A Pro-Inflammatory Biomarker-Profile Predicts Amputation-Free Survival in Patients with Severe Limb Ischemia

Higher levels of cytokines in patients with critical limb threatening ischemia

OBJECTIVE

Inflammation is a key element in the initiation and progression of peripheral arterial disease (PAD). Understanding the impact of inflammatory molecules, as cytokines in PAD could help us to improve the prognosis of these patients. The main goal of this study was to compare the serum level of cytokines between patients with claudication to those with critical limb treating ischemia (CLTI). The second objective was to evaluate the relationship between the levels of cytokines and death or amputation rate.

METHODS

An observational, single-centre and prospective study was conducted from January 2018 to July 2022. The study was approved by the ethical commission of the Local Hospital (75/2017). Patients with PAD, suggested by the clinical history and objective examination and, confirmed with ankle-brachial index (ABI) attending Vascular Surgery consultations of the first author were included. The following exclusion criteria were applied: i) bedridden individuals or subjects who refused to participate in the protocol; ii) diseases responsible for body composition changes or pro-inflammatory state; iii) recent diet change, iv) active malignancy, v) auto-immune disease, vi) active infection, vii) chronic renal failure (GFR <30 mL/min/1.73m2) or viii) heart failure in the past three months. This cohort was observed at admission, three, six and twelve months. A panel of 27 cytokines was determined with ELISA, at baseline.

RESULTS

We included 119 subjects (mean age: 67.58 ± 9.60 years-old; 79.80% males), 65 patients with claudication and 54 with CLTI. From the 27 cytokines analysed, patients with CLTI, when compared to those with claudication, had a higher serum level of 11 cytokines: IL1ra; IL-6; IL-8; IL12 p70; G-CSF; IP-10; MCP-1; MIP-1α; PDGF-β, RANTES, TNF-α. From the group of patients with CLTI those who underwent a major amputation had a higher serum level of FGF-basic [Median = 49.04; IQR = 37.03-52.49; versus Median = 33.04; IQR =28.60-38.98; p = 0.001].

CONCLUSIONS

Patients with CLTI have higher serum level of inflammatory cytokines, which may have role in the prognosis of these patients.

Evaluation of Plasma Biomarkers for Causal Association With Peripheral Artery Disease

BACKGROUND

Hundreds of biomarkers for peripheral artery disease (PAD) have been reported in the literature; however, the observational nature of these studies limits causal inference due to the potential of reverse causality and residual confounding. We sought to evaluate the potential causal impact of putative PAD biomarkers identified in human observational studies through genetic causal inference methods.

METHODS

Putative circulating PAD biomarkers were identified from human observational studies through a comprehensive literature search based on terms related to PAD using PubMed, Cochrane, and Embase. Genetic instruments were generated from publicly available genome-wide association studies of circulating biomarkers. Two-sample Mendelian randomization was used to test the association of genetically determined biomarker levels with PAD using summary statistics from a genome-wide association study of 31 307 individuals with and 211 753 individuals without PAD in the Veterans Affairs Million Veteran Program and replicated in data from FinnGen comprised of 11 924 individuals with and 288 638 individuals without PAD.

RESULTS

We identified 204 unique circulating biomarkers for PAD from the observational literature, of which 173 were genetically instrumented using genome-wide association study results. After accounting for multiple testing (false discovery rate, <0.05), 10 of 173 (5.8%) biomarkers had significant associations with PAD. These 10 biomarkers represented categories including plasma lipoprotein regulation, lipid homeostasis, and protein-lipid complex remodeling. Observational literature highlighted different pathways including inflammatory response, negative regulation of multicellular organismal processes, and regulation of response to external stimuli.

CONCLUSIONS

Integrating human observational studies and genetic causal inference highlights several key pathways in PAD pathophysiology. This work demonstrates that a substantial portion of biomarkers identified in observational studies are not well supported by human genetic evidence and emphasizes the importance of triangulating evidence to understand PAD pathophysiology. Although the identified biomarkers offer insights into atherosclerotic development in the lower limb, their specificity to PAD compared with more widespread atherosclerosis requires further study.

