Multiple pathogenic factor-induced complications of cirrhosis in rats: a new model of hepatopulmonary syndrome with intestinal endotoxemia

Abstract

Aim: To develop and characterize a practical model of Hepatopulmonary syndrome (HPS) in rats.

Methods: The experimental animals were randomized into five feeding groups: (1) control (fed standard diet), (2) control plus intraperitoneal injection with lipopolysaccharide (LPS), (3) cirrhosis (fed a diet of maize flour, lard, cholesterol, and alcohol plus subcutaneously injection with carbon tetrachloride (CCl(4)) oil solution), (4) cirrhosis plus LPS, and (5) cirrhosis plus glycine and LPS. The blood, liver and lung tissues of rats were sampled for analysis and characterization. Technetium 99m-labeled macroaggregated albumin (Tc99m-MAA) was used to test the dilatation of pulmonary microvasculature.

Results: Typical cirrhosis and subsequent hepato-pulmonary syndrome was observed in the cirrhosis groups after an 8 wk feeding period. In rats with cirrhosis, there were a decreased PaO(2) and PaCO(2) in arterial blood, markedly decreased arterial O(2) content, a significantly increased alveolar to arterial oxygen gradient, an increased number of bacterial translocated within mesenteric lymph node, a significant higher level of LPS and tumor necrosis factor-alpha (TNF-alpha) in plasma, and a significant greater ratio of Tc99m-MAA brain-over-lung radioactivity. After LPS administration in rats with cirrhosis, various pathological parameters got worse and pulmonary edema formed. The predisposition of glycine antagonized the effects of LPS and significantly alleviated various pathological alterations.

Conclusion: The results suggest that: (1) a characteristic rat model of HPS can be non-invasively induced by multiple pathogenic factors including high fat diet, alcohol, cholesterol and CCl(4); (2) this model can be used for study of hepatopulmonary syndrome and is clinically relevant; and (3) intestinal endotoxemia (IETM) and its accompanying cytokines, such as TNF-alpha, exert a crucial role in the pathogenesis of HPS in this model.

Figure 1

Histology of rat liver. Panel A: normal liver structure showing normal sinusoids and cord located around central vein (HE, × 400); Panel B: typical liver cirrhosis with regenerative nodules of hepatocytes separated by fibrous septa (HE, × 40).

Figure 2

Electron microscopy of lung from cirrhotic liver. Panel A: enlarged alveolar capillaries with narrowed alveolar space filled with exudates (× 6000); Panel B: destruction of the typeIalveolar epithelium, showing a discontinued zigzag lesion (× 6000).

Figure 3

Tc99m-MAA scanning images of the rat brain and lung. Panel A: representative rat from control group fed standard diet (see details in Method), showing a full distribution of Tc99m-MAA in the lung; Panel B: representative rat from the group fed standard diet plus intraperitoneal injection with lipopolysaccharide (LPS), showing slight radioactivity in the brain; Panel C: representative rat from the cirrhotic group fed a mixture of maize flour, lard, cholesterol, and alcohol plus intraperitoneal injection with carbon tetrachloride (CCl₄) oil solution for 8 wk, showing significant increased radioactivity in the brain; Panel D: representative rat from cirrhotic animals plus LPS injection, showing much increased radioactivity in the brain.

Figure 4

Ratio of brain-over-lung radioactivity in the rats. Control, fed standard diet; LPS, fed standard diet plus LPS injection; Cirrhosis, fed a mixture of maize flour, lard, cholesterol, and alcohol plus intraperitoneal injection with carbon tetrachloride (CCl₄) oil solution for 8 wk. ^aP < 0.05 vs normal control group; ^cP < 0.05 vs cirrhosis group.