Crosstalk mechanisms between glomerular endothelial cells and podocytes in renal diseases and kidney transplantation

The glomerular filtration barrier (GFB), composed of endothelial cells, glomerular basement membrane, and podocytes, is a unique structure for filtering blood while detaining plasma proteins according to size and charge selectivity. Structurally, the fenestrated endothelial cells, which align the capillary loops, are in close proximity to mesangial cells. Podocytes are connected by specialized intercellular junctions known as slit diaphragms and are separated from the endothelial compartment by the glomerular basement membrane. Podocyte-endothelial cell communication or crosstalk is required for the development and maintenance of an efficient filtration process in physiological conditions. In pathological situations, communication also has an essential role in promoting or delaying disease progression. Podocytes and endothelial cells can secrete signaling molecules, which act as crosstalk effectors and, through binding to their target receptors, can trigger bidirectional paracrine or autocrine signal transduction. Moreover, the emerging evidence of extracellular vesicles derived from various cell types engaging in cell communication has also been reported. In this review, we summarize the principal pathways involved in the development and maintenance of the GFB and the progression of kidney disease, particularly in kidney transplantation.

Frailty in kidney transplantation: a review on its evaluation, variation and long-term impact

The problem of frailty in kidney transplantation is an increasingly discussed topic in the transplant field, partially also generated by the multiple comorbidities by which these patients are affected. The criteria currently used to establish the presence and degree of frailty can be rapidly assessed in clinical practice, even in patients with chronic kidney disease (CKD). The main objectives of this work are: (i) to describe the method of evaluation and the impact that frailty has in patients affected by CKD, (ii) to explore how frailty should be studied in the pre-transplant evaluation, (iii) how frailty changes after a transplant and (iv) the impact frailty has over the long term on the survival of renal transplant patients.

Bone and Mineral Disorder in Renal Transplant Patients: Overview of Pathology, Clinical, and Therapeutic Aspects

Renal transplantation (RTx) allows us to obtain the resolution of the uremic status but is not frequently able to solve all the metabolic complications present during end-stage renal disease. Mineral and bone disorders (MBDs) are frequent since the early stages of chronic kidney disease (CKD) and strongly influence the morbidity and mortality of patients with CKD. Some mineral metabolism (MM) alterations can persist in patients with RTx (RTx-p), as well as in the presence of complete renal function recovery. In those patients, anomalies of calcium, phosphorus, parathormone, fibroblast growth factor 23, and vitamin D such as bone and vessels are frequent and related to both pre-RTx and post-RTx specific factors. Many treatments are present for the management of post-RTx MBD. Despite that, the guidelines that can give clear directives in MBD treatment of RTx-p are still missed. For the future, to obtain an ever-greater individualisation of therapy, an increase of the evidence, the specificity of international guidelines, and more uniform management of these anomalies worldwide should be expected. In this review, the major factors related to post-renal transplant MBD (post-RTx-MBD), the main mineral metabolism biochemical anomalies, and the principal treatment for post-RTx MBD will be reported.

Bone Effect and Safety of One-Year Denosumab Therapy in a Cohort of Renal Transplanted Patients: An Observational Monocentric Study

In 32-kidney transplanted patients (KTxps), the safety and the effects on BMD and mineral metabolism (MM) of one-year treatment with denosumab (DB) were studied. Femoral and vertebral BMD and T-score, FRAX score and vertebral fractures (sVF) before (T0) and after 12 months (T12) of treatment were measured. MM, renal parameters, hypocalcemic episodes (HpCa), urinary tract infections (UTI), major graft and KTxps outcomes were monitored. The cohort was composed mainly of females, n = 21. We had 29 KTxps on steroid therapy and 22 KTxps on vitamin D supplementation. At T0, 25 and 7 KTxps had femoral osteoporosis (F-OPS) and osteopenia (F-OPS), respectively. Twenty-three and six KTxps had vertebral osteoporosis (V-OPS) and osteopenia (V-OPS), respectively. Seventeen KTxps had sVF. At T12, T-score increased at femoral and vertebral sites (p = 0.05, p = 0.008). The prevalence of F-OPS and V-OPS reduced from 78% to 69% and from 72% to 50%, respectively. Twenty-five KTxps ameliorated FRAX score and two KTxps had novel sVF. At T12, a slight reduction of Ca was present, without HpCa. Four KTxps had UTI. No graft rejections, loss of graft or deaths were reported. Our preliminary results show a good efficacy and safety of DB in KTxps. Longer and randomized studies involving more KTxps might elucidate the possible primary role of DB in the treatment of bone disorders in KTxps.