Narrative Review of Biological Markers in Chronic Limb-Threatening Ischemia

BACKGROUND

Chronic limb-threatening ischemia (CLTI), the advanced stage of peripheral arterial disease, is diagnosed in the presence of ischemic rest pain, non-healing ulcers, or gangrene. Several studies have demonstrated that inflammation and endothelial dysfunction are some of the main substrates of CLTI.

METHODS

A narrative review was conducted and reported according to PRISMA guidelines. Three databases were searched-Web of Science, Medline, and EMBASE-for the studies assessing CLTI and the biological markers related to it.

RESULTS

We included 22 studies, and all the markers identified (C-reactive protein, D-dimers, fibrinogen, cytokines, IL-6, TNF-α, ICAM-1 (Intracellular Adhesion Molecule-1), VCAM-1 (Vascular Cell Adhesion Molecule-1), neutrophile-to-lymphocytes ratio (NLR), IL-8, Pentraxin-3, neutrophil gelatinase-associated lipocalin (NGAL), calprotectin, E-selectin, P-selectin, neopterin, High-Mobility Group Box-1 protein (HGMB-1), Osteoprotegerin (OPG) and Sortilin) were positively associated with advanced CLTI, with major limb or major cardiovascular events in these patients.

CONCLUSIONS

All the studied markers had increased values in patients with CLTI, especially when associated with diabetes mellitus, proving a very important association between diabetes and major limb or cardiovascular events in these patients. There is a need for more studies to validate these markers in terms of diagnosis or prognosis in CLTI patients and in trying to find new medical strategies that target inflammation or endothelial dysfunction in these patients.

Patients living farther from a tertiary care center are more likely to undergo peripheral arterial bypass for acute and chronic limb-threatening ischemia

OBJECTIVE

The aim of this study was to assess the association between the proximity to the tertiary care hospital and the severity of peripheral arterial disease (PAD) at the time of lower extremity bypass (LEB) in a rural-urban mix region.

METHODS

Patients undergoing LEB from 2010 to 2020 at Penn State Milton S. Hershey Medical Center were reviewed and stratified into two study groups based on a median distance from hospital (ie, Group I: ≥34 miles and Group II: <34 miles). Patients' demographic features, preoperative data including comorbidities, and medications were analyzed. A univariate analysis for the patient characteristics between the two study groups, along with evaluation of postoperative outcomes, and a multivariate predictive modeling to study the PAD stage as the indication of LEB was performed. A P-value of < .05 was set as a significant difference between the groups for all the analyses.

RESULTS

There were 175 patients (49.9%) in Group I and 176 patients (50.1%) in Group II with a mean age of 65 ± 11.92 years (median, 64.61 years). No significant difference was observed in gender (P = .530), age (P = .906), and functional status (P = .830) between study groups. It was observed that patients in Group I were more likely to be overweight or obese (71.3% vs 57%; P = .007) and had a prior history of myocardial infarction (24.3% vs 15.3%; P = .036) in comparison to Group II. No postoperative outcomes were found to be statistically different between the study groups. The multivariate analyses based on various confounders displayed that patients in Group I had 56% higher likelihood of LEB for chronic limb-threatening ischemia (adjusted odds ratio, 1.56; 95% confidence interval, 0.92-2.62; P = .042). Group I patients also had five times higher odds of LEB for acute limb ischemia (adjusted odds ratio, 5.07; 95% confidence interval, 1.42-18.13; P = .012) as compared with those in the Group II.

CONCLUSIONS

Patients' proximity to a major tertiary hospital may have implications on the disease progression for patients with PAD and could also be related to inadequate vascular services in primary and secondary hospitals. Lack of preventive care and disease management in regions afar from a tertiary hospital could be other implicating factors and highlights the need for outreach programs, along with distribution of vascular specialists, to reduce geographical disparities and ensure equity in access to care.

