Urinary Excretion Of Free Carnitine Research Articles

Kinetics of Serum Carnitine Fractions in Patients with Chronic Kidney Disease Not on Dialysis.

Carnitine plays a pivotal role in energy synthesis through β-oxidation in mitochondria. Serum and tissue levels of free carnitine are significantly decreased in dialysis patients, whereas acylcarnitine levels are increased. However, the precise kinetics and fate of carnitine fractions in chronic kidney disease (CKD) patients who are not on dialysis have not been clarified. This study aims to determine the kinetics of serum carnitine fractions in patients who were not on dialysis. Seventy-five CKD patients not on dialysis were recruited in this study. Serum and urinary carnitine fraction levels were measured to evaluate the kinetics and regulation of serum carnitine fractions. Carnitine fractions were measured by the enzymatic cycling method. Total and free serum carnitine levels did not change with progression of CKD, whereas acylcarnitine levels and the acyl/free carnitine ratio significantly increased. Serum acylcarnitine levels were inversely associated with estimated glomerular filtration rate (r2 = 0.239, p < 0.001), but free carnitine levels were not. Serum free carnitine levels were positively associated with urinary free carnitine excretion (r2 = 0.214, p < 0.001), but serum acylcarnitine levels were not. Multiple stepwise regression analysis revealed that urinary free carnitine excretion and blood urea nitrogen were independent determinants of serum free carnitine and acylcarnitine levels, respectively. The present study demonstrated that serum acylcarnitine levels increased with renal dysfunction independent of urinary excretion levels. Serum free carnitine was not affected by renal function in CKD patients who were not on dialysis.

Carnitine supplementation alleviates lipid metabolism derangements and protects against oxidative stress in non-obese hereditary hypertriglyceridemic rats.

The aim of this study was to estimate the effect of carnitine supplementation on lipid disorders and peripheral tissue insulin sensitivity in a non-obese animal model of insulin resistance, the hereditary hypertriglyceridemic (HHTg) rat. Male HHTg rats were fed a standard diet, and half of them received daily doses of carnitine (500 mg·kg(-1) body weight) for 8 weeks. Rats of the original Wistar strain were used for comparison. HHTg rats exhibited increased urinary excretion of free carnitine and reduced carnitine content in the liver and blood. Carnitine supplementation compensated for this shortage and promoted urinary excretion of acetylcarnitine without any signs of (acyl)carnitine accumulation in skeletal muscle. Compared with their untreated littermates, carnitine-treated HHTg rats exhibited lower weight gain, reduced liver steatosis, lower fasting triglyceridemia, and greater reduction of serum free fatty acid content after glucose load. Carnitine treatment was associated with increased mitochondrial biogenesis and oxidative capacity for fatty acids, amelioration of oxidative stress, and restored substrate switching in the liver. In skeletal muscle (diaphragm), carnitine supplementation was associated with significantly higher palmitate oxidation and a more favorable complete to incomplete oxidation products ratio. Carnitine supplementation further enhanced insulin sensitivity ex vivo. No effects on whole-body glucose tolerance were observed. Our data suggest that some metabolic syndrome-related disorders, particularly fatty acid oxidation, steatosis, and oxidative stress in the liver, could be attenuated by carnitine supplementation. The effect of carnitine could be explained, at least partly, by enhanced substrate oxidation and increased fatty acid transport from tissues in the form of short-chain acylcarnitines.

L-Carnitine prevents the development of ventricular fibrosis and heart failure with preserved ejection fraction in hypertensive heart disease

Prognosis of heart failure with preserved ejection fraction (HFpEF) remains poor because of unknown pathophysiology and unestablished therapeutic strategy. This study aimed to identify a potential therapeutic intervention for HFpEF through metabolomics-based analysis. Metabolomics with capillary electrophoresis time-of-flight mass spectrometry was performed using plasma of Dahl salt-sensitive rats fed high-salt diet, a model of hypertensive HFpEF, and showed decreased free-carnitine levels. Reassessment with enzymatic cycling method revealed the decreased plasma and left-ventricular free-carnitine levels in the HFpEF model. Urinary free-carnitine excretion was increased, and the expression of organic cation/carnitine transporter 2, which transports free-carnitine into cells, was down-regulated in the left ventricle (LV) and kidney in the HFpEF model. L-Carnitine was administered to the hypertensive HFpEF model. L-Carnitine treatment restored left-ventricular free-carnitine levels, attenuated left-ventricular fibrosis and stiffening, prevented pulmonary congestion, and improved survival in the HFpEF model independent of the antihypertensive effects, accompanied with increased expression of fatty acid desaturase (FADS) 1/2, rate-limiting enzymes in forming arachidonic acid, and enhanced production of arachidonic acid, a precursor of prostacyclin, and prostacyclin in the LV. In cultured cardiac fibroblasts, L-carnitine attenuated the angiotensin II-induced collagen production with increased FADS1/2 expression and enhanced production of arachidonic acid and prostacyclin. L-Carnitine-induced increase of arachidonic acid was canceled by knock-down of FADS1 or FADS2 in cultured cardiac fibroblasts. Serum free-carnitine levels were decreased in HFpEF patients. L-carnitine supplementation attenuates cardiac fibrosis by increasing prostacyclin production through arachidonic acid pathway, and may be a promising therapeutic option for HFpEF.

