Effects of acetyl-L-carnitine on regional cerebral glucose metabolism in awake rats

Analgesic and Antidepressant Effects of the Clinical Glutamate Modulators Acetyl-L-Carnitine and Ketamine

Pain and depression are leading causes of disability and of profound social and economic burden. Their impact is aggravated by their chronicity and comorbidity and the insufficient efficacy of current treatments. Morphological and functional metabolism studies link chronic pain and depressive disorders to dysfunctional neuroplastic changes in fronto-limbic brain regions that control emotional responses to painful injuries and stressful events. Glutamate modulators are emerging new therapies targeting dysfunctional brain areas implicated in the generation and maintenance of chronic pain and depression. Here, we report the effects of two clinically approved glutamate modulators: acetyl-L-carnitine (ALCAR) and S, R(±)ketamine (KET). ALCAR is a natural neurotrophic compound currently marketed for the treatment of neuropathies. KET is the prototypical non-competitive antagonist at N-methyl-D-aspartate glutamate receptors and a clinically approved anesthetic. Although they differ in pharmacological profiles, ALCAR and KET both modulate aminergic and glutamatergic neurotransmissions and pain and mood. We assessed in rats the effects of ALCAR and KET on cerebral metabolic rates for glucose (rCMRglc) and assessed clinically the effects of ALCAR in chronic pain and of KET in post-operative pain. ALCAR and KET increased rCMRglc at similar degrees in prefrontal, somatosensory, and cingulate cortices, and KET increased rCMRglc at a different, much larger, degree in limbic and dopaminergic areas. While rCMRglc increases in prefrontal cortical areas have been associated with analgesic and antidepressant effects of ALCAR and KET, the marked metabolic increases KET induces in limbic and dopaminergic areas have been related to its psychotomimetic and abuse properties. In patients with chronic neuropathic pain, ALCAR (1,000 mg/day) yielded to a fast (2 weeks) improvement of mood and then of pain and quality of life. In day-surgery patients, KET improved dischargeability and satisfaction. In obese patients undergoing bariatric surgery, a single, low dose of KET (0.5 mg/kg) at induction of anesthesia determined a very fast (hours) amelioration of post-operative depression and pain and an opioid-sparing effect. These findings indicate that ALCAR and KET, two non-selective glutamate modulators, still offer viable therapeutic options in comorbid pain and depression.

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.

Possible promoting effects of melatonin, leptin and alcar on regeneration of the sciatic nerve

Peripheral nerve injury is a widespread and disabling condition that can impair the individual's daily life. Studies involving medications that may positively affect peripheral nerve regeneration are rare. The aim of this study was to investigate new treatments after peripheral nerve injury using various neuroprotectants, melatonin, alcar and leptin, in the regenerative process in an experimental rat model. Wistar albino rats were randomly divided into eight groups containing equal number of animals. Intraperitoneal injection of melatonin (50mg/kg, for 21days), leptin (1mg/kg, for 21days) and acetyl-l-carnitine (50mg/kg, for six weeks) was performed postoperatively. Histological and electromyographical assessments of the regenerated nerves were performed 12 weeks after surgery. Stereological analysis was performed to estimate myelinated and unmyelinated axon numbers, surface area, myelin thickness and the myelin thickness/axon diameter ratio for each group. The results showed that only alcar has a beneficial effect on the regeneration of unmyelinated axons. Neither melatonin and leptin nor alcar were observed to have any therapeutic effect on the regeneration of myelinated axons. Alcar therapy has a positive effect on the regeneration of unmyelinated fiber in the sciatic nerve. However, the same effect was not observed in myelinated nerve fibers after intraperitoneal application of melatonin and leptin.

Dietary supplementation with acetyl-l-carnitine in seizure treatment of pentylenetetrazole kindled mice

