L-Carnitine Supplementation and Physical Exercise Restore Age-Associated Decline in Some Mitochondrial Functions in the Rat

Arnaud Bernard, Caroline Rigault, Fre´de´ric Mazue, Franc¸oise Le Borgne, and Jean Demarquoy Downloaded from https://academic.oup.com/biomedgerontology/article/63/10/1027/559196 by guest on 30 September 2021

INSERM, U866, Universite´ de Bourgogne, Dijon, France.

In mammals, during the aging process, an atrophy of the muscle ﬁbers, an increase in body fat mass, and a decrease in skeletal muscle oxidative capacities occur. Compounds and activities that interact with lipid oxidative metabolism may be useful in limiting damages that occur in aging muscle. In this study, we evaluated the effect of L-carnitine and physical exercise on several parameters related to muscle physiology. We described that supplementing old rats with L- carnitine at 30 mg/kg body weight for 12 weeks (a) allowed the restoration of L-carnitine level in muscle cells, (b) restored muscle oxidative activity in the soleus, and (c) induced positive changes in body composition: a decrease in abdominal fat mass and an increase in muscle capabilities without any change in food intake. Moderate physical exercise was also effective in (a) limiting fat mass gain and (b) inducing an increase in the capacities of the soleus to oxidize fatty acids. Key Words: L-carnitine—Muscle—Rat—Aging.

GING is a highly complex phenomenon involving pathway. The final step in L-carnitine biosynthesis is made Aboth genetic and environmental factors. Aging causes by the cytosolic c butyrobetaine hydroxylase (BBH). In rats, a multitude of detrimental changes in the organism; it this enzyme is mainly found in the liver (9). decreases many maximum functional capacities and in- There is a lack of consistency in results regarding whether creases the probability of suffering degenerative diseases physical exercise increases or decreases oxidative stress (1). Several hypotheses have been enunciated to explain (10). The production of reactive oxygen species may con- aging, most of them linked to the mitochondria and the siderably increase when mitochondria increase their oxygen dysregulation of the mitochondrial metabolism (2). input (11) such as during physical exercise. In contrast, Aging is associated with a decrease in muscle mass and moderate physical exercise ameliorates mitochondrial func- muscle oxidative capacities associated with an atrophy of tion in the liver (12). the muscle fibers, an increase in fat gain, and a decrease in Thus, one can hypothesize that nutritional supplementa- lean mass. These changes are probably influenced by tion with L-carnitine and moderate physical exercise may hormonal status and also by alterations in the structure improve the mitochondrial oxidative metabolism and sub- and the metabolism of muscle cells which could lead to sequently limit the side effects of aging. This was the aim of a progressive degeneration and a mitochondrial release of this study. cytochrome c (3) and eventually apoptosis (4). Although aging is not reversible, several compounds MATERIALS AND METHODS seem to be able to slow down the negative aspects of aging. Among those are antioxidants and agents such as L-carnitine Chemicals known to regulate energy production (5). One can also L-carnitine (Carnipure) was provided by Lonza (Basel, include moderate physical exercise, an activity that can Switzerland). All other chemicals were of reagent grade and regulate the production of oxidants, as a factor favorably were obtained from Sigma (St. Louis, MO). influencing aging. L-carnitine is a cofactor in the channeling of fatty acids Animals inside the cell. It plays two major functions in the cell: It is Male Wistar rats, approximately 4 months old (young) involved in fatty acid oxidation as it acts as a cofactor in and 24 month old (old), were used in this study. Animals the transport of acyl groups across the inner mitochondrial were housed in individual cages at a temperature of 22 6 membrane, through the carnitine palmitoyl transferase/ 28C with a 12-hour day/night cycle. The rats were adapted to carnitine acyl-carnitine transferase (CPT/CACT) system the housing conditions for at least 2 weeks before the (6). It also removes acyl groups from the mitochondria experimentation. Animals had free access to food (AO 4; and the cell as acylcarnitines (7). L-carnitine found in the U.A.R., Charlette sur Loing, France) and water. body is either provided by food stuffs (especially meat The young animals were randomly assigned to two products) (8) or comes from an endogenous biosynthetic different groups: a control group receiving tap water and

