Effect of propionyl-L-carnitine on quality of life in intermittent claudication

Effect of Dietary Supplements Which Upregulate Nitric Oxide on Walking and Quality of Life in Patients with Peripheral Artery Disease: A Meta-Analysis

This systematic review pooled evidence from randomised controlled trials (RCTs) on the effectiveness of dietary upregulators of nitric oxide (NO) in improving the walking and quality of life of patients with peripheral artery disease (PAD). RCTs examining the effect of dietary upregulators of NO in patients with PAD were included. The primary outcome was the maximum walking distance. Secondary outcomes were the initial claudication distance, the six-minute walking distance, quality of life, the ankle-brachial pressure index (ABI), adverse events and risk of mortality, revascularisation or amputation. Meta-analyses were performed using random effects models. The risk of bias was assessed using Cochrane's ROB-2 tool. Leave-one-out and subgroup analyses were conducted to assess the effect of individual studies, the risk of bias and intervention type on pooled estimates. Thirty-four RCTs involving 3472 participants were included. Seven trials tested NO donors, nineteen tested antioxidants, three tested NO synthase inducers and five tested enhancers of NO availability. Overall, the dietary supplements significantly improved the initial claudication (SMD 0.34; 95%CI 0.04, 0.64; p = 0.03) but not maximum walking (SMD 0.13; 95%CI -0.17, 0.43; p = 0.39) distances. Antioxidant supplements significantly increased both the maximum walking (SMD 0.36; 95%CI 0.14, 0.59; p = 0.001) and initial claudication (SMD 0.58; 95%CI 0.26, 0.90; p < 0.001) distances. The dietary interventions did not improve the physical function domain of the Short Form-36 (SMD -0.16; 95%CI -0.32, 0.00; p = 0.38), ABI or risk of adverse events, mortality, revascularisation or amputation. Dietary NO upregulators, especially antioxidants, appear to improve the initial claudication distance in patients with PAD. Larger high-quality RCTs are needed to fully examine the benefits and risks of these treatments. PROSPERO Registration: CRD42022256653.

Acylcarnitines: Nomenclature, Biomarkers, Therapeutic Potential, Drug Targets, and Clinical Trials

Acylcarnitines are fatty acid metabolites that play important roles in many cellular energy metabolism pathways. They have historically been used as important diagnostic markers for inborn errors of fatty acid oxidation and are being intensively studied as markers of energy metabolism, deficits in mitochondrial and peroxisomal β -oxidation activity, insulin resistance, and physical activity. Acylcarnitines are increasingly being identified as important indicators in metabolic studies of many diseases, including metabolic disorders, cardiovascular diseases, diabetes, depression, neurologic disorders, and certain cancers. The US Food and Drug Administration-approved drug L-carnitine, along with short-chain acylcarnitines (acetylcarnitine and propionylcarnitine), is now widely used as a dietary supplement. In light of their growing importance, we have undertaken an extensive review of acylcarnitines and provided a detailed description of their identity, nomenclature, classification, biochemistry, pathophysiology, supplementary use, potential drug targets, and clinical trials. We also summarize these updates in the Human Metabolome Database, which now includes information on the structures, chemical formulae, chemical/spectral properties, descriptions, and pathways for 1240 acylcarnitines. This work lays a solid foundation for identifying, characterizing, and understanding acylcarnitines in human biosamples. We also discuss the emerging opportunities for using acylcarnitines as biomarkers and as dietary interventions or supplements for many wide-ranging indications. The opportunity to identify new drug targets involved in controlling acylcarnitine levels is also discussed. SIGNIFICANCE STATEMENT: This review provides a comprehensive overview of acylcarnitines, including their nomenclature, structure and biochemistry, and use as disease biomarkers and pharmaceutical agents. We present updated information contained in the Human Metabolome Database website as well as substantial mapping of the known biochemical pathways associated with acylcarnitines, thereby providing a strong foundation for further clarification of their physiological roles.

Propionyl-L-carnitine for intermittent claudication

BACKGROUND

Peripheral arterial disease (PAD) is a manifestation of systemic atherosclerosis. Intermittent claudication is a symptomatic form of PAD that is characterized by pain in the lower limbs caused by chronic occlusive arterial disease. This pain develops in a limb during exercise and is relieved with rest. Propionyl-L-carnitine (PLC) is a drug that may alleviate the symptoms of PAD through a metabolic pathway, thereby improving exercise performance.

OBJECTIVES

The objective of this review is to determine whether propionyl-L-carnitine is efficacious compared with placebo, other drugs, or other interventions used for treatment of intermittent claudication (e.g. exercise, endovascular intervention, surgery) in increasing pain-free and maximum walking distance for people with stable intermittent claudication, Fontaine stage II.

SEARCH METHODS

The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase, and CINAHL databases and the World Health Organization International Clinical Trials Registry Platform and the ClinicalTrials.gov trials register to July 7, 2021. We undertook reference checking and contact with study authors and pharmaceutical companies to identify additional unpublished and ongoing studies.

