Effect of acetyl-L-carnitine on forebrain cholinergic neurons of developing rats

Acetyl-L-carnitine and Amyotrophic Lateral Sclerosis: Current Evidence and Potential use

BACKGROUND

The management of neurodegenerative diseases can be frustrating for clinicians, given the limited progress of conventional medicine in this context.

AIM

For this reason, a more comprehensive, integrative approach is urgently needed. Among various emerging focuses for intervention, the modulation of central nervous system energetics, oxidative stress, and inflammation is becoming more and more promising.

METHODS

In particular, electrons leakage involved in the mitochondrial energetics can generate reactive oxygen-free radical-related mitochondrial dysfunction that would contribute to the etiopathology of many disorders, such as Alzheimer's and other dementias, Parkinson's disease, multiple sclerosis, stroke, and amyotrophic lateral sclerosis (ALS).

RESULTS

In this context, using agents, like acetyl L-carnitine (ALCAR), provides mitochondrial support, reduces oxidative stress, and improves synaptic transmission.

CONCLUSION

This narrative review aims to update the existing literature on ALCAR molecular profile, tolerability, and translational clinical potential use in neurodegeneration, focusing on ALS.

L-Carnitine and Acetyl-L-carnitine Roles and Neuroprotection in Developing Brain

L-Carnitine functions to transport long chain fatty acyl-CoAs into the mitochondria for degradation by β-oxidation. Treatment with L-carnitine can ameliorate metabolic imbalances in many inborn errors of metabolism. In recent years there has been considerable interest in the therapeutic potential of L-carnitine and its acetylated derivative acetyl-L-carnitine (ALCAR) for neuroprotection in a number of disorders including hypoxia-ischemia, traumatic brain injury, Alzheimer's disease and in conditions leading to central or peripheral nervous system injury. There is compelling evidence from preclinical studies that L-carnitine and ALCAR can improve energy status, decrease oxidative stress and prevent subsequent cell death in models of adult, neonatal and pediatric brain injury. ALCAR can provide an acetyl moiety that can be oxidized for energy, used as a precursor for acetylcholine, or incorporated into glutamate, glutamine and GABA, or into lipids for myelination and cell growth. Administration of ALCAR after brain injury in rat pups improved long-term functional outcomes, including memory. Additional studies are needed to better explore the potential of L-carnitine and ALCAR for protection of developing brain as there is an urgent need for therapies that can improve outcome after neonatal and pediatric brain injury.

L-acetylcarnitine: a proposed therapeutic agent for painful peripheral neuropathies

During the past two decades, many pharmacological strategies have been investigated for the management of painful neuropathies. However, neuropathic pain still remains a clinical challenge. A combination of therapies is often required, but unfortunately in most cases adequate pain relief is not achieved. Recently, attention has been focused on the physiological and pharmacological effects of L-acetylcarnitine in neurological disorders. There are a number of reports indicating that L-acetylcarnitine can be considered as a therapeutic agent in neuropathic disorders including painful peripheral neuropathies. In this review article, we will examine the antinociceptive and the neuroprotective effects of Lacetylcarnitine as tested in clinical studies and in animal models of nerve injury.

Effect of acetyl-l-carnitine on ovarian cancer cells' proliferation, nerve growth factor receptor (Trk-A and p75) expression, and the cytotoxic potential of paclitaxel and carboplatin

OBJECTIVES

The incidence of chemotherapy induced peripheral neuropathy (CIPN) is 15-25% with platinum and taxanes. CIPN can be permanent and often requires dose reduction or change in chemotherapy. Acetyl-l-carnitine (ALCAR), an ester of l-carnitine, is used to treat CIPN in humans and in animal models. The goals of this study are: 1) examine the effects of ALCAR on ovarian cancer cells, 2) determine if ALCAR affects the cytotoxicity of standard chemotherapy on ovarian cancer cells.

METHODS

OVCAR-3 and SKOV-3 ovarian cancer lines were incubated in ALCAR containing media. Viability, proliferation, and expression of the nerve growth factor receptors (NGFR) Trk-A and p-75 were determined by flow cytometry. Cytotoxicity assays examining ALCAR's effect on paclitaxel and carboplatin were done by flow cytometry and infrared plate-reader.

