Surviving Native β-Cells Determine Outcome of Syngeneic Intraportal Islet Transplantation

Effect of Inspired Oxygen on Portal and Hepatic Oxygenation: Effective Arterialization of Portal Blood by Hyperoxia

Because hypoxia may compromise the survival of intraportally transplanted pancreatic islets, we have measured portal blood flow and both portal and hepatic oxygenation in normal and diabetic rats breathing graded inspired oxygen concentrations. Portal blood flow and hepatic tissue oxygenation were measured using a transonic flowmeter and near infrared spectroscopy while gas analysis was carried out on portal venous blood samples. The effects of breathing 13%, 21%, 50%, or 100% oxygen were compared in animals with steptozotocin-induced diabetes and in controls. In diabetic rats breathing 21% oxygen, portal blood flow was significantly lower than in controls (7.2 ± 0.7 vs. 9.1 ± 0.8 ml/min, p < 0.05). In both groups, breathing 100% oxygen significantly increased portal flow (to 8.4 ± 1.0 and 12.2 ± 0.7 ml/min, respectively). This effect was not secondary to hepatic arterial vasoconstriction because it was not prevented by hepatic artery ligation. In controls, breathing 100% oxygen increased portal pO2 from 5.0 ± 0.9 to 14.4 ± 1.4 kPa (p < 0.05) and portal venous oxygen saturation (PSaO2) from 53.9 ± 12.1% to 92.9 ± 1.4% (p < 0.05), a value not significantly different from peripheral (arterial) saturation. Similarly, in diabetic animals pO2 rose from 5.6 ± 0.3 to 11.7 ± 0.4 kPa (p < 0.01) and SO2 from 55.5 ± 5.2% to 88.5 ± 0.6% (p < 0.05). Hepatic oxyhemoglobin rose and deoxyhemoglobin fell reciprocally as a function of the inspired oxygen concentration. Improved hepatic oxygenation observed in animals breathing oxygen-enriched gas mixtures results from an increase in splanchnic blood flow coupled with a marked increase in portal oxygen saturation. This effective arterialization of portal blood may have important consequences for the success of intraportal transplantation of pancreatic islets.

Therapeutic potential of HDL in cardioprotection and tissue repair

Epidemiological studies support a strong association between high-density lipoprotein (HDL) cholesterol levels and heart failure incidence. Experimental evidence from different angles supports the view that low HDL is unlikely an innocent bystander in the development of heart failure. HDL exerts direct cardioprotective effects, which are mediated via its interactions with the myocardium and more specifically with cardiomyocytes. HDL may improve cardiac function in several ways. Firstly, HDL may protect the heart against ischaemia/reperfusion injury resulting in a reduction of infarct size and thus in myocardial salvage. Secondly, HDL can improve cardiac function in the absence of ischaemic heart disease as illustrated by beneficial effects conferred by these lipoproteins in diabetic cardiomyopathy. Thirdly, HDL may improve cardiac function by reducing infarct expansion and by attenuating ventricular remodelling post-myocardial infarction. These different mechanisms are substantiated by in vitro, ex vivo, and in vivo intervention studies that applied treatment with native HDL, treatment with reconstituted HDL, or human apo A-I gene transfer. The effect of human apo A-I gene transfer on infarct expansion and ventricular remodelling post-myocardial infarction illustrates the beneficial effects of HDL on tissue repair. The role of HDL in tissue repair is further underpinned by the potent effects of these lipoproteins on endothelial progenitor cell number, function, and incorporation, which may in particular be relevant under conditions of high endothelial cell turnover. Furthermore, topical HDL therapy enhances cutaneous wound healing in different models. In conclusion, the development of HDL-targeted interventions in these strategically chosen therapeutic areas is supported by a strong clinical rationale and significant preclinical data.

