In patients suffering from chronic kidney disease, there is an increased activation of platelets  as a result of dialysis, increased inflammation, and oxidative stress, and hence an increased production of thromboxane and HETE acids, amongst other factors. It has also been shown that peritoneal dialysis leads to an increased synthesis of eicosanoids by peritoneal macrophages and mesenchymal cells due to the properties of the dialysis fluid, which are generally not biocompatible . Therefore, knowledge of the relationship between the type of renal replacement therapy and the level of arachidonic acid derivatives is extremely important. According to the literature, it is possible to use this knowledge to gain insights into the chances of survival of a patient following kidney transplantation, whether dialysis is still providing effective treatment, or which type of renal replacement therapy is suitable for a given patient.
Thromboxane A2 (TXA2) is mainly synthesized by activated platelets, in response to platelet aggregation and vasoconstriction. It has a very short half-life (about 30 seconds). In aqueous solutions, TXA2 is unstable and rapidly degraded to an inactive but more stable form of TXB2. Although TXA2 appears to be of minor importance in maintaining renal function under physiological conditions, increased TXA2 biosynthesis in the kidney is confirmed in various animal models of kidney disease. One of the most important events that occurs in a transplanted organ is ischemia-reperfusion injury (I/R), which unfortunately is an inherent aspect of transplantation. The mechanism of I/R damage includes activation of the inflammatory response, formation of reactive oxygen species, and microcirculation disorders. In addition, several mediators such as TNF-α, endothelin, and arachidonic acid eicosanoid metabolites contribute to such mechanisms, including hydroxyeicosatetraenoic (HETE) acids and thromboxane . Several authors have already reported that during I/R injury and allograft rejection, there is increased production of thromboxane synthase and consequently increased TXB2 concentration. Inhibition of TXA2 synthesis during reperfusion significantly improves graft function in animal models of kidney transplantation [10,18].
Kidney mesangial cells and podocytes produce TXA2. Glomerulonephritis, cyclosporine overdose, or rejection of kidney transplants reduce renal blood flow to the kidney afferent and efferent arterioles, supplying the glomerulus, reduce mesangial cell count, increase plasminogen activator inhibitor-1 (PAI-1) activity, decrease tissue plasminogen activator (t-PA) activity, and increase TGF-β levels. This leads to the deposition of fibrin and matrix proteins in the glomeruli and mesangium, and leads to the worsening of renal failure [19,20].
In our study, a statistically significant relationship was found between the concentration of thromboxane B2 and the groups studied. The lowest concentration of TXB2 was found in the control group and the highest in patients before renal transplantation. Statistically significant differences were also observed between the concentration of TXB2 in the TE and NK groups and TE A and NK. In patients after kidney transplantation, a decrease in thromboxane concentration was observed, however, it was not statistically significant. There was no statistically significant difference between TXB2 concentration in patients before or after hemodialysis. On the other hand, there were significant differences between the concentration of thromboxane in hemodialysis patients and peritoneal dialysis, with a lower concentration of TBX2 in the PD group.
In the literature, there are many reports on the concentration of thromboxane in patients with different types of renal replacement therapy. Dołęgowska et al. showed that kidney transplantation is associated with changes in TXB2 concentration, and that thromboxane alone may be a marker of organ function. In addition, after kidney transplant patients were divided into three groups: early graft function (EGF), slow graft function (SGF), and delayed graft function (DGF), the authors showed that the concentration of thromboxane increased within the first five minutes after transplantation in each of these groups . However, our own studies showed a decrease in TXB2 concentration within a few days after kidney transplantation. Averna et al. showed that the administration of drugs that reduce or eliminate thromboxane-dependent activation of platelets in vivo may reduce the risk of cardiovascular events but may also prevent the long-term survival of patients with kidney transplantation . Considering that an increase in thromboxane concentration may be indicative of transplant rejection and may lead to an increase in TGF-β concentration, which is also a sign of poor functioning of the transplanted kidney [19,20], together with the results obtained in our own studies, it can be suggested that the decrease in TXB2 and TGF-β after kidney transplantation may be a sign of good prognosis for this group of patients. The relationship between the concentration of thromboxane and TGF-β is also confirmed by correlations obtained in our own studies. A positive correlation was found between the concentrations of thromboxane and TGF-β and platelet-derived growth factor-B (PDGF-B) in patients treated conservatively, as well as the positive correlation between PDGF-B and TXB2 concentrations after renal transplantation, and a strong positive correlation between the concentration of thromboxane and TGF-β in the control group. Orlińska et al. showed that both exogenous and endogenous transforming growth factor (TGF) regulates the production of thromboxane, And elevated levels of TGF-β lead to the increased production of TXB2 .
