Current and future drug therapies for claudication

Chelation therapy for atherosclerotic cardiovascular disease

BACKGROUND

Chelation therapy is promoted and practiced around the world as a form of alternative medicine in the treatment of atherosclerotic cardiovascular disease. It has been suggested as a safe, relatively inexpensive, non-surgical method of restoring blood flow in atherosclerotic vessels. However, there is currently limited high-quality, adequately-powered research informing evidence-based medicine on the topic, specifically regarding clinical outcomes. Due to this limited evidence, the benefit of chelation therapy remains controversial at present. This is an update of a review first published in 2002.

OBJECTIVES

To assess the effects of ethylene diamine tetra-acetic acid (EDTA) chelation therapy versus placebo or no treatment on clinical outcomes among people with atherosclerotic cardiovascular disease.

SEARCH METHODS

For this update, the Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase and Cumulative Index to Nursing and Allied Health Literature (CINAHL) databases, the World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials register to 6 August 2019. We searched the bibliographies of the studies retrieved by the literature searches for further trials.

SELECTION CRITERIA

We included studies if they were randomised controlled trials of EDTA chelation therapy versus placebo or no treatment in participants with atherosclerotic cardiovascular disease. The main outcome measures we considered include all-cause or cause-specific mortality, non-fatal cardiovascular events, direct or indirect measurement of disease severity, and subjective measures of improvement or adverse events.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed trial quality using standard Cochrane procedures. A third author considered any unresolved issues, and we discussed any discrepancies until a consensus was reached. We contacted study authors for additional information.

MAIN RESULTS

We included five studies with a total of 1993 randomised participants. Three studies enrolled participants with peripheral vascular disease and two studies included participants with coronary artery disease, one of which specifically recruited people who had had a myocardial infarction. The number of participants in each study varied widely (from 10 to 1708 participants), but all studies compared EDTA chelation to a placebo. Risk of bias for the included studies was generally moderate to low, but one study had high risk of bias because the study investigators broke their randomisation code halfway through the study and rolled the placebo participants over to active treatment. Certainty of the evidence, as assessed by GRADE, was generally low to very low, which was mostly due to a paucity of data in each outcome's meta-analysis. This limited our ability to draw any strong conclusions. We also had concerns about one study's risk of bias regarding blinding and outcome assessment that may have biased the results. Two studies with coronary artery disease participants reported no evidence of a difference in all-cause mortality between chelation therapy and placebo (risk ratio (RR) 0.97, 95% CI 0.73 to 1.28; 1792 participants; low-certainty). One study with coronary artery disease participants reported no evidence of a difference in coronary heart disease deaths between chelation therapy and placebo (RR 1.02, 95% CI 0.70 to 1.48; 1708 participants; very low-certainty). Two studies with coronary artery disease participants reported no evidence of a difference in myocardial infarction (RR 0.81, 95% CI 0.57 to 1.14; 1792 participants; moderate-certainty), angina (RR 0.95, 95% CI 0.55 to 1.67; 1792 participants; very low-certainty), and coronary revascularisation (RR 0.46, 95% CI 0.07 to 3.25; 1792 participants). Two studies (one with coronary artery disease participants and one with peripheral vascular disease participants) reported no evidence of a difference in stroke (RR 0.88, 95% CI 0.40 to 1.92; 1867 participants; low-certainty). Ankle-brachial pressure index (ABPI; also known as ankle brachial index) was measured in three studies, all including participants with peripheral vascular disease; two studies found no evidence of a difference in the treatment groups after three months after treatment (mean difference (MD) 0.02, 95% CI -0.03 to 0.06; 181 participants; low-certainty). A third study reported an improvement in ABPI in the EDTA chelation group, but this study was at high risk of bias. Meta-analysis of maximum and pain-free walking distances three months after treatment included participants with peripheral vascular disease and showed no evidence of a difference between the treatment groups (MD -31.46, 95% CI -87.63 to 24.71; 165 participants; 2 studies; low-certainty). Quality of life outcomes were reported by two studies that included participants with coronary artery disease, but we were unable to pool the data due to different methods of reporting and varied criteria. However, there did not appear to be any major differences between the treatment groups. None of the included studies reported on vascular deaths. Overall, there was no evidence of major or minor adverse events associated with EDTA chelation treatment.

AUTHORS' CONCLUSIONS

There is currently insufficient evidence to determine the effectiveness or ineffectiveness of chelation therapy in improving clinical outcomes of people with atherosclerotic cardiovascular disease. More high-quality, randomised controlled trials are needed that assess the effects of chelation therapy on longevity and quality of life among people with atherosclerotic cardiovascular disease.

