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.

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.

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.

Behavioral Evaluation of Laboratory-housed Ferrets (Mustela Putorius Furo) in Different Enclosure Sizes.

The domestic ferret (Mustela putorius furo) is a common research model for infectious disease and behavioral studies. Ferrets are social animals that are commonly pair-housed. The United States has no species-specific regulatory standards for housing ferrets. Optimal enclosure dimensions have also not been investigated in this species, and cage sizes reported in the literature vary. Adequate space is an important animal welfare consideration, as smaller cages have been linked to increased incidence of stress- or boredom-related behaviors in some species. Here, we evaluated activity budget and space utilization in 2 different enclosure sizes for pair-housed female ferrets (n = 12). Single cages measured 78.7×78.7×45.7cm; double cages were comprised of 2 single cages connected by a short tunnel measuring 17.8 cm. Three pairs of ferrets were housed in each cage size and continuous video recordings were captured for 2 wk prior to crossover to the other cage size. The overall activity budget was similar between groups, with the predominant behavior being inactivity (89%). Stereotypic behaviors, such as cage biting or escape attempts, were infrequent (<0.1%) in both groups. Ferrets in double cages remained in the same cage as their partner 96% of the time, suggesting that social support is very valuable. Our results suggest that ferrets in both cage sizes experienced satisfactory welfare conditions. Our findings also suggest that while cage size is not the only determinant of conspecific aggression, larger cages may be an effective intervention to ameliorate aggression in certain ferrets based on signalment or behavioral history, with particular utility as a potential alternative to re-pairing or single-housing. This study provides valuable information to guide animal care and use programs regarding appropriate ferret housing.