The data also supports the hypothesis that a lower concentration of TXB2 and TGF-β after transplantation is a good prognosis for these patients, because no significant correlation was found between TXB2 and TGF-β after kidney transplantation. Stępniewska et al. observed a significantly lower concentration of thromboxane in hemodialysis patients than in peritoneal dialyses patients and in those treated conservatively (stage 3–5). They also showed that the type of renal replacement therapy affects the concentration of arachidonic acid metabolites, and the concentrations of thromboxane, 20-HETE acid and 15-HETE acid can be indicators of kidney damage and possible cardiovascular diseases . Zhao et al. in turn found that in patients on peritoneal dialysis, there was an increased synthesis of eicosanoids by macrophages and peritoneal mesenchymal cells due to the properties of dialysis fluids, which are generally not biocompatible .
In other studies, however, the platelets of patients undergoing regular hemodialysis have been shown to be exposed to increased oxidative stress due to endothelial damage and carbohydrate and lipid metabolism disorders. They are activated excessively because their function is weakened due to ineffective antioxidant activity [23,24]. Platelets are the main source of TXB2, and so the excessive activation of platelets may lead to an increased release of TXB2.
In our own studies, thromboxane concentrations were low in the PD group, and significantly higher in the groups before and after hemodialysis, as well as in patients treated conservatively. This may support the thesis that platelets are excessively activated during hemodialysis and that these patients are more exposed to oxidative stress than PD patients.
The 5-, 12-, and 15-HETE acids are formed from arachidonic acid on the lipoxygenase pathway . The relationship between HETE acids, chronic kidney disease, and platelet activation and the type of renal replacement therapy is not yet fully understood. Studies show that lipoxygenases are involved in kidney damage in the course of diabetic nephropathy, and the concentration of 12-HETE acid in urine significantly increases in this group of patients. Higher expression of 12/15 LOX (12/15 lipoxygenase) is associated with an increase in fibronectin and other mediators of diabetic nephropathy [25,26].
According to the latest research, HETE acids can strongly influence the intensity of the inflammatory process. Namely, 5-HETE levels promote the production of T lymphocytes, whereas 12-HETE and 15-HETE stimulate the overexpression of pro-inflammatory genes in macrophages. In addition, 12-HETE, together with 15-HETE, induces the synthesis of TGF-β1 in mesangial cells, where it stimulates the synthesis of extracellular matrix proteins that lead to kidney fibrosis. Interestingly, these HETE activities are exerted only in an autocrine or paracrine manner due to the unstable nature of HETE and its very short half-life [27, 28, 29, 30,31].
It has also been shown that AA lipoxygenase derivatives are involved in the regulation of blood pressure. Increased urinary excretion of 12-HETE was found in patients with primary hypertension . HETE acids may also affect early kidney transplantation, as evidenced by significant changes in 5-HETE, 12-HETE, and 15-HETE concentrations after renal transplantation [27,32]. Matsuyama et al. reported that the activity of AA derivatives formed on the cyclooxygenase and lipoxygenase pathway correlates with the intensity of I/R [27,33]. In addition, several other authors report that elevated HETE levels in animals were detected during allograft rejection. These observations clearly justify the need to study this pathway of AA metabolism during human kidney transplantation [16, 27, 34, 35].
Wang et al. have shown that free fatty acids (FFA) are best removed during low flow hemodialysis. As much as 60% of FFA is removed from the plasma after 4 hours of hemodialysis. Lipids with a higher molecular weight such as triglycerides and sphingomyelin are not effectively removed. The concentration of FFA and SFA (saturated fatty acids) is increased between successive hemodialysis procedures, which is crucial to prevent the risk of cardiovascular events . During peritoneal dialysis, however, there is an increased synthesis of eicosanoids by macrophages and peritoneal mesenchymal cells due to the properties of dialysis fluids, which are generally not biocompatible. The volume and nutritional status of peritoneal dialysis patients also affect the plasma lipid profile and are associated with inflammatory biomarkers (e.g., isoprostanes) and oxidative stress . In our own studies, confirmation was obtained in the form of significantly higher concentrations of 5-HETE and 15-HETE in the group PD than in the group before hemodialysis, and also after hemodialysis in the case of 5-HETE.
