Muscle carnitine deficiency in patients with severe peripheral vascular disease

Metabolomics of peripheral artery disease

The science of metabolomics has emerged as a novel tool for studying changes in metabolism that accompany different disease states. Several studies have applied this evolving field to the study of various cardiovascular disease states, which has led to improved understanding of metabolic changes that underlie heart failure and ischemic heart disease. A significant amount of progress has also been made in the identification of novel biomarkers of cardiovascular disease. Another common atherosclerotic disease, peripheral artery disease (PAD) affects arteries of the lower extremities. Although certain aspects of the disease pathophysiology overlap with other cardiovascular diseases in general, PAD patients suffer unique manifestations that lead to significant morbidity and mortality as well as severe functional limitations. Furthermore, because over half of PAD patients are asymptomatic, there is a need for improved diagnostic and screening methods. Identification of metabolites associated with the disease may thus be a promising approach for PAD. However, PAD remains highly understudied. In this chapter, we discuss the application of metabolomics to the study of PAD.

Pathophysiology of Peripheral Arterial Disease (PAD): A Review on Oxidative Disorders

Peripheral arterial disease (PAD) is an atherosclerotic disease that affects a wide range of the world’s population, reaching up to 200 million individuals worldwide. PAD particularly affects elderly individuals (>65 years old). PAD is often underdiagnosed or underestimated, although specificity in diagnosis is shown by an ankle/brachial approach, and the high cardiovascular event risk that affected the PAD patients. A number of pathophysiologic pathways operate in chronic arterial ischemia of lower limbs, giving the possibility to improve therapeutic strategies and the outcome of patients. This review aims to provide a well detailed description of such fundamental issues as physical exercise, biochemistry of physical exercise, skeletal muscle in PAD, heme oxygenase 1 (HO-1) in PAD, and antioxidants in PAD. These issues are closely related to the oxidative stress in PAD. We want to draw attention to the pathophysiologic pathways that are considered to be beneficial in order to achieve more effective options to treat PAD patients.

Pathophysiology of chronic peripheral ischemia: new perspectives

Peripheral arterial disease (PAD) affects individuals particularly over 65 years old in the more advanced countries. Hemodynamic, inflammatory, and oxidative mechanisms interact in the pathophysiological scenario of this chronic arterial disease. We discuss the hemodynamic, muscle tissue, and oxidative stress (OxS) conditions related to chronic ischemia of the peripheral arteries. This review summarizes the results of evaluating both metabolic and oxidative markers, and also therapy to counteract OxS. In conclusion, we believe different pathways should be highlighted to discover new drugs to treat patients suffering from PAD.

Altered Metabolomic Profile in Patients with Peripheral Artery Disease

Peripheral artery disease (PAD) is a common atherosclerotic disease characterized by narrowed or blocked arteries in the lower extremities. Circulating serum biomarkers can provide significant insight regarding the disease progression. Here, we explore the metabolomics signatures associated with different stages of PAD and investigate potential mechanisms of the disease. We compared the serum metabolites of a cohort of 26 PAD patients presenting with claudication and 26 PAD patients presenting with critical limb ischemia (CLI) to those of 26 non-PAD controls. A difference between the metabolite profiles of PAD patients from non-PAD controls was observed for several amino acids, acylcarnitines, ceramides, and cholesteryl esters. Furthermore, our data demonstrate that patients with CLI possess an altered metabolomic signature different from that of both claudicants and non-PAD controls. These findings provide new insight into the pathophysiology of PAD and may help develop future diagnostic procedures and therapies for PAD patients.

Characterization of two ETFDH mutations in a novel case of riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency

BACKGROUND

Deficiency of electron transfer flavoprotein dehydrogenase (ETFDH) is associated with multiple acyl-CoA dehydrogenase deficiency (MADD). This disorder is an autosomal recessive lipid storage myopathy (LSM) that exhibits a wide range of clinical features, including myopathy, weakness and multisystem dysfunctions. Many patients with late onset of MADD improve when treated with riboflavin and are also referred to as RR-MADD (riboflavin-responsive multiple Acyl-CoA dehydrogenase disorder).

METHODS

In this study, we report the clinical and genetic characterization of a novel RR-MADD patient. Biochemical data were obtained from analysis of muscle and plasma samples. DNA and RNA were extracted from peripheral blood, and sequence analysis and expression study of ETFDH gene were performed. Finally, the impact of mutations on ETFDH folding was evaluated using bioinformatic tools.

RESULTS

Patient initially presented with vomiting, muscle weakness, and acidosis. Muscle biopsy revealed typical myopathological patterns of lipid storage myopathy and blood acylcarnitine profiles showed a combined elevation of long and medium chain acylcarnitines, supporting the diagnosis of RR-MADD. Molecular analysis of ETFDH gene revealed two heterozygous mutations, a novel splice variation in intron 10, c.1285 + 1G > A, and the previously reported c.560C > T missense mutation. RT-PCR analysis showed an alteration of ETFDH RNA splicing which in turn should lead to the production of a truncated protein. The in silico prediction analysis of ETFDH tridimensional structure demonstrated that the missense mutation resulted in instability and loss of protein activation, while the splice site variation induced a dramatic conformational change of the truncated protein. After MCT diet supplemented with carnitine and riboflavin, the patient showed significant biochemical and clinical improvement, in spite of severe molecular defect.

CONCLUSION

This case report extends the spectrum of ETFDH mutations in MADD, providing further evidence that patients presenting at least one missense mutation in the FAD-binding domain may respond to either carnitine or riboflavin treatment, due to the recovery of some enzymatic activity.