L-propionyl-carnitine protects tissues from ischaemic injury in an 'in vivo' human ischaemia-reperfusion model

OBJECTIVE

To assess the acute effects of L-propionyl-carnitine (LPC) on vaso-motion, tissue perfusion and tissue acidosis during an ischaemia-reperfusion test in patients with intermittent claudication.

DESIGN

Open pharmacodynamic study.

STUDY PARTICIPANTS

Sixteen male patients with intermittent claudication (mean absolute claudication distance 193.19 ± 51.51m).

INTERVENTIONS

Intravenous infusion of LPC 600mg.

MAIN OUTCOME MEASURES AND RESULTS

Laser-Doppler perfusion units and power spectrum, transcutaneous oxygen pressure (TcPO(2)) and transcutaneous carbon dioxide pressure (TcPCO(2)) were measured at baseline, during ischaemia (which was induced by means of an inflated pneumatic cuff wrapped around the calf) and during reperfusion, before and after LPC infusion. Perfusion units and TcPO(2) did not change significantly after LPC infusion compared with pretreatment values. Conversely, mean laser-Doppler power spectrum, which was 0.20 units at rest and 1.13 during reperfusion before treatment, increased significantly to 0.89 and 2.24, respectively, after LPC infusion (p = 0.01 and p = 0.00074, respectively, vs pretreatment values). LPC had no significant effects on resting TcPCO(2), but induced a significant decrease in TcPCO(2) measured at hypoxia point (96.9mm Hg before treatmentvs 90.2mm Hg after treatment; p = 0.001) and during reperfusion (115.9vs 103.5mm Hg, respectively; p = 0.0006).

CONCLUSIONS

These results show that LPC protects tissues from ischaemic injury by improving arteriolar function and reducing acidosis, without affecting arterial inflow. This may explain the beneficial effects of LPC in patients with intermittent claudication and suggests a potential use of this drug in other stages of peripheral arterial disease and in patients undergoing surgery.

Cilostazol increases tissue blood flow in contracting rabbit gastrocnemius muscle

BACKGROUND

The mechanisms underlying the ability of cilostazol to improve walking distance in patients with intermittent claudication (IC) are not fully understood, but may be related to its phosphodiesterase type 3 (PDE3) and adenosine uptake inhibition. In the present study the effect of cilostazol on blood flow and interstitial adenosine concentration was compared with that of the PDE3 inhibitor, milrinone, and the adenosine uptake inhibitor, draflazine.

METHODS AND RESULTS

Rabbit gastrocnemius muscle blood flow was measured under resting, contracting and ischemic conditions. Interstitial adenosine was sampled by microdialysis. None of the drugs affected tissue blood flow at rest. Blood flow in electrically stimulated muscle was 2- to 3-fold higher in vehicle-, milrinone- and draflazine-treated animals. However, cilostazol caused an 8-fold increase. Ligation of the femoral artery decreased blood flow in the stimulated muscle in all groups to a similar degree. Cilostazol and draflazine increased the dialysate adenosine concentration during the first 10 min of muscle contraction, but had no effect during ischemia, most likely because of the high AMP deaminase activity in skeletal muscle.

CONCLUSIONS

Cilostazol increases blood flow in the gastrocnemius muscle during contraction and it is this effect that may be partially responsible for the improved walking distance in IC patients. (Circ J 2010; 74: 181 - 187).

Levo-Propionyl-Carnitine Improves the Effectiveness of Supervised Physical Training on the Absolute Claudication Distance in Patients With Intermittent Claudication

The mechanisms by which supervised physical training improves walking ability in patients with intermittent claudication (IC) are microcirculatory, rheological, and metabolic. The main mechanism of levo-propionylcarnitine (LPC) is metabolic; it increases the walking ability in claudicants, providing an additional energy to the ischemic muscle by an anaplerotic activity. Therefore, the current study was carried out to ascertain whether the combined treatment has a synergistic effect. The results confirm the effectiveness of supervised physical training in patients with IC, and we recommend the use of LPC during the exercise training program, at least in patients with severe claudication. Finally, underlining the similar mechanisms of physical training and LPC treatment, the study suggests that a cycle of LPC infusions could be advised in patients with severe claudication who cannot be included, for various reasons, in an exercise rehabilitation program.

Effect of PLC on functional parameters and oxidative profile in type 2 diabetes-associated PAD

OBJECTIVE

To investigate the effects of propionyl l-carnitine (PLC) on clinical and functional parameters, and markers of the overall oxidation state in patients with peripheral arterial disease (PAD) associated with non-insulin-dependent diabetes mellitus (NIDDM).

DESIGN AND SETTING

Randomised, double-blind, clinical trial, conducted in the Unit of Medical Angiology of the University of Catania.

