Study design
This study was designed as a prospective non-randomized study to verify the relationship between omentin-1 levels and the incidence of MACE and MALE after LER performed in T2DM patients with PAD and CLTI. The study was approved by the Ethics Committee of the Fondazione Policlinico Universitario A. Gemelli IRCCS and adhered to the principles of the Declaration of Helsinki. All the individuals agreed to participate in the study and provided informed consent.
Study population and clinical assessment
Overall, 207 T2DM patients with PAD and CLTI below-the-knee were included and followed for the entire duration of the study. Patients were consecutively enrolled during a period between 30/05/2018 and 15/04/2019 at the Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy. Inclusion criteria were age of 18 years or older, T2DM diagnosis[17] at least 1 year prior to the study, ankle/brachial index (ABI) lower than 0.80, peripheral artery stenosis greater than 50% documented by duplex ultrasound (US), presence of PAD at Rutherford category 4 or 5, presence of CLTI requiring endovascular treatment, no infections at present or in the previous month. In case of diabetic foot ulcers, additional criteria would be no local signs of infection and no need for antibiotic therapy. The wound, ischemia, foot infection (WIfI) classification system was used to stratify T2DM patients with foot ulcers. Radiological examination was performed, according to clinical judgment, to exclude osteomyelitis. Exclusion criteria were lower limb endovascular treatment or previous lower limb bypass surgery within the past 3 months, diabetic peripheral neuropathy, systemic steroid use or a prior history of use in the previous month, pregnancy, active cancer, life expectancy < 12 months, known liver disease with a functional status of B or above according to the Child-Pugh classification, congenital or acquired thrombophilia and active autoimmune disease[18].
All subjects were studied to rule out the presence of diabetic peripheral neuropathy, as previously described[19, 20]. Briefly, an assessment of vibration perception threshold was performed with a biothesiometer. All diabetic patients received a definite diagnosis of peripheral neuropathy with a Neuropathy Disability Score >5 and a pathological conduction velocity. Autonomic neuropathy was diagnosed according to the standardized procedure of Ewing and Clarke, including four cardiovascular autonomic tests[21].
For all patients, additional clinical data was collected, including age, body mass index (BMI), history of cardiovascular diseases (CAD), cerebrovascular disease (CVD), hypertension, hypercholesterolemia, smoking, renal failure [defined as an estimated glomerular filtration rate (eGRF) < 60 mL/min]. All patients underwent a complete US peripheral vascular evaluation, and PAD was defined according to the criteria established by the ad hoc Committee on Reporting Standards of the Society for Vascular Surgery and the International Society for Cardiovascular Surgery[22]. In subjects with an ABI of 1.40 or more (uncertain arterial calcification), US evaluation was performed to assess significant stenosis of the peripheral arteries[23].
At the time of enrollment, all patients were on statin treatment, and they continued therapy after LER, aiming at low-density lipoprotein cholesterol (LDL-C) levels less than 70 mg/dl.
Patients were on single antiplatelet therapy, which was modified to dual antiplatelet therapy after LER for the following month.
Revascularization treatment and follow-up
Angiography of the lower limb arteries, balloon angioplasty and, if indicated, stenting were performed as previously described[24]. The procedure was successful if the residual arterial stenosis was less than 30%[25]. No major complications, defined according to the definitions of the Society of Interventional Radiology[25], were observed. Of the 224 patients who underwent LER, 17 (7.6%) had a poor primary outcome and were excluded from the study follow-up.
For the follow-up, patients were evaluated 1, 3, 6 and 12 months after the LER to assess incidence of MACE and MALE. MACE were defined as composite of myocardial infarction, stroke and cardiovascular death. MALE were defined as composite of acute limb ischemia, major vascular amputations, limb-threatening ischemia leading to urgent revascularization.
Blood sampling procedures and biochemical assays
Blood sampling of patients was performed at baseline, just before the LER, after an overnight fast. Fasting glucose, serum creatinine, total cholesterol, LDL-C, triglycerides, and glycated hemoglobin, were determined. Renal function was calculated using eGFR, which was performed using the modification of diet in renal disease formula. Serum was prepared by centrifugation of blood samples, which was stored at −80°C until assayed. Serum omentin-1 levels were determined by a commercially available ELISA kit (E-EL-H2028, Elabscience) according to its protocol. The intra- and inter-assay coefficients of variation were 3.5% and 10.5%, respectively. The sensitivity, defined as the mean ± 3 SD of the 0 standard, was calculated to be 0.15 pmol/mL. For each patient, the serum levels were measured twice, and the results were averaged.
Statistical analysis
Data was summarized as means (standard deviations) for continuous variables and counts (percentages) for categorical variables. Demographic and clinical data of the groups were compared using Chi-square and t-test. Omentin-1 serum levels were compared with Mann–Whitney, Kruskal–Wallis and Dunn’s Multiple Comparison, when appropriate. A log transformation was applied to the not normally distributed variables prior to performing further analysis. A multivariate stepwise logistic regression analysis was performed, adjusted for traditional risk factors and omentin-1 levels. The area under the receiver operating characteristics (ROC) curve was calculated to test the predictive discrimination of MACE. The freedom from MACE according to the quartiles of serum omentin-1 was estimated using the Kaplan–Meier method and compared using the Log-Rank test. All analyses were performed using STATA version 14.0 for MacOS (Statistics/Data Analysis, Stata Corporation, College Station, TX, USA) and SPSS version 25.0 for MacOS (IBM Corporation, Armonk, NY, USA). Statistical significance was established at p < 0.05.