Increased Urinary Excretion of Carnitine and Acylcarnitine by Mercuric Chloride Is Reversed by 2,3-Dimercapto-1-Propanesulfonic Acid in Rats

This investigation was aimed to study the effect of 2,3-dimercapto-1-propanesulfonic acid (DMPS) on mercuric chloride (HgCl(2))-induced alterations in urinary excretion of various carnitine fractions including free carnitine (FC), acylcarnitine (AC), and total carnitine (TC). Different groups of Wistar male rats were treated with HgCl(2) at the doses of 0.1, 0.5, 1.0, 2.0, and 3.0 mg/kg body weight, and the animals were sacrificed at 24 hours following HgCl(2) injection. A separate batch of animals received HgCl(2) (2 mg/kg) with or without DMPS (100 mg/kg) and sacrificed at 24 or 48 hours after dosing. Administration of HgCl(2) resulted in statistically significant and dose-dependent increase in the urinary excretion of FC, AC, and TC in rats. However, the ratio of urinary AC:FC was significantly decreased by HgCl(2). Pretreatment with DMPS offered statistically significant protection against HgCl(2)-induced alterations in various urinary carnitine fractions in rats.

Labeled Trimethyllysine Load Depletes Unlabeled Carnitine in Premature Infants without Evidence of Incorporation

6-N-Trimethyl-[d₉]-L-lysine (dTML), the labeled form of a mammalian carnitine precursor, was administered to two groups of premature infants. Although the urinary output of dTML significantly increased in the low-dose-treated group (100 μmol/day), this amount did not affect the urinary output or plasma levels of carnitine and carnitine esters. In the second group of infants, after administration of 500 μmol dTML the plasma-free carnitine concentration increased (from 9.95 ± 0.63 to 12.9 ± 0.87 nmol/ml, p > 0.05) with a significant increase in the urinary excretion of free carnitine on the day of dTML administration and on the posttreatment day (from 4.79 ± 1.36 to 9.85 ± 1.18 and to 17.5 ± 2.31 μmol/day, respectively). Analysis of urine using fast atom bombardment mass spectrometry (FAB-MS) revealed only the presence of the dTML in the urine of the newborns; no change was detected in the relative abundance of any other carnitine precursor. Surprisingly, in the second group, which received the higher dose of dTML supplement, only the signal intensity of the unlabeled carnitine increased after dTML administration; no new peak appeared in the urine that would correspond to the de novo synthesized carnitine containing the stable isotope-labeled trimethyl group of dTML. Thus, the FAB-MS analysis clearly demonstrated that contrary to the likely prediction, the 270% extra free carnitine output was a consequence of a dose-dependent dTML-induced depletion of the free carnitine reserves from the newborns. The absence of the incorporation of the label from dTML into carnitine strongly suggests that circulating TML is not the precursor of carnitine in premature infants.

Urinary carnitine excretion in patients with heart failure.

To evaluate the fatty acid metabolism in heart failure, the semiquantitative analysis of urinary free carnitine and acylcarnitine was made by fast atom bombardment mass spectrometry (FABMS) in 22 patients (mean age 67.3 years) with heart failure and 19 age-matched healthy controls (average age 60.4 years). Urinary excretion of free carnitine was 0.20 +/- 0.118 ratio/mg creatinine in the healthy controls and 1.32 +/- 1.170 ratio/mg creatinine in the patients with heart failure. The latter value was significantly higher (p < 0.01). Patients with heart failure were classified into two groups according to the urinary free carnitine concentration. One was the high excretion group (2.19 +/- 0.102 ratio/mg creatinine, 12 cases) and the other was the low excretion group (0.37 +/- 0.212 ratio/mg creatinine, 10 cases). In the high excretion group, urinary acetylcarnitine was also increased, but no significant abnormalities were observed in the urinary organic acid profile. In the high group, 1 patient was classified as NYHA class III and 11 as NYHA class IV. Four patients died in the hospital. In the low excretion group, five patients were classified as NYHA class III and five as NYHA class IV. Only one patient died in the hospital. In the high group, patients with severe and prolonged heart failure tended to maintain higher values of urinary free carnitine. We could not find any abnormalities in fatty acid metabolism in patients with heart failure, but it is suspected that the patients who excrete large amounts of free carnitine into the urine, namely the patients with severe heart failure, have some possibility of carnitine deficiency.