PATIENTS AND INTERVENTIONS

Seventy-four patients with NIDDM-associated PAD were treated with PLC (2 g/day) or placebo for 12 months.

MAIN OUTCOME MEASURES

Ankle/brachial index (ABI) and the distance of pain-free walking were evaluated at baseline, 6 and 12 months. Malondialdehyde, 4-hydroxynonenal, oxidation time of low-density lipoproteins, and nitrite/nitrate ratio were measured as indices of the overall oxidation profiles at baseline and 12 months.

RESULTS

In the PLC group, ABI progressively increased (0.78, 0.83, and 0.88 at 0, 6 and 12 months, respectively). The distance of pain-free walking also improved (366.4, 441.9 and 519.8 m, respectively). In the placebo group, these parameters were relatively unchanged. Significant improvements in all parameters of the oxidative profile were seen in the PLC-treated group, with only minor variations observed in the placebo group.

CONCLUSIONS

These results suggest that adjunct therapy with PLC may be warranted in type 2 diabetes-associated PAD.

Effects of propionyl-carnitine in patients with type 2 diabetes and peripheral vascular disease: results of a pilot trial

OBJECTIVE

To assess the efficacy of propionyl-carnitine (PC) in patients with type 2 diabetes and peripheral arterial disease (PAD).

PATIENTS AND METHODS

This was an open pharmacodynamic study. Twenty-four obese patients with type 2 diabetes and PAD (stage IIb) were enrolled in the study. After an initial run-in period of 7 days on a low-calorie diet (1600 +/- 150 kcal/day), patients received intravenous PC (600mg in 100mL saline solution Na/K 0.9%) twice daily for 10 days (T1).

RESULTS

Treatment with PC produced statistically significant increases in maximal walking distance (30%; p < 0.05) and initial claudication distance (15%; p < 0.05) in 15 and eight patients, respectively. In addition, a decrease in dosage of oral antihyperglycaemic agents was observed in 21 patients at T1. No PC-related adverse effects were reported.

CONCLUSIONS

This study showed that acute intravenous administration of PC in patients with type 2 diabetes with PAD improved PAD-related symptoms as well as glycaemic control.

Effects of OP-1206 alpha-CD on walking dysfunction in the rat neuropathic intermittent claudication model: comparison with nifedipine, ticlopidine and cilostazol

The systemic treatment effects of OP-1206 alpha-CD (17S-20-dimethyl-trans-delta 2-PGE1 alpha-cyclodextrin clathrate), a prostaglandin E1 (PGE1) analogue, on walking dysfunction, spinal cord blood flow (SCBF) and skin blood flow (SKBF) were assessed in the rat neuropathic intermittent claudication (IC) model in comparison with nifedipine (dimethyl 1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridinedicarboxylate), ticlopidine (5-[(2-chlorophenyl)methyl]-4,5,6,7-tetrahydrothieno[3,2-C]pyridine hydrochloride) and cilostazol (6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)-butoxy]-3,4-dihydro-2(1H)-quinolinone). Two pieces of silicone rubber strips were placed in the lumbar (L4 and L6) epidural space in rats. After surgery, walking function was measured using a treadmill apparatus. SCBF and SKBF were measured using a laser-Doppler flow meter. Drugs were administered orally twice a day for 11 days from day 3 post-surgery. Treatment with OP-1206 alpha-CD significantly improved walking dysfunction on days 5, 7 and 14, and improved SCBF on day 14 post-surgery. SKBF remained unaffected. Treatment with nifedipine, ticlopidine or cilostazol had no significant effects on any of the parameters measured in this model. These data suggest that the therapeutic effect of OP-1206 alpha-CD is primarily mediated by the improved local SCBF at the territory of spinal stenosis and not due to improvement of peripheral perfusion and/or antiplatelet activity.

A method for evaluating drug effects on intermittent claudication using a treadmill in rats with unilateral hindlimb artery occlusion

INTRODUCTION

We have developed an in vivo experimental model for evaluating peripheral arterial insufficiency and predicting the efficacy of drugs on intermittent claudication (IC). We found that rats that had been running normally on a treadmill developed a gait disturbance when a hindlimb artery was unilaterally occluded. We hypothesized that the distance run before gait disturbance developed (DGD) in rats with occlusion of a hindlimb artery might be an appropriate index of the severity of peripheral insufficiency, and that the model might serve as a test bed for evaluating drug efficacy. To prove this hypothesis, we examined whether DGD was determined by severity of hindlimb ischemia. Furthermore, we also examined whether cilostazol, which has been proved to have ameliorative effects in patients with IC, increased DGD.