1027 1028 BERNARD ET AL.

a group receiving L-carnitine at 30 mg/kg body weight of the cytosolic fraction was routinely estimated with through the drinking water (based on a 17.5 mL water intake specific markers as in (13). per day). The old animals were divided into four groups (control, L-carnitine-supplemented rats, rats doing physical L-Carnitine Determination exercise, rats doing physical exercise and supplemented L-carnitine concentration was determined in the cytosolic with L-carnitine). Each group consisted of six animals. fraction using a radioisotopic method (8). Physical exercise was done under a moderate protocol. Three times a week animals were put on a treadmill for 20 Determination of Biochemical Parameters minutes at a speed of 13 m/min. Control animals were Downloaded from https://academic.oup.com/biomedgerontology/article/63/10/1027/559196 by guest on 30 September 2021 mock-treated and were placed on the treadmill once a week. b-oxidation determination.—The b-oxidation of Thus, six groups of animals were used: Group I ¼ control [1-14C]oleic acid by liver and skeletal muscle mitochondria young rats; Group II ¼L-carnitine-supplemented young rats; was assessed according to (14). The incubation vials con- Group III ¼ control old rats; Group IV ¼ old rats receiving tained 500 lg of mitochondrial protein in 900 lL of incu- L-carnitine; Group V ¼ old rats doing physical exercise; and bation solution. They were closed with a rubber stopper and Group VI ¼ old rats administered L-carnitine and doing incubated for 15 minutes at 378C. physical exercise. The experimental procedure was conducted for 12 weeks. Enzymatic activities.—CPT activity was determined on On completion of the experimental period, animals were mitochondrial fractions obtained from liver and muscles. anesthetized using isoflurane and were quickly killed by CPT activity was measured by the formation of palmitoyl- cervical dislocation. Organs were immediately excised and [3H]carnitine from palmitoyl-coenzyme A (CoA) and L- kept on ice for immediate use or were frozen in liquid [3H]carnitine (15). The activity of c BBH, the enzyme nitrogen and kept at 828C. responsible for L-carnitine biosynthesis, was measured by the formation of L-carnitine as in (9). Physiological Parameters All animals had their body weight recorded once a week Protein content.—Protein concentration was estimated during the experiment. Food intake was estimated regularly using the Pierce BCA (bicinchoninic acid) procedure with (on a weekly basis) by differential weighing of food offered bovine serum albumin as a standard (16). and food remaining the next day. Water intake per day was also estimated on a weekly basis. At the end of the training, Statistical Analysis the mass of the liver, the brain, the soleus and the tibialis Data shown in the table and the figures are the means 6 anterioris muscles, the periepididymal fat, the kidney, and standard error of the mean. Comparison between the the brain was measured. After all the organs were removed, different groups was done with a Kruskal–Wallis test. the abdominal fat was removed and weighed. Pairwise comparison between each group of animals was done with a Mann–Whitney U test. Significance was Subcellular Fractionation assumed at p , .05. Mitochondrial isolation.—The liver and the muscles were washed in homogenizing medium (0.25 M sucrose, 5 mM RESULTS HEPES buffer, and 1 mM EDTA, pH 7.2), minced into small pieces (around 100 mg), and homogenized using a L-Carnitine Content in Plasma, Liver, and Muscles Teflon-on-glass (Potter–Elvehjem) homogenizer. The homo- L-carnitine content was determined in the plasma, the genate was centrifuged at 500 3 g for 10 minutes and the liver, the soleus (a lipolytic muscle), and the tibialis pellet discarded. The supernatant (S1) was centrifuged at anterioris (a mixed-glycolytic muscle; Table 1). 10,000 3 g for 10 minutes. The resulting supernatant (S2) In young animals, L-carnitine supplementation induced was used for cytosol preparation as described in the an increase in the L-carnitine plasma level (21%, p , .05). following paragraph. The pellet was resuspended into the In old animals receiving L-carnitine (groups IV and VI), homogenizing buffer and centrifuged again at 10,000 3 g supplementation induced a statistically significant increase for 10 minutes. The final pellet was resuspended in a small in L-carnitine plasma levels whereas physical exercise alone volume of the homogenizing buffer and represents the did not alter L-carnitine content in the plasma. mitochondrial fraction. The content of the fractions was In the liver, L-carnitine content remained the same along estimated by determining the activity of markers in the the experiments in all groups of animals. No significant fractions as in (13). Only fractionations with relevant results difference was found between young and old rats, and were used in this article. L-carnitine supplementation or physical exercise remained ineffective in modifying liver L-carnitine level. Cytosol isolation.—The S2 supernatant was centrifuged In the soleus muscle of old rats, L-carnitine concentration at 18,000 3 g for 20 minutes at 48C to remove the was found to be significantly decreased (34%, p , .05) as mitochondria, the peroxisomes, and the lysosomes. The compared to young animals. L-carnitine supplementation supernatant was centrifuged again at 100,000 3 g for 60 allowed an increase in L-carnitine content reaching levels minutes to remove remaining microsomes. The final observed in the young rats. Physical activity alone did not supernatant was used as the cytosolic fraction. The nature alter L-carnitine content in the soleus of old animals, L-CARNITINE AND MITOCHONDRIAL FUNCTIONS 1029

