Acetyl-L-carnitine supplementation differently influences nutrient partitioning, serum leptin concentration and skeletal muscle mitochondrial respiration in young and old rats

Functional Nutrients to Ameliorate Neurogenic Muscle Atrophy

Neurogenic muscle atrophy is a debilitating condition that occurs from nerve trauma in association with diseases or during aging, leading to reduced interaction between motoneurons and skeletal fibers. Current therapeutic approaches aiming at preserving muscle mass in a scenario of decreased nervous input include physical activity and employment of drugs that slow down the progression of the condition yet provide no concrete resolution. Nutritional support appears as a precious tool, adding to the success of personalized medicine, and could thus play a relevant part in mitigating neurogenic muscle atrophy. We herein summarize the molecular pathways triggered by denervation of the skeletal muscle that could be affected by functional nutrients. In this narrative review, we examine and discuss studies pertaining to the use of functional ingredients to counteract neurogenic muscle atrophy, focusing on their preventive or curative means of action within the skeletal muscle. We reviewed experimental models of denervation in rodents and in amyotrophic lateral sclerosis, as well as that caused by aging, considering the knowledge generated with use of animal experimental models and, also, from human studies.

Exposure to inorganic arsenic and its methylated metabolites alters metabolomics profiles in INS-1 832/13 insulinoma cells and isolated pancreatic islets

Inorganic arsenic (iAs) is an environmental diabetogen, but mechanisms underlying its diabetogenic effects are poorly understood. Exposures to arsenite (iAsIII) and its methylated metabolites, methylarsonite (MAsIII) and dimethylarsinite (DMAsIII), have been shown to inhibit glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells and isolated pancreatic islets. GSIS is regulated by complex mechanisms. Increase in ATP production through metabolism of glucose and other substrates is the ultimate trigger for GSIS in β-cells. In the present study, we used metabolomics to identify metabolites and pathways perturbed in cultured INS-1 832/13 rat insulinoma cells and isolated murine pancreatic islets by exposures to iAsIII, MAsIII and DMAsIII. We found that the exposures perturbed multiple metabolites, which were enriched primarily in the pathways of amino acid, carbohydrate, phospholipid and carnitine metabolism. However, the effects of arsenicals in INS-1 832/13 cells differed from those in the islets and were exposure specific with very few overlaps between the three arsenicals. In INS-1 832/13 cells, all three arsenicals decreased succinate, a metabolite of Krebs cycle, which provides substrates for ATP synthesis in mitochondria. Acetylcarnitine was decreased consistently by exposures to arsenicals in both the cells and the islets. Acetylcarnitine is usually found in equilibrium with acetyl-CoA, which is the central metabolite in the catabolism of macronutrients and the key substrate for Krebs cycle. It is also thought to play an antioxidant function in mitochondria. Thus, while each of the three trivalent arsenicals perturbed specific metabolic pathways, which may or may not be associated with GSIS, all three arsenicals appeared to impair mechanisms that support ATP production or antioxidant defense in mitochondria. These results suggest that impaired ATP production and/or mitochondrial dysfunction caused by oxidative stress may be the mechanisms underlying the inhibition of GSIS in β-cells exposed to trivalent arsenicals.

Isolation of soluble scFv antibody fragments specific for small biomarker molecule, L-Carnitine, using phage display

Isolation of single chain antibody fragment (scFv) clones from naïve Tomlinson I+J phage display libraries that specifically bind a small biomarker molecule, L-Carnitine, was performed using iterative affinity selection procedures. L-Carnitine has been described as a conditionally essential nutrient for humans. Abnormally high concentrations of L-Carnitine in urine are related to many health disorders including diabetes mellitus type 2 and lung cancer. ELISA-based affinity characterization results indicate that selectants preferentially bind to L-Carnitine in the presence of key bioselecting component materials and closely related L-Carnitine derivatives. In addition, the affinity results were confirmed using biophysical fluorescence quenching for tyrosine residues in the V segment. Small-scale production of the soluble fragment yielded 1.3mg/L using immunopure-immobilized protein A affinity column. Circular Dichroism data revealed that the antibody fragment (Ab) represents a folded protein that mainly consists of β-sheets. These novel antibody fragments may find utility as molecular affinity interface receptors in various electrochemical biosensor platforms to provide specific L-Carnitine binding capability with potential applications in metabolomic devices for companion diagnostics and personalized medicine applications. It may also be used in any other biomedical application where detection of the L-Carnitine level is important.

