G Brandacher

Tetrahydrobiopterin Attenuates Microvascular Reperfusion Injury Following Murine Pancreas Transplantation

In this study we investigated the effect of tetrahydrobiopterin (BH4), an essential cofactor for nitric oxide synthases, on ischemia‐reperfusion injury (IRI) following murine pancreas transplantation. Pancreatic grafts were exposed to prolonged cold ischemia times (CIT) and different treatment regimens: normal saline (S), S + 16 h CIT, BH4 50 mg/kg + 16 h CIT. Nontransplanted animals served as controls. Graft microcirculation was analyzed by means of functional capillary density (FCD) and capillary diameters (CD) after 2 h reperfusion using intravital microscopy. Quantification of inflammatory responses (mononuclear infiltration) and endothelial disintegration (edema formation) was done by histology (hematoxylin and eosin), and peroxynitrite formation assessed by nitrotyrosine immunostaining. FCD was significantly reduced after prolonged CIT, paralleled by increased peroxynitrite formation as compared with controls (all p < 0.05). Microcirculatory changes correlated significantly with intragraft peroxynitrite generation (Spearman: r=−0.56; p < 0.01). Pancreatic grafts treated with BH4 displayed markedly higher FCD values (p < 0.01) and abrogated nitrotyrosine staining (p = 0.03). CD were not significantly different in any group. Histology showed increased inflammation, interstitial edema, hemorrhage, acinar vacuolization and focal areas of necrosis after 16 h CIT, which was diminished by BH4 administration (p < 0.01). BH4 treatment significantly reduces post‐ischemic deterioration of microcirculation as well as histologic damage and might be a promising novel strategy in attenuating IRI following pancreas transplantation.

Percutaneous portal vein embolisation in preparation for extended hepatic resection of primary nonresectable liver tumours

BACKGROUND In patients with malignant primary and secondary liver tumours or proximal bile duct carcinoma radical surgery is superior to all other therapeutic modalities in terms of survival and quality of life. Radical resection, however, often requires the removal of a large amount of liver parenchyma, resulting in a marked reduction of functional liver tissue with the risk of liver failure. AIM Preoperative partial portal vein embolisation induces hypertrophy of the controlateral liver and thereby increases the safety of extended liver resections. PATIENTS AND METHODS Between January 1997 and February 2001 we applied this strategy in 19 patients with primary and secondary nonresectable hepatobiliary malignancies, in whom the estimated amount of the remnant liver was < or =25% of the liver volume. RESULTS The increase in volume ranged between 7 and 245%. Radical extended liver resection was performed in 13 patients (68%) without mortality. After a mean observation time of 22 months patient survival was 19 months with six tumour-related deaths during the second year after surgery. The remaining seven patients are alive and well with tumour recurrence in one. CONCLUSION Preoperative partial portal vein embolisation allows more patients with previously unresectable liver tumours to benefit from a potentially curative resection.

Donor Pretreatment with Tetrahydrobiopterin Saves Pancreatic Isografts from Ischemia Reperfusion Injury in a Mouse Model

Depletion of the nitric oxide synthase cofactor tetrahydrobiopterin (H4B) during ischemia and reperfusion is associated with severe graft pancreatitis. Since clinically feasible approaches to prevent ischemia reperfusion injury (IRI) by H4B‐substitution are missing we investigated its therapeutic potential in a murine pancreas transplantation model using different treatment regimens. Grafts were subjected to 16 h cold ischemia time (CIT) and different treatment regimens: no treatment, 160 μM H4B to perfusion solution, H4B 50 mg/kg prior to reperfusion and H4B 50 mg/kg before recovery of organs. Nontransplanted animals served as controls. Recipient survival and endocrine graft function were assessed. Graft microcirculation was analyzed 2 h after reperfusion by intravital fluorescence microscopy. Parenchymal damage was assessed by histology and nitrotyrosine immunohistochemistry, H4B tissue levels by high pressure liquid chromatography (HPLC). Compared to nontransplanted controls prolonged CIT resulted in significant microcirculatory deterioration. Different efficacy according to route and timing of administration could be observed. Only donor pretreatment with H4B resulted in almost completely abrogated IRI‐related damage showing graft microcirculation comparable to nontransplanted controls and restored intragraft H4B levels, resulting in significant reduction of parenchymal damage (p < 0.002) and improved survival and endocrine function (p = 0.0002 each). H4B donor pretreatment abrogates ischemia‐induced parenchymal damage and represents a promising strategy to prevent IRI following pancreas transplantation.

Immunosuppressive Effects of the 4-Amino Analogue of Tetrahydrobiopterin

Nitric oxide synthases catalyze a complex reaction converting L-arginine to citrulline and nitric oxide. In addition to heme, FAD, FMN and NADPH, nitric oxide synthases require tetrahydrobiopterin as cofactor. Tetrahydrobiopterin is known to stabilize the active, dimeric conformation of the enzyme (1), which has a high-spin heme iron (2) and an increased affinity for the substrate L-arginine (3). In addition to these allosteric roles, an electronic contribution of the tetrahydrobiopterin cofactor to the nitric oxide synthase reaction has been intensely searched for. The most convincing evidence for such an electronic contribution provided the detection of tetrahydrobiopterin-derived radicals being formed in dependence of the nitric oxide synthase reaction (4, 5, 6).