The effect of donor specific transfusions and dietary fatty acids on rat cardiac allograft survival

Dietary omega-3 and omega-9 fatty acids uniquely enhance allograft survival in cyclosporine-treated and donor-specific transfusion-treated rats

BACKGROUND

Both laboratory and clinical studies have shown that dietary lipids may affect immunologic responses. This study was conducted to compare different classes of long-chain unsaturated fatty acids for their effect on allograft survival in animals receiving a donor-specific transfusion and a short course of low-dose cyclosporine (CsA).

METHODS

Heterotopic ACI strain cardiac allografts were transplanted to Lewis strain rat recipients given diets with different lipid composition. In experiment 1, animals received CsA for 14 days and different diets were enriched with lipids with high concentrations of omega-3, omega-6, or omega-9 fatty acids. In experiment 2, animals received CsA for only 8 days and different diets were enriched with corn oil (omega-6), canola oil (omega-3 and omega-9), fish oil (omega-3) or a mixture of sunflower oil and fish oil (omega-3 and omega-9).

RESULTS

In experiment 1, animals receiving the diet with 30% sunflower oil had the best allograft survival (200+/-42 days vs. 53+/-8 days for regular chow plus donor-specific transfusion and CsA, P<0.05). In experiment 2, diets containing canola oil (a mixture of omega-3 and omega-9 fatty acids) were associated with the best survival (P=0.0011 vs. regular chow).

CONCLUSION

Dietary omega-3 and omega-9 fatty acids both enhanced cardiac allograft survival in a stringent rat strain combination. Canola oil is a convenient oil for administering both alpha-linoleic acid (omega-3) and oleic acid (omega-9) in a palatable form for human consumption. Further investigation of the potential usefulness of lipids in transplant therapy is warranted.

The effect of 5,8,11,14-eicosatetraynoic acid on endothelial cell gene expression

The endothelium plays a key role in inflammation, hemostasis and organ rejection. We report here that a synthetic polyunsaturated fatty acid, 5,8,11,14-eicosatetraynoic acid (ETYA), selectively inhibits the up-regulation of several genes on endothelial cells. ETYA suppresses endothelial cell activation by inhibiting the up-regulation of adhesion molecules like E-selectin. A runoff assay for E-selectin demonstrated that the suppression is at the level of transcription. The fact that ETYA inhibits E-selectin upon stimulation with a diverse group of stimuli like lipopolysaccharide, tumor necrosis factor-alpha or phorbol 12-myristate 13-acetate, suggests that ETYA does not exert its effect by modifying membrane-bound receptors. The messenger RNA for interleukin-8 and glyceraldehyde phosphate dehydrogenase are not affected. Pre-treatment of endothelial cells with ETYA also prevents the adherence of monocytes to tumor necrosis factor-alpha-stimulated cells.

Selective suppression of endothelial cell activation by arachidonic acid

Endothelial cell (EC) activation plays a key role in inflammation, thrombosis and organ rejection. Normally, EC are in a quiescent state in which their function is to prevent coagulation and thrombosis, and to participate in the regulation of leukocyte migration from the bloodstream into the tissue. Upon activation with cytokines or other stimuli, EC up-regulate a number of genes, including E-selectin (ELAM-1), intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, interleukin (IL)-1, IL-8, tissue factor (TF), plasminogen activator inhibitor-1 (PAI-1), MCP-1 (monocyte chemoattractant protein-1) and endothelial cell inducible gene (ECI-6). Arachidonic acid (AA) is produced by several cell types, including EC, and acts on various cells. We report here that AA inhibits the up-regulation of some, but not all genes that are induced with EC activation in a dose-dependent manner. AA suppresses TNF-alpha, IL-1 alpha, LPS or PMA-induced E-selectin expression, as well as mRNA accumulation of E-selectin, ICAM-1 and IL-8 stimulated by TNF-alpha. The inhibition appears to be at the level of transcription. At the same time under the same conditions AA does not, repress mRNA accumulation for PAI-1, ECI-6, MCP-1 and VCAM-1. We suggest that the induced expression of AA with EC activation may result in a negative feedback loop regulating further activation.