METHODS

To vary the severity of ischemia, either the superficial femoral artery, the distal portion of the iliac artery, or the proximal portion of iliac artery was unilaterally occluded. After a recovery period, these rats were subjected to a treadmill test (15 m/min and 15% incline) to determine DGD and examine the effect of cilostazol on DGD.

RESULTS

DGD was the longest and shortest in rats with superficial femoral artery and proximal portion of iliac artery occlusion, respectively. Intermediate DGD was observed in rats with distal portion of iliac artery occlusion. These data suggest that DGD is correlated with the severity of hindlimb ischemia. Two weeks or longer administration of cilostazol 30 and 100 mg/kg twice a day evoked a significant increase in DGD.

DISCUSSION

Peripheral arterial insufficiency and its modulation by drugs can be evaluated in rats with unilateral hindlimb artery occlusion, on a treadmill, by measuring DGD.

Current status of mind-body interventions for vascular complications of diabetes

Impaired peripheral blood flow causes complications, disabilities, expenses, and deaths among persons with diabetes mellitus. Many individuals suffer from lower-extremity pain, reduced functional status, and impaired quality of life. Current conventional treatments include lifestyle modification, exercise, medication, and surgery. However, these approaches are often impractical or insufficient. Thermal biofeedback, however, alone or in conjunction with other mind-body techniques, improves peripheral circulation, pain, neuropathy, ulcer healing, ambulatory activity, and quality of life. It is noninvasive, inexpensive, and consistent with community-based approaches to diabetes self-management. As an adjunct to the medical management of diabetes, thermal biofeedback may help ameliorate some of the vascular complications.

Failure of pentoxifylline or cilostazol to improve blood and plasma viscosity, fibrinogen, and erythrocyte deformability in claudication

Peripheral artery disease is associated with altered blood rheologic properties, including increased viscosity and decreased red blood cell (RBC) deformability. Pentoxifylline and cilostazol are available therapies for intermittent claudication. Improvement of blood viscosity and erythrocyte deformability have been cited as potential mechanisms of action for pentoxifylline. Cilostazol is a new drug with antiplatelet and vasodilating activity, but the mechanism by which it promotes an improvement in walking is not known. This study was performed to evaluate and compare the hemorheologic effects of pentoxifylline and cilostazol on viscosity, fibrinogen levels, and erythrocyte deformability when administered to adults with moderate to severe claudication. A double-blind, controlled study was conducted and included 59 patients (46 male, 13 female; mean age 65 yr) randomized to pentoxifylline 400 mg orally thrice daily (n=20), cilostazol 100 mg orally twice daily (n=19), or placebo (n=20); all subjects were observed for 24 weeks. Walking ability was assessed before, during, and at the conclusion of treatment by standard constant speed, variable grade treadmill testing. Erythrocyte deformability was measured by passage of washed RBCs, 10% hematocrit in phosphate buffered saline (PBS), through a polycarbonate membrane with 4.7 to 5.0 microm pores. Whole blood and plasma viscosity were measured using a cone/plate viscometer at variable shear rates (from 4.5 to 450 sec(-1)). Erythrocyte sedimentation rate was measured by a modified Westergren technique. Fibrinogen was assayed by a commercial reference laboratory. Plasma viscosities did not change significantly in any treatment group. Within-group comparisons demonstrated a significant (p<0.01) drop in whole blood viscosity (week 24 compared with week 0) for cilostazol-treated subjects (at shear rates of 45, 90, 225, and 450 sec(-1)), but these changes were not significantly different from those in the placebo group. There were no significant changes in whole blood viscosity for subjects treated with pentoxifylline or placebo. There were no significant changes in erythrocyte deformability, fibrinogen, or erythrocyte sedimentation rate. A trend toward improved walking distances was noted for both pentoxifylline and cilostazol in comparison with placebo. This trend was not correlated with changes in any underlying rheologic parameter. Ex vivo rheologic characteristics of blood from patients with intermittent claudication are not significantly affected by long-term administration of pentoxifylline or cilostazol. Pentoxifylline did not modulate viscosity or red cell deformability, a finding at variance with its putative mechanism of action. Pentoxifylline cannot be differentiated from cilostazol based on specific hemorheologic effects evaluated in this study. Different mechanisms of action for these medications should be considered.

