Cardioprotective profile of MET-88, an inhibitor of carnitine synthesis, and insulin during hypoxia in isolated perfused rat hearts

Neuroprotective effect of mildronate and L-carnitine on the cognitive parameters of aged mice and mice with LPS-induced inflammation

Mildronate (MD) is a cardioprotective drug used for the treatment of cardiovascular diseases by switching metabolism from the fatty acids to glucose oxidation. This effect is achieved via inhibition of synthesis of L-carnitine (L-car), a common supplement, which is used for improving of fatty acid metabolism. Both MD and L-car have similar neuroprotective effect. Our goal was to investigate the effect of two drugs on the cognitive parameters of mice under different conditions (aging and lipopolysaccharide (LPS)-induced inflammation). We showed that L-car partly improved the memory and decreased the extent of mtDNA damage in the hippocampus of mice with the LPS-induced inflammation. L-car induced mitochondrial biogenesis and mitophagy in the Nrf2-dependent manner. Both MD and L-car upregulated expression of genes involved in the mitochondrial quality control. In 15-month-old mice, MD improved long-term and short-term memory, reduced the extent of mtDNA damage, and decreased the concentration of diene conjugates in the hippocampus in the Nrf2-independent manner. L-car as a Nrf2 activator had a better neuroprotective effect by normalizing mitochondrial quality control in the reversible cognitive impairment caused by the LPS-induced inflammation, while MD had a better neuroprotective effect in the irreversible cognitive impairment in aged mice, possibly due to a deeper restructuring of metabolism and reduction of oxidative stress.

The Effects of Meldonium on the Renal Acute Ischemia/Reperfusion Injury in Rats

Acute renal ischemia/reperfusion (I/R) injury is a clinical condition that is challenging to treat. Meldonium is an anti-ischemic agent that shifts energy production from fatty acid oxidation to less oxygen-consuming glycolysis. Thus, in this study we investigated the effects of a four-week meldonium pre-treatment (300 mg/kg b.m./day) on acute renal I/R in male rats (Wistar strain). Our results showed that meldonium decreased animal body mass gain, food and water intake, and carnitine, glucose, and lactic acid kidney content. In kidneys of animals subjected to I/R, meldonium increased phosphorylation of mitogen-activated protein kinase p38 and protein kinase B, and increased the expression of nuclear factor erythroid 2-related factor 2 and haeme oxygenase 1, causing manganese superoxide dismutase expression and activity to increase, as well as lipid peroxidation, cooper-zinc superoxide dismutase, glutathione peroxidase, and glutathione reductase activities to decrease. By decreasing the kidney Bax/Bcl2 expression ratio and kidney and serum high mobility group box 1 protein content, meldonium reduced apoptotic and necrotic events in I/R, as confirmed by kidney histology. Meldonium increased adrenal noradrenaline content and serum, adrenal, hepatic, and renal ascorbic/dehydroascorbic acid ratio, which caused complex changes in renal lipidomics. Taken together, our results have confirmed that meldonium pre-treatment protects against I/R-induced oxidative stress and apoptosis/necrosis.

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.

[The influence of mildronate on peripheral neuropathy and some characteristics of glucose and lipid metabolism in rat streptozotocin-induced diabetes mellitus model]

Streptozotocin (STZ) was used to induce the diabetic rat model. STZ rats were treated with mildronate (100 mg/kg daily, per os or intraperitoneally for 6 weeks). Body weight, blood glucose, triglyceride, ketone body concentrations, glycated hemoglobin percent (HbA1c%), glucose tolerance, and the development of neuropathic pain were monitored throughout the experiment. In the STZ + mildronate group, mildronate treatment caused a significant decrease in mean blood glucose (on week 4) and triglyceride concentrations (on weeks 3-6), significantly slowed the increase in HbA1c% (on week 6) and improved glucose tolerance 120 minutes after glucose ingestion during oral glucose tolerance test versus the STZ group. Mildronate completely protected development of STZ-induced neuropathic pain from the first administration week up to end of the experiment. The obtained data indicate clinical usefulness of the drug for the treatment of diabetes mellitus and its complications.

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.

