A half century (1961-2011) of applying microsurgery to experimental liver research

The development of microsurgery has been dependent on experimental animals. Microsurgery could be a very valuable technique to improve experimental models of liver diseases. Microdissection and microsutures are the two main microsurgical techniques that can be considered for classifying the experimental models developed for liver research in the rat. Partial portal vein ligation, extrahepatic cholestasis and hepatectomies are all models based on microdissection. On the other hand, in portacaval shunts, orthotopic liver transplantation and partial heterotopic liver transplantation, the microsuture techniques stand out. By reducing surgical complications, these microsurgical techniques allow for improving the resulting experimental models. If good experimental models for liver research are successfully developed, the results obtained from their study might be particularly useful in patients with liver disease. Therefore experimental liver microsurgery could be an invaluable way to translate laboratory data on liver research into new clinical diagnostic and therapeutic strategies.

Prophylaxis with ketotifen in rats with portal hypertension:involvement of mast cell and eicosanoids

BACKGROUND:Since we have previously shown an increase of mast cells in the small bowel and in the mesenteric lymph nodes in the rats with prehepatic portal hypertension,it can be hypothesized that this essential inflammatory cell would be involved in the pathogeny of the splanchnic changes related to portal hypertension. METHODS:To verify this hypothesis,we first studied mast cell infiltration in the ileum and in the mesenteric lymph nodes in sham-operated male Wistar rats(n=12) and in short-term prehepatic portal hypertensive rats (n=12),and the serum levels of rat mast cell protease Ⅱ(RMCP-Ⅱ)by ELISA.In a second set of experiments ketotifen,a mast cell stabilizer drug,was administered to sham-operated(n=10)and portal hypertensive(n=12) rats 24 hours before the intervention and prostanoids (PGE2,PGI2,TXB2)and leukotrienes(LTC4,LTB4)were assayed by RIA,mast cell infiltration in the ileum and in the mesenteric lymph nodes and the serum levels of RMCP-Ⅱwere also studied,to show its effectiveness to prevent the mesenteric alterations produced by the inflammatory mediators released by the mast cell. RESULTS:Forty-eight hours after the intervention RMCP-Ⅱ (P<0.05),PGE2(P<0.001)and LTC4 serum levels decreased and mast cell number and RMCP-Ⅱlevels increased in mesenteric lymph nodes in portal hypertensive rats.Prophylactic administration of ketotifen reduced portal pressure(P<0.001),serum levels of PGE2(P<0.001)and RMCP-Ⅱ(P<0.001)in mesenteric lymph nodes. CONCLUSIONS:In acute portal hypertension in the rat,the mast cell translocation from intestinal mucosa to mesenteric lymph nodes,where they are activated and degranulates,would represent a defence mechanism to avoid the activation of an acute and massive inflammatory response in this location.Prophylactic administration of ketotifen is able to reduce the splanchnic inflammatory changes related to acute portal hypertension in the rat.

Hepatic lipid metabolism changes in short-and long-term prehepatic portal hypertensive rats

AIM: To verify the impairment of the hepatic lipid metabolism in prehepatic portal hypertension. METHODS: The concentrations of free fatty acids, diacylglycerol, triglycerides, and phospholipids were assayed by using D-[U-14C] glucose incorporation in the different lipid fractions and thin-layer chromatography and cholesterol was measured by spectrophotometry, in liver samples of Wistar rats with partial portal vein ligation at short- (1 mo) and long-term (1 year) (i.e. portal hypertensive rats) and the control rats. RESULTS: In the portal hypertensive rats, liver phospholipid synthesis significantly decreased (7.42 ± 0.50 vs 4.70 ± 0.44 nCi/g protein; P < 0.01) and was associated with an increased synthesis of free fatty acids (2.08 ± 0.14 vs 3.36 ± 0.33 nCi/g protein; P < 0.05), diacylglycerol (1.93 ± 0.2 vs 2.26 ± 0.28 nCi/g protein), triglycerides (2.40 ± 0.30 vs 4.49 ± 0.15 nCi/g protein) and cholesterol (24.28 ± 2.12 vs 57.66 ± 3.26 mg/g protein; P < 0.01). CONCLUSION: Prehepatic portal hypertension in rats impairs the liver lipid metabolism. This impairment consists in an increase in lipid deposits (triglycerides,diacylglycerol and cholesterol) in the liver, accompanied by a decrease in phospholipid synthesis.

Splanchnic-aortic inflammatory axis in experimental portal hypertension

Splanchnic and systemic low-grade inflammation has been proposed to be a consequence of long-term prehepatic portal hypertension.This experimental model causes minimal alternations in the liver,thus making a more selective study possible for the pathological changes characteristic of prehepatic portal hypertension.Low-grade splanchnic inflammation after longterm triple partial portal vein ligation could be associated with liver steatosis and portal hypertensive intestinal vasculopathy.In fact,we have previously shown that prehepatic portal hypertension in the rat induces liver steatosis and changes in lipid and carbohydrate metabolism similar to those produced in chronic inflammatory conditions described in metabolic syndrome in humans.Dysbiosis and bacterial translocation in this experimental model suggest the existence of a portal hypertensive intestinal microbiome implicated in both the splanchnic and systemic alterations related to prehepatic portal hypertension.Among the systemic impairments,aortopathy characterized by oxidative stress,increased levels of proinflammatory cytokines and profibrogenic mediators stand out.In this experimental model of long-term triple portal vein ligated-rats,the abdominal aortic proinflammatory response could be attributed to oxidative stress.Thus,the increased aortic reduced-nicotinamide-adenine dinucleotide phosphate[NAD(P)H]oxidase activity could be associated with reactive oxygen species production and promote aortic inflammation.Also,oxidative stress mediated by NAD(P)H oxidase has been associated with risk factors for inflammation and atherosclerosis.The splanchnic and systemic pathology that is produced in the long term after triple partial portal vein ligation in the rat reinforces the validity of this experimental model to study the chronic low-grade inflammatory response induced by prehepatic portal hypertension.