Carnitine Acetyltransferase Mitigates Metabolic Inertia and Muscle Fatigue during Exercise

Acylcarnitine metabolites have gained attention as biomarkers of nutrient stress, but their physiological relevance and metabolic purpose remain poorly understood. Short-chain carnitine conjugates, including acetylcarnitine, derive from their corresponding acyl-CoA precursors via the action of carnitine acetyltransferase (CrAT), a bidirectional mitochondrial matrix enzyme. We show here that contractile activity reverses acetylcarnitine flux in muscle, from net production and efflux at rest to net uptake and consumption during exercise. Disruption of this switch in mice with muscle-specific CrAT deficiency resulted in acetyl-CoA deficit, perturbed energy charge, and diminished exercise tolerance, whereas acetylcarnitine supplementation produced opposite outcomes in a CrAT-dependent manner. Likewise, in exercise-trained compared to untrained humans, post-exercise phosphocreatine recovery rates were positively associated with CrAT activity and coincided with dramatic shifts in muscle acetylcarnitine dynamics. These findings show acetylcarnitine serves as a critical acetyl buffer for working muscles and provide insight into potential therapeutic strategies for combatting exercise intolerance.

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.

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

Development of an in vitro model of myotube ischemia

Critical limb ischemia causes severe damage to the skeletal muscle. This study develops a reproducible model of myotube ischemia by simulating, in vitro, the critical parameters that occur in skeletal muscle ischemia. Monolayers of C2C12 myoblasts were differentiated into mature myotubes and exposed to nutrition depletion, hypoxia and hypercapnia for variable time periods. A range of culture media and gas mixture combinations were used to obtain an optimum ischemic environment. Nuclear staining, cleaved caspase-3 and lactate dehydrogenase (LDH) release assay were used to assess apoptosis and myotube survival. HIF-1α concentration of cell lysates, pH of conditioned media as well as partial pressures of oxygen (PO₂) and carbon dioxide (PCO₂) in the media were used to confirm ischemic simulation. Culturing myotubes in depleted media, in a gas mixture containing 20% CO+80% N₂ for 6-12 h increased the PCO₂ and decreased the pH and PO₂ of culture media. This attempts to mimic the in vivo ischemic state of skeletal muscle. These conditions were used to study the potential tissue-protective effects of erythropoietin (EPO) in C2C12 myotubes exposed to ischemia. EPO (60 ng/ml) suppressed LDH release, decreased cleaved caspase-3 and reduced the number of apoptotic nuclei, suggesting significantly decreased ischemia-induced apoptosis in myotubes (P<0.01) and a potential role in tissue protection. Additional therapeutic agents designed for tissue protection can also be evaluated using this model.

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.

Effect of carnitine on cutaneous wound healing in immunosuppressed rats

BACKGROUND

The wound is ischemic in nature. Chronic steroid administration impairs wound healing by changing enzymes in the glycolytic pathway. Carnitine supplementation may help to restore the energy deficiency caused by chronic steroid administration in the wound. The aim of this study was to evaluate the effect of carnitine on impaired wound healing.

METHODS

The study was conducted in three groups. Surgical intervention was a 4 cm long midline skin incision at the back. In Group A, eight rats received methylprednisolone for 7 d prior to surgical intervention, and it was continued until the end of the experiment. In Group B, 12 rats received methylprednisolone for 7 d prior to surgical intervention. After surgery, methylprednisolone injection was continued and carnitine was supplemented until the end of the experiment. In Group C, eight rats received no medication. The wound of half of the animals in each group was harvested on the seventh day after surgical intervention and the remaining on the 14th d. Tensile strength and hydroxyproline content were measured in all groups.

RESULTS

There was no significant difference in parameters in any of the groups on day seven. On day 14, all parameters were statistically different between methylprednisolone and control groups (P < 0.05). Values for tensile strength were higher in the methylprednisolone/carnitine group compared with methylprednisolone group (P < 0.05). Carnitine administration had also increased hydroxyproline levels in the methylprednisolone/carnitine group compared with the control group (P < 0.05).

CONCLUSIONS

Carnitine is shown to increase tensile strength of the wound when supplemented to immunosuppressed rats in which wound healing is impaired by methylprednisolone.

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.

L-Carnitine treatment reduces severity of physical and mental fatigue and increases cognitive functions in centenarians: a randomized and controlled clinical trial

BACKGROUND

Centenarians are characterized by weakness, decreasing mental health, impaired mobility, and poor endurance. L-Carnitine is an important contributor to cellular energy metabolism.

OBJECTIVE

This study evaluated the efficacy of L-carnitine on physical and mental fatigue and on cognitive functions of centenarians.

DESIGN

This was a placebo-controlled, randomized, double-blind, 2-phase study. Sixty-six centenarians with onset of fatigue after even slight physical activity were recruited to the study. The 2 groups received either 2 g levocarnitine once daily (n = 32) or placebo (n = 34). Efficacy measures included changes in total fat mass, total muscle mass, serum triacylglycerol, total cholesterol, HDL cholesterol, LDL cholesterol, Mini-Mental State Examination (MMSE), Activities of Daily Living, and a 6-min walking corridor test.

