2.1 Materials and Machines
Adalimumab (Humira, 40 mg/0.8 ml) was purchased from the manufacturer(Vetter Pharma-Fertigung GmbH & Co. KG, Germany), and etanercept (Enbrel, 25 mg) was purchased and used as received from the provider (Pfizer, New York, NY, USA). Recombinant human TNF-α (Peprotech) was used to capture the adalimumab or etanercept by being immobilized on the solid phase surface of ninety-six-well plates (Greiner, Germany). A 5% solution of nonfat dried milk (Dingguo Changsheng Biotechnology, China) was dissolved in phosphate-buffered saline (PBS) (Dingguo Changsheng Biotechnology) for sealing the solid phase surface of each well. 0.5% Tween-20 (Damao Chemical Reagent Factory, China) was added into PBS to prepare a wash solution. Horseradish peroxidase (HRP)-goat anti-human IgG (H+L) conjugate (ABclonal Technology, Woburn, MA, USA) was used for detecting adalimumab or etanercept. Tetramethyl benzidine (TMB) (Solarbio, China) was used as the substrate solution, and 2 mol/L hydrogen chloride (Sinopharm Chemical Reagent, China) were prepared in the laboratory to be used as a stop solution.
2.2 Novel Method for Sample Storage and Preparations
2.2.1 Freeze-drying Device
The novel freeze-drying device consisted of two tubes. The inner tube was used for intercepting the analytes with a membrane, and the outer tube was used for reserving the filtered samples (Figure 1). The heights of the tubes were 31.6 mm and 35 mm, respectively. The diameters of the inner tube and outer tube were 7 mm and 8.6 mm, respectively. The membrane placed at the bottom of the inner tube evenly dispersed the samples and efficiently filter them. After adding 50 µL 5% nonfat dried milk, 200 µL plasma or serum samples were placed into the inner tube and ultrasonically blended for 5 min. The filtered sample then flowed out from the inner tube through the "#" -shaped bottom pore and was reserved in the outer tube. Eventually, the inner tube was freeze-dried in a vacuum freeze dryer. The volume of the sample stored in each tube was 200 µL.
2.2.2 Freeze-drying Process
The samples were previously frozen at -40°C in the freeze dryer for 3 h. Then the vacuum pump began to work, and all samples were heated to -37°C. The freeze drier was programmed to slowly increase the temperature until it reached 20°C. After completing all programmed settings, the freeze-dried tubes were removed and stored in low-gas-permeable sealed bags at 4℃ until analysis.
2.2.3 Sample Preparations
To each freeze-dried tube, 800 μL of normal saline was added, followed by soaking for 30 min, and then the contents of the tube were sonicated for 10 min. After all tubes were centrifuged at 15,700 ×g for 10 min at 4°C, the supernatants were analyzed by enzyme-linked immunosorbent assay (ELISA) to detect the concentrations of adalimumab and etanercept.
2.3 Conventional Method for Sample Storage and Preparations
As the biological samples (plasma or serum) of adalimumab or etanercept were collected, they were transferred to polyethylene tubes and then stored in a low-temperature freezer until the time of the assay. Prior to the detection of adalimumab or etanercept, 200 μL of thawed sample was transferred to another tube and then centrifuged at 440 × g for 5 min. Then, 20 μL of the supernatant was analyzed by the ELISA method.
