Antioxidant and semicarbazide‐sensitive amine oxidase inhibitory activities of alginic acid hydroxamates

Abstract

The commercial polysaccharides of alginic acid (medium (3500 cps, 2% solution) and low (250 cps, 2% solution) viscosities) were esterified with acidic methanol (1 mmol L −1 HCl) at 4 • C with gentle stirring for 5 days to obtain methyl esters of medium-viscosity alginic acid (ME-MVA) and low-viscosity alginic acid (ME-LVA). These ME-MVA and ME-LVA were reacted with alkaline hydroxylamine to obtain medium-viscosity alginic acid hydroxamates (MVA-NHOH) and LVA-NHOH. The percentages of hydroxamic acid content in MVA-NHOH and LVA-NHOH were calculated as 25% and 20%, respectively. The hydroxamate derivatives of alginic acid were used to test the antioxidant and semicarbazide-sensitive amine oxidase (SSAO) inhibitory activities in comparison with original materials (MVA and LVA). The half-inhibition concentrations, IC 50 , of scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) were 24.5 and 29.8 µg mL −1 for MVA-NHOH and LVA-NHOH, respectively. However, few scavenging activities of the MVA and LVA were found at the same concentrations. The IC 50 of the positive control of butylated hydroxytoluene was 5 µg mL −1 . The scavenging activity of DPPH radical was pHdependent, and the optimal pH for both of MVA-NHOH and LVA-NHOH was the Tris-HCl buffer (pH 7.9). Using electron spin resonance (ESR) to detect the activity of scavenging hydroxyl radicals, both alginic acid hydroxamates showed dose-dependent scavenging activities, and the IC 50 was 90 and 92 µg mL −1 , respectively, for MVA-NHOH and LVA-NHOH. Both alginic acid hydroxamates also exhibited protection against hydroxyl radical-mediated DNA damage. Both MVA-NHOH and LVA-NHOH showed dose-dependent inhibitory activities against bovine SSAO (2.53 units); the IC 50 was 0.16 and 0.09 µg mL −1 , respectively, for MVA-NHOH and LVA-NHOH, compared with 3.81 µg mL −1 of semicarbazide (positive controls). Amine oxidase activity staining also revealed that both MVA-NHOH and LVA-NHOH exhibited SSAO inhibitory activities. Both MVA-NHOH and LVA-NHOH showed mixed non-competitive inhibition against bovine SSAO. It was found that the V max value was reduced and the K m value was either increased (added MVA-NHOH, 0.05 µg mL −1 ) or reduced (added LVA-NHOH, 0.11 µg mL −1 ) in the presence of alginic acid hydroxamate.

Preparation, antioxidant and antimicrobial evaluation of hydroxamated degraded polysaccharides from Enteromorpha prolifera

“…It was reported that the DPPH scavenging activity of low-viscosity alginic acid hydroxamates (LVA-NHOH) and medium-viscosity alginic acid hydroxamates (MVA-NHOH) were greatly increased, with IC 50 values of 0.0298 and 0.0245 mg/ml, respectively (Liu, Wu, Liang, & Hou, 2007), while little or no DPPH scavenging activity of low-viscosity alginic acid or medium-viscosity alginic acid (original material) was found at the same concentrations. Improved DPPH scavenging activity of a hydroxamate derivative of pectin was also reported (Yang, Cheng, Lin, Liu, & Hou, 2004).…”

Antiglycation, radical scavenging, and semicarbazide-sensitive amine oxidase inhibitory activities of acetohydroxamic acid in vitro

“… 34 Few hydroxamate derivatives were reported to be antiglycation agents, and the results of this study showed that both clinical drugs containing the hydroxamate moieties of acetH and HU to be better than AG in the reduction of AGE formation. The self-prepared pectin hydroxamates 35 , 36 and alginic acid hydroxamates 37 in our previous reports exhibited SSAO inhibitory activities and DPPH radical and hydroxyl radical scavenging activities, and both pectin hydroxamates 35 , 36 and alginic acid hydroxamates belonged to macromolecular polysaccharides. The self-prepared galacturonic acid hydroxamate 38 showed DPPH radical scavenging activities with IC 50 of 82 μM, 38 which was about 2.5-fold higher than that of acetH in this study; the self-prepared galacturonic acid hydroxamate 22 showed SSAO inhibitory activities with IC 50 of 41 μM, 22 which was about 4-fold higher than that of acetH in this study.…”