Prostaglandin E2 and thromboxane B2 levels in rats subjected to pancreas transplantation

Characterization of microcirculatory disturbance in a novel model of pancreatic ischemia-reperfusion using intravital fluorescence-microscopy

INTRODUCTION

Microcirculatory disturbances caused by ischemia-reperfusion injury (IRI) are the crucial hallmarks of pancreatitis following pancreas transplantation.

AIMS

To develop a novel rodent model of normothermic in situ ischemia of a pancreatic tail-segment that simulates the clinical situation of pancreas transplantation by flushing the organ via an inserted microcatheter and thus enables selective treatment of the organ via this access.

METHODOLOGY

Four experimental groups were investigated (n = 7 Wistar rats/group): sham animals without ischemia and dissection of the pancreas; control animals with dissection of a pancreatic tail segment pedunculated on the splenic vessels and flushing od this segment with saline via a microcatheter; and two groups of animals treated like controls with a pancreatic ischemia time of 1 hour or 2 hours. With use of intravital epifluorescence microscopy, the microcirculatory damage was characterized by investigation of functional capillary density (FCD) and leukocyte adherence in postcapillary venules (LAV) before ischemia and during a reperfusion time of 2 hours. Dry:wet ratio determinations, light microscopy, and electron microscopic investigations were performed to characterize the histologic organ damage.

RESULTS

FCD decreased significantly (p < 0.05) 2 hours after reperfusion in the groups of 1-hour (-29.21%) and 2-hour ischemia (-42.73%), in comparison with baseline values. LAV increased significantly (p < 0.05), 4.3- and 5.8-fold, after 1-hour and 2-hour ischemia during the observation time. The histologic damage was similar to posttransplantation pancreatitis in humans 1 hour after reperfusion. In sham and control animals these alterations were not significant.

CONCLUSIONS

The rodent in situ model of pancreatic IRI showed standardized microcirculatory damage dependent on the ischemia time. Offering the possibility of selective treatment by the direct artery access to the ischemic pancreatic area, the model enables investigations of questions related to human pancreas transplantation.

Impairment of microcirculation in the early reperfusion period predicts the degree of graft pancreatitis in clinical pancreas transplantation

BACKGROUND

Graft pancreatitis is thought to be induced by ischemia/reperfusion. Animal experiments have suggested that an impaired microcirculation is crucial in this process. We have therefore studied the relevance of microcirculation in clinical pancreas transplantation.

METHODS

In 17 patients undergoing pancreas transplantation, tissue pO2 was monitored continuously by an electrode implanted into the pancreatic tail. A catheter was inserted in the distal part of the splenic vein of the pancreas graft. After reperfusion blood samples were taken from this catheter and blood flow was measured by the venous outflow method. The degree of graft pancreatitis was assessed by peak-C-reactive protein (CRP) defined as highest CRP within 3 days after transplantation.

RESULTS

Tissue pO2 increased within 5 min after reperfusion. Thereafter, in most patients a transient decrease was noted, indicating impairment of nutritive perfusion. During this period there was an increasing negative correlation between peak-CRP and tissue pO2 which was highly significant at 60 min after reperfusion (r=-0.70, P<0.002). Also donor age correlated significantly with peak-CRP (r=0.64, P<0.005) and to a somewhat lesser extend with tissue pO2 60 min after reperfusion (r= -0.55, P<0.03).

CONCLUSION

These data show that the degree of organ damage in clinical pancreas transplantation is directly related to an impairment of microcirculation in the early reperfusion period. These data also support the idea that grafts from older donors have a higher probability to develop graft pancreatitis and that this might be due to an increased incidence of microcirculatory disturbances in these organs.

Extending the margin of safety of preservation period for resuscitation of ischemically damaged pancreas during preservation using the two-layer (University of Wisconsin solution/perfluorochemical) method at 20 degrees C with thromboxane A2 synthesis inhibitor OKY046

