Introduction:: The development of techniques to predict the passive permeability of drugs are of significant interest due to the high cost of the drug discovery process, especially for neurodegenerative diseases which have lower success rates. The use of more biomimetic in vitro techniques during the preclinical stage has the potential to allow for better drug candidates to move forward to clinical trials. Droplet Interface Bilayers (DIBs) are lipid bilayers that are created when bringing two lipid monolayer covered aqueous droplets together. When they come into contact with each other, a lipid bilayer is formed between the droplets. By dosing one of these droplets with a drug of interest, we can use DIBs to study the permeability of drugs through passive diffusion, similar to the process at a cellular level. Here we show the use of biomimetic DIBs for the permeability study of neurodegenerative disease treating drugs.
Materials and Methods:: We use an oil-in-water system to form droplets in a concave glass microscope slide. The oil phase consists of hexadecane that has been dosed with dioleoylphosphatidylcholine (DOPC) at a concentration of 1 mg/mL, cholesterol and a treating drug (niacin or memantine, in this case) at varying concentrations (2:1, and 4:1 mol ratio). This oil mixture is stirred for increasing amounts of time at 50 C and used as the medium in which the aqueous droplets are suspended. Two aqueous droplets (one water, and one containing a 0.1 M NaCl solution) are used to form a DIB after a monolayer has formed at the surface of each droplet. The osmolality gradient across this bilayer allows us to study the effect of water permeability across the formed lipid membrane.
Results, Conclusions, and Discussions:: Our preliminary findings demonstrate that the presence of cholesterol in the bilayer hinders water diffusion across the membrane. However, we observed that increased drug concentration and longer oil solution mixing resulted in higher water diffusion rates, which we quantified using permeability coefficients. These findings suggest that drug-cholesterol interactions affect water permeability across bilayers, mimicking the cellular-level effects of higher cholesterol levels, which are commonly observed in patients with Alzheimer's disease (50% cholesterol/lipids). Conversely, normal cholesterol levels (20% or less cholesterol/lipids) are typically observed in healthy patients.
Droplet Interface Bilayers (DIBs) are a promising technique for studying the passive permeability of drugs, as they allow for the creation of lipid bilayers that mimic the biological cell membranes. Here, we have demonstrated the use of DIBs for the permeability study of neurodegenerative diseases treating drugs, showing the reduction of water diffusion across the membrane with increasing cholesterol concentration, typical in the presence of Alzheimer’s disease. Our findings pave the way for further studies using total lipid extracts and lipophilic drugs, potentially leading to the development of more effective drugs for neurodegenerative diseases.