RESULTS

Flow cytometry showed no change in percent live (p = 0.87) or proliferation (p = 0.95) of OVCAR-3 cells when comparing controls with up to 100 microM ALCAR. However, there was a slight but significant decrease in the proliferation of SKOV-3 cells incubated at higher ALCAR concentrations (p = < 0.01). Flow cytometry showed no difference in the viability of OVCAR-3 cells when comparing ALCAR: +/- paclitaxel (p = 1), +/- carboplatin (p = 0.8), or both (p = 0.4). Proliferation assays indicated that paclitaxel's cytotoxicity on OVCAR-3 and SKOV-3 cells was unchanged at higher ALCAR concentrations (p = < 0.01-0.4). ALCAR did not affect the expression of NGFR on OVCAR-3 or SKOV-3 cells.

CONCLUSION

ALCAR does not affect the cytotoxicity of paclitaxel or carboplatin. There was no increase in proliferation, or NGFR of OVCAR-3 or SKOV-3 cells exposed to ALCAR.

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.

Nerve growth factor and acetyl-L-carnitine evoked shifts in acetyl-CoA and cholinergic SN56 cell vulnerability to neurotoxic inputs

Different groups of brain cholinergic neurons display variable susceptibility to similar neurotoxic inputs. The aim of this work was to find out whether changes in cholinergic phenotype may alter the availability of acetyl-CoA in mitochondrial compartment and thereby the viability of cholinergic neurons. Cyclic AMP (cAMP) and retinoic acid caused differentiation (DC) of T17 TrkA(+) cholinergic neuroblastoma cells. In addition, it increased the choline acetyltransferase (ChAT) activity, Ca(2+) accumulation and cytoplasmic acetyl-CoA level, but decreased mitochondrial acetyl-CoA and cell resistance to amyloid-beta(25-35) (Abeta) toxicity. Nerve growth factor (NGF) caused similar alterations in the nondifferentiated cells (NC). On the other hand, in DC NGF suppressed ChAT activity and elevated mitochondrial level of acetyl-CoA but also caused a further increase of Ca(2+) content and cell susceptibility to Abeta. The significant inverse correlation was found between ChAT activity and mitochondrial levels of acetyl-CoA. Abeta markedly reduced the expression of cholinergic phenotype, acetyl-CoA content, and viability of DC. These effects were absent or much less pronounced in NC. Acetyl-L-carnitine reversed suppressing effects of Abeta on acetyl-CoA levels and ChAT activity but did not reverse increased mortality in DC. Presented data indicate that increased transmitter activity in highly differentiated cholinergic neurons, decreased acetyl-CoA level in their mitochondrial compartment, and increased Ca(2+) accumulation can make them more prone to neurotoxic conditions. Phenotype-dependent changes in intracellular distribution of acetyl-CoA thus play an important role in regulation of viability and transmitter function in brain cholinergic neurons.

Acetyl-L-carnitine (levacecarnine) in the treatment of diabetic neuropathy. A long-term, randomised, double-blind, placebo-controlled study

OBJECTIVE

To assess the efficacy and tolerability of acetyl-L-carnitine (levacecarnine; LAC) versus placebo in the treatment of diabetic neuropathy, mainly by evaluating the effects of treatment on electrophysiological parameters and pain symptoms.

DESIGN

This was a multicentre (n = 20), randomised, double-blind, placebo-controlled, parallel-group study.

PATIENTS

333 patients meeting clinical and/or neurophysiological criteria for diabetic neuropathy were enrolled.

