Summary
Background
Osteoprotegerin plays a critical role in the pathogenesis of atherosclerosis. Elevated osteoprotegerin concentrations have been reported in microvascular complications of diabetes. Patients with diabetes are at increased risk of macrovascular complications, particularly peripheral artery disease (PAD).
Aim
To investigate the association between osteoprotegerin concentration and PAD in diabetes.
Methods
In a cross-sectional setting, patients with type 2 diabetes for > 5 years and no apparent diabetic foot ulcer were recruited. Patients underwent colour Doppler ultrasonography of lower limbs and were designated PAD+ if arterial narrowing was detected. Ankle-brachial index (ABI) was measured. Serum osteoprotegerin concentrations were determined.
Results
Ninety-eight patients (47 PAD+, 51 PAD–) were recruited. Osteoprotegerin concentrations (median [interquartile range]) were significantly higher in PAD+ versus PAD– patients (0.80 [0.50–1.95] ng/mL vs 0.30 [0.25–0.40] ng/mL; P < 0.001). In logistic regression, log-osteoprotegerin was a predictor of PAD in univariate and multivariable analyses. In the final multivariable model, adjusting for age, sex, body mass index, smoking, hypertension, glycaemic control, lipid profile, renal function and C-reactive protein, one standard deviation increase in log-osteoprotegerin was associated with a more than twofold increase in the risk of having PAD (odds ratio 2.26, 95% confidence interval 1.50–3.40). In PAD+ patients, osteoprotegerin was a significant predictor of disease severity, determined by ABI and percentage of vessel occlusion in univariate and multivariable models.
Conclusions
Osteoprotegerin concentrations are increased in patients with diabetes and PAD. Osteoprotegerin is an independent predictor of the presence and severity of PAD in diabetic patients.
Résumé
Justification
L’ostéoprotégérine joue un rôle critique dans la pathogénie de l’athérosclérose. Des concentrations élevées d’ostéoprotégérine sont associées aux complications microvasculaires du diabète. Les patients diabétiques sont à risque accru de complications macrovasculaires en particulier d’artériopathie oblitérante des membres inférieurs (AOMI).
Objectif
Évaluer l’association entre les concentrations d’ostéoprotégérine et l’artériopathie oblitérante des membres inférieurs chez les patients diabétiques.
Méthode
Cette étude transversale a inclus des patients ayant un diabète de type 2 datant de plus de 5 ans et pas de pied diabétique. Les patients ont eu une échographie Doppler des membres inférieurs et ont été caractérisés comme ayant une artériopathie oblitérante des membres inférieurs en présence d’une sténose artérielle. L’index de pression systolique a été mesuré. Les concentrations d’ostéoprotégérine ont été déterminées.
Résultats
Quatre-vingt-dix-huit patients (47 AOMI+, 51 AOMI–) ont été inclus. Les concentrations d’ostéoprotégérine (valeur médiane, interquartile range) ont été significativement plus élevées chez les patients à AOMI+ versus les patients AOMI– (0,80 (0,50–1,95) ng/mL versus 0,30 (0,25–0,40) ng/mL, p < 0,001). En régression logistique, le log ostéoprotégérine était un prédicteur de l’AOMI en analyses univariée et multivariée. Dans le modèle d’analyse multivariée final, ajusté sur l’âge, le sexe, l’indice de masse corporelle, le tabac, l’hypertension artérielle, le contrôle glycémique, le profil lipidique, la fonction rénale et la CRP, une augmentation d’une déviation standard de la valeur log-ostéoprotégérine est associée avec une augmentation d’au moins deux fois le risque de présenter une AOMI (odds ratio 2,26), IC 95 % 1,50–3,40). Chez les patients AOMI+, l’ostéoprotégérine est un prédicteur significatif de la sévérité de la maladie artérielle périphérique déterminée par l’index de pression systolique et la sévérité de l’occlusion artérielle en analyse univariée et mutivariée.
Conclusion
Les concentrations d’ostéoprotégérine sont augmentées chez les patients diabétiques ayant une AOMI. L’ostéoprotégérine est un prédicteur indépendant de la présence et de la sévérité d’une AOMI chez les patients diabétiques.
Background
Peripheral artery disease (PAD) is characterized by gradual and progressive narrowing and subsequent occlusion of the arteries of the lower extremities secondary to atherosclerosis . Potentially life-threatening in cases with complete vessel blockade, PAD is associated with significant pain, loss of function and disability . Given the shared cause, patients with PAD are also at increased risk of cardiovascular and cerebrovascular diseases .
