guidelines for Fab fragment administration in children include (i) dilution to a final Fab concentration of 10 g/L in either 5% (w/v) dextrose or 0.9% (w/v) sodium chloride; (ii) infusion through a 0.22 microm filter; (iii) administration of the total dose over a minimum of 30 minutes; and (iv) avoiding coadministration of other drugs and/or electrolyte solutions. Fab fragments are generally well tolerated. Adverse effects attributable to Fab treatment include hypokalaemia and exacerbation of congestive cardiac failure; renal function could be impaired in some patients. Fab fragment preparations for treating acute colchicine and tricyclic antidepressant poisoning have been developed, but are not available commercially. Colchicine poisoning is rare in Western countries, and pharmacological management together with supportive care is usually effective even in severe tricyclic antidepressant overdosage. Attempts have been made to produce anti-paraquat antibodies capable of enhancing paraquat elimination from the lung, but thus far all such attempts have proved unsuccessful.

The Management of Tricyclic Antidepressant Poisoning

Although there have been descriptive, uncontrolled clinical reports of removal of tablet debris by gastric lavage, there have been no clinical studies that have demonstrated that this has any impact on outcome in patients with tricyclic antidepressant (TCA) poisoning. There is also the possibility that lavage may increase drug absorption by pushing tablets into the small intestine. Furthermore, gastric lavage in patients with TCA poisoning may induce hypoxia and a tachycardia potentially increasing the risk of severe complications such as arrhythmias and convulsions. In view of the paucity of evidence that gastric lavage removes a significant amount of drug and the risk of complications associated with the procedure, the routine use of gastric lavage in the management of patients with TCA poisoning is not appropriate. Volunteer studies have shown generally that activated charcoal is more likely to reduce drug absorption if it is administered within 1 hour of drug ingestion. In the one volunteer study that looked at later administration of activated charcoal, there was a 37% decrease in plasma concentration associated with administration of activated charcoal at 2 hours post-ingestion. There have been no clinical studies that enable an estimate of the effect of activated charcoal administration on outcome in the management of patients with TCA poisoning. Volunteer studies have shown that multiple-dose activated charcoal increases the elimination of therapeutic doses of amitriptyline and nortriptyline, but not of doxepin or imipramine; however, these studies cannot be directly extrapolated to the management of patients with TCA poisoning. There have been no well designed controlled studies that have assessed the impact of multiple-dose activated charcoal in the management of patients with TCA poisoning. Because of the large volume of distribution of TCAs, it would not be expected that their elimination would be significantly increased by multiple-dose activated charcoal.Haemoperfusion, haemodialysis and the combination of these procedures do not result in significant removal of TCAs and are not recommended in the management of patients with TCA poisoning.

Tricyclic antidepressant overdose: a review

Overdoses of tricyclic antidepressants are among the commonest causes of drug poisoning seen in accident and emergency departments. This review discusses the pharmacokinetics, clinical presentation and treatment of tricyclic overdose.

Intradermal anti-loxosceles Fab fragments attenuate dermonecrotic arachnidism

OBJECTIVE

Bites from the brown recluse spider and other arachnids from the genus Loxosceles frequently induce necrotic skin lesions that can be recalcitrant to treatment and disfiguring. The authors used a rabbit model of dermonecrotic arachnidism to address the therapeutic efficacy of intradermal (id) polyclonal anti-Loxosceles Fab fragments (alphaLoxd Fab) raised against Loxosceles deserta spider venom.

METHODS

Fab fragments were prepared by papain digestion and affinity chromatography from the IgG fraction of L. deserta antivenom raised in rabbits. Eighteen inbred New Zealand white rabbits were assigned to six groups of three. The rabbits received L. deserta venom (3 microg, id) injections into each flank. Cohorts of rabbits received single id injections (at one venom site/rabbit) of 30 microg alphaLoxd Fab at different times (T = 0, 1, 2, 4, 8, and 12 hours) after venom injection. In each rabbit the opposite flank was left untreated. As an additional control, one group of rabbits (T = 0) received nonspecific Fab (30 microg, id) in the opposite flank. Dermal lesions were quantified as a function of time through the use of a series of digital photographs and imaging software. In addition, myeloperoxidase (MPO) activity, a measure ofneutrophil accumulation, was determined in lesion biopsies. Lesion areas and MPO activities were analyzed by repeated-measures analysis of variance (ANOVA).

RESULTS

Lesion areas and MPO activity were markedly reduced when alphaLoxd Fab was administered very early after venom injections. As the interval between venom inoculation and antivenom treatment increased, the therapeutic benefit of alphaLoxd Fab decreased. The final time tested that demonstrated therapeutic efficacy of alphaLoxd Fab was T = 4 hours. Lesion attenuation was no longer apparent when alphaLoxd Fab was given 8 hours post inoculation.

CONCLUSIONS

Intradermal administration of alphaLoxd Fab attenuates Loxosceles-induced dermonecrotic lesion formation when given up to 4 hours after venom inoculation in this rabbit model.

Approach to the poisoned patient

Routine poison management involves the following: (1) stabilization, (2) toxidrome recognition, (3) decontamination, (4) antidote administration, (5) enhanced elimination of toxin, and (6) supportive care. Stabilization involves airway, ventilation, and circulation support. In the patient with altered mental status, oxygen, naloxone, glucose, and thiamine should be administered. Symptom complexes that relate to specific classifications of toxins are referred to as toxidromes. Emesis by means of syrup of ipecac is rarely used for in-hospital gastric decontamination. Activated charcoal is a useful adsorbent for gastric decontamination. Whole bowel irrigation is useful for iron, lead, and lithium poisoning and for the body packer phenomenon. Enhancement of elimination may involve multiple doses of activated charcoal, hemodialysis, or charcoal hemoperfusion.

Drug-specific antibodies as antidotes for tricyclic antidepressant overdose

Drug-specific antibodies have been used clinically to treat digoxin or colchicine overdose. The lethal dose of tricyclic antidepressants (TCAs) is 100 times higher, and will require higher doses of antibodies (up to several g/kg) to reverse toxicity. Preliminary studies suggest that this is feasible. High affinity TCA-specific monoclonal Fab' or polyclonal Fab fragments rapidly reverse the cardiovascular toxicity of the TCA desipramine (DMI) in rats, and prolong survival. TCA-specific Fab' or Fab is generally well tolerated in rats, but doses several times higher than anticipated for human use may have adverse effects. Combining Fab with standard therapies for TCA overdose, such as NaHCO3, can reduce the required Fab dose. As an alternative, a recombinant single chain Fv fragment (sFv), one half the size of Fab, has been cloned which retains a high affinity for DMI and is able to alter DMI distribution in vivo. Because sFv has a shorter elimination half-life and more extensive renal excretion than Fab, it may have therapeutic advantages.