Progression of atherosclerosis in patients with peripheral arterial disease as a function of angiotensin-converting enzyme gene insertion/deletion polymorphism

Angiotensin-converting enzyme insertion/deletion (I/D) gene polymorphism plays a role in determining the inter-individual variability of circulating angiotensin-converting enzyme activity and intracellular angiotensin-converting enzyme levels. Angiotensin-converting enzyme, as a key enzyme in the renin-angiotensin system, catalyzes the activation of the vasoconstricting and proliferation-stimulating angiotensin II and breaks down the vasodilatory peptide bradykinin. It is assumed that the excess supply of angiotensin II (due to the deletion polymorphism of the angiotensin-converting enzyme gene) contributes to endothelial dysfunction and in this way promotes the onset and progression of atherosclerosis. The aim of this study was to test whether the presence of the deletion allele of the angiotensin-converting enzyme gene predisposes a more rapid systemic progression of a preexisting peripheral arterial disease. To this end, the course of disease was surveyed for an average of 5 years in 97 patients who were angiotensin-converting enzyme gene-typed and suffered from a stable stage II peripheral arterial disease according to Fontaine. These patients did not suffer from an additional coronary artery disease, a cerebrovascular disease, or other serious illness. A local progression in the periphery or a systemic progression in the coronary or cerebrovascular areas was regarded as study endpoints. Of the patients, 49.5% showed an atherosclerosis progression during the surveillance period. With II-carriers, a progression was registered in 42.1% and with DD carriers, progression was seen in 59.4%. D/I allele frequencies were seen in patients with progression at a level of 0.60/0.40 vs 0.55/0.45 for patients without progression. The average duration of disease in stable stage II (before progression appeared) amounted to 108 +/- 14 months for II carriers, 88 +/- 8 months for ID carriers, and 92 +/- 11 months for DD carriers (p = 0.21). Based on these findings, the deletion polymorphism of the angiotensin-converting enzyme gene is not an independent risk factor for progression of atherosclerosis in patients with peripheral arterial disease.

Cilostazol (pletal): a dual inhibitor of cyclic nucleotide phosphodiesterase type 3 and adenosine uptake

Cilostazol (Pletal), a quinolinone derivative, has been approved in the U.S. for the treatment of symptoms of intermittent claudication (IC) since 1999 and for related indications since 1988 in Japan and other Asian countries. The vasodilatory and antiplatelet actions of cilostazol are due mainly to the inhibition of phosphodiesterase 3 (PDE3) and subsequent elevation of intracellular cAMP levels. Recent preclinical studies have demonstrated that cilostazol also possesses the ability to inhibit adenosine uptake, a property that may distinguish it from other PDE3 inhibitors, such as milrinone. Elevation of interstitial and circulating adenosine levels by cilostazol has been found to potentiate the cAMP-elevating effect of PDE3 inhibition in platelets and smooth muscle, thereby augmenting antiplatelet and vasodilatory effects of the drug. In contrast, elevation of interstitial adenosine by cilostazol in the heart has been shown to reduce increases in cAMP caused by the PDE3-inhibitory action of cilostazol, thus attenuating the cardiotonic effects. Cilostazol has also been reported to inhibit smooth muscle cell proliferation in vitro and has been demonstrated in a clinical study to favorably alter plasma lipids: to decrease triglyceride and to increase HDL-cholesterol levels. One, or a combination of several of these effects may contribute to the clinical benefits and safety of this drug in IC and other disease conditions secondary to atherosclerosis. In eight double-blind randomized placebo-controlled trials, cilostazol significantly increased maximal walking distance, or absolute claudication distance on a treadmill. In addition, cilostazol improved quality of life indices as assessed by patient questionnaire. One large randomized, double-blinded, placebo-controlled, multicenter competitor trial demonstrated the superiority of cilostazol over pentoxifylline, the only other drug approved for IC. Cilostazol has been generally well-tolerated, with the most common adverse events being headache, diarrhea, abnormal stools and dizziness. Studies involving off-label use of cilostazol for prevention of coronary thrombosis/restenosis and stroke recurrence have also recently been reported.

Physical training for intermittent claudication: a comparison of structured rehabilitation versus home-based training

