Acetyl-L-carnitine affects aged brain receptorial system in rodents

Neuroprotective Effects of Carnitine and Its Potential Application to Ameliorate Neurotoxicity

Carnitine is an essential metabolite that is absorbed from the diet and synthesized in the kidney, liver, and brain. It ferries fatty acids across the mitochondrial membrane to undergo β-oxidation. Carnitine has been studied as a therapy or protective agent for many neurological diseases and neurotoxicity (e.g., prolonged anesthetic exposure-induced developmental neurotoxicity in preclinical models). Preclinical and clinical data support the notion that carnitine or acetyl carnitine may improve a patient's quality of life through increased mitochondrial respiration, release of neurotransmitters, and global gene expression changes, showing the potential of carnitine beyond its approved use to treat primary and secondary carnitine deficiency. In this review, we summarize the beneficial effects of carnitine or acetyl carnitine on the central nervous system, highlighting protective effects against neurotoxicity-induced damage caused by various chemicals and encouraging a thorough evaluation of carnitine use as a therapy for patients suffering from neurotoxicant exposure.

Attention deficit/hyperactivity disorder as an associated feature in OCTN2 deficiency with novel deletion (p.T440-Y449)

This boy presented with ADHD at 3 years and at 8 years was hyperactive with no documented hypoglycemia and had myopathy, cardiomyopathy, and very low serum carnitine. L‐carnitine improved his exercise intolerance, cardiomyopathy, and behavior. Analysis of SLC22A5 revealed a premature stop codon (p.R282*) and a novel in‐frame deletion (p.T440‐Y449).

Distinct effects of ketamine and acetyl L-carnitine on the dopamine system in zebrafish

Ketamine, a noncompetitive N-methyl-D-aspartic acid (NMDA) receptor antagonist is commonly used as a pediatric anesthetic. We have previously shown that acetyl L-carnitine (ALCAR) prevents ketamine toxicity in zebrafish embryos. In mammals, ketamine is known to modulate the dopaminergic system. NMDA receptor antagonists are considered as promising anti-depressants, but the exact mechanism of their function is unclear. Here, we measured the levels of dopamine (DA) and its metabolites, 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the zebrafish embryos exposed to ketamine in the presence and absence of 0.5 mM ALCAR. Ketamine, at lower doses (0.1-0.3 mM), did not produce significant changes in DA, DOPAC or HVA levels in 52 h post-fertilization embryos treated for 24 h. In these embryos, tyrosine hydroxylase (TH) mRNA expression remained unchanged. However, 2 mM ketamine (internal embryo exposure levels equivalent to human anesthetic plasma concentration) significantly reduced DA level and TH mRNA indicating that DA synthesis was adversely affected. In the presence or absence of 2 mM ketamine, ALCAR showed similar effects on DA level and TH mRNA, but increased DOPAC level compared to control. ALCAR reversed 2 mM ketamine-induced reduction in HVA levels. With ALCAR alone, the expression of genes encoding the DA metabolizing enzymes, MAO (monoamine oxidase) and catechol-O-methyltransferase (COMT), was not affected. However, ketamine altered MAO mRNA expression, except at the 0.1 mM dose. COMT transcripts were reduced in the 2 mM ketamine-treated group. These distinct effects of ketamine and ALCAR on the DA system may shed some light on the mechanism on how ketamine can work as an anti-depressant, especially at sub-anesthetic doses that do not affect DA metabolism and suppress MAO gene expression.

Redox proteomics and the dynamic molecular landscape of the aging brain

It is well established that the risk to develop neurodegenerative disorders increases with chronological aging. Accumulating studies contributed to characterize the age-dependent changes either at gene and protein expression level which, taken together, show that aging of the human brain results from the combination of the normal decline of multiple biological functions with environmental factors that contribute to defining disease risk of late-life brain disorders. Finding the "way out" of the labyrinth of such complex molecular interactions may help to fill the gap between "normal" brain aging and development of age-dependent diseases. To this purpose, proteomics studies are a powerful tool to better understand where to set the boundary line of healthy aging and age-related disease by analyzing the variation of protein expression levels and the major post translational modifications that determine "protein" physio/pathological fate. Increasing attention has been focused on oxidative modifications due to the crucial role of oxidative stress in aging, in addition to the fact that this type of modification is irreversible and may alter protein function. Redox proteomics studies contributed to decipher the complexity of brain aging by identifying the proteins that were increasingly oxidized and eventually dysfunctional as a function of age. The purpose of this review is to summarize the most important findings obtained by applying proteomics approaches to murine models of aging with also a brief overview of some human studies, in particular those related to dementia.