2.4 Analytical Methods
2.4.1 ELISA Detection of Adalimumab
The 96-well plates were coated with 1 μg/mL recombinant human TNF-α (100 µl/well) on their solid phase surface and were then stored at 4°C for 12 h. After PBST was used to wash the wells 3 times, the wells were coated with blocking reagent (5% nonfat dried milk in PBST, 250 μL/well) at 37°C for 2 h. The serum samples, which were diluted in 1% nonfat dried milk solution, were added to the 96-well plate (50 μL/well) following removal of the blocking buffer and washing the wells with PBST for three times, and then the plate was placed in an incubator at 37°C for 1 h. Afterward, PBST was used to wash the wells 5 times, and 1 μg/mL HRP-goat anti-human IgG (H+L) conjugate was added (50 μL/well). The plates were subsequently incubated at 37°C for 30 min for detection of adalimumab. Next, after 5 washes, TMB substrate was added (100 μL/well) and allowed to develop for 10 minutes. Then, the stop solution (1 M sulfonic acid) was added to stop the reaction (50 μL/well). The OD values were read at 450 nm within 15 min after adding stop solution. All measurements were performed in duplicate. A standard concentration curve ranging from 31.25 to 1000 pg/mL was prepared using an adalimumab standard.
2.4.2 ELISA Detection for Etanercept
The detection of etanercept was performed with ELISA method15. First, 1.5 μg/mL recombinant human TNF-α was coated on the solid phase surface of the 96-well plates (100 μL/well), and they were stored overnight at 4°C. Second, after coating with the TNF-α, the wells were washed three times with PBST, and blocked with 5% nonfat dried milk/PBST (250 μL/well) in a stationary incubator at 37°C for 2 h. Third, after removal of the blocking solution and washing the wells three times with PBST, plasma samples (diluted in 1% nonfat dried milk/PBST) were added to the plate (50 μL/well), which was then incubated at 37°C for 1 h. Fourth, the wells were washed five times with PBST, and etanercept was detected with 1 μg/mL HRP-goat anti-human IgG (H+L) conjugate (50 μL/well) by incubating at 37°C for 30 min. Finally, after washing the wells five times with PBST, color development was performed by the addition of 100 μL TMB into each well, and then stopping the reaction with 1 mol/L sulfonic acid (50 μL/well). Optical density was measured at 450 nm with a correction at 630 nm. This method detected the free etanercept, and all measurements were performed twice. A standard curve was prepared with etanercept ranging from 6.25 to 500 pg/mL.
2.5 Validations of the New Storage Method
2.5.1 Validation with QC Samples of Adalimumab
QC samples of adalimumab were stored using either the new method or the conventional method. The ELISA method was used to detect adalimumab in all samples. The accuracy, precision, and stability of samples prepared with the two storage methods were evaluated using a modified method16.
Standard working solutions of adalimumab were prepared by diluting stock solutions with nonfat dry milk to six different concentration levels including 312.5, 625, 1250, 2500, 5000, and 10000 pg/mL. Standard working solutions were added to plasma from rats or healthy human volunteers to achieve the following calibration standard concentrations: 31.25, 62.5, 125, 250, 500, and 1000 pg/mL. The QC samples were similarly prepared at three concentration levels of 90, 600, and 750 pg/mL (n=5, at each concentration). All calibration standard samples and QC samples were freshly prepared daily.
Intra- and inter-day accuracy and precision were evaluated by measurement of QC samples at three concentration levels (90, 600, and 750 pg/mL) with five replicates. The concentration of each sample was calculated according to the calibration curve prepared the same day. Accuracy was defined as the relative deviation in the determined concentration of a standard from that of its nominal concentration, and the precision of the analyte is expressed as the relative standard deviation (RSD). The stability of adalimumab was evaluated by measurement of three replicate of QC samples after they were separately stored using either the new or the conventional method for 7 d and 14 d.
2.5.2 Validation with QC Samples of Etanercept
QC samples of etanercept were stored using either the new method or the conventional method. The accuracy, precision, and stability of the differently stored samples were evaluated by ELISA. The standard calibration concentrations were 6.25, 12.5, 25, 50, 100, 250, and 500 µg/mL, and the QC samples were prepared at three concentration levels of 12.5, 100, and 400 µg/mL. The intra- and inter-day accuracy, precision, and stability of etanercept were calculated in the same manner as those used in the validation with the QC samples of adalimumab.
2.6 PK Studies
2.6.1 Ethics
Animal studies were approved by the Animal Ethics Committee of the School of Pharmaceutical Sciences of Central South University (Changsha, China). All experiments were conducted in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals.
