Urinary Total Carnitine Research Articles

Carnitine Profile Changes in Pediatric Hematopoietic Stem Cell Transplant: New Role for Carnitine?

Carnitine is an essential cofactor for mitochondrial import and oxidation of fatty acids. High-dose chemotherapy and radiation, often required for hematopoietic stem cell transplant (HSCT), leads to tissue damage, mitochondrial dysfunction, and alterations in carnitine metabolism. The aim of this pilot cohort study was to describe plasma and urinary carnitine profiles during pediatric HSCT and their relationships with clinical outcomes. Plasma and urinary carnitine samples were collected from 22 pediatric patients before and through day 180 post-HSCT. Associations were observed between graft-versus-host disease and an elevated plasma total carnitine (P=0.019), and also increased plasma acyl:free carnitine ratio with veno-occlusive disease (P=0.016). Mortality was observed in those with their highest urinary total carnitine losses on day 0 (P=0.005), and in those with an abnormal day 28 plasma ratio either above or below the reference range (P=0.007). Changes in carnitine profiles were more reflective of metabolic stress and negative outcomes than of inadequate dietary intake. Associations observed direct larger studies to assess the validity of carnitine profiles as a prognostic indicator and also to assess whether prophylactic carnitine supplementation pre-HSCT could reduce mitochondrial injury and urinary losses and help mitigate inflammatory and metabolic comorbidities of HSCT.

Maximal-intensity exercise does not fully restore muscle pyruvate dehydrogenase complex activation after 3 days of high-fat dietary intake

Exercise activates muscle pyruvate dehydrogenase complex (PDC), but moderate intensity exercise fails to fully activate muscle PDC after high-fat diet [1]. We investigated whether maximal intensity exercise overcomes this inhibition. Quadriceps femoris muscle biopsy samples were obtained from healthy males at rest, and after 46 and 92 electrically-evoked maximal intermittent isometric contractions, which were preceded by 3 days of either low- (18%) or high- (69%) isocaloric dietary fat intake (LFD and HFD, respectively). The ratio of PDCa (active form) to total PDCt (fully activated) at rest was 50% less after HFD (0.32±0.01 vs 0.15±0.01; P<0.05). This ratio increased to 0.77±0.06 after 46 contractions (P<0.001) and to 0.98±0.07 after 92 contractions (P<0.001) in LFD. The corresponding values after HFD were less (0.54±0.06; P<0.01 and 0.70±0.07; P<0.01, respectively). Resting muscle acetyl-CoA and acetylcarnitine content was greater after HFD than LFD (both P<0.05), but their rate of accumulation in the former was reduced during contraction. Muscle lactate content after 92 contractions was 30% greater after HFD (P<0.05). Muscle force generation during contraction was no different between interventions, but HFD lengthened muscle relaxation time (P<0.05). Daily urinary total carnitine excretion after HFD was 2.5-fold greater than after LFD (P<0.01). A bout of maximal intense exercise did not overcome dietary fat-mediated inhibition of muscle pyruvate dehydrogenase complex activation, and was associated with greater muscle lactate accumulation, as a result of lower PDC flux, and increased muscle relaxation time.

Decreased carnitine biosynthesis in rats with secondary biliary cirrhosis.

Carnitine biosynthesis was investigated in rats with secondary biliary cirrhosis induced by bile duct ligation (BDL) for 4 weeks (n = 5) and in pair-fed, sham-operated control rats (n = 4). Control rats were pair-fed to BDL rats, and all rats were fed an artificial diet with negligible contents of carnitine, butyrobetaine, or trimethyllysine. Biosynthesis of carnitine and its precursors was determined by measuring their excretion in urine and accumulation in the body of the animals. Four weeks after BDL, total carnitine content was increased by 33% in livers from BDL rats when compared with control rats, but was unchanged in skeletal muscle and whole carcass. The plasma total carnitine concentration averaged 29.0 +/- 4.1 vs. 46.4 +/- 7.3 micromol/L in BDL rats and control rats, respectively. Urinary total carnitine excretion was reduced by 56% in BDL rats as compared with control rats. Carnitine biosynthesis was significantly decreased in BDL rats (0.45 +/- 0.19 vs. 0.93 +/- 0.08 micromol/100 g body weight/d in BDL and control rats, respectively). The tissue content of free and protein-linked trimethyllysine, a carnitine precursor, and trimethyllysine plasma concentrations were not different between BDL and control rats. However, urinary trimethyllysine excretion was increased 5-fold in BDL rats and approximated glomerular filtration. In contrast, urinary excretion of butyrobetaine, the direct carnitine precursor, was decreased by 40% in BDL rats as compared with control rats. Trimethyllysine biosynthesis was not different, but butyrobetaine biosynthesis was decreased by 51% in BDL as compared with control rats. In conclusion, carnitine biosynthesis is decreased in BDL rats as a result of a defect in the conversion of trimethyllysine to butyrobetaine.