The cardioprotective effect of mildronate is diminished after co-treatment with L-carnitine

Mildronate, an inhibitor of L-carnitine biosynthesis and uptake, is a cardioprotective drug whose mechanism of action is thought to rely on the changes in concentration of L-carnitine in heart tissue. In the present study, we compared the cardioprotective effect of mildronate (100 mg/kg) and a combination of mildronate and L-carnitine (100 + 100 mg/kg) administered for 14 days with respect to the observed changes in l-carnitine level and carnitine palmitoyltransferase I (CPT-I)-dependent fatty acid metabolism in the heart tissues. Concentrations of L-carnitine and its precursor γ-butyrobetaine (GBB) were measured by ultraperformance liquid chromatography with tandem mass spectrometry. In addition, mitochondrial respiration, activity of CPT-I, and expression of CPT-IA/B messenger RNA (mRNA) were measured. Isolated rat hearts were subjected to ischemia-reperfusion injury. Administration of mildronate induced a 69% decrease in L-carnitine concentration and a 6-fold increase in GBB concentration in the heart tissue as well as a 27% decrease in CPT-I-dependent mitochondrial respiration on palmitoyl-coenzyme A. In addition, mildronate treatment induced a significant reduction in infarct size and also diminished the ischemia-induced respiration stimulation by exogenous cytochrome c. Treatment with a combination had no significant impact on L-carnitine concentration, CPT-I-dependent mitochondrial respiration, and infarct size. Our results demonstrated that the mildronate-induced decrease in L-carnitine concentration, concomitant decrease in fatty acid transport, and maintenance of the intactness of outer mitochondrial membrane in heart mitochondria are the key mechanisms of action for the anti-infarction activity of mildronate.

Correction of glycaemia and GLUT1 level by mildronate in rat streptozotocin diabetes mellitus model

Anti-ischaemic drug mildronate suppresses fatty acid metabolism and increases glucose utilization in myocardium. It was proposed that it could produce a favourable effect on metabolic parameters and glucose transport in diabetic animals. Rats with streptozotocin diabetes mellitus were treated with mildronate (100 mg/kg daily, per os, 6 weeks). Therapeutic effect of mildronate was monitored by measuring animal weight, concentrations of blood glucose, insulin, blood triglycerides, free fatty acids, blood ketone bodies and cholesterol, glycated haemoglobin per cent (HbA1c%) and glucose tolerance. GLUT1 mRNA and protein expression in kidneys, heart, liver and muscles were studied by means of real time RT-PCR and immunohistochemistry correspondingly. In the streptozotocin + mildronate group, mildronate treatment caused a significant decrease in mean blood glucose, cholesterol, free fatty acid and HbA1c concentrations and improved glucose tolerance. Induction of streptozotocin diabetes mellitus provoked increase of both GLUT1 gene and protein expression in kidneys, heart and muscle, mildronate treatment produced normalization of the GLUT1 expression levels. In the liver a similar effect was observed for GLUT1 protein expression, while GLUT1 gene expression was increased by mildronate. Mildronate produces therapeutic effect in streptozotocin diabetes model. Mildronate normalizes the GLUT1 expression up-regulated by streptozotocin diabetes mellitus in kidneys, heart, muscle and liver. Copyright © 2011 John Wiley & Sons, Ltd.

Anti-diabetic effects of mildronate alone or in combination with metformin in obese Zucker rats

Mildronate is a cardioprotective drug, the mechanism of action of which is based on the regulation of l-carnitine concentration. We studied the metabolic effects of treatment with mildronate, metformin and a combination of the two in the Zucker rat model of obesity and impaired glucose tolerance. Zucker rats were p.o. treated daily with mildronate (200mg/kg), metformin (300 mg/kg), and a combination of both drugs for 4 weeks. Weight gain and plasma metabolites reflecting glucose metabolism were measured. The expression of peroxisome proliferator-activated receptor (PPAR)-α and PPAR-γ and target genes was measured in rat heart and liver tissues. Each treatment decreased the blood glucose concentration during the fed and fasted states by 1 to 2 mmol/l. Treatment with mildronate and metformin decreased the plasma insulin concentration by 31 and 29%, respectively, while the combination of both drugs significantly reduced fed insulin concentration by about 47%. Mildronate treatment increased the expression of PPAR-α in the heart tissue and PPAR-γ in the heart and liver tissues. In addition, treatment increased the expression of PPAR target genes in the heart, but not in the liver tissue. In contrast to monotherapy, treatment with the combination of mildronate and metformin significantly decreased weight gain by 19% and did not affect food intake. In conclusion, our results demonstrate that mildronate, an inhibitor of l-carnitine biosynthesis, improves adaptation to hyperglycemia- and hyperlipidemia-induced metabolic disturbances and increases PPAR-α activity.