Embrionary way to create a fatty liver in portal hypertension

Portal hypertension in the rat by triple partial portal vein ligation produces an array of splanchnic and systemic disorders, including hepatic steatosis. In the current review these alterations are considered components of a systemic inflammatory response that would develop through three overlapping phenotypes: The neurogenic, the immune and the endocrine. These three inflammatory phenotypes could resemble the functions expressed during embryonic development of mammals. In turn, the inflammatory phenotypes would be represented in the embryo by two functional axes, that is, a coelomic-amniotic axis and a trophoblastic yolk-sac or vitelline axis. In this sense, the inflammatory response developed after triple partial portal vein ligation in the rat would integrate both functional embryonic axes on the liver interstitial space of Disse. If so, this fact would favor the successive development of steatosis, steatohepatitis and fibrosis. Firstly, these recapitulated embryonic functions would produce the evolution of liver steatosis. In this way, this fat liver could represent a yolk-sac-like in portal hypertensive rats. After that, the systemic recapitulation of these embryonic functions in experimental prehepatic portal hypertension would consequently induce a gastrulationlike response in which a hepatic wound healing reaction or fibrosis occur. In conclusion, studying the mechanisms involved in embryonic development could provide key results for a better understanding of the nonalcoholic fatty liver disease etiopathogeny.

Gut Lymphangiopathy: Adding Fuel to the Fire in Chronic Liver Disease

The splanchnic inflammation inchronic liver disease increases intestinal angiogenesis. In the current study our aim was demonstrating that the small bowel lymphangiogenesis is associated with angiogenesis in chronic cholestasis in the rat. A stereological study of the lymphatic microcirculation in the small intestine was performed in cholestatic rats. Portal enteropathy in cholestasis increases lymphatic microvessels in the mucosa and submucosa layers. Thus, the lymphatic microvessel volume fraction was superior (p < 0.001) in the mucosa (0.16 ± 0.01) and submucosa (0.16 ± 0.01), in regard to the muscle layer 0.015 ± 0.01. The lymphatic microvessel length density was higher in the mucosa (76.89 ± 2.86 mm-2;p -2;p < 0.01), in relationship to the muscle layer (5.04 ± 2.92 mm-2). These alterations predominate in the duodenum (volume fraction: 0.10 ± 0.01 and length density: 33.55 ± 5.98 mm-2) and ileum (volume fraction: 0.16 ± 0.01 and length density: 38.62 ± 6.07 mm-2). This study demonstrates the predominance of an increased lymphangiogenic response in both end sides of the small bowel associated with chronic liver disease. Since the porto-systemic venous collateral circulation in the chronic liver insufficiency is developed in the ends of the gastrointestinal tract, the excessive duodeno-ileal lymphangiogenesis could suggest the development of amesenteric-systemic lymphatic bypass in the chronic portal hypertension.

Portal hypertension-related inflammatory phenotypes: From a vitelline and amniotic point of view

Prehepatic portal hypertension induces a splanchnic low-grade inflammatory response that could switch to high-grade inflammation with the development of severe and life-threatening complications when associated with chronic liver disease. The extraembryonic origin of the portal system maybe determines the regression to an extraembryonic phenotype, i.e., vitellogenic and amniotic, during the evolution of both types of portal hypertension. Thus, prehepatic portal hypertension, or compensated hypertension by portal vein ligation in the rat, is associated with molecular mechanisms related to vitellogenesis, where hepatic steatosis and splanchnic angiogenesis stand out. In turn, extrahepatic cholestasis in the rat induces intrahepatic portal hypertension, or decompensated hypertension, with ascites and hepatorenal syndrome. The splanchnic interstitium, the mesenteric lymphatic system, and the peritoneal mesothelium seem to create an inflammatory pathway that could have a key pathophysiological relevance in the production of ascites. The hypothetical comparison between the ascitic and the amniotic fluid also allows for translational investigation. The induced regression of the splanchnic system to extraembryonic functions by portal hypertension highlights the great relevance of the extraem-bryonic structures even during postnatal life.

Wound healing reaction:A switch from gestation to senescence

The repair of wounded tissue during postnatal life could be associated with the upregulation of some functions characteristic of the initial phases of embryonic development. The focusing of these recapitulated systemic functions in the interstitial space of the injured tissue is established through a heterogeneous endothelial barrier which has excretory-secretory abilities which in turn,would induce a gastrulation-like process. The repair of adult tissues using upregulated embryonic mechanisms could explain the universality of the inflammatory response against injury,regardless of its etiology. However,the early activation after the injury of embryonic mechanisms does not always guarantee tissue regeneration since their long-term execution is mediated by the host organism.