Regulation of skeletal muscle mitochondrial activity by thyroid hormones: focus on the "old" triiodothyronine and the "emerging" 3,5-diiodothyronine

3,5,3′-Triiodo-L-thyronine (T3) plays a crucial role in regulating metabolic rate and fuel oxidation; however, the mechanisms by which it affects whole-body energy metabolism are still not completely understood. Skeletal muscle (SKM) plays a relevant role in energy metabolism and responds to thyroid state by remodeling the metabolic characteristics and cytoarchitecture of myocytes. These processes are coordinated with changes in mitochondrial content, bioenergetics, substrate oxidation rate, and oxidative phosphorylation efficiency. Recent data indicate that “emerging” iodothyronines have biological activity. Among these, 3,5-diiodo-L-thyronine (T2) affects energy metabolism, SKM substrate utilization, and mitochondrial functionality. The effects it exerts on SKM mitochondria involve more aspects of mitochondrial bioenergetics; among these, respiratory chain activity, mitochondrial thermogenesis, and lipid-handling are stimulated rapidly. This mini review focuses on signaling and biochemical pathways activated by T3 and T2 in SKM that influence the above processes. These novel aspects of thyroid physiology could reveal new perspectives for understanding the involvement of SKM mitochondria in hypo- and hyper-thyroidism.

Skeletal muscle mitochondrial energetic efficiency and aging

Aging is associated with a progressive loss of maximal cell functionality, and mitochondria are considered a key factor in aging process, since they determine the ATP availability in the cells. Mitochondrial performance during aging in skeletal muscle is reported to be either decreased or unchanged. This heterogeneity of results could partly be due to the method used to assess mitochondrial performance. In addition, in skeletal muscle the mitochondrial population is heterogeneous, composed of subsarcolemmal and intermyofibrillar mitochondria. Therefore, the purpose of the present review is to summarize the results obtained on the functionality of the above mitochondrial populations during aging, taking into account that the mitochondrial performance depends on organelle number, organelle activity, and energetic efficiency of the mitochondrial machinery in synthesizing ATP from the oxidation of fuels.

Acetyl-L-carnitine increases mitochondrial protein acetylation in the aged rat heart

Previously we showed that in vivo treatment of elderly Fisher 344 rats with acetylcarnitine abolished the age-associated defect in respiratory chain complex III in interfibrillar mitochondria and improved the functional recovery of the ischemic/reperfused heart. Herein, we explored mitochondrial protein acetylation as a possible mechanism for acetylcarnitine's effect. In vivo treatment of elderly rats with acetylcarnitine restored cardiac acetylcarnitine content and increased mitochondrial protein lysine acetylation and increased the number of lysine-acetylated proteins in cardiac subsarcolemmal and interfibrillar mitochondria. Enzymes of the tricarboxylic acid cycle, mitochondrial β-oxidation, and ATP synthase of the respiratory chain showed the greatest acetylation. Acetylation of isocitrate dehydrogenase, long-chain acyl-CoA dehydrogenase, complex V, and aspartate aminotransferase was accompanied by decreased catalytic activity. Several proteins were found to be acetylated only after treatment with acetylcarnitine, suggesting that exogenous acetylcarnitine served as the acetyl-donor. Two-dimensional fluorescence difference gel electrophoresis analysis revealed that acetylcarnitine treatment also induced changes in mitochondrial protein amount; a two-fold or greater increase/decrease in abundance was observed for thirty one proteins. Collectively, our data provide evidence for the first time that in the aged rat heart in vivo administration of acetylcarnitine provides acetyl groups for protein acetylation and affects the amount of mitochondrial proteins.