Table 1. Evolution of Several Physiological and Biochemical Parameters During the 12-Week Period: Effect of L-Carnitine Supplementation and Physical Exercise

Group I Group II Group III Group IV Group V Group VI Age Young Young Old Old Old Old L-carnitine supplementation No Yes No Yes No Yes Physical exercise No No No No Yes Yes Body weight Initial 312 6 15a,b,c,d 308 6 20e,f,g,h 495 6 32a,e 501 6 24b,f 512 6 27c,g 497 6 17d,h a,b,c,d e,f,g,h a,e,i,j b,f,i,k c,g,k d,h,j Final 430 6 34 410 6 37 558 6 18 495 6 26 556 6 22 503 6 19 Downloaded from https://academic.oup.com/biomedgerontology/article/63/10/1027/559196 by guest on 30 September 2021 Evolution þ118 6 19a,b,c,d þ102 6 15e,f,g,h þ63 6 12a,e,i,j 6 6 3b,f,i,k þ44 6 6c,e,k,l þ6 6 3d,h,j,l Food intake 30 6 3286 4296 4306 3296 4306 2 Water intake 17 6 1176 2186 2176 2176 2186 1 Organ weight Liver 10.8 6 1.4 11.2 6 1.6 11.8 6 3.0 12.3 6 1.9 11.0 6 2.7 12.5 6 2.9 Kidney 1.38 6 0.2 1.39 6 0.3 1.29 6 0.2 1.40 6 0.2 1.37 6 0.1 1.28 6 0.3 Heart 1.27 6 0.3 1.33 6 0.3 1.31 6 0.1 1.27 6 0.2 1.33 6 0.3 1.42 6 0.3 Soleus 0.51 6 0.04 0.55 6 0.10 0.53 6 0.04 0.57 6 0.06 0.54 6 0.05 0.62 6 0.07 Tibialis 1.83 6 0.29 1.77 6 0.26 1.86 6 0.18 1.69 6 0.31 1.78 6 0.21 1.80 6 0.25 Periepididymal fat 3.1 6 0.2 3.2 6 0.2 3.0 6 0.1 3.2 6 0.2 3.3 6 0.4 3.1 6 0.2 Abdominal fat 25 6 3a,b 22 6 5a,b 53 6 6a,b 37 6 4a 45 6 6b 34 6 4c L-carnitine content in: Plasma 51 6 6a 62 6 6a 49 6 3b,c 77 6 9b,d 49 6 5d,e 75 6 11c,e Liver 3.0 6 0.3 3.1 6 0.4 3.3 6 0.3 3.2 6 0.2 3.0 6 0.3 3.3 6 0.3 Soleus 7.5 6 0.7a 7.4 6 0.4 4.9 6 0.4a,b,c,d 6.9 6 0.6b 6.8 6 0.9c 7.6 6 1.0d Tibialis 3.7 6 0.5 3.8 6 0.4 4.2 6 0.5 4.4 6 0.4 3.5 6 0.4 4.0 6 0.5 CPT I activity Liver 984 6 99a 962 6 137 807 6 93a,b,c,d 951 6 69b 1005 6 132c 957 6 112d Soleus 192 6 21a 195 6 34 161 6 17a,b,c,d 189 6 22b 185 6 30c 188 6 17d Tibialis anterioris 91 6 24 111 6 27 102 6 26 94 6 11 93 6 17 103 6 13 BBH activity Liver 247 6 21 234 6 30 228 6 26 219 6 18 227 6 20 213 6 22 Notes: Young animals were 3 months old, and old animals were between 18 and 24 months old. Body weight as well as organ weight are expressed in grams. Average food intake (during the whole experiment) was expressed in g/day. Water intake was expressed in mL/day. Muscle weight data are the sum of both legs’ muscles. L-carnitine content is expressed in