We have shown that 5-hr preservation using the two-layer (University of Wisconsin solution/perfluorochemical) method at 20 degrees C allows ATP synthesis and makes it possible to resuscitate a canine pancreas subjected to 90 min of warm ischemia. However, 8 hr of preservation using this method caused a disturbance of vascular microcirculation and did not resuscitate the grafts. The aim of this study was to examine the effect of thromboxane A2 synthesis inhibitor OKY046 on vascular endothelial cells and ATP tissue levels of canine pancreas during preservation using the two-layer (University of Wisconsin solution/perfluorochemical) method at 20 degrees C, and vascular microcirculation and pancreas viability after transplantation. Graft viability was judged by graft survival following autotransplantation. ATP tissue levels were measured by high-performance liquid chromatography at the end of preservation. Viability of the vascular endothelial cells was judged using nuclear trypan blue uptake of the graft after preservation. Pancreatic tissue perfusion was measured using an H2 clearance technique after reperfusion. Pancreas grafts subjected to 90 min of warm ischemia were not viable (0/5). However, 5-hr preservation made it possible to recover the pancreas (5/5); 8-hr preservation was not successful (0/3). ATP tissue levels after 5-hr and 8-hr preservation were 9.40+/-2.09 and 7.37+/-1.06 micromol/g dry weight, respectively, and OKY046 did not affect ATP synthesis during 8-hr preservation (8.44+/-0.92 micromol/g dry weight). The percentage of nuclear trypan blue uptake of endothelial cells in 8-hr-preserved grafts was 37.6+/-11.6% and was significantly higher than the value in 5-hr-preserved grafts (5.0+/-3.0%; P<0.01). However, OKY046 significantly reduced trypan blue uptake in 8-hr-preserved grafts (8.2+/-3.6%; P<0.01). Pancreatic tissue perfusion in 8-hr-preserved grafts after 2 hr of reperfusion was 28.5+/-7.5 ml/min/100 g, and was significantly lower than the value in 5-hr-preserved grafts (57.1+/-4.4 ml/ min/100 g; P<0.01), but OKY046 dramatically improved pancreatic tissue perfusion (97.1+/-14.6 ml/min/100 g; P<0.01). As a consequence, 8-hr-preserved grafts were resuscitated (4/5). We conclude that OKY046 protects the vascular endothelium during preservation by the two-layer method at 20 degrees C and consequently improves vascular microcirculation on reperfusion. Together with ATP synthesis, which is essential for repairing damaged cells, the canine pancreas graft subjected to 90 min of warm ischemia is resuscitated during 8-hr preservation by the two-layer method at 20 degrees C. This method holds promise for pancreas-kidney transplantation from cardiac arrest donors.

Role of xanthine oxidase and eicosanoids in development of pancreatic ischemia-reperfusion injury

The implication of different eicosanoids and oxygen free radicals in the development of pancreatic injury after an ischemia-reperfusion process has been evaluated. For this purpose we have compared the effect of allopurinol and indomethacin administration on the pancreatic levels of eicosanoids in a rat model of pancreatic ischemia-reperfusion. After 60 min of pancreatic ischemia and 2 h of reperfusion, significant increases in 6-keto-PGF1 alpha, PGE2, and LTB4 in pancreas tissue were detected. Allopurinol before the ischemic period reduced 6-keto-PGF1 alpha, PGE2, and LTB4 levels to the range of basal values, while prior indomethacin treatment significantly reduced 6-keto-PGF1 alpha and PGE2 levels, with LTB4 remaining unmodified. Increased postischemic plasma lipases were also significantly reduced by allopurinol to the range of sham-operated animals whereas indomethacin did not modify these levels. The data suggest a role for lipoxygenase metabolites in the development of pancreatic injury and the importance of the enzyme xanthine oxidase as an inductor of eicosanoid biosynthesis.

Prostanoids and cyclosporin-mediated nephrotoxicity in rats: a critical appraisal

The involvement of arachidonic acid metabolism in cyclosporin (CsA) nephrotoxicity depending on CsA vehicle has been explored in this study. For this purpose creatinine clearance, urinary excretion and renal levels of eicosanoids were measured in the following rat experimental groups: group I, control; group II, CsA was administered in olive oil by gavage at 15 mg/kg/d for 7 d; group III, same as group II but 30 mg/kg/d; group IV, CsA was administered in fish oil by gavage at 15 mg/kg/d for 7 d; group V, same as group IV but 30 mg/kg/d; group VI, CsA was administered in olive oil at 15 mg/kg/d with prednisolone (1 mg/kg/d). The results indicate that (1) CsA nephrotoxicity and prostanoid alterations seem to be greatly improved when fish results indicate that (1) CsA nephrotoxicity and prostanoid alterations seem to be greatly improved when fish oil substitutes olive oil as a vehicle for CsA administration and (2) a correlation was found between eicosanoids measured and renal function, except in group II in which creatinine clearance remains unmodified but eicosanoids were altered, thus suggesting that other factors play a role in mediating nephrotoxicity due to cyclosporin.

Altered leukotriene B4 levels by HL-60 cells after monocytic/macrophage differentiation

The differentiation of HL-60 human promyelocytic leukaemia cells into specific monocytic or granulocytic lineage cells depending of the inductor agent is accompanied by selective regulation of several key enzymes involved in the synthesis of eicosanoids. In this communication we have investigated the changes in arachidonic acid metabolic profiles during phorbol 12-myristate 13-acetate (PMA)-induced monocytic differentiation of HL-60 cells. Our results show that HL-60 cells have spontaneous capacity to synthesize large amounts of LTB4, but PMA-differentiated cells lose the ability to release LTB4. Significant differences are found between HL-60 cells and PMA-treated cells in basal conditions and under ionophore stimulation. The addition of LTB4 at the time of PMA differentiation did not have effects on cell proliferation, but nordihydroguaiaretic acid (NDGA), a potent 5-lipoxygenase inhibitor, also inhibited HL-60 cell proliferation and did not have any effect on PMA-differentiated cell proliferation.