The trials of adalimumab in patients and the trials of etanercept in healthy volunteers and patients were both approved by the Ethics Committee of the School of Pharmaceutical Sciences of Central South University. Written informed consent was obtained from all individual participants included in the study in accordance with the Good Clinical Practice guidelines published by the National Medical Products Administration of China.
2.6.2 PK Study of Adalimumab in Rats
For the PK study, 0.5 ml blood was collected from each of 10 rats that subsequently received one subcutaneous injection of 0.5 mg adalimumab. After the single-dose administration of adalimumab, 0.5 ml blood was collected before and at 0.5, 1, 2, 6, 12, 24, 48, 96, 168, 264, 336, and 504 h. After the blood was collected, the serum samples were centrifuged at 780 × g for 10 min and maintained at 4℃ for 30 min. All serum samples were divided into two groups to be separately stored using the new or conventional method until analysis.
2.6.3 PK Study of Adalimumab in Patients with Rheumatoid Arthritis
Six Chinese male patients with rheumatoid arthritis (RA), between 27 and 39 years old and the body weights from 60 to 75 kg, were enrolled to receive multiple injections of adalimumab. Inclusion in the study was made according to a diagnosis of RA based on rigid criteria15. Exclusion criteria included the following: complete tetanus; serious disease of the heart, liver, kidney, or endocrine system; infection (acute or chronic); HbsAg-positive status; HIV-positive status; and a history of tuberculosis or a positive tuberculosis skin test.
All patients received consecutive subcutaneous injections of 40 mg adalimumab once every two weeks in the abdomen. 2 mL blood samples were collected in heparinized centrifuge tubes before the fifth, sixth, and seventh administration. The plasma samples were separated by centrifugal force at 3500 rpm for 10 min, and then samples were divided into two groups to be separately stored using the new or conventional method until analysis.
2.6.4 PK Study of Etanercept in Healthy Volunteers
Six Chinese healthy volunteers including 3 males and 3 females, between 21 and 31 years old, and weighting from 50 to 63 kg, were enrolled to receive single subcutaneous injections of etanercept. Exclusion criteria included any clinically significant medical history or physical findings, presence of pregnancy or lactation, blood or blood product donation within 30 days of medication administration, serious disease of the heart, liver, kidney, or endocrine system, prior anti-TNF-α therapy, infection (acute or chronic), HbsAg-positive status, HIV-positive status, a history of tuberculosis or a positive tuberculosis skin test, and psychotic, emotional or intellectual problems likely to limit the validity of the consent15.
Prior to the subcutaneous injection of 50 mg etanercept, 5 mL blood was collected from the 6 healthy volunteers. After administration of etanercept, 5 mL blood samples were collected in heparinized centrifuge tubes at 2, 4, 8, 12, 24, 36, 48, 72, 120, 168, 336, 504, 672, 744, and 888 h. All plasma samples were separated by centrifugation at 3500 rpm for 10 min, and then, the samples were stored separately using either the new method or the conventional method until analysis.
2.6.5 PK Study of Etanercept in Patients with Ankylosing Spondylitis
Six Chinese male patients with ankylosing spondylitis (AS), between 23 and 52 years old and weighting from 60 to 84 kg, were enrolled to receive multiple injections of etanercept. Inclusion into the study was made according to a diagnosis of AS based on rigid criteria15. Exclusion criteria included the following: complete tetanus; serious disease of the heart, liver, kidney, or endocrine system; infection (acute or chronic); HbsAg-positive status; HIV-positive status; and a history of tuberculosis or a positive tuberculosis skin test.
All patients received eight consecutive subcutaneous injections of 50 mg etanercept once a week in the abdomen. 2 mL blood samples were collected in heparinized centrifuge tubes before the fifth, sixth, and seventh administration. The plasma samples were separated by centrifugal force at 3500 rpm for 10 min, and then samples were separately stored using the new or conventional method until analysis.