Journals of Gerontology Series A: Biological Sciences and Medical Sciences Large Type Edition
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Juliet, P. A. R.
Right arrow Articles by Panneerselvam, C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Juliet, P. A. R.
Right arrow Articles by Panneerselvam, C.
The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 58:B970-B974 (2003)
© 2003 The Gerontological Society of America

Carnitine: A Neuromodulator in Aged Rats

Packiasamy A. R. Juliet1, Deepak Balasubramaniam2, Naveen Balasubramaniam2 and Chinnakannu Panneerselvam3

1 Department of Geriatrics, Nagoya University School of Medicine, Japan.
2 Madras Medical College, M.G.R. Medical University, Chennai, India.
3 Department of Medical Biochemistry, Dr. ALM Post Graduate Institute of Basic Medical Sciences, University of Madras, Chennai, India.


   Abstract
Top
 Abstract
Materials
 Results
 Discussion
 References
 
A wide range of morphological and biochemical changes occur in the central nervous system with increasing age. L-carnitine, a naturally occurring compound, plays a vital role in fatty acid transport across the mitochondrial membrane. L-carnitine (300 mg/kg body wt/day) was administered intraperitoneally to young and old male Wistar rats for 7, 14, and 21 days. Carnitine, dopamine, epinephrine, and serotonin levels were assayed in discrete regions of the brain. Carnitine supplementation increased the levels of dopamine, epinephrine, and serotonin in the experimental animals in our study. Response to carnitine supplementation varied among the brain regions that have been studied. The regions rich in cholinergic neurons such as the cortex, hippocampus, and striatum showed more response after 21 days of carnitine treatment. The results of the present study suggest the role of L-carnitine as a neuromodulator and antiaging medication.

Aging has been defined as the sum total of all changes that occur in living organisms with passage of time that lead to functional impairment, increased pathology, and death (1). Loss of neurotransmitters, their receptors, and response to neurotransmitters are key manifestations of neurological aging (2). During aging, biochemical functions dealing with anabolism decrease, whereas those dealing with catabolism increase. Free radical theory of aging confirms that aging is associated with an impaired control of oxygen homeostasis (3). Gerlach and colleagues (4) proved that oxidative stress and iron are the key factors in neurodegeneration. Rapid auto-oxidation of catecholamines generate toxic free radicals, semiquinones, hydrogen peroxide, and neuromelanin, which further increases hydroxyl radical (•OH) production (5), thereby leading to neuronal loss (6). Toxic free radicals affect the sulfhydryl groups present in the carrier molecule and thus affect neurotransmitter transport (7). In nerve cells, neurotransmitter uptake by the presynaptic neurons and axonal transport in both directions requires adenosine triphosphate (ATP), which is provided by mitochondria (8). Oxidative stress by an increase in free radicals leads to an alteration of mitochondrial membrane ionic permeability, which causes a decline in ATP synthesis (9). Review of the literature suggests that oxidative stress and energy depletion may lead to imbalance and neurodegenerative processes.

The importance of nutrition in delaying the process of aging is well recognized by gerontologists. Attempts have been made to delay the onset of aging. Antioxidants are being administered to rodents to retard aging. L-carnitine is a naturally occurring compound. Carnitine therapy is used in many diseased conditions such as diabetes mellitus (13), atherosclerosis (14), and myocardial myopathy. Carnitine plays an important role in fatty acid transport across the mitochondrial membrane (10). Research data (11) have shown that a long treatment with carnitine spared pyramidal cells in the hippocampus. Carnitine concentration has been shown to decrease during aging in various regions of the aged rat brain (12). The present study was carried out to assess the neuromodulating action of L-carnitine in various brain regions by supplementing it to aged rats.


   Materials
Top
 Abstract
 Materials
Results
 Discussion
 References
 
L-carnitine (inner salt) was purchased from Sigma Chemical Co. (St. Louis, MO). All other chemicals were of reagent grade.

