IAM LC and LEKC Compared for Assessing Drug Passage through the Respiratory Tract

Scientists from Edinburgh Napier University in Edinburgh, UK and the University of Helsinki in Finland compared two techniques for their effectiveness in assessing drug passage through respiratory mucosa. Their findings were published in the Journal of Chromatography A (1).

Asian woman with symptoms of sinusitis and inflammation of the mucous membrane | Image Credit: © blackday - stock.adobe.com

The respiratory mucosa is a mucous membrane lining the respiratory tract, including the nasal cavity, the larynx, the trachea, and the bronchi tree (2). The inhalation route is of increasing interest for local and systemic drug delivery, including macromolecular biopharmaceuticals like peptides, proteins, and gene therapeutics.

In the initial phases of drug development, evaluating physicochemical properties of drug candidates extends beyond biological activity assessment. Lipophilicity and solubility are also essential parameters that play roles in the absorption of drugs administered via parenteral and enteral routes, including the pulmonary route. Because of this, there is a need for reliable, reproducible, and high-throughput screening methods to characterize these parameters, the scientists wrote. When drugs exist in non-ionized forms, lipophilicity is commonly assessed through the determination of the partition coefficient (log P_o/w) between immiscible phases. Log P_o/w is usually assessed using an isotropic n-octanol/water system, with n-octanol representing the body's lipophilic environment and water depicting the characteristics of extracellular fluids. Further, log P_o/w determination is often employed as an indicator of transmembrane permeability.

For this study, the scientists compared the application of biomimetic techniques, immobilized artificial membrane liquid chromatography (IAM LC) and liposome electrokinetic capillary chromatography (LEKC), for the prediction of pulmonary drug permeability. The pulmonary absorption profiles of 26 structurally unrelated drug-like molecules were evaluated using their IAM hydrophobicity index (CHI IAM) measured in IAM LC, and the logarithm of distribution constants (log KLEKC) derived from the LEKC experiments. Lipophilicity parameters obtained from IAM LC and most LEKC analyses were linearly related to n-octanol/water partitioning coefficients of neutral forms (such as log P_o/w values) to a moderate extent. However, the relationships with distribution coefficients at the experimental pH of 7.40 were overall weaker for IAM LC data and sigmoidal for some liposome compositions (phosphatidyl choline (PC): phosphatidyl inositol (PI) 85:15 mol% and 90:10 mol%) and concentrations (4 mM) in LEKC. These findings suggest that phospholipid portioning supports hydrophobic and electrostatic interactions between ionized drugs and charged phospholipid moieties. The latter type of interactions is original compared to those occurring in the more established n-octanol/water partitioning systems.

The scientists found stronger correlations (R² > 0.65) between LEKC retention parameters and the experimental apparent lung permeability, as opposed to values obtained by IAM LC. Therefore, they concluded that LEKC offers more advantages over IAM LC in simulating cell membrane partitioning processes in the pulmonary delivery of drugs. However, though LEKC can more effectively simulate electrostatic and hydrophobic forces in drug/pulmonary membrane interactions in vitro, it is unsuitable for analyzing highly hydrophilic neutral or anionic compounds at the experimental pH. In contrast, IAM LC is useful for analyzing compounds spanning a wider range of lipophilicity. With its simpler and more robust implementation, in addition to its propensity for high-throughput automation, IAM LC is a more favorable choice for researchers in drug development and pharmacological studies.

References

(1) Orzel, D.; Ravald, H.; Dillon, A.; Rantala, J.; Wiedmer, S. K.; Russo, G. Immobilised artificial Membrane Liquid Chromatography vs Liposome Electrokinetic Capillary Chromatography: Suitability in Drug/Bio Membrane Partitioning Studies and Effectiveness in the Assessment of the Passage of Drugs Through the Respiratory Mucosa. J. Chromatogr. A 2024, 4565286. DOI: 10.1016/j.chroma.2024.465286

(2) Respiratory Mucosa. National Library of Medicine 2000. https://www.ncbi.nlm.nih.gov/mesh?Cmd=DetailsSearch&Term=%22Respiratory+Mucosa%22%5BMeSH+Terms%5D (accessed 2024-8-26)

(3) Ehrhardt, C.; Fiegel, J.; Fuchs, S.; et al. Drug Absorption by the Respiratory Mucosa: Cell Culture Models and Particulate Drug Carriers. J. Aerosol Med. 2022, 15 (2), 131–139. DOI: 10.1089/089426802320282257