003 1 -3998/93/3404-0460$03.00/0 PEDIATRIC RESEARCH Vol. 34. No. 4. 1993 Copynght tc~1993 lnternat~onalPed~atnc Research Foundation. Inc Prinrc~din L' S..1.

Relationship of Carnitine and Carnitine Precursors Lysine, t-N-Trimethyllysine, and y-Butyrobetaine in Drug-Induced Carnitine Depletion

BELA MELEGH. MARIA PAP, ILDIKO BOCK. AND CHARLES J. REBOUCHE Dc~purttnc~nr.~c?f'Prdiu~ric.s /B.h-I.. hl. P.1 und Biocllcmis~rylI.B.1. L'nivc.rsir~~hf~dicul Scl~ool c?/'PCc~.s. Pkcs. Ilrm,yur!* and Dc~purlmcnlo~j'Pc~diu/ric.s /C7.J.R.I. Univcr.sirj~ c?f'lo~r~. 1o11.u C'iry. 1011.u 52-74?

ABSTRACT. Plasma concentrations and rates of urinary healthy humans carnitine depletion can develop under certain excretion of carnitine and some of its precursors were conditions, such as with drug therapies (3-5). Pivampicillin studied in three groups of children receiving drugs known (pivaloyloxymethyl ester of ampicillin) generates carnitine deple- to cause carnitine depletion. Patients in group A received tion because, after enteral absorption of the drug, the liberated pivampicillin and a molar equivalent of carnitine for 7 d. pivalate is esterified with carnitine. Sustained renal excretion of Patients in group B received pivampicillin with a 5.8-fold this metabolite leads to depletion of the carnitine reserves of the molar excess of carnitine for I wk. Patients in group C body (4, 6). This decrease of the body stores of carnitine (prin- were treated chronically with valproic acid and received a cipally in plasma and muscle) is known to be associated with molar equivalent (to valproic acid) of carnitine for 14 d. secondary metabolic changes (hypoketonemia) that can be ex- Patients in group A had markedly increased (16-fold) plained by the function of carnitine in fatty acid oxidation (4, urinary carnitine ester excretion concomitant with dimin- 5). Similarly, by a mechanism not clearly understood, valproic ished urinary free carnitine and y-butyrobetaine output and acid therapy has been shown to generate carnitine depletion. lower plasma free carnitine concentration. Supplementa- characterized by a decrease of plasma and muscle carnitine tion with one molar equivalent of carnitine (to pivampicil- concentrations and hypoketonemia (3, 6. 7). Rates of endoge- lin) was ineffective in preventing the reduction of plasma nous carnitine biosynthesis in patients receiving these therapies carnitine concentration observed with pivampicillin treat- are not sufficient to overcome the negative carnitine balance ment alone. For group B patients, administration of excess associated with these drugs. carnitine resulted in a further increase (35-fold) of urinary In mammals, carnitine is synthesized from peptide-bound carnitine ester output with no decrease of plasma carnitine lysine via posttranslational methylation (2. 8). After liberation concentration, urinary y-butyrobetaine, or free carnitine by proteolytic digestion. c-N-trimethyllysine is converted to car- excretion. For patients in group C, the initially low plasma nitine by four distinct enzymatic reactions (8). Numerous studies free and total carnitine concentrations and urinary output have described the characteristics of these reactions in vitro (9- of carnitine and carnitine esters markedlv increased with 12). For humans, the mechanisms underlying regulation of car- carnitine supplementation, but urinary eicretion of y-bu- nitine biosynthesis are not well defined. It is clear that the final tyrobetaine remained unchanged. The plasma concentra- enzymatic step in the pathway, catalyzed by 7-butyrobetaine tions and urinary output of L-lysine and c-N-trimethyllysine hydroxylase, is not rate limiting (13, 14). In rats, the availability remained unchanged within each group before and after of t-N-trimethyllysine apparently limits the overall rate of car- treatment. A positive linear correlation was found between nitine synthesis (15. 