Reddan John R, Giblin Frank J, Sevilla Michael, Padgaonkar Vanita, Dziedzic Dorothy C, Leverenz Victor R, Misra Indira C, Chang Justin S, Pena John T
Department of Biological Sciences, Oakland University, Rochester, MI 48039, USA.
Exp Eye Res. 2003 Jan;76(1):49-59. doi: 10.1016/s0014-4835(02)00256-7.
n-Propyl gallate (nPG) is a food preservative that is generally regarded as safe by the US FDA. It suppresses oxidation in biological systems. The mechanism by which nPG acts in biological systems is uncertain. We investigated whether nPG protected cultured lens epithelial cells from H(2)O(2)-induced damage. Cells were treated with H(2)O(2) or with nPG and then H(2)O(2). H(2)O(2) inhibited growth, caused membrane blebbing, decreased lactate production, increased the level of GSSG, decreased the levels of GSH, ATP and NAD(+), and G3PDH activity, stimulated the hexose monophosphate shunt and induced single-strand breaks in DNA. nPG prevented the H(2)O(2)-induced growth inhibition, membrane blebbing, drop in NAD(+) and single-strand breaks in DNA. The mechanism by which nPG acts at the chemical level was investigated using electron paramagnetic resonance (EPR), direct spectrophotometric kinetic measurements, and cyclic voltammetry. When nPG at low concentrations (nM to microM) was mixed with a large excess of O(2)(-), the superoxide signal was destroyed as indicated by UV visible spectroscopy and EPR. Kinetic analysis indicated that nPG dismutated O(2)(-) in repetitive additions of superoxide with little loss of activity. The rate constant for the overall reaction of nPG with O(2)(-)* was ca. 10(6)M(-1)s(-1). nPG had a very low specific binding constant for Fe(2+) as determined by cyclic voltammetry. The evidence indicates that nPG dismutates the superoxide ion in a catalytic manner.
没食子酸正丙酯（nPG）是一种食品防腐剂，美国食品药品监督管理局（FDA）普遍认为其是安全的。它能抑制生物系统中的氧化作用。nPG在生物系统中的作用机制尚不确定。我们研究了nPG是否能保护培养的晶状体上皮细胞免受过氧化氢（H₂O₂）诱导的损伤。细胞分别用H₂O₂处理，或先用nPG处理然后再用H₂O₂处理。H₂O₂抑制细胞生长，导致细胞膜起泡，降低乳酸生成，增加氧化型谷胱甘肽（GSSG）水平，降低还原型谷胱甘肽（GSH）、三磷酸腺苷（ATP）和烟酰胺腺嘌呤二核苷酸（NAD⁺）水平以及甘油醛-3-磷酸脱氢酶（G3PDH）活性，刺激磷酸戊糖途径并诱导DNA单链断裂。nPG可防止H₂O₂诱导的细胞生长抑制、细胞膜起泡、NAD⁺水平下降以及DNA单链断裂。使用电子顺磁共振（EPR）、直接分光光度动力学测量和循环伏安法研究了nPG在化学层面的作用机制。当低浓度（纳摩尔至微摩尔）的nPG与大量过量的超氧阴离子（O₂⁻*）混合时，紫外可见光谱和EPR显示超氧阴离子信号被破坏。动力学分析表明，在重复添加超氧阴离子的情况下，nPG能使O₂⁻*发生歧化反应且活性损失很小。nPG与O₂⁻*总体反应的速率常数约为10⁶M⁻¹s⁻¹。通过循环伏安法测定，nPG对亚铁离子（Fe²⁺）的特异性结合常数非常低。证据表明nPG以催化方式使超氧阴离子发生歧化反应。
