Tan Kah Poh, Kosuge Kazuhiro, Yang Mingdong, Ito Shinya
Division of Clinical Pharmacology and Toxicology, Physiology and Experimental Medicine Program, The Research Institute, The Hospital for Sick Children, Department of Pediatrics and Department of Pharmacology, University of Toronto, Toronto, ON, Canada.
Free Radic Biol Med. 2008 Dec 15;45(12):1663-73. doi: 10.1016/j.freeradbiomed.2008.09.010. Epub 2008 Sep 23.
Clinical use of retinoic acids (RA) is hindered by toxicity possibly related to oxidative stress. Recently, RA at relatively low concentrations was shown to inhibit NRF2 and the expression of its target antioxidative genes. This raises the possibility that RA toxicity may result from cellular inability to cope with resultant oxidative stress. Using in vitro cell and in vivo mouse models, we report that RA, specifically all-trans-RA (atRA) at concentrations implicated in toxicity, can activate NRF2 and induce NRF2 target genes, particularly the subunits of the rate-limiting enzyme of glutathione biosynthesis, glutamate cysteine ligase (GCLM/GCLC). RNA interference-mediated silencing of NRF2, but not of retinoid X receptor-alpha and -beta, reduced basal and atRA-induced GCLM/GCLC gene expression. Moreover, RA increased nuclear accumulation of NRF2, antioxidant response element (ARE) reporter activity, and NRF2 occupancy at AREs. 4-Hydroxynonenal, a lipid peroxidation product, was increased by RA. Inhibition of MEK1/ERK mitogen-activated protein kinases significantly suppressed atRA-induced NRF2 activation and ARE-regulated gene expression, reducing cell resistance against toxic concentrations of RA. NRF2-silenced cells were vulnerable to atRA-induced mitochondrial toxicity and apoptosis. In conclusion, toxic RA activates NRF2, thereby triggering an adaptive response against the resultant oxidative stress. NRF2 enhancement as a therapeutic target of retinoid toxicity awaits further investigation.
维甲酸（RA）的临床应用受到可能与氧化应激相关的毒性的阻碍。最近，相对低浓度的RA被证明可抑制NRF2及其靶标抗氧化基因的表达。这增加了RA毒性可能源于细胞无法应对由此产生的氧化应激的可能性。利用体外细胞和体内小鼠模型，我们报告称，RA，特别是在涉及毒性的浓度下的全反式维甲酸（atRA），可以激活NRF2并诱导NRF2靶基因，特别是谷胱甘肽生物合成限速酶谷氨酸半胱氨酸连接酶（GCLM/GCLC）的亚基。RNA干扰介导的NRF2沉默，而非视黄酸X受体α和β的沉默，降低了基础和atRA诱导的GCLM/GCLC基因表达。此外，RA增加了NRF2的核积累、抗氧化反应元件（ARE）报告基因活性以及NRF2在AREs处的占据。4-羟基壬烯醛，一种脂质过氧化产物，被RA增加。抑制MEK1/ERK丝裂原活化蛋白激酶显著抑制atRA诱导的NRF2激活和ARE调节的基因表达，降低细胞对毒性浓度RA的抗性。NRF2沉默的细胞易受atRA诱导的线粒体毒性和凋亡影响。总之，有毒的RA激活NRF2，从而引发针对由此产生的氧化应激的适应性反应。将NRF2增强作为维甲酸毒性的治疗靶点有待进一步研究。