16), but this finding has not been extended urinary t-N-trimethyllysine and 3-methylhistidine output, unequivocally to humans. This investigation was undertaken to indicating that the rate of t-N-trimethyllysine excretion assess the effects of the carnitine-depleting drugs pivampicillin correlates with the amount of 3-methylhistidine liberated and valproate on carnitine-precursor appearance and metabo- by protein turnover. The data indicate that generation of lism in children acutely (pivampicillin) or chronically (valproic t-N-trimethyllysine probably depends on protein break- acid) treated with these drugs. down but its use for carnitine synthesis is not necessarily regulated by carnitine status. (Pediatr Res 34: 460-464, MATERIALS AND METHODS 1993) Patients. Groltp A: pivampiciflin and eqltimolar carnitinc.- Abbreviations treated group. Five children (all females; clinical data summa- rized in Table I) were selected for the study. All patients were NMR, nuclear magnetic resonance treated previously for urogenital infection with bacteriuria but were not treated with pivampicillin immediately before the start Table 1. Clluructeristicv (1fst1td.v participants* Age (y) Weight (kg) Height (cm) Although the carnitine reserves of the humans derive from endogenous synthesis and from alimentary sources ( 1, 2), carni- A 9.4 (7-1 3) 3 1.9 (24-45) 135 (123-155) tine has to be considered as a vitamin-like compound because in I I .4 (5- 16) 35.2 (14-59) 141 (97-162) Group C 12.0(7-16) 35.5(25-51) 144(124-164) Received March 9. 1993; accepted May 21. 1993. Correspondence and reprint requests: Bela Melegh, MD. PhD. Department of * Values are means with ranges given in parentheses. n = 5 for each Pediatrics. University Medical School of Ptcs. Jozsef Attila 11.7.7623 Pecs, Hungary. group. 460 DRUG-INDUCED CARNlTlNE DEPLETION 46 1 of the study. At the time of the study, they were receiving follow- found in creatinine excretion within groups comparing the data up treatment to prevent relapse and were healthy with no clinical before (d 0) and on the last day (d 7 or 14) of the study (Table or laboratory evidence of disease. After a control day (24-h period 2). Similarly, no differences in creatinine excretion were observed before start of carnitine and pivampicillin treatment. during across patient groups. which urine and plasma samples were collected: d O), the patients In the two pivampicillin-treated groups (groups A and B), rates received 1500 mg (3.24 mmol) of pivampicillin and 525 mg of urinary esterified carnitine excretion were markedly increased (3.26 mmol) of L-carnitine, divided into three equal doses, daily after treatment compared with rates before treatment within for 7 d. each group: the difference was much more pronounced in group Grottp B: pivampicillin and molar rsccJss carnitinr-treated B subjects than in group A subjects (Table 2). Whereas in group group. Three female and two male children were enrolled in this A the output of free carnitine decreased precipitiously after group (Table 1). These patients were treated for pharyngeal treatment. in group B administration of the higher dose of colonization by ampicillin-sensitive streptococci or staphylo- carnitine resulted in free carnitine output unchanged from the cocci. Their clinical condition at the time of the study was pretreatment rate. normal, and they were not being treated with pivampicillin By contrast, subjects in group C excreted significantly less free immediately before the start of the study. After a control day (d carnitine on d 0 than their counterparts in groups A and B (who. 0), patients in group A were given 1500 mg (3.24 mmol) of on d 0, may be regarded as untreated controls for the chronic pivampicillin per day, divided into three equal doses, for 