Mildronate decreases carnitine availability and up-regulates glucose uptake and related gene expression in the mouse heart

AIMS

l-carnitine has been shown to play a central role in both fat and carbohydrate metabolisms. This study investigated whether acute and long-term treatments with an l-carnitine biosynthesis inhibitor, mildronate (3-(2,2,2-trimethylhydrazinium) propionate), modulate glucose uptake.

MAIN METHODS

The effects of acute and long-term administration of mildronate at a dose of 200 mg/kg (i.p. daily for 20 days) were tested in mouse blood plasma and heart.

KEY FINDINGS

Acute administration of mildronate in vivo, or in vitro administration with perfusion buffer in isolated heart experiments, did not induce any effects on glucose blood concentration and uptake in the heart. Mildronate long-term treatment significantly decreased carnitine concentration in plasma and heart tissues, as well as increased the rate of insulin-stimulated glucose uptake by 35% and the expression of glucose transporter 4, hexokinase II, and insulin receptor proteins in mouse hearts. In addition, expression of both carnitine palmitoyltransferases IA and IB were significantly increased. Mildronate long-term treatment statistically significantly decreased fed state blood glucose from 6+/-0.2 to 5+/-0.1 mM, but did not affect plasma insulin and C-peptide levels.

SIGNIFICANCE

Our experiments demonstrate for the first time that long-term mildronate treatment decreases carnitine content in the mouse heart and leads to increased glucose uptake and glucose metabolism-related gene expression.

Mildronate, an inhibitor of carnitine biosynthesis, induces an increase in gamma-butyrobetaine contents and cardioprotection in isolated rat heart infarction

The inhibition of gamma-butyrobetaine (GBB) hydroxylase, a key enzyme in the biosynthesis of carnitine, contributes to lay ground for the cardioprotective mechanism of action of mildronate. By inhibiting the biosynthesis of carnitine, mildronate is supposed to induce the accumulation of GBB, a substrate of GBB hydroxylase. This study describes the changes in content of carnitine and GBB in rat plasma and heart tissues during long-term (28 days) treatment of mildronate [i.p. (intraperitoneal) 100 mg/kg/daily]. Obtained data show that in concert with a decrease in carnitine concentration, the administration of mildronate caused a significant increase in GBB concentration. We detected about a 5-fold increase in GBB contents in the plasma and brain and a 7-fold increase in the heart. In addition, we tested the cardioprotective effect of mildronate in isolated rat heart infarction model after 3, 7, and 14 days of administration. We found a statistically significant decrease in necrotic area of infarcted rat hearts after 14 days of treatment with mildronate. The cardioprotective effect of mildronate correlated with an increase in GBB contents. In conclusion, our study, for the first time, provides experimental evidence that the long-term administration of mildronate not only decreases free carnitine concentration, but also causes a significant increase in GBB concentration, which correlates with the cardioprotection of mildronate.

Mildronate, a novel fatty acid oxidation inhibitor and antianginal agent, reduces myocardial infarct size without affecting hemodynamics