INTERVENTIONS

Patients were randomised to treatment with LAC or placebo. LAC (or placebo) was started intramuscularly at a dosage of 1000 mg/day for 10 days and continued orally at a dosage of 2000 mg/day for the remainder of the study (355 days). MAIN OUTCOME PARAMETERS AND RESULTS: The main efficacy parameter was the effect of treatment on 6- and 12-month changes from baseline in nerve conduction velocity (NCV) and amplitude in the sensory (ulnar, sural and median) and motor (median, ulnar and peroneal) nerves. The effect of treatment on pain was also evaluated by means of a visual analogue scale (VAS). Among the 294 patients with impaired electrophysiological parameters at baseline, those treated with LAC showed a statistically significant improvement in mean NCV and amplitude compared with placebo (p < 0.01). The greatest changes in NCV (at 12 months) were observed in the sensory sural nerve (7 m/sec in the LAC group vs +1.0 m/sec in the placebo group), sensory ulnar nerve (+2.9 vs +0.1 m/sec, respectively) and motor peroneal nerve (+2.7 vs -0.2 m/sec), whereas the greatest changes in amplitude were recorded in the motor peroneal nerve (+2.2 vs +0.1 mV). After 12 months of treatment, mean VAS scores for pain were significantly reduced from baseline by 39% in LAC-treated patients (p < 0.0 vs baseline) compared with 8% in placebo recipients. LAC was well tolerated over the study period.

CONCLUSIONS

LAC was effective and well tolerated in improving neurophysiological parameters and in reducing pain over a 1-year period. LAC is, therefore, a promising treatment option in patients with diabetic neuropathy.

Protective efficacy of L-carnitine on acetylcholinesterase activity in aged rat brain

The purpose of this research was to study the activity of acetylcholinesterase in various regions of young and aged rat brain before and after L-carnitine supplementation. Two groups of male albino rats were used for this study (4 and 24 months of age). L-carnitine was administered intraperitoneally 300 mg/kg/d using physiological saline as a vehicle for 7, 14, and 21 days. The activity of acetylcholinesterase was measured in the cerebral cortex, the hippocampus, the hypothalamus, the striatum and the cerebellum. Highly significant variation was observed in a duration dependent manner in the hippocampus, the striatum, and the cortex of aged rats after L-carnitine supplementation when compared with young controls. Our results indicate that treatment of aged rats with L-carnitine restored the level of acetylcholinesterase.

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.

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.

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.

Stimulation of choline acetyl transferase activity by l- and d-carnitine in brain areas of neonate rats

Acetyl-CoA supply to the cytosol and its regulatory influence on acetylcholine biosynthesis is still an unsolved question. Acetylcarnitine through the carnitine acetyl transferase (CarAT) system has been proposed to be the acetyl donor in this process. Carnitine isomers were injected into rat developing brains every day for 14 days after birth. Results showed that carnitine and its associated forms produced a choline acetyl transferase (ChAT) activity increase in the striatum and the hippocampus. Carnitine acetyl transferase activity was stimulated by the treatment of l-carnitine in the hippocampus but it remained unchanged in the striatum and the cerebral cortex. These results suggest that ChAT and CarAT activities might be modulated by Acetyl-CoA derived preferentially from acetylcarnitine. It is suggested that ChAT activity enhancement depends on intrinsic and extrinsic cholinergic afferents to these brain areas.

Acetyl-L-carnitine restores choline acetyltransferase activity in the hippocampus of rats with partial unilateral fimbria-fornix transection

Transection of the fimbria-fornix bundle in adult rats results in degeneration of the septohippocampal cholinergic pathway, reminiscent of that occurring in aging as well as Alzheimer disease. We report here a study of the effect of a treatment with acetyl-L-carnitine (ALCAR) in three-month-old Fischer 344 rats bearing a partial unilateral fimbria-fornix transection. ALCAR is known to ameliorate some morphological and functional disturbances in the aged central nervous system (CNS). We used choline acetyltransferase (ChAT) and acetyl cholinesterase (AChE) as markers of central cholinergic function, and nerve growth factor (NGF) levels as indicative of the trophic regulation of the medio-septal cholinergic system. ChAT and AChE activities were significantly reduced in the hippocampus (HIPP) ipsilateral to the lesion as compared to the contralateral one, while no changes were observed in the septum (SPT), nucleus basalis magnocellularis (NBM) or frontal cortex (FCX). ALCAR treatment restored ChAT activity in the ipsilateral HIPP, while AChE levels were not different from those of untreated animals, and did not affect NGF content in either SPT or HIPP.

