Normal carnitine levels in patients with chronic fatigue syndrome

The Netherlands Journal of Medicine 2000;57:20–24

Original article

Normal carnitine levels in patients with chronic fatigue syndrome Patricia M.M.B. Soetekouw a , *, Ron A. Wevers b , Peter Vreken c , Lammy D. Elving a , Antoon J.M. Janssen b , Yvette van der Veen b , Gijs Bleijenberg d , Jos W.M. van der Meer a a

Department of Medicine, Division of General Internal Medicine 541, University Medical Center St. Radboud, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands b Laboratory of Pediatrics and Neurology, University Medical Center St. Radboud, Nijmegen, The Netherlands c Laboratory of Genetic and Metabolic Diseases, Academic Medical Center, Amsterdam, The Netherlands d Department of Medical Psychology, University Medical Center St. Radboud, Nijmegen, The Netherlands Received 14 February 2000; accepted 6 March 2000

Abstract Background: Patients with chronic fatigue syndrome (CFS) complain of muscle pain and impaired exercise tolerance. Previous studies show that this is due to systemic carnitine deficiency. We investigated the hypothesis that carnitine deficiency plays an important role in CFS in female CFS patients and compared their results with neighbourhood controls. Methods: The level of total carnitine, free carnitine, acylcarnitine and carnitine esters were measured in 25 female CFS patients and 25 healthy matched neighbourhood controls in a blinded fashion. Results: The previously reported decreased level of acylcarnitine in CFS patients was not confirmed. There were also no significant differences in levels of total carnitine, free carnitine and 20 carnitine esters between CFS patients and controls. Conclusions: The present study demonstrates that serum carnitine deficiency does not contribute to or causes the symptoms in many CFS patients.  2000 Elsevier Science B.V. All rights reserved. Keywords: Chronic fatigue syndrome; Systemic carnitine deficiency

Introduction Chronic fatigue syndrome (CFS) is a syndrome of unknown origin, characterised by severe disabling fatigue of at least 6 months duration that has led to *Corresponding author. Tel.: 1 31-24-3614-782; fax: 1 31-243541-734. E-mail address: [email protected] (P.M.M.B. Soetekouw)

considerable impairment in daily functioning [1]. The fatigue is often accompanied by a variety of complaints. Because myalgia, reduced exercise tolerance and post-exercise fatigue are prominent symptoms, one of the hypotheses on the aetiology of CFS is that it is caused by a muscle abnormality. A deficiency of carnitine has been put forward as the cause of CFS [2–4]. Carnitine is essential in mitochondrial energy metabolism. It has important roles in the transport of

0300-2977 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0300-2977( 00 )00030-9

P.M.M.B. Soetekouw et al. / Chronic fatigue and carnitine

long chain fatty acids into the mitochondria where they undergo oxidation [5,6]. Thus, deficiency of carnitine results in a disturbance of energy metabolism. Carnitine deficiencies are classified into four groups [5,6]. Primary systemic carnitine deficiency is due to a defect in the sodium ion-dependent carnitine cotransporter OCTN2 (organic cation transporter 2). Secondary carnitine deficiency is due to organic acidemias, fatty acid oxidation defects and other primary genetic defects. In the third form, carnitine deficiency with myopathy, only the muscles are deficient in carnitine, perhaps as a result of primary anomaly of the carnitine transport system in muscles. Finally, the cause of acquired carnitine deficiency is inadequate intake and renal loss. Clinical symptoms of carnitine deficiency include (cardio)myopathy and encephalopathy. Carnitine treatment is effective in systemic carnitine deficiency. In Japanese and Swedish CFS patients the levels of acylcarnitine (and not free carnitine and total carnitine) were reported to be significantly decreased compared to controls [2,3]. In an American study serum total carnitine, free carnitine and acylcarnitine levels were lower in CFS patients compared to controls [4]. These studies found that higher serum carnitine levels correlated with less general fatigue and better functional capacity [2,4]. Furthermore, skeletal muscle carnitine was found to be normal in patients with CFS [7]. Carnitine supplementation in CFS patients gave clinical improvement after 8 weeks of treatment [8]. Since many CFS patients in The Netherlands ask for measurement of carnitine and for carnitine supplementation, we felt that a carefully controlled study was needed to assess the occurrence of carnitine abnormalities in a group of CFS patients. Furthermore, the relation between different carnitine levels and experienced fatigue, as well as functional impairment, will be investigated.

