Propionyl-L-carnitine effects on postischemic recovery of heart function and substrate oxidation in the diabetic rat

Natural and synthetic antioxidants targeting cardiac oxidative stress and redox signaling in cardiometabolic diseases

Cardiometabolic diseases (CMDs) are metabolic diseases (e.g., obesity, diabetes, atherosclerosis, rare genetic metabolic diseases, etc.) associated with cardiac pathologies. Pathophysiology of most CMDs involves increased production of reactive oxygen species and impaired antioxidant defense systems, resulting in cardiac oxidative stress (OxS). To alleviate OxS, various antioxidants have been investigated in several diseases with conflicting results. Here we review the effect of CMDs on cardiac redox homeostasis, the role of OxS in cardiac pathologies, as well as experimental and clinical data on the therapeutic potential of natural antioxidants (including resveratrol, quercetin, curcumin, vitamins A, C, and E, coenzyme Q10, etc.), synthetic antioxidants (including N-acetylcysteine, SOD mimetics, mitoTEMPO, SkQ1, etc.), and promoters of antioxidant enzymes in CMDs. As no antioxidant indicated for the prevention and/or treatment of CMDs has reached the market despite the large number of preclinical and clinical studies, a sizeable translational gap is evident in this field. Thus, we also highlight potential underlying factors that may contribute to the failure of translation of antioxidant therapies in CMDs.

Skeletal muscle metabolic changes in peripheral arterial disease contribute to exercise intolerance: a point-counterpoint discussion

Patients with claudication have a marked impairment in exercise performance. Several factors contribute to this limitation, including reductions in large vessel blood flow and oxygen delivery as well as metabolic abnormalities in skeletal muscle. The relative contribution of these factors and their role in the pathophysiology of the exercise limitation is discussed using a point-counterpoint approach. Future directions for research conclude the discussion.

Role of carnitine in the regulation of glucose homeostasis and insulin sensitivity: evidence from in vivo and in vitro studies with carnitine supplementation and carnitine deficiency

BACKGROUND

Although carnitine is best known for its role in the import of long-chain fatty acids (acyl groups) into the mitochondrial matrix for subsequent β-oxidation, carnitine is also necessary for the efflux of acyl groups out of the mitochondria. Since intracellular accumulation of acyl-CoA derivatives has been implicated in the development of insulin resistance, carnitine supplementation has gained attention as a tool for the treatment of insulin resistance. More recent studies even point toward a causative role for carnitine insufficiency in developing insulin resistance during states of chronic metabolic stress, such as obesity, which can be reversed by carnitine supplementation.

METHODS

The present review provides an overview about data from both animal and human studies reporting effects of either carnitine supplementation or carnitine deficiency on parameters of glucose homeostasis and insulin sensitivity in order to establish the less well-recognized role of carnitine in regulating glucose homeostasis.

RESULTS

Carnitine supplementation studies in both humans and animals demonstrate an improvement of glucose tolerance, in particular during insulin-resistant states. In contrast, less consistent results are available from animal studies investigating the association between carnitine deficiency and glucose intolerance. The majority of studies dealing with this question could either find no association or even reported that carnitine deficiency lowers blood glucose and improves insulin sensitivity.

CONCLUSIONS

In view of the abovementioned beneficial effect of carnitine supplementation on glucose tolerance during insulin-resistant states, carnitine supplementation might be an effective tool for improvement of glucose utilization in obese type 2 diabetic patients. However, further studies are necessary to explain the conflicting observations from studies dealing with carnitine deficiency.

Cardiac anaplerosis in health and disease: food for thought

There has been a resurgence of interest for the field of cardiac metabolism catalysed by the increased need for new therapeutic targets for patients with heart failure. The primary focus of research in this area to date has been on the impact of substrate selection for oxidative energy metabolism; however, anaplerotic metabolism also has significant interest for its potential cardioprotective role. Anaplerosis refers to metabolic pathways that replenish the citric acid cycle intermediates, which are essential to energy metabolism; however, our understanding of the role and regulation of this process in the heart, particularly under pathophysiological conditions, is very limited. Therefore, the goal of this article is to provide a foundation for future directions of research on cardiac anaplerosis and heart disease. We include an overview of anaplerotic metabolism, a critical evaluation of current methods available for its quantitation in the intact heart, and a discussion of its role and regulation both in health and disease as it is currently understood based mostly on animal studies. We also consider genetic diseases affecting anaplerotic pathways in humans and acute intervention studies with anaplerotic substrates in the clinics. Finally, as future perspectives, we will share our thoughts about potential benefits and practical considerations on modalities of interventions targeting anaplerosis in heart disease, including heart failure.