RESULTS

At the end of the study period, the levocarnitine-treated centenarians, compared with the placebo group, showed significant improvements in the following markers: total fat mass (-1.80 compared with 0.6 kg; P < 0.01), total muscle mass (3.80 compared with 0.8 kg; P < 0.01), plasma concentrations of total carnitine (12.60 compared with -1.70 mumol; P < 0.05), plasma long-chain acylcarnitine (1.50 compared with -0.1 micromol; P < 0.001), and plasma short-chain acylcarnitine (6.0 compared with -1.50 micromol; P < 0.001). Significant differences were also found in physical fatigue (-4.10 compared with -1.10; P < 0.01), mental fatigue (-2.70 compared with 0.30; P < 0.001), fatigue severity (-23.60 compared with 1.90; P < 0.001), and MMSE (4.1 compared with 0.6; P < 0.001).

CONCLUSIONS

Our study indicates that oral administration of levocarnitine produces a reduction of total fat mass, increases total muscular mass, and facilitates an increased capacity for physical and cognitive activity by reducing fatigue and improving cognitive functions.

Propionyl-L-Carnitine Therapy: Effects on Endothelin-1 and Homocysteine Levels in Patients with Peripheral Arterial Disease and End-Stage Renal Disease

BACKGROUND/AIMS

Recent data have addressed the issue of higher levels of homocysteine (Hcy) and endothelin-1 (ET-1) in end-stage renal disease (ESRD) that may be considered an independent predictor for cardiovascular disease. The prevalence of peripheral arterial disease (PAD) in patients with ESRD has been reported to be relevant, highlighting its clinical importance. We aimed to explore the therapeutic role of propionyl-L-carnitine (PLC) in hemodialysis patients with PAD by measuring ankle/brachial index (ABI), ET-1 and Hcy.

DESIGN

Randomized, double-blind, placebo-controlled trial.

METHODS

Sixty-four patients on hemodialysis with chronic renal insufficiency and PAD were assigned to receive either intravenous PLC (600 mg) or placebo 3 times weekly for 12 months. The ABI and plasma levels of ET-1 and Hcy were measured at baseline, 6 and 12 months.

RESULTS

In the PLC-treated group, progressive increases in ABI were observed, while in the placebo group the reverse trend was seen. Highly significant and progressive reductions in plasma levels of ET-1 and Hcy, compared to baseline, were also seen in the PLC-treated group.

CONCLUSIONS

Hemodynamic flow, endothelial profile and Hcy levels were ameliorated by the administration of PLC in hemodialysis patients with ESRD and PAD.

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.

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.

A Randomised, Controlled Clinical Trial Evaluating Changes in Therapeutic Efficacy and Oxidative Parameters after Treatment with Propionyl L-Carnitine in Patients with Peripheral Arterial Disease Requiring Haemodialysis

OBJECTIVE

We explored the efficacy of intravenous therapy with propionyl L-carnitine in patients with both peripheral arterial disease (PAD) and chronic renal insufficiency requiring haemodialysis.

METHODS

The trial was a randomised, double-blind, placebo-controlled trial. Sixty-four patients on haemodialysis (32 per treatment arm) with chronic renal insufficiency and PAD were assigned to receive either intravenous propionyl L-carnitine 600 mg or placebo 3 times weekly for 12 months. The main outcome measures were the ankle/brachial index (ABI), plasma malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) concentrations, and the plasma nitrite/nitrate ratio (NO(2)/NO(3)); these were measured at baseline and at 6 and 12 months.

RESULTS

Significant increases in ABI were observed in the propionyl L-carnitine group, whereas in the placebo group the reverse trend was seen. In patients treated with propionyl L-carnitine, significant progressive decreases were seen in plasma MDA, 4-HNE and the NO(2)/NO(3) ratio from baseline. In the placebo-treated group, only weakly significant or no differences were seen.

CONCLUSION

Intravenous administration of propionyl L-carnitine to haemodialysis patients with PAD improves both haemodynamic flow and the oxidative profile.

Insulin stimulates L-carnitine accumulation in human skeletal muscle

Increasing skeletal muscle carnitine content may alleviate the decline in muscle fat oxidation seen during intense exercise. Studies to date, however, have failed to increase muscle carnitine content, in healthy humans, by dietary or intravenous L-carnitine administration. We hypothesized that insulin could augment Na+-dependent skeletal muscle carnitine transport. On two randomized visits, eight healthy men underwent 5 h of intravenous L-carnitine infusion with serum insulin maintained at fasting (7.4+/-0.4 mIU*l(-1)) or physiologically high (149.2+/-6.9 mIU*l(-1)) concentrations. The combination of hypercarnitinemia (approximately 500 micromol*l(-1)) and hyperinsulinemia increased muscle total carnitine (TC) content from 22.0 +/- 0.9 to 24.7 +/- 1.4 mmol*(kg dm)(-1) (P<0.05) and was associated with a 2.3 +/- 0.3-fold increase in carnitine transporter protein (OCTN2) mRNA expression (P<0.05). Hypercarnitinemia in the presence of a fasting insulin concentration had no effect on either of these parameters. This study demonstrates that insulin can acutely increase muscle TC content in humans during hypercarnitinemia, which is associated with an increase in OCTN2 transcription. These novel findings may be of importance to the regulation of muscle fat oxidation during exercise, particularly in obesity and type 2 diabetes where it is known to be impaired.

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.