SELECTION CRITERIA

Double-blind randomized controlled trials (RCTs) in people with intermittent claudication (Fontaine stage II) receiving PLC compared with placebo or another intervention. Outcomes included pain-free walking performance (initial claudication distance - ICD) and maximal walking performance (absolute claudication distance - ACD), analyzed by standardized treadmill exercise test, as well as ankle brachial index (ABI), quality of life, progression of disease, and adverse events.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials, extracted data, and evaluated trials for risk of bias. We contacted study authors for additional information. We resolved any disagreements by consensus. We performed fixed-effect model meta-analyses with mean differences (MDs) and 95% confidence intervals (CIs). We graded the certainty of evidence according to GRADE.

MAIN RESULTS

We included 12 studies in this review with a total number of 1423 randomized participants. A majority of the included studies assessed PLC versus placebo (11 studies, 1395 participants), and one study assessed PLC versus L-carnitine (1 study, 26 participants). We identified no RCTs that assessed PLC versus any other medication, exercise, endovascular intervention, or surgery. Participants received PLC 1 grams to 2 grams orally (9 studies) or intravenously (3 studies) per day or placebo. For the comparison PLC versus placebo, there was a high level of both clinical and statistical heterogeneity due to study size, participants coming from different countries and centres, the combination of participants with and without diabetes, and use of different treadmill protocols. We found a high proportion of drug company-backed studies. The overall certainty of the evidence was moderate. For PLC compared with placebo, improvement in maximal walking performance (ACD) was greater for PLC than for placebo, with a mean difference in absolute improvement of 50.86 meters (95% CI 50.34 to 51.38; 9 studies, 1121 participants), or a 26% relative improvement (95% CI 23% to 28%). Improvement in pain-free walking distance (ICD) was also greater for PLC than for placebo, with a mean difference in absolute improvement of 32.98 meters (95% CI 32.60 to 33.37; 9 studies, 1151 participants), or a 31% relative improvement (95% CI 28% to 34%). Improvement in ABI was greater for PLC than for placebo, with a mean difference in improvement of 0.09 (95% CI 0.08 to 0.09; 4 studies, 369 participants). Quality of life improvement was greater with PLC (MD 0.06, 95% CI 0.05 to 0.07; 1 study, 126 participants). Progression of disease and adverse events including nausea, gastric intolerance, and flu-like symptoms did not differ greatly between PLC and placebo. For the comparison of PLC with L-carnitine, the certainty of evidence was low because this included a single, very small, cross-over study. Mean improvement in ACD was slightly greater for PLC compared to L-carnitine, with a mean difference in absolute improvement of 20.00 meters (95% CI 0.47 to 39.53; 1 study, 14 participants) or a 16% relative improvement (95% CI 0.4% to 31.6%). We found no evidence of a clear difference in the ICD (absolute improvement 4.00 meters, 95% CI -9.86 to 17.86; 1 study, 14 participants); or a 3% relative improvement (95% CI -7.4% to 13.4%). None of the other outcomes of this review were reported in this study.

AUTHORS' CONCLUSIONS

When PLC was compared with placebo, improvement in walking distance was mild to moderate and safety profiles were similar, with moderate overall certainty of evidence. Although In clinical practice, PLC might be considered as an alternative or an adjuvant to standard treatment when such therapies are found to be contraindicated or ineffective, we found no RCT evidence comparing PLC with standard treatment to directly support such use.

Neurolitic block of the lumbar sympathetic chain improves chronic pain in a patient with critical lower limb ischemia

Background and objectives

Sympathectomy is one of the therapies used in the treatment of chronic obstructive arterial disease (COAD). Although not considered as first-line strategy, it should be considered in the management of pain difficult to control. This clinical case describes the evolution of a patient with inoperable COAD who responded properly to the lumbar sympathetic block.

Case report

A female patient, afro-descendant, 69 years old, ASA II, admitted to the algology service due to refractory ischemic pain in the lower limbs. The patient had undergone several surgical procedures and conservative treatments without success. Vascular surgery considered the case as out of therapeutic possibility, unless limb amputation. At that time, sympathectomy was indicated. After admission to the operating room, the patient was monitored, positioned and sedated. The blockade was performed with the aid of radioscopy, bilaterally, at L2–L3–L4 right and L3 left levels. On the right side, at each level cited, 3 mL of absolute alcohol with 0.25% bupivacaine were injected without vasoconstrictor, and on the left side only local anesthetic. The procedure was performed uneventfully. The patient was discharged with complete remission of the pain.

Conclusion

Neurolitic block of the lumbar sympathetic chain is an effective and safe treatment option for pain control in patients with critical limb ischemia patients in whom the only possible intervention would be limb amputation.

Functional outcomes and quality of life in peripheral arterial disease: current status

This review examines current evidence for baseline functional impairment and changes with therapy in patients with peripheral arterial disease (PAD) - ranging from patients without claudication or critical limb ischemia (CLI) but other exertional leg symptoms (erroneously referred to as asymptomatic in the Fontaine classifi cation system), to patients with claudication and those with CLI. The review points out that the status of functional outcomes research is markedly different in focus and development in the different levels of disease severity - paradoxically less studied in the more severe CLI population than in patients with claudication, for example.

[Neurolitic block of the lumbar sympathetic chain improves chronic pain in a patient with critical lower limb ischemia]

BACKGROUND AND OBJECTIVES

Sympathectomy is one of the therapies used in the treatment of chronic obstructive arterial disease (COAD). Although not considered as first-line strategy, it should be considered in the management of pain difficult to control. This clinical case describes the evolution of a patient with inoperable COAD who responded properly to the lumbar sympathetic block.

