Blood-Brain Barrier Biomarkers before and after Kidney Transplantation

Abstract

Kidney transplantation (KT) may improve the neurological status of chronic kidney disease (CKD) patients, reflected by the altered levels of circulating BBB-specific biomarkers. This study compares the levels of neuron specific enolase (NSE), brain-derived neurotrophic factor (BDNF), neurofilament light chain (NfL), and circulating plasma extracellular vesicles (EVs) in kidney-failure patients before KT and at a two-year follow up. Using ELISA, NSE, BDNF, and NfL levels were measured in the plasma of 74 living-donor KT patients. Plasma EVs were isolated with ultracentrifugation, and characterized for concentration/size and surface protein expression using flow cytometry from a subset of 25 patients. Lower NSE levels, and higher BDNF and NfL were observed at the two-year follow-up compared to the baseline (p < 0.05). Male patients had significantly higher BDNF levels compared to those of females. BBB biomarkers correlated with the baseline lipid profile and with glucose, vitamin D, and inflammation markers after KT. BBB surrogate marker changes in the microcirculation of early vascular aging phenotype patients with calcification and/or fibrosis were observed only in NSE and BDNF. CD31+ microparticles from endothelial cells expressing inflammatory markers such as CD40 and integrins were significantly reduced after KT. KT may, thus, improve the neurological status of CKD patients, as reflected by changes in BBB-specific biomarkers.

Keywords: BBB; BDNF; CKD; NSE; NfL; end-stage kidney failure; extracellular vesicles; kidney transplantation.

Figure 1

Comparison of biomarker (A) NSE, (B) BDNF, and (C) NfL levels at the baseline and two-year follow-up among KT patients. Results are presented as the median and IQR. The differences between baseline and two years post-KT were analyzed using the Wilcoxon paired test. * p < 0.05, ** p < 0.01, **** p < 0.0001.

Figure 2

Correlation of biomarkers NfL, BDNF, and NSE with clinical and laboratory parameters in KT patients. * p < 0.05, ** p < 0.01, *** p < 0.001. Abbreviations: Apo-B—apolipoprotein–B; HDL—high density lipoprotein; Apo-A1—apolipoprotein-A1; hsCRP—high sensitivity C-reactive protein; HBA1c—hemoglobin A1c, NfL—neurofilament light chain; BDNF—brain-derived neurotrophic factor; NSE—neuron-specific enolase. Red dotted lines mark demarcation indicators for baseline and 2 years follow-up.

Figure 3

Levels of NSE, BDNF, and NfL at baseline vs. 2 years post-KT according to calcification scores. Results are presented as median and IQR. Differences between baseline and two years post-KT were analyzed using the Wilcoxon paired test. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 4

Levels of NSE, BDNF, and NfL at baseline vs. 2 years post-KT according to fibrosis score. Results are presented as the median and IQR. Differences between baseline and two years post-KT were analyzed using the Wilcoxon paired test. * p < 0.05, ** p < 0.01, **** p < 0.0001.

Figure 5

Levels of BBB biomarkers NSE, BDNF, and NfL at the baseline vs. 2 years post-KT among patients with calcification (score 1–3) and fibrosis (score 1–3). Results are presented as the median and IQR. Differences between the baseline and two years post-KT were analyzed using the Wilcoxon paired test. * p < 0.05.

Figure 6

(A) Nanosight analysis of plasma EV concentration before (T0) and after KT (T2); (B) flow cytometry analysis of the surface protein expression of CD31, alpha 5 integrin, CD40, alpha 2, and beta 1 integrins. Results are presented as the median and IQR. Differences between the baseline (T0) and two years post-KT (T2) were analyzed using the Wilcoxon paired test. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001. Abbreviations: NTA—nanoparticle tracking analysis; CD—cluster of differentiation.