Myocardial function and energy metabolism in carnitine-deficient rats

Quantitative Profiling of Serum Carnitines Facilitates the Etiology Diagnosis and Prognosis Prediction in Heart Failure

BACKGROUND

The perturbation of fatty acid metabolism in heart failure (HF) has been a critical issue. It is unclear whether the amounts of circulating carnitines will benefit primary etiology diagnosis and prognostic prediction in HF. This study was designed to assess the diagnostic and prognostic values of serum carnitine profiles between ischemic and non-ischemic derived heart failure.

METHODS

HF patients (non-ischemic dilated cardiomyopathy: DCM-HF, n = 98; ischemic heart disease: IHD-HF, n = 63) and control individuals (n = 48) were enrolled consecutively. The serum carnitines were quantitatively measured using the UHPLC-MS/MS method. All patients underwent a median follow-up of 28.3 months. Multivariate Cox regression analysis was performed during the prognosis evaluation.

RESULTS

Amongst 25 carnitines measured, all of them were increased in HF patients, and 20 acylcarnitines were associated with HF diagnosis independently. Seven acylcarnitines were confirmed to increase the probability of DCM diagnosis independently. The addition of isobutyryl-L-carnitine and stearoyl-L-carnitine to conventional clinical factors significantly improved the area under the receiver operating characteristic curve (ROC) from 0.771 to 0.832 (p = 0.023) for DCM-HF diagnosis (calibration test for the composite model: Hosmer-Lemeshow χ² = 7.376, p = 0.497 > 0.05). Using a multivariate COX survival analysis adjusted with clinical factors simultaneously, oleoyl L-carnitine >300 nmol/L (HR = 2.364, 95% CI = 1.122-4.976, p = 0.024) and isovaleryl-L-carnitine <100 nmol/L (HR = 2.108, 95% CI = 1.091-4.074, p = 0.026) increased the prediction of all-cause mortality independently, while linoleoyl-L-carnitine >420 nmol/L, succinyl carnitine >60 nmol/L and isovaleryl-L-carnitine <100 nmol/L increased the risk of HF rehospitalization independently.

CONCLUSIONS

Serum carnitines could not only serve as diagnostic and predictive biomarkers in HF but also benefit the identification of HF primary etiology and prognosis.

A comparison of L-carnitine and several cardiovascular-related biomarkers between healthy vegetarians and omnivores

OBJECTIVE

A plant-based diet has been associated with a reduced risk of cardiovascular (CV) diseases. This study aimed to determine the levels and correlations of CV-related biomarkers and the beneficial role of dietary habits.

METHODS

A total of 63 healthy vegetarians (n = 32) and omnivores (n = 31) were recruited. The baseline characteristics were recorded and measured (including lipid profiles, blood glucose, etc.). Liquid chromatography-mass spectrometry method was developed for the simultaneous determination of seven circulating CV-related biomarkers.

RESULTS

L-carnitine (L-Car), L-methionine, and ascorbic acid (AA) were significantly higher in vegetarians than in omnivores. In the vegetarians, L-Car had a negative correlation with triacylglycerols (P = 0.042) and blood glucose (P = 0.048) and a positive correlation with high-density lipoprotein cholesterol (P = 0.049). L-Car was also positively correlated with L-lysine (P = 0.009), L-methionine (P = 0.006), and AA (P = 0.035). The vegetarians' AA also had a negative correlation with L-homocysteine (P = 0.028). In the omnivores, L-Car was negatively correlated with total cholesterol (P = 0.008), low-density lipoprotein cholesterol (P = 0.004), and high-density lipoprotein cholesterol (P = 0.038). Omnivores' body mass index was positively correlated with L-homocysteine (P = 0.033), and age was positively correlated with trimethylamine N-oxide (P < 0.001) and blood glucose (P = 0.007), but not in vegetarians.

CONCLUSIONS

Our results suggest that vegetarians have an elevated level of L-Car, which might be associated with endogenous biosynthesis and diet composition. Circulating L-Car might play an important role in CV protection, especially in vegetarians.

