J. Inher. Metab. Dis. 21 (1998) 136È140SSIEM and Kluwer Academic Publishers. Printed in the Netherlands(

Improvement in exercise tolerance in isovalericacidaemia with L-carnitine therapy

P. J. LEE1*, E. L. HARRISON1, M. G. JONES1, R. A. CHALMERS1,J. V. LEONARD2 and B. J. WHIPP3Departments of 1 Child Health, 3 Physiology, St GeorgeÏs Hospital Medical School,L ondon, UK ; 2 Medical Unit, Great Ormond Street Hospital for Children, L ondon,UK

* Correspondence : Metabolic Unit, T he Middlesex Hospital, Mortimer Street,L ondon W 1N 8AA, UK

MS received 27.5.97 Accepted 31.8.97

Summary : The e†ect of 4 weeksÏ treatment with oral-L-carnitine (100 mg/kg perday) on carnitine status and metabolic parameters during an incremental rampexercise test in a 12-year-old girl with isovaleric acidaemia was examined todetermine its possible therapeutic role. The maximum work rate achievedincreased from 110 to 120 watts ; oxygen consumption at anaerobic thresholdfrom 600 to 800 L/min ; peak oxygen consumption from 1270 to 1450 L/min ;and oxygen pulse, a measure of cardiac output, from 7.0 to 8.1 L/beat. Thesechanges were associated with increases in plasma and urinary free and acylcarnitine concentrations but no change in physical activity. This observed e†ectof L-carnitine on exercise performance may be on cardiac or skeletal musclefunction or both. We conclude that, in this single patient with isovaleric acid-aemia, L-carnitine supplementation had objective beneÐts and further studieson more patients are warranted.

Isovaleric acidaemia (McKusick 243500) is an autosomal recessively inherited dis-order of leucine catabolism due to deÐciency of isovaleryl-CoA dehydrogenase (EC1.3.99.10). It results in the toxic accumulation of isovaleryl-CoA within mitochon-dria that can be conjugated with either glycine (Yudko† et al 1978) or carnitine (Roeet al 1984) for excretion in the urine. Currently treatment consists of a reducedprotein intake with or without conjugation therapy of glycine and/or L-carnitine(Sweetman and Williams 1995).

Secondary carnitine deÐciency is thought to occur in isovaleric acidaemia becauseof excess renal losses of isovalerylcarnitine (Chalmers et al 1984). Supplementationwith L-carnitine may be more e†ective than glycine at removing toxic products (DeSousa et al 1986) and its long-term use can reduce the frequency of ketoacidoticepisodes (Mayatepek et al 1991). However, there are few objective clinical end-

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L-Carnitine and exercise in isovaleric acidaemia 137

points for measuring the efficacy of such therapy. As secondary carnitine deÐciencyis associated with muscle dysfunction in other disorders that may respond to L-carnitine supplementation (Ahmad et al 1990), we hypothesized that L-carnitine sup-plementation would improve exercise tolerance in isovaleric acidaemia.

PATIENT AND METHODS

A single female caucasian patient aged 12.4 years was studied. At the age of 4 yearsshe presented in coma during a diarrhoeal illness. The diagnosis of isovaleric acid-aemia was made on the basis of increased isovalerylglycine and isovaleric acid exc-retion in urine detected by GC-MS. Her subsequent progress was satisfactory on adiet restricted to 1 g/kg per day of protein. She has never received glycine supple-ments and L-carnitine has been administered only during acidotic crises. At the timeof the study she was on no medication and complained of no symptoms. Her weightwas 38.1 kg (25th centile), her height was 153.2 cm (50th centile), and she hadreached Tanner breast stage 3.

The day before the Ðrst study, the patient was familiarized with the cycle ergome-ter. After a 12-hour overnight fast, blood samples were drawn from an intravenouscannula for the determination of plasma glucose, lactate, 3-hydroxybutyrate andnon-esteriÐed fatty acids, as well as total and free carnitines. A urine sample wascollected for measurement of carnitines and organic acids. After a 2-minute periodwith zero load, an incremental ramp exercise of 15 watts per minute was performedusing an electronically braked cycle ergometer (Medical Graphics Corporation, StPaul, MN, USA). Oxygen uptake carbon dioxide output, respiratory(VO2),exchange ratio (RER), and oxygen pulse were determined breath-by-(VO2/HR)breath throughout. Heart rate and electrocardiogram were recorded continuously.Blood samples were collected immediately after the test and the next availablevoided urine was also collected. The anaerobic threshold (AT) and peak oxygenuptake peak) as measures of exercise tolerance and as a measure of(VO2 VO2/HRcardiac output were examined.

Basal activity over the preceding year was estimated by questionnaire (Aaron et al1995) adapted for use in the United Kingdom before and 4 weeks after commence-ment of L-carnitine therapy. In the week following the initial exercise test, a 3-dayweighed dietary assessment was performed to calculate average caloric intake andpercentage intake of carbohydrate, protein and fat. L-Carnitine (Shire Phar-maceuticals Ltd, UK) was prescribed at 100 mg/kg per day in two divided doses for4 weeks. After this period, an exercise test using the same protocol was repeated.