PAD is a major risk factor for lower-extremity amputation, especially in patients with diabetes . Indeed, diabetes carries an additional risk for having PAD . Determining the exact prevalence of PAD in patients with diabetes has been difficult, but available estimates suggest that about 10.8% of diabetic patients have PAD, roughly three times as many as non-diabetic individuals . If a patient is diagnosed with PAD, there is a 26.4% chance of diabetes being present . Furthermore, in patients with diabetes, PAD assumes a more notorious trajectory, leading to more amputations and a higher risk of mortality .
Osteoprotegerin, a secretory basic glycoprotein, is a member of the tumour necrosis factor receptor superfamily and acts as an inhibitor of bone resorption . Osteoprotegerin is produced by various organs and tissues, such as the lungs, intestines, kidneys, bones and the cardiovascular system (heart, arteries and veins), and also by haematopoietic and immune cells ; it acts as an important regulatory molecule in the vasculature . Osteoprotegerin-deficient mice develop severe osteoporosis and calcification of the aorta and renal artery. Interestingly, the process follows a pattern similar to that of the medial calcification commonly seen in vascular complications of diabetes . Serum osteoprotegerin concentrations are associated with the severity of coronary artery stenosis, and a modest correlation is also found with the number of involved vessels . Moreover, Ziegler et al. reported a positive correlation between serum concentrations of osteoprotegerin and severity of PAD .
Previous studies have shown that plasma concentrations of osteoprotegerin are increased in diabetic versus non-diabetic individuals . Elevated concentrations of osteoprotegerin have also been reported in diabetic patients with non-proliferative retinopathy or microalbuminuria . Despite a confirmed role for osteoprotegerin in macro- and microvascular complications of diabetes, the possibility of a link between osteoprotegerin and PAD in patients with diabetes has received little attention. Therefore, the present study was designed to investigate whether serum osteoprotegerin concentrations are associated with PAD in patients with type 2 diabetes.
Methods
Patients
In the present cross-sectional study, consecutive patients with type 2 diabetes who visited the outpatient diabetes clinic of Vali-Asr Hospital (a teaching hospital affiliated with Tehran University of Medical Sciences, Tehran, Iran) from March 2012 to March 2013, were assessed and, if eligible, were enrolled. Patients were included if they had had type 2 diabetes for > 5 years and agreed to undergo colour Doppler ultrasonographic evaluation of the lower extremities. Diabetes was diagnosed according to the criteria delineated by the American Diabetes Association . As the diagnosis had been made at least 5 years earlier, the recently annexed HbA 1c criterion was not employed. Patients were not included if they were diagnosed with chronic diseases of the liver, lungs or kidneys, or if they had had a recent acute infection. Patients were also ineligible if they were taking vitamin D, calcium supplements, bisphosphonates or corticosteroids. A complete medical history was obtained and a thorough physical examination performed. Patients were then sent for ultrasonographic evaluation of the lower extremities in the hospital’s radiology department. Written informed consent was obtained from all participants. All procedures dealing with human subjects were conducted in accordance with the latest revision of the Declaration of Helsinki. The ethics committee of the hospital approved the study protocol.
Assessments
Physical examination included the measurement of height and weight and determination of ankle-brachial index (ABI). Height was measured with the patient standing erect in front of a standard stadiometer and was recorded to the nearest 0.1 cm. Weight was measured with subjects wearing only light clothing, using a calibrated scale, and was recorded to the nearest 0.1 kg. Body mass index (BMI) was calculated as weight divided by height squared (kg/m 2 ). ABI was measured with patient lying in the supine position. After at least 10 minutes of resting, brachial systolic blood pressure was measured with an appropriately sized cuff and a Doppler ultrasonographic probe being placed in the antecubital fossa. Systolic blood pressure was measured from both arms and the higher of the two readings was designated as brachial pressure. An appropriately sized cuff was then placed around the leg between malleolus and the calf. Using a similar technique, systolic blood pressure was measured by placing the probe on the anterior tibialis and dorsalis pedis arteries, and the point of signal reappearance when deflating the cuff was recorded. The higher of the two measurements was then regarded as the ankle pressure. Finally, ABI was calculated by dividing ankle by brachial systolic pressures.