In the rat brain acetyl-L-carnitine treatment modulates the expression of genes involved in neuronal ceroid lipofuscinosis

Acetyl-L-carnitine (ALC) is a naturally occurring substance that, when administered at supraphysiological concentration, is neuroprotective. It is a molecule of considerable interest for its clinical application in various neural disorders, including Alzheimer's disease and painful neuropathies. Suppression subtractive hybridization methodology was used for the generation of subtracted cDNA libraries and the subsequent identification of differentially expressed transcripts in the rat brain after ALC treatment. The method generates an equalized representation of differentially expressed genes irrespective of their relative abundance and it is based on the construction of forward and reverse cDNA libraries that allow the identification of the genes which are regulated by ALC. We report that ALC treatment: (1) upregulates lysosomal H(+)/ATPase gene expression and (2) downregulates myelin basic protein gene expression. The expression of these genes is altered in some forms of neuronal ceroid lipofuscinosis (NCL) pathologies. In this case, ALC might rebalance the disorders underlying NCL disease represented by a disturbance in pH homeostasis affecting the acidification of vesicles transported to lysosomal compartment for degradation. This study provides evidence that ALC controls genes involved in these serious neurological pathologies and provides insights into the ways in which ALC might exert its therapeutic benefits.

Expression patterns of the organic cation/carnitine transporter family in adult murine brain

Organic cation/carnitine transporters transport carnitine, drugs, and xenobiotics (e.g. choline, acetylcarnitine, betaine, valproic acid), and are expressed in muscle, heart, blood vessels, kidney, gut, etc.

OBJECTIVE

To characterize expression patterns of mOctn1, -2 and -3 in murine brain.

METHODS

We applied our transporter-specific antibodies to mOctn1, -2 and -3, followed by 2 0 antibody and DAB peroxidase detection to serial adult murine brain sections counterstained with hematoxylin.

RESULTS

All three transporters showed strong expression in the external plexiform layer of the olfactory bulb and in olfactory nerve, the molecular layer and neuronal processes of input fibres extending vertically in motor cortex, in the dendritic arborization of the cornu ammonis and dendate gyrus (hippocampus), neuronal processes in the arcuate nucleus (hypothalamus), choroid plexus cells, and neuronal cell bodies and dendrites of cranial nerve nuclei V and VII. In the cerebellum, all three transporters were strongly expressed in dendritic processes of Purkinje cells, but Octn1 and -2 were expressed more strongly than Octn3 in Purkinje cell bodies. In spinal cord, Octn1, -2 and -3 were prominent in axons and dendritic end-arborizations of spinal cord neurons in both ascending and descending white matter tracts, whereas Octn3 was also strongly expressed in grey matter, specifically in anterior horn cell bodies. Octn3 was weakly expressed in glomerular layer neuronal cell bodies of olfactory bulb.

CONCLUSIONS

hOCTN2 deficiency presents with carnitine-responsive cardiomyopathy, myopathy and hypoglycemic, hypoketotic coma with strokes, seizures and delays. In mouse, Octn1, -2 and -3 are expressed in many regions throughout the central nervous system with a pattern suggestive of roles in modulating cerebral bioenergetics and in acetylcholine generation for neurotransmission in olfactory, satiety, limbic, memory, motor and sensory functions. This distribution may play a role in the pattern of neurological injury that occurs in hOCTN2 deficiency during catabolic episodes of hypoglycemic, hypoketotic encephalopathy and which may manifest with cognitive impairment, hypotonia and seizures.