Oxygenation of the portal vein by intraperitoneal administration of oxygenated perfluorochemical improves the engraftment and function of intraportally transplanted islets

OBJECTIVES

One of the major obstacles for successful intraportal islet transplantation (IPIT) is early graft loss due to hypoxia. We therefore examined the effect of intraperitoneal oxygenated perfluorochemical (PFC) on oxygenation of the portal vein with respect to islet engraftment and function after IPIT in a rat model.

METHODS

First, we measured the oxygen tension and saturation in the portal vein of Lewis rats before and after intraperitoneal injection of oxygenated PFC. Second, blood glucose levels, glucose tolerance, and the number of surviving islets were measured after IPIT with oxygenated PFC (group 1), with PFC saturated by nitrogen (group 2), and without any PFC (control).

RESULTS

Both oxygen tension and saturation in the portal vein significantly increased after injection of oxygenated PFC. In IPIT, the functional success rate in group 1 was 83.3%, compared with 16.7% in group 2 and 16.7% in the control. On the 28th posttransplantation day, the number of engrafted islets in the liver in group 1 (12.8 [SD, 3.3]) was significantly higher than that in group 2 (4.7 [SD, 3.0]) and in the control group (6.5 [SD, 3.3]).

CONCLUSIONS

We clearly demonstrated the effect of intraperitoneal oxygenated PFC on oxygenation of the portal vein, resulting in better IPIT outcomes.

Hyperoxia improves the survival of intraportally transplanted syngeneic pancreatic islets

BACKGROUND

Hypoxia in the portal vein may compromise the survival of intraportally transplanted pancreatic islets. We therefore examined the effect of inspired oxygen on the outcome of islet transplantation.

METHODS

Blood glucose concentrations, glucose tolerance, and the size and number of surviving islets were measured in diabetic rats housed for 48 hr under hyperoxic (100% O(2)), hypoxic (11% O(2)), or normoxic (21%O(2)) conditions after intraportal transplantation of 350, 500, 700, or 1,000 syngeneic islets.

RESULTS

In normoxic diabetic rats, the smallest graft size to consistently restore normoglycemia was 1,000 islets. A graft size of 700 islets was effective in only three of nine animals, whereas 500 islets were ineffective in all eight animals undergoing transplantation. In contrast, in hyperoxically housed rats, graft sizes of 700 or 500 islets restored normoglycemia in eight of nine or five of eight animals, respectively. In those animals that became normoglycemic, the glucose tolerance of the hyperoxically treated rats receiving 700 islets was almost identical to that of normoxically housed animals receiving 1,000 islets. The average size of the islets 6 weeks after transplantation was the same in livers of hyperoxic and control rats. However, the total islet area and number of islets engrafted in hyperoxic rats was significantly increased when compared with livers from normoxic animals receiving the same graft size, so the area in hyperoxic rats receiving 700 islets was not significantly different from normoxic recipients of 1,000 islets.

CONCLUSIONS

Hyperoxia posttransplantation increases the number of islets that survive the engraftment process and allows normalization of plasma glucose levels with a smaller number of transplanted islets.

Molecular detection of circulating beta-cells after islet transplantation

Islet transplantation is a promising treatment for type 1 diabetes. However, islet grafts are submitted to multiple injuries, including immunosuppressive drug toxicity, hyperglycemia, hypoxia, unspecific inflammatory reactions, as well as allo- and autoimmune destruction. Therapeutic approaches to these damage mechanisms require early detection of islet injury, which is currently not feasible because of the lack of efficient markers. Based on the hypothesis of islet dissociation and release of islet cells into the circulation during islet injury, we designed a highly sensitive and specific molecular assay, able to detect two beta-cells per milliliter of venous blood by RT-PCR of insulin mRNA. We report that circulating beta-cells can be demonstrated up to 10 weeks after intraportal islet transplantation, as assessed after six islet grafts in four type 1 diabetic patients. Furthermore, our results suggest that the time during which circulating islet cells can be detected may depend on the graft environment and the immunosuppressive regimen. This test may allow better estimation of islet cell loss and identification of factors involved in islet graft injury.