STAT-1 Knockout Mice as a Model for Wild-Type Sudan Virus (SUDV)

Currently there is no FDA-licensed vaccine or therapeutic against Sudan ebolavirus (SUDV) infections. The largest ever reported 2014–2016 West Africa outbreak, as well as the 2021 outbreak in the Democratic Republic of Congo, highlight the critical need for countermeasures against filovirus infections. A well-characterized small animal model that is susceptible to wild-type filoviruses would greatly add to the screening of antivirals and vaccines. Here, we infected signal transducer and activator of transcription-1 knock out (STAT-1 KO) mice with five different wildtype filoviruses to determine susceptibility. SUDV and Marburg virus (MARV) were the most virulent, and caused 100% or 80% lethality, respectively. Zaire ebolavirus (EBOV), Bundibugyo ebolavirus (BDBV), and Taï Forest ebolavirus (TAFV) caused 40%, 20%, and no mortality, respectively. Further characterization of SUDV in STAT-1 KO mice demonstrated lethality down to 3.1 × 10¹ pfu. Viral genomic material was detectable in serum as early as 1 to 2 days post-challenge. The onset of viremia was closely followed by significant changes in total white blood cells and proportion of neutrophils and lymphocytes, as well as by an influx of neutrophils in the liver and spleen. Concomitant significant fluctuations in blood glucose, albumin, globulin, and alanine aminotransferase were also noted, altogether consistent with other models of filovirus infection. Finally, favipiravir treatment fully protected STAT-1 KO mice from lethal SUDV challenge, suggesting that this may be an appropriate small animal model to screen anti-SUDV countermeasures.

Filovirus Virulence in Interferon α/β and γ Double Knockout Mice, and Treatment with Favipiravir

The 2014 Ebolavirus outbreak in West Africa highlighted the need for vaccines and therapeutics to prevent and treat filovirus infections. A well-characterized small animal model that is susceptible to wild-type filoviruses would facilitate the screening of anti-filovirus agents. To that end, we characterized knockout mice lacking α/β and γ interferon receptors (IFNAGR KO) as a model for wild-type filovirus infection. Intraperitoneal challenge of IFNAGR KO mice with several known human pathogenic species from the genus Ebolavirus and Marburgvirus, except Bundibugyo ebolavirus and Taï Forest ebolavirus, caused variable mortality rate. Further characterization of the prototype Ebola virus Kikwit isolate infection in this KO mouse model showed 100% lethality down to a dilution equivalent to 1.0 × 10⁻¹ pfu with all deaths occurring between 7 and 9 days post-challenge. Viral RNA was detectable in serum after challenge with 1.0 × 10² pfu as early as one day after infection. Changes in hematology and serum chemistry became pronounced as the disease progressed and mirrored the histological changes in the spleen and liver that were also consistent with those described for patients with Ebola virus disease. In a proof-of-principle study, treatment of Ebola virus infected IFNAGR KO mice with favipiravir resulted in 83% protection. Taken together, the data suggest that IFNAGR KO mice may be a useful model for early screening of anti-filovirus medical countermeasures.

Severe Acquired Idiopathic Thrombocytopenia in a Female Cynomolgus Macaque (Macaca fascicularis)

A 4-y-old female cynomolgus macaque presented for veterinary evaluation prior to placement in a preclinical study showed markedly low platelet counts that continued to decrease over time. Physical examination over the next several days showed areas of pale red discoloration in forelimbs, anterior thorax, and inguinal area and multifocal pinpoint areas of erythema or scabs. An area of dark red discoloration approximately 2 cm in diameter on the dorsal surface of the tongue was discovered on day 9. The macaque was euthanized, and histopathologic evaluation showed multifocal, ulcerative or erosive, hemorrhagic, lymphohistiocytic and neutrophilic glossitis and tonsillitis. The lesions on the tongue were associated with opportunistic fungi consistent with Candida albicans. The bone marrow showed megakaryocytic hyperplasia. There was no evidence of increased consumption of platelets, sequestration of platelets, or bone marrow suppression. The monkey was serologically negative for simian retrovirus, SIV, and simian T-lymphotropic virus. In light of cases reported in humans, immune-mediated destruction of platelets due to autoantibodies secondary to Candida albicans infection was considered. However, we were unable to detect antiplatelet antibodies on the platelet surface or in serum to support this etiology; therefore idiopathic thrombocytopenia was diagnosed. To our knowledge, this case represents the second reported observation of acquired thrombocytopenia in a nonhuman primate and the first reported observation in a cynomolgus macaque.