Mitochondrial dysfunction in aging and longevity: a causal or protective role?

SIGNIFICANCE

Among the most highly investigated theories of aging is the mitochondrial theory of aging. The basis of this theory includes a central role for altered or compromised mitochondrial function in the pathophysiologic declines associated with aging. In general, studies in various organisms, including nematodes, rodents, and humans, have largely upheld that aging is associated with mitochondrial dysfunction. However, results from a number of studies directly testing the mitochondrial theory of aging by modulating oxidant production or scavenging in vivo in rodents have generally been inconsistent with predictions of the theory.

RECENT ADVANCES

Interestingly, electron transport chain mutations or deletions in invertebrates and mice that causes mitochondrial dysfunction paradoxically leads to enhanced longevity, further challenging the mitochondrial theory of aging.

CRITICAL ISSUES

How can mitochondrial dysfunction contribute to lifespan extension in the mitochondrial mutants, and what does it mean for the mitochondrial theory of aging?

FUTURE DIRECTIONS

It will be important to determine the potential mechanisms that lead to enhanced longevity in the mammalian mitochondrial mutants.

Acetyl-L-carnitine and lipoic acid improve mitochondrial abnormalities and serum levels of liver enzymes in a mouse model of nonalcoholic fatty liver disease

Mitochondrial abnormalities are suggested to be associated with the development of nonalcoholic fatty liver. Liver mitochondrial content and function have been shown to improve in oral feeding of acetyl-L-carnitine (ALC) to rodents. Carnitine is involved in the transport of acyl-coenzyme A across the mitochondrial membrane to be used in mitochondrial β-oxidation. We hypothesized that oral administration ALC with the antioxidant lipoic acid (ALC + LA) would benefit nonalcoholic fatty liver. To test our hypothesis, we fed Balb/C mice a standard diet (SF) or SF with ALC + LA or high-fat diet (HF) or HF with ALC + LA for 6 months. Acetyl-L-carnitine and LA were dissolved at 0.2:0.1% (wt/vol) in drinking water, and mice were allowed free access to food and water. Along with physical parameters, insulin resistance (blood glucose, insulin, glucose tolerance), liver function (alanine transaminase [ALT], aspartate transaminase [AST]), liver histology (hematoxylin and eosin), oxidative stress (malondialdehyde), and mitochondrial abnormalities (carbamoyl phosphate synthase 1 and electron microscopy) were done. Compared with SF, HF had higher body, liver, liver-to-body weight ratio, white adipose tissue, ALT, AST, liver fat, oxidative stress, and insulin resistance. Coadministration of ALC + LA to HF animals significantly improved the mitochondrial marker carbamoyl phosphate synthase 1 and the size of the mitochondria in liver. Alanine transaminase and AST levels were decreased. In a nonalcoholic fatty liver mice model, ALC + LA combination improved liver mitochondrial content, size, serum ALT, and AST without significant changes in oxidative stress, insulin resistance, and liver fat accumulation.

An integrated clinico-metabolomic model improves prediction of death in sepsis

Sepsis is a common cause of death, but outcomes in individual patients are difficult to predict. Elucidating the molecular processes that differ between sepsis patients who survive and those who die may permit more appropriate treatments to be deployed. We examined the clinical features and the plasma metabolome and proteome of patients with and without community-acquired sepsis, upon their arrival at hospital emergency departments and 24 hours later. The metabolomes and proteomes of patients at hospital admittance who would ultimately die differed markedly from those of patients who would survive. The different profiles of proteins and metabolites clustered into the following groups: fatty acid transport and β-oxidation, gluconeogenesis, and the citric acid cycle. They differed consistently among several sets of patients, and diverged more as death approached. In contrast, the metabolomes and proteomes of surviving patients with mild sepsis did not differ from survivors with severe sepsis or septic shock. An algorithm derived from clinical features together with measurements of five metabolites predicted patient survival. This algorithm may help to guide the treatment of individual patients with sepsis.

