Larsson Nirina, Rankin Gregory D, Bicer Elif M, Roos-Engstrand Ester, Pourazar Jamshid, Blomberg Anders, Mudway Ian S, Behndig Annelie F
Department of Public Health and Clinical Medicine, Division of Medicine/Respiratory Medicine and Allergy, Umeå University, Umeå, Sweden.
MRC-PHE Centre for Environment & Health, Faculty of Life Sciences & Medicine, Kings College London, London, UK.
BMJ Open. 2015 Apr 8;5(4):e006979. doi: 10.1136/bmjopen-2014-006979.
Vitamin C is an important low-molecular weight antioxidant at the air-lung interface. Despite its critical role as a sacrificial antioxidant, little is known about its transport into the respiratory tract lining fluid (RTLF), or the underlying airway epithelial cells. While several vitamin C transporters have been identified, such as sodium-ascorbate cotransporters (SVCT1/2) and glucose transporters (GLUTs), the latter transporting dehydroascorbate, knowledge of their protein distribution within the human lung is limited, in the case of GLUTs or unknown for SVCTs.
Protein expression of vitamin C transporters (SVCT1/2 and GLUT1-4) was examined by immunohistochemistry in endobronchial biopsies, and by FACS in airway leucocytes from lavage fluid, obtained from 32 volunteers; 16 healthy and 16 mild asthmatic subjects. In addition, antioxidant concentrations were determined in RTLF. The study was performed at one Swedish centre.
The primary outcome measure was to establish the location of vitamin C transporters in the human airways. As secondary outcome measures, RTLF vitamin C concentration was measured and related to transporter expression, as well as bronchial epithelial inflammatory and goblet cells numbers.
Positive staining was identified for SVCT1 and 2 in the vascular endothelium. SVCT2 and GLUT2 were present in the apical bronchial epithelium, where SVCT2 staining was predominately localised to goblet cells and inversely related to RTLF vitamin C concentrations.
This experimental study is the first to demonstrate protein expression of GLUT2 and SVCT2 in the human bronchial epithelium. A negative correlation between SVCT2-positive goblet cells and bronchial RTLF vitamin C concentrations suggests a possible role for goblet cells in regulating the extracellular vitamin C pool.
维生素C是气-肺界面重要的低分子量抗氧化剂。尽管其作为牺牲性抗氧化剂发挥着关键作用，但关于其转运至呼吸道内衬液（RTLF）或其下方气道上皮细胞的情况却知之甚少。虽然已鉴定出几种维生素C转运蛋白，如钠-抗坏血酸共转运蛋白（SVCT1/2）和葡萄糖转运蛋白（GLUTs，后者转运脱氢抗坏血酸），但它们在人肺内的蛋白质分布情况，对于GLUTs来说了解有限，对于SVCTs则尚不清楚。
通过免疫组织化学检测支气管活检组织中维生素C转运蛋白（SVCT1/2和GLUT1 - 4）的蛋白表达，并通过流式细胞术检测32名志愿者灌洗液中气道白细胞的蛋白表达；其中16名健康受试者和16名轻度哮喘患者。此外，还测定了RTLF中的抗氧化剂浓度。该研究在瑞典的一个中心进行。
主要结局指标是确定维生素C转运蛋白在人类气道中的位置。作为次要结局指标，测量RTLF维生素C浓度并将其与转运蛋白表达以及支气管上皮炎症细胞和杯状细胞数量相关联。
在血管内皮中鉴定出SVCT1和2呈阳性染色。SVCT2和GLUT2存在于支气管顶端上皮，其中SVCT2染色主要定位于杯状细胞，且与RTLF维生素C浓度呈负相关。
本实验研究首次证明了GLUT2和SVCT2在人支气管上皮中的蛋白表达。SVCT2阳性杯状细胞与支气管RTLF维生素C浓度之间的负相关表明杯状细胞在调节细胞外维生素C池方面可能发挥作用。