Carnitine and Peripheral Arterial Disease

Patients with peripheral arterial disease (PAD) who become symptomatic with claudication (approximately one-third of the population) have a marked impairment in exercise performance and overall functional capacity. Patients with claudication have a peak oxygen consumption measured during graded treadmill exercise testing that is 50% of that in age-matched normal subjects, and also report great difficulty in walking relatively short distances, even at a slow walking speed. The reduced walking capacity is associated with impairment in activities of daily living and quality of life. Thus, claudication is highly limiting to the physical functioning of daily activities. Improving mobility and improving the reduced quality of life are therefore major goals of treatment. Patients with PAD develop metabolic abnormalities in the skeletal muscles of the lower extremity. These abnormalities include impairment in ischemic muscle mitochondrial electron transport chain activity and accumulation of intermediates of oxidative metabolism (acylcarnitines). Patients with the greatest accumulation of muscle acylcarnitines have the most impaired exercise performance. Thus, claudication is not simply the result of reduced blood flow, and alterations in skeletal muscle metabolism are part of the pathophysiology of the disease. L-carnitine and propionyl-L-carnitine may improve the metabolism and exercise performance of ischemic muscles. L-carnitine in a dose of 2 grams twice daily improved treadmill performance, but propionyl-L-carnitine (an acyl form of carnitine) was more effective than L-carnitine in improving treadmill walking distance. In two multicenter trials of a total of 730 patients, initial and maximal treadmill walking distance improved more with propionyl-L-carnitine than placebo. The drug also improved quality of life and had minimal side effects as compared with placebo. Propionyl-L-carnitine has not been approved for use in the United States.

Redesign of carnitine acetyltransferase specificity by protein engineering

In eukaryotes, L-carnitine is involved in energy metabolism by facilitating beta-oxidation of fatty acids. Carnitine acetyltransferases (CrAT) catalyze the reversible conversion of acetyl-CoA and carnitine to acetylcarnitine and free CoA. To redesign the specificity of rat CrAT toward its substrates, we mutated Met564. The M564G mutated CrAT showed higher activity toward longer chain acyl-CoAs: activity toward myristoyl-CoA was 1250-fold higher than that of the wild-type CrAT, and lower activity toward its natural substrate, acetyl-CoA. Kinetic constants of the mutant CrAT showed modification in favor of longer acyl-CoAs as substrates. In the reverse case, mutation of the orthologous glycine (Gly553) to methionine in carnitine octanoyltransferase (COT) decreased activity toward its natural substrates, medium- and long-chain acyl-CoAs, and increased activity toward short-chain acyl-CoAs. Another CrAT mutant, M564A, was prepared and tested in the same way, with similar results. We conclude that Met564 blocks the entry of medium- and long-chain acyl-CoAs to the catalytic site of CrAT. Three-dimensional models of wild-type and mutated CrAT and COT support this hypothesis. We show for the first time that a single amino acid is able to determine the substrate specificity of CrAT and COT.

The effects of carnitine on distally-burned dorsal skin flap: an experimental study in rats

OBJECTIVE

In ischemia and burn injuries, there are major alterations threatening tissue survival. Increased energy flow requirements are among the major problems in these disorders. Carnitine is an endogenous cofactor, which has a regulatory action on the energy flow from different oxidative sources. The purpose of this study was to determine the effects of carnitine in an experimental flap model. Biochemically, nitric oxide (NO), malondialdehyde (MDA), and acetylcholinesterase levels, and histopathologically tissue examination under light microscope were studied.

METHODS

In the rat dorsal skin, a 10 cm x 3 cm flap was marked. The most distal 3 cm x 3 cm of the flap was burned to full-thickness. The dorsal flap was elevated, and sutured back to its original site. Sixteen rats were divided into two groups (a control (1) and a study group (2)), consisting of eight rats in each. While the animals in the control group were just followed, the animals in the study group were administrated carnitine with a dose of 100 mg/kg per day for 7 days.

RESULTS

At the end of the experiment: the mean surviving areas of the flaps were 15.22 cm(2) (50.73%) in group 1, 20.53 cm(2) (68.43%) in group 2, and the difference was statistically significant (P=0.008). In the analysis of blood samples; the mean levels of NO were 22.63 and 40.78 micromol/l; of MDA were 6.74 and 3.79 ng/ml; and of acetylcholinesterase were 136.14 and 222.85 U/l in groups 1 and 2, respectively. The differences in the levels of NO (P=0.001), MDA (0.027) and acetylcholinesterase (P=0.006) were statistically significant. Histopathological examination revealed a full-thickness muscle necrosis in addition to skin tissue in the control group, while healing tissue was present with marked cellularity including mixed inflammatory cells and fibroblast proliferation with an increased vascularity in the form of capillary budding in the study group.

CONCLUSION

Carnitine has a positive effect in such a model, particularly in preventing the progressive effect of burn, and limiting the necrosis in the full-thickness burned part.

Management of intermittent claudication

Medical management of PAD is a considerable challenge. Although patients typically present with IC, there is a substantial pool of subclinical PAD patients. PAD, whether symptomatic or not, confers a marked cardiovascular risk; with affected patients dying of heart attack or stroke, identification of index patients and aggressive medical treatment can offer health benefits far in excess of improvement in IC or related symptoms. Management of risk factors, lifestyle interventions, and pharmacologic treatment with agents to provide symptomatic relief have a central role in improving function and quality of life and slowing the progression to advanced endpoints, such as the rest pain, nonhealing ulcers, gangrene, and cardiac death. Surgical or percutaneous revascularization for aorto-iliac disease provides durable treatment for individuals with disabling symptoms. Newer treatments, such as angiogenic growth factor treatments, are being tested in clinical trials and seem promising. There are limited treatment choices for individuals with predominant infra-popliteal disease. In the future, the availability of newer stents and therapies to prevent re-stenosis may extend the applicability of endovascular treatment to difficult-to-treat infra-inguinal lesions.