Animals and Experimental Design
Male albino rats of the Wistar strain, which belonged to 2 different groups, aged 4 months and 24 months, respectively (Groups I and II), were used. Each age group was subdivided into 4 groups. One control group (Group IA and IIA) and 3 experimental groups were based on the duration of carnitine administration, for 7 days (Group IB and II B), 14 days (Group IC and II C), and 21 days (Group ID and II D). The animals were maintained on commercial rat feed that contained 5% fat, 21% protein, 55% nitrogen-free extract, and 4% fiber (w/w) with adequate mineral and vitamin content. Each group consisted of 6 animals that had accessed food and water ad libitum. Experimental animals were administered L-carnitine (300 mg/kg body wt/day) intraperitoneally in 0.89% physiological saline. Control group animals received the vehicle alone.

Twenty-four hours after the last injection in the respective groups, all the animals were decapitated and the brains were quickly removed and dissected into hypothalamus, hippocampus, cortex, cerebellum, and striatum according to the method of Glowinski and Iverson (15) and immersed in saline. Carnitine and neurotransmitters such as dopamine, serotonin, and epinephrine were measured (16,17). The tissue levels of nerve growth factor (NGF) were assayed according to the methods previously described by Piovesan and colleagues (18). Statistically significant changes in the different groups were evaluated by student's t test. The levels of significance were evaluated with p values.


   Results
Top
 Abstract
 Materials
 Results
Discussion
 References
 
Figure 1 shows the level of carnitine in various brain regions of control and carnitine-treated young and aged rats.



View larger version (49K):
[in this window]
[in a new window]
  		Figure 1. Level of carnitine in carnitine-treated young and aged rat brain regions. Values are expressed as mean ± SD (standard deviation) for 6 animals in each group. On comparing groups IB, IC, and ID with group IA and groups IIB, IIC, and IID with group IIA: *p <.05; **p <.01; ***p <.001. Comparison of group IIA with group IA: #p <.01; ##p <.001

 
The level of carnitine was found to be decreased in the cortex, hippocampus, striatum, cerebellum, and hypothalamus of aged rat brain. A highly significant reduction was observed in the cortex and hippocampus followed by the striatum. There was no significant increment in carnitine levels in young rat brain regions, even at the end of 21 days of carnitine administration, whereas aged rats showed a highly significant increase (cortex, striatum, and hippocampus: p <.001) in carnitine status after 21 days of carnitine treatment. Table 1 shows the level of dopamine in various regions of control and carnitine-treated young and aged rat brain.


View this table:
[in this window]
[in a new window]
  		Table 1. Dopamine Level in Control and Carnitine-Treated Young and Aged Rat Brain Regions (Cortex, Hippocampus, Striatum, Cerebellum, and Hypothalamus).

 
The dopamine turnover is an important factor in determining the degree of dopaminergic neuron loss because neurons with a physiologically higher dopamine metabolism could be subjected to a greater oxidative stress from dopamine-derived oxyradicals. It can be seen from the figure that the level of dopamine decreased during aging. The level of dopamine was significantly low in the cortex and striatum followed by the hippocampus (p <.001), cerebellum, and hypothalamus (p <.05) of the aged rat brain. Significant increase in the level of dopamine was observed in the cortex, hippocampus (p <.001), and striatum (p <.01), whereas only a mild increase was observed in the cerebellum and hypothalamus (p <.05) of aged rat brain after carnitine administration. Table 2 depicts the effect of carnitine on the level of epinephrine in young and aged rat brain regions.


View this table:
[in this window]
[in a new window]
  		Table 2. Epinephrine Concentration in Control and Carnitine-Treated Young and Aged Rat Brain Regions (Cortex, Hippocampus, Striatum, Cerebellum, and Hypothalamus).

 
The level of epinephrine was found to be low in aged rat brain regions [cortex, hippocampus, and striatum (p <.01)] when compared with young rats. In young rats, carnitine administration did not produce any statistically significant changes while in aged rats, carnitine treatment enhanced the level of epinephrine. The percentage of significance varied among the 5 regions. Highly significant changes were observed in the cortex, hippocampus, and striatum (p <.01) of the 21-day carnitine-treated rats. Table 3 shows the effect of L-carnitine on the level of 5HT in young and aged rat brain.