7 d. valproate-treated subjects in group C). After carnitine treatment, L-Carnitine was administered at a higher level, 3 g ( 18.6 mmol)/ free carnitine excretion increased dramatically in group C pa- d. divided into three equal doses. tients to rates much higher than that in groups A and B. By Grotcp C: valproic acid and carnitinc~trmtrd group. Three contrast, water-soluble acylcarnitine ester excretion also in- female and two male epileptic children (asymptomatic and oth- creased after carnitine treatment of group C patients but to a erwise in good health; age, 12-48 mo; average age, 26 mo) on much lesser extent than for subjects in groups A and B. chronic valproic acid treatment (600 to 1200 mg daily: average, The presence of pivaloylcarnitine as the predominant (or 1050 mg) were enrolled in the study (Table 1). After a control exclusive, >85% of total acylcarnitine esters) carnitine ester in day (d 0). these patients were given a quantity of L-carnitine urine was demonstrated in random samples (n = 7) selected equal to the valproic acid treatment dose, on a mole-for-mole from patients in groups A and B on d 7 directly by "C NMR basis [for each capsule containing 1.07 mmol (150 mg) of val- (Fig. I), or pivaloic acid was determined by gas-liquid chroma- proic acid administered. 172 mg ( 1.07 mmol) of carnitine was tography after ester hydrolysis (data not shown). given], for 2 wk. Acid-soluble acylcarnitine ester concentrations in plasma of Procrdttrrs. Before the onset (d 0) and on the last day (d 7 or subjects in groups A and B were increased with pivampicillin 14) of carnitine treatment, a 24-h urine collection was obtained, plus carnitine treatment (Table 3). This increase was due perhaps and blood was collected after an overnight fast. Plasma and urine to increased circulating pivaloylcarnitine (6). In group A, a were stored at -40°C until analysis. The diet was a standard decrease in the free carnitine concentration was observed on the clinical mixed diet. Informed consent was obtained from the last day of treatment, whereas in group B, a moderate increase parents of each participant in the study. The study design was was found compared with the pretreatment concentration (on d approved by the local ethical committee and by the National 0). For patients in group C, the levels of free, acyl. and total Pharmacological Institute. Budapest. carnitine were lower before the start of carnitine supplementation M~jthods.Plasma and urinary acid-soluble carnitine and acyl- compared with d 0 levels in subjects in groups A and B. and on carnitine esters were quantified as described (17). y-Butyrobe- the last day increases were found in each of these fractions. taine concentrations were determined by conversion of y-bu- The rate of urinary excretion of y-butyrobetaine was different tyrobetaine to carnitine by partially purified y-butyrobetaine in the two groups of pivampicillin-treated subjects (Table 4). In hydroxylase ( 18). followed by measurement of carnitine formed. group A, a decrease was observed in y-butyrobetaine output. In c-N-trimethyllysine in plasma and urine was quantified by fluo- three patients. it dropped to the level of detection (0.1 pmol/L) rescence after HPLC separation of o-phthalaldehyde derivatives after treatment; by contrast, in group B, the rate of y-butyrobe- ( 19). The presence of pivaloylcarnitine in urine was identified by taine excretion remained unchanged compared with the pretreat- "C NMR, using a high resolution GN 500 spectrometer (General ment control day. For all data for patients in groups A and B, Electric. Fremont. CA) at 11.5 T. The acyl groups of carnitine urinary excretion of y-butyrobetaine was positively correlated to esters in urine were determined by gas-liquid chromatography excretion of free carnitine (r = 0.75: p < 0.05: data not shown).

