UBC Theses and Dissertations
The plasma lipoprotein distribution of liposomal nystatin is influenced by the apolipoprotein content of high density lipoproteins Cassidy, Shawn Michael
It has been demonstrated that numerous hydrophobic compounds associate with the plasma lipoproteins. One such compound is the polyene macrolide antibiotic, nystatin (Nys). The purpose of this study was to compare the human plasma lipoprotein distribution of free nystatin (Nys) versus liposomal nystatin (L-Nys) in plasma of varying lipoprotein composition. Furthermore, the relationship of drug distribution to lipid or protein concentration of the lipoprotein fractions was also investigated. To assess the lipoprotein distribution of free and liposomal nystatin (Nys and L-Nys), human plasma was incubated with Nys and L-Nys (equivalent to 20 µg of Nys per mL of plasma) for 5 minutes at 37°C. The plasma was subsequently partitioned into its lipoprotein and lipoprotein-deficient plasma (LPDP) fractions by step-gradient ultracentrifugation, each fraction being analyzed for Nys content by high pressure liquid chromatography. Furthermore, the lipid and protein content and composition of each fraction was also determined. That is, the cholesterol (total, esterified, and unesterified), triglyceride, phospholipid, and protein concentration of very low density lipoprotein (VLDL), low density lipoprotein (LDL), high density lipoprotein (HDL), and LPDP were measured. Upon the incubation of Nys and L-Nys in human plasma the majority of Nys found within the lipoprotein fractions was recovered from HDL. With the incorporation of Nys into liposomes comprised of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylglycerol (DMPG) phospholipids, a significant increase in the percentage of drug recovered from HDL was observed when compared to Nys. This increase in the distribution of drug into the HDL fraction upon incubation of plasma with L-Nys (compared to Nys) suggests that the phospholipid composition of the liposome may play a role in the distribution of Nys within lipoproteins. With the incorporation of Nys into liposomes composed of DMPC and DMPG in a 7: 3 (wt.: wt.) ratio, a targeting of Nys to HDL appears to occur. In fact, the distribution of Nys into the combined lipoprotein fractions was increase by approximately 50% when the liposomal formulation was employed. Furthermore, it was demonstrated that as the amount of HDL protein decreased in succession from one plasma sample to the next, a subsequent decrease in the amount of Nys and L-Nys recovered was similarly observed. In light of these findings, it may be speculated that a relationship exists between the distribution of Nys and L-Nys into HDL and the apolipoprotein content of HDL. However, due to the lack of specificity of the protein assay it was not possible to conclude with confidence that any individual apolipoprotein was responsible for the distribution of the drug into the HDL fraction. In summary, the work described herein illustrates the need for understanding the effects that differences in the lipoprotein profiles have on the distribution of Nys and L-Nys in human plasma. Since diseased patient populations frequently exhibit abnormal lipoprotein profiles, this work may further help to elucidate the effect that their lipid load has on the distribution of the drug in plasma. This may ultimately lead to observable changes in the pharmacokinetics, pharmacodynamics, or even toxicity of nystatin thereby demonstrating the importance of the interaction between hydrophobic or lipid-based drugs with plasma lipoproteins.