View this table:
[in this window]
[in a new window]
  		Table 3. Status of Serotonin in Control and Carnitine-Treated Young and Aged Rat Brain Regions (Cortex, Hippocampus, Striatum, Cerebellum, and Hypothalamus).

 
In the central nervous system (CNS), serotonin is implicated in a wide range of physiological and behavioral functions. Decrease in the level of serotonin was observed in all the 5 regions of the aged rat brain. A highly significant decrease was observed in the cortex (p <.001) followed by the hippocampus and striatum (p <.01). Duration-dependent treatment of carnitine enhanced the level of serotonin in aged rat brain regions. At the end of 21 days of carnitine treatment, a highly significant increase in the level of serotonin was observed in the cortex, hippocampus, and striatum (p <.001) of the aged rat brain.

NGF is the best-characterized neurotrophin and is critical to the survival and maintenance of some populations of sympathetic and sensory neurons. In the CNS, NGF and its receptors have been found to be associated with cholinergic innervations. Unlike other enzymes, the level of NGF is moderately decreased during aging. NGF was significantly low in the cortex and in hippocampus (p <.001) followed by the striatum and hypothalamus (p <.01), whereas no age-related changes were observed in the cerebellum of the aged rat brain (Figure 2). The level of NGF was gradually increased after carnitine supplementation. The cerebellum region did not show any response to carnitine supplementation. The regions that are highly affected during aging, such as the cortex and hippocampus, show high response to carnitine supplementation.



View larger version (25K):
[in this window]
[in a new window]
  		Figure 2. Nerve growth factor (NGF) level in control and carnitine-treated young and aged rat brain regions (cortex, hippocampus, striatum, cerebellum, and hypothalamus). Values are expressed as mean ± SD (standard deviation) for 6 animals in each group. On comparing groups IB, IC, and ID with group IA and groups IIB, IIC, and IID with group IIA: *p <.05; **p <.01; ***p <.001. Comparison of group IIA with group IA: #p <.05; ##p <.01; ###p <.001

 

   Discussion
Top
 Abstract
 Materials
 Results
 Discussion
References
 
Aging induces several alterations in brain structure and functions. In old age, the level of neurotransmitter synthesis and their transport are decreased (19). Age-related changes in the brain are regionally variable since some brain regions are more age sensitive than others because of their biochemical make-up and also because functions differ from region to region (20). The present study was carried out to assess the effect of carnitine on age-associated alterations in different regions of the rat brain.

Carnitine is found in all areas of the CNS suggesting that a metabolic pool of carnitine exists in the brain (21). In the present study, the level of carnitine was found to be significantly low in aged rat brain regions (Figure 1). Our observations were consistent with those of Costell and colleagues (22) who demonstrated lower levels of carnitine in tissue of aged mice and humans. The changes in the level of tissue carnitine are pronounced in particular brain regions. It is well known that the brain is supplied with their carnitine requirements solely through hepatic synthesis and blood transport. The decrease in the level of carnitine may be due to factors such as reduced biosynthesis in the liver, defective carnitine transport, or failure of carnitine reabsorbtion by the kidney. Deficiency of any of the cofactors such as vitamin C, vitamin B, and pyridoxal phosphate and methionine during old age may be another reason (23–25).

Supplementation of L-carnitine significantly enhanced the status of carnitine in various regions of the brain of study animals while no significant increase was observed in young rats. The increase in the level of brain carnitine observed in the experimental animals treated with carnitine indicates that there is proper intestinal absorption (26) and adequate blood concentration due to exogenous administration.

Dopamine is easily auto-oxidized, and excessive oxidation of dopamine may lead to the accumulation of cytotoxic compounds with increasing age (27). Brain dopamine undergoes oxidation resulting in an increased level of oxygen free radicals, which might affect the cellular antioxidant defense mechanisms, which in turn could result in the degeneration of dopaminergic neurons (28). Dopamine oxidation products such as dopamine quinones and dihydroxy phenylacetic acid quinones bind to sulfhydryl groups of proteins and accumulate in the brain and are responsible for the physiological changes that take place during aging (29).