CASE REPORT

A female patient, afro-descendant, 69 years old, ASA II, admitted to the algology service due to refractory ischemic pain in the lower limbs. The patient had undergone several surgical procedures and conservative treatments without success. Vascular surgery considered the case as out of therapeutic possibility, unless limb amputation. At that time, sympathectomy was indicated. After admission to the operating room, the patient was monitored, positioned and sedated. The blockade was performed with the aid of radioscopy, bilaterally, at L2-L3-L4 right and L3 left levels. On the right side, at each level cited, 3mL of absolute alcohol with 0.25% bupivacaine were injected without vasoconstrictor, and on the left side only local anesthetic. The procedure was performed uneventfully. The patient was discharged with complete remission of the pain.

CONCLUSION

Neurolitic block of the lumbar sympathetic chain is an effective and safe treatment option for pain control in patients with critical limb ischemia patients in whom the only possible intervention would be limb amputation.

Carnitine and acylcarnitines: pharmacokinetic, pharmacological and clinical aspects

L-Carnitine (levocarnitine) is a naturally occurring compound found in all mammalian species. The most important biological function of L-carnitine is in the transport of fatty acids into the mitochondria for subsequent β-oxidation, a process which results in the esterification of L-carnitine to form acylcarnitine derivatives. As such, the endogenous carnitine pool is comprised of L-carnitine and various short-, medium- and long-chain acylcarnitines. The physiological importance of L-carnitine and its obligatory role in the mitochondrial metabolism of fatty acids has been clearly established; however, more recently, additional functions of the carnitine system have been described, including the removal of excess acyl groups from the body and the modulation of intracellular coenzyme A (CoA) homeostasis. In light of this, acylcarnitines cannot simply be considered by-products of the enzymatic carnitine transfer system, but provide indirect evidence of altered mitochondrial metabolism. Consequently, examination of the contribution of L-carnitine and acylcarnitines to the endogenous carnitine pool (i.e. carnitine pool composition) is critical in order to adequately characterize metabolic status. The concentrations of L-carnitine and its esters are maintained within relatively narrow limits for normal biological functioning in their pivotal roles in fatty acid oxidation and maintenance of free CoA availability. The homeostasis of carnitine is multifaceted with concentrations achieved and maintained by a combination of oral absorption, de novo biosynthesis, carrier-mediated distribution into tissues and extensive, but saturable, renal tubular reabsorption. Various disorders of carnitine insufficiency have been described but ultimately all result in impaired entry of fatty acids into the mitochondria and consequently disturbed lipid oxidation. Given the sensitivity of acylcarnitine concentrations and the relative carnitine pool composition in reflecting the intramitochondrial acyl-CoA to free CoA ratio (and, hence, any disturbances in mitochondrial metabolism), the relative contribution of L-carnitine and acylcarnitines within the total carnitine pool is therefore considered critical in the identification of mitochondria dysfunction. Although there is considerable research in the literature focused on disorders of carnitine insufficiency, relatively few have examined relative carnitine pool composition in these conditions; consequently, the complexity of these disorders may not be fully understood. Similarly, although important studies have been conducted establishing the pharmacokinetics of exogenous carnitine and short-chain carnitine esters in healthy volunteers, few studies have examined carnitine pharmacokinetics in patient groups. Furthermore, the impact of L-carnitine administration on the kinetics of acylcarnitines has not been established. Given the importance of L-carnitine as well as acylcarnitines in maintaining normal mitochondrial function, this review seeks to examine previous research associated with the homeostasis and pharmacokinetics of L-carnitine and its esters, and highlight potential areas of future research.

l-Carnitine plus cilostazol versus cilostazol alone for the treatment of claudication in patients with peripheral artery disease: A multicenter, randomized, double-blind, placebo-controlled trial

Intermittent claudication (IC) is the predominant symptom of peripheral artery disease (PAD), and is associated with reduced exercise capacity. The pathophysiology of IC is related to reduced blood flow and impaired skeletal muscle oxidative metabolism; however, the efficacy of metabolic therapies is not well established. We evaluated the effect of cilostazol plus l-carnitine versus cilostazol alone on exercise performance, quality of life (QOL), and safety. In a double-blind, placebo-controlled trial, PAD patients with stable IC were randomized to either l-carnitine 1 g or matching placebo twice-daily, on a background of cilostazol. Treadmill and QOL assessments were performed at baseline, 90, and 180 days. The primary endpoint was the difference between groups in the natural-log-transformed ( ln) ratio in peak walking time (PWT) between baseline and 180 days. The combination of cilostazol and l-carnitine was well tolerated. In the modified intent-to-treat population ( n = 145), the mean ln ratio in PWT was 0.241 for cilostazol/l-carnitine versus 0.134 for cilostazol/placebo ( p = 0.076), corresponding to mean increases of 1.99 and 1.36 minutes, respectively. In the per-protocol population ( n = 120), the mean ln ratio in PWT was 0.267 for cilostazol/l-carnitine versus 0.145 for cilostazol/placebo ( p = 0.048). QOL measures were also improved in the cilostazol/l-carnitine group. These findings support larger trials of l-carnitine in combination with cilostazol in the treatment of IC. ClinicalTrials.gov Identifier: NCT00822172