Acetyl-l-carnitine affects nonassociative learning processes in the leech Hirudo medicinalis

Acetyl-L-carnitine is a natural molecule widely distributed in vertebrate and invertebrate nervous system. It is known to have significant effects on neuronal activity playing a role as neuroprotective and anti-nociceptive agent, as well as neuromodulatory factor. About its capability of affecting learning processes the available data are controversial. In the present study, we utilized the simplified model system of the leech Hirudo medicinalis to analyze the effects of acetyl-L-carnitine, assessing whether and how it might affect elementary forms of nonassociative learning processes. In leeches with the head ganglion disconnected from the first segmental ganglion, repetitive application of weak electrical shocks onto the caudal portion of the body wall induces habituation of swim induction whereas brush strokes on the dorsal skin produces sensitization or dishabituation when the nociceptive stimulus is delivered on previously habituated animals. Herein, the effects of different concentrations of acetyl-L-carnitine (2 mM - 0.05 mM) have been tested at different times on both sensitization and dishabituation. The results show that a single treatment of acetyl-L-carnitine blocked the onset of sensitization in a dose- and time-dependent manner. In fact, the most effective concentration able to block this process was 2 mM, which induced its major effects 11 days after the treatment, whereas 0.05 mM was unable to affect the sensitization process at all considered time points. On the contrary, acetyl-L-carnitine did not completely abolish dishabituation at the tested concentrations and at every time point. Finally, acetyl-L-carnitine also impaired the habituation of swim induction, but only 11 days after treatment.

Reduction of glutamate levels in HIV-infected subjects treated with acetylcarnitine

The excitotoxic amino acid glutamate, which is elevated in blood and cerebrospinal fluid from subjects with AIDS dementia complex, is crucially implicated in the neurotoxicity of HIV infection. We describe a subject with AIDS dementia complex who showed a significant motor and cognitive improvement after a course of intravenous acetylcarnitine therapy. The clinical improvement was paralleled by a significant reduction of glutamate concentrations in both blood and cerebrospinal fluid. A prospective pilot study confirmed that acetylcarnitine administration resulted indeed to reduce the blood levels of glutamate in AIDS patients treated with acetylcarnitine therapy in order to prevent the neurotoxicity of nucleoside analogs. Even though the mechanisms responsible for the reduction of glutamate concentrations remain to be established, we suggest that acetylcarnitine should be added to the list of drugs under investigation for the treatment of AIDS dementia complex. The anti-apoptotic activity of carnitines and their safety profile further support this view.

Proteomics analyses of specific protein oxidation and protein expression in aged rat brain and its modulation by L-acetylcarnitine: insights into the mechanisms of action of this proposed therapeutic agent for CNS disorders associated with oxidative stress

Impaired function of the central nervous system (CNS) in aged animals is associated with increased susceptibility to the development of many neurodegenerative diseases. Age-related functional deterioration in brain is consistent with the free radical theory of aging that predicts, among other things, that free radical reactions with and damage to biomolecules, such as proteins and membrane lipid bilayers, leads to loss of neurons and subsequently diminished cognition. These oxidatively modified biomolecules are believed to contribute to the decreased antioxidant content, mitochondrial dysfunction, and impaired plasticity in aged brains. Treatment of rodents with L-acetylcarnitine (LAC; gamma-trimethyl-beta-acetylbutyrobetaine) can improve these functional losses. Although it is well established that administration of LAC can decrease protein oxidation in aged brains, it is not clear which proteins are decreased in their level of oxidation in the brains of aged rats treated with LAC. The current study used a parallel redox proteomics approach to identify the proteins that are oxidized in aged rat cortex and hippocampus of aged rats. Moreover, those proteins that are reduced in oxidation status were identified in aged brains from rats treated in vivo with LAC. The findings are discussed in reference to brain aging and age-related cognitive impairment.

