In this study, we used a nomogram incorporating the ER stress marker serum GRP78 along with the established biomarker eGFR 1 year post-transplant to predict long-term survival of renal grafts. This nomogram showed improved calibration compared to the eGFR-only model. Furthermore, in DCA, the nomogram showed a larger net benefit over a wider range of threshold probabilities, indicating its improved clinical value. Considering the paramount importance of long-term graft survival for recipients and its impact on life plans, it is essential to set a low probability threshold for DCA in clinical intervention. This approach ensures that recipients at high risk of long-term graft loss are not overlooked and, despite the potentially large numbers needed for prediction, clinical interventions are made in view of the importance of important outcomes. Priority will be given. Therefore, it is noteworthy that at low threshold probabilities of DCA, we observed significantly larger net benefits for the nomogram compared to the eGFR model. Our nomogram may facilitate early and targeted selection of cases requiring various clinical interventions aimed at preserving transplant kidney function. It is important to create a treatment plan that addresses two components of the nomogram: (1) treatments that preserve eGFR of the transplanted kidney, and (2) treatments that reduce ER stress as indicated by serum GRP78. Regarding (1), the essential KT treatment, approaches are based on scientific evidence, such as appropriate immunosuppressive therapy and management of lifestyle-related diseases. Regarding (2), knowledge is still limited, but an interesting report suggests that lifestyle-related disease interventions that overlap with (1) may alleviate ER stress and reduce serum GRP78 levels. There are also some. It has been reported that people with obesity, diabetes, and metabolic syndrome have elevated serum GRP78 levels compared to healthy individuals, and that there is a positive correlation between the number of metabolic syndrome components and serum GRP78 levels.14. In these patients, exercise improves obesity.15 Treatment of hypertriglyceridemia with administration of nicotinic acid14 These interventions were accompanied by a decrease in serum GRP78 levels, and it has been speculated that the degree of reduction in ER stress that mediates the clinical effects of these interventions may be reflected in serum GRP78 levels. Furthermore, although no studies have yet investigated whether it can reduce serum GRP78 levels, animal studies have shown that febuxostat, a drug used to treat hyperuricemia, can reduce GRP78 mRNA expression in kidney tissue. It has been shown that it exerts a renal protective effect against renal ischemia-reperfusion injury by inhibiting renal ischemia-reperfusion injury.16Therefore, clinical application to the pathology of ischemia-reperfusion injury in transplanted kidneys is expected in the future. Furthermore, a new renal protective mechanism has been reported for sodium-glucose cotransporter protein-2 (SGLT-2) inhibitors, which are currently the mainstay of treatment for chronic kidney disease (CKD). In diabetes-associated kidney disease, GRP78 is secreted into the urine from proximal tubular cells and causes inflammation in surrounding tubular cells. Canagliflozin, an SGLT-2 inhibitor, has been shown to inhibit this process. These interventions may have potential as specific strategies to reduce serum GRP78 levels and the risk of graft loss.17. Unfortunately, our study did not find any correlation with factors that may increase serum GRP78 levels, such as hypertension, smoking, high CNI blood concentrations, and the presence of CNI nephrotoxicity in renal biopsy. . However, there is no research question: “Does intervention on these specific modifiable factors influence the prognosis of KT through reducing serum GRP78 levels?” The extent to which ER stress, quantified by serum GRP78 levels, mediates interventions and outcomes cannot be accurately estimated without using directed acyclic graphs to organize the causal structure and perform mediation analysis. .
Despite being an exploratory study, we found a negative correlation between changes in serum adiponectin levels, particularly bioactive high molecular weight adiponectin, and changes in serum GRP78 levels. Previous studies have shown that adiponectin reduces ER stress in various tissues.18including renal glomeruli19. A group at the University of Tokyo is currently working on the clinical application of adiponectin-activating antibodies for lifestyle-related diseases such as diabetes and non-alcoholic steatohepatitis.20. In the future, this drug may contribute to the long-term survival of transplanted kidney grafts, and the nomogram developed in this study may serve as an indicator of therapeutic efficacy in such cases.
