There are four groups of unsaturated fatty acids in the human body, namely, soft fat oleic acid group (ω-7), oleic acid group (ω-9), linoleic acid group (ω-6) and linolenic acid group (ω-3). The human body can synthesize soft fat oleic acid group (ω-7) and oleic acid group (ω-9) on its own, both of which are called non-nutritional essential fatty acids. However, linoleic acid (ω-6) and linolenic acid (ω-3) cannot be synthesized in the human body and can only be obtained from food, so they are called nutritionally essential fatty acids. The human body can synthesize the ω-6 and ω-3 groups of nutritionally essential fatty acids with linoleic acid and linolenic acid as the parent in turn. Therefore, linoleic acid and linolenic acid are the real nutritionally essential fatty acids. The use of fish oil in kidney transplant patients can reduce acute and chronic rejection and improve the long-term survival rate of kidney transplantation. The clinical application of fish oil in kidney transplantation and its mechanism of action 1. Fish oil improves the function and hemodynamics of transplanted kidney Cyclosporine A (CsA) can effectively improve the long-term survival rate of transplanted kidney and is effective in treating certain immune glomerulonephritis. However, CsA has many side effects, the most significant of which remains CsA nephrotoxicity. Recent studies have shown that CsA causes constriction of the small inlet arteries, resulting in a dramatic decrease in effective renal plasma flow (ERPF) and glomerular filtration rate (GFR), an increase in renal vascular resistance (RVR), and an increase in blood pressure. Replacing olive oil with fish oil as a mediator of CsA competes with arachidonic acid for cyclooxygenase and limb oxygenase, thereby inhibiting arachidonic acid metabolism, reducing the amount of TXA2 and LTB4 synthesized by CsA that has a constricting effect on renal vasculature, and ameliorating CsA-induced acute and chronic renal damage.Wang et al. determined that renal TXA has a strong vasoconstrictive effect.CsA causes transplant-induced renal function Rogers et al. showed that CsA (12.5 mg.kg-1/d) caused an increase in TXA2 synthesis in renal cortex and peripheral macrophages and a decrease in PGE2 and PGI2 synthesis in animals. The application of fish oil can competitively inhibit the metabolism of arachidonic acid, selectively inhibit the production of TXA2, and protect the function of transplanted kidney. In 1990, Homan Van der Heide et al. first reported that fish oil consumption could at least partially correct CsA-induced renal function abnormalities in renal transplant patients; later, the application of fish oil rich in EPA (30%.C 20:5 . n-3) and DHA (20%.C 22:6.n-3) in 66 kidney transplant recipients in a randomized double-blind controlled study, kidney transplant patients showed significant improvements in transplant renal function and hemodynamics after 1 year compared with the control group (coconut oil group): GFR (53 vs. 40 ml.min-1/1.73 m2. P=0. 038) and ERPF (214 vs. 178 ml・min-1/1.73 m2. p=0.023). Mean arterial pressure was significantly lower (13.7 versus 15.7 kPa,P=0.0011). The study suggests that fish oil improves transplant kidney hemodynamics probably through the inhibition of TXA2 production by fish oil on AA in the cyclooxygenase pathway. 2 , Fish oil reduces the incidence of transplant kidney rejection The literature reports 33 cases on oral fish oil 6.0/d (fish oil group) and 33 cases on coconut oil 6.0/d (control group). The same immunosuppressive regimen (CsA+Pred) was applied in both groups, and it was found that there were 6 and 10 cases of acute rejection in the two groups in the 1st month after transplantation, and the acute rejection in the fish oil group was significantly lower than that in the control group in the 1st year of kidney transplantation (8 vs. 20, P=0.029). The fish oil treatment group received significantly less methylprednisolone (MP) than the control group (0.71 versus 2.56 g/patient, P=0.013), but the difference in the amount of MP treatment per acute rejection was not significant between the two groups (3.8 versus 4.5 g/dose, P=0.12). The results of the study suggest that fish oil reduces the incidence of acute rejection in transplanted kidneys. In another group of patients with chronic rejection treated with fish oil for own control observation, the function of transplanted kidney was significantly improved, 1/Scr (umol/L・month) -13.5 X10-5 before treatment and 1/Scr (umol/L・month) -3.6 X10-5 after 6 months of treatment. p<0.05. Whether fish oil can reduce acute and chronic rejection of transplanted kidney has been a controversial issue. Animal tests have shown that fish oil increases the immunosuppressive effect of CsA during heart transplantation in mice and suppresses delayed allergic reactions in the same animals. Two hypotheses have been proposed for fish oil to reduce rejection of transplanted kidneys: (1) fish