In a non-randomized, open-label study results after a structured institution-based peripheral arterial occlusive disease (PAD) rehabilitation program were compared with the results of training at home. Three groups were compared: group 1 (n = 19) PAD rehabilitation; group 2 (n = 19) PAD rehabilitation + clopidogrel 75 mg once daily; group 3 (n = 21) home-based training. The training period was 3 months for all groups, which was followed by a 3-month observation phase (without prescribed training). The rehabilitation program consisted of 3 training hours per week. Background variables, demographics, and baseline claudication distances were comparable between groups. After 3 months of training the absolute claudication distances (ACD) improved by 82.7%, 131.4%, and 5.4% for groups 1, 2 and 3. The initial claudication distances (ICD) changed by 163.8%, 200.6%, and 44.4%, respectively. All changes, except the ACD result for group 3, were statistically significant (p < or = 0.05). Structured training groups (1 and 2) performed significantly better than group 3 (p < or = 0.05). When results from groups 1 and 2 were pooled, ACDs changed from 493.3 +/- 218.1 to 1026.0 +/- 468.9 m, delta 546.0 +/- 378.8 m [95% CI 417.8-674.2 ml; p < or = 0.05. ICDs improved from 175.3 +/- 110.8 m to 493.1 +/- 326.7 m, delta 320.8 +/- 315.9 m [95% CI 213.9-427.7 m]; p < or = 0.05. The difference between the pooled mean results of the structured training groups and the results of group 3 amounted to 474.3 m [95% CI 270.2-678.4 m] and 242.4 m [95% CI 99.0-385.7 m], for ACD and ICD, respectively. Structured, supervised PAD rehabilitation is a highly efficacious treatment for intermittent claudication and may be regarded as the present gold standard among conservative treatment options.

Chelation therapy for atherosclerotic cardiovascular disease

BACKGROUND

Chelation therapy is being promoted and practiced all over the world as a form of alternative medicine in the treatment of atherosclerotic cardiovascular disease. It has been recommended as a safe, relatively inexpensive and non-surgical method of restoring blood flow in atherosclerotic vessels. At present the benefit of chelation therapy remains controversial at best.

OBJECTIVES

The objective of this review is to assess the effects of ethylene diamine tetraacetic acid (EDTA) chelation therapy on clinical outcomes among patients with atherosclerotic cardiovascular disease.

SEARCH STRATEGY

The reviewers searched the Cochrane Peripheral Vascular Diseases Group Trials Register, (last searched July 2002), the Cochrane Controlled Trials Register, (Cochrane Library Issue 2, 2002), MEDLINE and EMBASE for published articles and other relevant articles. Studies were also requested through correspondence with known Filipino practitioners of the procedure.

SELECTION CRITERIA

Studies were included if they were randomized controlled trials of EDTA chelation therapy versus placebo or no treatment in patients with atherosclerotic cardiovascular disease. Main outcome measures considered included either total or cause-specific mortality, non-fatal cardiovascular events, direct or indirect measurement of disease severity, subjective measures of improvement or adverse events.

DATA COLLECTION AND ANALYSIS

Two reviewers (MVV, FT) extracted data and assessed trial quality independently. Unresolved issues were considered by a third reviewer (ALD). Discrepancies were discussed until a consensus was reached. Authors were contacted for additional information.

MAIN RESULTS

A total of five studies was included in the review. Mortality, non-fatal events, and cerebrovascular events were not reported in any of the studies. Four of the studies, with a total recruitment rate of 250 participants, showed no significant difference in the following outcomes: direct or indirect measurement of disease severity and subjective measures of improvement. One of the studies, which included only 10 patients, was interrupted prematurely, because of an apparent treatment effect. However, relevant data were not available in the report and have been requested from the authors.

REVIEWER'S CONCLUSIONS

At present, there is insufficient evidence to decide on the effectiveness or ineffectiveness of chelation therapy in improving clinical outcomes of patients with atherosclerotic cardiovascular disease. This decision must be preceded by conducting randomized controlled trials that would include endpoints that show the effects of chelation therapy on longevity and quality of life among patients with atherosclerotic cardiovascular disease.

Interplay between inhibition of adenosine uptake and phosphodiesterase type 3 on cardiac function by cilostazol, an agent to treat intermittent claudication

The authors have recently shown that cilostazol, a type 3 cyclic nucleotide phosphodiesterase (PDE3) inhibitor, has a much weaker positive inotropic effect than milrinone, a PDE3 inhibitor of similar potency. They have also shown that cilostazol inhibits adenosine uptake, whereas milrinone has no such effect. This study investigated the possible cardiac functional significance of cilostazol on adenosine uptake inhibition. In isolated rabbit hearts, 10 microM of cilostazol elevated adenosine concentration in interstitial dialysate (0.16 +/- 0.01 microM, or approximately 0.81 microM in the interstitial space when adjusted for recovery rate of microdialysis) and coronary effluent (0.69 +/- 0.03 microM ). The values are significantly higher than those for 10 microM of milrinone (0.11 +/- 0.1 microM in interstitial dialysate and 0.2 +/- 0.04 microM in coronary effluent). Although cilostazol increased contractility, heart rate, and coronary flow in isolated rabbit hearts, the effect on contractility and heart rate was significantly augmented in the presence of an adenosine A 1 receptor antagonist. Conversely, an adenosine A 1 receptor agonist or an adenosine uptake inhibitor attenuated the positive inotropic effect of milrinone. These results indicate that adenosine uptake inhibition by cilostazol increases interstitial and circulatory adenosine concentration, and antagonizes PDE3 inhibition-induced contractility and heart rate increases through an adenosine A 1 receptor-mediated mechanism.

