Ds Visser

Altered bile composition after liver transplantation is associated with the development of nonanastomotic biliary strictures

BACKGROUND/AIMS Nonanastomotic biliary strictures are troublesome complications after liver transplantation. The pathogenesis of NAS is not completely clear, but experimental studies suggest that bile salt toxicity is involved. METHODS In one hundred and eleven adult liver transplants, bile samples were collected daily posttransplantation for determination of bile composition. Expression of bile transporters was studied perioperatively. RESULTS Nonanastomotic biliary strictures were detected in 14 patients (13%) within one year after transplantation. Patient and donor characteristics and postoperative serum liver enzymes were similar between patients who developed nonanastomotic biliary strictures and those who did not. Secretions of bile salts, phospholipids and cholesterol were significantly lower in patients who developed strictures. In parallel, biliary phospholipids/bile salt ratio was lower in patients developing strictures, suggestive for increased bile cytotoxicity. There were no differences in bile salt pool composition or in hepatobiliary transporter expression. CONCLUSIONS Although patients who develop nonanastomotic biliary strictures are initially clinically indiscernible from patients who do not develop nonanastomotic biliary strictures, the biliary bile salts and phospholipids secretion, as well as biliary phospholipids/bile salt ratio in the first week after transplantation, was significantly lower in the former group. This supports the concept that bile cytotoxicity is involved in the pathogenesis of nonanastomotic biliary strictures.

Heme Oxygenase-1 Genotype of the Donor Is Associated With Graft Survival After Liver Transplantation

Heme oxygenase‐1 (HO‐1) has been suggested as a cytoprotective gene during liver transplantation. Inducibility of HO‐1 is modulated by a (GT)n polymorphism and a single nucleotide polymorphism (SNP) A(‐413)T in the promoter. Both a short (GT)n allele and the A‐allele have been associated with increased HO‐1 promoter activity. In 308 liver transplantations, we assessed donor HO‐1 genotype and correlated this with outcome variables. For (GT)n genotype, livers were divided into two classes: short alleles (<25 repeats; class S) and long alleles (≥25 repeats; class L). In a subset, hepatic messenger ribonucleic acid (mRNA) expression was correlated with genotypes. Graft survival at 1 year was significantly better for A‐allele genotype compared to TT‐genotype (84% vs. 63%, p = 0.004). Graft loss due to primary dysfunction (PDF) occurred more frequently in TT‐genotype compared to A‐receivers (p = 0.03). Recipients of a liver with TT‐genotype had significantly higher serum transaminases after transplantation and hepatic HO‐1 mRNA levels were significantly lower compared to the A‐allele livers (p = 0.03). No differences were found for any outcome variable between class S and LL‐variant of the (GT)n polymorphism. Haplotype analysis confirmed dominance of the A(‐413)T SNP over the (GT)n polymorphism. In conclusion, HO‐1 genotype is associated with outcome after liver transplantation. These findings suggest that HO‐1 mediates graft survival after liver transplantation.

Hepatic expression of ABC transporters G5 and G8 does not correlate with biliary cholesterol secretion in liver transplant patients

The adenosine triphosphate (ATP)‐binding cassette (ABC)‐transporters ABCG5 and ABCG8 have been shown to mediate hepatic and intestinal excretion of cholesterol. In various (genetically modified) murine models, a strong relationship was found between hepatic expression of ABCG5/ABCG8 and biliary cholesterol content. Our study aimed to relate levels of hepatic expression of ABCG5 and ABCG8 to biliary excretion of cholesterol in man. From 24 patients who had received a liver transplant, bile samples were collected daily after transplantation over a 2‐week period to determine biliary composition. Expression of ABCG5, ABCG8, MDR3, and BSEP was assessed by real‐time polymerase chain reaction (PCR) in liver biopsy specimens collected before and after transplantation. Levels of hepatic ABCG5, ABCG8, and MDR3 messenger RNA (mRNA) were strongly correlated. After transplantation, the biliary secretion rate of cholesterol continuously increased, coinciding with gradual increases in bile salt and phospholipid secretion. In contrast, hepatic levels of ABCG5 and ABCG8 mRNA remained unchanged. Surprisingly, no correlation was found between the hepatic expression of ABCG5 and ABCG8 and rates of biliary cholesterol secretion, normalized for biliary phospholipid secretion. As expected, the concentration of biliary phospholipids correlated well with MDR3 expression. In conclusion, the strong relationship between ABCG5 and ABCG8 gene expression is consistent with the coordinate regulation of both genes, and in line with heterodimerization of both proteins into a functional transporter. Hepatic ABCG5/ABCG8 expression, at least during the early phase after transplantation, is not directly related to biliary cholesterol secretion in humans. This finding suggests the existence of alternative pathways for the hepatobiliary transport of cholesterol that are not controlled by ABCG5/ABCG8. (HEPATOLOGY 2005;42:1166–1174.)

Spatiotemporal expression of heme oxygenase‐1 detected by in vivo bioluminescence after hepatic ischemia in HO‐1/luc mice

Upregulation of heme oxygenase‐1 (HO‐1) has been proposed as a critical mechanism protecting against cellular stress during liver transplantation, providing a potential target for new therapeutic interventions. We investigated the feasibility of in vivo bioluminescence imaging (BLI) to noninvasively quantify the spatiotemporal expression of HO‐1 after warm hepatic ischemia in living animals. Luciferase activity was measured by BLI as an index of HO‐1 transcription in transgenic reporter mice (Ho1‐luc) at standardized time points after 60 minutes of warm hepatic ischemia. HO‐1 mRNA levels were measured in postischemic livers of mice sacrificed at the same time points in separate experiments. Bioluminescent signals from postischemic liver lobes were first detected at 3 hours after reperfusion. Peak levels were reached at 9 hours, after which bioluminescent activity declined and returned to baseline values at 48 hours after reperfusion. Upregulation of HO‐1 as detected by in vivo BLI was preceded by increased HO‐1 mRNA expression and confirmed by enhanced immunohistochemical staining of hepatocytes. In conclusion, this study shows that in vivo BLI allows a sensitive assessment of HO‐1 expression after hepatic ischemia in living animals. The capability of whole‐body temporal imaging of HO‐1 expression provides a valuable tool in the development of novel strategies to modulate HO‐1 expression in liver transplantation. Liver Transpl 12:1634–1639, 2006.