Materials and methods

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Radboud, Nijmegen between 1996 and 1998. In these patients, diagnosis of CFS was made according to inclusion and exclusion criteria of Fukuda et al. [1]. Because approximately 75% of CFS patients are female [9] and there is a sex difference in carnitine levels, only female CFS patients were allowed to participate in this study. For reasons of homogeneity only Caucasian patients were selected. These patients had to have fatigue with substantial impairment in their daily life activities, which means a score of 35 or more on the subjective fatigue subscale of the Checklist Individual Strength (see below), and a score of 750 or more on the weighted total score of the Sickness Impact Profile (see below). To be included in the study, the patients had to bring with them a healthy neighbourhood control, matched for sex and age ( , 5 years difference). Twenty-five patients and 25 controls were enrolled. Neither patients nor controls received carnitine supplementation for at least 3 months before venipuncture. Age and body mass index were not significantly different between patients and controls (mean6S.D.; age, 35.969.8 vs. 37.4610.8 years; body mass index, 24.264.7 vs. 25.063.8 kg / m 2 ). Median time between onset of fatigue and investigation was 4 years (range 1–17 years). All subjects gave informed consent. Questionnaires All subjects had to complete two questionnaires. The Checklist Individual Strength (CIS) is a reliable and validated questionnaire which measures four aspects of fatigue, namely subjective level of fatigue, concentration, motivation and physical activity [10]. The Sickness Impact Profile (SIP) measures the influence of symptoms on daily functioning [11,12], using the following eight subscales: home management, mobility, alertness behaviour, sleep / rest, ambulation, social interactions, work and recreation and pastimes.

Subjects

Carnitine

Patients were recruited from a database of CFS patients of the Department of General Internal Medicine of the University Medical Center, St.

Serum was collected from patients and controls between 09.00 and 10.30 h on the same day. This time range was necessary because of the travelling

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time to our hospital, and was considered acceptable since there does not seem to be a circadian rhythm. All subjects were in the fasting state for at least 4 h before the venipuncture. Serum samples were immediately frozen (2208C). Samples were blinded and subsequently delivered to the laboratory. Levels of total carnitine, free carnitine and acylcarnitine were evaluated by a radiochemical assay using [114 C]acetyl CoA essentially according to Parvin and Pande [13] with minor modifications. Carnitine ester profiles were measured using tandem mass spectrometry essentially as described by Vreken et al. [14].

Data analysis Results are given as mean6S.D. unless indicated otherwise. Differences between patients and controls were tested using the unpaired Student’s t-test. The Spearman rank correlation coefficient was used for analysing the relations between fatigue severity and functional impairment on the one hand, and levels of total carnitine, free carnitine and acylcarnitine on the other. A two-sided P , 0.05 was taken as the level of significance.

Table 1 Concentration (mean6S.D.) of total carnitine, free carnitine, acylcarnitine and carnitine esters in serum of females with chronic fatigue syndrome (CFS) (n 5 25) and matched neighbourhood controls (n 5 25)a

Total carnitine Free carnitine Acylcarnitine C2 C3 C4 C5 C5-OH C5:1 C6 C8 C8:1 C10 C10:1 C12 C12:1 C14:1 C16 C16:1 C16-OH C18 C18:1 C18:1-OH a

CFS (n 5 25)

Neighbourhood controls (n 5 25)

P

46.9067.57 35.3767.58 11.5363.52 5.4561.58 0.3660.15 0.2260.10 0.1160.03 0.0360.01 0.0260.01 0.0660.02 0.1360.07 0.1460.06 0.1960.10 0.1360.07 0.0760.03 0.0760.03 0.0660.03 0.1060.03 0.0360.01 0.0260.01 0.0560.02 0.1060.04 0.0260.01

48.9168.19 36.7766.51 12.1463.88 5.8562.71 0.3260.13 0.2060.08 0.1160.06 0.0460.02 0.0260.01 0.0660.03 0.1160.05 0.1860.09 0.1760.07 0.1360.05 0.0760.02 0.0860.03 0.0760.04 0.1160.04 0.0460.02 0.0260.01 0.0660.02 0.1160.01 0.0260.01

NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS

NS, not significant; Student’s t-test, P , 0.05.

