Yang Shaojun, Jan Yi-Hua, Mishin Vladimir, Heck Diane E, Laskin Debra L, Laskin Jeffrey D
Department of Environmental and Occupational Health, Rutgers University School of Public Health , Piscataway, New Jersey 08854, United States.
Department of Pharmacology and Toxicology, Rutgers University Ernest Mario School of Pharmacy , Piscataway, New Jersey 08854, United States.
Chem Res Toxicol. 2017 Jul 17;30(7):1406-1418. doi: 10.1021/acs.chemrestox.7b00052. Epub 2017 Jun 26.
Reactive carbonyls such as diacetyl (2,3-butanedione) and 2,3-pentanedione in tobacco and many food and consumer products are known to cause severe respiratory diseases. Many of these chemicals are detoxified by carbonyl reductases in the lung, in particular, dicarbonyl/l-xylulose reductase (DCXR), a multifunctional enzyme important in glucose metabolism. DCXR is a member of the short-chain dehydrogenase/reductase (SDR) superfamily. Using recombinant human enzyme, we discovered that DCXR mediates redox cycling of a variety of quinones generating superoxide anion, hydrogen peroxide, and, in the presence of transition metals, hydroxyl radicals. Redox cycling activity preferentially utilized NADH as a cosubstrate and was greatest for 9,10-phenanthrenequinone and 1,2-naphthoquinone, followed by 1,4-naphthoquinone and 2-methyl-1,4-naphthoquinone (menadione). Using 9,10-phenanthrenequinone as the substrate, quinone redox cycling was found to inhibit DCXR reduction of l-xylulose and diacetyl. Competitive inhibition of enzyme activity by the quinone was observed with respect to diacetyl (K = 190 μM) and l-xylulose (K = 940 μM). Abundant DCXR activity was identified in A549 lung epithelial cells when diacetyl was used as a substrate. Quinones inhibited reduction of this dicarbonyl, causing an accumulation of diacetyl in the cells and culture medium and a decrease in acetoin, the reduced product of diacetyl. The identification of DCXR as an enzyme activity mediating chemical redox cycling suggests that it may be important in generating cytotoxic reactive oxygen species in the lung. These activities, together with the inhibition of dicarbonyl/l-xylulose metabolism by redox-active chemicals, as well as consequent deficiencies in pentose metabolism, are likely to contribute to lung injury following exposure to dicarbonyls and quinones.
烟草以及许多食品和消费品中的反应性羰基化合物，如双乙酰（2,3-丁二酮）和2,3-戊二酮，已知会导致严重的呼吸道疾病。这些化学物质中的许多会被肺部的羰基还原酶解毒，特别是二羰基/l-木酮糖还原酶（DCXR），这是一种在葡萄糖代谢中起重要作用的多功能酶。DCXR是短链脱氢酶/还原酶（SDR）超家族的成员。使用重组人酶，我们发现DCXR介导多种醌的氧化还原循环，产生超氧阴离子、过氧化氢，并且在过渡金属存在的情况下产生羟基自由基。氧化还原循环活性优先利用NADH作为共底物，对9,10-菲醌和1,2-萘醌的活性最大，其次是1,4-萘醌和2-甲基-1,4-萘醌（甲萘醌）。以9,10-菲醌为底物时，发现醌氧化还原循环会抑制DCXR对l-木酮糖和双乙酰的还原作用。观察到醌对酶活性的竞争性抑制作用，双乙酰的抑制常数（K）为190μM，l-木酮糖的抑制常数（K）为940μM。当以双乙酰为底物时，在A549肺上皮细胞中鉴定出丰富的DCXR活性。醌抑制这种二羰基化合物的还原，导致双乙酰在细胞和培养基中积累，以及双乙酰的还原产物乙偶姻减少。DCXR作为介导化学氧化还原循环的酶活性的鉴定表明，它可能在肺部产生细胞毒性活性氧物种方面很重要。这些活性，连同氧化还原活性化学物质对二羰基/l-木酮糖代谢的抑制作用，以及随之而来的戊糖代谢缺陷，可能会导致接触二羰基化合物和醌后肺部损伤。
