Detailed comparison of anatomy and airflow dynamics in human and cynomolgus monkey nasal cavity

Is the mouse nose a miniature version of a rat nose? A computational comparative study

BACKGROUND AND OBJECTIVE

Although the mouse is a widely used animal model in biomedical research, there are few published studies on its nasal aerodynamics, potentially due to its small size. It is not appropriate to assume that mice and rats' nasal structure and airflow characteristics are the same because the ratio of nasal surface area to nasal volume and body weight is much higher in a mouse than in a rat. The aim of this work is to use anatomically accurate image-based computational fluid dynamic modeling to quantitatively reveal the characteristics of mouse nasal airflow and mass transport that haven't been detailed before and find key differences to that of rat nose, which will deepen our understanding of the mouse's physiological functions.

METHODS

We created an anatomically accurate 3D computational nasal model of a B6 mouse using postmortem high-resolution micro-CT scans and simulated the airflow distribution and odor transport patterns under restful breathing conditions. The deposition pattern of airborne particles was also simulated and validated against experimental data. In addition, we calculated the gas chromatograph efficiency of odor transport in the mouse employing the theoretical plate concept and compared it with previous studies involving cat and rat models.

RESULTS

Similar to the published rat model, respiratory and olfactory flow regimes are clearly separated in the mouse nasal cavity. A high-speed dorsal medial (DM) stream was observed, which enhances the delivery speed and efficiency of odor to the ethmoid (olfactory) recess (ER). The DM stream split into axial and secondary paths in the ER. However, the secondary flow in the mouse is less extensive than in the rat. The gas chromatograph efficiency calculations suggest that the rat may possess a moderately higher odorant transport efficiency than that of the mouse due to its more complex ethmoid recess structure and extensive secondary flow. However, the mouse's nasal structure seems to adapt better to varying airflow velocity.

CONCLUSIONS

Due to the inherent structural disparities, the rat and mouse models exhibit moderate differences in airflow and mass transport patterns, potentially impacting their olfaction and other behavioral habits.

Comparison of Nasal Dimensions According to the Facial and Nasal Indices Using Cone-Beam Computed Tomography

The nasal cavity constitutes the foremost portion of the respiratory system, composed of the anterior nasal aperture, nostrils, and choanae. It has an intricate anatomical structure since it has various functions, such as heat exchange, humidification, and filtration. Accordingly, clinical symptoms related to the nose, such as nasal congestion, snoring, and nasal septal deviation, are closely linked to the complex anatomical structure of the nasal cavity. Thus, the nasal cavity stands as a paramount structure in both forensic and clinical contexts. The majority of relevant studies have performed comparisons between sexes, with studies making comparisons according to the FI and NI only and examining relative percentages. Furthermore, the nasal cavity was measured in 2D, and not 3D, in most cases. In this study, we conducted a 3D modeling and anthropometric assessment of the nasal cavity using a 3D analysis software. Furthermore, we aimed to investigate whether the size of the nasal cavity differs according to sex, facial index (FI), and nasal index (NI). We retrospectively reviewed the cone-beam computed tomography (CBCT) data of 100 participants (50 males, 50 females) aged 20-29 years who visited the dental hospital of Dankook University (IRB approval no. DKUDH IRB 2020-01-007). Our findings showed that nasal cavity sizes generally differed according to sex, FI, and NI. These findings provide implications for performing patient-tailored surgeries in clinical practice and conducting further research on the nasal cavity. Therefore, we believe that our study makes a significant contribution to the literature.