Mildronate is a fatty acid oxidation inhibitor approved as an antianginal drug in parts of Europe. We carried out the first study to determine whether a 10-day course of mildronate could reduce myocardial infarct size (IS) during acute myocardial ischemia. Sprague Dawley rats received 200 mg/kg/d of mildronate (treated group, n = 16) or sterile water (control group, n = 14) subcutaneously for 10 days before ischemia-reperfusion. Rats were then subjected to 45 minutes of left coronary artery occlusion and 2 hours of reperfusion. The 2 groups had identical areas at risk: treated 38 +/- 3%; controls 38 +/- 2%. The amount of necrosis was smaller in the mildronate group at 16 +/- 2% of the left ventricle versus controls, 22 +/- 2% (P = 0.05); and for any amount of risk >25%, necrosis was smaller in the treated group (P = 0.0035). Myocardial IS (% of risk zone) was 43+/-3% in the mildronate-treated rats, and 57+/-4% in controls (P = 0.004). During occlusion, there were no differences between the 2 groups in heart rate (216 +/- 12 bpm, mildronate and 210 +/- 9 bpm, control), in mean arterial pressure (60 +/- 2 mm Hg, mildronate and 64 +/- 3 mm Hg, control) or in the frequency of arrhythmias. Our study for the first time demonstrated that a 10-day treatment with mildronate reduced myocardial IS in an experimental model of acute myocardial ischemia, without any effect on hemodynamics.

Role of intrapartum hypoxia in carnitine nutritional status during the early neonatal period

We analyze markers of carnitine insufficiency and deficiency, lysine (LYS) and methionine (MET), in 39 neonates with intrapartum hypoxia (selection criteria: umbilical artery pH <7.20, lactate >1.8 mmol/l and PaO2 <25 mm Hg), and in 35 healthy newborn infants (control group) in the early neonatal period (1-7 days of life). Free (FC), total (TC) carnitine and acylcarnitines (AC=short-chain+long-chain acylcarnitines) were measured using a radioisotopic micromethod; LYS and MET were determined by high-pressure liquid chromatography. AC and TC plasma concentrations and AC/FC ratio were higher while FC/TC ratio was lower in the hypoxic neonates than in the control group. Hypoxic newborn infants (59%) presented "carnitine deficiency" (FC/TC <0.7) and 60% of them "carnitine insufficiency" (AC/FC ratio >0.4) vs. 31% and 28%, respectively, for the neonates of the control group (p<0.05). In the healthy neonates group, MET correlated with FC/TC and the AC/FC ratio. FC, TC, AC, AC/FC and umbilical artery pH (pHua) were inversely correlated. FC/TC and MET correlated with pHua. We conclude that: (1) an important percentage of newborn infants with intrapartum hypoxia suffer carnitine deficiency and carnitine insufficiency in the early neonatal period, related to MET plasma levels; (2) the carnitine deficiency or insufficiency in the neonate is determined by the degree of intrapartum acidosis.

Effect of various levels of supplementation with sodium pivalate on tissue carnitine concentrations and urinary excretion of carnitine in the rat

In previous studies, sodium pivalate has been administered to rats in their drinking water (20 mmoles/L; equivalent to 0.3% of the diet) as a way to lower the concentration of carnitine in tissues and to produce a model of secondary carnitine deficiency. Although this level of supplementation results in a marked decrease in carnitine concentration in a variety of tissues, it does not produce the classical signs of carnitine deficiency (i.e., decreased fatty acid oxidation and ketogenesis). The present study was designed (1) to determine if increasing the level of pivalate supplementation (0.6, 1.0% of the diet) would further reduce the concentrations of total and free carnitine in rat tissues without altering growth or food intake, and (2) to examine the effect of length of feeding (4 vs. 8 weeks) on these variables. Male, Sprague-Dawley rats were randomly assigned to either a control (0.2% sodium bicarbonate) or experimental diet (0.3, 0.6, 1.0% sodium pivalate) for either four or eight weeks. Animals (n = 6/group) were housed in metabolic cages; food and water were provided ad libitum throughout the study. Supplementation with sodium pivalate did not alter water intake or urine output. Ingestion of a diet containing 1.0% pivalic acid decreased food intake (g/day; P < 0.05), final body weight (P < 0.007), and growth rate (P < 0.001) after four weeks. The concentration of total carnitine in plasma, heart, liver, muscle, and kidney was reduced in all experimental groups (P < 0.001), regardless of level of supplementation or length of feeding. The concentration of free carnitine in heart, muscle, and kidney was also reduced (P < 0.001) in rats treated with pivalate for either four or eight weeks. The concentration of free carnitine in liver was reduced in animals supplemented with pivalate for eight weeks (P < 0.05), but no effect was observed in livers from rats treated for four weeks. Excretion of total carnitine and short chain acylcarnitine in urine was increased in pivalate supplemented rats throughout the entire feeding period (P < 0.001). Free carnitine excretion was increased during Weeks 1 and 2 (P < 0.01), but began to decline during Week 3 in experimental groups. During Weeks 6 and 8, free carnitine excretion in pivalate supplemented rats was less than that of control animals (P < 0.01). In summary, no further reduction in tissue carnitine concentration was observed when rats were supplemented with sodium pivalate at levels greater than 0.3% of the diet. Food intake (g/day) and growth were decreased in rats fed a diet containing 1.0% sodium pivalate. These data indicate that maximal lowering of tissue carnitine concentrations is achieved by feeding diets containing 0.3% sodium pivalate or less.

