Application of magnetic resonance (MR) imaging for the development and validation of computational fluid dynamic (CFD) models of the rat respiratory system

Computational fluid dynamic (CFD) models of the respiratory system provide a quantitative basis for extrapolating the localized dose of inhaled materials and improving human health risk assessments based upon inhalation studies conducted in animals. Nevertheless, model development and validation have historically been tedious and time-consuming tasks. In recognition of this, we previously reported on the use of proton (1H) magnetic resonance (MR) imaging for visualizing nasal-sinus passages in the rat, and for speeding computational mesh generation. Here, the generation and refinement of meshes for rat nasal airways are described in more detail and simulated airflows are presented. To extend the CFD models to the complete respiratory tract, three-dimensional (3D) 1H MR imaging of rat pulmonary casts was also utilized to construct pulmonary airway meshes using procedures developed for the nasal airways. Furthermore, the feasibility of validating CFD predictions with MR was tested by imaging hyperpolarized 3He gas at physiological flow rates in a straight pipe with a diameter comparable to the rat trachea. Results from these diverse studies highlight the potential utility of MR imaging not only for speeding CFD development but also possibly for model validation.     

Synthesis, stereochemistry, and antimicrobial evaluation of substituted piperidin-4-one oxime ethers

In a wide search program toward new and efficient antimicrobial agents, a series of substituted piperidin-4-one oxime ethers (5a-5k) was synthesized and tested for their in vitro antibacterial and antifungal activities. Also, the structures of these oxime ethers and their relative stereochemistries have been investigated by nuclear magnetic resonance spectroscopy. In all the oxime ethers synthesized, the orientation of the N-O bond of the oxime ether moiety syn to C-5 (E-isomer) was deduced based on (1)H NMR and (13)C NMR spectra. It was found that the sterically less hindered compounds, either C-3 (H) and C-5 (H)- or C-3 (Me) and C-5 (H) -substituted ones 5a, 5c, 5d, 5f, 5g, 5i and 5j prefer chair conformation, whereas the sterically more hindered C-3 (Me) and C-5 (Me) -substituted ones 5b, 5e, 5h, and 5k prefer twist-boat conformation. Among the oxime ethers tested, 1,3,5-trimethyl-2,6-diphenylpiperidin-4-one O-(2-chlorophenylmethyl)oxime (5h) exhibited good antibacterial property against Bacillus subtilis, with minimum inhibitory concentration (MIC) closer to that of reference drug, streptomycin. Compounds, 1,3-dimethyl-2,6-diphenylpiperidin-4-one O-(2-chlorophenylmethyl)oxime (5g) and 1,3-dimethyl-2,6-diphenylpiperidin-4-one O-(2-bromophenylmethyl)oxime (5j) showed potent antifungal activity against Aspergillus flavus and Candida-51, respectively. The later compound 5j is more active than the reference drug while the activity of the former one 5g is similar to that of the reference drug, amphotericin B in terms of MIC. The present results may be used as key steps for the construction of novel chemical entities with better pharmacological profiles than standard drugs.     

Aggregatibacter actinomycetemcomitans as an Early Colonizer of Oral Tissues: Epithelium as a Reservoir?