GRP78, a member of the heat shock protein family, plays an important role in the unfolded protein response.twenty one,twenty two,twenty three. GRP78, expressed in the endoplasmic reticulum of various tissues, contains at least four domainstwenty three Can bind to various ligands such as viruses24,25peptide (RoY)26and autoantibodies. Binding of different ligands to GRP78 can cause various effects upon activation, including promoting angiogenesis, inhibiting cell proliferation, and inducing apoptosis.26,27. Activated cell surface GRP78 is released into the bloodstream. Therefore, even in healthy individuals, trace amounts of free GRP78 are present in the peripheral blood. However, under ER stress, the increase in serum GRP78 reflects the upregulation of tissue expression of GRP78.28. The normal range of serum GRP78 levels has not been well studied. However, in a case-control study investigating serum GRP78 levels in COVID-19-associated mucormycosis, the upper limit of normal serum GRP78 levels was determined to be 231.2 pg/mL, which is two standard deviations (23.2 pg/mL). was established by adding . mL) to the average serum GRP78 level in healthy people (184.8 pg/mL). Using this criterion, mean serum GRP78 levels (404.5 pg/mL) at the 1-year posttransplant assessment in this study were significantly elevated, suggesting that KT recipients are exposed to ER stress . Furthermore, among patients who underwent KT in this cohort, those who experienced graft loss had higher serum GRP78 levels at 1 year post-transplant compared to patients who did not experience graft loss (cut Off value: 394.6 pg/mL). We speculate that this is due to a combination of multiple factors: (1) ER stress is involved in the pathophysiology of acute kidney injury (AKI) and CKD, and the transition from AKI to CKD;29however, the pathophysiology of transplanted kidneys includes conditions such as AKI due to ischemia-reperfusion injury or rejection, CKD secondary to a functional single kidney state, and transition from AKI to CKD.30(2) ER stress is speculated to be exacerbated by calcineurin inhibitors, which are the mainstay of post-transplant immunosuppressive therapy.31(3) ER stress may be caused by coexisting lifestyle-related diseases. To further improve KT survival, intervention methods aimed at bringing ER stress levels, as indicated by serum GRP78, as close to normal levels as possible should be considered. The nomogram developed this time is expected to be useful in this regard.
Our study has major strengths, particularly that we demonstrated for the first time the added value of serum GRP78 in predicting long-term survival of renal grafts. Our nomogram, which includes the pathophysiology of AKI, CKD, and the transition from AKI to CKD in KT, may have broader applicability beyond KT and risk assessment for dialysis initiation in non-KT AKI and CKD cases. It may also be applicable to Furthermore, we obtained the important finding that serum GRP78 levels 1 year after transplantation functioned as a predictor of eGFR slope independently of eGFR. This finding may demonstrate the robustness of our main analysis results, particularly the added value of serum GRP78 in predicting the prognosis of transplanted kidneys. Disadvantages of eGFR gradient, which has recently attracted attention as a surrogate marker of end-stage renal disease in early CKD patients32which means that eGFR observation for at least 2 years is required to calculate the eGFR slope. For example, when investigating the effect of an intervention on improving renal function, calculating the pre- and post-intervention eGFR slope requires eGFR data from 2 years before and after the intervention. Therefore, the effectiveness of the intervention will be retrospectively evaluated 2 years after implementation of the intervention. However, if the slope of eGFR can be predicted by serum GRP78 levels, the effect of the intervention can be quickly assessed by measuring serum GRP78 before and after the intervention and comparing the two results.
This study also has some limitations. First, the number of factors included in the nomogram had to be reduced due to the limited number of outcome occurrences. Conducting future studies using accumulated cases and ensuring an appropriate number of occurrences of outcomes is important to create a more accurate nomogram. Considering the univariate Cox regression results of this study, adding serum CHOP or PMI may improve the performance of the nomogram. Second, it is a single-center study with a small sample size and lack of external validation, which limits the generalizability of our findings. Third, the actual clinical impact of using the constructed nomogram remains unclear and clinical impact studies are needed.
In conclusion, a predictive model combining eGFR and serum GRP78 at 1 year after KT suggests its utility in predicting graft survival 15 years after transplantation.
