Study participants
Patients who had hyperlipidaemia [diagnosed with hypercholesterolemia (cholesterol>5.18 mmol/L) or hypertriglyceridemia (triglycerides>2.3 mmol/L), mixed hyperlipidaemia (cholesterol>5.18 mmol/L and triglycerides>2.3 mmol/L), and high low-density lipoproteinemia (low-density lipoprotein>3.4 mmol/L) according to the 2019 guidelines of the European Society of Cardiology] with no other diseases were selected for this study. No statins or other lipid-lowering drugs were prescribed for the patients. All patients provided and signed informed consent. The study was approved by the Ethical Committee of Shanghai Pudong Hospital (Fudan University, Pudong Medical Center, Shanghai, China), and experiments were performed in accordance with the Ethical Committee’s guidelines and regulations. The ClinicalTrials.gov number was NCT 03491956.
Exclusion criteria: Patients were excluded if (1) they had coexisting diabetes or hypertension; (2) they had tumours, liver and kidney dysfunction, severe oedema, cardiac insufficiency, respiratory insufficiency caused by severe lung disease, or pregnancy; and (3) they were over 80 years old.
Treatment procedure
Plasmapheresis using a Plasauto iQ automatic blood purification system, model KM-9000 (Kawasumi, Tokyo, Japan), was performed in this study, with a PE-08 primary membrane plasma separator and an EC-4A20 secondary membrane plasma component separator. Cubital elbow median veins on both arms were selected for artery and vein access. The blood flow was 60-100 mL/min, the plasma separation rate was 30% of the blood flow, and the plasma rejection rate was 15% of the plasma separation rate. Ordinary heparin was used as an anticoagulant, with an initial dose of 3000 U, followed by an additional maintenance dose of 20-40 U/(kg·h). The therapeutic target was calculated as weight (kg) ´40 mL (1-1.4 times blood volume). Each session lasted for 3-4 hours.
Laboratory examination
Isolation of PBMCs
Blood samples were taken from patients with hyperlipidaemia, and acidic citrate dextrose (Walvax, Yunnan, China) was added as an anticoagulant. To isolate PBMCs, the blood samples were diluted with PBS, and lymphocyte separation medium was added (Hao Yang Biological Manufacture Co., Tianjin, China). The samples were centrifuged at 1000 rpm for 40 min, the middle cell layer was collected, and PBMCs were obtained after washing three times with PBS.
Detection of lipid metabolism-related, ER stress-related and apoptosis-related proteins
The proteins subjected to western blotting were extracted using lysis buffer (Invent, Beijing, China), separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and transferred onto polyvinylidene difluoride (PVDF) membranes (Millipore, MA, USA). The membrane carrying the protein bands was blocked in Tris-buffered saline with Tween (TBST) containing 5% skim milk for 1 hour and incubated with primary antibodies at 4 ℃ overnight. After washing, the membrane was incubated with secondary antibodies conjugated to horseradish peroxidase for 1 hour at room temperature. Secondary antibodies included goat anti-rabbit IgG and goat anti-mouse IgG. After washing, the membranes were incubated with Immobilon Western Chemiluminescent HRP Substrate (Millipore, MA, USA). Protein signals were captured using a Bio-Rad ChemiDoc™ XRS system (Bio-Rad, CA, USA). Data were quantified by Quantity One software (Bio-Rad, CA, USA) [19]. Primary antibodies against LDLR, CD36, PCSK9, GRP78, CHOP, ATF4, p-EIF2, Bcl-2, BAX and Caspase-3 and secondary antibodies were obtained from Proteintech (Proteintech Group, Inc., IL, USA), and an antibody against EIF2 was purchased from CST (Cell Signaling Technology, MA, USA). The antibodies are diluted according to the instructions, usually 1:2000-5000.
Detection of ROS and serum inflammatory factors
Nonstimulated PBMCs were detected with a ROS assay kit (Beyotime, Shanghai, China) after isolation. PBMCs in each sample were washed twice with PBS. The fluorescent probe used to determine the level of ROS in PBMCs was diluted to a concentration of 10 umol/L. PBMCs were suspended in the diluted fluorescent probes and incubated in a plate at 37°C for 20 min. The PBMCs were washed three times with cell culture medium to remove probe that did not enter the cells. Finally, the ROS level was detected by flow cytometry (BD, NH, USA). Serum inflammatory factors [Interleukin 1b (IL-1b) Interleukin 6 (IL-6), Tumor necrosis factor α (TNF-a)] were detected by ELISA using commercial kits (Neobioscience, Shanghai, China).
Statistical analysis
Data are expressed as the means ± SDs, with the exception of skewed data, which are expressed as the median (range). After correcting non-normally distributed data, the differences were analysed with a paired t test, and a P value < 0.05 was considered statistically significant. Statistical analyses were performed using SPSS 22.0 statistical software (IBM, IL, USA).