In spite of the availability of new antiepileptic drugs a considerable number of epilepsy patients still have pharmacoresistant seizures, and thus there is a need for novel approaches. Acetyl-l-carnitine (ALCAR), which delivers acetyl units to mitochondria for acetyl-CoA production, has been shown to improve brain energy homeostasis and protects against various neurotoxic insults. To our knowledge, this is the first study of ALCAR's effect on metabolism in pentylenetetrazole (PTZ) kindled mice. ALCAR or the commonly used antiepileptic drug valproate, was added to the drinking water of mice for 25days, and animals were injected with PTZ or saline three times a week during the last 21 days. In order to investigate ALCAR's effects on glucose metabolism, mice were injected with [1-(13)C]glucose 15 min prior to microwave fixation. Brain extracts from cortex and the hippocampal formation (HF) were studied using (1)H and (13)C NMR spectroscopy and HPLC. PTZ kindling caused glucose hypometabolism, evidenced by a reduction in both glycolysis and TCA cycle turnover in both brain regions investigated. Glutamatergic and GABAergic neurons were affected in cortex and HF, but the amount of glutamate was only reduced in HF. Slight astrocytic involvement could be detected in the cortex. Interestingly, the dopamine content was increased in the HF. ALCAR attenuated the PTZ induced reduction in [3-(13)C]alanine and the increase in dopamine in the HF. However, TCA cycle metabolism was not different from that seen in PTZ kindled animals. In conclusion, even though ALCAR did not delay the kindling process, it did show some promising ameliorative effects, worthy of further investigation.

Chronic acetyl-L-carnitine alters brain energy metabolism and increases noradrenaline and serotonin content in healthy mice

Acetyl-L-carnitine (ALCAR), the short-chain ester of carnitine, is a common dietary supplement readily available in health food stores, claimed to improve energy levels and muscle strength. ALCAR has numerous effects on brain and muscle metabolism, protects against neurotoxic insults and may be an effective treatment for certain forms of depression. However, little is known about the effect of chronic ALCAR supplementation on the brain metabolism of healthy mice. Here, we investigated ALCAR's effect on cerebral energy and neurotransmitter metabolism after supplementing the drinking water of mice with ALCAR for 25 days, providing a daily dose of about 0.5 g/kg. Thereafter the animals were injected with [1-(13)C]glucose, and (13)C incorporation into and levels of various metabolites were quantified in extracts of the hippocampal formation (HF) and cortex using (1)H- and (13)C-nuclear magnetic resonance (NMR) spectroscopy and high performance liquid chromatography (HPLC). Increased glucose levels were detected in both regions together with a decreased amount of [3-(13)C]lactate, but no alterations in incorporation of (13)C derived from [1-(13)C]glucose into the amino acids glutamate, GABA and glutamine. These findings are consistent with decreased metabolism of glucose to lactate but not via the TCA cycle. Higher amounts of the sum of adenosine nucleotides, phosphocreatine and the phosphocreatine/creatine ratio found in the cortex of ALCAR-treated mice are indicative of increased energy levels. Furthermore, ALCAR supplementation increased the levels of the neurotransmitters noradrenaline in the HF and serotonin in cortex, consistent with ALCAR's potential efficacy for depressive symptoms. Other ALCAR-induced changes observed included reduced amounts of GABA in the HF and increased myo-inositol. In conclusion, chronic ALCAR supplementation decreased glucose metabolism to lactate, resulted in increased energy metabolite and altered monoamine neurotransmitter levels in the mouse brain.

Metabolism of acetyl-L-carnitine for energy and neurotransmitter synthesis in the immature rat brain

Acetyl-L-carnitine (ALCAR) is an endogenous metabolic intermediate that facilitates the influx and efflux of acetyl groups across the mitochondrial inner membrane. Exogenously administered ALCAR has been used as a nutritional supplement and also as an experimental drug with reported neuroprotective properties and effects on brain metabolism. The aim of this study was to determine oxidative metabolism of ALCAR in the immature rat forebrain. Metabolism was studied in 21-22 day-old rat brain at 15, 60 and 120 min after an intraperitoneal injection of [2-(13)C]acetyl-L-carnitine. The amount, pattern, and fractional enrichment of (13)C-labeled metabolites were determined by ex vivo(13)C-NMR spectroscopy. Metabolism of the acetyl moiety from [2-(13)C]ALCAR via the tricarboxylic acid cycle led to incorporation of label into the C4, C3 and C2 positions of glutamate (GLU), glutamine (GLN) and GABA. Labeling patterns indicated that [2-(13)C]ALCAR was metabolized by both neurons and glia; however, the percent enrichment was higher in GLN and GABA than in GLU, demonstrating high metabolism in astrocytes and GABAergic neurons. Incorporation of label into the C3 position of alanine, both C3 and C2 positions of lactate, and the C1 and C5 positions of glutamate and glutamine demonstrated that [2-(13)C]ALCAR was actively metabolized via the pyruvate recycling pathway. The enrichment of metabolites with (13)C from metabolism of ALCAR was highest in alanine C3 (11%) and lactate C3 (10%), with considerable enrichment in GABA C4 (8%), GLN C3 (approximately 4%) and GLN C5 (5%). Overall, our (13)C-NMR studies reveal that the acetyl moiety of ALCAR is metabolized for energy in both astrocytes and neurons and the label incorporated into the neurotransmitters glutamate and GABA. Cycling ratios showed prolonged cycling of carbon from the acetyl moiety of ALCAR in the tricarboxylic acid cycle. Labeling of compounds formed from metabolism of [2-(13)C]ALCAR via the pyruvate recycling pathway was higher than values reported for other precursors and may reflect high activity of this pathway in the developing brain. This is, to our knowledge, the first study to determine the extent and pathways of ALCAR metabolism for energy and neurotransmitter biosynthesis in the brain.