Degraded cardiomyocytes and dysfunctional energy metabolism; their relationship with canine cardiomyopathies

Tissue sections from hearts of dogs suffering from cardiomyopathies were studied histologically and ultrastructurally. Two types of mitochondrial changes were defined and quantitated. Mitochondrial hypertrophy occurred in cardiomyocytes of middle-aged and older dogs. Significant numbers of degraded cardiomyocytes related to hydropic degeneration of hypertrophied mitochondria associated with autolysis of contractile elements and loss of cellular physiochemical functions were seen in hearts of old dogs with cardiomyopathy. Dogs with cardiac disease that were treated to enhance dysfunctional energy production early in the course of disease had cellular changes similar to those seen in old dogs but they survived heart disease and ultimately died of other causes.

Efficacy of carnitine in the treatment of children with attention-deficit hyperactivity disorder

To determine safety and the efficacy of carnitine treatment in children with attention-deficit hyperactivity disorder (ADHD). The ADHD behavior was observed by parents completing the Child Behavior Checklist (CBCL) and by teachers completing the Conners teacher-rating score, in a randomized, double-blind, placebo-controlled double-crossover trial. In 13/24 boys receiving carnitine, home behavior improved as assessed with the CBCL total score (P < 0.02). In 13/24 boys, school behavior improved as assessed with the Conners teacher-rating score (P < 0.05). Before treatment, the CBCL total and sub-scores were significantly different from those of normal Dutch boys (P < 0.0001). Responders showed a significant improvement of the CBCL total scores compared to baseline (P < 0.0001). In the majority of boys no side effects were seen. At baseline and after carnitine treatment, responders showed higher levels of plasma-free carnitine (P < 0.03) and acetylcarnitine (P < 0.05). Compared to baseline, the carnitine treatment caused in the responsive patients a decrease of 20-65% (8-48 points) as assessed by the CBCL total problem rating scale. Treatment with carnitine significantly decreased the attention problems and aggressive behavior in boys with ADHD.

The effect of L-carnitine on T-maze learning ability in aged rats

L-carnitine is of considerable interest because of its capacity to counteract several physiological and pathological phenomena typical of brain aging processes. We examined the effects of L-carnitine on the learning ability of old rats. 100 mg/kg per body weight per day L-carnitine was administered orally to old (21 months) male Sprague-Dawley rats (OLD-CAR) for a period of 2 months. Old (21 months, OLD-CO) and young (7 months, YG-CO) control animals received tap water exclusively. Performance of the OLD-CAR and OLD-CO was compared with that of YG-CO in a multiple T-maze. The mean run time values showed a significant (P=0.01) difference of the OLD-CAR rats to the OLD-CO but no significant differences between OLD-CAR and YG-CO. For the T-maze parameter mean correct responses we were able to demonstrate that L-carnitine treated old rats made significantly (P=0.03) less errors and significantly (P=0.01) more animals reached the T-maze goal compared with OLD-CO but no significant differences were observed between OLD-CAR and YG-CO. The results of the present study clearly demonstrate that carnitine treatment improves the learning ability of old rats and seems to be able to reduce the loss of cognitive functions that occur with aging.

Acetyl-L-carnitine physical-chemical, metabolic, and therapeutic properties: relevance for its mode of action in Alzheimer's disease and geriatric depression

Acetyl-L-carnitine (ALCAR) contains carnitine and acetyl moieties, both of which have neurobiological properties. Carnitine is important in the beta-oxidation of fatty acids and the acetyl moiety can be used to maintain acetyl-CoA levels. Other reported neurobiological effects of ALCAR include modulation of: (1) brain energy and phospholipid metabolism; (2) cellular macromolecules, including neurotrophic factors and neurohormones; (3) synaptic morphology; and (4) synaptic transmission of multiple neurotransmitters. Potential molecular mechanisms of ALCAR activity include: (1) acetylation of -NH2 and -OH functional groups in amino acids and N terminal amino acids in peptides and proteins resulting in modification of their structure, dynamics, function and turnover; and (2) acting as a molecular chaperone to larger molecules resulting in a change in the structure, molecular dynamics, and function of the larger molecule. ALCAR is reported in double-blind controlled studies to have beneficial effects in major depressive disorders and Alzheimer's disease (AD), both of which are highly prevalent in the geriatric population.

Insulin exposure and unifying aging

BACKGROUND

Absence of a widely agreed upon central paradigm for mammalian aging.

OBJECTIVE

Detailed elaboration of a proposed mammalian aging paradigm.