Stępniewska et al. did not demonstrate a relationship between the concentration of 5- and 15-HETE acids and the type of renal replacement therapy used . In the studies described in this work, however, this relationship was found. The lowest concentration of 5-HETE was observed in patients before hemodialysis and the highest in the control group. In the case of 15-HETE acid, the lowest concentration was observed in patients before hemodialysis and in the control group, and the highest concentration in the group of patients after hemodialysis. Reinhold et al. studied the relationship between concentrations 12- and 15-HETE and the function of a transplanted kidney. In this study, they observed a correlation between the concentration of HETE acids and kidney function two weeks post-transplantation but did not find a relationship between 12- and 15-HETE concentrations and acute transplant rejection .
Dołęgowska et al. showed that kidney transplants in humans are accompanied by significant perioperative changes in the metabolism of AA derivatives arising on the LOX pathway, expressed by changes in 5-, 12- and 15-HETE concentrations. These changes concern early kidney function after transplantation. In addition, after division of kidney transplant patients into three graft function groups, early, slow, and delayed, 5-, 12- and 15-HETE concentrations decreased in the first 5 minutes after transplantation in both the slow and delayed graft function groups, but not the early graft function group . HETE acids may in the future serve as new perioperative predictor of early organ function after transplantation. Dołęgowska et al., however, confirmed the results obtained by Reinhard et al. showing no relationship between HETE concentration and acute rejection of the transplant. This study also updates the hypothesis previously suggested by other scientists, which is that knowledge of AA metabolism in the early phase of allograft reperfusion may offer a completely new way to attenuate reperfusion injury during organ transplantation in humans .
In our study, there was a significant relationship between 5-HETE concentration before and after kidney transplantation and the control group. The concentration of 5-HETE was highest in the control group, and lowest after kidney transplantation. There was also a significant difference between 15-HETE concentration before and after kidney transplantation, with an increase in the concentration of 15-HETE acid after kidney transplantation. There was no relationship between serum 12-HETE concentrations between the groups, however, a significantly lower concentration of 12-HETE acid after renal transplantation was demonstrated compared to the control group and patients who were treated conservatively. Considering the results obtained by other scientists, and taking into account the high importance of these acids in the body's inflammatory response, an increase in the concentration of HETE acids after transplantation may indicate poor functioning of a transplanted kidney.
On the basis of our own results, it is difficult to state clearly whether the concentration of HETE acids can indicate the possibility of graft rejection or not, due to the increase in 15-HETE acid concentration and decrease in 5-HETE acid concentration after kidney transplantation, and the lower concentration of 12-HETE compared, for example, compared with patients treated conservatively or the control group. Long-term observation of patients after kidney transplantation would be necessary to fully understand the importance of HETE acids in predicting graft rejection.
It should also be pointed out that eicosanoids are mediators of inflammation, and can also influence the metabolism of fibroblasts in wound healing processes and the reorganization of connective tissue . The creation of vascular access in hemodialysis patients would also explain the increase in systemic compounds whose function is the chemotaxis of fibroblasts and the stimulation of healing processes.
In our study, there was a relationship between the concentration of thromboxane, 12-HETE and 15-HETE, and the duration of dialysis and the type of therapy used. It has been shown that the longer the dialysis takes, the lower the concentration of TXB2 and 15-HETE acid. In the case of 12-HETE acid, its highest concentration occurred in patients before kidney transplantation, who, on average, had the longest duration of dialysis. In addition, based on a multivariate regression analysis, it was found that parameters such as the type of renal replacement therapy, age of patients, duration of dialysis, cause and stage of CKD had an effect on thromboxane concentration in 37% of. The type of renal replacement therapy (p = 0.042) and duration dialysis (p = 0.004) both had a significant effect on the concentration of thromboxane.
The results obtained in this study do not confirm those obtained by other scientists, except the concentration of 12-HETE, which indicates increased activation of platelets in patients undergoing long-term dialysis. Because increased production of thromboxane leads to the deposition of fibrin and matrix proteins in the glomeruli and mesangium, and subsequently leads to the worsening of renal failure [19,20], a lower thromboxane concentration is an indicator of good prognosis for patients on long-term dialysis. A decreasing concentration of 15-HETE may in turn indicate a lower chance of graft rejection after transplant.
There are no reports on the dependence of 5-HETE on the subject of chronic disease and the stage of chronic kidney disease. It has been shown, however, that supplementation with polyunsaturated fatty acids (PUFA) over a period of 8 weeks results in a decrease in the pro-inflammatory leukotriene-B4 (LTB4) and 5-HETE, and increases the synthesis of less inflammatory leukotriene, LTB5 and 5-hydroperoxyeicosatetraenoic (5-HPETE) in patients with CKD stages 2–5 . In our own studies, the concentration of 5-HETE decreased as kidney disease progressed. This may indicate less pro-inflammatory processes and a good prognosis for patients in the fifth stage of CKD.