Effect of cloricromene on intermittent claudication. A randomized, double-blind, placebo-controlled trial in patients treated with aspirin: effect on claudication distance and quality of life. CRAMPS Investigator Group. Cloricromene Randomized Arteriopathy Multicenter Prospective Study

The main aim of medical treatment for intermittent claudication (IC) is the reduction of mortality and morbidity from ischemic cardiovascular disease. However, symptomatic treatment with the aim of improving exercise performance and the overall quality of life may also be an important target of the clinical management of patients with intermittent claudication. Cloricromene, a drug with antithrombotic and anti-ischemic activities, has previously shown some promising results in patients with claudication. We have carried out a clinical trial to assess the effect of cloricromene on the claudication distance and on the quality of life of patients with IC chronically treated with aspirin. A total of 159 patients with IC, Stage II (Fontaine), were enrolled in a double-blind, randomized, prospective, multicenter study comparing cloricromene (100 mg orally b.i.d.) or an identical placebo for 6 months. All patients received 160 mg/day aspirin. The primary end-point was the improvement of initial claudication distance (ICD) at 6 months as measured by a standardized treadmill test. The secondary end-points were the absolute claudication distance (ACD) at 6 months, the percentage of patients defined as responders to treatment (improvement of ICD of at least 40%), changes in the ischemic window (IW), quality of life as assessed by the SF-36 questionnaire, and the occurrence of major cardiovascular events. The ICD increased in both treatment groups, with a non-significant difference at 6 months in favor of cloricromene of +12.3 m. The ACD, percentage of responders to treatment and ischemic window also improved in both groups with a slight, non-significant trend in favor of cloricromene. Pretreatment quality of life scores showed only a slight worsening compared with an age-matched, healthy population and did not change upon treatment. A post hoc subgroup analysis showed a significant benefit from cloricromene in patients with an ICD at enrollment higher than the median of the patient population. In conclusion, treatment with cloricromene for 6 months does not significantly improve claudication in patients with Stage II Fontaine peripheral arteriopathy chronically treated with aspirin. An improvement of 40-60 m in the ICD on a standardized treadmill test does not translate into a self-perceived improvement in the quality of life as assessed by the SF-36 questionnaire.

Inhibition of adenosine uptake and augmentation of ischemia-induced increase of interstitial adenosine by cilostazol, an agent to treat intermittent claudication

Cilostazol (Pletal), a quinolinone derivative with a cyclic nucleotide phosphodiesterase type 3 (PDE3) inhibitory activity, was recently approved by the Food and Drug Administration for treatment of symptoms of intermittent claudication (IC). However, the underlying mechanisms of action are not entirely clear. In this study, we showed that cilostazol inhibited adenosine uptake into cardiac ventricular myocytes, coronary artery smooth muscle, and endothelial cells with a median effective concentration (EC50) approximately 10 microM. In vivo, cilostazol increased cardiac interstitial adenosine levels after a 2-min ischemia in rabbit hearts (329 +/- 92% increase vs. 102 +/- 29% ischemia alone). The combination of cilostazol and 2-min ischemia reduced infarction from subsequent 30-min regional ischemia and 3 h of reperfusion (infarct size was 18 +/- 4% vs. 53 +/- 3% in the hearts with 2-min ischemia alone or 48 +/- 2% in the hearts treated with cilostazol alone). In contrast, milrinone had no effect on either adenosine uptake or interstitial adenosine levels. These data show that cilostazol, unlike milrinone, inhibits adenosine uptake, and thus potentiates adenosine accumulation from a 2-min ischemia. Future studies are needed to investigate the role of adenosine in the treatment of IC by cilostazol.

European multicenter study on propionyl-L-carnitine in intermittent claudication

OBJECTIVES

This study was performed to identify a target population of claudicants for propionyl-L-carnitine treatment.

BACKGROUND

Previous studies suggest that the efficacy of propionyl-L-carnitine in intermittent claudication is greater in patients with severe functional impairment than in those with mild walking disability.

METHODS

After run-in, 485 claudicant patients were randomized to placebo or propionyl-L-carnitine (1 g bid, p.o.) and then stratified on the basis of maximal walking distance (cutoff point 250 m) and maximal walking distance variability (cutoff point 25%). Treatment lasted 12 months. Walking capacity was assessed by treadmill and quality of life by a questionnaire exploring various aspects of daily life.