Aerosol Inhalation of Chimpanzee Adenovirus Vectors (ChAd68) Expressing Ancestral or Omicron BA.1 Stabilized Pre-Fusion Spike Glycoproteins Protects Non-Human Primates against SARS-CoV-2 Infection

Current COVID-19 vaccines are effective countermeasures to control the SARS-CoV-2 virus pandemic by inducing systemic immune responses through intramuscular injection. However, respiratory mucosal immunization will be needed to elicit local sterilizing immunity to prevent virus replication in the nasopharynx, shedding, and transmission. In this study, we first compared the immunoprotective ability of a chimpanzee replication-deficient adenovirus-vectored COVID-19 vaccine expressing a stabilized pre-fusion spike glycoprotein from the ancestral SARS-CoV-2 strain Wuhan-Hu-1 (BV-AdCoV-1) administered through either aerosol inhalation, intranasal spray, or intramuscular injection in cynomolgus monkeys and rhesus macaques. Compared with intranasal administration, aerosol inhalation of BV-AdCoV-1 elicited stronger humoral and mucosal immunity that conferred excellent protection against SARS-CoV-2 infection in rhesus macaques. Importantly, aerosol inhalation induced immunity comparable to that obtained by intramuscular injection, although at a significantly lower dose. Furthermore, to address the problem of immune escape variants, we evaluated the merits of heterologous boosting with an adenovirus-based Omicron BA.1 vaccine (C68-COA04). Boosting rhesus macaques vaccinated with two doses of BV-AdCoV-1 with either the homologous or the heterologous C68-COA04 vector resulted in cross-neutralizing immunity against WT, Delta, and Omicron subvariants, including BA.4/5 stronger than that obtained by administering a bivalent BV-AdCoV-1/C68-COA04 vaccine. These results demonstrate that the administration of BV-AdCoV-1 or C68-COA04 via aerosol inhalation is a promising approach to prevent SARS-CoV-2 infection and transmission and curtail the pandemic spread.

Nasal anatomy and sniffing in respiration and olfaction of wild and domestic animals

Animals have been widely utilized as surrogate models for humans in exposure testing, infectious disease experiments, and immunology studies. However, respiratory diseases affect both humans and animals. These disorders can spontaneously affect wild and domestic animals, impacting their quality and quantity of life. The origin of such responses can primarily be traced back to the pathogens deposited in the respiratory tract. There is a lack of understanding of the transport and deposition of respirable particulate matter (bio-aerosols or viruses) in either wild or domestic animals. Moreover, local dosimetry is more relevant than the total or regionally averaged doses in assessing exposure risks or therapeutic outcomes. An accurate prediction of the total and local dosimetry is the crucial first step to quantifying the dose-response relationship, which in turn necessitates detailed knowledge of animals' respiratory tract and flow/aerosol dynamics within it. In this review, we examined the nasal anatomy and physiology (i.e., structure-function relationship) of different animals, including the dog, rat, rabbit, deer, rhombus monkey, cat, and other domestic and wild animals. Special attention was paid to the similarities and differences in the vestibular, respiratory, and olfactory regions among different species. The ventilation airflow and behaviors of inhaled aerosols were described as pertinent to the animals' mechanisms for ventilation modulation and olfaction enhancement. In particular, sniffing, a breathing maneuver that animals often practice enhancing olfaction, was examined in detail in different animals. Animal models used in COVID-19 research were discussed. The advances and challenges of using numerical modeling in place of animal studies were discussed. The application of this technique in animals is relevant for bidirectional improvements in animal and human health.

Comparison of Aerosol Deposition Between a Cynomolgus Macaque and a 3D Printed Cast Model of the Animal

PURPOSE

Preclinical aerosol studies using animals are essential for evaluating toxic or therapeutic effects on human respiratory tract. Macaques are relevant animal models for respiratory studies, but they are sensitive, expensive and difficult-to-access.

METHODS

In the context of preliminary studies before animal experiments, we set up an alternative in vitro anatomical model of macaque airways to reduce, refine and replace (3Rs) the animals. We printed an in vitro anatomical cast until the third bronchial division from X-ray computed tomography data of a healthy cynomolgus macaque. This in vitro model was then connected to a respiratory pump to mimic macaque's breathing. We assessed the relevance of this in vitro model, by comparing aerosol deposition patterns obtained with the anatomical model and in three macaques using planar gamma camera imaging. DTPA-^99mTechnetium aerosols were produced using three jet nebulizers, generating three different particle sizes: 13.1, 3.2 and 0.93 µm in terms of the mass median aerodynamic diameter (MMAD).