The levels of dopamine and epinephrine are found to be near normal after the supplementation of carnitine because carnitine is able to enhance the glutathione level due to its energy-promoting property (30). The enhanced glutathione binds to quinone and prevents its reaction with the sulfhydryl group of protein, which in turn inhibits the formation of 5-s-CDA (chenodeoxycholic acid). Apart from this, glutathione prevents an excess of cysteine from binding to dopamine to form quinines, which inhibit complex-I activity (31). The ATP-enhancing effect of carnitine is also responsible for the amelioration of the neurotransmitter storage, release, and reuptake process that is necessary for maintaining the normal level of neurotransmitter in the rat brain (32).

Elevated level of NGF after carnitine administration protects the brain from oxidative damage induced by dopamine auto-oxidation product. NGF enhances the activities of tyrosine hydroxylase and dopamine decarboxylase (33,34). This neurotrophin increases the availability of glutathione (35), which in turn protects the dopaminergic neurons from dopamine toxicity and also enhances the activities of catalase and glutathione peroxidase (36), which helps the brain to overcome catecholamine-induced toxicity during aging.

In contrast to catecholamines, serotonin was found to be decreased during aging (Table 3). The decreased activity of tryptophan hydroxylase in some brain areas may be responsible for this. The concentration of 5-HIAA (hydroxyindoleacetic acid) was shown to be increased in aged rats, and this increase may be correlated with the increased monoamine oxidase (MAO) activity during aging (37). In the cortex and striatum, the activities of MAO and carboxy-o-methyl transferase (COMT) were shown to be increased with age. There is evidence that cholinergic and serotonergic transmission could interact in the CNS (38). Recently, Lohninger and colleagues reported that the learning ability of old rats is improved by carnitine (39).

Conclusion
The results of the present study confirm that carnitine acts as a neuromodulator during aging. The antioxidant-replenishing, NGF-enhancing, and ATP-promoting actions of carnitine could be the factors responsible for its beneficial role in neurotransmitter metabolism. Aging is also associated with an increase in occurrence of heart, kidney, and immunological disorders. The beneficial role of L-carnitine has already been confirmed in the above conditions. The present findings suggest that L-carnitine could be used for the treatment of neuorological disorders in view of its beneficial neuromodulatory activity and may also serve as an antiaging medication.


   Acknowledgments
 
This study was supported by the University Grant Commission, New Delhi, India.

Address correspondence to Chinnakannu Panneerselvam, Department of Medical Biochemistry, Dr. ALM Post Graduate Institute of Basic Medical Sciences, University of Madras, Taramani Campus, Chennai 113, Tamil Nadu, India. E-mail: panneerselvam{at}eth.net


