Gene expression and immunochemical localization of major cytochrome P450 drug-metabolizing enzymes in bovine nasal olfactory and respiratory mucosa.

Despite tremendous advancement in the characterization of nasal enzyme expression, knowledge of the role of the nasal mucosa in the metabolism of xenobiotics is still inadequate, primarily due to the limited availability of in vitro models for nasal metabolism screening studies. An extensive knowledge of the oxidative and conjugative metabolizing capacity of the cattle (Bos taurus) olfactory and respiratory mucosa can aid in efficient use of these tissues for pre-clinical investigations of the biotransformation and toxicity of therapeutic agents following nasal administration or inhalation. Cows are also exposed to a variety of airborne pollutants and pesticides during their lifetime, the metabolism of which can have profound toxicological and ecological consequences. The aim of the present study was to characterize cytochrome P450 (CYP) enzyme expression in the bovine nasal mucosa. Amplification of the specific genes through RT-PCR confirmed expression of several CYP enzymes in bovine hepatic and nasal tissues. The results demonstrate that bovine nasal olfactory and respiratory mucosal and liver tissues express similar populations, families, and distributions of CYP enzymes, as has been previously reported with other species, including humans. Bovine ex vivo tissues can serve as a readily available reference tissue to elucidate preclinical toxico-kinetic effects resulting from exposure to substances in the environment or following drug administration.

Use of Physiologically Based Pharmacokinetic (PBPK) Modeling for Predicting Drug-Food Interactions: an Industry Perspective.

The effect of food on pharmacokinetic properties of drugs is a commonly observed occurrence affecting about 40% of orally administered drugs. Within the pharmaceutical industry, significant resources are invested to predict and characterize a clinically relevant food effect. Here, the predictive performance of physiologically based pharmacokinetic (PBPK) food effect models was assessed via de novo mechanistic absorption models for 30 compounds using controlled, pre-defined in vitro, and modeling methodology. Compounds for which absorption was known to be limited by intestinal transporters were excluded in this analysis. A decision tree for model verification and optimization was followed, leading to high, moderate, or low food effect prediction confidence. High (within 0.8- to 1.25-fold) to moderate confidence (within 0.5- to 2-fold) was achieved for most of the compounds (15 and 8, respectively). While for 7 compounds, prediction confidence was found to be low (> 2-fold). There was no clear difference in prediction success for positive or negative food effects and no clear relationship to the BCS category of tested drug molecules. However, an association could be demonstrated when the food effect was mainly related to changes in the gastrointestinal luminal fluids or physiology, including fluid volume, motility, pH, micellar entrapment, and bile salts. Considering these findings, it is recommended that appropriately verified mechanistic PBPK modeling can be leveraged with high to moderate confidence as a key approach to predicting potential food effect, especially related to mechanisms highlighted here.

Correction to: Use of Physiologically Based Pharmacokinetic (PBPK) Modeling for Predicting Drug-Food Interactions: an Industry Perspective.

An Erratum to this paper has been published: https://doi.org/10.1208/s12248-020-00535-z.

Modulating nasal mucosal permeation using metabolic saturation and enzyme inhibition techniques.

OBJECTIVE: Presystemic elimination resulting from local enzymatic degradation can play a key role in limiting the bioavailability of intranasally administered drugs. The aim of this study was to evaluate the transfer of a metabolically susceptible drug across the nasal mucosa to illustrate the relative contributions of drug diffusivity and metabolic susceptibility on overall nasal mucosal permeation and to understand the effects of changes in enzymatic activity on the transfer across nasal epithelial and submucosal tissues. METHODS: The concentration-dependent permeation of melatonin, a CYP450 substrate, across excised bovine nasal olfactory and respiratory explants was studied along with quantifying the extent of melatonin 6-hydroxylation. Microsomal preparations were also used to determine the kinetic parameters for melatonin to 6-hydroxymelatonin biotransformation. KEY FINDINGS: Enzyme saturation at higher melatonin concentrations and inclusion of a CYP450 inhibitor both resulted in the significant increase in melatonin permeation across the nasal mucosa. CONCLUSIONS: Metabolic loss of melatonin during nasal permeation demonstrates CYP450 activity in the nasal epithelium and submucosal tissues. The extent of biotransformation of melatonin during its transport across the nasal mucosal explants suggests that, although the nasal route bypasses hepatic first-pass metabolism, nasal bioavailability can be significantly influenced by mucosal enzymatic activity.