Age-associated mitochondrial oxidative decay: improvement of carnitine acetyltransferase substrate-binding affinity and activity in brain by feeding old rats acetyl-L- carnitine and/or R-alpha -lipoic acid

We test whether the dysfunction with age of carnitine acetyltransferase (CAT), a key mitochondrial enzyme for fuel utilization, is due to decreased binding affinity for substrate and whether this substrate, fed to old rats, restores CAT activity. The kinetics of CAT were analyzed by using the brains of young and old rats and of old rats supplemented for 7 weeks with the CAT substrate acetyl-l-carnitine (ALCAR) and/or the mitochondrial antioxidant precursor R-alpha-lipoic acid (LA). Old rats, compared with young rats, showed a decrease in CAT activity and in CAT-binding affinity for both substrates, ALCAR and CoA. Feeding ALCAR or ALCAR plus LA to old rats significantly restored CAT-binding affinity for ALCAR and CoA, and CAT activity. To explore the underlying mechanism, lipid peroxidation and total iron and copper levels were assayed; all increased in old rats. Feeding old rats LA or LA plus ALCAR inhibited lipid peroxidation but did not decrease iron and copper levels. Ex vivo oxidation of young-rat brain with Fe(II) caused loss of CAT activity and binding affinity. In vitro oxidation of purified CAT with Fe(II) inactivated the enzyme but did not alter binding affinity. However, in vitro treatment of CAT with the lipid peroxidation products malondialdehyde or 4-hydroxy-nonenal caused a decrease in CAT-binding affinity and activity, thus mimicking age-related change. Preincubation of CAT with ALCAR or CoA prevented malondialdehyde-induced dysfunction. Thus, feeding old rats high levels of key mitochondrial metabolites can ameliorate oxidative damage, enzyme activity, substrate-binding affinity, and mitochondrial dysfunction.

Effects of ischaemic stress on leukocyte activation processes in patients with chronic peripheral occlusive arterial disease: role of L-propionyl carnitine administration

An open study was carried out to assess whether, in patients with occlusive peripheral arterial disease (PAD), ischaemic stress induced by maximal physical exercise is associated with leukocyte activation processes, and to evaluate the effects of L-propionyl carnitine (LPC) administration on such processes. Fifteen patients with occlusive PAD (stage II-A), with a mean pain-free walking distance (PWD) of 199 +/- 70.66 m were orally treated with 2000 mg/day LPC for 2 months. Serum levels of E-selectin, P-selectin, L-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-I (VCAM-1) were measured at rest and after the performance of a treadmill walking test (treadmill speed 3.5 km h(-1), inclination 12%) in the untreated condition, and again after treatment with LPC. Significant increases of these factors were observed after maximal exercise compared with resting values. Such increase was significantly reduced after LPC treatment compared with the untreated condition. This study shows that ischaemia induced by maximal stress is associated with leukocyte activation processes, and that LPC is capable of modulating these processes. LPC, therefore, may have a protecting role during ischaemia.

The effect of carnitine on random-pattern flap survival in rats

Carnitine is an endogenous cofactor involved in the transport of long-chain fatty acids into the mitochondria where they undergo beta-oxidation. Through another reaction, carnitine produces free coenzyme A and reduces the ratio of acetyl-coenzyme A to coenzyme A, thereby enhancing oxidative use of glucose, augmenting adenosine triphosphate synthesis, and reducing lactate production and acidosis. Because of its regulatory action on the energy flow from the different oxidative sources, especially under ischemic conditions, carnitine has been used in cardiovascular diseases such as coronary heart disease, congestive heart failure, peripheral vascular disease, dyslipidemia, diabetes, and chronic renal diseases with satisfactory results. A flap is also a relatively ischemic tissue and may obtain benefit from carnitine. To investigate this, 30 rats were divided into three groups of 10 animals: a control group and two carnitine-treated groups. Random dorsal skin flaps were elevated on the rats. In the control group, no pharmacologic agents were used. Of the two treated groups, group 1 was treated with 50 mg/kg/day carnitine for 1 week and group 2 was treated with 100 mg/kg/day carnitine for 1 week. The areas of flap necrosis were measured in each group. The median areas of flap necrosis of the groups were 12.55, 9.23, and 4.9 cm2, respectively. There was a statistically significant improvement of flap necrosis in carnitine-treated groups compared with the control group (group 2, p = 0.001; group 3, p = 0.000). Furthermore, there was less necrosis in the high-dose carnitine-treated group than the low-dose carnitine-treated group. As a conclusion, carnitine may have a dose-dependent effect to increase flap survival in random skin flaps.

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.

Propionyl-L-carnitine dilates human subcutaneous arteries through an endothelium-dependent mechanism

PURPOSE

The vasoactive effects of propionyl-L-carnitine (PLC) on human arteries, including endothelial and smooth muscle cell influences, were studied.

METHODS

Small (less than 200 microm) subcutaneous fat arteries (n = 19), obtained from human patients undergoing vascular surgery, were dissected and mounted in an arteriograph system that allowed measurement of lumen diameter and control of transmural pressure. To investigate the role of the endothelium, arteries were compared intact, intact and in the presence of either 0.3 mmol/L nitro-L-arginine (an inhibitor of nitric oxide synthesis) or 10 micromol/L indomethacin (an inhibitor of prostaglandin synthesis), or denuded of endothelium. After a 1-hour equilibration at a pressure of 50 mm Hg, arteries were precontracted 50% with an intermediate concentration of norepinephrine, and clinically relevant concentrations of PLC (0.1 to 100 micromol/L) were cumulatively added to the bath while the lumen diameter was continually measured.

