Panigrahi P, Gewolb I H, Bamford P, Horvath K
Division of Neonatology, University of Maryland School of Medicine, Baltimore 21201-1595, USA.
JPEN J Parenter Enteral Nutr. 1997 Mar-Apr;21(2):75-80. doi: 10.1177/014860719702100275.
L-Glutamine is the principal energy source for small intestinal enterocytes. Diminution of intestinal function, mucosal atrophy, and increased bacterial translocation have been noted during total parenteral nutrition (TPN). In a rat model of glutamine starvation, we previously showed that luminal glutamine is essential for optimal intestinal function. In this study, we examined the effect of apical vs basolateral glutamine on bacterial translocation in a Caco-2 cell culture system and bacteria-induced tissue injury in a weanling rabbit ileal loop model.
Caco-2 cells were grown in a transwell system. After confluence, apical and basolateral chambers received defined media, and glutamine deprivation was carried out over a 4- to 48-hour period. Escherichia coli transcytosis and structure/function studies were then performed. In a second series of experiments, the effect of intraluminal glutamine supplementation was evaluated in an E. coli-induced tissue injury model in weanling rabbit ileal loops.
Expression of disaccharidases, glucoamylase, and Na+/K(+)-adenosine 5'-triphosphatase (ATPase) were significantly reduced when cells were deprived of glutamine from the apical side, and there was increased bacterial translocation across the monolayer. Transepithelial epithelial resistance (TEER) across the monolayer was also reduced in the glutamine-free cultures. Glutamine replenishment over 24 to 48 hours restored the original functions. Basolateral deprivation had a smaller effect on the Caco-2 cells. Typical necrotic mucosal injury caused by E. coli in the ileal loops was blocked by co-infiltration of the loops with glutamine.
This study demonstrates for the first time that the supply of glutamine from the apical side is of critical importance for maintaining optimal structure and function of the enterocytes. The effects are not acute or energy related. These observations have important clinical implications in the management of patients under critical care, including premature infants and patients receiving TPN, for whom lack of glutamine from the luminal side could produce mucosal dysfunction, resulting ultimately in severe atrophic/necrotic complications.
L-谷氨酰胺是小肠肠上皮细胞的主要能量来源。在全肠外营养（TPN）期间，已注意到肠道功能减退、黏膜萎缩和细菌易位增加。在谷氨酰胺饥饿的大鼠模型中，我们先前表明管腔谷氨酰胺对最佳肠道功能至关重要。在本研究中，我们在Caco-2细胞培养系统中研究了顶端与基底侧谷氨酰胺对细菌易位的影响，以及在断奶幼兔回肠袢模型中对细菌诱导的组织损伤的影响。
Caco-2细胞在Transwell系统中培养。汇合后，顶端和基底侧腔室接受特定培养基，并在4至48小时内进行谷氨酰胺剥夺。然后进行大肠杆菌转胞吞作用及结构/功能研究。在第二系列实验中，在断奶幼兔回肠袢的大肠杆菌诱导的组织损伤模型中评估管腔内补充谷氨酰胺的效果。
当从顶端侧剥夺细胞谷氨酰胺时，双糖酶、葡糖淀粉酶和Na+/K(+)-三磷酸腺苷酶（ATP酶）的表达显著降低，并且跨单层的细菌易位增加。无谷氨酰胺培养物中跨单层的跨上皮电阻（TEER）也降低。在24至48小时内补充谷氨酰胺可恢复原始功能。基底侧剥夺对Caco-2细胞的影响较小。回肠袢中由大肠杆菌引起的典型坏死性黏膜损伤可通过谷氨酰胺共同注入回肠袢而被阻断。
本研究首次证明从顶端侧供应谷氨酰胺对于维持肠上皮细胞的最佳结构和功能至关重要。这些作用并非急性的或与能量相关。这些观察结果在危重症患者的管理中具有重要的临床意义，包括早产儿和接受TPN的患者，对于他们而言，管腔侧缺乏谷氨酰胺可能导致黏膜功能障碍，最终导致严重的萎缩性/坏死性并发症。