Dynamic morphology of the synaptic junctional areas during aging: the effect of chronic acetyl-L-carnitine administration

The ultrastructural features of hippocampal synaptic contact zones have been investigated by means of computer-assisted morphometry in rats of 6, 12 and 22 months of age and in age-matched animals chronically treated with ALCAR at a daily dose of 50 mg/100 g body weight from the age of 1 month up to the day of sacrifice. The number of synapses/microns 3 (Nv), the average size of the junctional areas (S) and the total area of the synaptic contact zones/microns 3 (Sv) were measured in tissue samples stained by means of the ethanol phosphotungstic acid (E-PTA) preferential technique for synaptic membranes. In control animals Nv was constant between 6 and 12 months of age, but significantly decreased in 22-month-old rats; S did not show significant differences due to age; Sv was unchanged between 6 and 12 months, but it decreased significantly in the old animals. In ALCAR treated rats Nv increased and S decreased significantly vs. Age-matched controls. Sv showed a lifespan constancy among the groups of age analysed. In ALCAR treated rats the number of contact areas smaller than 0.08 micron 2 increased by 18, 9 and 10% at 6, 12 and 22 months of age, respectively. ALCAR administration resulted in a lifespan modulation of synaptic structural dynamics. A proper metabolism at nerve terminals is accounted to play a crucial role in synaptic remodelling potential: on the basis of current research data, it is suggested that ALCAR may improve neuronal bioenergetic mechanisms.

Acetyl-L-carnitine treatment increases choline acetyltransferase activity and NGF levels in the CNS of adult rats following total fimbria-fornix transection

Transection of the fimbria-fornix in adult rats is a useful model for producing impairments of cholinergic activity in the hippocampus (HIPP) and atrophy of the medial septum cholinergic perikarya, similar to those observed during senescence, that are possibly due to the lack of nerve growth factor (NGF) retrogradely transported from the hippocampus. In our investigation we used choline acetyltransferase (ChAT) as an index of cholinergic activity in HIPP, frontal cortex (FCX), septum and nucleus basalis magnocellularis (NBM) along with measurements of NGF levels in the HIPP. Three-month-old rats with unilateral total fimbria transection received acetyl-L-carnitine (ALCAR) (150 mg/kg/day) in drinking water for 1 week before and 4 weeks after the lesion). ALCAR is a substance known to ameliorate some morphological and functional disturbances in the aging central nervous system (CNS). ChAT activity in septum and FCX, and NGF levels in HIPP were significantly increased in the treated group, compared with untreated control groups, while no changes were found in the NBM. On the other hand, a similar ALCAR treatment in unoperated animals induced an increase in ChAT activity in FCX but not in septum nor in NBM. These data are suggestive of a neurotrophic property of ALCAR exerted on those central cholinergic pathways typically damaged by aging.

Stimulation of gonadotropin-releasing hormone secretion by acetyl-L-carnitine in hypothalamic neurons and GT1 neuronal cells

Pulsatile gonadotropin-releasing hormone (GnRH) secretion from perifused hypothalamic cells and GT1-1 neuronal cells was significantly increased after culture in medium containing 100 microM acetyl-L-carnitine (ALC). This action of ALC was largely due to an increase in the spike amplitude of GnRH release. In addition, the receptor-mediated release of GnRH by N-methyl-D-aspartic acid and endothelin was significantly increased in perifused cells cultured in ALC-enriched medium. Stimulatory effects of ALC on basal, high K(+)- and agonist-induced GnRH release were also observed during long-term culture of primary hypothalamic neurons. Similar effects of ALC were evident in cultured GT1-1 cells and were accompanied by a significant increase in cell number. These observations in normal and transformed GnRH neurons demonstrate that ALC promotes the growth and secretory activity of neuropeptide-producing cells of the hypothalamus.

Oxidative stress: free radical production in neural degeneration

It is not yet established whether oxidative stress is a major cause of cell death or simply a consequence of an unknown pathogenetic factor. Concerning chronic diseases, as Parkinson's and Alzheimer's disease are assumed to be, it is possible that a gradual impairment of cellular defense mechanisms leads to cell damage because of toxic substances being increasingly formed during normal cellular metabolism. This point of view brings into consideration the possibility that, besides exogenous factors, the pathogenetic process of neurodegeration is triggered by endogenous mechanisms, either by an endogenous toxin or by inherited metabolic disorders, which become progressively more evident with aging. In the following review, we focus on the oxidative stress theory of neurodegeneration, on excitotoxin-induced cell damage and on impairment of mitochondrial function as three major noxae being the most likely causes of cell death either independently or in connection with each other. First, having discussed clinical, pathophysiological, pathological and biochemical features of movement and cognitive disorders, we discuss the common features of these biochemical theories of neurodegeneration separately. Second, we attempt to evaluate possible biochemical links between them and third, we discuss experimental findings that confirm or rule out the involvement of any of these theories in neurodegeneration. Finally, we report some therapeutic strategies evolved from each of these theories.

