Generation and characterization of a humanized ACE2 mouse model to study long-term impacts of SARS-CoV-2 infection.

Although the COVID-19 pandemic has officially ended, the persistent challenge of long-COVID or post-acute COVID sequelae (PASC) continues to impact societies globally, highlighting the urgent need for ongoing research into its mechanisms and therapeutic approaches. Our team has recently developed a novel humanized ACE2 mouse model (hACE2ki) designed explicitly for long-COVID/PASC research. This model exhibits human ACE2 expression in tissue and cell-specific patterns akin to mouse Ace2. When we exposed young adult hACE2ki mice (6 weeks old) to various SARS-CoV-2 lineages, including WA, Delta, and Omicron, at a dose of 5 × 105 PFU/mouse via nasal instillation, the mice demonstrated distinctive phenotypes characterized by differences in viral load in the lung, trachea, and nasal turbinate, weight loss, and changes in pro-inflammatory cytokines and immune cell profiles in bronchoalveolar lavage fluid. Notably, no mortality was observed in this age group. Further, to assess the model's relevance for long-COVID studies, we investigated tau protein pathologies, which are linked to Alzheimer's disease, in the brains of these mice post SARS-CoV-2 infection. Our findings revealed the accumulation and longitudinal propagation of tau, confirming the potential of our hACE2ki mouse model for preclinical studies of long-COVID.

Pharmacokinetics of Extended-release Buprenorphine and Clinical Efficacy for Postoperative Pain Management in the Domestic Ferret (Mustela putorius furo).

Buprenorphine hydrochloride (Bup-HCl) is a common injectable opioid analgesic. In ferrets, Bup-HCl must be administered every 8 to 12 h to maintain clinical efficacy. Extended-release analgesics offer multiple advantages, including reduced handling and injection frequency, improved compliance, and increased protection from end-of-dose failure. Although efficacy of extended-release buprenorphine formulations has been demonstrated in other species, their use in the domestic ferret has not been investigated. In this study, we evaluated the pharmacokinetics of a compounded polymeric formulation of buprenorphine (Bup-ER) and a pharmaceutical-grade, FDA-indexed liposomal suspension (Bup-XR). Two doses each of Bup-ER (0.12 and 0.2 mg/kg) and Bup-XR (0.2 and 0.6 mg/kg SC) were administered to young adult female ferrets and plasma concentrations were measured between 0 and 96 h (n = 4 animals per timepoint). All doses of both drugs achieved therapeutic plasma levels by 30 min. Furthermore, high-dose Bup-XR maintained therapeutic levels for 72 h, followed by high-dose Bup-ER (less than 48 h), low-dose Bup-XR (24 h), and low-dose Bup-ER (less than 24 h). In this study, we also developed a pain scoring system and utilized this to compare analgesic efficacy between single high-dose Bup-XR (0.6 mg/kg SC) and a standard postoperative course of Bup-HCl (0.02 mg/kg SC every 10 to 12 h for 8 doses) after ovariohysterectomy. Ferrets receiving Bup-XR had significantly lower respiratory rate and posture scores in the first 24 h postoperatively than did those that received Bup-HCl and were less likely to react to palpation of the surgical incision. Of note, ferrets that received high-dose Bup-ER had a significantly higher incidence of injection site reactions than ferrets that received Bup-HCl (P = 0.0137). This study demonstrates that a single dose of Bup-XR (0.6 mg/kg SC) is a safe and effective analgesic in female ferrets, with a duration of action up to 72 h and minimal side effects, offering a refinement to analgesia in this species.

Antigen-display exosomes provide adjuvant-free protection against SARS-CoV-2 disease at nanogram levels of spike protein.

As the only bionormal nanovesicle, exosomes have high potential as a nanovesicle for delivering vaccines and therapeutics. We show here that the loading of type-1 membrane proteins into the exosome membrane is induced by exosome membrane anchor domains, EMADs, that maximize protein delivery to the plasma membrane, minimize protein sorting to other compartments, and direct proteins into exosome membranes. Using SARS-CoV-2 spike as an example and EMAD13 as our most effective exosome membrane anchor, we show that cells expressing a spike-EMAD13 fusion protein produced exosomes that carry dense arrays of spike trimers on 50% of all exosomes. Moreover, we find that immunization with spike-EMAD13 exosomes induced strong neutralizing antibody responses and protected hamsters against SARS-CoV-2 disease at doses of just 0.5-5 ng of spike protein, without adjuvant, demonstrating that antigen-display exosomes are particularly immunogenic, with important implications for both structural and expression-dependent vaccines.

Comparison of Rodent Infectious Agent Detection by Exhaust Dust Testing and Traditional Sentinel Testing Using Quantitative Polymerase Chain Reaction.

