REQUIMTE, Laboratório de Toxicologia, Departamento de Ciências Biológicas, Faculdade de Farmácia, Universidade do Porto, Rua Aníbal Cunha, 164, 4099-030 Porto, Portugal.
Arch Toxicol. 2011 Aug;85(8):929-39. doi: 10.1007/s00204-010-0630-9. Epub 2010 Dec 8.
Synephrine is a natural compound, frequently added to ephedra-free dietary supplements for weight-loss, due to its effects as a nonspecific adrenergic agonist. Though only p-synephrine has been documented in plants, the presence of m-synephrine has also been reported in weight-loss products. The use of synephrine in dietary supplements was accompanied by reports of adverse effects, especially at the cardiovascular level. It is well known that the imbalance in cardiac glutathione levels can increase the risk of cardiomyopathy. The present work aimed to study the role of organic cation-mediated transport of m- and p-synephrine and the possibility that p- and m-synephrine induce intracellular changes in glutathione levels in calcium-tolerant freshly isolated cardiomyocytes from adult rat. After a 3 h incubation with 1 mM p- or m-synephrine, the intracellular content of synephrine was measured by gas chromatography/ion trap-mass spectrometry (GC/IT-MS); cell viability and intracellular glutathione levels were also determined. To evaluate the potential protective effects of antioxidants against the adverse effects elicited by m-synephrine, cells were pre-incubated for 30 min with Tiron (100 μM) or N-acetyl-cysteine (NAC) (1 mM). To assess the influence of α(1)-adrenoceptors activation in glutathione depletion, a study with prazosin (100 nM) was also performed. The results obtained provide evidence that organic cation transporters OCT3 and OCT1 play a major role in m- and p-synephrine-mediated transport into the cardiomyocytes. The importance of these transporters seems similar for both isomers, although p-synephrine enters more into the cardiomyocytes. Furthermore, only m-synephrine induced intracellular total glutathione (GSHt) and reduced glutathione (GSH) depletion. NAC and Tiron were able to counteract the m-synephrine-induced GSH and GSHt decrease. On the other hand, the incubation with prazosin was not able to change m-synephrine-induced glutathione depletion showing that this effect is independent of α(1)-adrenoceptor stimulation. In conclusion, both positional isomers require OCT3 and OCT1-mediated transport to enter into the cardiomyocytes; however, the hydroxyl group in the p-position favours the OCT-mediated transport into cardiomyocytes. Furthermore, the structural isomerization of synephrine influences its toxicological profile since only m-synephrine caused GSH depletion.
辛弗林是一种天然化合物，常被添加到不含麻黄的减肥膳食补充剂中，因为它具有非特异性肾上腺素能激动剂的作用。尽管只有 p-辛弗林在植物中被记录，但 m-辛弗林也在减肥产品中被报道过。辛弗林在膳食补充剂中的使用伴随着不良反应的报告，尤其是在心血管水平。众所周知，心脏谷胱甘肽水平的失衡会增加患心肌病的风险。本研究旨在研究 m-和 p-辛弗林的有机阳离子介导转运的作用，以及 p-和 m-辛弗林是否会诱导钙耐受的成年大鼠新鲜分离的心肌细胞内谷胱甘肽水平的变化。在与 1mM p-或 m-辛弗林孵育 3 小时后，通过气相色谱/离子阱质谱（GC/IT-MS）测量细胞内辛弗林的含量；还测定了细胞活力和细胞内谷胱甘肽水平。为了评估抗氧化剂对 m-辛弗林引起的不良反应的潜在保护作用，将细胞用 Tiron（100μM）或 N-乙酰半胱氨酸（NAC）（1mM）预孵育 30min。为了评估α（1）-肾上腺素受体激活对谷胱甘肽耗竭的影响，还进行了普萘洛尔（100nM）的研究。研究结果表明，有机阳离子转运体 OCT3 和 OCT1 在 m-和 p-辛弗林介导的转运进入心肌细胞中起主要作用。这些转运体对两种异构体的重要性似乎相似，尽管 p-辛弗林进入心肌细胞的量更多。此外，只有 m-辛弗林诱导细胞内总谷胱甘肽（GSHt）和还原型谷胱甘肽（GSH）耗竭。NAC 和 Tiron 能够拮抗 m-辛弗林诱导的 GSH 和 GSHt 减少。另一方面，普萘洛尔孵育不能改变 m-辛弗林诱导的谷胱甘肽耗竭，表明这种作用独立于α（1）-肾上腺素受体刺激。总之，两种位置异构体都需要 OCT3 和 OCT1 介导的转运进入心肌细胞；然而，p 位的羟基有利于 OCT 介导的向心肌细胞的转运。此外，辛弗林的结构异构化影响其毒理学特征，因为只有 m-辛弗林引起 GSH 耗竭。