Pharmacological effects and clinical applications of propionyl-L-carnitine

Propionyl-L-carnitine (PLC) is a naturally occurring derivative of carnitine that plays an important role in the metabolism of both carbohydrates and lipids, leading to an increase of ATP generation. PLC, however, is not only a metabolic drug; it is also a potent antiradical agent and thus may protect tissues from oxidative damage. PLC has been demonstrated to exert a protective effect in different models of both cardiac and endothelial dysfunction, to prevent the progression of atherosclerosis, and, more recently, to improve some of the cardiometabolic alterations that frequently accompany insulin resistance. As a result, most of the clinical trials conducted in humans highlight PLC as a potential treatment option in cardiovascular diseases such as peripheral arterial disease, chronic heart failure, or stable angina, especially when type 2 diabetes mellitus or hyperglycemia (i.e., patients on hemodialysis) are also present. The aim of this review is to summarize the pharmacological effects and possible therapeutic applications of PLC, including the most recent findings to date.

Critical update for the clinical use of L-carnitine analogs in cardiometabolic disorders

Acetyl-L-carnitine (ALC) and propionyl-L-carnitine (PLC) are two naturally occurring carnitine derivates formed by carnitine acetyltransferase. The beneficial cardiovascular effects of ALC and PLC have been extensively evaluated in animals and humans during the last 20 years. For instance, many clinical trials have suggested ALC and PLC as potential strategies in the management of peripheral arterial disease, heart and cerebral ischemia, and congestive heart failure. As a result, several experts have already aimed to revise the clinical evidence supporting the therapeutic use of ALC and PLC. On the basis of their conclusions, our aim was a critical review of the effectiveness of ALC and PLC in the treatment of cardiovascular diseases. Type 2 diabetes mellitus is an independent risk factor for the development of cardiovascular disease. Therefore we also describe recent studies that have addressed the emerging use of ALC and PLC amelioration of the insulin resistant state and its related morbidities.

Assessment of functional status and quality of life in claudication

BACKGROUND

Treadmill walking is commonly used to evaluate walking impairment and efficacy of treatment for intermittent claudication (IC) in clinical and research settings. Although this is an important measure, it does not provide information about how patients perceive the effects of their treatments on more global measures of health-related quality of life (HRQOL).

METHODS

PubMed/Medline was searched to find publications about the most commonly used questionnaires to assess functional status and/or general and disease-specific HRQOL in patients with peripheral artery disease (PAD) who experience IC. Inclusion criteria for questionnaires were based on existence of a body of literature in symptomatic PAD.

RESULTS

Six general questionnaires and seven disease-specific questionnaires are included, with details about the number of domains covered and how each tool is scored. The Medical Outcomes Study Short Form 36-item questionnaire and Walking Impairment Questionnaire are currently the most used general and disease-specific questionnaires at baseline and after treatment for IC, respectively.

CONCLUSIONS

The use of tools that assess functional status and HRQOL has importance in both the clinical and research areas to assess treatment efficacy from the patient's perspective. Therefore, assessing HRQOL in addition to treadmill-measured walking ability provides insight as to the effects of treatments on patient outcomes and may help guide therapy.

Propionyl l-carnitine: intermittent claudication and peripheral arterial disease

Peripheral arterial disease (PAD) is a clinical manifestation of underlying aorto-iliac and leg atherosclerosis that is characterized by different stages of stenosis and obstruction. It affects approximately 12% of the adult population and about 20% of people over the age of 70 years, and is associated with increased cardiovascular (CV) and cerebrovascular morbidity. Intermittent claudication (IC) is the major symptom of PAD; it is defined as cramping leg pain (in the buttock, thigh, or calf) while/after clim bing one or two flights of stairs, or during walking. The goals of IC management are to: slow the progression of local and systemic atherosclerosis, prevent major fatal and nonfatal CV events (myocardial infarction and stroke), improve walking capacity, prevent and reduce resting pain and cutaneous lesions. Propionyl L-carnitine is an acyl derivative of levocarnitine (L-carnitine) and is indicated for patients with peripheral arterial occlusive disease. It corrects secondary muscle carnitine deficiency in patients with PAD, significantly improving the walking capacity; it is a free radical that produces positive effects on endothelial function; it protects from oxidative stress; and it enhances most measures of quality of life. The recent Trans-Atlantic Inter-Society Consensus II update recommends the use of propionyl L-carnitine in combination with physical training to improve the symptoms associated with PAD.

Pharmacological treatment of patients with chronic critical limb ischemia: L-propionyl-carnitine enhances the short-term effects of PGE-1

PURPOSE

To evaluate the therapeutic effects of L-propionyl-carnitine (LPC) in patients with critical limb ischemia (CLI), as defined by the TASC guidelines.

METHODS

The study, double-blinded, randomised, assessed intravenous infusion of LPC 1.2 g/day in combination with PGE-1, 60 mg/day (LPC group: 37 patients), or PGE-1 only (control group: 38 patients) in a total of 75 patients suffering from CLI. Treatment duration was 20 days. We evaluated rest pain, maximum walking distance (MWD) and skin ulcer size.