Behavioral and degeneration changes in the basal forebrain systems of aged rats: a quantitative study in the region of the basal forebrain after levo-acetyl-carnitine treatments assessed by Abercrombie estimation

One group of six male control rats [21 months old] and one group of six male rats of the same age, singularly stored in a cage, and treated with acetyl-l-carnitine-HCl (ALCAR: 60 mg/kg/day/p.o.) for six months were tested in the spatial learning/memory Morris maze-water task and for atrophy and cell loss in seven myelo- and cytostructurally defined basal forebrain (BF) cholinergic regions [Gritti et al., 1993 J Comp Neurol 329: 438-457]. Coronal sections 25 mum thick were cut through the BF regions and processed every 200 mum for choline acetyltransferase (ChAT) immunohistochemistry. The ALCAR-treated rats had significantly shorter exit times on the Morris maze-water task test than the control rats (ANOVA-enzyme: F(1,39)=112.5, P=0.0001; sessions: F(3,39)=10.41, P=0.0001; interaction: F(3,39)=5.09, P=0.0044). Degenerative morphological changes in the BF ChAT-positive cells were observed in the control rats, but not in the treated animals, in: the diagonal band of Broca, the magnocellular preoptic nucleus, the olfactory tubercle, the substantia innominata, and the globus pallidus (ANOVA-enzyme: F(1,2)=14, P=0,0003; structures: F(6,7)=4, P=0,0018; interaction: F(6,7)=3, P=0,0043). In the diagonal band of Broca (P<0.0494) and in the magnocellular preoptic nucleus (P<0.0117) there were significantly fewer ChAT-positive neurons in the aged control rats than in the ALCAR-treated rats. These results demonstrate that in rats aged from 15 to 21 months ALCAR treatment significantly attenuated spatial learning/memory impairment on the Morris maze-water task and also importantly reduced the degeneration in size and number of cholinergic cells in the BF.

Neuroprotective effects of acetyl-L-carnitine on neuropathic pain and apoptosis: a role for the nicotinic receptor

Several pathologies related to nervous tissue alterations are characterized by a chronic pain syndrome defined by persistent or paroxysmal pain independent or dependent on a stimulus. Pathophysiological mechanisms related to neuropathic disease are associated with mitochondrial dysfunctions that lead to an activation of the apoptotic cascade. In a model of peripheral neuropathy obtained by the loose ligation of the rat sciatic nerve, acetyl-L-Carnitine (ALCAR; 100 mg/kg intraperitoneally [i.p.] twice daily for 14 days) was able to reduce hyperalgesia and apoptosis. In the present study, different mechanisms for the analgesic and the antineuropathic effect of ALCAR are described. The muscarinic blocker atropine (5 mg/kg i.p.) injected simultaneously with ALCAR did not antagonize the ALCAR antihyperalgesic effect on the paw-pressure test but significantly reduced the analgesic effect of ALCAR. Conversely, the antineuropathic effect of ALCAR was prevented by cotreatment with the nicotinic antagonist mecamylamine (2 mg/kg i.p. twice daily for 14 days). A pharmacological silencing of the nicotinic receptors significantly reduced the X-linked inhibitor of apoptosis protein-related protective effect of ALCAR on the apoptosis induced by ligation of the sciatic nerve. Taken together, these data highlight the relevance of nicotinic modulation in neuropathy treatment.