   Footnotes
 
Decision Editor: James R. Smith, PhD

Received May 9, 2003

Accepted July 3, 2003


   References
Top
 Abstract
 Materials
 Results
 Discussion
 References
 

  1. Timiras PS. Oxidative stress and loss of receptor sensitivity in aging. In: Timiras PS, Quay WD, Vernadakis A, eds. Hormones and Aging. Boca Raton, FL: CRC Press; 1995:3–22.
  2. Enna SJ, Samirajski T, Beer B, eds. Brain Neurotransmitters and Receptors in Aging and Age-Related Disorders. New York: Raven Press; 1987.
  3. Evans PH. Free radicals in brain metabolism and pathology. Br Med Bull.. 1993;49:577-587.[Abstract/Free Full Text]
  4. Gerlach M, Ben-Shachar D, Riederer P. Altered brain metabolism of iron as a cause of neurodegenerative diseases? J Neurochem.. 1994;63:793-807.[Medline]
  5. Urabe K, Aroca P, Tsukamoto K. The inherent cytotoxicity of melanin precursors: a revision. Biochem Biophys Acta.. 1994;1221:272-278.[Medline]
  6. Kish SJ, Shannak K, Rajput A, Deck JHN, Hornykiewicz O. Aging produces a specific pattern of striatal dopamine loss—implications for the etiology of idiopathic Parkinson's disease. J Neurochem.. 1992;58:642-648.[Medline]
  7. Berman SB, Zigmond NJ, Hastings TG. Modification of dopamine transporter function: effect of reactive oxygen species and dopamine. J Neurochem.. 1996;67:593-600.[Medline]
  8. Erecinska M, Dagani F. Relationship between the neuronal sodium/potassium pump and energy metabolism. Effects of K+/Na+ and adenosine triphosphate in isolated brain synaptosomes. J General Physiol.. 1990;95:591-616.[Abstract/Free Full Text]
  9. Orrinus S, Nicotera P. The calcium ion and cell death. J Neural Trans. 1994;43:(Suppl.): 1-11.
  10. Nalecz KA, Nalecz MJ. Carnitine—a known compound a novel function in neural cells. Acta Neurobiol Exper.. 1996;56:597-609.
  11. Angelucci, , Ramacci MT, Taglilatela G, et al. Nerve growth factor binding in aged rat central nervous system: effect of acetyl-L-carnitine. J Neurosci Res.. 1988;20:491-496.[Medline]
  12. Kalaiselvi CJ, Panneerselvam C. Effect of L-carnitine on the status of lipid peroxidation and antioxidants in aging rats. J Nutr Biochem. 1998;9:575-578.
  13. Paulson DJ, Schmidt MJ, Traxler JS, Ramacci MT, Shug AL. Improvement of myocardial function in diabetic rats after treatment with L-carnitine. Metabol.. 1984;33:358-363.
  14. Dayanandan A, Kumar P, Kalaiselvi T, Panneerselvam C. Effect of L-carnitine on blood lipid composition in athrosclerotic rat. J Clin Biochem Nutr.. 1994;17:81-89.
  15. Glowinski K, Iverson LL. Regional studies of catecholamines in the rat brain. The disposition of [3H] dopamine and [3H] DOPA in various regions of rat brain. J Neurochem.. 1966;13:655-699.[Medline]
  16. Pearson DJ, Tubbs PK, Chase FA. Carnitine and acyl carnitines. In: Bergmeyer HV, ed. Methods in Enzymatic Analysis. New York: Academic Press; 1974:1762–1769.
  17. Kari HP, Davision PP, Kohl HH, Kochar MM. Effects of ketamine on brain monoamine levels in rats. Res Commun Chem Pathol Physiol.. 1978;20:175-185.
  18. Piovesan P, Pacifici L, Taglialatela G, Ramacci MT, Angelucci L. L-Acetyl-L-carnitine treatment increase choline acetyltransferase activity and NGF levels in the CNS of adult rats following total fimbria-fornix transection. Brain Res.. 1994;633:77-82.[Medline]
  19. Ponzio F, Calderini G, Lomuscio G, Vantini G, Taffano G, Algeri S. Changes in monoamines and their metabolite levels in some brain regions of aged rats. Neurobiol Aging.. 1982;3:23-29.[Medline]
  20. Rajalakshmi R, Thrivikraman V, Ramakrishnan CV. Protein deficiency and regional chemistry of the brain: part I—effects of protein deficiency on regional distribution of protein, glutathione and ascorbic acid in rat brain. Ind J Biochem Biophys.. 1971;8:295-299.[Medline]
  21. Shug AL, Schmidt MJ, Golden GT, Fariello RG. The distribution of carnitine in the mammalian brain. Life Sci.. 1982;31:2869-2874.[Medline]