RESULTS

In both groups we observed a significant reduction in pain score and ulcer size and an increase in MWD. In the patients treated with the combination, the improvement was greater: median value for pain score decreased from 2.75 to 0.85 in the LPC group and from 2.51 to 1.71 in the control group; MWD increased from 55 M to 130 M in the LPC group, and from 55 M to 102 M in the control group; median decrease of ulcer size was significantly greater in patients treated with LPC + PGE1.

CONCLUSIONS

Our study shows that LPC, whose effectiveness on claudication is already known, has favourable effects in patients with CLI, since it reinforces the effects produced by PGE-1.

Treatment strategies for peripheral artery disease

Peripheral arterial disease is an underecognized manifestation of systemic atherosclerosis associated with high rates of cardiovascular morbidity and mortality. The rationale of therapy is to reduce cardiovascular risk, improve symptoms of intermittent claudication, and prevent the development of critical limb ischemia and amputation. Exercise therapy and several pharmacologic agents have been shown to improve walking distance in patients with intermittent claudication. Patients with lifestyle-interfering symptoms despite exercise, or those who progress to critical limb ischemia, frequently undergo revascularization. Endovascular techniques are commonly used in these patients. Combined pharmacological and endovascular strategies will play an increasing role in management of these patients in the future.

Pharmacologic therapy for intermittent claudication

Peripheral artery disease, defined as atherosclerosis in the lower extremities, affects nearly 8.5 million people in the United States. Due to the frequent asymptomatic manifestation of peripheral artery disease, diagnosis may be delayed and its true incidence underestimated. However, some patients may experience aching pain, numbness, weakness, or fatigue, a condition termed intermittent claudication. Peripheral atherosclerosis is associated with cardiovascular risk and physical impairment; therefore, treatment goals are aimed at decreasing cardiovascular risk, as well as improving quality of life. Little debate exists regarding the management of cardiovascular risk reduction, which consists of both antiplatelet therapy and risk factor modification. Despite recently published guidelines, the treatment of intermittent claudication is less well established and the management remains controversial and uncertain. Exercise remains the first-line therapy for intermittent claudication; however, pharmacologic treatment is often necessary. Although only two prescription drugs have been approved by the U.S. Food and Drug Administration for the treatment of intermittent claudication, several supplements and investigational agents have been evaluated. Therapeutic optimization should balance the anticipated improvements in quality of life with the potential safety risks.

Risk assessment for carnitine

Carnitine is a conditionally essential amino acid-like compound involved in the transport of long-chain fatty acids into the mitochondria during the beta-oxidation process. Carnitine has become an increasingly popular ingredient in dietary supplements, especially weight loss and some sports nutrition products. A number of clinical trials have been conducted examining the effect of carnitine supplementation on weight loss and energy balance. Regarding safety, systematic evaluation of the research designs and data do not provide a basis for risk assessment and the usual safe upper level of intake (UL) derived from it unless the newer methods described as the observed safe level (OSL) or highest observed intake (HOI) are utilized. The OSL risk assessment method indicates that the evidence of safety is strong at intakes up to 2000mg/day l-carnitine equivalents for chronic supplementation, and this level is identified as the OSL. Although much higher levels have been tested without adverse effects and may be safe, the data for intakes above 2000mg/day are not sufficient for a confident conclusion of long-term safety.

Effect of propionylcarnitine on changes in endothelial function and plasma levels of adhesion molecules induced by acute exercise in patients with intermittent claudication

In patients with intermittent claudication, treadmill exercise may cause acute deterioration of endothelial function and increase in plasma concentrations of adhesion molecules. The authors evaluated the efficacy of intravenously administered propionylcarnitine (PLC)in preventing these phenomena. Thirty-six claudicants with postexercise decrease in brachial artery flow-mediated dilation (FMD)were randomized to either placebo or PLC (600 mg as a single bolus followed by 1 mg/kg/min for 60 minutes).In the 18 patients randomized to placebo, FMD markedly decreased with exercise before (from 6.8 +/-0.4% to 4.0 +/-0.4%; p < 0.001) and after treatment (from 6.5 +/-0.4% to 4.4 +/-0.5%; p < 0.001). By contrast, in the PLC group, FMD significantly decreased with exercise before treatment (from 8.0 +/-0.7% to 4.4 +/-0.4%; p < 0.001), but not after active drug administration (from 7.1 +/-0.7% to 6.0 +/-0.6%; p = 0.067). The difference between treatments was not significant (p = 0.099; ANOVA). However, in the PLC group, the authors found that the greater the exercise-induced deterioration in endothelial function before treatment, the greater the capacity of PLC to prevent a postexercise decrease in FMD (r = -0.50, p = 0.034). Accordingly, they analyzed data in the 19 patients with a baseline exercise-induced decrease in FMD >or=45% (ie, the median FMD reduction in the entire group of 36 patients), and found that the exercise-induced FMD decrease was less after PLC than after placebo (p = 0.046, ANOVA). In the same subgroup, the exercise-induced increase in plasma concentrations of soluble vascular cell adhesion molecule-1 (sVCAM-1) was significantly higher before than after treatment in patients randomized to PLC (23.4 +/-5% vs 15.3 +/-7%, p = 0.007). In conclusion, in patients with intermittent claudication suffering from a greater endothelial derangement after treadmill, PLC administration provided a protective effect against deterioration of FMD and increase of sVCAM-1 induced by exercise.