Effects of nerve growth factor and acetyl-L-carnitine arginyl amide on the human neuronal line HCN-1A

The HCN-1A clonal cell line, derived from the cortical tissue of a patient with unilateral megencephaly, was shown to differentiate into a mature neuronal-like state in the presence of the nerve growth factor, dibutyryl cyclic adenosine, 3',5'-monophosphate and either 1-isobutyl-3-methylxanthine or forskolin. Differentiation was assessed by measuring the percentage of cells that displayed branched, varicose processes that stained for synaptophysin. Treatment of cultures with a cocktail containing forskolin increased immunocytochemical staining for gamma aminobutyric (GABA), neurofilament protein and the nerve growth factor receptor species p75NGFR. Treatment with acetyl-L-carnitine alone had some effects on the cell morphology while acetyl-L-carnitine arginyl amide and nerve growth factor together increased the GABA content. Positive staining levels for the neurotransmitters gamma aminobutyric acid, glutamate, somatostatin, cholecystokinin and vasoactive intestinal polypeptide were measured quantitatively for HCN-1A under basal conditions.

Acetyl-L-carnitine releases dopamine in rat corpus striatum: an in vivo microdialysis study

The effect of acetyl-L-carnitine, a compound reported to be beneficial for senile patients, on the release of dopamine (DA) from the striatum was studied by using in vivo brain dialysis in anesthetized rats coupled with HPLC-electrochemical detection. Striatal infusion of acetyl-L-carnitine increased the efflux of DA with no apparent changes in efflux of DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 4-hydroxy-3-methoxyphenylacetic acid (HVA). The DA-releasing effect of acetyl-L-carnitine was concentration- and Ca(2+)-dependent, and was abolished by omega-conotoxin fraction GVIA and tetrodotoxin, inhibitors of the voltage-dependent Ca2+ and Na+ channels, respectively. Nomifensine, an inhibitor of DA reuptake did not alter the DA-releasing property of acetyl-L-carnitine. DA released from the striatum by acetyl-L-carnitine was decreased by reserpine pretreatment whereas the d-amphetamine-evoked DA outflow was not affected. In contrast to acetyl-L-carnitine, d-amphetamine reduced the extracellular concentrations of DOPAC and HVA. We conclude from the present data that acetyl-L-carnitine evokes DA release from the vesicular pools of the nigrostriatal dopaminergic neurons by a Ca(2+)-dependent, exocytotic process.

Effect of acetyl-L-carnitine on the dopaminergic system in aging brain

We studied the effect of acetyl-L-carnitine (ALCAR) on dopamine release and the effect of long-term acetyl-L-carnitine treatment on age-related changes in striatal dopamine receptors and brain amino acid levels. In striatal tissue that had been incubated with [3H]dopamine, acetyl-L-carnitine increased the release of [3H]dopamine evoked by electrical stimulation. In striatal tissue from aged mice administered acetyl-L-carnitine for 3 months, the release of [3H]dopamine evoked by electrical stimulation was higher than that of its aged control; the release after a second stimulation was similar in the two groups. There was a significant decline in the number of D1 striatal dopamine receptors with age. The Bmax was 51% lower in 1.5-year-old mice than in 4-month-old animals. Administration of acetyl-L-carnitine for 3 months diminished the reduction in the binding of [3H]SCH-23390. [3H]Spiperone binding to D2 receptors was not decreased with age and was not affected by acetyl-L-carnitine treatment. Age-related decreases in levels of several amino acids were observed in several brain regions. Acetyl-L-carnitine lessened the reduction in the level of taurine only in the striatum. The findings confirm the multiple effects of acetyl-L-carnitine in brain, and suggest that its administration can have a positive effect on age-related changes in the dopaminergic system.