The antioxidant effect of hydroxyl‐substituent Schiff bases on the free‐radical‐induced hemolysis of human erythrocytes

Abstract

The major objectives of the present work were focused on assessing the antioxidant capacities of two hydroxyl-substituent Schiff bases, 2-((o-hydroxylphenylimino)methyl)phenol (OSAP) and 2-((p-hydroxylphenylimino)methyl)phenol (PSAP) either used alone or in combination with some familiar water-soluble antioxidants i.e. 6-hydroxyl-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) and L-ascorbic acid (VC), and lipophilic ones i.e. alpha-tocopherol (TOH) and L-ascorbyl-6-laurate (VC-12). 2,2'-Azobis(2-amidinopropane hydrochloride) (AAPH). Induced hemolysis of human erythrocytes functioned as the evaluation experimental system in this research. The present findings showed that either OSAP or PSAP not only was an antioxidant with high activity in protecting erythrocytes against AAPH-induced hemolysis concentration-dependently, but can also protect erythrocytes by acting with Trolox, TOH, VC and VC-12 synergistically. Based on chemical kinetic deduction, the number of trapping peroxyl radicals, n, of the above-mentioned antioxidants can be calculated in relation to Trolox that traps two peroxyl radicals; thus, TOH can trap 3.83 peroxyl radicals, VC-12 traps 2.87 and VC can only trap 1.08. As for OSAP and PSAP, 8.71 and 13.7 peroxyl radicals can be trapped, respectively, indicating that they were the most efficient inhibitors against AAPH-induced hemolysis. Moreover, the total number of peroxyl radicals trapped by OSAP+Trolox, OSAP+TOH, OSAP+VC and PSAP+VC were higher than the sum of the above individual antioxidant used alone, demonstrating that a mutual promotive effect existed in the above mixed antioxidants. In contrast, owing to the fact that the total number of peroxyl radicals trapped by OSAP+VC-12, PSAP+Trolox, PSAP+TOH and PSAP+VC-12 were less than the sum of the above individual antioxidant used alone, a mutual antagonistic effect was suggested in these combinative usages. This information may be helpful in the pharmaceutical application of two Schiff bases.

Insight into the free‐radical‐scavenging mechanism of hydroxyl‐substituent Schiff bases in the free‐radical‐induced hemolysis of erythrocytes

“…10 Table 3 lists t inh value Table 3. Inhibition periods generated by the addition of Schiff bases and other antioxidants Run no.…”

“…18 R i represents the real free-radical-initiating rate that can be determined by a standard antioxidant with a known n. Our previous work reported that R i ¼ 1.68 mM/min in the case of Trolox being the standard antioxidant. 10 Therefore, the linear relationship between the concentration of Schiff base and t inh in Figure 2 can be understood theoretically by Equation (2) and n of Schiff bases can be calculated by (the corresponding slope  R i ) and collected in Table 2. By the comparison of n, the free-radical-scavenging capacities of these Schiff bases is PSAP > OSAP > OBH > PBH > BAH > BAN.…”

“…Moreover, the lag time, t lag , is prolonged to various degrees by the addition of different concentrations of Schiff bases. In order to avoid the influence of erythrocytes from different donors, the inhibition period, t inh ¼ t lag À t lag0 , was defined to reveal the protective effect of Schiff bases themselves on erythrocytes, 10 and listed in Table 1. Moreover, the correlations between the concentration of various Schiff bases and the corresponding t inh are illustrated in Figure 2.…”

“…The aforementioned influence can be expressed quantitatively by Equation (3), 10 and Table 4 lists the multiple correlation of t inh with the concentrations of Schiff bases and other antioxidants. The n values of Schiff bases (n Schiff ) and other antioxidants (n other ) in this case are calculated based on R i ¼ 1.68 mM/min, and listed in Table 4 also.…”

“…10 Briefly, the Schiff base/DMSO solution and AAPH/PBS solution (20 mM as the final concentration) were added successively to the 3.0% erythrocytes suspension in PBS (v/v). Then, the above mixture was incubated at 378C to initiate the hemolysis.…”