Does nutrition have a role in peripheral vascular disease?

Peripheral vascular disease (PVD) is a manifestation of systemic atherosclerosis in the lower limbs, and PVD patients have a 3- to 5-fold increased risk of cardiovascular mortality compared with age-matched controls. Nevertheless, recent reports show how PVD patients are undertreated with regard to CVD risk-factor reduction and the use of lipid-lowering or antiplatelet drugs. There is appreciable evidence that demonstrates the beneficial effects of certain nutrients and dietary habits in the prevention of CVD, but there has been little attention paid to the role of nutrients in PVD. The purpose of the present review is to provide an overview of our understanding of how foods could possibly benefit PVD. In the last few decades, several nutrients have arisen as potentially health-promoting in PVD. While nutritional interventions in PVD show positive clinical effects for fish oil, carnitine or vitamin E, others such as olive oil or vitamin C seem to interact only at a biochemical level by decreasing risk factors. Moreover, only epidemiological associations exist for the potential role of fibre, folates or vitamin B6 in this disease. In all cases, the limited data available provide no clear-cut evidence in favour of the clinical benefit of nutritional interventions aimed at reducing risk factors and ameliorating symptoms in PVD patients. No practical recommendations can be given at this stage, and further studies are clearly needed.

Predictors of treatment outcome in intermittent claudication

OBJECTIVE

To derive formulae to predict the likely 12-month health-related quality of life outcome following different treatments for intermittent claudication (IC).

DESIGN

A prospective, randomized, controlled study.

MATERIALS

One hundred and seventy-one unselected patients with stable IC were sequentially randomized to invasive therapy, supervised physical training or observation. Hierarchical analysis was used to identify significant predictors of outcome.

RESULTS

The strongest outcome predictors were baseline values of the respective outcome variables in all groups. No more than two significant secondary predictors were identified for each outcome variable and no outcome variable was a predictor of any other outcome variable. Resulting prediction equations achieved between 61 and 90% concordance with improvement (75% considered adequate), with best prediction for invasive therapy and poorest for observation. Suggested cutpoints for the various endpoints in the three groups had sensitivities ranging between 65 and 100% and false positive rates between 5 and 50%.

CONCLUSIONS

The derived equations adequately predicted improvement on the various outcome variables in invasive therapy and supervised physical training, and may serve as aids in selecting patients likely to benefit most from a particular treatment strategy. The uniqueness of the outcome variables underscores the importance of implementing a comprehensive set of endpoints relevant to the impacts of the condition.

Drug Treatment of Intermittent Claudication

The US FDA has approved two drugs for the management of intermittent claudication: pentoxifylline and cilostazol. The mechanism of action that provides symptom relief with pentoxifylline is poorly understood but is thought to involve red blood cell deformability as well as a reduction in fibrinogen concentration, platelet adhesiveness and whole blood viscosity. The recommended dose of pentoxifylline is 400 mg three times daily with meals. Cilostazol is a potent, reversible, phosphodiesterase III inhibitor. The inhibition of phosphodiesterase allows for the increased availability of cyclic adenosine monophosphate (cAMP). cAMP mediates many agonist-induced platelet inhibitory, vasodilatory and vascular antiproliferative responses. Cilostazol, at a dose of 100 mg twice daily, is recommended to be taken 30 minutes before or 2 hours after breakfast and dinner. In addition to pentoxifylline and cilostazol, clinical trials indicate many other drugs may relieve the symptoms of intermittent claudication. Ginkgo biloba, available as an over-the-counter extract, provides symptom relief comparable to pentoxifylline. Two European agents, naftidrofuryl and buflomedil, also have efficacy that is reported to be similar to pentoxifylline. Policosanol is a mixture of fatty alcohols derived from honeybee wax which, according to very limited data, reduces symptoms of claudication. Amino acids, certain peptides and prostaglandins may have a therapeutic role. Finally, novel approaches including angiogenesis mediated by growth factors, are currently under investigation.

Pharmacotherapy for peripheral arterial disease: emerging therapeutic options

Although endovascular therapy has revolutionized the management of patients with peripheral arterial disease (PAD), noninterventional regimens, such as structured exercise therapy, atherosclerotic risk factor modification, and pharmacotherapy, are effective in patients suffering from mild-to-moderate PAD and intermittent claudication (IC). For more than a decade, the only pharmacologic therapy for IC available in the United States was pentoxifylline, which had demonstrated superiority in improving walking distances but offered minimal clinical benefit. Recently, basic research into the pathophysiology of IC has led to the development of cilostazol, a new pharmacologic agent approved for treatment of this condition in 1999. Ongoing research in the use of angiogenic growth factors has further broadened the range of potential alternatives to treatment in patients with PAD. Revascularization procedures, including nonsurgical and surgical techniques, can thus be reserved to improve patency and reduce the risk of limb loss in patients with PAD and IC with more severe impairment.

