G-protein-coupled receptor kinase interactor-1 (GIT1) is a new endothelial nitric-oxide synthase (eNOS) interactor with functional effects on vascular homeostasis.

Endothelial cell nitric-oxide (NO) synthase (eNOS), the enzyme responsible for synthesis of NO in the vasculature, undergoes extensive post-translational modifications that modulate its activity. Here we have identified a novel eNOS interactor, G-protein-coupled receptor (GPCR) kinase interactor-1 (GIT1), which plays an unexpected role in GPCR stimulated NO signaling. GIT1 interacted with eNOS in the endothelial cell cytoplasm, and this robust association was associated with stimulatory eNOS phosphorylation (Ser(1177)), enzyme activation, and NO synthesis. GIT1 knockdown had the opposite effect. Additionally, GIT1 expression was reduced in sinusoidal endothelial cells after liver injury, consistent with previously described endothelial dysfunction in this disease. Re-expression of GIT1 after liver injury rescued the endothelial phenotype. These data emphasize the role of GPCR signaling partners in eNOS function and have fundamental implications for vascular disorders involving dysregulated eNOS.

Lobular distribution pattern of lactate dehydrogenase and 6-phosphogluconate dehydrogenase activity in rat liver.

Lactate dehydrogenase (LDH) and 6-phosphogluconate dehydrogenase (6-PGDH) activities were measured in lobular areas expanding between 3 portal tracts and an efferent central vein in the livers of male Wistar rats, using a Lowry technique. The maximum of LDH activity was found in a nearly uniform broad area in the lobular periphery. From that area values decreased along periportal/septal-->perivenous gradients, but only slightly within that area along the periportal-->septal axis of the vascular septum. Maximum values of 6-PGDH activity were present in an intermediate area close to the central vein demonstrating a rather inhomogeneous distribution pattern without a clear definition of zonal limits. Our data on the distribution pattern of LDH are in agreement with the concept of the metabolic lobulus and are supported by a recent evaluation of the vascular architecture in rat liver. The lobular distribution pattern of 6-PGDH cannot be interpreted without doubt in accordance with that concept.

Study of the changes of serum hyaluronic acid during porcine liver transplantation: influence of warm ischemia.

Twelve porcine liver transplantations were performed to investigate whether serum hyaluronic acid (HA) serves as a marker of warm ischemic injury. Group 1 was a control without warm ischemia (n = 7), and pigs in Group 2 were sacrificed by intracardiac KCl injection 60 min before harvesting (n = 5). All pigs survived more than 4 days in Group 1. In Group 2, all died within 2 days due to graft failure. Arterial and hepatic venous glutamic-oxaloacetic transaminase (GOT) in Group 2 were higher after revascularization. However, there were no differences between the 2 groups in arterial and hepatic venous HA levels. HA clearance by the graft also showed no differences between the groups. Although GOT reflected the degree of warm ischemia, HA and its hepatic clearance were not influenced by warm ischemic damage. In conclusion, HA was not thought to serve as a marker of liver injury when the graft suffered from warm ischemia.

The release of cytokines, adhesion molecules, and extracellular matrix parameters during and after reperfusion in human liver transplantation.

Poor initial graft function may increase postoperative morbidity including the risk of early allograft rejection. Various mediators, including immunostimulatory cytokines, may be released during reperfusion in relation to the extent of preservation and reperfusion injury. For this purpose, 81 patients with 85 liver transplants were monitored for cytokines, adhesion molecules, extracellular matrix (ECM) parameters, and neopterin at predefined time-points during and after transplantation. To estimate the origin of cytokine release, blood was obtained central and hepatic venously for the first 48 hr after reperfusion and subsequently from a peripheral vein. One-year patient survival was 88.9%; no relation to initial graft function was observed. Poor initial graft function failed to increase the risk for subsequent infectious complications but was associated with an increased risk of early allograft rejection. The incidence of steroid-resistant rejection was significantly increased in patients with poor initial graft function (35.7% versus 12.7% in patients with good and moderate initial graft function; P < or = 0.05). Various cytokines, adhesion molecules, and ECM parameters including sTNF-RII, sIL-2R, IL-8, IL-10, sVCAM-1, E-selectin, hyaluronic acid, sialic acid, and laminin correlated significantly with the extent of preservation and reperfusion injury. Although none of these parameters was more appropriate in determining the extent of preservation and reperfusion injury than currently established parameters (AST, ALT, and color and amount of bile production), the combined increase in these parameters may not only promote tissue repair but may also perpetuate liver allograft injury and thereby cause significant morbidity. Besides cytokines and adhesion molecules, the ECM may play a pivotal role in determining repair or ongoing tissue injury. Ongoing changes at the microvasculature and basement membrane may result in an increase of local and circulating cytokines and adhesion molecules, which increase the risk of subsequent early allograft rejection. Furthermore, the increase in sTNF-RII, E-selectin, and laminin during reperfusion was predictive of subsequent development of acute allograft rejection. These observations may be of value for further strategies to decrease reperfusion injury and prevent early allograft rejection.