Recent accumulating epidemiological evidence underlines the important role of environmental exposures on kidney diseases. Among environmental exposures, this study addresses “Green space,” which has been recognized as one of the major environmental exposures at the population level. We review a total of seven epidemiological studies currently published on greenness and kidney disease. We also discuss knowledge gaps in the epidemiological evidence in relation to study design, greenness exposure index, emerging kidney outcomes, and inequalities. With an increase in public attention regarding environmental risks and climate change, an improved understanding of the beneficial effects of green space can play an important role in promoting kidney health.

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.

The pathophysiological mechanism of cardiovascular disease in patients with chronic kidney disease (CKD) is complicated. Mediation analysis is an important statistical tool for gaining insight into the complex mechanisms of exposure-outcome effects. We investigated the potential mediating role of the left ventricular mass index (LVMI) on the association between fluid balance (overhydration/extracellular water, OH/ECW) and left ventricular diastolic function (E/e´ ratio) in patients with CKD not yet on dialysis. Methods: Bioimpedance spectroscopy, echocardiography, and laboratory evaluations were performed on 425 consecutive patients on the same day. The patients were classified into two groups according to the estimated glomerular filtration rate corresponding to CKD stages 3 and 5. Mediation analysis was performed using the PROCESS macro and bootstrapping methods. Results: OH/ECW and LVMI were positively correlated with the E/e´ ratio in both the CKD stages 3 and five groups. In CKD stage 5, there was a statistically significant association between OH/ECW and LVMI, whereas no correlation was observed in CKD stage 3. In the mediation analysis, LVMI positively mediated the relationship between OH/ECW and E/e´ ratio when controlling for confounders in patients with CKD stage 5 (B = 2.602; Boot 95% confidence interval, 1.313–4.076). Conclusion: In our analysis, the indirect effect of mediators was significant in patients with advanced CKD. Therefore, our study suggests that further research on several other risk factors may be needed to determine the underlying mechanisms of association between the associated factors in all CKD stages.

Fluid overload is an independent risk factor of mortality in patients with acute kidney injury (AKI) receiving continuous kidney replacement therapy (CKRT). However, the association between fluid status, as assessed by bioelectrical impedance analysis (BIA) or lung ultrasound, and survival in patients with AKI requiring CKRT has not been established. Methods: We analyzed 36 participants with sepsis-associated AKI who received CKRT at a tertiary hospital. The main exposures were volume surrogates: 1) overhydration normalized by extracellular water (OH/ECW, L/L) assessed by BIA, 2) the number of B-lines measured by lung ultrasound, and 3) weight change ([body weight at CKRT initiation – body weight at admission] × 100/body weight at admission). The primary outcome was the 28-day mortality. Results: Seventeen participants (47.2%) died within 28 days. There were no significant correlations between OH/ECW and weight change (R2 = 0.040, p = 0.24), number of B-lines and OH/ECW (R2 = 0.056, p = 0.16), or weight change and number of B-lines (R2 = 0.014, p = 0.49). Kaplan-Meier analyses revealed that patients in the highest tertile of OH/ECW showed a significantly lower cumulative 28-day survival probability than the others (the lowest + middle tertiles). The survival probability of participants in the highest tertile of the number of B-lines or weight change did not differ from that of their counterparts. In a multivariate Cox proportional hazard model, the hazard ratio for the highest tertile of OH/ECW was 3.83 (95% confidence interval, 1.04–14.03). Conclusion: Volume overload assessed using BIA (OH/ECW) was associated with the 28-day survival rate in patients with sepsis-associated AKI who received CKRT.

Pathologic diagnosis of antibody-mediated rejection (ABMR) in ABO-incompatible (ABOi) transplantation patients is often challenging because patients without ABMR are frequently immunopositive for C4d. The aim of this study was to determine whether C4d positivity with microvascular inflammation (MVI), in the absence of any detectable donor-specific antibodies (DSAs) in ABOi patients, could be considered as ABMR. Methods: A retrospective study of 214 for-cause biopsies from 126 ABOi kidney transplantation patients was performed. Patients with MVI score of ≥2 and glomerulitis score of ≥1 (n = 62) were divided into three groups: the absolute ABMR group (DSA-positive, C4d-positive or C4d-negative; n = 36), the C4d-positive group (DSA-negative, C4d-positive; n = 22), and the C4d-negative group (DSA-negative, C4d-negative; n = 4). The Banff scores, estimated glomerular filtration rates (eGFRs), and graft failure rates were compared among groups. Results: C4d-positive biopsies showed higher glomerulitis, peritubular capillaritis, and MVI scores compared with C4d-negative specimens. The C4d-positive group did not show significant differences in eGFRs and graft survival compared with the absolute ABMR group. Conclusion: The results indicate that C4d positivity, MVI score of ≥2, and glomerulitis score of ≥1 in ABOi allograft biopsies may be categorized and treated as ABMR cases.