Centenarians and supercentenarians: a black swan. Emerging social, medical and surgical problems

The Black Swan Theory was described by Nassim Nicholas Taleb in his book “The Black Swan”. This theory refers to “high-impact, hard-to-predict, and rare events beyond the realm of normal expectations”. According to Taleb’s criteria, a Black Swan Event is a surprise, it has a major impact and after the fact, the event is rationalized by hindsight, as if it had been expected. For most of human history centenarians were a rare and unpredictable phenomenon. The improvements of the social-environmental conditions, of medical care, and the quality of life caused a general improvement of the health status of the population and a consequent reduction of the overall morbidity and mortality, resulting in an overall increase of life expectancy. The study of centenarians and supercentenarians had the objective to consider this black swan and to evaluate the health, welfare, social and economic consequences of this phenomenon.

Mitochondria in the elderly: Is acetylcarnitine a rejuvenator?

Endogenous acetylcarnitine is an indicator of acetyl-CoA synthesized by multiple metabolic pathways involving carbohydrates, amino acids, fatty acids, sterols, and ketone bodies, and utilized mainly by the tricarboxylic acid cycle. Acetylcarnitine supplementation has beneficial effects in elderly animals and humans, including restoration of mitochondrial content and function. These effects appear to be dose-dependent and occur even after short-term therapy. In order to set the stage for understanding the mechanism of action of acetylcarnitine, we review the metabolism and role of this compound. We suggest that acetylation of mitochondrial proteins leads to a specific increase in mitochondrial gene expression and mitochondrial protein synthesis. In the aged rat heart, this effect is translated to increased cytochrome b content, restoration of complex III activity, and oxidative phosphorylation, resulting in amelioration of the age-related mitochondrial defect.

Accumulation of overoxidized Peroxiredoxin III in aged rat liver mitochondria

Overoxidation and subsequent inactivation of Peroxiredoxin III (PrxIII), a mitochondrial H(2)O(2) scavenging enzyme, have been reported in oxidative stress conditions. No data are available in the literature about the presence of overoxidized forms of PrxIII in aged tissues. Liver mitochondria from 12-month-old rats and 28-month-old rats were here analyzed by two-dimensional gel electrophoresis. A spot corresponding to the native form of PrxIII was present in adult and old rats with the same volume, whereas an additional, more acidic spot, of the same molecular weight of the native form, accumulated only in old rats. The acidic spot was identified, by MALDI-MS analysis, as a form of PrxIII bearing the cysteine of the catalytic site overoxidized to sulphonic acid. This modified PrxIII form corresponds to the irreversibly inactivated enzyme, here reported, for the first time, in aging. Three groups of 28-month-old rats treated with acetyl-l-carnitine were also examined. Reduced accumulation of the overoxidized PrxIII form was found in all ALCAR-treated groups.

Acetyl-L-carnitine provides effective in vivo neuroprotection over 3,4-methylenedioximethamphetamine-induced mitochondrial neurotoxicity in the adolescent rat brain