All ultrasonographic evaluations were performed by a single experienced radiologist. Colour Doppler ultrasonography was used to detect PAD and its severity. Peak systolic velocity (PSV) was determined by using a 7 MHz convex transducer (SonoScape, Shenzhen, China) in each arterial segment. The PSV ratio was then defined as the ratio of the PSV at the site of measurement divided by the PSV in the proximal (approximately 4 cm) artery. A PSV ratio of 2.4 was used to define significant stenosis, corresponding to > 50% narrowing in the diameter of the arterial lumen. For severity of stenosis, reference PSV ratio values developed by Ranke et al. were used. Based on their report, PSV ratio values of ≥2.9, ≥3.4, ≥4.7 and ≥7.0 correlated with ≥60%, ≥70%, ≥80% and ≥90% stenosis, respectively, in angiographic assessment .
Laboratory evaluations
Antecubital venous blood samples were collected after at least 12 hours of fasting. Serum concentrations of fasting plasma glucose were determined using the glucose oxidase method. Percentage of glycated haemoglobin A 1c (HbA 1c ) was determined using the high performance liquid chromatography method. The lipid profiles of patients, including total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and triglycerides, were determined using enzymatic methods (ParsAzmun, Karaj, Iran). The Jaffe method was employed to assess serum concentrations of creatinine (ParsAzmun, Karaj, Iran). In PAD+ patients, high sensitivity C-reactive protein (hsCRP) concentrations were assessed with commercial kits (Diagnostics Biochem Canada Inc., Dorchester, ON, Canada), using the enzyme-linked immunosorbent assay method. Serum calcium and phosphorus concentrations were measured with an autoanalyser (Hitachi 704, Tokyo, Japan). Serum osteoprotegerin concentrations were determined using a human osteoprotegerin enzyme-linked immunosorbent assay kit (Cusabio, Wuhan, China).
Statistical analysis
Data were analysed using SPSS version 16 for Windows (SPSS Inc., Chicago, IL, USA). Continuous variables with normal distribution are presented as means ± standard deviations and categorical variables are presented as proportions. Baseline characteristics of patients with and without PAD were compared using an independent t test or the chi-square test. Initially, given the non-normal distribution and right-sided skewness, osteoprotegerin concentrations were presented as medians (25th–75th percentiles) and were compared between patients with and without PAD using the Mann-Whitney U test. For all subsequent parametric analyses, a logarithmic transformation was done and log-osteoprotegerin was used instead. To assess the association between log-osteoprotegerin and the presence of PAD, univariate and multivariable logistic regression models were constructed. Odds ratios and 95% confidence intervals were calculated in each model per one standard deviation increase in log-osteoprotegerin. To investigate the association between osteoprotegerin and PAD severity, linear regression was used in the subset of PAD+ patients. In univariate and multivariable regression models, ABI (or the percentage of arterial occlusion) served as the dependent variable and the standardized beta coefficient for log-osteoprotegerin was calculated. In all tests, the null hypothesis was rejected where P was < 0.05.
Results
A total of 98 patients (51 PAD–, 47 PAD+) were included in the analysis. Baseline characteristics of enrolled patients are presented in Table 1 , according to PAD group. The average age of the participants was 64 years (range, 36–89 years) and was not different between the two groups. Patients in the PAD–group were more likely to be female (65% vs 45%); however, the difference did not reach statistical significance. Mean BMI was also similar in the two groups. Patients with PAD were more likely to have hypertension and also to have a positive history of PAD in their first-degree relatives; in both cases the difference was not statistically significant. Patients were diagnosed with type 2 diabetes for a minimum and maximum of 5 and 30 years, respectively. Duration of diabetes was similar in the two groups. Significantly better glycaemic control was achieved in PAD– patients; on average, their HbA 1c values were 0.9% lower than in those with PAD ( P = 0.016). A worse lipid profile was observed in PAD+ patients; they had higher concentrations of serum triglycerides, total cholesterol and LDL-C, but not HDL-C ( Table 1 ). No patient had a serum creatinine concentration > 1.4 mg/dL. On average, patients in the PAD+ group had higher serum creatinine concentrations ( P = 0.046). Calcium and phosphorus concentrations were similar in the two groups. Osteoprotegerin concentrations were significantly higher in PAD+ versus PAD– patients (0.80 [0.50–1.95] ng/mL vs 0.30 [0.25–0.40] ng/mL; P < 0.001). Osteoprotegerin concentrations were similar in women and men (0.40 [0.30–0.73] ng/mL in women and 0.50 [0.30–0.80] ng/mL in men; P = 0.60).