RESULTS

Intact arteries dose-dependently dilated to PLC, with the half maximal dilation occurring at 2.9 +/- 1.2 micromol/L, increasing diameter 91% +/- 5% at 100 micromol/L. In contrast, PLC had significantly less effect on deendothelialized arteries, increasing diameter only 24% +/- 11% at 100 micromol/L (P <.01 vs. intact). This indicates the endothelial dependency of this compound. Blockade of nitric oxide did not inhibit this vasodilation, with the half-maximal response occurring at 8.6 +/- 7 micromol/L, increasing diameter 85% +/- 8% at 100 micromol/L ( P >.05 vs. intact). However, this vasodilation was significantly diminished in the presence of indomethacin, which dilated arteries only 53% +/- 18% at 100 micromol/L (P <.01 vs. intact; P >.05 vs. denuded).

CONCLUSION

PLC is an endothelium-dependent vasodilator, the mechanism of which is partially mediated by prostaglandin synthesis, not nitric oxide. The beneficial effects of this compound may, in part, be related to vasodilation and enhanced blood flow.

Changes in energy metabolism of calf muscle in patients with intermittent claudication assessed by 31P magnetic resonance spectroscopy: a phase II open study

Energy status and metabolism in skeletal muscle of nine patients with peripheral arterial disease and suffering from intermittent claudication were evaluated using 31phosphorus magnetic resonance spectroscopy (MRS) before and after treatment for 3 months with propionyl-L-carnitine (PLC; 2 g/day p.o.). Maximum walking distance (MWD) was assessed on a standard treadmill (4 km/h, zero incline). For the group as a whole 31P MRS results did not change significantly with PLC. Although MWD increased by a mean of 36%, this change did not reach significance. However, when these variables were assessed with respect to the change in MWD, there were significant differences between those who increased MWD by > 30% (responders, R; n = 5) and those who did not (nonresponders, NR; n = 4). Compared with pretreatment values, during exercise the decrease in muscle pH in R relative to the decrease in phosphocreatine was less after PLC (p = 0.04). After exercise there was a significant inverse correlation between the changes in recovery half-time (t1/2) for phosphocreatine and in MWD (r = -0.91, p = 0.01). With PLC, Vmax increased in R (p = 0.04), but not in NR. For the patient group as a whole, the changes in Vmax and MWD correlated positively (r = 0.90, p = 0.01). This study helps to identify the changes in muscle metabolism that correlate with changes in exercise performance, and may accompany treatment with PLC.

Carnitines increase plasma levels of adenosine and ATP in humans

In order to help to clarify the mode of action of carnitine derivatives, plasma levels of adenosine, ATP and inosine were evaluated following the infusion of 0.75, 0.50 and 0.25 mg/kg/min propionyl-L-carnitine (PLC) for 30 min in patients affected with peripheral arterial disease. Moreover, the effects of 0.75 mg/kg/min acetyl-L-carnitine (ALC) and L-carnitine (LC) were studied in the same conditions. Finally, the activity of 7.5 mg/kg/min PLC administered for 3 min was also evaluated. PLC and ALC produced a significant increase in plasma levels of adenosine and ATP, whereas LC induced less relevant changes. The administration of the compounds did not affect the adenosine/inosine ratio. Peak plasma levels of adenosine preceded in any case those of ATP. The possibility can be suggested that the pharmacological activity of PLC, ALC, and LC may be mediated, at least in part, by an interference with the endogenous purine system. Since these effects may be related to physiological mechanisms of tissue protection, new pharmacological perspectives for the compounds may arise.

Carnitine and its derivatives in cardiovascular disease

Carnitine and its derivative propionyl-L-carnitine are endogenous cofactors which enhance carbohydrate metabolism and reduce the intracellular buildup of toxic metabolites in ischemic conditions. The carnitines have been, and are being used in a spectrum of diseases including multiple cardiovascular conditions. These include angina, acute myocardial infarction, postmyocardial infarction, congestive heart failure, peripheral vascular disease, dyslipidemia, and diabetes. Most published data on carnitine, propionyl-L-carnitine, and other carnitine congeners are favorable but the clinical trials have been relatively small. In currently used doses, these substances are virtually devoid of significant side effects.

Changes in skeletal muscle histology and metabolism in patients undergoing exercise deconditioning: effect of propionyl-L-carnitine

To define the skeletal muscle abnormalities in patients undergoing exercise deconditioning and evaluate the metabolic effect of propionyl-L-carnitine (PLC), muscle biopsies were obtained from 28 patients with effort angina and 31 control subjects. Coronary artery disease patients received either placebo (n = 12), PLC (1.5 g i.v. followed by infusion of 1 mg/kg/min for 30 min, n = 10), or L-carnitine (1 g i.v. followed by infusion of 0.65 mg/kg/min for 30 min, n = 6) for 2 days. Exercise deconditioned patients treated with placebo showed normal muscle content of total carnitine and glycogen, and decrease in percentage of type 1 fibers (P < 0.01) and in the activity of citrate synthase (P < 0.05), succinate dehydrogenase (P < 0.05), and cytochrome oxidase (P < 0.05), as compared to controls. Both PLC and L-carnitine did not modify muscle fiber composition or enzyme activities, but significantly increased muscle levels of total carnitine by 42% and 31%, respectively (P < 0.05). Moreover, PLC significantly increased glycogen muscle content (P < 0.01), while the equimolar dose of L-carnitine did not. This effect, probably due to the anaplerotic activity of the propionic group of PLC, suggests that this drug may be effective in improving energy metabolism of muscles with impaired oxidative capacity.