Oral supplementation of propionyl-l-carnitine reduces body weight and hyperinsulinaemia in obese Zucker rats

Propionyl-L-carnitine (PLC) is an SCFA esterified to carnitine that plays an important role in fatty acid oxidation and energy expenditure, in addition to having a protective effect on the endothelium. In order to evaluate the effect of PLC on an animal model of obesity, insulin resistance and, consequently, endothelial dysfunction, lean and obese Zucker rats (OZR) received either vehicle- or PLC-supplemented drinking water (200 mg/kg per d) for 20 weeks. Body weight, food intake, systolic blood pressure and heart rate were controlled weekly and an oral glucose tolerance test was performed. Fasting glucose, TAG, cholesterol, HDL, NEFA, adiponectin and insulin were analysed in serum. Visceral adipose tissue and liver were weighed and liver TAG liver composition was evaluated. Endothelial and vascular functions were assessed in the aorta and small mesenteric arteries by response to acetylcholine, sodium nitroprusside and phenylephrine (Phe); NO participation was evaluated after incubation with the NO synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME) and endothelial NOS protein expression by Western blotting. PLC decreased body-weight gain, food intake, adiposity, insulin serum concentration and TAG liver content and improved insulin resistance. Aortae from OZR receiving either vehicle or PLC exhibited a lower contractile response to Phe. PLC-treated OZR showed an enhanced release of endothelial NO upon the adrenergic stimulation. The protection of vascular function found after treatment with PLC in an animal model of insulin resistance supports the necessity of clinical trials showing the effect of L-carnitine supplements on metabolic disorders.

ATP production and TCA activity are stimulated by propionyl-L-carnitine in the diabetic rat heart

BACKGROUND AND OBJECTIVE

The beneficial effect of propionyl-L-carnitine (PLC) on cardiac function in diabetes mellitus is well documented. This study was designed to determine whether the improvement in cardiac function mediated by PLC in the diabetic rat heart is associated with an increase in ATP production and tricarboxylic acid (TCA) cycle activity.

METHODS

Diabetes was induced by an intravenous injection of streptozotocin (60 mg/kg). Following diagnosis of diabetes, treatment was initiated by supplementing the drinking water with PLC at a concentration of 1 g/L for a period of 6 weeks. ATP production and TCA cycle activity were determined from oxidative rates of glucose and palmitate measured in isolated working hearts from control and diabetic animals.

RESULTS

The effect of diabetes was associated with a decrease in heart function, expressed as rate-pressure product (RPP), and in rates of myocardial glucose oxidation. Rates of palmitate oxidation in diabetic hearts were similar to those of control hearts. In PLC-treated diabetic hearts, rates of both glucose and palmitate oxidation were increased and a significant improvement in RPP was observed. As a result, overall ATP production and TCA cycle activity from glucose and palmitate oxidation were increased in diabetic hearts.

CONCLUSION

Our results indicate that the depression in RPP in the diabetic rat heart can be prevented with chronic PLC treatment. Increases in glucose and palmitate utilization with resultant increases in ATP production and TCA cycle activity may explain the benefit of PLC on diabetic rat heart function.

Propionyl-L-Carnitine Prevents Age-Related Myocardial Remodeling in the Rabbit

Age-related cardiac remodeling is characterized by changes in myocardial structure, which include fibrosis (ie, increased collagen concentration). The pathogenetic mechanisms of age-related cardiac changes and possible pharmacologic interventions are still a matter of investigation. A morphometric analysis of collagen accumulation was performed in Sirius Red-stained left ventricular sections of 3-month-old and 5-6-year-old animals after a 9-month period of propionyl-L-carnitine treatment (PLC; 120 mg Kg(-1) day(-1) per os); aged rabbits showed decreased interstitial collagen accumulation and no changes in cellularity and apoptotic rate compared to controls. Age-related expression of vascular cell adhesion molecule-1 (VCAM-1)-positive microvessels was also reduced in PLC-treated rabbits. In vitro, the 16-hour, 10-microM PLC treatment reduced collagen type 1 and VCAM-1 transcripts, which were investigated by reverse transcription-polymerase chain reaction, more markedly in cardiac fibroblasts from aged donors. In the latter, the anti-VCAM-1 antibody treatment was found to be associated with a reduction in collagen type I transcripts. Our results demonstrated that long-term PLC treatment partially prevents age-related interstitial remodeling and suggests that a more complex interstitial cell-to-cell signaling regulates senescent myocardium properties.