Cerebral metabolic effects of acetyl-l-carnitine in rats during aging

The aim of the present study was to investigate the neuronal structures that mediate the antiaging properties of acetyl-l-carnitine (ALCAR). The regional cerebral metabolic rates for glucose (rCMRglc) have been determined with the quantitative autoradiographic [(14)C]2-deoxyglucose procedure at different times after i.v. administration of saline or ALCAR 500 mg/kg to naïve, non pretreated 3-, 12- and 24-month-old rats and to 24-month-old rats pretreated with ALCAR (100 mg/kg/day, for 3 months). rCMRglc increased maximally at 30 min after ALCAR in 3-, 12- and 24-month old rats (14, 15 and 15 areas affected, 19, 24 and 22% mean increments). Peak metabolic activations occurred with similar magnitude in motor, visual, limbic and thalamic areas in all age rats and with larger magnitude in hippocampal and thalamic areas in aged rats. Cerebral metabolic activations subsided by 60 min after ALCAR in 3-month rats (3 brain regions affected, 4% decrease) and persisted by that time in 12- and 24-month-old rats (14 and 12 regions affected, 15 and 20% increases). Cerebral activations were enhanced in aged rats after chronic treatment with ALCAR (24 brain regions affected, 20% mean increase). Hence, during aging, metabolic responsivity to ALCAR is maintained in most brain areas and increased in limbic and thalamic regions. Increased responsivity to ALCAR may result from undetermined pharmacokinetic factors and/or from a higher sensitivity and contribute to the aging reversal properties of ALCAR.

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.

Acetyl-L-carnitine reduces impulsive behaviour in adolescent rats

The attention deficit/hyperactivity disorder (ADHD) can affect human infants and adolescents. One important feature of this disorder is behavioural impulsivity. This study assessed the ability of chronic acetyl-L-carnitine (ALC, saline or 100 mg/kg SC, plus 50 mg/kg orally) to reduce impulsivity in a validated animal model for ADHD. Food-restricted rats were tested during adolescence (postnatal days, pnd, 30-45) in operant chambers with two nose-poking holes, one delivering one food pellet immediately, and the other five pellets after a delay. Delay length was increased over days (from 0 to 80 s). Individual differences in the preference-delay curve emerged, with the identification of two distinct subpopulations, i.e. one with a nearly horizontal curve and another with a very steep ("impulsive") slope. The impulsivity profile was slightly but consistently reduced by chronic ALC administration. Consistent results were also obtained with methylphenidate (MPH, saline or 3 mg/kg IP twice daily). Impulsive rats exhibited a lower metabolite/serotonin (5HIAA/5HT) ratio in the medial frontal cortex (MFC) and lower noradrenaline (NA) levels in the MFC and cingulate cortex (CC) when compared with the other subgroup. The ALC treatment increased NA levels in the CC and the 5HIAA/5HT ratio in both CC and MFC. Present data suggest that ALC, a drug devoid of psychostimulant properties, may have some beneficial effects in the treatment of ADHD children.

Repeated acetyl-l-carnitine administration increases phospho-Thr34 DARPP-32 levels and antagonizes cocaine-induced increase in Cdk5 and phospho-Thr75 DARPP-32 levels in rat striatum

Abstract Acute cocaine administration increases phosphorylation of dopamine and cAMP-regulated phosphoprotein (M(r) 32 kDa) (DARPP-32) at threonine (Thr)-34, whereas repeated cocaine administration increases DARPP-32 phosphorylation at Thr-75 in Sprague-Dawley rat striatum. Repeated acetyl-l-carnitine (ALCAR) administration persistently increases dopamine outflow in the nucleus accumbens. The present study examined the effect of repeated ALCAR administration on the DARPP-32 phosphorylation pattern in the nucleus accumbens and caudate-putamen. ALCAR increased phosphoThr-34 DARPP-32 levels and decreased phosphoThr-75 DARPP-32 levels, after 1 and 10 days of washout. We compared the effects of repeated cocaine and repeated ALCAR administrations on the behavioural response to cocaine challenge and on the DARPP-32 phosphorylation pattern and cyclin-dependent kinase 5 (Cdk5) levels in the striatum. We also studied whether ALCAR administered daily during or after cocaine sensitization procedure would interfere with the effects of cocaine. When the response to the cocaine challenge was assessed, cocaine- and ALCAR-treated rats showed a similar sensitized behavioural response, and rats receiving combined cocaine and ALCAR treatments, irrespective of treatment order, also showed a sensitized response. A week after the cocaine challenge, the two drugs had induced opposite modifications in DARPP-32 phosphorylation, as cocaine increased phosphorylation at Thr-75, while ALCAR increased phosphorylation at Thr-34. In cocaine plus ALCAR treated rats, irrespective of treatment order, ALCAR administration antagonized cocaine effects on DARPP-32 phosphorylation. Moreover, cocaine, but not ALCAR, increased DeltaFosB and Cdk5 expression, and the increase in Cdk5 was antagonized by ALCAR administration in rats receiving combined treatments. These effects were relatively persistent, as they were still present 7 days after the last treatment.