Aminopyridines Restore Ventilation and Reverse Respiratory Acidosis at Late Stages of Botulism in Mice

Abstract

Botulinum neurotoxin (BoNT) is a potent protein toxin that causes muscle paralysis and death by asphyxiation. Treatments for symptomatic botulism are intubation and supportive care until respiratory function recovers. Aminopyridines have recently emerged as potential treatments for botulism. The clinically approved drug 3,4-diaminopyridine (3,4-DAP) rapidly reverses toxic signs of botulism and has antidotal effects when continuously administered in rodent models of lethal botulism. Although the therapeutic effects of 3,4-DAP likely result from the reversal of diaphragm paralysis, the corresponding effects on respiratory physiology are not understood. Here, we combined unrestrained whole-body plethysmography (UWBP) with arterial blood gas measurements to study the effects of 3,4-DAP, and other aminopyridines, on ventilation and respiration at terminal stages of botulism in mice. Treatment with clinically relevant doses of 3,4-DAP restored ventilation in a dose-dependent manner, producing significant improvements in ventilatory parameters within 10 minutes. Concomitant with improved ventilation, 3,4-DAP treatment reversed botulism-induced respiratory acidosis, restoring blood levels of CO 2 , pH, and lactate to normal physiologic levels. Having established that 3,4-DAP–mediated improvements in ventilation were directly correlated with improved respiration, we used UWBP to quantitatively evaluate nine additional aminopyridines in BoNT/A-intoxicated mice. Multiple aminopyridines were identified with comparable or enhanced therapeutic efficacies compared with 3,4-DAP, including aminopyridines that selectively improved tidal volume versus respiratory rate and vice versa. In addition to contributing to a growing body of evidence supporting the use of aminopyridines to treat clinical botulism, these data lay the groundwork for the development of aminopyridine derivatives with improved pharmacological properties. SIGNIFICANCE STATEMENT There is a critical need for fast-acting treatments to reverse respiratory paralysis in patients with botulism. This study used unrestrained, whole-body plethysmography and arterial blood gas analysis to show that aminopyridines rapidly restore ventilation and respiration and reverse respiratory acidosis when administered to mice at terminal stages of botulism. In addition to supporting the use of aminopyridines as first-line treatments for botulism symptoms, these data are expected to contribute to the development of new aminopyridine derivatives with improved pharmacological properties.

Progress and Challenges in Developing Medical Countermeasures for Chemical, Biological, Radiological, and Nuclear Threat Agents

“…Currently, there are limited treatment options for botulism, particularly for respiratory paralysis. However, a recent study by McNutt and colleagues suggests that aminopyridines, such as the clinically approved drug 3,4-diaminopyridine, may offer a promising new treatment approach ( McClintic et al, 2024 ). They demonstrate that 3,4-diaminopyridine and other aminopyridines can rapidly reverse respiratory paralysis in botulism-infected mice.…”

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“…The second paper identifies hydroxyquinoline analogs as potential antagonists for oxygen/superoxide-mediated radio-sensitizing effects for mitigating ionizing radiation (Pearce et al, 2024b). The third paper identifies aminopyridines as MCs for protecting against botulism (McClintic et al, 2024). The final paper identifies the potential use of ketamine for treating Gulf War illness-related neuropsychiatric dysfunction (Ribeiro-Davis et al, 2024).…”