METHODS

Elaboration of a new theoretical model.

RESULTS

Hormonal imbalance-growth factor exposure theory (HI-GFE theory) can account for two major aging phenomena: (1) decline in mammalian 'reserve capacity' and consequent rise of diseases of maintenance, and (2) rise then peaking of most age-associated proliferative diseases. Reserve capacity decline via gradual decline in mitochondrial maximal energy production (state 3) accounts for the gradual redirection of declined maximal energy production toward survival functions like ion pumping to the relative detriment of RNA and protein synthesis as seen in lesser synthetic rates and slower turnover with consequent gradual cellular impairment. Developmental program triggered, and over-ample nutritionally driven, growth factor exposure in youth to middle age encourages promotional events that lead to proliferative diseases that rise coincident to rapidly declining reserve capacity and cumulative increased mutational status of age.

CONCLUSIONS

Declining mitochondrial state 3 aging energy production status is easily and safely reversible with probable consequences of greatly postponing the decline in overall 'reserve capacity' which may also improve insulin: growth hormone balance and result in lower overall growth factor exposure and consequent longer healthy life of a potentially greater magnitude increase in life spans than that seen in calorie-restricted animals.

Effects of ALCAR on the fast axoplasmic transport in cultured sensory neurons of streptozotocin-induced diabetic rats

The effects of acetyl-L-carnitine (ALCAR) on fast axoplasmic transport were studied in cultured dorsal root ganglion (DRG) neurons of diabetic rats. Three-month-old male rats were used 7 days after streptozotocin injection. Neurons obtained from ganglia were cultured with a high concentration of glucose. The amount and the mean velocity of retrogradely transported particles, reduced in the diabetic animal, were transiently recovered by 1 mM ALCAR. The number of particles moving at 0.8-1.2 microm/s, considered to be lysosomes, increased in the velocity distribution. ALCAR did not modify the amount and mean velocity of anterograde particles which were unaffected by diabetes, or of bidirectional particles in neurons of control rats. This study suggests that diabetic neuropathy may be relieved by ALCAR via recovering retrograde axoplasmic transport.

Reduction in the MK-801 binding sites of the NMDA sub-type of glutamate receptor in a mouse model of congenital hyperammonemia: prevention by acetyl-L-carnitine

Our earlier studies on the pharmacotherapeutic effects of acetyl-L-carnitine (ALCAR), in sparse-fur (spf) mutant mice with X linked ornithine transcarbamylase deficiency, have shown a restoration of cerebral ATP, depleted by congenital hyperammonemia and hyperglutaminemia. The reduced cortical glutamate and increased quinolinate may cause a down-regulation of the N-methyl-D-aspartate (NMDA) receptors, observed by us in adult spf mice. We have now studied the kinetics of [3H]-MK-801 binding to NMDA receptors in spf mice of different ages to see the effect of chronic hyperammonemia on the glutamate neurotransmission. We have also studied the Ca2+-dependent and independent (4-aminopyridine (AP) and veratridine-mediated) release of glutamate and the uptake of [3H]-glutamate in synaptosomes isolated from mutant spf mice and normal CD-1 controls. All these studies were done with and without ALCAR treatment (4 mmol/kg wt i.p. daily for 2 weeks), to see if its effect on ATP repletion could correct the glutamate neurotransmitter abnormalities. Our results indicate a normal MK-801 binding in 12-day-old spf mice but a significant reduction immediately after weaning (21 day), continuing into the adult stage. The Ca2+-independent release of endogenous glutamate from synaptosomes was significantly elevated at 35 days, while the uptake of glutamate into synaptosomes was significantly reduced in spf mice. ALCAR treatment significantly enhanced the MK-801 binding, neutralized the increased glutamate release and restored the glutamate uptake into synaptosomes of spf mice. These studies point out that: (a) the developmental abnormalities of the NMDA sub-type of glutamate receptor in spf mice could be due to the effect of sustained hyperammonemia, causing a persistent release of excess glutamate and inhibition of the ATP-dependent glutamate transport, (b) the modulatory effects of ALCAR on the NMDA binding sites could be through a repletion of ATP, required by the transporters to efficiently remove extracellular glutamate.