3,4-Methylenedioximethamphetamine (MDMA, ecstasy) is a worldwide abused stimulant drug, with persistent neurotoxic effects and high prevalence among adolescents. The massive release of 5-HT from pre-synaptic storage vesicles induced by MDMA followed by monoamine oxidase B (MAO-B) metabolism, significantly increases oxidative stress at the mitochondrial level. l-Carnitine and its ester, acetyl-l-carnitine (ALC), facilitate the transport of long chain free fatty acids across the mitochondrial membrane enhancing neuronal anti-oxidative defense. Here, we show the potential of ALC against the neurotoxic effects of MDMA exposure. Adolescent male Wistar rats were assigned to four groups: control saline solution, isovolumetric to the MDMA solution, administered i.p.; MDMA (4x10 mg/kg MDMA, i.p.); ALC/MDMA (100 mg/kg 30 min of ALC prior to MDMA, i.p.) and ALC (100 mg/kg, i.p.). Rats were killed 2 weeks after exposure and brains were analyzed for lipid peroxidation, carbonyl formation, mitochondrial DNA (mtDNA) deletion and altered expression of the DNA-encoded subunits of the mitochondrial complexes I (NADH dehydrogenase, NDII) and IV (cytochrome c oxidase, COXI) from the respiratory chain. Levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) were also assessed. The present work is the first to successfully demonstrate that pretreatment with ALC exerts effective neuroprotection against the MDMA-induced neurotoxicity at the mitochondrial level, reducing carbonyl formation, decreasing mtDNA deletion, improving the expression of the respiratory chain components and preventing the decrease of 5-HT levels in several regions of the rat brain. These results indicate potential benefits of ALC application in the prevention and treatment of neurodegenerative disorders.

Acetyl l-carnitine (ALC) treatment in elderly patients with fatigue

Fatigue is one of the conditions most frequently complained by the elderly. There are few effective treatment options for patients with chronic fatigue syndrome. To determine the efficacy, tolerability and impact on the fatigue, as well as on cognitive and functional status of elderly subjects with acetyl L-carnitine (ALC), 96 aged subjects (>70 years, range 71-88) were investigated (50 females and 46 males; mean age 76.2+/-7.6 and 78.4+/-6.4 years, respectively). They met four or more of the Holmes major criteria or at least six of Fukuda minor criteria. Fatigue was measured with the Wessely and Powell [Wessely, S., Powell, R., 1989. Fatigue syndromes: a comparison of chronic postviral fatigue with neuromuscular and affective disorders. J. Neurol. Neurosurg. Psychiatry 52, 940-948] scores, with the fatigue severity scale. At the end of the treatment, we observed a decrease of physical fatigue: 6.2 (p<0.001), of mental fatigue: 2.8 (p<0.001), of severity fatigue: 21.0 (p<0.001) and improvements in functional status: 16.1 (p<0.001) and cognitive functions: 2.7 (p<0.001). By the end of the treatment, significant differences between the two groups were found for the following parameters: muscle pain -27% versus -3% (p<0.05); prolonged fatigue after exercise: 51% versus -4% (p<0.0001); sleep disorders: 28% versus 4% (p<0.05); physical fatigue: 7 versus -0.5 (p<0.0001); mental fatigue: -3.3 versus 0.6 (p<0.0001); fatigue severity scale: -22.5 versus 1.2 (p<0.0001); functional status 17.1 versus 0.6 (p<0.0001); mini mental state examination (MMSE) improvements: 3.4 versus 0.5 (p<0.0001). Our data show that administering ALC may reduce both physical and mental fatigue in elderly and improves both the cognitive status and physical functions.

Carnitine and lipoate ameliorates lipofuscin accumulation and monoamine oxidase activity in aged rat heart

In this study we have focused on the levels of lipofuscin, monoamine oxidase and cholesterol phospholipid ratio in the heart muscle of young, middle aged and aged rats. In parallel, we have also investigated the levels of carnitine and lipoic acid during aging. We observed an increase in lipofuscin accumulation and monoamine oxidase activity in both middle aged and aged rats. Levels of both carnitine and lipoic acid decreased along with a decrease in cholesterol phospholipid ratio. These changes were normalized upon cosupplementation of carnitine and lipoic acid. Our results thus reveal that carnitine along with lipoic acid can be used as an effective supplement against free radical induced damage to the cardiac tissue.

l-Carnitine increases liver α-tocopherol and lowers liver and plasma triglycerides in aging ovariectomized rats