the plasma in lmol/L and in the organs in lmol/g tissue. Carnitine palmitoyl transferase (CPT) I and c butyrobetaine hydroxylase (BBH) activity are respectively expressed in nmol/h/g tissue and pmol/h/g tissue. Comparisons were done between the two groups of young rats to determine if L-carnitine supplementation may have had an effect on young animals. Comparisons were also done among the four groups of old animals to determine the respective effect of L-carnitine supplementation, of physical exercise, or of both L-carnitine supplementation and physical exercise. Comparisons were also done between the control young rat group and the four groups of old rats to determine if the treatment or the physical activity may restore in old rats some biochemical parameters to the level observed in young rats. Superscript letters indicate a significant difference between values of a same line. whereas the combination of physical activity and L-carnitine 118 6 19 g. This increase was the same in young animals supplementation increased L-carnitine content in this receiving L-carnitine. muscle. In young rats, L-carnitine supplementation did not In control old rats, the weight increase was 63 6 12 g. alter the soleus muscle L-carnitine content. Old rats receiving L-carnitine showed no weight increase In the tibialis anterioris, L-carnitine level was found to be during the 12-week period. Animals doing physical exercise slightly lower than in the soleus (52%) in all animals. In this exhibited a weight increase of 44 6 6 g (which was muscle, whatever the age or the treatment, no significant significantly different from the control and the L-carnitine- differences were found between young and old rats. In old treated animals), and old animals receiving L-carnitine and rats, neither L-carnitine treatment nor physical exercise (alone exercising had a weight increase of 6 6 3 g. This value was or with an L-carnitine supplementation) induced any change found to be the same as in L-carnitine–treated animals. The in L-carnitine content or the tibialis anterioris (Table 1). increase in body weight did not appear to be associated with an increase in either food intake or water consumption. Food and water intakes were recorded all during the experiment, Evolution of Various Physiological Parameters and no change was found.

