2.3.6. Circular Dichroism

Analysis of secondary structure change with glycating agent 'glucose' alone or together with garlic extract with varying concentrations (0–100 µg/mL) was investigated using a Jasco J 810 spectropolarimeter (Table 2). The presence of secondary structural elements was estimated as relative percentages by using the Chen and Yang equation [19] via a computer data processor. CD spectra were recorded for all the samples at a similar wavelength range (200 to 280 nm). As we have shown previously, there is a significant change in α-helix (−10.5%) and β-sheet (+14.9%) structures upon glycation of HSA [1]. Inhibition in the change of both α-helix (−2.8%) and β-sheet (+4.6%) structures of glycated samples were observed when incubated with garlic extract of 100 (µg/mL). Significant decreases in all the secondary structure (α-helix (*p* < 0.05), β-sheet (*p* < 0.01), β-turns (*p* < 0.01), and random coils (*p* < 0.05)) changes in glycated HSA samples were observed at 25 µg/mL concentration of garlic extract. Furthermore, the highest reduction in all the secondary structures was achieved at 100 µg/mL concentration of extract used (Table 2).

**Table 2.** Secondary structure composition of N-HSA, G-HSA, and G-HSA incubated with different concentrations of garlic extract (0–100 µg/mL).


The values are in percentage. Each sample was read in triplicate. Data are mean ± standard deviation. \* *p* < 0.05, \*\* *p* < 0.01, and \*\*\* *p* < 0.001 vs. control (N-HSA). Values in parentheses represent the percentage change in the secondary structure from N-HSA. Percentage decrease and increase are denoted by "–" and "+" signs. Different GE concentrations were used in µg/mL. The 5 mm of AG was used as negative control. The *t* test was adopted for the comparison between the groups.
