The Effect of Selected Flavonoids and Lipoic Acid on Natural and Model Cell Membranes: Langmuir and Microelectrophoretic Methods

The influence of kaempferol (K), myricetin (M) and lipoic acid (LA) on the properties of natural erythrocytes, isolated from animal blood and biological membrane models (monolayers and liposomes) made of phosphatidylcholine (PC), cholesterol (CHOL), and sphingomyelin (SM), CHOL in a ratio of 10:9, was investigated. The Langmuir method, Brewster angle microscopy (BAM) and microelectrophoresis were used. The presented results showed that modification of liposomes with kaempferol, myricetin and lipoic acid caused changes in the surface charge density and the isoelectric point value. Comparing the tested systems, several conclusions were made. (1) The isoelectric point for the DPPC:Chol:M (~2.2) had lower pH values compared to lipoic acid (pH~2.5) and kaempferol (pH~2.6). (2) The isoelectric point for the SM-Chol with myricetin (~3.0) had lower pH values compared to kaempferol (pH~3.4) and lipoic acid (pH~4.7). (3) The surface charge density values for the DPPC:Chol:M system in the range of pH 2–9 showed values from 0.2 to −2.5 × 10(−2) C m(−2). Meanwhile, for the DPPC:Chol:K and DPPC:Chol:LA systems, these values were higher at pH~2 (0.7 × 10(−2) C m(−2) and 0.8 × 10(−2) C m(−2)) and lower at pH~9 (−2.1 × 10(−2) C m(−2) and −1.8 × 10(−2) C m(−2)), respectively. (4) The surface charge density values for the SM:Chol:M system in the range of pH 2–9 showed values from 0.5 to −2.3 × 10(−2) C m(−2). Meanwhile, for the DPPC:Chol:K and DPPC:Chol:LA systems, these values were higher at pH~2 (0.8 × 10(−2) C m(−2)), and lower at pH~9 (−1.0 × 10(−2) C m(−2) and −1.8 × 10(−2) C m(−2)), respectively. (5) The surface charge density values for the erythrocytes with myricetin in the range of pH 2–9 showed values from 1.0 to −1.8 × 10(−2) C m(−2). Meanwhile, for the erythrocytes:K and erythrocytes:LA systems, these values, at pH~2, were 1.3 × 10(−2) C m(−2) and 0.8 × 10(−2) C m(−2) and, at pH~9, −1.7 × 10(−2) C m(−2) and −1.0 × 10(−2) C m(−2), respectively.