The objective of this study was to determine whether dietary L-carnitine can influence the status of alpha-tocopherol, retinol and selected lipid parameters in aging ovariectomized rats, an animal model for the menopausal state. Fourteen Fisher-344 female rats 18 months old were acclimated for 4 weeks and ovarectomized. Seven rats per treatment were assigned to either a control group fed ad libitum AIN-93M diet or a carnitine group fed the same diet supplemented with L-carnitine. After an 8-week feeding period, blood and selected tissues were taken for analyses. No differences were noted in food intake, body weight, or organ weights due to L-carnitine. Dietary carnitine significantly increased liver alpha-tocopherol and tended to increase plasma alpha-tocopherol (P<.09). No changes in alpha-tocopherol were observed in other tissues including the brain, lungs and retroperitoneal fat. Retinol levels in plasma and tissues were not affected by supplemental L-carnitine. Significant decreases in liver and plasma triglyceride (TG) levels were noted, suggesting increased utilization of fatty acids. No differences were observed in the fatty acid profile of tissues. The results provide evidence that dietary supplementation of L-carnitine enhances the alpha-tocopherol status and improves the utilization of fat leading to lowering of the liver and plasma levels of TG in aging ovariectomized rats. Whether supplemental L-carnitine may be of benefit to postmenopausal women in lowering plasma TG and improving the antioxidant status remains to be studied.

The association of acetyl-l-carnitine and nicotinamide remits the experimental diabetes in mice by multiple low-dose streptozotocin

OBJECTIVES

We studied the effect of acetyl-l-carnitine plus nicotinamide (AC + N) on murine diabetes mellitus induced by multiple low doses of streptozotocin.

METHODS

Male C57BL/6J inbred mice were injected intraperitoneally with citrate buffer or streptozotocin (40 mg/kg) for 5 consecutive days, followed by injections of saline solution or AC + N (50 + 25 mg/kg) from days 6 to 110. Four groups were studied: normal control mice (C), treated normal control mice (TC), diabetic mice (D), and treated diabetic mice (TD). TD group was divided into 2 at day 86; treatment was suspended in one group (TDs) and continued in the other until day 110.

RESULTS

Weight, plasma glucose, plasma insulin, cellular immune aggression, glucose-stimulated insulin secretion from perifused pancreatic slices, and pancreas histology were studied in each experimental group. Diabetic mice treated with AC + N showed improvements in weight, plasma glucose, and plasma insulin levels without mortality, reaching control values at day 110. Cellular immune aggression and insulin release from pancreatic slices perfusions improved without reaching control values. Histology showed that insulin-immunostained area, the index of insulin immunostained beta cells and beta-cell size, was normalized at the end of the study.

CONCLUSIONS

The treatment with AC + N induced remission of autoimmune type 1 diabetes in mice produced by multiple low doses of streptozotocin.

Acetyl-l-carnitine feeding to unloaded rats triggers in soleus muscle the coordinated expression of genes involved in mitochondrial biogenesis

The expressional profile of mitochondrial transcripts and of genes involved in the mitochondrial biogenesis pathway induced by ALCAR daily supplementation in soleus muscle of control and unloaded 3-month-old rats has been analyzed. It has been found that ALCAR treatment is able to upregulate the expression level of mitochondrial transcripts (COX I, ATP6, ND6, 16 S rRNA) in both control and unloaded animals. Interestingly, ALCAR feeding to unloaded rats resulted in the increase of transcript level for master factors involved in mitochondrial biogenesis (PGC-1alpha, NRF-1, TFAM). It also prevented the unloading-induced downregulation of mRNA levels for kinases able to transduce metabolic (AMPK) and neuronal stimuli (CaMKIIbeta) into mitochondrial biogenesis. No significant effect on the expressional level of such genes was found in control ALCAR-treated rats. In addition, ALCAR feeding was able to prevent the loss of mitochondrial protein content due to unloading condition. Correlation analysis revealed a strong coordination in the expression of genes involved in mitochondrial biogenesis only in ALCAR-treated suspended animals, supporting a differentiated effect of ALCAR treatment in relation to the loading state of the soleus muscle. In conclusions, we demonstrated the ability of ALCAR supplementation to promote only in soleus muscle of hindlimb suspended rats an orchestrated expression of genes involved in mitochondrial biogenesis, which might counteract the unloading-induced metabolic changes, preventing the loss of mitochondrial proteins.