oil reduces inflammatory cytokines and leukocyte chemotaxis. il-1 and tumor necrosis factor (TNF) are peptide cytokines synthesized by monocytes stimulated by injury, infection, inflammation or immune response. These cytokines cause local inflammatory changes and mediate systemic acute chronological changes. Thus, IL-1 and TNF often have synergistic effects on vascular endothelial cytokine production and AA anabolism. Involvement in transplant renal rejection. Recently, Endres et al. stimulated the production of inflammatory cytokines by peripheral blood mononuclear cells by in vitro endotoxin in an in vitro assay. demonstrated that the consumption of fish oil reduced the synthesis of IL-1 and TNF. Fish oil (18 g/d) was consumed for 1 week. Self-controlled observations in 9 healthy volunteers revealed a 32% reduction in IL-1 after 6 weeks of fish oil consumption (16. 0 vs. 10. 9. p = NS) and a 39% reduction in IL-1 after week 16 (16. 0 vs. 9. 7 . p = 0. 022 ). p = 0. 022 ) TNF was reduced by 40% ( 8. 5 vs. 5. 1. p = 0.008). However . At week 26 IL-1 and TNF returned to pre-treatment levels, while fish oil was found to inhibit leukocyte chemotaxis. The results suggest that. Fish oil consumption has a significant anti-inflammatory effect and reduces the production of cytokines (IL-1 and TNF). Does fish oil itself have immunosuppressive effects? Kelley et al. observed fish oil (FO), FO plus CsA on animal models of delayed-type hypersensitivity (DTH) in BALB/C rats and mice heart transplants, respectively. In fact, FO enhanced the immunosuppressive effect of CsA. Even the administration of a small amount of FO ( 0.05 ml) as adjuvant for CsA had a strong immunosuppressive effect, compared with the same amount of olive oil (OO). The inhibitory effect on DTH depended on the dose of FO, with 0.05 ml FO injected daily inhibiting DTH. increasing FO by 0. 3 ml per day also significantly reduced DTH, and the same amount of OO group did not change significantly. The results suggest that FO enhances the immunosuppressive effect of CsA and that FO itself has an immunosuppressive effect. However, this was not clinically confirmed, and if fish oil itself has immunosuppressive effects, it has been hypothesized that in the context of renal transplantation fish oil reduces the production of inflammatory cytokines (IL-1, TNF) and CsA blocks the transcription of IL-2. Therefore, the combination of FO and CsA could exert a stronger immune effect by blocking two different immune response pathways and reduce the rejection of transplanted kidneys. Of course, a lot of basic and clinical research remains to be done in this area. (2) Fish oil selectively reduces the synthesis of renal TXA2. Acute rejection of transplanted kidney may be related to the altered metabolism of arachidonic acid, including the increased production of the potent vasoconstrictor TXA2. Animal experiments demonstrated an increase in renal cortical and renal arterial TXA2 on day 3 and renal infarction on day 7 after kidney transplantation. Within 2-6 d of kidney transplantation in mice, TXA2 in renal tissue increased significantly and renal function deteriorated sharply. During the rejection reaction, TXA2 acted directly on platelets, vascular smooth muscle cells and promoted lymphocytotoxic T lymphocytes to participate in the rejection reaction. Fish oil can selectively reduce the synthesis of renal TXA2 and stop the process of rejection reaction. 3. fish oil improves graft survival Kelley et al. observed in an animal model of mouse heart transplantation that FO +CsA prolonged graft survival. homan Vander Heide et al. applied FO treatment to 33 kidney transplant recipients for 1 year. The results showed that the 1-year kidney survival rate in the FO-treated group was significantly higher than that in the control group, 97% and 84%, respectively, p=0.097. However, whether fish oil can improve the long-term survival rate of transplanted kidneys still needs a lot of clinical observation. In conclusion ω-3 and ω-6 PUFA are nutritionally essential fatty acids in the human body. The human body can form EPA and DHA through carbon chain extension and desaturation, but the synthesis rate is slow and can only be extracted from cold water fish and cold sea animals for consumption. Fish oil rich in ω-3 and ω-6 PUFA can significantly improve the hemodynamic changes caused by CsA nephrotoxicity in kidney transplant patients, reduce acute and chronic rejection reactions, and improve the survival rate of transplanted kidneys. In vitro tests have shown that fish oil itself has anti-inflammatory effects, decreases the production of inflammatory cytokines (IL-1. TNF) and inhibits the chemotaxis of leukocytes. Therefore, the combination of fish oil and CsA can exert a stronger immunosuppressive effect by blocking two different immune response pathways, reduce the rejection of transplanted kidney and improve the long-term survival rate of kidney transplantation.