P1430BETA C-TERMINAL TELOPEPTIDE OF TYPE I COLLAGEN: CORRELATIONS WITH MINERAL METABOLISM PARAMETERS AND CARDIAC VALVULAR CALCIFICATIONS IN A COHORT OF HEAMODIALYSIS PATIENTS

Background and Aims

Beta-carboxyterminal telopeptide of type I collagen (beta-CTx) is considered a marker of bone resorption in patients affected by osteoporosis. Nevertheless, its role in mineral bone disorder (MBD) of CKD patients is not clear. The aim of this study was to explore in a group of haemodialysis patients (HDp): 1) The levels of beta-CTx; 2) The correlation between beta-CTx levels and other mineral metabolism (MM) parameters; 3) The association between beta-CTx and CKD-MBD specific therapy 4) The relation between beta-CTx and cardiac valvular calcifications (VC).

Method

We studied a group of 21 HDp (F/M 9/12, age 68[54-78] years) randomly selected from the HDp actually followed-up in our Department. Dialysis vintage was 52[23-80] months. All HDp were on a three-weekly hemodialysis schedule, with a prescribed dialysate calcium of 1.5 mmol/l. Before the first dialysis session of the week, after the long interdialytic interval, the levels of beta-CTx, total and ionized calcium (tCa and iCa), Phosphorus (P), Magnesium (Mg), intact PTH (iPTH), total and bone isoform of alkaline phosphatase (tALP and bALP), 25-hydroxyvitamin D (25OHVD), 1,25-dihydroxyvitamin D (1,25OH2VD), and other general biochemical parameters were measured (Figure 1). At the same time, data concerning MM therapies were recorded. In all the studied patients, the presence of VC was searched in the the most recent echocardiographic study.

Results

Beta-CTx levels showed a significant positive correlation with tALP (r 0.92, p <0.0001), bALP (r 0.89, p <0.0001) and iPTH (r 0.87, p<0.0001) and a negative correlation with tCa (r – 0.43, p=0.05) and iCa (r – 0.52, p=0.01). No significant correlation was found with the other MM and general biochemical parameters and with the general features of the studied cohort. 18 patients (85.7%) were taking P binders (72.2% Ca-based and 27.8% Ca-free). In 20 patients (95.2%) vitamin D therapy, either in the natural, active or both natural and active form (35%, 15% and 50%, respectively) was prescribed. 6 patients (28.6%) were in therapy with Cinacalcet.

No difference was found in beta-CTx levels according to the presence and the type of each of the above mentioned therapies.

Conclusion

Taking into account the limitations of this preliminary small size observational study, our data showed that beta-CTx levels are high in HDp. Beta-CTx correlates with iPTH, tALP and bALP. The negative correlation with tCa and iCa probably might be influenced by the negative correlation between iPTH and serum Calcium. Beta-CTx levels are not associated with CKD-MBD specific therapy or with cardiac valvular calcifications. Further prospective and randomized studies, including a higher number of HDp and possibly bone histology are needed to elucidate the possible role of beta-CTx as a marker of bone disease in HDp.

P0893BONE EFFECTS AND SAFETY OF ONE YEAR DENOSUMAB THERAPY IN A COHORT OF RENAL TRANSPLANTED PATIENTS: AN OBSERVATIONAL MONOCENTRIC STUDY

Background and aims

Bone and mineral metabolism (MM) disorders are relevant problems in renal transplanted patients (RTxp). In our observational monocentric study, we evaluated the effects on femoral and lumbar bone mineral density (BMD) and on MM parameters, and the safety of one year-treatment with Denosumab (DB) in a cohort of RTxp.

Method

We recorded data about 32 RTxp treated with DB in our Center in the last year. RTxp were evaluated for BMD and T-score (Ts) before the start (T0) and after 12 months (T12) of treatment. Osteopenia was defined, at femoral (F-OPN) and lumbar (L-OPN) sites as Ts:-1>Ts>-2.5 whereas osteoporosis, in the same sites (F-OPS and L-OPS) as Ts<-2.5. X ray evaluation for spontaneous vertebral fractures (sVF) was made at T0 and, in 25 RTxp repeated at T12. MM and renal function parameters (serum creatinine, sCr and daily urinary protein excretion, ProtU) were recorded at T0 and after 1,3,6, and 12 months of therapy. The clinical indications for DB therapy, in the presence of Ca>9.0 mg/dL were the finding at T0 of: 1) F-OPS and/or V-OPS; 2) sVF. During the year of treatment, hypocalcemic (HpCa=Ca<8.0 mg/dL) episodes, infections, graft rejections and loss and RTxp survival were monitored.