Serum free carnitine levels in children with recurrent pulmonary infections

The serum free carnitine levels of 33 children with recurrent pulmonary infection and 30 healthy children were measured and found to be 26.12 +/- 0.98 nmol/mL and that of the control group 38.98 +/- 0.79 nmol/mL on the average. The mean free carnitine level was statistically determined to be significantly lower when compared with that of the control group (P < 0.01). The results indicate that oral L-carnitine therapy is recommended for pediatric patients with recurrent pulmonary infection.

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

A double-blind, dose titration study was designed to assess the efficacy of propionyl-L-carnitine in intermittent claudication. The effect on walking capacity was described in a previous article. This study reports on the effect on quality of life, assessed by the McMaster Health Index Questionnaire (MHIQ). After 24 weeks of treatment, the global MHIQ score did not show any difference from baseline in patients randomized to placebo (n = 102). Conversely, it increased from 0.59 +/- 0.12 to 0.64 +/- 0.12 in those taking propionyl-L-carnitine (n = 85). Analysis of variance showed a significant difference between treatments (p = 0.018). Stepwise multiple regression analysis identified baseline maximal walking capacity (cutoff point 250 m) as a predictor of treatment outcome. In patients walking < 250 m, propionyl-L-carnitine significantly improved physical function (p = 0.027), emotional function (p = 0.002), and global MHIQ score (p = 0.002) compared with placebo. Also, for maximal walking capacity, group difference significantly favored propionyl-L-carnitine (p = 0.009). In patients with baseline maximal walking capacity > or = 250 m, propionyl-L-carnitine did not affect the MHIQ scores, nor improve walking performance. These data indicate that propionyl-L-carnitine exerts beneficial effects on quality of life and walking performance in patients with more severely limited walking capacity.

Determination of L-carnitine, acetyl-L-carnitine and propionyl-L-carnitine in human plasma by high-performance liquid chromatography after pre-column derivatization with 1-aminoanthracene

A new sensitive high-performance liquid chromatographic procedure for the determination of L-carnitine (LC), acetyl-L-carnitine (ALC) and propionyl-L-carnitine (PLC) in human plasma has been developed. Precolumn derivatization with 1-aminoanthracene (1AA), performed in phosphate buffer in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) as catalyst, is involved. The fluorescent derivatives were isocratically separated on a reversed-phase column (C18). The eluate was monitored with a fluorimetric detector set at 248 nm (excitation wavelength) and 418 nm (emission wavelength). Because of the presence of endogenous carnitines, the validation was performed using dialyzed plasma. The identity of the derivatized compounds was assessed by mass spectrometry and the purity of the chromatographic peaks was confirmed by HPLC-tandem mass spectrometry. The limits of quantitation were 5 nmol/ml for LC, 1 nmol/ml for ALC and 0.25 nmol/ml for PLC. The recovery of the extraction procedure was in the range 82.6%-95.4% for all 3 compounds. Good linearity (R approximately 0.99) was observed within the calibration ranges studied: 5-160 nmol/ml for LC, 1-32 nmol/ml for ALC and 0.25-8 nmol/ml for PLC. Precision was in the range 0.3-16.8% and accuracy was always lower than 10.6%.

Hyperglycemia-induced latent scurvy and atherosclerosis: the scorbutic-metaplasia hypothesis

Latent scurvy is characterized by a reversible atherosclerosis that closely resembles the clinical form of this disease. Acute scurvy is characterized by microvascular complications such as widespread capillary hemorrhaging. Vitamin C (ascorbate) is required for the synthesis of collagen, the protein most critical in the maintenance of vascular integrity. We suggest that in latent scurvy, large blood vessels use modified LDL--in particular lipoprotein(a)--in addition to collagen to maintain macrovascular integrity. By this mechanism, collagen is spared for the maintenance of capillaries, the sites of gas and nutrient exchange. The foam-cell phenotype of atherosclerosis is identified as a mesenchymal genetic program, regulated by the availability of ascorbate. When vitamin C is limited, foam cells develop and induce oxidative modification of LDL, thereby stabilizing large blood vessels via the deposition of LDL. The structural similarity between vitamin C and glucose suggests that hyperglycemia will inhibit cellular uptake of ascorbate, inducing local vitamin C deficiency.

Propionyl-L-carnitine in intermittent claudication: double-blind, placebo-controlled, dose titration, multicenter study

OBJECTIVES

The aim of this double-blind, placebo-controlled, dose titration, multicenter trial was to assess the efficacy and safety of propionyl-carnitine in intermittent claudication.

BACKGROUND

Human and animal studies indicate that propionyl-L-carnitine increases carnitine content and improves energy metabolism in the ischemic skeletal muscle.

METHODS

After a 2-week preliminary period to assess maximal walking distance, 245 patients were randomly assigned to receive propionyl-L-carnitine (n = 118) or placebo (n = 127). The initial oral dose of 500 mg twice daily was increased at 2-month intervals to 2 g/day and then to 3 g/day in patients showing improvement in treadmill performance < 30% over baseline. Efficacy analysis was conducted for the 214 patients who completed the 24 weeks of treatment by comparing the effect of placebo and propionyl-L-carnitine on day 180.