A Systematic Review of Interleukins as Diagnostic and Prognostic Biomarkers for Peripheral Artery Disease

Background: Peripheral artery disease (PAD) involves atherosclerosis of the lower extremity arteries and is a major contributor to limb loss and death worldwide. Several studies have demonstrated that interleukins (ILs) play an important role in the development and progression of PAD; however, a comprehensive literature review has not been performed. Methods: A systematic review was conducted and reported according to PRISMA guidelines. MEDLINE was searched from inception to 5 December 2022, and all studies assessing the association between ILs and PAD were included. Results: We included 17 studies from a pool of 771 unique articles. Five pro-inflammatory ILs (IL-1β, IL-2, IL-5, IL-6, and IL-8) and one pro-atherogenic IL (IL-12) were positively correlated with PAD diagnosis and progression. In contrast, two anti-inflammatory ILs (IL-4 and IL-10) were protective against PAD diagnosis and adverse limb events. Specifically, IL-6 and IL-8 were the most strongly associated with PAD and can act as potential disease biomarkers to support the identification and treatment of PAD. Conclusions: Ongoing work to identify and validate diagnostic/prognostic inflammatory biomarkers for PAD has the potential to assist clinicians in identifying high-risk patients for further evaluation and management which could reduce the risk of adverse cardiovascular and limb events.

Plasma Gut Microbe-Derived Metabolites Associated with Peripheral Artery Disease and Major Adverse Cardiac Events

Cardiovascular diseases are associated with gut dysbiosis, but the role of microbe-derived metabolites as biomarkers or modulators of cardiovascular disease are not well understood. This is a targeted metabolomics study to investigate the association of nine microbe-derived metabolites with lower extremity peripheral artery disease (PAD), a form of atherosclerosis, and major adverse cardiac events (MACE). The study cohort consists of individuals with intermittent claudication and ankle-brachial index (ABI) < 0.9 (N = 119) and controls without clinically-apparent atherosclerosis (N = 37). The primary endpoint was MACE, a composite endpoint of myocardial infarction, coronary revascularization, stroke, transient ischemic attack, or cardiac-related death. Plasma metabolite concentrations differed significantly between the PAD and control groups. After adjustment for traditional atherosclerosis risk factors, kynurenine, hippuric acid, indole-3-propionic acid (IPA), and indole-3-aldehyde (I3A) concentrations were negatively associated with PAD, whereas indoxyl sulfate and 3-hydroxyanthranilic acid were positively associated. Hippuric acid, IPA, and I3A correlated with ABI, a surrogate for atherosclerotic disease burden. Those in the highest I3A concentration quartile had significantly improved freedom from MACE during follow-up compared to those in the lowest quartile. This study identifies specific indole- and phenyl-derived species impacted by gut microbial metabolic pathways that could represent novel microbiome-related biomarkers of PAD.

Inflammatory and Prothrombotic Biomarkers, DNA Polymorphisms, MicroRNAs and Personalized Medicine for Patients with Peripheral Arterial Disease

Classical risk factors play a major role in the initiation and development of atherosclerosis. However, the estimation of risk for cardiovascular events based only on risk factors is often insufficient. Efforts have been made to identify biomarkers that indicate ongoing atherosclerosis. Among important circulating biomarkers associated with peripheral arterial disease (PAD) are inflammatory markers which are determined by the expression of different genes and epigenetic processes. Among these proinflammatory molecules, interleukin-6, C-reactive protein, several adhesion molecules, CD40 ligand, osteoprotegerin and others are associated with the presence and progression of PAD. Additionally, several circulating prothrombotic markers have a predictive value in PAD. Genetic polymorphisms significantly, albeit moderately, affect risk factors for PAD via altered lipoprotein metabolism, diabetes, arterial hypertension, smoking, inflammation and thrombosis. However, most of the risk variants for PAD are located in noncoding regions of the genome and their influence on gene expression remains to be explored. MicroRNAs (miRNAs) are single-stranded, noncoding RNAs that modulate gene expression at the post-transcriptional level. Patterns of miRNA expression, to some extent, vary in different atherosclerotic cardiovascular diseases. miRNAs appear to be useful in the detection of PAD and the prediction of progression and revascularization outcomes. In conclusion, taking into account one’s predisposition to PAD, i.e., DNA polymorphisms and miRNAs, together with circulating inflammatory and coagulation markers, holds promise for more accurate prediction models and personalized therapeutic options.