Impaired Exercise Performance and Skeletal Muscle Mitochondrial Function in Rats with Secondary Carnitine Deficiency

Purpose: The effects of carnitine depletion upon exercise performance and skeletal muscle mitochondrial function remain largely unexplored. We therefore investigated the effect of N-trimethyl-hydrazine-3-propionate (THP), a carnitine analog inhibiting carnitine biosynthesis and renal carnitine reabsorption, on physical performance and skeletal muscle mitochondrial function in rats.

Methods: Male Sprague Dawley rats were treated daily with water (control rats; n = 12) or with 20 mg/100 g body weight THP (n = 12) via oral gavage for 3 weeks. Following treatment, half of the animals of each group performed an exercise test until exhaustion.

Results: Distance covered and exercise performance were lower in THP-treated compared to control rats. In the oxidative soleus muscle, carnitine depletion caused atrophy (–24%) and impaired function of complex II and IV of the mitochondrial electron transport chain. The free radical leak (ROS production relative to oxygen consumption) was increased and the cellular glutathione pool decreased. Moreover, mRNA expression of markers of mitochondrial biogenesis and mitochondrial DNA were decreased in THP-treated compared to control rats. In comparison, in the glycolytic gastrocnemius muscle, carnitine depletion was associated with impaired function of complex IV and increased free radical leak, whilst muscle weight and cellular glutathione pool were maintained. Markers of mitochondrial proliferation and mitochondrial DNA were unaffected.

Conclusions: Carnitine deficiency is associated with impaired exercise capacity in rats treated with THP. THP-induced carnitine deficiency is associated with impaired function of the electron transport chain in oxidative and glycolytic muscle as well as with atrophy and decreased mitochondrial DNA in oxidative muscle.

Pharmacological effects of meldonium: Biochemical mechanisms and biomarkers of cardiometabolic activity

Meldonium (mildronate; 3-(2,2,2-trimethylhydrazinium)propionate; THP; MET-88) is a clinically used cardioprotective drug, which mechanism of action is based on the regulation of energy metabolism pathways through l-carnitine lowering effect. l-Carnitine biosynthesis enzyme γ-butyrobetaine hydroxylase and carnitine/organic cation transporter type 2 (OCTN2) are the main known drug targets of meldonium, and through inhibition of these activities meldonium induces adaptive changes in the cellular energy homeostasis. Since l-carnitine is involved in the metabolism of fatty acids, the decline in its levels stimulates glucose metabolism and decreases concentrations of l-carnitine related metabolites, such as long-chain acylcarnitines and trimethylamine-N-oxide. Here, we briefly reviewed the pharmacological effects and mechanisms of meldonium in treatment of heart failure, myocardial infarction, arrhythmia, atherosclerosis and diabetes.

Contractile function and energy metabolism of skeletal muscle in rats with secondary carnitine deficiency

The consequences of carnitine depletion upon metabolic and contractile characteristics of skeletal muscle remain largely unexplored. Therefore, we investigated the effect of N-trimethyl-hydrazine-3-propionate (THP) administration, a carnitine analog inhibiting carnitine biosynthesis and renal reabsorption of carnitine, on skeletal muscle function and energy metabolism. Male Sprague-Dawley rats were fed a standard rat chow in the absence (CON; n = 8) or presence of THP (n = 8) for 3 wk. Following treatment, rats were fasted for 24 h prior to excision of their soleus and EDL muscles for biochemical characterization at rest and following 5 min of contraction in vitro. THP treatment reduced the carnitine pool by ∼80% in both soleus and EDL muscles compared with CON. Carnitine depletion was associated with a 30% decrease soleus muscle weight, whereas contractile function (expressed per gram of muscle), free coenzyme A, and water content remained unaltered from CON. Muscle fiber distribution and fiber area remained unaffected, whereas markers of apoptosis were increased in soleus muscle of THP-treated rats. In EDL muscle, carnitine depletion was associated with reduced free coenzyme A availability (-25%, P < 0.05), impaired peak tension development (-44%, P < 0.05), and increased glycogen hydrolysis (52%, P < 0.05) during muscle contraction, whereas PDC activation, muscle weight, and water content remained unaltered from CON. In conclusion, myopathy associated with carnitine deficiency can have different causes. Although muscle atrophy, most likely due to increased apoptosis, is predominant in muscle composed predominantly of type I fibers (soleus), disturbance of energy metabolism appears to be the major cause in muscle composed of type II fibers (EDL).