Results

Discussion

As expected, patients with CFS scored significantly higher for each subscale of the questionnaires as compared to the control group. They were more fatigued (CIS fatigue score, 50.265.4 vs. 14.765.7) (P , 0.001) and experienced more functional impairment (SIP total score, 1483.66498.1 vs. 88.66141.8) (P , 0.001). The levels of total carnitine, free carnitine, acylcarnitine and the whole series of carnitine esters were all in the normal range in patients and controls compared to the reference values. There were also no significant differences for either of the measurements between both groups (Table 1). No correlation was found between levels of fatigue and functional impairment at one side and levels of total carnitine, free carnitine and acylcarnitine at the other side.

In this study, carnitine levels in 25 female CFS patients were found to be all in the normal range and not significantly different from matched controls. These results are not consistent with those of previous reports. According to Kuratsune et al., Japanese [2] and Swedish [3] CFS patients have a significantly lower acylcarnitine level compared to controls. It is not clear from their study whether the concentrations in the individual patients were in the normal range or not. Plioplys and Plioplys [4] found significantly lower levels of total carnitine, free carnitine and acylcarnitine in American patients with CFS compared to those levels in controls from the study of Kuratsune et al. [2,3]. They also found that four of the 35 patients had a total carnitine level below the normal limits and one patient had a free carnitine

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P.M.M.B. Soetekouw et al. / Chronic fatigue and carnitine

level lower than the normal range. The reference values of acylcarnitine were not available. In our study there was no significant correlation between the levels of total carnitine, free carnitine and acylcarnitine and the score of the CIS fatigue and SIP total subscales. This is again in contrast to others who found a direct correlation between free carnitine and fatigue severity and physical abilities (higher free carnitine correlated with lower fatigue severity and better physical abilities), and who found that a higher total carnitine correlated with lower fatigue severity [4]. There was no significant correlation between acylcarnitine levels and any of the clinical scales used in the study of Plioplys and Plioplys [4]. The discrepancies may be due to patient selection and characteristics, choice of control group, and differences in methods of assessment. In studies on carnitine in CFS, investigators rarely described the method of patient selection and control selection. In the published reports on carnitine, CFS patients of both sexes were investigated [2–4]. We included severely affected CFS patients referred to the Department of General Internal Medicine of our university hospital. Before entering the study, the patients had to experience severe fatigue that caused functional impairment, which was assessed by two validated questionnaires (CIS and SIP). Furthermore, we only included female CFS patients because of the sex differences in carnitine levels, and because approximately 75% of CFS patients are female [9]. This implies that our results may not necessarily be extrapolated to males with CFS. We used neighbourhood controls to avoid confounding effects such as duration and stress of travelling and correction of unknown effects (e.g., environmental pollution). Kuratsune et al. refrained from describing the selection of their controls [2]. Plioplys and Plioplys [4] used the reference values for total and free carnitine of their laboratory; the reference value of acylcarnitine was not available. Furthermore, they compared their results with those previously published by other investigators [2] obtained in a different laboratory. In the present study we used two methods to assess the carnitine status (radiochemical assay using [1- 14 C]acetyl CoA and tandem mass spectrometry)

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[13,14]. Both methods have proven to be reliable. In contrast to other studies [2–4], all measurements in our study were performed on blinded serum samples. According to our results there is no scientific basis for carnitine substitution in CFS patients. This, however, does not completely preclude a pharmacological effect of orally administered carnitine. There is only one study that compared treatment with amantadine and carnitine in CFS patients. In this cross-over study, carnitine treatment during 8 weeks appeared to give clinical improvement in CFS patients [8]. However, this study was not blinded, and 15 of the 28 patients did not complete the 8-week amantadine treatment compared to one patient during carnitine supplementation. Others did not find any improvement in clinical condition of the patients after 3 months of carnitine therapy [15]. Further studies in this area are warranted. Other illnesses in which fatigue is a prominent symptom are, for example, multiple sclerosis (MS) and fibromyalgia syndrome. Fukazawa et al. found that the levels of acylcarnitine were similar between MS patients and controls [16]. There was also no difference in these carnitine levels between MS patients with and without fatigue. According to these authors, acylcarnitine deficiency is not relevant to the excessive fatigue in patients with MS. The same conclusion has been drawn regarding fibromyalgia syndrome [17]. In conclusion, our study does not support the idea that either deficiencies of total carnitine, free carnitine, acylcarnitine or specific deficiency of any of the individual acylcarnitines plays an important role in the aetiology of CFS. Thus a carnitine deficiency is at least not common in patients with CFS.

Acknowledgements The authors would like to thank P.M.W. Janssens and H.J.L.M. Timmers for their contributions to this study.

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