Wesley Wong

Differences in Lipoprotein Lipid Concentration and Composition Modify the Plasma Distribution of Cyclosporine

AbstractPurpose. The purpose of this study was to define the relationship between lipoprotein (LP) lipid concentration and composition and the distribution of cyclosporine (CSA) in human plasma. Methods. 3H-CSA LP distribution was determined in normolipidemic human plasma that had been separated into different LP and lipoprotein-deficient plasma (LPDP) fractions by either affinity chromatography coupled with ultracentrifugation, density gradient ultracentrifugation or fast protein liquid chromatography. 3H-CSA LP distribution (at a concentration of 1000 ng/ml) was also determined in patient plasma samples with defined dyslipidemias. Furthermore, 3H-CSA LP distribution was determined in patient plasma samples of varying LP lipid concentrations. Following incubation, the plasma samples were separated into their LP and LPDP fractions by sequential phosphotungistic acid precipitation in the dyslipidemia studies and by density gradient ultracentrifugation in the specific lipid profile studies and assayed for CSA by radioactivity. Total plasma and lipoprotein cholesterol (TC), triglyceride (TG) and protein (TP) concentrations in each sample were determined by enzymatic assays. Results. When the LP distribution of CSA was determined using three different LP separation techniques, the percent of CSA recovered in the LP-rich fraction was greater than 90% and the LP binding profiles were similar with most of the drug bound to plasma high-density (HDL) and low-density (LDL) lipoproteins. When 3H-CSA was incubated in dyslipidemic human plasma or specific patient plasma of varying LP lipid concentrations the following relationships were observed. As the very low-density (VLDL) and LDL cholesterol and triglyceride concentrations increased, the percent of CSA recovered within the VLDL and LDL fractions increased. The percent of CSA recovered within the HDL fraction significantly decreased as HDL triglyceride concentrations increased. The percent of CSA recovered in the LPDP fraction remained constant except in hypercholesterolemic/hypertriglyceridemic plasma where the percent of CSA recovered decreased. Furthermore, increases in VLDL and HDL TG/TC ratio resulted in a greater percentage of CSA recovered in VLDL but less in HDL. Conclusions. These findings suggest that changes in the total and plasma LP lipid concentration and composition influence the LP binding of CSA and may explain differences in the pharmacological activity and toxicity of CSA when administered to patients with different lipid profiles.

Development of biodegradable polymeric paste formulations for taxol: An in vitro and in vivo study

Abstract Biodegradable polymeric paste formulations (‘surgical pastes’) for local delivery of taxol were developed and characterized. Taxol was mixed into melted poly(D,L-lactide)- block -poly(ethylene glycol)- block -poly(D,L-lactide) (PDLLA-PEG-PDLLA) copolymers and blends of low molecular weight poly(D,L-lactic acid) and poly-ϵ-caprolactone (PDLLA:PCL) to obtain the paste formulations. The release of taxol into PBS albumin buffer was measured by HPLC. The polymers and pastes were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). Taxol was released in a sustained manner from the PDLLA-PEG-PDLLA paste over a period of 2 months by diffusion and polymer erosion. The release from the blend was mainly erosion controlled and consisted of a burst followed by a period of slow release. Efficacy of the pastes in inhibiting tumor growth in mice was evaluated. Molten, taxol loaded paste formulations were placed at subcutaneous tumor sites in mice (pastes harden at 37°C). After 16 days, the reduction in tumor weight was measured. Both the taxol loaded copolymer and 90:10 PDLLA:PCL blend formulations significantly inhibited tumor growth in mice. The pastes with faster in vitro release rates resulted in greater efficacy in inhibiting tumor growth. The results showed that biodegradable polymeric surgical pastes are promising formulations for the local delivery of taxol to inhibit tumor growth.

The inhibition of collagenase induced degradation of collagen by the galloyl-containing polyphenols tannic acid, epigallocatechin gallate and epicatechin gallate

Collagen based cosmetic fillers require repeat treatments due to collagenase derived degradation of the filler in the intradermal injection site. The objective of this study was to investigate the inhibition of this degradation by the galloyl-containing compounds tannic acid, epigallocatechin gallate (EGCG), epicatechin gallate (ECG) and gallic acid (GA). A gel permeation chromatography assay was developed to quantitate the collagenase induced reductions in collagen molecular weight. The binding of the compounds to collagen was measured using HPLC. The stabilization of collagen was measured using Differential Scanning Calorimetry (DSC). Tannic acid, EGCG and ECG (but not GA) were found to strongly inhibit collagen degradation at concentrations in the low micromolar range. The compounds bound strongly to collagen and stabilized collagen. It is concluded that tannic acid, EGCG and ECG bind to collagen via extensive hydrogen bonding augmented by some hydrophobic interactions and prevent the free access of collagenase to active sites on the collagen chains.

P-Glycoprotein Efflux Inhibition by Amphiphilic Diblock Copolymers: Relationship between Copolymer Concentration and Substrate Hydrophobicity

The utilization of surfactants to increase intestinal absorption of drugs is a viable strategy that benefits from increases in drug solubilization and the potential for inhibition of P-glycoprotein (P-gp) mediated efflux. However, the effective concentration range for P-gp inhibition of most surfactants is defined over a narrow concentration range, below the critical micelle concentration (CMC), as a result of significant micelle sequestration of drug. Therefore, the objectives of these studies were to assess if association of P-gp substrates differing in hydrophobicity will impact the effective concentration range for P-gp inhibition by amphiphilic diblock copolymers based on methoxypolyethylene glycol-block-polycaprolatone (MePEG-b-PCL). Comparisons between the micelle association and Caco-2 cellular accumulation were evaluated using two structurally homologous P-gp substrates, the relatively hydrophobic R-6G and the hydrophilic R-123, over concentrations above and below the CMC for MePEG-b-PCL diblock copolymers. An approximately 3.75-fold enhancement of R-123 accumulation occurred with 2 mM MePEG17-b-PCL5, compared to approximately 1.25-fold for R-6G. This decrease in the accumulation enhancement corresponds with the higher R-6G fraction (0.75) associated at 2 mM MePEG17-b-PCL5 compared with R-123 (0.25). Interestingly, R-6G accumulation was enhanced over a very broad range of MePEG17-b-PCL5 concentrations below the CMC. This was in contrast to R-123, which demonstrated no enhancement below the CMC. A similar concentration dependent accumulation profile was seen with other surfactants such as vitamin E TPGS and Cremophor EL and with two other P-gp substrates differing in hydrophobicity, the relatively hydrophobic paclitaxel and hydrophilic doxorubicin. In conclusion, the effective concentration range for surfactant mediated inhibition of P-gp appears to depend on the P-gp substrate hydrophobicity.