In HepG2 cells, coexisting carnitine deficiency masks important indicators of marginal biotin deficiency

BACKGROUND

A large number of birth defects are related to nutrient deficiencies; concern that biotin deficiency is teratogenic in humans is reasonable. Surprisingly, studies indicate that increased urinary 3-hydroxyisovalerylcarnitine (3HIAc), a previously validated marker of biotin deficiency, is not a valid biomarker in pregnancy.

OBJECTIVE

In this study we hypothesized that coexisting carnitine deficiency can prevent the increase in 3HIAc due to biotin deficiency.

METHODS

We used a 2-factor nutrient depletion design to induce isolated and combined biotin and carnitine deficiency in HepG2 cells and then repleted cells with carnitine. To elucidate the metabolic pathogenesis, we quantitated intracellular and extracellular free carnitine, acylcarnitines, and acylcarnitine ratios using liquid chromatography-tandem mass spectrometry.

RESULTS

Relative to biotin-sufficient, carnitine-sufficient cells, intracellular acetylcarnitine increased by 90%, propionylcarnitine more than doubled, and 3HIAc increased by >10-fold in biotin-deficient, carnitine-sufficient (BDCS) cells, consistent with a defensive mechanism in which biotin-deficient cells transesterify the acyl-coenzyme A (acyl-CoA) substrates of the biotin-dependent carboxylases to the related acylcarnitines. Likewise, in BDCS cells, the ratio of acetylcarnitine to malonylcarnitine and the ratio of propionylcarnitine to methylmalonylcarnitine both more than tripled, and the ratio of 3HIAc to 3-methylglutarylcarnitine (MGc) increased by >10-fold. In biotin-deficient, carnitine-deficient (BDCD) cells, the 3 substrate-derived acylcarnitines changed little, but the substrate:product ratios were masked to a lesser extent. Moreover, carnitine repletion unmasked biotin deficiency in BDCD cells as shown by increases in acetylcarnitine, propionylcarnitine, and 3HIAc (each increased by >50-fold). Likewise, ratios of acetylcarnitine:malonylcarnitine, propionylcarnitine:methylmalonylcarnitine, and 3HIAc:MGc all increased by >8-fold.

CONCLUSIONS

Our findings provide strong evidence that coexisting carnitine deficiency masks some indicators of biotin deficiency and support the potential importance of the ratios of acylcarnitines arising from the acyl-CoA substrates and products for biotin-dependent carboxylases in detecting the biotin deficiency that is masked by coexisting carnitine deficiency.

Carnitine modulates crucial myocardial adenosine triphosphatases and acetylcholinesterase enzyme activities in choline-deprived rats

Choline is an essential nutrient, and choline deficiency has been associated with cardiovascular morbidity. Choline is also the precursor of acetylcholine (cholinergic component of the heart's autonomic nervous system), whose levels are regulated by acetylcholinesterase (AChE). Cardiac contraction-relaxation cycles depend on ion gradients established by pumps like the adenosine triphosphatases (ATPases) Na(+)/K(+)-ATPase and Mg(2+)-ATPase. This study aimed to investigate the impact of dietary choline deprivation on the activity of rat myocardial AChE (cholinergic marker), Na(+)/K(+)-ATPase, and Mg(2+)-ATPase, and the possible effects of carnitine supplementation (carnitine, structurally relevant to choline, is used as an adjunct in treating cardiac diseases). Adult male albino Wistar rats were distributed among 4 groups, and were fed a standard or choline-deficient diet for one month with or without carnitine in their drinking water (0.15% w/v). The enzyme activities were determined spectrophotometrically in the myocardium homogenate. Choline deficiency seems to affect the activity of the aforementioned parameters, but only the combination of choline deprivation and carnitine supplementation increased myocardial Na(+)/K(+)-ATPase activity along with a concomitant decrease in the activities of Mg(2+)-ATPase and AChE. The results suggest that carnitine, in the setting of choline deficiency, modulates cholinergic myocardial neurotransmission and the ATPase activity in favour of cardiac work efficiency.