Age-associated deficit of mitochondrial oxidative phosphorylation in skeletal muscle: Role of carnitine and lipoic acid

Mitochondrial damage has implicated a major contributor for ageing process. In the present study, we measured mitochondrial membrane swelling, mitochondrial respiration (state 3 and 4) by using oxygen electrode in skeletal muscle of young (3-4 months old) and aged rats (above 24 months old) with supplementation of L: -carnitine and DL: -alpha-lipoic acid. Our results shows that the mitochondrial membrane swelling and state 4 respiration were increased more in skeletal muscle mitochondria of aged rats than in young control rats, whereas the state 3 respiration, respiratory control ratio (RCR) and ADP:O ratio decreased more in aged rats than in young rats. After supplementation of carnitine and lipoic acid to aged rats for 30 days, the state 3 respiration and RCR were increased, whereas the state 4 and mitochondrial membrane swelling were decreased to near normal rats. From our results, we conclude that combined supplementation of carnitine and lipoic acids to aged rats increases the skeletal muscle mitochondrial respiration, thereby increasing the level of ATP.

Supplementation of L-carnitine improves mitochondrial enzymes in heart and skeletal muscle of aged rats

Aging is characterized by a general decline in physiological functions that affects many tissues and increases the risk of death. Deterioration of mitochondria, the major source and target of reactive oxygen species (ROS), is implicated in aging and a variety of age-related diseases. In the present study, the activities of citric acid cycle enzymes, such as isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, and malate dehydrogenase, were found to be decreased in aged rats as well as that of electron-transferring enzymes such as NADH dehydrogenase and cytochrome c oxidase. After supplementation of carnitine to aged rats, the activities of these enzymes reverted nearer to that of young control rats. These findings suggest that L-carnitine improves the activities of mitochondrial enzymes, increases the electron flow through the electron transport chain, and improves reducing equivalence, thereby improves energy status in aged rats.

Comparison of the effects of L-carnitine and acetyl-L-carnitine on carnitine levels, ambulatory activity, and oxidative stress biomarkers in the brain of old rats

L-carnitine and acetyl-L-carnitine (ALC) are both used to improve mitochondrial function. Although it has been argued that ALC is better than l-carnitine in absorption and activity, there has been no experiment to compare the two compounds at the same dose. In the present experiment, the effects of ALC and L-carnitine on the levels of free, acyl, and total L-carnitine in plasma and brain, rat ambulatory activity, and biomarkers of oxidative stress are investigated. Aged rats (23 months old) were given ALC or L-carnitine at 0.15% in drinking water for 4 weeks. L-carnitine and ALC were similar in elevating carnitine levels in plasma and brain. Both increased ambulatory activity similarly. However, ALC decreased the lipid peroxidation (malondialdehyde, MDA) in the old rat brain, while L-carnitine did not. ALC decreased the extent of oxidized nucleotides (oxo8dG/oxo8G) immunostaining in the hippocampal CA1 and cortex, while L-carnitine did not. ALC decreased nitrotyrosine immunostaining in the hippocampal CA1 and white matter, while L-carnitine did not. In conclusion, ALC and L-carnitine were similar in increasing ambulatory activity in old rats and elevating carnitine levels in blood and brain. However, ALC was effective, unlike L-carnitine, in decreasing oxidative damage, including MDA, oxo8dG/oxo8G, and nitrotyrosine, in old rat brain. These data suggest that ALC may be a better dietary supplement than L-carnitine.