Evolution of body weight.—The data concerning the Organ weights.—The weight of various organs and evolution of body weight are presented in Table 1. For all tissues were recorded at the end of the experiment. These rats, body weight increased during the 12-week period. values are summarized in Table 1. No differences were For the control young rats, the increase was found to be observed in the liver, the heart, the kidney, the brain, the 1030 BERNARD ET AL. Downloaded from https://academic.oup.com/biomedgerontology/article/63/10/1027/559196 by guest on 30 September 2021

Figure 1. Fatty acid oxidation in the liver. Fatty acid oxidation was Figure 3. Fatty acid oxidation in the tibialis anterioris muscle. Fatty acid determined using oleic acid as a substrate. It is expressed in nanomoles of oxidation was determined using oleic acid as a substrate. It is expressed in oleate oxidized per hour and per gram of liver. Each value represents the average nanomoles of oleate oxidized per hour and per gram of muscle. Each value of six rats 6 standard error. Group I ¼ young control rats; II ¼ young rats represents the average of six rats 6 standard error. Group I ¼ young control rats; supplemented with L-carnitine; III ¼ old control rats; IV ¼ old rats supplemented II ¼ young rats supplemented with L-carnitine; III ¼ old control rats; IV ¼ old with L-carnitine; V ¼ old rats doing physical exercise; and VI ¼ old rats rats supplemented with L-carnitine; V ¼ old rats doing physical exercise; and receiving L-carnitine and doing physical exercise. VI ¼ old rats receiving L-carnitine and doing physical exercise. testis, the periepididymal fat, or the soleus and the tibialis b-oxidation was not altered by age, L-carnitine treatment, or anterioris muscles between the animals of the different physical exercise (Figure 1). Even if b-oxidation of old rats groups. In contrast, in old control animals, the amount of was always lower than in young rats, no significant abdominal fat was higher than in old animals of any other difference was found. group. However, only between old control animals and old In the soleus muscle of young animals, the b-oxidation of animals receiving L-carnitine supplementation and exercise oleic acid was not modified by L-carnitine supplementation was this difference statistically significant. (Figure 2). In old rats, the b-oxidation rate was generally reduced (24%) compared to the young rats. In old ani- Food and water intakes.—Food and water intakes were mals, physical exercise alone allowed an increase in the determined, and no alteration was observed during the mitochondrial ability to oxidize fatty acids (from 39.8 to experiment in young or old rats. 54.7 nmol/h/g tissue). Also adding L-carnitine to the drinking water of old rats induced a marked increase of Mitochondrial b-Oxidation the mitochondrial oxidation of oleic acid (55%). When b-oxidation rates were determined in the liver and in the L-carnitine was given to animals doing physical exercise, soleus and the tibialis anterioris muscles. In the liver, the no further increase in b-oxidation was observed. The tibialis anterioris exhibited, as expected, reduced b-oxidation activity compared to the soleus (about half in the tibialis compared to the soleus). The oxidative ability remained the same between young and old animals, and neither L-carnitine nor exercise modified this metabolic activity (Figure 3).

CPT I and BBH Activities CPT I activity was determined in the liver and the soleus and the tibialis anterioris of all animals (Table 1). In the liver, one can notice a slight decrease in CPT I activity when comparing young and old control rats (22%). In old rats, L-carnitine supplementation induced an 18% increase in CPT I activity. Physical activity induced a comparable increase, and no cumulative effect of L-carnitine and physical Figure 2. Fatty acid oxidation in the soleus muscle. Fatty acid oxidation was exercise was observed (Table 1). determined using oleic acid as a substrate. It is expressed in nanomoles of oleate In the soleus, the CPT I activity was lower in old animals oxidized per hour and per gram of soleus. Each value represents the average of compared to young animals of the control groups (18%). six rats 6 standard error. Superscript letters indicate signiﬁcant differences (p , Old rats supplemented with L-carnitine exhibited an increase .05). Group I ¼ young control rats; II ¼ young rats supplemented with L-carnitine; III ¼ old control rats; IV ¼ old rats supplemented with L-carnitine; in their CPT I activity (18%). Interestingly, the same increase V ¼ old rats doing physical exercise; and VI ¼ old rats receiving L-carnitine was found for animals doing physical exercise and those and doing physical exercise. receiving L-carnitine and doing physical exercise. L-CARNITINE AND MITOCHONDRIAL FUNCTIONS 1031