14., 61.. Concentrations of lvsine and 3-methvlhistidine were de- The equation describing the regression line was !, = 0.03s + termined by spectrophotometry, after ion-exchange chromatog- 1.39. For patients in group C, the rate of y-butyrobetaine excre- raphy and postcolumn ninhydrin derivization (20). Urinary total nitrogen output was measured by quantification of ammonia Table 2. Urinarjvevcrcvion c!f'curnirinr, acid-sollrhle liberated by Kjeldahl digestion, and creatinine was determined uc~~lcarnitinc~esters, und crcwtininc* spectrophotometrically, as described previously (2 1). Acid-soluble Total acid- The t test was used for statistical analysis of data within each acylcarnitine soluble experimental group. Data for d 0 and d 7 or 14 were paired for Free carnitine esters carnitine Creatinine each individual to increase the accuracy of comparisons. Be- (pmolld) (mmol/d) tween-group comparisons were by analysis of variance, using the (pmolld) (pmolld) SOLO PC program (version 4.0, 1991; BMDP Statistical Soft- Group A ware. Los Angeles, CA). Differences were considered significant Day 0 115 f 6.30 109 + 18.6 224 + 20.9 3.17 + 0.66 at p < 0.05. The method of least squares was used for linear Day 7 0.06 r 0.06t 1790 f 276t I790 f 276t 3.44 f 0.68 regression analysis. Group B Day 0 126 f 48.4 89.4 f 27.5 216 + 74.7 4.38 f 1.07 Day 7 127 + 49.7 3120 + 604t 3250 f 628t 5.05 f 1.57 RESULTS Group C Characteristics of patient groups are summarized in Table I. Day 0 12.1 f 1.98$ 53.6 f 9.49 65.7 f 9.54$ 4.70 f 0.92 Day 14 910 f 139t 334 f 39.8t 1240 + 12.5t 5.51 f 1.06 There were no statistically significant differences in the age, body -- -- weight, or height between the three groups. The height and weight * Values are mean f SEM: n = 5 for each group. of each patient were within the 40th to 60th percentile range t p < 0.05 vs d 0 within the same group. using local standards. No statistically significant differences were $ p < 0.05 vs d 0 in group A or group B. MELEGH ET .4L Table 5. Concentrations of L-1j:~incand C-N-tritnc~t/~j~llj~.~inc~in plasma* - -- - ... - ~ I.-Lysine c-N-trimethyllysine (P~OIIL) (rrmollL) Group A Day 0 178 + 7.93 0.40 + 0.03 Day 7 171 + 16.4 0.46 + 0.03 Group B Day 0 166 + 18.3 0.42 + 0.05 Day 7 179 + 15.6 0.42 + 0.06 Group C Day 0 196 + 17.3 0.42 + 0.03 Day 14 176 + 11.9 0.47 + 0.04 lL'l'llll'l''''I'~ - - -- 5 0 40 3 0 20 PPI! * Values are mean + SEM: n = 5 for each group. Fig. I. "C NMR spectrum of authentic pivaloylcarnitine (~rppcr,spcJc- trttrn) and representative "C NMR spectrum of concentrated urine from a patient in group A (lo~,er.spectnrm). In urine from patients in groups A and B, a characteristic peak was found at about 26 ppm that corre- sponds to the three methyl groups of pivalate in pivaloylcarnitine. Another peak was found at 54 ppm. corresponding to the three methyl groups of carnitine. Table 3. Concentrations ofcarnitine and acid-.soluble ac.vlcarnitine esters in plasma* Acid-soluble acylcarnitine Total acid-soluble Free carnitine esters carnitine (rmol/L) (rmol/L) (rmol/L) Group A Day 0 32.3 + 3.48 1 I. l + 1.94 43.4 + 3.65 Day 7 9.46 + 2.69t 20.0 + 2.91t 29.5 + 2.69t Group B E -N-Trimethyllysine (mmollmol Creatinlne) Day 0 34.0 + 2.46 9.24 + 0.99 43.3 + 1.83 Day 7 44.0 + 5.70t 16.3 + 4.14t 60.3 + 9.12t Fig. 2. Relationship between urinary 6-N-trimethyllysine and 3-meth- Group C ylhistidine excretion. For analysis. data from all patients in each of the Day 0 24.6 + 2.95$ 6.24 + 1.82$ 30.8 + 3.73$ three groups were used (30 observations from 15 individuals). Open Day 14 46.0 + 3.19t 10.2 + 1.17t 56.2 + 4.1 It circles. group A before treatment: c,lo.sc~fc,ircles. group A after treatment: opm rriun,y/c~.s.group B before treatment: c,lo.rc.d triun,yles. group B after * Values are mean + SEM: n = 5 for each group. treatment: opcn .sqliurev. group C before carnitine supplementation: and t p < 0.05 tls d 0 within the same group. c1osc.d .rqrrures. group C after carnitine supplementation. Solid line. indi- $ p i0.05 vs d 0 in group A or group B. cates linear regression of the data. described by the equation. j' = 3.26.1- + 7.37 (r= 0.641). Table 4. Urinary e-~cretionofr-1-vsine, c-N-trimethj~llj~sine,and 7-hutvrohetaine* 0.05) between rates of urinary 3-methylhistidine and c-N-trime- thyllysine excretion (Fig. 2). Although data for each group alone did not provide significant correlations (perhaps due