MET-88, a gamma-butyrobetaine hydroxylase inhibitor, improves cardiac SR Ca2+ uptake activity in rats with congestive heart failure following myocardial infarction

We previously reported that MET-88, 3-(2,2,2-trimethylhydrazinium) propionate, improved left ventricular diastolic dysfunction induced by congestive heart failure (CHF) in rats. The present study was designed to investigate the mechanism by which MET-88 improved the cardiac relaxation impaired in CHF rats. The left coronary artery of the animals was ligated, and the rats were then orally administered vehicle (control), MET-88 at 50 or 100 mg/kg or captopril at 20 mg/kg for 20 days. Myocytes were isolated from the non-infarcted region in the left ventricle, and cell shortening and [Ca2+]i transients were measured with a video-edge detector and by fluorescence analysis, respectively. In CHF control rats, the diastolic phase of cell shortening was prolonged compared with that of the sham-operated (sham) rats. This prolongation was prevented by treatment with MET-88 at 100 mg/kg or captopril at 20 mg/kg. CHF control rats also showed an increase in the decay time of [Ca2+]i transients compared with sham rats. MET-88 at 100 mg/kg and captopril at 20 mg/kg attenuated the increase in decay time of [Ca2+]i transients. Ca2+ uptake activity of the sarcoplasmic reticulum (SR) isolated from the non-infarcted region in the left ventricle was measured, and Lineweaver-Burk plot analysis of the activity was performed. CHF control rats revealed a decrease in the Vmax for SR Ca2+ uptake activity without alteration in Kd. MET-88 at 100 mg/kg significantly prevented the decrease in Vmax, but had no effect on Kd. Also, treatment with MET-88 at 100 mg/kg improved myocardial high-energy phosphate levels impaired in CHF rats. These results suggest that one of the mechanisms by which MET-88 improved cardiac relaxation in CHF rats is based on the amelioration of [Ca2+]i transients through increase of SR Ca2+ uptake activity.

Beneficial effects of MET-88, a gamma-butyrobetaine hydroxylase inhibitor in rats with heart failure following myocardial infarction

Myocardial ischemia can cause myocardial infarction and as a consequence, heart failure. 3-(2,2,2-trimethylhydrazinium) propionate (MET-88) inhibits gamma-butyrobetaine hydroxylase and has cardioprotective effects on the ischemic heart. We now examined the effects of MET-88 in rats with congestive heart failure following myocardial infarction. Congestive heart failure was produced by left coronary artery ligation in rats. MET-88 at 100 mg/kg/day was orally administered from the 2nd day after surgery. We performed a survival study for 181 days, and measured ventricular remodeling, cardiac function, and myocardial high-energy phosphate levels after treatment for 20 days. MET-88 prolonged survival with a median 50% survival of 103 days compared to 79 days for the heart-failure control rats. The expansion of the left ventricular cavity (ventricular remodeling) in heart-failure rats was prevented by treatment with MET-88, and the effect of MET-88 was similar to that of captopril at 20 mg/kg. MET-88 attenuated the rise in right atrial pressure in heart-failure rats and augmented cardiac functional adaptability against an increased load. Also, MET-88 improved the myocardial energy state in heart-failure rats. The present results indicate that MET-88 improves the pathosis in rats with heart failure induced by myocardial infarction.