The Clinical Utility of D-Dimer and Prothrombin Fragment (F1+2) for Peripheral Artery Disease: A Prospective Study

D-dimer and prothrombin fragment (F1+2) levels are elevated in patients with peripheral artery disease (PAD). We examined their prognostic potential in predicting decreasing ABI and major adverse limb events (MALE). A total of 206 patients were recruited from St. Michael’s Hospital and followed for two years. Baseline plasma concentrations of D-dimer and F1+2 were recorded. Pearson’s correlation was used to assess the correlation between the biomarkers and ABI at year 2. During follow-up, multivariable Cox proportional hazard analysis was performed to investigate their role in predicting decreasing ABI (defined as change in ABI > −0.15) and MALE (defined as the need for arterial intervention or major limb amputation). Cumulative survival was assessed using Kaplan−Meier analysis. Baseline D-dimer and F1+2 levels were elevated in PAD patients (median (IQR) 1.34 (0.80−2.20) for D-dimer and 3.60 (2.30−4.74) for F1+2; p = 0.001) compared to non-PAD controls (median (IQR) 0.69 (0.29−1.20) for D-dimer and 1.84 (1.17−3.09) for F1+2; p = 0.001). Both markers were negatively correlated with ABI at year 2 (r = −0.231 for D-dimer, r = −0.49 for F1+2; p = 0.001). Cox analysis demonstrated F1+2 and D-dimer to be independent predictors of PAD status (HR = 1.27, 95% CI = 1.15−1.54; p = 0.013 for D-dimer and HR = 1.28, 95% CI = 1.14−1.58; p = 0.019 for F1+2). Elevated baseline concentrations of D-dimer and F1+2 were associated with high incidence of decreasing ABI and 1- and 2-year event-free survival (62% and 86%, respectively). Combined analysis of D-dimer and F1+2 provides important prognostic information that facilitates risk stratification for future disease progression and MALE outcomes in patients with PAD.

Regenerative Effects of Hypoxia Primed Flowable Placental Formulation in Muscle and Dermal Injury

The placental tissue, due to its angiogenic, anti-inflammatory, antioxidative, antimicrobial, and anti-fibrotic properties, has become a compelling source towards a solution for several indications in regenerative medicine. However, methods to enhance and capture the therapeutic properties with formulations that can further the applications of viable placental tissue have not been explored. In this study, we investigated the regenerative effects of a hypoxia primed flowable placental formulation (FPF), composed of amnion/chorion and umbilical tissue, in two in vivo injury models. Laser Doppler data from rodent ischemia hindlimbs treated with FPF revealed significant tissue perfusion improvements compared to control ischemic hindlimbs. To further corroborate FPF’s effects, we used a rodent ischemic bipedicle skin flap wound model. FPF treatment significantly increased the rate of wound closure and the quality of wound healing. FPF-treated wounds displayed reduced inflammation and an increase in angiogenesis. Furthermore, quantitative PCR and next-generation sequencing analysis confirmed these changes in the FPF-treated group at both the gene and transcriptional level. The observed modulation in miRNAs was associated with angiogenesis, regulation of inflammatory microenvironment, cell migration and apoptosis, reactive oxygen species generation, and restoring epithelial barrier function, all processes involved in impaired tissue healing. Taken together, these data validate the tissue regenerative properties of the flowable placental formulation configuration tested.

Plasma Methylglyoxal Levels Are Associated With Amputations and Mortality in Severe Limb Ischemia Patients With and Without Diabetes

OBJECTIVE

Diabetes is a risk factor for severe limb ischemia (SLI), a condition associated with high mortality, morbidity, and limb loss. The reactive glucose-derived dicarbonyl methylglyoxal (MGO) is a major precursor for advanced glycation end products (AGEs) and a potential driver of cardiovascular disease. We investigated whether plasma MGO levels are associated with poor outcomes in SLI.

RESEARCH DESIGN AND METHODS

We measured plasma levels of MGO, free AGEs, and d-lactate, the detoxification end product of MGO, with ultraperformance liquid chromatography-tandem mass spectrometry at baseline in 160 patients (64.8 ± 13.3 years, 67.5% male, 37.5% with diabetes) with no-option SLI and recorded major adverse outcomes (n = 86, comprising n = 53 deaths and n = 49 amputations [first event counted]) over the 5-year follow-up. Data were analyzed with linear or Cox regression, after Ln-transformation of the independent variables, adjusted for sex, age, trial arm, diabetes, estimated glomerular filtration rate, systolic blood pressure, cholesterol levels, and BMI. Associations are reported per 1 SD plasma marker.