  22. Costell M, O'Connor JE, Grisolis S. Age-dependent decrease of carnitine content in muscle of mice and humans. Biochem Biophy Res Commun.. 1989;161:1135-1143.[Medline]
  23. Ribaya-Mercado JD, Russell RM, Sahyoun N, Morrow FD, Gersholf SN. Vitamin B6 requirement of elderly men and women. J Nutr.. 1991;12:1062-1074.
  24. Cohary EF, Gersholf SN, Sadowski JA. Effects of vitamin B6 deficiency and aging on pyridoxal 5'-phosphate levels and glycogen phosphorylase activity in rats. J Nutr Biochem.. 1991;2:135-141.
  25. Morley JE. Nutritional status of the elderly. Am J Med.. 1986;81:679-695.[Medline]
  26. Maccari F, Arseni A, Chiodi P.M, Ramacci T, Angelucci L. Levels of carnitine in brain and other tissues of rats of different aged: effect of acetyl-L-carnitine administration. Exp Gerontol.. 1990;35:127-134.
  27. Fornstedt B, Pileblad E, Carlsson A. In vivo autooxidation of dopamine in guinea pig striatum increases with age. J Neurochem.. 1990;55:655-659.[Medline]
  28. Chiueh CC, Miyake H, Peng MT. Role of dopamine autooxidation, hydroxyl radical generation, and calcium overload in underlying mechanisms involved in MPTP-induced Parkinsonism. In: Narabayashi H, Nagatsu N, Yanagisawa T, Mizuno Y, eds. Advances in Neurobiology. New York: Raven Press; 1993:251–256.
  29. Jenner P, Dexter DT, Schapira AHV, Marsden CD. Free radical involvement and altered iron metabolism as a cause of Parkinson's disease. In: Narsden CD, Fahns, eds. The Assessment and Therapy of Parkinsonism. Lancashire, England: The Parthenon Publishing Group; 1990:17–30.
  30. Juliet Arockia Rani P, Panneerselvam C. Carnitine as a free radical scavenger in aged rats. Exp Gerontol.. 2001;36:1713-1726.[Medline]
  31. Li H, Dryhurst G. Irreversible inhibition of mitochondrial complex-I by 7-(-2aminoethyl) 3,4-dihydro-5-hydroxy 2H 1,4-benzothiazine-3-corboxylic acid (DHBT-1) a putative nigral endotoxin of relevance to Parkinson's disease. J Neurochem.. 1997;69:1530-1541.[Medline]
  32. Erecinska M, Dagani F. Relationship between the neuronal sodium/potassium pump and energy metabolism. Effects of K+/Na+ and adenosine triphosphate in isolated brain synaptosomes. J General Physiol.. 1990;95:591-616.
  33. Jackson GR, Apfell L, Werrbach-Parex, Perez-Polo JR. Role of nerve growth factor in oxidant and antioxidant balance and neuronal injury. I. Stimulation of hydrogen peroxide resistance. J Neurosci.. 1990;25:360-369.
  34. Levi-Monlalcini R. The nerve growth factor 35 years later. Science.. 1987;237:1154-1162.[Free Full Text]
  35. Whittemore SR, Seiger A. The expression, localization and functional significance of ß-nerve growth factor in the central nervous system. Brain Res.. 1987;12:439-464.
  36. Sampath D, Jackson GR, Werrbach-Perez K, Perez-Polo JR. Effects of nerve growth factor on glutathione peroxidase and catalase in PC12 cells. J Neurochem.. 1994;62:2476-2479.[Medline]
  37. Pradhan SN. Central neurotransmitters and aging. Life Sci.. 1980;26:1643-1656.[Medline]
  38. Tempesta E, Janiri L, Pirrongelli C. Stereospecific effects of acetylcarnitine on the spontaneous activity of brainstem neurons and their responses to acetylcholine and serotonin. Neuropharmacol.. 1985;24:43-50.[Medline]
  39. Lohninger S, Strasser A, Bubna- Littitz H. The effect of L-carnitine on T-maze learning ability in aged rats. Arch Gerontol Geriatr.. 2001;32:245-253.[Medline]




This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Juliet, P. A. R.
Right arrow Articles by Panneerselvam, C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Juliet, P. A. R.
Right arrow Articles by Panneerselvam, C.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
All GSA journals The Gerontologist
Journals of Gerontology Series B: Psychological Sciences and Social Sciences