Improved diagnostic capabilities and a desire to reduce or refine the use of animals as soiled bedding sentinels (SBS) have driven interest in developing the use of PCR-based testing methods, such as exhaust dust testing (EDT), for routine rodent health surveillance. We compared the absolute and quantitative PCR results from EDT filters with SBS mice by routine screening via a panel of 19 infectious agents including agents known to be excluded or present in the colony. In this study, EDT and SBS were compared at days 0, 90, and 180 in 3 facilities (n = 12 rooms) with animals housed on IVC racks (n = 19 double-sided and 23 single-sided racks). All racks were negative for excluded agents (n = 15 agents) during the study. The bacterial agent Helicobacter spp. was consistently detected on EDT filters while less consistently detected via SBS. EDT filters detected Corynebacterium bovis better than SBS in areas where the agent was present. EDT filters and SBS mice tested for murine norovirus (MNV) demonstrated agreement for positive tests by both PCR and serology. For rodent chaphamaparvovirus-1 (RCHPV-1) we compared EDT to urine and feces from SBS. Six cages of SBS were positive for RCHPV-1 by fecal PCR with 5 out of 6 testing positive on urine, while only 3 out of 6 EDT filters tested positive. Since real-time fluorogenic PCR was used for testing, relative PCR copy numbers for each positive finding were evaluated to estimate organism load at the rack level. Copy numbers allowed for further characterization of agent presence within a colony. Furthermore, we compared copy numbers with cage census for MNV and Helicobacter spp., which was positively correlated for EDT testing but not for SBS. Overall, our results demonstrate that EDT's ability to detect many commonly excluded agents is comparable to or better than SBS.

Innate Immune Activation and Mitochondrial ROS Invoke Persistent Cardiac Conduction System Dysfunction after COVID-19.

Background: Cardiac risk rises during acute SARS-CoV-2 infection and in long COVID syndrome in humans, but the mechanisms behind COVID-19-linked arrhythmias are unknown. This study explores the acute and long term effects of SARS-CoV-2 on the cardiac conduction system (CCS) in a hamster model of COVID-19. Methods: Radiotelemetry in conscious animals was used to non-invasively record electrocardiograms and subpleural pressures after intranasal SARS-CoV-2 infection. Cardiac cytokines, interferon-stimulated gene expression, and macrophage infiltration of the CCS, were assessed at 4 days and 4 weeks post-infection. A double-stranded RNA mimetic, polyinosinic:polycytidylic acid (PIC), was used in vivo and in vitro to activate viral pattern recognition receptors in the absence of SARS-CoV-2 infection. Results: COVID-19 induced pronounced tachypnea and severe cardiac conduction system (CCS) dysfunction, spanning from bradycardia to persistent atrioventricular block, although no viral protein expression was detected in the heart. Arrhythmias developed rapidly, partially reversed, and then redeveloped after the pulmonary infection was resolved, indicating persistent CCS injury. Increased cardiac cytokines, interferon-stimulated gene expression, and macrophage remodeling in the CCS accompanied the electrophysiological abnormalities. Interestingly, the arrhythmia phenotype was reproduced by cardiac injection of PIC in the absence of virus, indicating that innate immune activation was sufficient to drive the response. PIC also strongly induced cytokine secretion and robust interferon signaling in hearts, human iPSC-derived cardiomyocytes (hiPSC-CMs), and engineered heart tissues, accompanied by alterations in electrical and Ca 2+ handling properties. Importantly, the pulmonary and cardiac effects of COVID-19 were blunted by in vivo inhibition of JAK/STAT signaling or by a mitochondrially-targeted antioxidant. Conclusions: The findings indicate that long term dysfunction and immune cell remodeling of the CCS is induced by COVID-19, arising indirectly from oxidative stress and excessive activation of cardiac innate immune responses during infection, with implications for long COVID Syndrome.

Evolution of nasal and olfactory infection characteristics of SARS-CoV-2 variants.

SARS-CoV-2 infection of the upper airway and the subsequent immune response are early, critical factors in COVID-19 pathogenesis. By studying infection of human biopsies in vitro and in a hamster model in vivo, we demonstrated a transition in nasal tropism from olfactory to respiratory epithelium as the virus evolved. Analyzing each variant revealed that SARS-CoV-2 WA1 or Delta infect a proportion of olfactory neurons in addition to the primary target sustentacular cells. The Delta variant possessed broader cellular invasion capacity into the submucosa, while Omicron displayed enhanced nasal respiratory infection and longer retention in the sinonasal epithelium. The olfactory neuronal infection by WA1 and the subsequent olfactory bulb transport via axon were more pronounced in younger hosts. In addition, the observed viral clearance delay and phagocytic dysfunction in aged olfactory mucosa were accompanied by a decline of phagocytosis-related genes. Further, robust basal stem cell activation contributed to neuroepithelial regeneration and restored ACE2 expression postinfection. Together, our study characterized the nasal tropism of SARS-CoV-2 strains, immune clearance, and regeneration after infection. The shifting characteristics of viral infection at the airway portal provide insight into the variability of COVID-19 clinical features, particularly long COVID, and may suggest differing strategies for early local intervention.