RESULTS

Higher plasma MGO levels were associated with more adverse outcomes (relative risk 1.44; 95% CI 1.11-1.86) and amputations separately (1.55; 1.13-2.21). We observed a similar but weaker trend for mortality (1.28; 0.93-1.77). The MGO-derived AGE N^ε-(carboxyethyl)lysine was also associated with more adverse outcomes (1.46; 1.00-2.15) and amputations (1.71; 1.04-2.79). d-Lactate was not associated with adverse incident outcomes. Higher plasma MGO levels were also associated with more inflammation and white blood cells and fewer progenitor cells.

CONCLUSIONS

Plasma MGO levels are associated with adverse outcomes in SLI. Future studies should investigate whether MGO-targeting therapies improve outcomes in SLI.

External validation of the Vascular Quality Initiative prediction model for survival in no-option chronic limb-threatening ischemia patients

OBJECTIVE

Chronic limb-threatening ischemia (CLTI) is associated with high morbidity and mortality rates. More than 50% of all CLTI patients die within 5 years after presentation. Patient-specific survival prediction is critical for informing treatment strategies, even for those without a clear option for revascularization. We validated a survival prediction model, developed in a revascularized Vascular Quality Initiative (VQI) cohort, in a Western European no-option CLTI cohort.

METHODS

The VQI survival prediction model was applied to the validation cohort (N = 150) to compare estimated mortality and observed mortality at 2 years after baseline. Performance of the VQI model was tested by evaluating discrimination using the receiver operating characteristic area under the curve and calibration using the Hosmer-Lemeshow goodness-of-fit test.

RESULTS

The 2-year survival rate was 79% in the validation cohort compared with 83% in the VQI cohort. Baseline characteristics were significantly different for 13 of 17 variables. The C statistic was 0.86 (95% confidence interval, 0.78-0.95), which indicates good discrimination. The Hosmer-Lemeshow goodness-of-fit test had a P value of .30, which indicates good fit.

CONCLUSIONS

This is the first external validation of the VQI survival prediction model. The good model performance suggests that this model can be used in different CLTI populations, including no-option CLTI, and underlines its contributory role in this challenging population.

Interferon gamma-induced protein 10 (IP-10) and cardiovascular disease in African Americans

Biomarkers of chronic inflammation (such as C-reactive protein) have long been associated with cardiovascular disease and mortality; however, biomarkers involved in antiviral cytokine induction and adaptive immune system activation remain largely unexamined. We hypothesized the cytokine interferon gamma inducible protein 10 (IP-10) would be associated with clinical and subclinical cardiovascular disease and all-cause mortality in African Americans. We assessed these associations in the Jackson Heart Study (JHS) cohort and the REasons for Geographic and Racial Differences in Stroke (REGARDS) study. There was a modest association of IP-10 with higher odds of left ventricular hypertrophy (OR = 1.20 (95% confidence interval (CI) 1.03, 1.41) per standard deviation (SD) higher natural log-transformed IP-10 in JHS). We did not observe associations with ankle brachial index, intima-media thickness, or arterial calcification. Each SD higher increment of ln-transformed IP-10 concentration was associated with incident heart failure (hazard ratio (HR) 1.26; 95% CI 1.11, 1.42, p = 4x10-4) in JHS, and with overall mortality in both JHS (HR 1.12 per SD, 95% CI 1.03, 1.21, p = 7.5x10-3) and REGARDS (HR 1.31 per SD, 95% CI 1.10, 1.55, p = 2.0 x 10-3), adjusting for cardiovascular risk factors and C-reactive protein. However, we found no association between IP-10 and stroke or coronary heart disease. These results suggest a role of IP-10 in heart failure and mortality risk independent of C-reactive protein. Further research is needed to investigate how the body's response to chronic viral infection may mediate heart failure and overall mortality risk in African Americans.