对内耳氧化抗氧化失衡的反思

Introspection of oxidant/antioxidant imbalance in the inner ear

生物氧化是指生物细胞内通过对代谢物的一系列氧化一还原反应产生能量的化合过程，也被称之为细胞呼吸或组织呼吸，因此生物氧化可以说是生物存活须臾不可缺少的生命活动，一旦生物氧化终止则意味着生命的终结。伴随生物氧化过程所产生的活性氧自由基（reactiveoxygenspecies，ROs）是生命体活动中多种生化反应的正常中间代谢产物，作为机体的有效防御系统之一，自由基在维持能量供应、促进机体新陈代谢、剿灭细菌病原体、清除机体内毒素、调节机体内多种信号传递通路等许多方面都发挥着十分重要的积极作用。

Summary Free radicals are atoms, molecules or ions with unpaired electrons. In biological systems, free radicals can have a dual role, being beneficial in some situations and deleterious in others. Free radicals are re- quired for normal cellular metabolism, but they lead to cellular degeneration if overproduced. To prevent the ex- cessive buildup of free radicals, cells have developed an elaborate series of antioxidant enzymes that counteract oxi- dative stress and protect cells by maintaining the proper balance of oxidation and anti-oxidation. Therefore, when there is an oxidant/anti-oxidant imbalance, no matter what direction, cells are likely to be damaged. Numerous re- ports in the literature indicate that free radicals play important roles in diseases of the inner ear as a result of noise exposure, ototoxic drugs, aging, and other pathological conditions. Therefore, there have been many attempts to employ antioxidants treat inner ear damage. However, antioxidant therapy could be harmful if the improper com- pound or dose is employed. Effective antioxidant therapy requires prior knowledge of the type（s） of oxidative stress occurring in real time in the inner ear. Since most techniques for detecting free radicals in the inner ear are not clinically feasible, systemic anti-oxidant therapy is generally performed ＂blindly＂ and therefore likely to disrupt normal antioxidant levels in the inner ear or elsewhere in the body. If only a single anti-oxidant is used to treat a disease, it may disturb subsequent steps the oxidative/anti-oxidative chain reaction. An alternative approach, hy- drogen therapy represents a promising therapeutic tool because it can selectively scavenge the strongest oxidant species, the hydroxyl radical and peroxynitrite anion, without disturbing normal oxidant/anti-oxidant cellular processes. In addition, hydrogen has no cytotoxic effects to cells so that it provides a near ideal therapy to elimi- nate toxic free radicals.