Effects of long-term mildronate treatment on cardiac and liver functions in rats

Mildronate is a cardioprotective drug that improves cardiac function during ischaemia and functions by lowering l-carnitine concentration in body tissues and modulating myocardial energy metabolism. The aim of the present study was to characterise cardiovascular function and liver condition after long-term mildronate treatment in rats. In addition, changes in the plasma lipid profile, along with changes in the concentration of mildronate, l-carnitine and gamma-butyrobetaine were monitored in the rat tissues. Wistar rats were perorally treated daily with a mildronate dose of either 100, 200 or 400 mg/kg for 4, 8 or 12 weeks. The l-carnitine-lowering effect of mildronate was dose-dependent. However, the carnitine levels reached a plateau after about four weeks of treatment. During the additional weeks of treatment, the carnitine levels were not considerably changed. The obtained results provide evidence that even a high dose of mildronate does not alter cardiovascular parameters and the function of isolated rat hearts. Furthermore, the histological evaluation of liver tissue cryosections and measurement of biochemical markers of hepatic toxicity showed that all the measured values were within the normal reference range. Our results provide evidence that long-term mildronate administration induces significant changes in carnitine homeostasis, but it is not associated with cardiac impairment or disturbances in liver function.

Protective effects of mildronate in an experimental model of type 2 diabetes in Goto-Kakizaki rats

BACKGROUND AND PURPOSE

Mildronate [3-(2,2,2-trimethylhydrazinium) propionate] is an anti-ischaemic drug whose mechanism of action is based on its inhibition of L-carnitine biosynthesis and uptake. As L-carnitine plays a pivotal role in the balanced metabolism of fatty acids and carbohydrates, this study was carried out to investigate whether long-term mildronate treatment could influence glucose levels and prevent diabetic complications in an experimental model of type 2 diabetes in Goto-Kakizaki (GK) rats.

EXPERIMENTAL APPROACH

GK rats were treated orally with mildronate at doses of 100 and 200 mg.kg(-1) daily for 8 weeks. Plasma metabolites reflecting glucose and lipids, as well as fructosamine and beta-hydroxybutyrate, were assessed. L-carnitine concentrations were measured by ultra performance liquid chromatography with tandem mass spectrometry. An isolated rat heart ischaemia-reperfusion model was used to investigate possible cardioprotective effects. Pain sensitivity was measured with a tail-flick latency test.

KEY RESULTS

Mildronate treatment significantly decreased L-carnitine concentrations in rat plasma and gradually decreased both the fed- and fasted-state blood glucose. Mildronate strongly inhibited fructosamine accumulation and loss of pain sensitivity and also ameliorated the enhanced contractile responsiveness of GK rat aortic rings to phenylephrine. In addition, in mildronate-treated hearts, the necrosis zone following coronary occlusion was significantly decreased by 30%.

CONCLUSIONS AND IMPLICATIONS

These results demonstrate for the first time that in GK rats, an experimental model of type 2 diabetes, mildronate decreased L-carnitine contents and exhibited cardioprotective effects, decreased blood glucose concentrations and prevented the loss of pain sensitivity. These findings indicate that mildronate treatment could be beneficial in diabetes patients with cardiovascular problems.

Interaction of mildronate with the mitochondrial carnitine/acylcarnitine transport protein

The interaction of mildronate [3-(2,2,2-trimethylhydrazine) propionate] with the purified mitochondrial carnitine/acylcarnitine transporter reconstituted in liposomes has been studied. Mildronate, externally added to the proteoliposomes, strongly inhibited the carnitine/carnitine antiport catalyzed by the reconstituted transporter with an IC(50) of 560 muM. A kinetic analysis revealed that the inhibition is completely competitive, that is, mildronate interacts with the substrate-binding site. The half-saturation constant of the transporter for external mildronate (K(i)) is 530 muM. Carnitine/mildronate antiport has been measured as [(3)H]carnitine uptake into proteoliposomes containing internal mildronate or as [(3)H]carnitine efflux from proteoliposomes in the presence of external mildronate, indicating that mildronate is transported by the carnitine/acylcarnitine transporter and that the inhibition observed was due to the transport of mildronate in the place of carnitine. The intraliposomal half-saturation constant for mildronate transport (K(m)) has been determined. Its value, 18 mM, is much higher than the external half-saturation constant (K(i)) in agreement with the asymmetric properties of the transporter. In vivo, the antiport reaction between cytosolic (administered) mildronate and matrix carnitine may cause intramitochondrial carnitine depletion. This effect, together with the inhibition of the physiological transport, will lead to impairment of fatty acid utilization.