This study examined in vivo and in vitro colonization by Aggregatibacter actinomycetemcomitans, an organism highly associated with aggressive periodontitis. Thirteen volunteers (5 were A. actinomycetemcomitans positive for buccal epithelial cells [BECs] and teeth, 5 were A. actinomycetemcomitans positive for teeth only, and 3 were A. actinomycetemcomitans-negative controls) had two mandibular stents fabricated. Each stent contained 3 removable hydroxyapatite (HA) tooth surrogates. One HA square was removed from a stent at 5 time points over 7 h to assess the transfer of A. actinomycetemcomitans from teeth or BECs to HA. Streptococcus, Actinomyces, A. actinomycetemcomitans, and total anaerobic counts were evaluated on each square over time. In vitro experiments evaluated binding, desorption, transfer, and reattachment of A. actinomycetemcomitans wild-type and mutant strains to BECs and saliva-coated HA (SHA). Streptococcus and Actinomyces formed 80% of the cultivable flora on HA in all subjects. Transfer of A. actinomycetemcomitans to HA was not seen in subjects with A. actinomycetemcomitans on teeth only. All 5 subjects with A. actinomycetemcomitans on BECs showed transfer of A. actinomycetemcomitans to HA. In vitro, A. actinomycetemcomitans desorbed from BECs and transferred to SHA. A. actinomycetemcomitans binding to SHA was irreversible and did not transfer to BECs. The adhesin Aae showed specificity for BECs. Fimbrial mutants showed the greatest reduction in binding to SHA. A. actinomycetemcomitans migrated from BECs to HA in vivo and to SHA in vitro; however, A. actinomycetemcomitans movement from teeth and SHA to BECs did not occur. In vivo, A. actinomycetemcomitans colonized HA within 6 h and thus can be considered an early colonizer. BECs are a likely reservoir for A. actinomycetemcomitans tooth colonization.Aggregatibacter actinomycetemcomitans has frequently been associated with the etiology of localized aggressive periodontitis (LAP) (41). More recently, longitudinal studies of both humans and animals have added to this evidence and made the association between A. actinomycetemcomitans and LAP even more compelling (10, 14). Furthermore, virulence factors associated with A. actinomycetemcomitans and studied on a molecular level appear to be consistent with the pathogenesis described for LAP (11, 12, 17). Taken together, these data suggest that A. actinomycetemcomitans could play an important role in the initiation and progression of LAP.A. actinomycetemcomitans resides in the oral cavity, is a member of the Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, and Kingella (HACEK) group of “pathogenic” microorganisms, and has been found on six continents (21). While population-based data are far from extensive, A. actinomycetemcomitans has been found in a small subset of individuals in the North and South American continents as well as in Europe, with a lower prevalence in Caucasian individuals and a higher prevalence in individuals from Asia and Africa (2, 3, 15, 16, 28, 29). These demographic patterns raise questions as to how and why certain groups of individuals are more prone to A. actinomycetemcomitans colonization. This global distribution could result from infection due to random but more frequent exposure to A. actinomycetemcomitans by individuals or groups of individuals on one continent than on another (21). Alternatively, A. actinomycetemcomitans colonization could be dependent on the specificity of the outer membrane proteins (OMPs) of the infecting bacteria and their interaction and coupling with surface receptors of host cells (1, 37). If exposure is the driving force for attachment, then colonization would occur in a nonspecific fashion and could be dependent upon the level of A. actinomycetemcomitans in the environment. If specificity is the driving force, then one would expect host selection to dictate A. actinomycetemcomitans attachment and that only those bacteria that interact with appropriate tissue receptors would be colonized by A. actinomycetemcomitans (37).Several groups have been working on the identification and characterization of adherence factors that allow A. actinomycetemcomitans to colonize the oral cavity (8, 24, 35). In vitro studies have suggested that soft tissue binding occurs in a specific manner and is mediated by the autotransporter adhesins ApiA and Aae (11, 24, 40). In contrast, binding of A. actinomycetemcomitans to tooth surfaces appears to occur in a nonspecific manner and is dominated by OMPs such as Flp (19, 31). There is no general agreement as to whether tooth or tissue surfaces form the primary site for A. actinomycetemcomitans colonization in the oral cavity (8, 23). In a longitudinal study of LAP, we confirmed reports by others and identified buccal epithelial cells (BECs) as a primary site for A. actinomycetemcomitans colonization in the oral cavities of healthy A. actinomycetemcomitans-positive individuals (10). However, definitive proof showing that buccal cells can seed tooth surfaces is lacking.Because A. actinomycetemcomitans is typically found in the mouth in <20% of the population (41), studying the role of A. actinomycetemcomitans colonization of clean tooth surfaces in the general population has presented a difficult challenge. As a result, studies that have examined the relationship of A. actinomycetemcomitans to early events in the colonization process in humans are rare (26). However, one study of monkeys, though limited in scope, has shown that A. actinomycetemcomitans can colonize teeth within a 5- to 8-h period after tooth cleaning (22). In that study, the main goal was to determine the influence of a carbohydrate diet on Streptococcus mutans colonization of thoroughly cleaned teeth, and identification of A. actinomycetemcomitans on tooth surfaces was discovered by chance. However, because these teeth were cleaned, the likely source of A. actinomycetemcomitans was the primate mucosa (22). Recent studies have shown that A. actinomycetemcomitans can be found in predentate children, suggesting that the mucosa can serve as a potential reservoir for tooth colonization (33).In an effort to help resolve questions related to early tooth and tissue colonization in humans, we explored the possibility of examining the colonization patterns of a number of A. actinomycetemcomitans-positive participants already enrolled in an ongoing longitudinal study (9). Since we had access to these subjects and had knowledge of their carriage of A. actinomycetemcomitans, we felt that we could recruit an appropriate subject population to study A. actinomycetemcomitans colonization of tooth surrogates in vivo (9). Overall, examination of the colonization patterns of A. actinomycetemcomitans can lead to a better understanding of the role of OMPs in A. actinomycetemcomitans binding, which could lead to potentially useful preventive and therapeutic strategies for LAP. The studies we report herein were designed to begin to address the following two important biological questions related to A. actinomycetemcomitans colonization of the oral cavity. Is A. actinomycetemcomitans an early colonizer of hydroxyapatite (HA) tooth surrogate surfaces? Do BECs serve as an effective reservoir for A. actinomycetemcomitans transfer to HA tooth surrogates?     