to the small number of observations within each group and clustering of data Group A in group C, and to a lesser extent in group B, within a narrow Day 0 range of c-N-trimethyllysine concentrations) the data analyzed Day 7 in aggregate provide evidence for a significant positive relation- Group B ship between excretion of c-N-trimethyllysine and 3-methyl- Day 0 histidine. Day 7 Urinary total nitrogen and urea excretion were not different Group C within any of the three groups before and after treatment. Day 0 Day 14 DISCUSSION * Values are mean + SEM; n = 5 for each group. t p < 0.05 vs d 0. Pivalic acid is conjugated to several antibacterial drugs to promote their efficient absorption (22. 23). These conjugates. tion was not statistically different from the untreated control once absorbed, are hydrolyzed to the parent drug and pivalic subjects (groups A and B, d O), and remained unchanged on the acid. In humans, pivalic acid is excreted predominantly as an last day of carnitine administration. ester of L-carnitine (4, 24). Like other esters of carnitine, frac- Urinary output of lysine and c-N-trimethyllysine did not tional excretion of pivaloylcarnitine is greater than that for free change significantly on the last day of the study period compared carnitine. Administration of pharmacologic amounts of pivalate- with the pretreatment control day (Table 4). Similarly, no conjugated drugs results in carnitine depletion, characterized by changes were found in the plasma concentrations of these amino reduced concentrations of carnitine in the circulation and tissues, acids before and after the various treatments (Table 5). and hypoketonemia. These effects are overcome by pharmaco- Regression analysis of data for all patients obtained before and logic administration of carnitine with the drug. Results from this on the last day of treatments revealed a positive correlation (p< study show that administration of one molar equivalent of DRUG-INDUCED CARNITINE DEPLETION 463 carnitine with pivampicillin is insufficient to prevent the carni- into mitochondria may present a significant rate-limiting obsta- tine-depleting effects of the drug. The lack of efficacy of a molar cle for use of t-N-trimethyllysine for carnitine synthesis. equivalent of orally administered carnitine probably is a conse- The second factor is the affinity of the hydroxylase for its quence of poor absorption of pharmacologic amounts of this substrate, relative to the concentration of the substrate. t-N- compound. Pharmacologic amounts (I or more g per day) ad- trimethyllysine concentration in rat muscle was estimated to be ministered orally to humans are less than 20% absorbed (25- about 24 pmol/L (and somewhat lower in other tissues) (16). 27). By contrast, when a 6-fold molar excess of carnitine was The Km for t-N-trimethyllysine hydroxylase in rat tissues was given orally with pivampicillin, free carnitine concentration in reported to be about 0.1 mmol/L (31). Thus, the enzyme prob- plasma remained unchanged from the pretreatment level, and ably is not saturated under most conditions, and fluctuations in the rate of urinary excretion of free carnitine also was not substrate concentration should be reflected in changes in the rate different. of /3-hydroxy-t-N-trimethyllysine formation. Availability of in- Urinary excretion of y-butyrobetaine was different in the creased substrate, by oral administration of t-N-trimethyllysine. two groups of pivampicillin-treated subjects (Table 4). In group significantly increased the rate of carnitine synthesis in both rats A, a marked decrease was observed in the y-butyrobetaine (1 5) and humans (13, 14), suggesting that the capacity both to output from d 0 to d 7. By contrast. in group B, the rate of transport c-N-trimethyllysine into mitochondria and to hydrox- y-butyrobetaine excretion remained unchanged after carnitine ylate this substrate is not fully used under normal conditions. and pivampicillin treatment compared with the rate before treat- Thus, the appearance of significant amounts of t-N-trimethylly- ment. This observation may be explained by changes in one or sine in urine must reflect partitioning of the substrate at the a combination of metabolic processes, including differences in cellular level, between export into the circulation and import the tissue and circulating concentrations of y-butyrobetaine. into mitochondria