Hypocarnitinaemia Induced by Sodium Pivalate in the Rat is Associated with Left Ventricular Dysfunction and Impaired Energy Metabolism

Carnitine is a naturally occurring compound that is essential in energy metabolism of the mammalian heart. In addition to its essential role in facilitating beta-oxidation, carnitine eliminates excess toxic acyl residues and regulates the mitochondrial acetyl coenzyme A (CoA)/CoA ratio. Thus, it is not surprising that patients with carnitine deficiency syndromes exhibit defects in energy metabolism and in some cases demonstrate left ventricular dysfunction. Pivalic acid is commonly used to create prodrugs, such as pivampicillin and pivmecillinam, to facilitate enteral absorption and increase oral bioavailability. Pivalic acid released from the drug following absorption readily forms an ester with carnitine, which is then excreted as pivaloylcarnitine. Sustained loss of carnitine in the form of this ester induces a state of carnitine deficiency, exemplified by low plasma and tissue carnitine content. This review examines the effects in the rat of short- and long-term sodium pivalate treatment on: (1) cardiac carnitine content; (2) in vitro mechanical function; (3) markers of glycolytic and fatty acid metabolism; and (4) energy substrate metabolism. Treatment with sodium pivalate induces a gradual loss of cardiac carnitine content for up to 12 weeks. Doubling the duration of treatment is not associated with any further decrease in cardiac carnitine content. While heart function following short-term treatment (2 weeks) is normal under aerobic conditions, impaired recovery of function following ischaemia is seen. In contrast, long-term treatment (11-28 weeks) is associated with impaired heart function, which is dependent on workload and substrate availability. Impaired heart function is also associated with reductions in activity of 3-hydroxyacyl CoA dehydrogenase and rates of fatty acid oxidation. However, to maintain adenosine triphosphate production, glucose metabolism, expressed as hexokinase activity and glucose oxidation, is increased in carnitine-deficient hearts. Hearts from sodium pivalate-treated animals demonstrate a cardiomyopathy that is dependent on duration of treatment, workload and substrate supply. This model of hypocarnitinaemia may thus be useful to study the metabolic and cardiac consequences of carnitine-deficiency syndromes.

Effect of L-carnitine on cardiomyocyte apoptosis and cardiac function in patients undergoing heart valve replacement operation

The effects of L-carnitine, as an ingredient of cardioplegia solution, on cardiac function and cardiomyocyte apoptosis in patients undergoing heart valve replacement operation were investigated. Twenty-three cases undergoing heart valve replacement with cardiopulmonary bypass (CPB) were randomly allocated into two groups: L-carnitine group (n = 12, 12 g/L L-carnitine was put in the ST. Thomas cardioplegia) and control group (n = 11, identical to the L-carnitine group except that normal saline was administered instead of L-carnitine). Serum cardial troponin I (cTnI) levels, the left ventricular ejection fraction (LVEF), and cardiac index (CI) were measured perioperatively. A bit of myocardial tissue obtained from right atria was taken before CPB and by the end of intracardiac procedure to undergo electron microscopy examination and estimate apoptosis by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL). From the end of CPB to 3 days after operation, the serum levels of cTnI in the L-carnitine group was significantly lower than that in the control group (P < 0.05). Heart color ultrasonogram showed that the CI index and LVEF at 7th day postoperatively in the L-carnitine group were significantly higher than in the control group (P < 0.05). Compared to the control group, L-carnitine significantly alleviated the morphologic changes of cardiac muscle cells (electron microscopy examination) and decreased the amounts of apoptotic cardiac muscle cells (TUNEL). Furthermore, the dosage of vasoactive drugs used after operation was significantly less in the L-carnitine group (P < 0.01). It was concluded that L-carnitine cardioplegia solution could improve cardiac function in patients undergoing heart valve replacement operation and alleviate CPB-mediated apoptosis of cardiac muscle cells.

