Table 4.
Change in the reciprocal of the retention factor (1/k) for gliclazide in the presence of increasing concentrations of fatty acids applied to normal HSA and glycated HSA columns
| Fatty Acid | Correlation Coefficienta | Type of Competitionb |
|---|---|---|
| Lauric acid (1.5–6 nM) | ||
| Normal HSA | r = 0.902 (n = 6) | Mixed mode |
| Glycated HSA | r = 0.513 (n = 6)c | Direct(?)c, KaI = 1.8 (± 1.5) × 107 M−1 |
| Linoleic acid (100–250 nM) | ||
| Normal HSA | r = 0.961 (n = 7) | Mixed mode |
| Glycated HSA | r = 0.972 (n = 7) | Direct, KaI = 1.6 (± 0.2) × 106 M−1 |
| Myristic acid (4–24 nM) | ||
| Normal HSA | r = 0.885 (n = 6) | Direct, KaI = 6.4 (± 1.7) × 106 M−1 |
| Glycated HSA | r = 0.965 (n = 6) | Direct, KaI = 2.4 (± 0.3) × 107 M−1 |
| Oleic acid (125–546 nM) | ||
| Normal HSA | r = 0.894 (n = 6) | Mixed mode |
| Glycated HSA | r = 0.796 (n = 7) | Direct, KaI = 6.2 (± 2.1) × 104 M−1 |
| Palmitic acid (100–400 nM) | ||
| Normal HSA | r = 0.965 (n = 6) | Direct, KaI = 6.3 (± 0.9) × 105 M−1 |
| Glycated HSA | r = 0.905 (n = 7) | Direct(?)c, KaI = 4.5 (± 10.2) × 107 M−1 |
| Stearic acid (10–80 nM) | ||
| Normal HSA | r = 0.885 (n = 7) | Direct, KaI = 7.4 (± 1.8) × 105 M−1 |
| Glycated HSA | r = 0.982 (n = 8) | Direct, KaI = 3.6 (± 0.3) × 106 M−1 |
The correlation coefficients are those obtained for a plot made according to Eqn. (1).
The values in parentheses represent a range of ± 1 S.D. A mixed mode interaction (e.g., direct competition plus a positive allosteric effect) was indicated in plots made according to Eqn. (1) by an initial decrease and then gradual increase in the retention factor for the injected drug as the concentration of fatty acids in the mobile phase was increased. A decrease in the retention factor for the drug when there was an increase in the concentration of the fatty acids could be produced by either a net negative allosteric effect or direct competition; in this study, the overall fit of the results to Eqn. (1) generally suggested that direct competition was present in most of these cases. In these latter cases, the apparent value of KaI for the fatty acid, as obtained by using Eqn. (1), is provided.
The correlation coefficient obtained in this case was not significant at the 95% confidence level or, in the case of palmitic acid and glycated HSA, the resulting value of KaI had a level of uncertainty that made it difficult to determine if direct competition was present in the given system. The symbol “(?)” indicates that the variation in the data was too large or the change in the retention factor was too small to obtain a reliable determination of exact type of interaction that was present or of the corresponding value of KaI in the case of direct competition.