The Relationship of Glucokinase Activator–induced Hypoglycemia with Arteriopathy, Neuronal Necrosis, and Peripheral Neuropathy in Nonclinical Studies

Glucokinase activators (GKAs) are being developed for the treatment of type 2 diabetes. The toxicity of 4 GKAs (PF-04279405, PF-04651887, piragliatin, and PF-04937319) was assessed in mice, rats, dogs, and/or monkeys. GKAs were administered for 2 to 8 weeks. Standard endpoints, glucose, and insulin were assessed. All compounds produced varying degrees of hypoglycemia in all species. Brain neuronal necrosis and/or peripheral neuropathy were observed with most compounds. These findings are consistent with literature reports linking hypoglycemia with nervous system effects. Arteriopathy, mainly of cardiac vessels, was observed at a low frequency in monkey and/or dog. Arteriopathy occurred only at doses that produced severe and prolonged periods of repeated hypoglycemia. Since this lesion occurred in multiple studies with structurally distinct GKAs, these results suggested arteriopathy was related to GKA pharmacology. The morphological characteristics of the arteriopathy were consistent with that produced by experimental catecholamine administration. We hypothesize that the prolonged periods of hypoglycemia resulted in increased local and/or systemic concentrations of catecholamines via a counterregulatory and/or stress-related mechanism. Alternatively, prolonged hypoglycemia may have resulted in endothelial dysfunction leading to arteriopathy. This risk can be managed in human patients in clinical studies by careful glucose monitoring and intervention to avoid prolonged episodes of hypoglycemia.

Regulatory Forum Opinion Piece: Blind Reading of Histopathology Slides in General Toxicology Studies*

With the intention of reducing bias, a recent European Food Safety Authority draft guidance document included a recommendation for blinded evaluation of histopathology slides in general toxicology studies (EFSA 2011). Although blinding as to treatment status reduces bias in many types of scientific experiment and is sometimes also appropriate in toxicologic pathology (Holland and Holland 2011), it is most unlikely to help achieve the overall goal of improved human safety when used for routine histopathology evaluation of tissues in general toxicology studies. This is the case because (1) blinding is not applicable to the inductive reasoning process used to identify test article effects in the tissues and would dramatically reduce the chances of these being successfully identified; and (2) in any case, the bias that would be reduced by blinding is actually a bias favoring diagnosis of a toxicological hazard and a conservative safety evaluation, which is appropriate in this context. Other unintended consequences of blinding histopathology evaluation include reductions in sensitivity for a variety of additional reasons and increased subjectivity of the pathology data.

Interpretation and prediction of inhaled drug particle accumulation in the lung and its associated toxicity

The increasing use of poorly-soluble inhaled dry powder pharmaceuticals means that animal toxicology studies of these drugs frequently produce lung changes related to the physical presence of undissolved particulate material within the alveolar spaces. These changes are independent of any chemically- or pharmacologically-mediated toxicity and present a challenge to drug developers and regulators in that risk depends on the retained lung burden of undissolved drug material, rather than the delivered dose, systemic exposure or duration of dosing as traditionally used in risk assessment for inhaled compounds. The methodology presented uses basic pharmacokinetic principles to estimate lung particulate burdens achieved in rat inhalation toxicity studies for four inhaled compounds which have reached clinical evaluation. The estimated lung particulate burdens and associated histopathological findings were compared with published thresholds for similar effects caused by inert particulates such as titanium dioxide. Results of the analysis illustrate that regardless of the duration of the study, estimated lung burdens in excess of ∼1 mg drug per g lung were associated with adverse changes consistent with those described in the literature for inert insoluble particles. For all low solubility inhaled pharmaceuticals so far examined, the calculated steady-state retained lung burden of drug in humans is several orders of magnitude lower than that associated with adverse effects in human or animals.

Reproduction of porcine proliferative enteropathy with pure cultures of ileal symbiont intracellularis

Porcine proliferative enteropathy is consistently associated with the presence of intracellular curved bacteria in epithelial cells in affected portions of intestine. Two strains of these intracellular bacteria were cultured in a cell culture system with rat enterocytes (IEC-18) and passaged several times and used as oral inocula for 14 gnotobiotic and 8 conventional pigs. DNA and immunological studies had identified these bacteria as belonging to a new taxon, Ileal symbiont (IS) intracellularis. Conventional pigs dosed with approximately 3.7 x 10(6) of these organisms passaged six times in cell culture developed severe lesions of proliferative enteropathy in the ileum. Other conventional pigs dosed with a lower titer or with organisms passaged 13 times developed moderate and minor lesions, respectively. All gnotobiotic pigs dosed with organisms failed to develop lesions. Control pigs, eight conventional and two gnotobiotic, dosed with diluent, uninfected cell material or left undosed failed to develop lesions also. Reisolation of IS intracellularis and demonstration of the organism in mucosal and fecal samples only occurred in conventional pigs dosed with organisms. Gnotobiotic pigs lacking a normal intestinal flora have not been shown to be colonized by the organism. Seroconversion to IS intracellularis or mucosal infiltration by inflammatory cells was not observed in experimentally affected pigs, confirming the weak immune response characteristic of the natural disease. These results support the identification of IS intracellularis as an etiological agent of proliferative enteropathy in pigs.