and/or hydroxylation within the mitochon- perhaps affecting its use for carnitine synthesis, and differences dria. In humans. t-N-trimethyllysine is not reabsorbed to any in the efficiency of reabsorption of y-butyrobetaine before and significant extent (32). Coupled with its poor uptake from the after treatment. The data available are not sufficient to distin- circulation by tissues, export from the cell effectively consigns guish between these alternative hypotheses. this amino acid to disposal from the body. Because t-N-tri- Numerous studies in experimental animals and humans have methyllysine is readily reabsorbed by rats, its efficiency of use shown that chronic valproic acid treatment leads to depletion of for carnitine biosynthesis should be more than in humans. Davis carnitine in blood and tissues and reduces the rate of urinary and Hoppel (16) estimated that normally about 80% of r-N- carnitine excretion. The mechanism for this effect is unknown. trimethyllysine is used for carnitine synthesis in rats. Based on Unlike pivalic acid, valproic acid is a poor substrate for carnitine relative rates of carnitine synthesis (estimated as described above) ester formation (6. 28). Data from this study are consistent with and rates of excretion of c-N-trimethyllysine in this study (d 0 previous findings: Most of the carnitine supplement administered for children in groups A and B), the efficiency of use of t-N- was not used for ester formation (as was the case with pivampi- trimethyllysine for carnitine synthesis in humans is about 63%. cillin treatment) but was eliminated in the urine as free carnitine. In summary. an excess molar equivalent of carnitine is neces- Valproic acid administration resulted in a lower rate of excre- sary to overcome the carnitine-depleting effects of pivalate ad- tion of carnitine. 1.85 pmol. kg body wt-' .d-' for subjects in ministered as the oral antibiotic ampicillin. Conversely. one group C (d 0). compared with 6.58 pmol. kg body wt-' .d-' for molar equivalent of carnitine, administered as an oral supple- subjects in groups A and B (d 0). A large measure of this decrease ment, is sufficient to normalize plasma carnitine concentrations was probably due to decreased filtered load of carnitine (plasma and increase the rate of urinary carnitine excretion in patients total carnitine in valproic acid-treated subjects was 30.8 pmoll treated with valproic acid. For all patients taken together, t-N- L compared with controls, 43.4 pmol/L). Nevertheless, the dif- trimethyllysine excretion was significantly correlated with 3- ference in the rates of excretion of carnitine was larger (by almost methylhistidine excretion, suggesting that the rate of excretion 4-fold) than the estimated rate of carnitine synthesis [I .20 pmol. of t-N-trimethyllysine is determined by the rate of protein turn- kg body wt-' .d-': estimated from steady state carnitine excretion over and not by the rate of carnitine biosynthesis. by strict vegetarians (29)] suggesting that the effect of valproic acid on carnitine homeostasis may be manifest in the efficiency Acknon~ledgmmts.The authors thank C. Trevisani (Sigma-tau of carnitine absorption, reabsorption, or both. Pharmaceuticals, Pomezia-Rome, Italy) for providing carnitine. Circulating concentrations and rates of excretion of t-N-tri- W. 0. Godtfredsen (Leo Pharmaceuticals. Ballemp. Denmark) methyllysine were not different before and after treatment in any for providing pivampicillin and D. A. Sherry and B. Sumegi of the three treatment groups. Thus, t-N-trimethyllysine produc- (University of Texas at Dallas, Richardson, TX) for providing tion and use does not seem to be altered by substantial changes NMR spectra and for assistance in their evaluation. in carnitine status. t-N-trimethyllysine excretion correlated with 3-methylhistidine excretion, indicating that the rate of t-N-tri- REFERENCES methyllysine excretion probably is determined by the rate of I. Bremer J 1983 Carnitine: metabolism and funct~ons.Physiol Rev 63:1420- protein turnover and not necessarily by the rate of carnitine 1480 synthesis. The normal rate of t-N-trimethyllysine excretion (0.7 1 2. Rebouche CJ, Paulson DJ 1986 Carnitine metabolism and function in humans. pmol. kg body wt-' .d-', estimated from d 0 rates by patients in Ann Rev Nutr 6:4 1-66 3. Ohtani Y. Endo F. 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