RESULTS

The data showed no statistical differences between the animal and anatomical in vitro models in terms of total aerosol deposited in the airways. However, the distribution of the deposition in the airways showed a higher deposited fraction in the upper respiratory tract in the animals than the in vitro model for all particle sizes.

CONCLUSIONS

The anatomical printed model appears to be a relevant in vitro tool to predict total aerosol deposition in macaque airways.

Preclinical In-Vivo Safety of a Novel Thyrotropin-Releasing Hormone-Loaded Biodegradable Nanoparticles After Intranasal Administration in Rats and Primates

Thyrotropin-releasing hormone (TRH) and TRH-like peptides carry a therapeutic potential for neurological conditions. Nanoparticles (NP) made of the biodegradable polymer, Poly(Sebacic Anhydride) (PSA), have been developed to carry TRH, intended for intranasal administration to patients. There is limited information on the safety of biodegradable polymers when given intranasally, and therefore, we have performed two preclinical safety and toxicity studies in cynomolgus monkeys and rats using TRH-PSA nanoparticles. The rats and monkeys were dosed intranasally for 42 days or 28 days, respectively, and several animals were followed for additional 14 days. Animals received either placebo, vehicle (PSA), or different concentrations of TRH-PSA. No systemic adverse effects were seen. Changes in T3 or T4 concentrations were observed in some TRH-PSA-treated animals, which did not have clinical or microscopic correlates. No effect was seen on TSH or prolactin concentrations. In the monkey study, microscopic changes in the nasal turbinates were observed, which were attributed to incidental mechanical trauma caused during administration. Taken together, the TRH-loaded PSA NPs have proven to be safe, with no local or systemic adverse effects attributed to the drug loaded nanoparticles. These findings provide additional support to the growing evidence of the safety of peptide-loaded NPs for intranasal delivery and pave the way for future clinical trials in humans.

Detailed comparative analysis of environmental microparticle deposition characteristics between human and monkey nasal cavities using a surface mapping technique

Inhaled particulate matter is associated with nasal diseases such as allergic rhinitis, rhinosinusitis and neural disorders. Its health risks on humans are usually evaluated by measurements on monkeys as they share close phylogenetic relationship. However, the reliability of cross-species toxicological extrapolation is in doubt due to physiological and anatomical variations, which greatly undermine the reliability of these expensive human surrogate models. This study numerically investigated in-depth microparticle transport and deposition characteristics on human and monkey (Macaca fuscata) nasal cavities that were reconstructed from CT-images. Deposition characteristics of 1-30μm particles were investigated under resting and active breathing conditions. Similar trends were observed for total deposition efficiencies and a single correlation using Stokes Number was fitted for both species and both breathing conditions, which is convenient for monkey-human extrapolation. Regional deposition patterns were carefully compared using the surface mapping technique. Deposition patterns of low, medium and high inertial particles, classified based on their total deposition efficiencies, were further analyzed in the 3D view and the mapped 2D view, which allows locating particle depositions on specific nasal regions. According to the particle intensity contours and regional deposition profiles, the major differences were observed at the vestibule and the floor of the nasal cavity, where higher deposition intensities of medium and high inertial particles were shown in the monkey case than the human case. Comparisons of airflow streamlines indicated that the cross-species variations of microparticle deposition patterns are mainly contributed by two factors. First, the more oblique directions of monkey nostrils result in a sharper airflow turn in the vestibule region. Second, the monkey's relatively narrower nasal valves lead to higher impaction of medium and high inertial particles on the nasal cavity floor. The methods and findings in this study would contribute to an improved cross-species toxicological extrapolation between human and monkey nasal cavities.