In the tibialis anterioris, CPT I activities remained stable and/or aging. This stability may result from a tight control of between young and old animals. Adding L-carnitine to the L-carnitine uptake by hepatic cells and/or a control of drinking water of young or old animals did not significantly L-carnitine on its biosynthesis. As determined by BBH alter CPT I activity. Basic physical exercise did not modify activity, L-carnitine biosynthesis did not seem to be CPT I activity in old rats (Table 1). repressed by L-carnitine supplementation. Davis and The activity of BBH, the enzyme responsible for L- Monroe (33) reported earlier that modifying L-carnitine carnitine biosynthesis, was determined in the cytosolic frac- intake did not alter BBH messenger RNA level. Our results tions of the liver (Table 1). BBH activity remained stable confirmed their findings. whatever the treatment or the age of the animal. No signifi- We compared L-carnitine metabolism in two metaboli- Downloaded from https://academic.oup.com/biomedgerontology/article/63/10/1027/559196 by guest on 30 September 2021 cant differences were found between the different groups of cally and structurally different muscles, the mainly glyco- animals. lytic tibialis anterioris and the lipolytic soleus. In the tibialis anterioris muscle, no changes were observed during the experimental procedure. In the soleus, the results are dif- DISCUSSION ferent; the content of L-carnitine in this muscle was reduced Aging affects all types of muscle cells. It has been shown during aging by 34%. L-carnitine supplementation had no that postmitotic tissues such as muscle cells accumulate effect in young rats. In old rats, L-carnitine supplementation mitochondrial damage faster than mitotically active tissues as well as physical exercise restored L-carnitine content (17). Thus, the maintenance of mitochondrial function may value. Together physical activity and L-carnitine supple- be important to maintain overall muscle function. Many mentation did not show any additive effects. authors have shown that oxidants are produced in the mito- The relationship between L-carnitine and body weight has chondria. This production increases with altered function always been unclear (34). From this study two different of the mitochondrial oxidative metabolism (12,18), and conclusions can be made. In young animals, during growth during aging the antioxidant defense mechanism is dimi- phase, supplementation with L-carnitine for 12 weeks had nished (19). no effect on body weight. In old rats, L-carnitine supple- b-oxidation of fatty acids is the major metabolic pathway mentation seemed to limit body weight increase by limiting for various organs and tissues to generate energy (20). It has fat gain and possibly by increasing fatty acid oxidation as been suggested that the b-oxidation capacities decrease suggested by several authors (29,30). Our data also clearly during aging [reviewed in part in (21)]. Impaired fat oxida- showed that food intake is not modified by L-carnitine tion may also play a role in the establishment of obesity. In supplementation. humans as well as in rodents, several studies [very recently In 3-month-old rats, L-carnitine supplementation did not by Westerterp and colleagues (22)] have shown an inverse significantly affect body weight. These rats were still in the relationship between fat oxidation and weight gain (23–25), growing process, and during the 12 weeks of the experiment even if this hypothesis was not confirmed by other these animals gained 118 g of body weight but their amount authors (26). of fat remained stable. L-carnitine is known to reduce the intramitochondrial In control old rats, one can observe an increase in total acyl-CoA/CoA ratio, to promote oxidative glucose utiliza- body weight during the 12-week period. This increase does tion, and to improve insulin sensitivity (27). L-carnitine not seem to be associated with an increase in muscle mass supplementation has been shown to alter lipid accumulation but to an increase in the amount of abdominal fat. During in the skeletal muscle by influencing the influx of fatty acids our 12-week protocol, these animals exhibited an increase in into the mitochondria (28) and to increase the oxidation of body weight of 63 g. This is much less than in young dietary fatty acids in healthy humans (29,30). In old rats animals, which seems normal because the growing process there is a significant decrease of total L-carnitine levels in of these old animals has ended. Adding L-carnitine to the the brain, serum, heart, and skeletal muscle, accompanied by diet allowed reducing the weight gain observed in these an increase in the liver level (31,32). animals. In fact, in L-carnitine-supplemented animals, no Our results showed that, in rats, plasma L-carnitine was increase of body weight during the 12-week period was not significantly reduced during aging; the values remaining observed. Physical exercise also reduced body weight gain, close to 50 lM. However, L-carnitine supplementation but this reduction was less than that seen with L-carnitine induced, both in young and old rats, a marked increase in the treatment. Physical exercise combined with L-carnitine sup- L-carnitine plasma levels, of 21% and 57%, respectively. plementation did not induce any cumulative effect. This difference between young and old animals could be Our results in old rats may look contradictory to those of explained either by a better capacity of absorbing L- several authors who reported no effect of L-carnitine sup- carnitine in older individuals or by a less effective transport plementation on body weight. However, the models were of L-carnitine into organs leading to an increase in L- different: In humans, Elmslie and colleagues(35) reported carnitine in the bloodstream. This alteration may also be no effect of L-carnitine in bipolar patients; in rodents, a consequence of a decrease in renal excretion of L-carnitine Brandsch and Eder (36) showed no positive effect of L- in old animals. Whatever the reasons are, in our study the carnitine supplementation on weight loss and body com- supplementation was found to be much more efficient in old position of adult (10-week-old) rats fed an energy-deficient than in young animals. diet. However, these authors stated that, in their models, L-carnitine content in the liver was not altered by L- endogenous L-carnitine synthesis was obviously adequate to carnitine supplementation or moderate physical exercise ensure efficient b-oxidation of fatty acids. Again Melton and 1032 BERNARD ET AL.

