Reduction in Urinary Chemokine (C-C Motif) Ligand 2 (CCL2) After Surgery-Induced Weight Loss

This is a prospective cohort study assessing the change in urinary CCL2 levels before and after bariatric surgery, conducted at a teaching university hospital from June 2016 to June 2018. The study was conducted following the principles of the Declaration of Helsinki. Ethics approval was obtained before the start of this study from our institutional review board, Universiti Kebangsaan Malaysia Research Ethics Committee (reference number: FF-2017-035). This study was also registered with the Thai Clinical Trials Registry with the number TCTR20190825002. Written informed consent was taken prior to study commencement. All data collected were kept confidential, and patients were allowed to refuse participation in the study. Data presented do not identify individuals.

Purposive sampling method was employed. We included patients of both genders aged 18–65 years, with a BMI of ≥37.5 kg/m2 with no history of renal disease who are planned for bariatric surgery. Patients who received steroid therapy within six months prior to the surgery, patients with malignancy, patients who are pregnant, and patients with stage 3 A kidney disease and beyond (defined as an eGFR < 60 mL/min/1.73 m2) were excluded.

A multidisciplinary team performed a thorough assessment, and the final bariatric procedure to be performed is decided, taking into consideration the patient's choice as well. These procedures include SAGB, RYGB, and SG, all performed via laparoscopic approach by a consultant upper gastrointestinal surgeon with more than five years' experience. Venous blood and midstream urine samples were taken preoperatively and six months after the surgery. Midstream urine was collected into sterile containers in the morning. The biochemical evaluation was performed for serum creatinine and HbA1c, urinary CCL2, and urine ACR. Serum creatinine and HbA1c were measured using standard laboratory methods.

EGFR was calculated using the MDRD 4 variable formula23. An abnormal glomerular filtration rate is defined as eGFR < 90 mL/min per 1.73 m2 based on the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (KDOQI)24. All urine samples were centrifuged at 1600g for 10 min at 4 °C, and the supernatant was stored at −80 °C until further analysis. The reading of urine albumin was expressed as urine albumin-creatinine ratio (ACR)17.

The level of urinary CCL2 was measured using specific enzyme-linked immunoassay (ELISA) kits (Minneapolis, Minn, USA, R&D Systems). Dilution of urine samples was performed according to the manufacturer's instructions. Samples were then incubated for two hours at room temperature. After washing the plates, a conjugate was added to erase any unbound substances and was left alone for an hour. A substrate solution was then added after washing the plates. Stop solution was added after incubation for 20 min at room temperature. The absorbance was then read at 450 nm with the correction wavelength set at 540 nm. All samples were assayed in duplicate. Urine CCL2 levels were expressed as pictogram per ml (pg/ml).

The study planned as a continuous response variable based on a previous study25. The difference in the response is normally distributed with a standard deviation of 25. If true difference in the mean response is 13, we will need 58 subjects to be able to reject the null hypothesis that this response difference is zero with probability (power) of 0.8, and confidence interval of 95%. Type I error probability associated with this test of this null hypothesis is 0.0526.

Variables with normal distribution were expressed as mean ± SD, whereas non-parametric variables were expressed as median (IQR). The significance of differences before and after bariatric surgery was evaluated with a paired t-test for parametric data and the Mann Whitney U test for non-parametric data. For comparisons among the LAGB, LRYGB, and LSG groups, the Kruskal Wallis one-way test was used. Correlation between variables was performed using the Pearson Bivariate test. All statistical analyses were performed using SPSS (version 24.0; SPSS, Chicago, IL). Statistical significance was set at p < 0.05.