Results

The cohort was composed mainly by females (n=21). The time of RTx was 144[59-232]mths. Steroid therapy was prescribed in 30 RTxp (93%), 22(68%) and in 2 (6%) RTxp were taking 25OHD and 1-25OH. Three RTxp (9%) were receiving Ca supplements. Bisphosphonate therapy was reported in 15 RTxp (46%) in the year before DB start. At T0, 25(78%) and 7 (22%) RTxp had F-OPS and F-OPN. Twenty-three (71%) and 6 (20%) RTxp had L-OPS and L-OPN. In 3 RTxp normal lumbar T-score was found. sVF were present in 17 RTxp (53%). Ca and P were 9.6±0.6 mg/dL and 3.1±0.6 mg/dL whereas PTH, ALP and 25OHD were 64±32 pg/mL, 80±37 U/L and 28±16 mg/dL. SCr and Prot-U were 1,32±0,4 mg/dL and 0,23±0,16 g/24h. At T12, F-Ts increased significantly (T0: -3.0[-3.5/-2.5] vs T12:-2.8[-3.5/-2.4) as like as V-Ts (T0: -3.0[-3.7/-1.9] vs T12:-2.8[-3.0/-1.6) both p<0.0001. A significant increase was found also in BMD: F-BMD +2.4%[-1.1%/+13%] (p<0.0001), V-BMD +2.6%[-3.4%/+12%] (p=0.009). The prevalence of F-OPS reduced from 78% to 73% (p<0.0001) and 4 RTxp ameliorated their Ts category. Prevalence of V-OPS reduced to 53% at T12 from 71% (p<0.001), and 4 RTxp ameliorated their Ts category. In 2 RTxp were found novel sVF. During the treatment no significant modifications of Ca were found, with only a slight but significant difference between T0 and T12 (T12 Ca: 9.22±1.17, p=0.01). PTH and ALP were significantly higher at T3, T6 and T12 respect T0. No differences in 25OH, sCr and ProtU were found. During the year of treatment, in 3 RTxp 25OHD supplementation was started. No one required novel Ca supplementation. DB therapy wasn’t associated to HpCa episodes. Four RTxp had infections during the time of treatment (mean time of DB treatment:114 days). They had positive pathologic anamnesis for urinary tract infections (UTI). Two of them had symptomatic UTI and 2 required hospitalization for sepsis. No biopsy proven graft rejections were observed during the time of treatment and no graft loss or RTxp death were reported.

Conclusions

The preliminary results presented in our study, limited by the monocentric, not randomized design and by the smallness of the cohort, reported a good bone efficacy of DB in RTxp, especially at lumbar level. The therapy was characterized by a good general safety. Future longer and randomized studies, involving more RTxp might elucidate the possible primary role of DB in the treatment of bone disorders in RTxp.

Membranous Nephropathy (MN) Recurrence After Renal Transplantation

Primary membranous nephropathy (MN) is a frequent cause of NS in adults. In native kidneys the disease may progress to ESRD in the long term, in some 40–50% of untreated patients. The identification of the pathogenic role of anti-podocyte autoantibodies and the development of new therapeutic options has achieved an amelioration in the prognosis of this disease. MN may also develop in renal allograft as a recurrent or a de novo disease. Since the de novo MN may have some different pathogenetic and morphologic features compared to recurrent MN, in the present paper we will deal only with the recurrent disease. The true incidence of the recurrent form is difficult to assess. This is mainly due to the variable graft biopsy policies in kidney transplantation, among the different transplant centers. Anti-phospholipase A2 receptor (PLA2R) autoantibodies are detected in 70–80% of patients. The knowledge of anti-PLA2R status before transplant is useful in predicting the risk of recurrence. In addition, the serial survey of the anti-PLA2R titers is important to assess the rate of disease progression and the response to treatment. Currently, there are no established guidelines for prevention and treatment of recurrent MN. Symptomatic therapy may help to reduce the signs and symptoms related to the nephrotic syndrome. Anecdotal cases of response to cyclical therapy with steroids and cyclophosphamide have been published. Promising results have been reported with rituximab in both prophylaxis and treatment of recurrence. However, these results are based on observational data, and prospective controlled trials are still missing.