colleagues (37) reported no obvious effect of L-carnitine on at the physiological and biochemical levels. Besides body weight on ovariectomized rats. Their study was done restoring L-carnitine content in tissues, L-carnitine supple- on young female rats, which may explain the difference mentation in old rats slowed down the body weight increase observed between their data and ours. Saldanha Aoki and due to an increase in fat mass. It restored also some aspects colleagues (38) reported results that may look contradictory of fatty acid metabolism. During this study, we also deter- on young rats doing intense physical exercise. They con- mined the effect of physical exercise on the same param- cluded that L-carnitine was unable to promote weight loss in eters. Physical exercise was able to limit body weight these animals. Those were again young animals. Concerning increase and to restore, at least partly, some mitochondrial the young animals, our results agreed with their results and functions. However, physical exercise and L-carnitine Downloaded from https://academic.oup.com/biomedgerontology/article/63/10/1027/559196 by guest on 30 September 2021 conclusions, but in old animals, L-carnitine supplementation supplementation did not exhibit any cumulative effects. was able to decrease body weight. Our results can also be Contradictory results of the effect of L-carnitine supple- compared with those of Malaguarnera and colleagues (39), mentation on body weight have been published. Several who very recently reported a decrease in fat mass and an studies have shown that L-carnitine supplementation can increase in lean mass in very old people supplemented with induce an increase in L-carnitine content in various tissues. L-carnitine. An increase in L-carnitine content has been shown to Apart from this conclusion, our results also showed that, increase fatty acid oxidation, and increased fatty acid oxida- in our model of aging Wistar rats, the amount of the tion has been described as effective in lowering fat mass. periepididymal fat is not correlated with the amount of Besides these connected results, little evidence existed on a abdominal fat and possible subsequent obesity. This makes net effect of L-carnitine on body weight. Our study showed sense because abdominal fat is largely used as an energetic that in old fat rats, a supplementation with L-carnitine may storage device (40) and periepididymal fat as a protective limit the increase in fat mass occurring during aging with no tissue. change in food intake and improve mitochondrial functions b-oxidation was determined in the liver and the soleus in oxidative tissues. Extrapolated to humans, this observa- and tibialis anterioris in the six groups of animals. In the tion may be interesting, because L-carnitine supplementa- liver, in control or L-carnitine–treated young or old animals, tion may allow humans with a reduced level of L-carnitine no changes were found for oleic oxidation. In the tibialis to reduce fat mass and to maintain a balanced diet with no anterioris, the b-oxidation (as measured by the oxidation of caloric restriction. oleic acid) remained unchanged whatever the treatment or the age of the rat. In the soleus, both the age and the treatment altered b- ACKNOWLEDGMENTS oxidation. The b-oxidation of oleic acid decreased by 27% We thank Dr. Palmer and Dr. Held for constructive reading of the in old versus young rats. L-carnitine supplementation was manuscript. ineffective in increasing b-oxidation in young rats whereas L-carnitine used in these experiments was provided by Lonza (Basel, Switzerland). No limitations of any kind were made by this company on in old animals the supplementation with L-carnitine induced our work and conclusions. a marked increase. Physical exercise alone signiﬁcantly increased b-oxidation, but when physical exercise was done by animals receiving L-carnitine no further increase in b- CORRESPONDENCE oxidation was observed. These results suggest that L- Address correspondence to Jean Demarquoy, PhD, INSERM, U866, carnitine and physical exercise may, at least in part, restore Universite´ de Bourgogne, 6 boulevard Gabriel, 21000 Dijon, France. b-oxidation in old rats. E-mail: [email protected] CPT I activity is usually considered as one of the key steps in b-oxidation and an important step for the REFERENCES management of weight gain (41). In our model of aging 1. Trifunovic A. Mitochondrial DNA and ageing. Biochim Biophys Acta. rats, there is a remarkable correlation between CPT I activity 2006;1757:611–617. 2. Birch-Machin MA. 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