RESULTS

In the target population, that is, patients who at baseline walked < or = 250 m and showed a maximal walking distance variability < or = 25%, per-protocol analysis showed that the effect of propinyl-L-carnitine was significantly greater than that with placebo for both maximal walking distance and initial claudication distance (ICD). In the intention-to-treat population, maximal walking distance increased by 62 +/- 14% on propionyl-L-carnitine and by 46 +/- 9% (p < 0.05) on placebo, while no difference between treatments was observed for ICD. The beneficial effect of propionyl-L-carnitine was confirmed when data of the target population were pooled with those of patients who at baseline walked < or = 250 m and showed a > 25% maximal walking distance < 50% variability. Actually, maximal walking distance increased by 98 +/- 16% in the propionyl-L-carnitine group and by only 54 +/- 10% in the placebo group (p < 0.01). The corresponding values for ICD were 99 +/- 21% and 51 +/- 8% (p < 0.05). For patients with baseline maximal walking distance > 250 m, no difference between treatments was observed.

CONCLUSIONS

Claudicants with maximal walking distance < or = 250 m benefited from the use of propionyl-L-carnitine, with improvement in walking distance and quality of life. However, patients with mild functional impairment (i.e., walking distance > 250 m) showed no response to propionyl-L-carnitine.

Ticlopidine and clopidogrel

The thienopyridines ticlopidine and clopidogrel are inhibitors of platelet function in vivo. Their mode of action has not been defined, but it appears that they require conversion to as yet unidentified metabolites that are noncompetitive antagonists of the platelet ADP receptor. Inhibition of platelet aggregation with these compounds is delayed until 24 to 48 hours after administration. Maximum inhibition occurs after 3 to 5 days, and recovery is slow after drug withdrawal. Ticlopidine is effective in preventing cardiovascular events in cerebrovascular, cardiovascular, and peripheral vascular disease, with an efficacy that is similar to aspirin. However, its use is associated with significant and sometimes fatal adverse reactions, specifically neutropenia and bone marrow aplasia. Gastrointestinal side effects and skin rashes are common and result in discontinuation of therapy in up to 10% of patients. Clopidogrel is at least as effective as aspirin in preventing cardiovascular events in patients with a history of vascular disease. It appears to be safer than ticlopidine, although its efficacy in acute coronary syndromes or post-coronary-stent insertion has not been reported. Important outstanding issues are whether clopidogrel adds to the benefit of aspirin and whether the combination of these agents is safe. If so, this combination may become the standard for antithrombotic therapy in cardiovascular disease.

Comparison of the effects of cilostazol and milrinone on intracellular cAMP levels and cellular function in platelets and cardiac cells

Cilostazol is a potent cyclic nucleotide phosphodiesterase (PDE) type 3 (PDE3) inhibitor that was recently approved by the Food and Drug Administration (FDA) for the treatment of intermittent claudication. Its efficacy is presumed to be due to its vasodilatory and platelet activation inhibitory activities. Compared with those treated with placebo, patients treated with cilostazol showed a minimal increase in cardiac adverse events. Because of its PDE3 inhibitory activity, however, the possibility that cilostazol exerts positive cardiac inotropic effects is a safety concern. Therefore we compared the effects of cilostazol with those of milrinone, a selective PDE3 inhibitor, on intracellular cyclic adenosine monophosphate (cAMP) levels in platelets, cardiac ventricular myocytes, and coronary smooth muscle cells. We also compared the corresponding functional changes in these cells. Cilostazol and milrinone both caused a concentration-dependent increase in the cAMP level in rabbit and human platelets with similar potency. Furthermore, cilostazol and milrinone were equally effective in inhibiting human platelet aggregation with a median inhibitory concentration (IC50) of 0.9 and 2 microM, respectively. In rabbit ventricular myocytes, however, cilostazol elevated cAMP levels to a significantly lesser extent (p < 0.05 vs. milrinone). By using isolated rabbit hearts with a Langendorff preparation, we showed that milrinone is a very potent cardiotonic agent; it concentration-dependently increased left ventricular developed pressure (LVDP) and contractility. Cilostazol was less effective in increasing LVDP and contractility (p < 0.05 vs. milrinone), which is consistent with the cardiac cAMP levels. The cardiac effect of OPC-13015, a metabolite of cilostazol with about sevenfold higher PDE3 inhibition, was similar to cilostazol. Whereas milrinone concentration-dependently increased cAMP in rabbit coronary smooth muscle cells, cilostazol did not have such an effect. However, both compounds increased coronary flow equally in rabbit hearts. Our results show that although cilostazol and milrinone both inhibit PDE3, cilostazol preferentially acts on vascular elements (platelets and flow). This unique profile of cilostazol is consistent with its beneficial and safe clinical outcomes in patients with intermittent claudication.