Metabolism of S-1108, a new oral cephem antibiotic, and metabolic profiles of its metabolites in humans.

The metabolism and pharmacokinetics of pivalic acid, a major metabolite of S-1108, were studied with three healthy volunteers. Concentrations of S-1006 (the active compound), pivalic acid, and pivaloylcarnitine in plasma and urine were measured after administration of S-1108. Recoveries in urine at the doses of S-1108 given (100 and 200 mg) were 33 to 41% for S-1006, 93% for total pivalic acid, and 89 to 94% for pivaloylcarnitine in 24 h, and maximum concentrations in plasma were 2 micrograms of S-1006 per ml, 1 micrograms of total pivalic acid per ml, and 2 micrograms of pivaloylcarnitine per ml after a 200-mg oral administration of S-1108. More than 90% of the pivalic acid was excreted as pivaloylcarnitine, and no measurable amount of free pivalic acid was present in urine samples, indicating that the pivalic acid liberated from S-1108 was almost quantitatively conjugated with carnitine in the human body. The level of free carnitine in plasma was unaffected by a single 200-mg administration of S-1108, whereas urinary excretion of free carnitine decreased as levels of acylcarnitine increased. The acylcarnitines were excreted primarily in the form of pivaloylcarnitine. This study clearly showed how the pivalic acid was metabolized and excreted in humans. The importance of monitoring carnitine, an essential cofactor in fatty acid metabolism, was also discussed in terms of its utilization by pivalic acid.

Carnitine femoral arterial-venous differences in the stressed critically ill.

Femoral arterial and venous carnitine concentrations from critically ill patients were measured in order to determine if the large urinary carnitine excretions seen in these patients was associated with a net loss of carnitine from skeletal muscle. Bloods were drawn two or three times during the 7-day study period. A 24-hr urine sample was obtained on the same day. The arterial-venous difference for free carnitine plus short chain acylcarnitine was -2.8 +/- 0.9 microM (means +/- SEM), and -2.7 +/- 1.0 microM for total carnitine. Both values were significantly less than zero (p less than 0.05). Median urinary free carnitine excretion was 1237 mumol/day while the median acylcarnitine excretion was 544 mumol/day. We conclude that skeletal muscle in these patients is in negative carnitine balance, and is at least one source of the increase in carnitine excretion seen in critically ill patients.

Decreased fasting free fatty acids with L-carnitine in children with carnitine deficiency.

At the time of acute presentation, children with carnitine deficiency may have increased free fatty acid concentrations and hypoglycemia. However, whether carnitine replacement affects the plasma concentration of these substrates remains to be determined. Therefore, to evaluate the effect of carnitine replacement on plasma substrate and hormone concentrations, five children with carnitine deficiency (two idiopathic, two secondary to long-chain acyl coenzyme A dehydrogenase deficiency, one secondary to isovaleric acidemia) were fasted overnight before and after treatment with oral carnitine (80 +/- 7 mg.kg-1.day-1). During carnitine supplementation, plasma total carnitine (19 +/- 4 versus 45 +/- 6 nmol/ml, pretreatment versus treatment, respectively) and free carnitine (11 +/- 3 versus 31 +/- 6 nmol/ml), as well as red blood cell total carnitine (0.057 +/- 0.019 versus 0.130 +/- 0.019 nmol/mg of hemoglobin) increased (p less than 0.05). Fasting plasma glucose (83 +/- 4 versus 85 +/- 3 mg/dl) and ketone body (0.54 +/- 0.18 and 0.56 +/- 0.20 mM) concentrations did not change with carnitine supplementation, but plasma free fatty acids (1.28 +/- 0.32 versus 0.77 +/- 0.07 mM) decreased (p less than 0.05). No differences in fasting insulin, growth hormone, or cortisol concentrations were observed. Urinary excretion of free carnitine (0.1 +/- 0.0 versus 2.4 +/- 0.7 mumol/mg creatinine), total carnitine (0.3 +/- 0.1 versus 3.4 +/- 0.9 mumol/mg creatinine) and acyl carnitine (0.2 +/- 0.1 versus 0.9 +/- 0.3 mumol/mg creatinine) increased (p less than 0.05) with carnitine supplementation. The decreased plasma free fatty acid concentrations with carnitine supplementation may be due to more efficient fatty acid oxidation and/or increased urinary excretion of fatty acids as acylcarnitines.

Plasma carnitine levels and urinary carnitine excretion during sepsis.

