HDL-CHOLESTEROL PLASMA CONCENTRATION IS INCREASED BY POLYMETHYLMETHACRYLATE MEMBRANE AND IS ASSOCIATED WITH A POSITIVE RESPONSE TO HBV VACCINATION IN HAEMODIALYSIS PATIENTS

Introduction

Uremia affects immune system of haemodialysis (HD) patients  through an inflammatory immune paralysis characterized by the overstated activation of innate response and impaired targeted adaptive response [Eleftheriadis T, Semin Dial 2007]. Hepatitis B Virus vaccine response (HBV-VR) rate is only 40-70% in HD population than 90% in the general population [Eleftheriadis T, World J Gastroenterol.2014]. High density cholesterol (HDL-C) modulates immunity but uremia impairs HDL-C maturation and function [Pahl MV, NDT 2009; Calabresi L, J Intern Med. 2015; Meier SM, LifeSci.2015]. Polymethylmethacrylate (PMMA) improves HBV-VR in not responders (NR) HD-patients  [Contin-Bordes C, NDT Plus 2010; Duranti E, Minerva Med 2011] than other traditional membranes such as polysulfone (Figure 1A). Through a controlled prospective study we aimed to investigate if HDL-Cs and apolipoprotein ApoA1 could influence HBV-VR in HD-patients, and to confirm if PMMA could improve HBV-VR in NR-subjects analyzing its effects on HDL-C levels.

Methods

87 HD-patients received three 40 µg HBV vaccine doses (HBVaxpro®, at 0–1–6 months; response assessment at 8 months): 50 in 2011, of which 29 (58%) were not responders (2011-NR). Twelve 2011-NR with twenty-five 2014 naive HBV-seronegative incident HD-patients (NAI) were enrolled in a controlled study of 12 month-length: 19 of these 37 HD-patients were in PMMA (11 NAI + 8 2011-NR), 18 in polysulfone (14 NAI + 4 2011-NR). The run-in period with PMMA or polysulfone lasted 3 months before the first HBV-vaccination dose. HDL-C and APoA1 were measured before start of new filter, 3 months before of the 1° vaccination dose (basal value), and after 8 months from 1° HBV vaccine, two months later the last vaccination dose (final value).

Results

In 2014 we observed 18 HBV-VR (18/37, 49%): 11 responders  (R) in polysulfone and 7 in PMMA (Chi²=2.18; p=0.140). ). 14 NAI (14/25, 56%) got response (NAI-R): 10 used polysulfone (10/14, 71%) and 4 used PMMA (4/11, 36%, Chi²=3.07; p=0.080). Among the 2011-NR, 4 (4/12, 33%) seroconverted (2011-NR-SC): 3 (3/8, 37.5%) in PMMA and one (1/4, 25%) in polysulfone (Chi²=0.19; p=0.665).

2014 and 2011-R had higher total cholesterol (p=0.013) and higher LDL-C (p=0.014). Moreover, there was a trend in difference in terms of HDL-Cs: R had higher basal HDL-C (R42.4±20.2mg/dlvsNR37.0±10.8;P=0.069) (Figure 1B) and the mean HDL-C (R43.5±22.1mg/dlvsNR38.1±10.6;P=0.082), obtained from basal and final HDL-C. In Multivariate Regression Logistic, HDL-C plasmatic level ≥40 mg/dl and patients’ age are respectively the only positive predictor and the only negative predictor of vaccine response (HDLs: OR=3.34, SE= 1.91, z= 2.1, p= 0.03; age: OR=0.94, SE= 0.02, z= -2.43, p= 0.01. Chi²= 22.54, p= 0.04) (Figure 2).Outstandingly, 2014-R showed a trend in higher basal HDL-C levels than NR (R 44±27vs NR 37±12mg/dl;P=0.154) and had significantly higher basal ApoA1 than in NR (R 137.5 ± 29.1 vs NR 120.5 ± 17.; p=0.043). Intriguingly HDL-Cs increased during the trial in PMMA group (basal 46 ± 26 mg/dl, final 53 ± 33 mg/dl; p=0.0018) but not in polysulfone group (basal 34 ± 11 mg/dl, final 36 ± 8mg/dl; p=0.128) (Figure 3). HDL-C PMMA-driven increase is maintained considering separately either 2011-NR-patients (basal 51 ± 37 mg/dl, final 61 ± 48 mg/dl; p=0.0211) and naïve patients (basal 42 ± 14 mg/dl, final 47 ± 17 mg/dl; p=0.0207).

In 11 patients with available data, HDL-Cs lowered after PMMA was suspended at the end of the trial and replaced with polysulfone: during PMMA treatment HDL-C increased from the basal value of 52 ± 25 mg/dl to the final value of 62 ± 38 mg/dl (p= 0.03); 6 months after switching PMMA to polysulfone HDL-C decreased to 54 ± 30 mg/dl (p= 0.02 versus the final value; p= ns versus the basal value). No difference  among the basal value, the final value and the value of 6 months after the trial end in polysulfone patients (Figure 4).

Discussion

There is  a correlation between HDL-C and ApoA1 levels and HBV-VR in HD-patients. HDLs and their specific apolipoproteins ApoA1s modulate immune response regulating free cholesterol content in lipid rafts (LRs), specific membrane microdomains rich in unesterified cholesterol and sphingolipids in which B cell and T cell receptors and Major Histocompatibility Complex (MHC)-class II are placed. Lipid rafts concentrate MHC-peptide complex on  APCs surface, decreasing the amount of antigen required for T cell activation [Zilber MT, Blood2005]. Stachowski et al [NDT1994] observed how non-responsiveness to HBV vaccination in HD-patients is associated with impaired interaction between APCs and T cells. The efflux of free cholesterol, that is LRs  major stabilizing component, depends on ApoA1. In uremia [Gillett MP,J Nephrol. 2001] and aging [Anis Larbi, AGE 2014], a progressive increase of free cholesterol induces a loss in T cell membrane fluidity, which means a T cell dysfunction [Fülöp T, Longevity and Healthspan.2012]. In NR-patients we found lower HDL-C and ApoA1 levels, so we supposed an impaired free cholesterol efflux from immune cell LRs, hence the impaired HBV-VR.

Another important finding is that  PMMA increases HDL-C plasma concentrations, mostly in 2011-NR-patients which become able to respond better to HBV vaccine. We can suggest that PMMA increases HDL-C through uremic inflammation improvement. In fact, PMMA membrane has the ability to absorb large weight pro-inflammatory molecules [Vanholder R, Blood Purif 2006], oxidative stress mediators [Aoike I, NDT2007],  cytokines [Memoli B, NDT1991;Stenvinkel P, Kidney Int 2005] and uremic toxins  [Campistol JM, Contrib Nephrol1999;Galli F, NDT2007] and it could ameliorate oxidative stress in HD-patients [Macías Núñez Juan F,Nephron Clin Pract 2010].