Effect of a Novel Molybdenum Ascorbate Complex on Ex Vivo Myocardial Performance in Chemical??Diabetes Mellitus

BACKGROUND

The insulin-like action of metal complexes on target tissues, including the heart, has been reported in experimental diabetes mellitus. Since streptozotocin-induced diabetes is associated with insulin deficiency and left ventricular dysfunction, this study was designed to determine whether the novel metal complex molybdenum ascorbate [MoO(2)(aa)(2)] would improve cardiac function in this model of diabetes.

METHODS

Diabetes was induced in Sprague-Dawley rats (n = 6) following an intravenous injection of streptozotocin (60 mg/kg). After 8 weeks of diabetes, cardiac function was determined in isolated working hearts perfused with 11 mmol/L glucose, 1.2 mmol/L palmitate and 3% albumin. MoO(2)(aa)(2 )was added directly into the perfusate of working hearts at a concentration of 200 micromol/L for a period of 30 minutes. Age-matched control rats served as controls (n = 6).

RESULTS

Cardiac function, expressed as heart rate (HR) and aortic flow, was significantly decreased in diabetic hearts compared with control hearts. The diabetic state was associated with 23% and 60% reductions in HR and aortic flow, respectively. Short-term addition of MoO(2)(aa)(2) was beneficial and partially prevented the attenuation in diabetic rat heart function. MoO(2)(aa)(2 )increased HR by 15%, while aortic flow was increased by 85%. In control hearts, MoO(2)(aa)(2) had no effect on HR and increased aortic flow by 12%.

CONCLUSION

This study extends previous observations on the benefit of metal complexes in experimental diabetes. Our results indicate that short-term treatment with MoO(2)(aa)(2) partially reversed the left ventricular dysfunction associated with the streptozotocin model of diabetes.

L-carnitine and propionyl-L-carnitine improve endothelial dysfunction in spontaneously hypertensive rats: Different participation of NO and COX-products

L-carnitine and propionyl-L-carnitine are supplements to therapy in cardiovascular pathologies. Their effect on endothelial dysfunction in hypertension was studied after treatment with either 200 mg/kg of L-carnitine or propionyl-L-carnitine during 8 weeks of spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). Endothelial function was assessed in aortic rings by carbachol-induced relaxation (CCh 10(-8) to 10(-4) M) and factors involved were characterized in the presence of the inhibitors: L-NAME, indomethacin, the TXA2/PGH2 Tp receptor antagonist ICI-192,605 and the thromboxane synthetase inhibitor-Tp receptor antagonist, Ro-68,070. The effect on phenylephrine-induced contractions was also observed. To identify the nature of vasoactive COX-derived products, enzyme-immunoassay of incubation media was assessed. Involvement of reactive oxygen species was evaluated by incubating with superoxide dismutase and catalase. Nitric oxide production was evaluated by serum concentration of NO2+NO3.Treatment with both compounds improved endothelial function of rings from SHR without blood pressure change. Propionyl-L-carnitine increased NO participation in WKY and SHR. L-carnitine reduced endothelium-dependent responses to CCh in WKY due to an increase of TXA2 production. In both SHR and WKY, L-carnitine enhanced concentration of PGI2 and increased participation of NO. Results in the presence of SOD plus catalase show that it might be related to antioxidant properties of L-carnitine and propionyl-L-carnitine. Comparison between the effect of both compounds shows that both may reduce reactive oxygen species and increase NO participation in endothelium-dependent relaxations in SHR. However, only L-carnitine was able to increase the release of the vasodilator PGI2 and even enhanced TXA2 production in normotensive rats.

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.

Improvement of cardiac function and β-adrenergic signal transduction by propionyl L-carnitine in congestive heart failure due to myocardial infarction

OBJECTIVES

Earlier studies have revealed beneficial effects of metabolic therapy in animals with congestive heart failure (CHF) due to myocardial infarction. Because heart failure is also associated with attenuated response to catecholamines, we examined the effects of propionyl L-carnitine (PLC) (a carnitine derivative) therapy on the beta-adrenoceptor (beta-AR) signal transduction in the failing heart.

METHODS

Heart failure in rats was induced by occluding the coronary artery and 3 weeks later the animals were treated with or without 100 mg/kg (intraperitoneally, daily) PLC for 5 weeks. The animals were assessed for their left ventricular function and inotropic responses to isoproterenol. Crude membranes were isolated from the remote, nonischemic (viable) left ventricle and examined for changes in beta-AR and adenylyl cyclase (AC) activity.

