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].

Conclusions

PMMA increases HDL-C concentrations, thus improving HBV-VR in NR-patients. Our trial confirms experimental data about the immunologic role of HDL-Cs and ApoA1s, in particular in course of HBV vaccination.