Carnitine depletion in rat pups from mothers given mildronate: a model of carnitine deficiency in late fetal and neonatal life

Mildronate (3-(2,2,2,-trimethylhydrazinium)propionate), is a butyrobetaine analogue that is known to inhibit gamma-butyrobetaine hydroxylase, the enzyme catalyzing the last step of carnitine biosynthesis. When administered to adult rats it determines a systemic carnitine deficiency and may therefore serve as an animal model for human carnitine depletion. The aim of this study was to evaluate the effect of mildronate administration to pregnant and lactating rats on tissue carnitine concentrations in 4- and 13-day-old rat pups. At 14 days of gestation female rats began to receive mildronate in the diet (200 mg/kg/d) and this continued for entire lactation period. Mildronate treatment determined a large reduction of carnitine levels in the milk of lactating dams. Because organ carnitine concentrations in neonatal rats are directly related to dietary supply, pups from mildronate group had significantly depleted levels of total carnitine in serum, heart, liver, muscle, brain and pancreas relative to controls, at 4 and 13 days of age. Correspondingly, an increase in triglyceride levels was observed in liver, heart and muscle of mildronate pups. This is in agreement with a reduction of basal rate of oxidation of [U-(14)C]-palmitate to (14)CO(2) and (14)C-acid-soluble products observed in liver homogenates from carnitine-deficient pups. All functional and biochemical modifications were compatible with a carnitine deficiency status. In conclusion our results describe a model of carnitine depletion in pups, suitable for the investigation of carnitine deficiency in fetal-neonatal nutrition, without any concomitant mildronate-mediated metabolic alterations.

Effect of methanol on endogenous and exogenous carnitine levels in rat plasma

The effect of methanol on the levels of endogenous carnitine and its derivatives was studied in male Sprague-Dawley rats aged three months. In addition, the effect of L-carnitine supplementation on metabolic disturbances caused by methanol intoxication was studied. The rats were randomized into six groups, including two control groups. Methanol was given at 1/4 LD(50) and 1/2 LD(50)/kg b.w. (or water in control) through an intragastric tube, and L-carnitine (or 0.9% NaCl in the control) was injected intraperitoneally. The levels of plasma L-carnitine and its derivatives were measured at selected time points for four days. Following methanol administration, the rats exhibited dose-dependent increases in L-carnitine levels and altered ratios of L-carnitine and its derivatives. L-carnitine supplementation accelerated the normalization of metabolic disturbances, as indicated by the acylcarnitine to free carnitine ratio (AC/FC). The protective effect of L-carnitine is supported by the fact that 100% of the methanol-treated rats supplemented with carnitine survived, while 8/60 rats and 27/101 rats died at methanol doses of 1/4 LD(50) and 1/2 LD(50), respectively, in groups without L-carnitine supplementation.

Evaluation of cardiac lesions and risk factors associated with myocarditis and dilated cardiomyopathy in southern sea otters (Enhydra lutris nereis)

OBJECTIVE

To describe cardiac lesions and identify risk factors associated with myocarditis and dilated cardiomyopathy (DCM) in beach-cast southern sea otters.

ANIMALS

Free-ranging southern sea otters.

PROCEDURE

Sea otters were necropsied at the Marine Wildlife Veterinary Care and Research Center from 1998 through 2001. Microscopic and gross necropsy findings were used to classify sea otters as myocarditis or DCM case otters or control otters. Univariate, multivariate, and spatial analytical techniques were used to evaluate associations among myocarditis; DCM; common sea otter pathogens; and potential infectious, toxic, and nutritional causes.

RESULTS

Clusters of sea otters with myocarditis and DCM were identified in the southern aspect of the sea otter range from May to November 2000. Risk factors for myocarditis included age, good body condition, and exposure to domoic acid and Sarcocystis neurona. Myocarditis associated with domoic acid occurred predominantly in the southern part of the range, whereas myocarditis associated with S. neurona occurred in the northern part of the range. Age and suspected previous exposure to domoic acid were identified as major risk factors for DCM. A sample of otters with DCM had significantly lower concentrations of myocardial L-carnitine than control and myocarditis case otters.

CONCLUSIONS AND CLINICAL RELEVANCE

Cardiac disease is an important cause of death in southern sea otters. Domoic acid toxicosis and infection with S. neurona are likely to be 2 important causes of myocarditis in sea otters. Domoic acid-induced myocarditis appears to progress to DCM, and depletion of myocardial L-carnitine may play a key role in this pathogenesis.