RESULTS

Analysis of variance showed a significant improvement of 73 +/- 9% (mean +/- SE) in maximal walking distance with propionyl-L-carnitine (n = 99) compared with 46 +/- 6% for placebo (n = 115, p = 0.03). For distance walked at onset of claudication, propionyl-L-carnitine showed about double the improvement of placebo; however, the difference was not statistically significant. There were no changes in electrocardiographic and routine biochemical and hematologic tests that would indicate an adverse effect of propionyl-L-carnitine. Adverse events requiring drug discontinuation (11 in the propionyl-L-carnitine group, 3 in the placebo group) were unrelated to study medication. The dose titration design of the study also provided information on the dose-response relation. Slightly less than 67% of patients were expected to improve their maximal walking distance by at least 30%, assuming 2 g/day of propionyl-L-carnitine (95% confidence interval 0.51 to 0.70). The response rate during the entire titration course was significantly in favor of propionyl-L-carnitine compared with placebo.

CONCLUSIONS

Although the precise mode of therapeutic action requires clarification, propionyl-L-carnitine, at a dose of 1 to 2 g/day, appears to be effective and well tolerated, with minimal adverse effects.

Effect of 8-day therapy with propionyl-L-carnitine on muscular and subcutaneous blood flow of the lower limbs in patients with peripheral arterial disease

The efficacy of propionyl-L-carnitine in increasing walking capacity in patients with peripheral arterial disease is primarily due to the metabolic effect of the drug, but a direct vasoactive action is also hypothesized. Muscular and subcutaneous blood flow of lower limbs were separately evaluated using the 133-Xenon washout technique in 10 patients with peripheral arterial disease of moderate degree, before and after 8-days of treatment with propionyl-L-carnitine (1 g orally b.i.d.). After treatment, muscular blood flow slightly increased, from 10.7 +/- 13.4 to 14.1 +/- 14.0 ml kg-1 min-1. This increase was not statistically significant (T = -1.6568, P = 0.136). Subcutaneous blood flow was not affected by the treatment (from 26.2 +/- 16.9 to 26.1 +/- 12.5 ml kg-1 min-1, T = 0.0141, P = 0.95). In conclusion, in patients with peripheral arterial disease, short-term therapy with propionyl-L-carnitine had no clinical significant effect on muscular and subcutaneous blood flow of the lower limbs. Therefore, this study suggests that the beneficial effect of this drug on the walking capacity of patients with peripheral arterial disease is not due to a direct vasoactive action. Oral administration of propionyl-L-carnitine was found to be safe, as it did not cause any change in heptic, renal or metabolic functional parameters.

Endothelium as a therapeutical target in peripheral occlusive arterial diseases: consideration for pharmacological interventions

The aim of this review is to consider the role of endothelium in the establishment of injury induced by ischaemia and reperfusion with particular emphasis on the vascular beds of the legs. We review the main abnormalities found in the macro- and microcirculation in these conditions and discuss the various theories put forward to explain the mechanism by which endothelial injury is induced. Endothelial cells play a key role in maintaining patent and functional capillaries. When blood vessels are damaged they become unresponsive to vasodilatory stimuli and intraluminal thrombosis may occur. The relative contribution of platelets and leukocytes in the formation of final ischaemic damage is widely discussed. Furthermore, the role of reperfusion in causing damage to post-ischaemic vascular beds is considered as well. The degree to which post-ischaemic injury is reversible might define the opportunity for therapeutic interventions.

Effect of propionyl-L-carnitine in a rat model of peripheral arteriopathy: a functional, histologic, and NMR spectroscopic study

Propionyl-L-carnitine (PLC) has been shown to exert beneficial effects in experimental models of peripheral arterial diseases, such as ergotamine-induced tail gangrene and bilateral femoral arteries occlusion in rats. These models, however, present some drawbacks. The present study was performed to determine whether repeated oral administration of PLC improves the functional, histologic, and metabolic parameters in rats with long-lasting chemically induced peripheral arteriopathy. Peripheral arteriopathy was induced by injecting Na laurate in both the femoral arteries of rats. The walking capacity of the animals (treadmill test) was evaluated at different times and up to 5 weeks after Na laurate injection. Histological examination of vessels and muscles was performed at the end of the experimental period (5 weeks). In separate experiments the level of high-energy phosphates was determined with 31P NMR methodology in the leg muscles. Injection of Na laurate impaired (p < 0.05) the walking capacity of rats, caused thickening of the intima and marked narrowing of the vasal lumen, and reduced the ATP and PCr levels in muscles by 42% and 25%, respectively. PLC given orally for 7 days at 30, 60, 120, and 250 mg/kg dose-dependently decreased the severity of walking capacity impairment by 19%, 41%, 64%, and 71%, respectively. Long-term administration (4 weeks) of PLC (60 and 250 mg/kg os) caused a significant improvement of walking capacity throughout the entire period. The improvement persisted 1 week after discontinuation of the treatment. The severity of the vascular and muscular damages was markedly reduced, particularly in animals treated with the highest dose. Alterations in ATP and PCr levels were significantly (p < 0.05) diminished by PLC (120 mg/kg os) administered daily for 15 days starting 24 hours after Na laurate injection, or for 11 days starting 4 days after Na laurate. The dextro-isomer of the compound was completely inactive, and L-carnitine improved motor performance to a much lesser degree than an identical dose of PLC. It is suggested that the activity of PLC is linked to its metabolic effects on fatty acid oxidation, with consequent preservation of high-energy phosphate levels.