Changes of systemic prostacyclin and thromboxane A2 in sodium taurocholate- and cerulein-induced acute pancreatitis in rats

Systemic prostacyclin and thromboxane A2 production in rat experimental acute pancreatitis has been evaluated by measuring the urinary excretion of the 2,3-dinor 6-keto prostaglandin F1 alpha and 2,3-dinor thromboxane B2, respectively. Acute pancreatitis was induced by intraductal administration of 4.5% sodium taurocholate (0.1 ml/100 mg body weight) and intravenous cerulein perfusion (5 micrograms/kg/hr) for 6 hr, respectively. Urinary excretion of 2,3-dinor 6-keto prostaglandin F1 alpha and 2,3-dinor thromboxane B2 were much more important in sodium taurocholate- than in cerulein-induced acute pancreatitis. These data confirm an altered prostacyclin and thromboxane metabolism occurring in experimental acute pancreatitis. Phospholipase A2 activity and the effect of gabexate mesilate on the arachidonate metabolism were also evaluated.

Altered systemic and tissue prostacyclin in cerulein induced acute pancreatitis in rats

Prostacyclin metabolism in rat acute pancreatitis was evaluated by measuring the tissue levels of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and the urinary excretion of 2, 3-dinor 6-keto-PGF1 alpha. Acute pancreatitis was induced by i.v. cerulein perfusion and was confirmed by the pancreas enzyme changes and the histological findings. Significantly enhanced tissue and urinary prostacyclin levels were found in acute pancreatitis rats, when compared to the controls. Concomitantly, an enhanced tissue phospholipase A2 (PLA2) activity was also found. These data show the importance of 2, 3-dinor PGF1 alpha as an inflammatory marker in cerulein-induced pancreatitis.

Successful 96-Hr cold-storage preservation of canine pancreas with UW solution containing the thromboxane A2 synthesis inhibitor OKY046

Prostanoids, such as prostacyclin (PGI) and thromboxane A2 (TxA), have been recently suggested to play an important role in preservation-induced injury of pancreas grafts. We have previously shown that the TxA synthesis inhibitor OKY046 prevents a decrease of both the PGI/TxA ratio and blood flow in pancreas grafts after 24-hr preservation with Euro-Collins solution. In our present study, we analyzed whether OKY046 added to University of Wisconsin (UW) solution could extend successful cold-storage preservation of segmental canine pancreas grafts, compared with UW alone. We divided 30 dogs into four preservation groups: Group 1, UW solution for 72 hr (n = 7); Group 2, UW solution for 96 hr (n = 8); Group 3, UW solution plus OKY046 (10(-4) M) for 72 hr (n = 7); and Group 4, UW solution plus OKY046 (10(-4) M) for 96 hr (n = 8). After the cold storage period, segmental pancreas auto-transplantation with immediate completion pancreatectomy was done. Preservation was deemed successful if serum glucose less than 150 mg/dl was maintained for at least 5 days. Intravenous glucose tolerance tests and biopsies were done in those dogs with functioning grafts 14 days post-transplant. Successful preservation rates were as follows: Group 1, 57.1%; Group 2, 12.5%; Group 3, 100%; and Group 4, 75%. The mean K values (+/- standard error) were: Group 1, 1.54 +/- 0.13; Group 2, 0.59; Group 3, 1.54 +/- 0.14; and Group 4, 1.59 +/- 0.24 (not statistically different).(ABSTRACT TRUNCATED AT 250 WORDS)

Pancreas prostanoid production in ischemia and reperfusion

This study was carried out to investigate the proportion of the 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha) and thromboxane B2 (TXB2) alteration that is due to ischemia in pancreas transplantation against the proportion due to reperfusion. For this purpose, Lewis rats were divided in three experimental groups: Group I = Control, Group II = Donor pancreas subjected to 15 minutes of cold ischemia, Group III = Same as group II but pancreas were transplanted to the recipient individual and then subjected to reperfusion. The results indicate that increases in pancreas 6-keto PGF1 alpha occur as a consequence of cold ischemia while TXB2 remains unchanged. When blood flow was restored, 6-keto PGF1 alpha remained unchanged compared to the ischemic group while pancreatic levels of TXB2 were significantly increased. These results suggest a different induction of prostanoid metabolism during ischemia and reperfusion in pancreatic tissue.