RESULTS

Animals with heart failure exhibited depressions in ventricular function, positive inotropic response to isoproterenol, beta-AR receptor density and basal AC activity; these changes were also attenuated by PLC treatment. The stimulation of AC activities with isoproterenol, 5'-guanyl imidodiphosphate, forskolin and sodium fluoride was decreased in the failing hearts and these changes were also prevented by PLC treatment.

CONCLUSION

The results indicate that metabolic therapy with PLC not only attenuates the defects in heart function but also prevents changes in the beta-AR signal transduction in CHF due to myocardial infarction.

Effects of Propionyl-Carnitine on Mitochondrial Respiration and Post-Ischaemic Cardiac Function in???the Ischaemic Underperfused Diabetic???Rat Heart

BACKGROUND AND OBJECTIVE

Carnitine and its derivatives, namely propionyl-carnitine (PC), have been shown to protect cardiac metabolism and function in diabetes mellitus and ischaemic heart disease. Since diabetes is associated with abnormalities in mitochondrial metabolism of fuels, we examined the effects of PC on mitochondrial respiration in ischaemic hearts from streptozotocin-diabetic rats.

METHODS

Diabetes was induced in Sprague-Dawley rats by an intravenous injection of streptozotocin. Following the diagnosis of diabetes, oral PC treatment was initiated for a period of 6 weeks. After treatment, cardiac function was determined from working hearts perfused under aerobic conditions and in a separate group of hearts subjected to ischaemia and reperfusion. Mitochondrial respiration was determined under aerobic conditions and following low-flow ischaemia.

RESULTS

Rates of state 3 mitochondria respiration with pyruvate were significantly lower in diabetic (n = 4) hearts compared with control (n = 6) hearts (80 +/- 5 vs 112 +/- 5 nanoatoms O2/mg protein/min, respectively), but those with palmitoylcarnitine were similar (101 +/- 11 vs 106 +/- 6 nanoatoms O2/mg protein/min). Diabetic rat heart (n = 8) function, expressed as rate pressure product, was also significantly decreased compared with control (n = 8) hearts (21.5 +/- 1.0 vs 29.5 +/- 0.9 beats x mm Hg x 10(-3)/min, respectively). In PC-treated diabetic (n = 6) hearts, state 3 respiration with pyruvate was increased, and a marked improvement in left ventricular function from 21.5 +/- 1.0 to 26.0 +/- 0.6 beats x mm Hg x 10(-3)/min was observed. During low-flow ischaemia, state 3 respiration with pyruvate remained lower in diabetic (n = 5) hearts compared with control (n = 5) hearts (64 +/- 3 vs 46 +/- 5 nanoatoms O2/mg protein/min, respectively). Following treatment with PC (n = 4), however, respiration with this substrate was significantly increased to 57 +/- 4 nanoatoms O2/mg protein/min. PC was also associated with a significant improvement in cardiac function in reperfused diabetic rat (n = 4) hearts (18.4 +/- 0.2 beats x mm Hg x 10(-3)/min).

CONCLUSION

Our results showed that PC has a beneficial effect on cardiac function and increases ischaemic tolerance of the diabetic rat heart. This beneficial effect of PC can be explained, in part, as an improvement in mitochondrial metabolism of pyruvate during the actual ischaemic period.

Effects of chronic caloric restriction on mitochondrial respiration in the ischemic reperfused rat heart

Dietary restriction increases life span and delays the development of age-related diseases in rodents. We have recently demonstrated that chronic dietary restriction is beneficial on recovery of heart function following ischemia. We studied whether the metabolic basis of this benefit is associated with alterations in mitochondrial respiration. Male Wistar rats were assigned to an ad libitum-fed (AL) group and a food restricted (FR) group, in which food intake was reduced to 55% of the amount consumed by the AL group. Following an 8-month period of restricted caloric intake, isolated working hearts perfused with glucose and high levels of fatty acids were subjected to global ischemia followed by reperfusion. At the end of reperfusion, total heart mitochondria respiration was assessed in the presence of pyruvate, tricarboxylic acid intermediates, and palmitoylcarnitine. Recovery of heart function following ischemia was greater in FR hearts compared to AL hearts. Paralleling these changes in heart function was an increase in state 3 respiration with pyruvate. The respiratory control ratios in the presence of pyruvate and tricarboxylic acid intermediates were higher in FR hearts compared to AL hearts, indicating well-coupled mitochondria. Overall energy production, expressed as the ADP:O ratio and the oxidative phosphorylation rate, was also improved in FR hearts. Our results indicate that the beneficial effect of FR on recovery of heart function following ischemia is associated with changes in mitochondrial respiration.