Omega-3 lipid infusion in a heart allotransplant model. Shift in fatty acid and lipid mediator profiles and prolongation of transplant survival

BACKGROUND

omega-3 Fatty acids may have a major impact on immune responses involved in heart transplant rejection. We compared the effects of posttransplant intravenous supplementation with omega-3-rich versus omega-6-rich lipid emulsions on graft survival, plasma fatty acid profiles, and levels of arachidonic acid versus eicosapentaenoic acid-derived lipid mediators.

METHODS AND RESULTS

Inbred PVG and Wistar-Kyoto rats were used as donors and recipients, respectively, in a model of heterotopic heart transplantation. Animals received 9 g/kg body wt per day of either fish oil-derived (n = 8) or soybean oil-derived fat (n = 7) in the form of a continuously infused lipid emulsion; controls were sham-infused with saline (n = 8). Graft rejection was assessed by loss of activity of the transplant. The fish oil-derived preparation but not that originating from soybean oil caused an increase in total and free plasma fatty acids. Substantial quantities of eicosapentaenoic acid and docosahexaenoic acid appeared in the free fatty acid fraction, surpassing those of arachidonic acid. Ex vivo stimulation of neutrophils with the Ca2+ ionophore A23187 demonstrated an increase in 5-series leukotriene (LT) generation in animals undergoing omega-3 lipid infusion (LTB5, omega-oxidation products of LTB5, LTA5 secretion), with 5-series/4-series LT ratios ranging between 0.08 and 0.36. Ratios of TX B3/B2 liberated from ex vivo stimulated platelets even approached 1:1 in omega-3 supplemented rats. Graft survival was 7.6 +/- 0.3 (mean +/- SEM) days in saline-infused, 10.4 +/- 0.7 in omega-6 lipid-infused, and 12.9 +/- 0.4 in omega-3 lipid-infused animals.

CONCLUSIONS

Posttransplant intravenous alimentation with fish oil-derived lipid emulsions prolongs heart transplant survival in excess to omega-6 lipids. Profound changes in fatty acid profiles and lipid mediator generation may underlie this finding.

Immunoregulation by parenteral lipids: impact of the n-3 to n-6 fatty acid ratio

BACKGROUND

The immune system is reported to be influenced by polyunsaturated fatty acids. Therefore, immunoregulation caused by intravenous fat emulsions with different n-3 to n-6 fatty acid ratios was studied in an in vivo model.

METHODS

Experimental rat heart allotransplantation served as a defined immunologic challenge. Twenty percent emulsions of safflower oil (n-3 to n-6 = 1:370), fish oil (n-3 to n-6 = 7.6:1), and soybean oil (n-3 to n-6 = 1:6.5), and a 1:1 mixture of safflower oil and fish oil (n-3 to n-6 = 1:2.1) were continuously infused (9 g of fat per kg of body weight per day) after transplantation until complete rejection. The prolongation of graft survival, an accepted parameter of immunosuppression, was assessed. Beyond that, cytokine release by mitogen-stimulated peripheral-blood mononuclear cells (PBMCs) from animals exsanguinated on day 4 after transplantation was evaluated.

RESULTS

The mean rejection time was 7.8 days in the sham-infused saline control group and 6.7 days in the safflower- and fish-oil-mixture group (oil control group). Continuous infusion of soybean oil prolonged the graft survival time to 10.4 days, fish oil to 12.3 days, and safflower oil to 13.3 days. PBMC alpha-tumor necrosis factor release was significantly reduced in the fish-oil group (51.9 +/- 13.0 pg/10(6) PBMCs vs 70.8 +/- 10.9 pg/10(6) PBMCs [controls], p < .004). Interleukin-6 release was diminished in both the fish-oil group (22.2 +/- 13.6 pg/10(6) PBMCs vs 40.7 +/- 8.3 pg/10(6) PBMCs [controls], p < .002) and the safflower-oil group (28.4 +/- 6.9 pg/10(6) PBMCs, p < .002).