A rational approach to diagnosis and treatment of intermittent claudication

Intermittent claudication (IC), the first recognizable symptom of peripheral arterial disease, is prevalent among older persons and associated with significant morbidity and mortality. The diagnosis of IC involves taking a thorough patient history, conducting a physical examination with an emphasis on the cardiovascular system, and noninvasive testing with functional assessment. The goals of treatment for IC are to prevent progression of vascular disease and cardiovascular complications and to improve exercise performance, functional status, and quality of life. The cornerstones of therapy are risk-factor modification, particularly smoking cessation, and exercise. In patients for whom non-pharmacologic therapy does not provide adequate pain relief and improvement in physical function, medical therapy with 1 of 2 drugs approved for the treatment of IC may be appropriate. Revascularization or intervention is generally reserved for patients with incapacitating disease. Early diagnosis of IC and implementation of effective therapy can reduce the development of morbidity and mortality.

Intermittent claudication: pharmacoeconomic and quality-of-life aspects of treatment

The purpose of this article is to review the literature on the pharmacoeconomics of treatment for intermittent claudication and to discuss the importance of quality-of-life assessment for evaluating treatment strategies. Systemic risk reduction is the primary objective in the treatment of patients with intermittent claudication, as these patients have a high future risk of cardiovascular morbidity and mortality. Modification of cardiovascular risk factors accompanied by antiplatelet therapy is likely to improve overall survival, reduce myocardial infarction and stroke, and will, perhaps, also reduce the risk of ulcers and amputation at acceptable cost-effectiveness ratios. The second goal in the treatment of patients with intermittent claudication is to improve their walking capacity and community-based functional status. Supervised exercise training is the most effective noninvasive intervention to improve walking capacity, but may have elevated indirect costs. Among patients with disabling claudication who are candidates for invasive therapeutic procedures, angioplasty is cost effective in those with femoropopliteal stenosis or occlusion and in those with critical limb ischaemia and a stenosis. For all these therapeutic strategies there is a need to relate the costs to a relevant and comprehensive measure of effectiveness. Quality-of-life evaluation by using questionnaires exploring the specific problems encountered by patients with intermittent claudication in their daily life appear to be the most appropriate tool to evaluate the net result of a treatment. Cost-utility studies by combining pecuniary and quality-of-life evaluations provide information that is extremely useful to patients with intermittent claudication, regulatory authorities, the pharmaceutical industry and healthcare providers.

Pharmacotherapy of intermittent claudication

Intermittent claudication (IC) is leg muscle pain, cramping and fatigue brought on by exercise and is the primary symptom of peripheral arterial disease. The goals of pharmacotherapy for IC are to increase the walking capacity/quality of life and to decrease rates of amputation. In 1988, pentoxifylline was the only drug that had reasonable supportive clinical trial evidence for being beneficial in IC. Since then a number of drugs have shown benefit or potential in IC. Cilostazol, a specific inhibitor of phosphodiesterase 3 and activator of lipoprotein lipase, clearly increases pain-free and absolute walking distances in claudicants. However, cilostazol does cause minor side effects including headache, diarrhoea, loose stools and flatulence. Naftidrofuryl, a serotonin (5-HT2) receptor antagonist and antiplatelet drug, is beneficial in claudicants. Inhibitors of platelet aggregation (including nitric oxide from L -arginine or glyceryl trinitrate) and anticoagulants (low molecular weight heparin, defibrotide) probably have both short and long-term benefits in IC. In addition, intravenous infusions of prostaglandins (PGs) PGE1 and PGI2 have an established role in severe peripheral arterial disease and the recent introduction of longer lasting and/or oral forms of the PGs makes them more likely to be useful in the IC associated with less severe forms of the disease. There are some exciting new approaches to the treatment of IC, including propionyl-L-carnitine and basic fibroblast growth factor (bFGF).

Quality-of-life assessment in comparative therapeutic trials and causal structure considerations in peripheral occlusive arterial disease

When considering the use of quality of life as a primary end-point in phase III to IV comparative trials, the trial designer generally faces some unresolved questions. These include: How does one explain that some dimensions [quality-of-life (QOL) instruments usually have more than 1 dimension] are directly influenced by the studied treatments whereas others are not? How can one interpret conflicting results between conventional clinical measurements and QOL measurements, when the relationships between conventional clinical measurement and quality of life are not known? In this paper, we consider the use of Structural Equation Modelling (SEM) as a methodological alternative to answer these problems. As an example, we analyse the internal causal structure of the Claudication Scale (CLAU-S), a specific QOL 5-dimensional instrument for peripheral occlusive arterial disease. In applying SEM to different studies and different types of calculation, we suggest that CLAU-S is based on a stable, simple and comprehensive QOL model, is compatible with the general International Classification of Impairments, Disabilities and Handicaps (ICIDH) classification, is coherent and complementary with clinical data measurements and, using differences in a prospective study, considerably improves specificity. We suggest that SEM can help in QOL scale validation, in providing a unified scheme of the inter-relationships between internal dimensions and with external variables, in particular, clinical measurements.

Pharmacokinetics of propionyl-L-carnitine in humans: evidence for saturable tubular reabsorption

AIMS

Propionyl-L-carnitine (PLC) is an endogenous compound which, along with L-carnitine (LC) and acetyl-L-carnitine (ALC), forms a component of the endogenous carnitine pool in humans and most, if not all, animal species. PLC is currently under investigation for the treatment of peripheral artery disease, and the present study was conducted to assess the pharmacokinetics of intravenous propionyl-L-carnitine hydrochloride.