Carnitine is an indispensable factor for the beta-oxidation of medium- and long-chain fatty acids, and it plays a possible role in the oxidation of branched-chain amino acids. Plasma and urinary levels of free carnitine and short-chain acyl-carnitines were studied in 67 surgical patients, after non-septic surgical procedures or during sepsis. The septic state was associated with increased urinary excretion of free carnitine (p less than 0.001), as well as with lower plasma levels of short-chain acyl-carnitines (p less than 0.001); the latter feature correlated with the level of hypermetabolism, as evaluated by the metabolic rate and by the arterial-mixed venous O2 difference. In 26 patients during total parenteral nutrition D, L-acetyl-carnitine was administered (100 mg/kg/24 hrs, in continuous iv infusion) and was associated, in septic patients only, with a significant decrease in the respiratory quotient, suggesting enhanced oxidation of low respiratory quotient substrates (fatty acids and/or branched-chain amino acids). Carnitine supplementation during total parenteral nutrition might be of theoretical benefit in some clinical conditions, such as sepsis, in which the following conditions coexist enhanced utilization of substrates whose oxidation is partially or totally carnitine dependent; prolonged absence of exogenous intake of carnitine (as in long-term total parenteral nutrition); eventual impairment of carnitine synthesis due to hepatic dysfunction; increased, massive urinary loss of carnitine.

Influence of kidney transplantation on carnitine metabolism : K.P. Kohse, Claudia Rössle, Elke Dech, P. Fürst, and H.-E. Franz Nephrol. Sect., Univ. of Ulm, and Inst. f. Biol. Chem., Univ, of Hohenheim (FRG)

In this study, we examined all three plasma carnitine fractions, free carnitine (FC), short-chain acyl- (SCC), and long-chain acylcarnitine (LCC), as well as the urinary excretion of FC and SCC in 62 patients with functioning renal allografts 1-70 months following the kidney transplantation (KT). Patients were classified into three groups according to their transplant function, as characterized by the serum creatinine concentration (CR). A comparison with normal subjects (n = 20) and with patients on chronic hemodialysis (HD, n = 46) revealed a complete normalization of all carnitine plasma fractions for group I patients (Cr less than 120 mumol/l). In contrast, significant elevations of plasma free and esterified carnitine were found in group II (Cr greater than 120, less than 200 mumol/l; with FC + 27%, SCC + 82%, and LCC + 49% and group III patients (Cr greater than 200 mumol/l; with FC + 39%, SCC + 122%, and LCC + 106%), as compared to healthy subjects (p less than 0.001). The elevations in concentrations of SCC were more pronounced than those of FC; consequently, we found a higher ratio of acylcarnitine (AC) to FC in group III than in group I patients (+ 41%, p less than 0.001). Yet even in the former group, this ratio was found to be markedly reduced when compared to HD patients (-41%, p less than 0.001). We found no significant differences in the urinary excretion of FC and SCC between the 3 groups of KT patients. It is thus to conclude that in patients with a well-functioning transplant, the pattern of carnitine fractions in plasma is fully normalized. The decrease in the ratio of AC to FC following a successful KT might suggest a better availability of FC and thereby be associated with an enhanced fatty acid oxidation.

Propionylcarnitine excretion in propionic and methylmalonic acidurias: a cause of carnitine deficiency

Two patients with propionic acidemia (PA) and two patients with methylmalonic aciduria (MMA) had low plasma free carnitine and increased short-chain acylcarnitines. Urinary excretion of free carnitine was decreased, while the excretion of short-chain acylcarnitines, mostly propionylcarnitine, was increased. Carnitine supplementation markedly increased the short-chain acylcarnitine fractions of both plasma and urine. Total carnitine content was decreased in skeletal muscle biopsies obtained from two of the patients. It is suggested that in these organic acidurias mitochondrial propionylcarnitine, formed from free carnitine and excess propionylCoA, exchanges with free cytosolic carnitine: propionylcarnitine is then lost in the urine, causing secondary carnitine deficiency in the tissues.

Carnitine metabolism in normal-weight and obese human subjects during fasting.

Carnitine metabolism was studied in normal-weight and obese subjects by measurement of carnitine and its acyl derivatives in plasma and urine. When first fed an isocaloric, low-carnitine diet, both groups showed a decrease in plasma total carnitine, primarily due to a decrease in the free carnitine fraction. Urinary free carnitine excretion also fell significantly. When fasting was instituted, plasma total carnitine concentration increased. This was the net result of a rapid increase in short-chain and long-chain acylcarnitine and a delayed decrease in free carnitine. Urinary excretion of short-chain acylcarnitines increased parallel to rising plasma concentrations, whereas free carnitine excretion first decreased and then tended to increase slightly. Both plasma and urinary short-chain acylcarnitine correlated with beta-hydroxybutyrate. All of these changes were reversed by refeeding, in the obese even with a low-carnitine hypocaloric intake. Obese subjects also developed hyperketonemia significantly more slowly than did normal-weight subjects, yet demonstrated substantially the same changes in magnitude and direction in carnitine and its metabolites.