Alpha melanocyte stimulating hormone (alpha-MSH) enhances eicosanoid production by bovine retinal pigment epithelium

Explants of bovine eyes consisting of retina, with its underlying choroid and sclera (termed retinal explants) were maintained in organ culture in the absence or presence of alpha-melanocyte stimulating hormone (alpha-MSH) for up to 19 days. The conditioned media was collected twice a week and assayed for the following eicosanoids, prostaglandin E2 (PGE2) and prostacyclin. The addition of alpha-MSH to the incubation media resulted in a 1.5 fold enhancement in the production of both PGE2 and prostacyclin. This stimulatory effect diminished after 11 days. Additionally, the three tissue components comprising the retinal explants i.e. 1. neural retina 2. retinal pigment epithelium (RPE) with its underlying vascular layer (choroid) and 3. scleral tissue were separated and incubated in the presence or absence of alpha-MSH. Hormone treatment caused an enhanced eicosanoid production by RPE tissue alone, while its production by the neuronal retina and sclera was reduced or unaffected respectively. This demonstrates that the RPE layer is the source for the alpha-MSH induced eicosanoid production observed in the whole retinal explant. Our findings demonstrate, for the first time that alpha-MSH can stimulate prostaglandin production by RPE maintained in organ culture.

Effect of prostaglandin E1 on graft function of kidneys from living related donors

Prostaglandin E1 (PGE1) was used in renal transplant recipients with living related donors. The drug was given intravenously from day 1 to day 7 after transplantation at a dose of 40 microg/kg twice a day. A total of 45 patients were studied divided into two groups: 25 patients were treated with PGE1 (group B) and the remaining 20 patients did not receive the drug (group A). In group B, 24-h creatinine clearance (Ccr) was 66 +/- 12.8 ml/min compared with 40.3 +/- 13.4 ml/min in group A on the fifth postoperative day (P < 0.05). Urinary levels of N-acetyl-beta-D-glucosaminidase (NAG) and serum levels of platelet factor 4 (PF4) in group B were significantly lower than in group A. On the fourth postoperative day, the urinary excretion of thromboxan B2 (TxB2) in group A was higher than in group B, but not significantly (5.1 +/- 3.0 ng/day and 2.8 +/- 1.1 ng/day, respectively). Acute rejection occurred in four patients in group B and in 10 patients (40%) in group A. The percentage of Leu2a-positive lymphocytes in group B was higher than in group A. We conclude that postoperative administration of PGE1 improves graft function in kidneys from living related donors.

Altered levels of tissue and urinary prostacyclin in rats subjected to pancreas transplantation

Significant increases of TXB2 and PGE2 are reported to occur in pancreas transplantation. These increases are prevented with scavengers of oxygen-free radicals. In this communication, we report on changes of prostacyclin metabolites such as tissue 6-keto prostaglandin F1 alpha and urinary 2,3-dinor 6-keto prostaglandin F1 alpha in rats subjected to pancreas transplantation after different periods of organ cold preservation ischemia as well as the effect of superoxide dismutase (SOD) on these changes. For this purpose, male Lewis rats were classified as follows: Group I, Control; Group II, syngenic pancreas transplantation after 15 min of organ preservation in Collins solution at 4 degrees C; Group III, same as II but with 12 hours of organ preservation; Group IV, same as III, but with SOD pretreatment. Results have shown significant posttransplantation increases of both tissue 6-keto PGF1 alpha and urinary 2, 3 dinor 6-keto PGF1 alpha, the latter being a useful marker to evaluate systemic prostacyclin (PGI2) production by rat pancreas. This effect was prevented when the organ had been exposed to SOD during the period of cold preservation ischemia. These results confirm the implication of oxygen-free radicals (OFR) in the ischemia-reperfusion process associated to rat pancreas transplantation leading to enhanced arachidonic acid metabolism.

Prostaglandin E2 changes in the retina and optic nerve of an eye with injured optic nerve

Changes in arachidonic acid metabolism were studied in the optic nerve, the chorioretina, and in the vitreous following crush injury to the optic nerve of rats. Crush injury led to: (i) a 3.9-fold increase in optic nerve prostaglandin type E2 in vitro production which peaked on day 5 and was followed by a gradual decline, but was still significantly higher than baseline levels by day 12; (ii) a two-fold increase in the chorioretina prostaglandin type E2 in vitro production which peaked on day 1, and resumed baseline levels by day 3; (iii) a 3.5-fold increase in vitreous prostaglandin type E2 levels on day 1 which remained at 1.5-2 times higher than baseline levels for the rest of the study period (12 days). The findings indicate that the pattern of changes in prostaglandin type E2 production by the optic nerve (consisting mostly of white matter) is different from that described for injured brain tissues. The prolonged accumulation of vitreal prostaglandin type E2 in eyes with damaged optic nerve may lead to undesirable effects on the retina beyond those directly manifested in the retina by altered axonal flow in the injured optic nerve.