Cold exposure differently influences mitochondrial energy efficiency in rat liver and skeletal muscle

This study deals with mitochondrial energy efficiency in liver and skeletal muscle mitochondria in 15 days cold exposed rats. Cold exposure strongly increases the sensitivity to uncoupling by added palmitate of skeletal muscle but not liver mitochondria, while mitochondrial energy coupling in the absence of fatty acids is only slightly affected by cold in liver and skeletal muscle. In addition, uncoupling protein 3 content does not follow changes in skeletal muscle mitochondrial coupling. It is therefore concluded that skeletal muscle could play a direct thermogenic role based on fatty acid-induced mild uncoupling of mitochondrial oxidative phosphorylation.

A possible link between skeletal muscle mitochondrial efficiency and age-induced insulin resistance

The transition from young to adult age is associated with decreased insulin sensitivity. To investigate whether changes in skeletal muscle mitochondrial function could be involved in the development of insulin resistance, we measured the oxidative capacity and energetic efficiency of subsarcolemmal and intermyofibrillar mitochondria isolated from the skeletal muscle of 60- and 180-day-old rats. Mitochondrial efficiency was tested by measuring the degree of thermodynamic coupling and optimal thermodynamic efficiency, as well as mitochondrial proton leak, which was determined in both the absence (basal) and the presence (fatty acid induced) of palmitate. Serum glucose, insulin, and HOMA index were also measured. The results show that in adult rats, concomitant with increased HOMA index, skeletal muscle mitochondria display higher respiratory capacity and energy efficiency. In fact, thermodynamic coupling and optimal thermodynamic efficiency significantly increased and fatty acid-induced proton leak was significantly lower in the skeletal muscle mitochondria from adult than in younger rats. A deleterious consequence of increased mitochondrial efficiency would be a reduced utilization of energy substrates, especially fatty acids, leading to intracellular triglyceride accumulation and lipotoxicity, thus contributing to the onset of skeletal muscle insulin resistance.

Age-associated decreased activities of mitochondrial electron transport chain complexes in heart and skeletal muscle: role of L-carnitine

The mitochondrial respiratory chain is a powerful source of reactive oxygen species (ROS), considered as the pathogenic agent of many diseases and aging. L-Carnitine (4-N-trimethylammonium-3-hydroxybutric acid) plays an important role in transport of fatty acid from cytoplasm to mitochondria for energy production. Previous studies in our laboratory reported L-carnitine as a free radical scavenger in aged rats. In the present study we focused the effect of L-carnitine on the activities of electron transport chain in young and aged rats. The activities of electron transport chain complexes were found to be significantly decreased in aged rats when compared to young control rats. Supplementation of carnitine to young and aged rats for 14 and 21 days improved the electron transport chain complexes levels in aged rats when compared with young rats in duration dependent manner. No significant changes were observed in young rats. Our result suggested that L-carnitine improved the activities of electron transport chain enzymes there by improving the energy status in aged rats.

Reversal of biochemical and behavioral parameters of brain aging by melatonin and acetyl L-carnitine

The potential utility of dietary supplementation in order to prevent some of the oxidative and inflammatory changes occurring in the brain with age, has been studied. The cerebral cortex of 27-month-old male B6C3F1 mice had elevated levels of nitric oxide synthase 1 (EC 1.14.13.39) (nNOS) and peptide nitrotyrosine relative to cortices of younger (4-month-old) animals. After 25-month-old mice received basal diet together with 300 mg/l acetyl L-carnitine in the drinking water for 8 weeks, these levels were fully restored to those found in younger animals. A partial restoration was found when old animals received basal diet supplemented with 200 ppm melatonin in the diet. Levels of mRNA (messenger RNA) for nNOS were unchanged following these treatments implying translational regulation of nNOS activity. Behavioral indices indicative of exploratory behavior were also depressed in aged animals. Dietary supplementation with melatonin or acetyl L-carnitine partially reversed these changes. These findings suggest that dietary supplementation cannot merely arrest but indeed reverse some age-related increases in markers of oxidative and inflammatory events occurring with the cortex.