Elevated circulating levels and tissue expression of pentraxin 3 in uremia: a reflection of endothelial dysfunction

Abstract

Elevated systemic pentraxin 3 (PTX3) levels appear to be a powerful marker of inflammatory status and a superior outcome predictor in patients with chronic kidney disease (CKD). As previous data imply that PTX3 is involved in vascular pathology and that adipose tissue mass may influence circulating PTX3 levels, we aimed to study the importance of adipose tissue expression of PTX3 in the uremic milieu and its relation to endothelial dysfunction parameters. Plasma PTX3 and abdominal subcutaneous adipose tissue (SAT) PTX3 mRNA levels were quantified in 56 stage 5 CKD patients (median age 57 [range 25-75] years, 30 males) and 40 age and gender matched controls (median age 58 [range 20-79] years, 27 males). Associations between PTX3 measures and an extensive panel of clinical parameters, including surrogate markers of endothelial function, were assessed. Functional ex vivo studies on endothelial status and immunohistochemical staining for PTX3 were conducted in resistance subcutaneous arteries isolated from SAT. SAT PTX3 mRNA expression correlated with plasma PTX3 concentrations (rho = 0.54, p = 0.0001) and was increased (3.7 [0.4-70.3] vs. 1.2 [0.2-49.3] RQ, p = 0.02) in CKD patients with cardiovascular disease (CVD), but was not significantly different between patients and controls. The association to CVD was lost after adjustments. SAT PTX3 mRNA levels were independently correlated to asymmetric dimethylarginine and basal resistance artery tone developed after inhibition with nitric oxide synthase and cyclooxygenase (rho = -0.58, p = 0.002). Apparent positive PTX3 immunoreactivity was observed in both patient and control arteries. In conclusion, fat PTX3 mRNA levels are associated with measures of endothelial cell function in patients with CKD. PTX3 may be involved in adipose tissue-orchestrated mechanisms that are restricted to the uremic milieu and modify inflammation and vascular complications in CKD patients.

Figure 1. PTX3 mRNA is expressed in isolated adipocytes and levels correlate with endothelial dysfunction in CKD patients.

(A) Plasma PTX3 concentrations (ng/ml) measured in 39 non-CKD controls and 53 patients with CKD stage 5. PTX3 mRNA quantities (relative quantity, RQ, arbitrary units) analysed in (B) abdominal subcutaneous adipose tissue of 40 non-CKD controls and 56 patients with CKD stage 5, (C) subcutaneous and visceral fat depots obtained from 20 non-CKD patients, (D) isolated adipocytes and intact adipose tissue (n = 14) as well as in (E) patients with CKD stage 5 and no diabetes mellitus (n = 35), diabetes mellitus type 1 (n = 8) or diabetes mellitus type 2 (n = 13). (F) Negative correlation (Spearman's rank) between subcutaneous adipose tissue PTX3 mRNA quantities (log transformed) and constriction (basal tone) after nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibition in 27 patients with CKD stage 5. Statistical differences between groups were evaluated with Wilcoxon rank sum test (A–B), Wilcoxon signed rank test (C–D) and Kruskal-Wallis one-way analysis of variance (E). **, p<0.01; ***, p<0.001; ****, p<0.0001.

Figure 2. Plasma levels of PTX3 are decreased after kidney transplantation (RTx).

One year after transplantation glomerular filtration rate (GFR) is improved and plasma PTX3 concentrations are significantly decreased compared to baseline (N = 28, Wilcoxon signed rank test). ***, p<0.001.

Figure 3. Positive immunohistochemical staining of PTX3 in resistance subcutaneous arteries from CKD stage 5 patients.

Positive staining (brown) is shown in representative biopsies of CKD-5 patients (A, C) and non-CKD controls (B, D). No immunoreactivity was observed when anti-PTX3 antibody was absent (E). The PTX3-immunoreactivity is abundant in arteries, especially in endothelial cells of tunica intima, indicated by black arrowheads, both in patients (C) and controls (D). The slides were counterstained with hematoxylin. Images are magnified x10 (B), x20 (A, D, E) or x40 (C); scale bar 100 µm.