Transcriptomic Characterization of Inhalation Phosphine‐Induced Cardiotoxicity in the Pediatric Rat
Authors: Thompson Lily , Hartog Matthew , Ma Ki , Nealley Eric , Bearden Ian , Holmes Wesley , Hoard-Fruchey Heidi 
Published: April 2020

Phosphine (PH3) is a highly toxic, colorless, and odorless gas commonly used as a pesticide and rodenticide in the agricultural industry. PH3 is generated from metal phosphide tablets that can be purchased in both over‐the‐counter and restricted commercial‐use formulations. Due to phosphine’s widespread use, human exposures are common. Across documented cases of PH3 exposure, children show higher morbidity and mortality than adults. In pediatric case reports, exposure often results in impaired cardiac output and cardiac arrest. PH3 has a poorly defined mechanism of toxicity, but is suspected to bind iron centers of proteins in the electron transport chain and disrupt mitochondrial function. The pathways by which PH3 toxicity develops are unknown, and previous studies have focused exclusively on adult models. In order to characterize the toxic mechanisms of PH3 exposure in children, a pediatric rodent model of inhalation phosphine exposure was developed. Male and female Sprague Dawley rats at post‐natal day (PND) ages 21, 28, and 42 were exposed to PH3 via nose‐only inhalation. Female rats at PND 28 were found to have the lowest median lethal concentration x time (LCt50). Female PND 28 rats were used for transcriptomic analysis to identify toxic pathways associated with PH3 inhalation. Rats were exposed to either air or the LCt50 of PH3 (14,119 ppm x min) for 20 minutes and removed from the nose‐only inhalation system after an additional 5‐minute “off gas” period. Cardiac tissue was collected at 0.5, 1, 3, 6, and 24 hours post‐exposure and immediately snap frozen in liquid nitrogen. Total RNA was extracted and processed for microarray. Differences in gene expression between exposure groups were identified using Partek Genomics Suite, and identified genes were mapped to relevant pathways using Ingenuity Pathway Analysis (IPA) software. Microarray analysis revealed a biphasic gene expression pattern with the most changes occurring at 3 and 24 hours after phosphine exposure. At 3 hours post‐exposure, the changes in gene expression mapped to pathways involved with cellular function and maintenance and cardiac enlargement. In addition, upstream analysis suggested a role for norepinephrine in phosphine‐induced cardiotoxicity. At 24 hours post‐exposure, activation of the sirtuin signaling pathway, modulation of the mitochondrial permeability transition pore, and altered expression of mitochondrial membrane translocases TOMM7, TOMM22, and TOMM40 were observed. In addition, gene expression changes associated with metabolic reprogramming were detected. Branched chain amino acid degradation and fatty acid beta oxidation pathways were predicted to be inhibited, with downregulation of electron transport chain complexes I and V. These data support PH3 as a metabolic poison. Future analyses of these data will be used to identify additional pathways associated with phosphine toxicity.Support or Funding InformationThe research described was supported by an interagency agreement (AOD18014‐001‐00000) between the NIH Office of the Director (OD) and the USAMRICD under the oversight of the Chemical Countermeasures Research Program at the National Institute of Allergy and Infectious Diseases.