Alterations of intestinal mucosa structure and barrier function following traumatic brain injury in rats

Abstract

Aim: Gastrointestinal dysfunction is a common complication in patients with traumatic brain injury (TBI). However, the effect of traumatic brain injury on intestinal mucosa has not been studied previously. The aim of the current study was to explore the alterations of intestinal mucosa morphology and barrier function, and to determine how rapidly the impairment of gut barrier function occurs and how long it persists following traumatic brain injury.

Methods: Male Wistar rats were randomly divided into six groups (6 rats each group) including controls without brain injury and traumatic brain injury groups at hours 3, 12, 24, and 72, and on day 7. The intestinal mucosa structure was detected by histopathological examination and electron microscopy. Gut barrier dysfunction was evaluated by detecting serum endotoxin and intestinal permeability. The level of serum endotoxin and intestinal permeability was measured by using chromogenic limulus amebocyte lysate and lactulose/mannitol (L/M) ratio, respectively.

Results: After traumatic brain injury, the histopathological alterations of gut mucosa occurred rapidly as early as 3 hours and progressed to a serious state, including shedding of epithelial cells, fracture of villi, focal ulcer, fusion of adjacent villi, dilation of central chyle duct, mucosal atrophy, and vascular dilation, congestion and edema in the villous interstitium and lamina propria. Apoptosis of epithelial cells, fracture and sparseness of microvilli, loss of tight junction between enterocytes, damage of mitochondria and endoplasm, were found by electron microscopy. The villous height, crypt depth and surface area in jejunum decreased progressively with the time of brain injury. As compared with that of control group (183.7 +/- 41.8 EU/L), serum endotoxin level was significantly increased at 3, 12, and 24 hours following TBI (434.8 +/- 54.9 EU/L, 324.2 +/- 61.7 EU/L and 303.3 +/- 60.2 EU/L, respectively), and peaked at 72 hours (560.5 +/- 76.2 EU/L), then declined on day 7 (306.7 +/- 62.4 EU/L, P<0.01). Two peaks of serum endotoxin level were found at hours 3 and 72 following TBI. L/M ratio was also significantly higher in TBI groups than that in control group (control, 0.0172 +/- 0.0009; 12 h, 0.0303 +/- 0.0013; 24 h, 0.0354 +/- 0.0025; 72 h, 0.0736 +/- 0.0105; 7 d, 0.0588 +/- 0.0083; P<0.01).

Conclusion: Traumatic brain injury can induce significant damages of gut structure and impairment of barrier function which occur rapidly as early as 3 hours following brain injury and lasts for more than 7 days with marked mucosal atrophy.

Figure 1

Epithelial cells shed from the top of villi with almost normal villous height and well defined arrangement of villi at 3 hours following TBI. H-E, magnification ×100.

Figure 2

Markedly altered villous morphology and decreased height at 72 hours following TBI. Note the focal mucosa ulcer with exposure of submucosal interstitium and disarrangement of villi. H-E, magnification ×100.

Figure 3

Marked alterations of villous morphology occurred 7 days following TBI, including mucosal atrophy, fusion of adjacent villi, inflammatory cell infiltration, and vascular dilation, congestion and edema in the villous interstitium and lamina propria. H-E, magnification ×100.

Figure 4

Dilation of central chyle duct of jejunal mucosa. H-E, magnification ×100.

Figure 5

Reduction of mitochondrial matrix and disruption of its cristae at 72 hours following TBI. TEM, magnification ×15 k.

Figure 6

Ruptured, distorted and sparse microvilli at 24 hours following TBI. TEM, magnification ×10 k.

Figure 7

Apoptosis bodies in epithelial cytoplasms of jejunum following TBI. TEM, magnification ×8000.

Figure 8

Disrupted and wider tight junction between epithe-lial cells at 72 hours and 7 days following TBI, shown as blank arrow. TEM, magnification ×5000.

Figure 9

Significant increase of level of plasma endotoxin following TBI compared with control. Two peaks of plasma endotoxin existed at 3 h and 72 h postinjury, respectively. ^aP < 0.05 vs control; ^cP < 0.05 vs 12 h, 24 h and 72 h following TBI, ^eP < 0.05 vs 3 h following TBI. Mean ± SD of six animals, control: 183.7 ± 41.8 EU/L, 3 h: 434.8 ± 54.9 EU/L, 12 h: 324.2 ± 61.7 EU/L, 24 h: 303.3 ± 60.2 EU/L, 72 h: 560.5 ± 76.2 EU/L, 7 d: 306.7 ± 62.4 EU/L.

Figure 10

Significant increase of L/M ratio at 12 h, 24 h and 72 h following TBI compared with control and significant decline on day 7 compared with group at 72 h. The L/M ratio on day 7 was still significantly higher than that at 12 h and 24 h. ^bP < 0.01 vs control, ^dP < 0.01 vs 12 h and 24 h, ^eP < 0.01 vs 7 d. Mean ± SD of six animals, control: 0.0172 ± 0.0009, 12 h: 0.0303 ± 0.0013, 24 h: 0.0354 ± 0.0025,72 h: 0.0736 ± 0.0105, 7 d: 0.0588 ± 0.0083.