RESULTS

The dietary assessment showed an average caloric intake of 2550 kcal/day (66.9 kcal/kg per day), which consisted of 6% protein, 52% carbohydrate and 42% fat. Herprotein intake was 1.1 g/kg per day. During the study period, level of activity didnot change substantially, being 31 metabolic equivalent hours per week before and

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138 L ee et al

28 after 4 weeks of L-carnitine therapy. Subjectively she felt no di†erent while takingL-carnitine nor did she report any side-e†ects.

Both the exercise tests were optimal as AT and peak were reached. TheVO2maximum heart rate achieved was 181 beats/min in the Ðrst test and 175 beats/minin the second (predicted for age 208^ 10 beats/min), with the maximum RERduring exercise being 1.16 and 1.20, respectively. The maximum work rate achievedincreased by 9% from 110 to 120 watts after L-carnitine therapy. at ATVO2increased by 33% (from 600 to 800 L/min), peak by 14% (from 1270 to 1450 L/VO2min), at a heart rate of 170 beats/min by 29% (from 1050 to 1361 L/min) andVO2

by 16% (7.0 to 8.1 L/beat).VO2/HRBefore and after L-carnitine therapy, plasma free carnitine was 7.1 kmol/l and

21.6 kmol/l (normal range 30.1È37.3), plasma acylcarnitine was 9.4 kmol/l and21.3 kmol/l (normal range 4.6È9.6), urinary free carnitine was 1.1 and 74.7 mmol/molcreatinine (normal range 8.4È11.6), and urinary acylcarnitine was 8.9 and346.1 mmol/mol creatinine (normal range 14.1È23.9), respectively. Plasma andurinary free carnitine and acylcarnitine concentrations altered little during exercise.During the Ðrst exercise test, urinary isovalerylglycine did not alter (991.8 mmol/molcreatinine before and 1010.1 mmol/mol creatinine after). After 4 weeksÏ L-carnitinesupplementation, isovalerylglycine during exercise rose slightly from 1121.0 to1217.2 mmol/mol creatinine. Intermediary metabolites varied little during thestudies, but plasma lactate, as expected, increased, from 1.1 to 7.7 mmol/L in the Ðrstand from 1.5 to 9.0 mmol/L in the second study.

DISCUSSION

Although secondary carnitine insufficiency is a feature of isovaleric acidaemia(Chalmers et al 1984) and there are theoretical reasons for using L-carnitine supple-mentation (Walter 1996), there are no reported large-scale studies regarding itspotential clinical beneÐts (Mayatepek et al 1991). We have shown in an open,uncontrolled study that L-carnitine administered over 4 weeks at 100 mg/kg per day,a dose shown to be adequate to improve excretion of acyl moieties, as well as nor-malizing plasma acylcarnitine concentrations (Van Hove et al 1994) can improvephysiological indices of exercise performance in a single patient with isovaleric acid-aemia. The two exercise tests were comparable as maximum heart rates and RERswere similar and yet there were consistent di†erences in oxygen uptake at anaerobicthreshold and at a heart rate of 170 beats/min, both of which are not e†ort depen-dent. Before treatment, the patient had low free carnitine and acylcarnitine concen-trations. Plasma free carnitine levels increased substantially after 4 weeksÏ therapy,but ethically it was not possible to study muscle carnitine concentrations. No alter-ations in general level of physical activity occurred, so the changes in exercise per-formance are likely to relate to L-carnitine supplementation. However, this study didnot address whether the patient had normal or abnormal exercise tolerance, whichL-carnitine dose might be optimal, or whether the response was maintained.

L-Carnitine may improve exercise tolerance via e†ects on skeletal or cardiacmuscle or both. If cardiac output improves, oxygen delivery to skeletal muscle will

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L-Carnitine and exercise in isovaleric acidaemia 139

improve as well and exercise tolerance would be expected to improve with concomi-tant increases in AT and peak In this study, oxygen pulse, which is numeri-VO2 .cally equivalent to the product of stroke volume and arteriovenous oxygen contentdi†erences (Wasserman et al 1994), increased with therapy and may therefore reÑectimproved cardiovascular status. At a biochemical level, carnitine is necessary for thetransport of long-chain fatty acids into mitochondria prior to b-oxidation. Chroniccarnitine deÐciency may be expected to impair fatty acid oxidation in muscle.Indeed, L-carnitine supplementation has been shown to improve exercise per-formance in patients with cardiac disease (Watanabe et al 1995), and renal failuretreated with haemodialysis (Hiatt et al 1992), conditions associated with carnitinedeÐciency. It is also important in conjugating acyl-CoA moieties and aiding theirexcretion. In carnitine deÐciency associated with isovaleric acidaemia, acyl-CoAesters may accumulate and may inhibit the process of fatty acid oxidation. Alterna-tively, the e†ect may be through disturbance of the balance between free carnitineand free intramitochondrial CoA, inhibiting mitochondrial energy production andso altering muscle function.

In conclusion, this study has shown that L-carnitine supplementation had objec-tive beneÐts in a single patient with isovaleric acidaemia. The mechanisms of thepositive e†ects on exercise performance may be multifactorial and relate to bothimproved cardiac and skeletal muscle function. The e†ect of glycine supplementa-tion on exercise performance could be studied similarly. Further larger-scale,blinded and controlled studies are required before extrapolation to other patientscan be considered.

ACKNOWLEDGEMENTS

We thank Frances Taylor for performing the analyses of intermediary metabolitesand Marjorie Dixon for the dietary analysis. The L-carnitine was generously sup-plied by Shire Pharmaceuticals plc, UK, through Dr Murray Bain.

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