Ethical approval for this study was provided by the Ethical Committee Institutional Helsinki committee of Galilee Medical Center, Nahariya, Israel (Chairman Prof. J. Bornstien; Ethical Committee N# 21311) on 14 june 2011. The study was performed in accordance with the relevant guidelines. Written informed consent was obtained from all patients.
Our study group included 20 patients who were admitted electively to the surgical ward for laparoscopic cholecystectomy due to symptomatic cholecystolithiasis. Surgery was done by the usual laparoscopic technique, under general anesthesia, while the patients are lying on a 15-degree reverse Trendelenburg position. The abdomen was insufflated by CO2 gas up to a pressure of 14 mmHg., under digital control. The mean time of PP was 40.4 ± 14.6 min (range 24 to 68 min.). After introducing four cannulas into the peritoneal cavity, the cystic duct and vessels were identified, clipped, and cut, followed by dissection, resection, and gallbladder extraction of the abdominal cavity, to conclude the operation. Before surgery and the morning of the first postoperative day, routine blood tests were done and included complete blood count, glucose, creatinine, urea, amylase lipase, electrolytes, and liver function tests. Blood analyses of the exogenous marker (1 cc) were done before surgery (awake state and at the end of anesthesia), at the end of laparoscopic surgery (abdominal CO2 evacuation), and about 2 hours later.
The technique using the exogenous marker has already been detailed in the scientific literature[25]. In brief, blood samples (1 ml) were collected in a glass tube containing heparin and 8 µl of the exogenic marker (from a stock solution of 20 mM marker dissolved in DSMO) or DSMO alone (control) and left to coagulate at room temperature [1, 26, 27]. After 1 hour, blood was extracted twice with a 3ml mixture of organic solvents of hexane:2-propanol (3:2 v/v) each, containing 10 ppm (0.02%) butylated hydroxyl toluene. Following centrifugation, the organic phase was collected, and the solvent was evaporated under nitrogen until dryness. The samples were kept under argon at -20ºC until analysis. Before analysis, samples were re-suspended with 20% methanol in acetonitrile and divided into two parts for liquid chromatography-mass spectrometry (LC/MS) and gas chromatography-mass spectrometry (GC/MS) analyses. Initial separation and detection of compounds were performed by LC/MS analysis (for LT marker and its oxidized products) using high-pressure liquid chromatography (HPLC) and a Waters photodiode array detector. The compounds were eluted using a gradient of solutions A (0.1% acetic acid in acetonitrile) and solution B (0.1% acetic acid in double-distilled water). MS/MS analysis of the oxidized products was performed in a multiple-reaction monitoring scan mode using negative ions electron spray. Peak spectra were monitored between 30–600 m/z. A calibration curve of LT and LTG was run with each set of analyses [1, 27]. Gas chromatography (GC)/MS analysis for oxysterol detection was performed using high-pressure gas chromatography [1]. Dried extracts were subjected to the silyating reagent (BSA, 200 µl), and 1,4-dioxane (dried on 4 A molecular sieves and passed through 200µ aluminum oxide) as a solvent, and heated to 80ºC for 60 min. Helium was used as the carrier gas. GC/MS detected samples in total monitoring mode [27]. For maximum sensitivity, the oxysterols were injected as their silyl ether derivatives, and the response factor for each oxysterol under the analytical conditions was calculated from the peak area ratio.
All the above analyses were done in MIGAL laboratories Center, Kiryat-Shmona, Israel.
In addition to our novel exogenous marker, various endogenous markers of oxidative stress were detected simultaneously as a reference. Those markers included: 7α-Hydroxylated cholesterol (7α-OH), 7β-Hydroxylated cholesterol (7β-OH), 5,6 α-epoxy cholesterol (α-epoxy), 5,6 β-epoxy cholesterol (β-epoxy), 7-ketocholesterol, 25-Hydroxylated cholesterol (25-OH), 27-Hydroxylated cholesterol (27-OH). The exogenous markers were labeled: OOH1 (representing cholesterol derivatives), Epoxy (representing the proteins LT), and 526 (stands for the nucleic acid). Statistical analysis was done using IBM SPSS statistics 19, and Quantitative variables were described by means, medians, range, and standard deviation. Frequencies and percentages detailed qualitative variables.
Regarding the changes in the levels of the exogenous and endogenous markers, we compared the data between every successive stage, as well as between the first and the last stage (first stage – wakefulness before surgery, followed by anesthesia, the end of laparoscopic surgery, and 2 hours later). The Wilcoxon signed-rank test was used to characterize our findings. Comparison between different groups was carried out by one-way analysis of variance test (ANOVA). A p-value of 0.05 or less was considered to be of statistical significance. Graphs were plotted to delineate the results (line bar). Every subject's first measure served as his control. The various markers were expressed as their relative levels and the rate/percentage of change (and not regarding their absolute quantity) to enable a more straightforward comparison with the changes of the various phases during surgery.