Magnetic resonance imaging and computational fluid dynamics (CFD) simulations of rabbit nasal airflows for the development of hybrid CFD/PBPK models

The percentages of total airflows over the nasal respiratory and olfactory epithelium of female rabbits were calculated from computational fluid dynamics (CFD) simulations of steady-state inhalation. These airflow calculations, along with nasal airway geometry determinations, are critical parameters for hybrid CFD/physiologically based pharmacokinetic models that describe the nasal dosimetry of water-soluble or reactive gases and vapors in rabbits. CFD simulations were based upon three-dimensional computational meshes derived from magnetic resonance images of three adult female New Zealand White (NZW) rabbits. In the anterior portion of the nose, the maxillary turbinates of rabbits are considerably more complex than comparable regions in rats, mice, monkeys, or humans. This leads to a greater surface area to volume ratio in this region and thus the potential for increased extraction of water soluble or reactive gases and vapors in the anterior portion of the nose compared to many other species. Although there was considerable interanimal variability in the fine structures of the nasal turbinates and airflows in the anterior portions of the nose, there was remarkable consistency between rabbits in the percentage of total inspired airflows that reached the ethmoid turbinate region (~50%) that is presumably lined with olfactory epithelium. These latter results (airflows reaching the ethmoid turbinate region) were higher than previous published estimates for the male F344 rat (19%) and human (7%). These differences in regional airflows can have significant implications in interspecies extrapolations of nasal dosimetry.     

Development of a Zealand white rabbit deposition model to study inhalation anthrax

Despite using rabbits in several inhalation exposure experiments to study diseases such as anthrax, there is a lack of understanding regarding deposition characteristics and fate of inhaled particles (bio-aerosols and viruses) in the respiratory tracts of rabbits. Such information allows dosimetric extrapolation to humans to inform human outcomes. The lung geometry of the New Zealand white rabbit (referred to simply as rabbits throughout the article) was constructed using recently acquired scanned images of the conducting airways of rabbits and available information on its acinar region. In addition, functional relationships were developed for the lung and breathing parameters of rabbits as a function of body weight. The lung geometry and breathing parameters were used to extend the existing deposition model for humans and several other species to rabbits. Evaluation of the deposition model for rabbits was made by comparing predictions with available measurements in the literature. Deposition predictions in the lungs of rabbits indicated smaller deposition fractions compared to those found in humans across various particle diameter ranges. The application of the deposition model for rabbits was demonstrated by extrapolating deposition predictions in rabbits to find equivalent human exposure concentrations assuming the same dose-response relationship between the two species. Human equivalent exposure concentration levels were found to be much smaller than those for rabbits.     

The inner tube sign in Ascariasis

Abdominal Radiology -     

Synthesis and spectral characterization of a new class of N-(N-methylpiperazinoacetyl)-2,6-diarylpiperidin-4-ones: antimicrobial, analgesic and antipyretic studies

A series of N-(N-methylpiperazinoacetyl)-2,6-diarylpiperidin-4-ones (13c-21c) were synthesized by the base catalyzed nucleophilic substitution of N-chloroacetyl-2,6-diarylpiperidin-4-ones obtained from their corresponding 2,6-diarylpiperidin-4-ones with N-methylpiperazine. These newly synthesized compounds were characterized by one- and two-dimensional NMR spectral studies. In all the cases, the piperazine ring adopted normal chair conformation with equatorial orientation of methyl group irrespective of the non-chair conformations of the piperidin-4-one moiety. All the compounds were screened for their possible antibacterial and antifungal activities against a spectrum of microbial agents besides analgesic and antipyretic activities. These biological studies proved that compounds 17c/18c against bacterial and 18c/20c against fungal strains exhibited promising antimicrobial activities whereas 17c/19c and 18c/19c showed beneficial analgesic and antipyretic profiles, respectively, at a concentration of 60mg/kg and were also found to be more potent than the reference drug.     

Synthesis and study of antibacterial and antifungal activities of novel 1-[2-(benzoxazol-2-yl)ethoxy]- 2,6-diarylpiperidin-4-ones

Some novel benzoxazolylethoxypiperidones have been synthesized and their antibacterial activity against streptococcus faecalis, bacillus subtilis, escherichia coli, staphylococcus aureus aand pseudomonas aeruginosa and antifungal activity against Candida-6, Candida albicans, Aspergillus niger, Candida-51 and Aspergillus flavus were evaluated. Compounds 37, 38 and 39 exerted potent in vitro antibacterial activity against Streptococcus faecalis while compounds 40 and 41 exhibited potent in vitro antifungal activity against Candida-51.