METHODS

This was a placebo-controlled, double-blind, parallel group, dose-escalating study in which 24 healthy males were divided into four groups of six. Four subjects from each group received propionyl-L-carnitine hydrochloride and two received placebo. The doses (1 g, 2 g, 4 g and 8 g) were administered as a constant rate infusion over 2 h and blood and urine were collected for 24 h from the start of the infusion. PLC, ALC and LC in plasma and urine were quantified by h.p. l.c.

RESULTS

All 24 subjects successfully completed the study and the infusions were well tolerated. In addition to the expected increase in PLC levels, the plasma concentrations and urinary excretion of LC and ALC also increased above baseline values following intravenous propionyl-L-carnitine hydrochloride administration. At a dose of 1 g, PLC was found to have a mean (+/- s.d.) half-life of 1.09 +/- 0.15 h, a clearance of 11.6 +/- 0.24 l h-1 and a volume of distribution of 18.3 +/- 2.4 l. None of these parameters changed with dose. In placebo-treated subjects, endogenous PLC, LC and ALC underwent extensive renal tubular reabsorption, as indicated by renal excretory clearance to GFR ratios of less than 0.1. The renal-excretory clearance of PLC, which was 0.33 +/- 0.38 l h-1 under baseline condition, increased (P < 0. 001) from 1.98 +/- 0.59 l h-1 at a dose of 1 g to 5.55 +/- 1.50 l h-1 at a dose of 8 g (95% confidence interval for the difference was 2.18,4.97). As a consequence, the percent of the dose excreted unchanged in urine increased (P < 0.001) from 18.1 +/- 5.5% (1 g) to 50.3 +/- 13.3% (8 g). The renal-excretory clearance of LC and ALC also increased substantially after PLC administration and there was evidence for renal metabolism of PLC to LC and ALC.

CONCLUSIONS

Intravenous administration of propionyl-L-carnitine hydrochloride caused significant increases in the renal excretory clearances of PLC, LC and ALC, due to saturation of the renal tubular reabsorption process - as a consequence there was a substantial increase with dose in the fraction excreted unchanged in urine. Despite the marked increase in the renal clearance of PLC, total clearance remained unchanged, suggesting a compensatory reduction in the clearance of the compound by non excretory routes.

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.

The role of carnitine and carnitine supplementation during exercise in man and in individuals with special needs

Carnitine is critical for normal skeletal muscle bioenergetics. Carnitine has a dual role as it is required for long-chain fatty acid oxidation, and also shuttles accumulated acyl groups out of the mitochondria. Muscle requires optimization of both of these metabolic processes during peak exercise performance. Theoretically, carnitine availability may become limiting for either fatty acid oxidation or the removal of acyl-CoAs during exercise. Despite the theoretical basis for carnitine supplementation in otherwise healthy persons to improve exercise performance, clinical data have not demonstrated consistent benefits of carnitine administration. Additionally, most of the anticipated metabolic effects of carnitine supplementation have not been observed in healthy persons. The failure to demonstrate clinical efficacy of carnitine may reflect the complex pharmacokinetics and pharmacodynamics of carnitine supplementation, the challenges of clinical trial design for performance endpoints, or the adequacy of endogenous carnitine content to meet even extreme metabolic demands in the healthy state. In patients with end stage renal disease there is evidence of impaired cellular metabolism, the accumulation of metabolic intermediates and increased carnitine demands to support acylcarnitine production. Years of nutritional changes and dialysis therapy may also lower skeletal muscle carnitine content in these patients. Preliminary data have demonstrated beneficial effects of carnitine supplementation to improve muscle function and exercise capacity in these patients. Peripheral arterial disease (PAD) is also associated with altered muscle metabolic function and endogenous acylcarnitine accumulation. Therapy with either carnitine or propionylcarnitine has been shown to increase claudication-limited exercise capacity in patients with PAD. Further clinical research is needed to define the optimal use of carnitine and acylcarnitines as therapeutic modalities to improve exercise performance in disease states, and any potential benefit in healthy individuals.

Current and future drug therapies for claudication

The primary objectives of claudication treatment are to reduce cardiovascular mortality and improve walking ability. Patients with claudication have 60% mortality over 10 years, with most deaths due to myocardial infarction and stroke. Aggressive risk-factor modification is required in all these patients, particularly smoking cessation, lipid modification, and treatment of hypertension, diabetes and elevated homocysteine levels. Aspirin, ticlopidine and clopidogrel are all effective in reducing the risk of myocardial infarction, stroke and vascular death, and thus antiplatelet therapy should be considered in all claudicants. Patients with disabling claudication should be considered for therapies that relieve claudication pain and improve exercise performance, the most effective being exercise training and smoking cessation. Pentoxifylline, the only approved claudication drug in the United States, has modest efficacy in improving treadmill exercise performance. Other drugs shown to be of some benefit in patients with claudication include propionyl-L-carnitine, cilostazol and possibly prostaglandin derivatives. Several antiplatelet agents and angiogenic growth factors are also being evaluated for the treatment of claudication.