CONCLUSIONS

The n-3 to n-6 fatty acid ratio determined the immunoregulatory potential of intravenous fat emulsions in vivo. Both n-3 and n-6 fatty acids were immunosuppressive when applied as the main polyunsaturated fatty acid sources. PBMC cytokine release was significantly reduced in these groups. The more balanced the n-3 to n-6 ratios, the less immunosuppressive the fat emulsion. There was no immunosuppressive effect at an n-3 to n-6 ratio of 1:2.1.

Lipid mediated modification of rat heart allograft survival

The effect on allograft survival of intravenous fat emulsions that differed in the ratio of functionally important n-3 and n-6 fatty acids was studied in a heterotopic cardiac transplant model in rats. Twenty percent fat emulsions were administered by continuous infusion at a dosage of 9 g fat/kg body weight per day, starting immediately after transplantation and continuing until complete rejection. The n-6 and n-3 fatty acids represent 75%, 43%, 60%, and 59% of all fatty acids in safflower oil, fish oil, soybean oil, and a 1:1 mixture of safflower and fish oil, respectively. The n-6 fatty acids predominate in safflower oil (370/1) and soybean oil (6.5/1), while the n-3 fatty acids dominate in the fish oil (7.6/1). The 1:1 mixture of safflower and fish oil has the balanced composition (n-6/n-3 = 2.1/1) recommended by Kinsella and served as oil-treated controls. Continuous infusion of safflower oil, fish oil, and soybean oil prolonged graft survival time to 13.3, 12.3, and 10.4 days, respectively, compared to 6.8 days in the oil-treated controls (P < 0.01 for all comparisons). Another control group infused with saline rejected the allografts after 7.8 days (P = NS compared to oil-treated controls; P < 0.01 for all other comparisons). The data suggest that intravenous administration of polyunsaturated fat emulsions results in an immunosuppressive effect that seems to be dependent on the n-3/n-6 fatty acid ratio of the fat emulsion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of aspirin, dipyridamole, and cod liver oil on accelerated myointimal proliferation in canine veno-arterial allografts

The effects of the administration of aspirin (ASA), dipyridamole (DPM), and cod liver oil (CLO) on graft patency rate and degree of intimal hyperplasia were investigated in a canine, hypercholesterolemic veno-arterial allograft model in an attempt to modify this immunologically mediated vascular injury. The drug regimens were ASA 1 mg/kg/day, DPM 10 mg/kg/day, combined ASA and DPM (ASA + DPM), and CLO (1.8 g/day eicosapentanoic acid [EPA] and 1.2 g/day docosahexanoic acid [DHA]), and control. The early angiographic patency rate (1-3 weeks) was 81% +/- 10% (+/- 70% confidence limits); the 90-day overall patency rate was 60% +/- 4% (87/144), with no statistically significant differences among the groups (range 46 +/- 10-71 +/- 9%). Qualitatively, there was no difference in luminal thrombus, intimal hemorrhage, or lesion eccentricity. Considering the relatively short time of graft implantation, an extensive amount of microscopic disease was observed; quantitatively, the mean intimal thickness was 515 +/- 17 microgram overall but was not statistically different between the groups. The fraction of potential lumenal area occupied by intimal thickening was 0.37 +/- 0.01 but again did not differ significantly between the groups. These doses of ASA, DPM, ASA + DPM, and CLO did not alter graft occlusion or retard the marked degree of subintimal myointimal cell hyperplasia that was generated in this hypercholesterolemic canine veno-arterial allograft preparation. Possible explanations for these negative findings include inadequate dosage or form of omega-3 fatty acids and the antiplatelet drugs administered, excessive variability in graft response due to uncharacterized immunologic histocompatibility, and the possible influence of non-platelet-mediated mechanisms. Nevertheless, this preparation is attractive as a reproducible model of accelerated (immunologically mediated) experimental arteriosclerosis.