Analysis of the mechanisms underlying the age-related impairment in long-term potentiation in the rat

The process of ageing is common to all organisms but despite its universality, understanding of the cellular and molecular changes which accompany ageing is poor. With the increase in the ageing population, the need for systematic study of the process becomes a priority but the development of a systematic approach to the problem requires the development of a testable theory of ageing. While several theories of ageing have been proposed /336/, between which there is at least some overlap, no generally-accepted theory has been identified. In relation to the brain, four interrelated theories of ageing have received significant attention; these are (1) the membrane hypothesis, (2) the free radical hypothesis, (3) the calcium hypothesis and (4) the glucocorticoid theory. The overlap between these hypotheses is such that a causal relationship between them is very likely with age-related changes in membrane composition triggered by changes in free radical production, while changes in membrane composition are likely to account for changes in membrane function including age-related changes in calcium homeostasis. The glucocorticoid theory could equally well be termed the stress hypothesis of ageing, which in the hippocampus at least, might trigger age-related changes in free radical production. This review is not intended to be a balanced appraisal of each theory but emphasizes aspects of the membrane hypothesis of ageing and discusses some relevant aspects of the other hypotheses. Attention is focussed on analysis of the biochemical changes which might underlie age-related changes in hippocampal function, particularly maintenance of long-term potentiation (LTP), and these changes are discussed in the context of the four hypotheses of ageing.

Acetyl-carnitine deficiency in AIDS patients with neurotoxicity on treatment with antiretroviral nucleoside analogues

OBJECTIVE

A severe dose limiting axonal peripheral neuropathy may develop in subjects on treatment with the nucleoside analogues didanosine (ddl), zalcitabine (ddC), and stavudine (d4T). The impairment of mitrochondrial DNA synthesis is crucial to the pathogenesis of this disorder although other mechanisms have not been ruled out. The depletion of acetyl-carnitine, which regulates the metabolism and function of peripheral nerves could contribute to the neurotoxicity of these compounds.

DESIGN

Non-randomized, cross-sectional study of selected patients.

METHODS

We measured the serum levels of acetyl- and total carnitine in 12 subjects with axonal peripheral neuropathy developed on treatment with different regimens of neurotoxic nucleoside analogues (ddl, ddC, d4T). Subjects who did not develop peripheral neuropathy while staying on treatment with ddl (n = 10) or zidovudine (n = 11) served as the control groups. HIV-negative subjects with axonal on demyelinating autoimmune neuropathies (n = 10) and healthy individuals (n = 13) were additional control groups.

RESULTS

Subjects experiencing axonal peripheral neuropathy on treatment with ddl, ddC and d4T had significantly reduced levels of acetyl-carnitine in comparison to the control groups. No difference was observed in the levels of total carnitine between study subjects and the control groups.

CONCLUSIONS

Our results demonstrate that subjects who developed peripheral neuropathy while staying on treatment with ddl, ddC and d4T had acetyl-carnitine deficiency. The normal levels of total carnitine in the study group appear to indicate the specificity of the defect and rule out coexisting relevant nutritional problems. The critical role of acetyl-carnitine for the metabolism and function of the peripheral nerves supports the view that the acetyl-carnitine deficiency found in these subjects may contribute to the neurotoxicity of ddl, ddC and d4T, even though the interference with mitochondrial DNA synthesis is regarded as the main cause of their toxicity.

Alterations of the thalamo-cortical system in rats prenatally exposed to ethanol are prevented by concurrent administration of acetyl-L-carnitine

We previously demonstrated that adult rats prenatally exposed to ethanol display permanent damages of thalamo-cortical connections [18,19,33]. Here the effect of simultaneous administration of ethanol and acetyl-L-carnitine has been investigated. Adult animals underwent cortical or thalamic injections of horseradish peroxidase and both anterograde and retrograde thalamic and cortical labeling have been analyzed. Ethanol-induced changes of thalamo-cortical circuits are prevented by concurrent administration of acetyl-L-carnitine. Possible mechanisms underlying this effect are discussed.