Diabetic patients with CLTI undergoing LER have a very high risk of MACE and MALE in the 12-month period following treatment [7]. Best medical therapies and risk factors control do not prevent the development of such complications [2]. In clinical practice, during the post-revascularization period patients with similar clinical features and endovascular approaches may unpredictably experience completely different procedural outcomes. Therefore, there is an urgent need to develop and validate non-invasive tools that include traditional and non-traditional risk factors for the prediction of the occurrence of complications after LER in this particular population.
It is well established that inflammation plays a key role in the complications of diabetes mellitus [39]. Several studies have shown that the pre-procedural inflammatory state is related to an increased risk for restenosis after coronary angioplasty [40]. We hypothesized that patients with an activation of the systemic inflammatory cascade and reduction of endogenous anti-inflammatory mechanisms have worse outcomes. The results of this study show that the baseline levels of IL-1, IL-6, TNF-α, CRP, HMGB-1, OPG and Sortilin were increased in patients who developed MALE and MACE during follow-up compared to those who did not present these outcomes. These findings are in agreement with previous studies that have individually analyzed each biomarker [7, 18, 23, 28]. Instead, Omentin-1 serum levels were reduced in patients who presented MALE and MACE, compared to patients who had no events. This inverse correlation has been previously found in populations affected by CAD [41], PAD [30, 31] and carotid artery stenosis [42] and confirms the anti-inflammatory role of this adipokine [43–46]. Remarkably, it is the first time this panel of cytokines has been studied simultaneously in the same population of patients.
In recent years, the CANTOS study raised the attention on the role of IL-1 in cardiovascular diseases. Researchers have shown that the intake of canakinumab, a monoclonal antibody directed against IL-1, that is used in clinical practice for treatment of some rheumatological diseases, significantly reduced the risk of recurrence of cardiovascular events in patients with history of myocardial infarction and persistently high CRP levels, confirming the close link between inflammation and atherosclerosis [14]. To our knowledge, this is the first prospective study that demonstrates the association of IL-1 and cardiovascular and limbs events in diabetic patients after endovascular revascularization for CLTI.
The multivariate analysis for MACE showed that, after adjusting for the factors of conventional cardiovascular risk and all biomarkers in analysis, IL-6, OPG e CRP levels are independently associated with the outcome. The ROC curve confirmed their high predictive power. These results confirm the association between IL-6, OPG, CRP and cardiovascular outcomes that already emerged in one of our previous study [7]. Multivariate analysis for MALE showed that after adjusting for factors of conventional cardiovascular risk and all cytokines in analysis, CRP, HMGB-1, OPG and Omentin-1 are independently associated with the outcome. The ROC curve confirmed their high predictive power. These results confirm the correlation between CRP, HMGB-1, OPG and Omentin-1 already highlighted in previous studies [7, 18, 23, 31].
In the past years, the little of awareness in PAD has led to scarce tools for the early diagnosis, progression and prognosis evaluation, resulting in inadequate therapeutic interventions. Non-invasive circulating serum biomarkers may be predictive effective tools in this setting. Several studies have evaluated the possible role of different molecules in the diagnosis and prognosis of PAD [47]. These studies have also offered insights into the complex pathophysiological mechanisms and numerous molecular pathways that are involved in PAD. Therefore, assessment of a single biomarker may not reflect those complex interactions [47]. Instead, the combination of a panel of biomarkers and conventional cardiovascular risk factors could be useful to obtain more accurate prediction algorithms.
There is a scarcity of scientific research on predictive models for MACE and MALE after LER in diabetic patients with CLTI. In a retrospective study, Stone et al. found that, after LER, elevated pre-procedural CRP levels were associated with MALE, and elevated levels of CRP and brain natriuretic peptide (BNP) were associated with late cardiovascular events [48]. Berger et al. identified 11 predictors, including patient age over 75 years, history of PAD, dementia, diabetes, hypertension, renal disease, cerebrovascular disease, chronic heart failure, smoking status, prior myocardial infarction, and chronic pulmonary disease, that are associated with the incidence of MACE/MALE in CAD and/or PAD patients [49]. Vieceli Dalla Sega et al. measured the circulating levels of a panel of 23 molecules related to inflammation, endothelial dysfunction, platelet activation, and thrombophilia in 92 patients with CLTI and diabetic foot ulcers requiring PTA and foot surgery. They found that PAI-1 and endothelin-1 are associated with the need for new revascularization and, the levels of thrombomodulin and sCD40L are associated with new lesions or recurrence [50].
To our knowledge, the present study is the first to demonstrate that a panel of circulating biomarkers easily measurable could predict the incidence of MACE and MALE over 90% in diabetic patients with CLTI after LER.
Study limitations
A limitation of this single-center study is the small number of patients included. However, this is a pilot study conducted on a carefully selected population with restrictive characteristics in order to select a population as homogeneous as possible. A further limitation of the study is the lack of a formal protocol to rule out possible bone infections (for example using standard radiographic examinations or computed tomography or magnetic resonance imaging of bone), although patients with obvious signs of infections were excluded from recruitment. The aim of this research was to find easily accessible and reproducible biomarkers for the typical diabetic patient with CLTI. The study also did not clarify the effect that the revascularization procedure could have on the levels of analyzed biomarkers. Therefore, it might be helpful to monitor cytokine levels after the procedure and in the follow-up period in order to evaluate the effect of the variations of these on MACE and MALE occurrence. In addition, more conclusive evidence about the real causal relationship between the studied biomarkers and the outcomes after LER in diabetic patients will only be found after clinical multi-centric studies, on larger cohorts and longer follow-up periods.