Effect of exogenous carnitine on carnitine homeostasis in the rat

The interaction of exogenous carnitine with whole body carnitine homeostasis was characterized in the rat. Carnitine was administered in pharmacologic doses (0-33.3 mumols/100 g body weight) by bolus, intravenous injection, and plasma, urine, liver, skeletal muscle and heart content of carnitine and acylcarnitines quantitated over a 48 h period. Pre-injection urinary carnitine excretion was circadian as excretion rates were increased 2-fold during the lights-off cycle as compared with the lights-on cycle. Following carnitine administration, there was an increase in urinary total carnitine excretion which accounted for approx. 60% of the administered carnitine at doses above 8.3 mumols/100 g body weight. Urinary acylcarnitine excretion was increased following carnitine administration in a dose-dependent fashion. During the 24 h following administration of 16.7 mumols [14C]carnitine/100 g body weight, urinary carnitine specific activity averaged only 72 +/- 4% of the injection solution specific activity. This dilution of the [14C]carnitine specific activity suggests that endogenous carnitine contributed to the increased net urinary carnitine excretion following carnitine administration. 5 min after administration of 16.7 mumol carnitine/100 g body weight approx. 80% of the injected carnitine was in the extracellular fluid compartment and 5% in the liver. Plasma, liver and soleus total carnitine contents were increased 6 h after administration of 16.7 mumols carnitine/100 g body weight. 6 h post-administration, 37% of the dose was recovered in the urine, 12% remained in the extracellular compartment, 9% was in the liver and 22% was distributed in the skeletal muscle. In liver and plasma, short chain acylcarnitine content was increased 5 min and 6 h post injection as compared with controls. Plasma, liver, skeletal muscle and heart carnitine contents were not different from control levels 48 h after carnitine administration. The results demonstrate that single, bolus administration of carnitine is effective in increasing urinary acylcarnitine elimination. While liver carnitine content is doubled for at least 6 h following carnitine administration, skeletal muscle and heart carnitine pools are only modestly perturbed following a single intravenous carnitine dose. The dilution of [14C]carnitine specific activity in the urine of treated animals suggests that tissue-blood carnitine or acylcarnitine exchange systems contribute to overall carnitine homeostasis following carnitine administration.

Measurement of L-carnitine and acylcarnitines in body fluids and tissues in children and in adults

We have developed a reliable and validated radio-enzymatic method for the assay of L-carnitine and acylcarnitines, using a modification of existing methods. The sensitivity of the assay is 10 mumol/l using 10 microliters of plasma or urine. It is also suitable for measurements of carnitine in a 10 mg sample of liver or muscle obtained by percutaneous biopsy. The use of N-ethylmaleimide in the reaction mixture together with an excess of [1-14C]acetyl CoA ensures that the reaction proceeds to completion and a linear response is obtained. Using this method control ranges have been established for plasma and urine carnitine concentrations in healthy children and adults, and for the carnitine content of liver and muscle in adults. No significant difference was found between fasting and post-prandial plasma carnitine levels. An age-related increase was found in urinary total carnitine and acylcarnitine concentration throughout childhood. These data provide a reliable basis for studies of patients with abnormal carnitine and acylcarnitine metabolism, distribution and excretion.

Urinary carnitine excretion in surgical patients on total parenteral nutrition.

Urinary free and total carnitine excretions were measured in 41 normal adults and seven surgical patients on fat-free total parenteral nutrition for 8 to 45 days. The means (+/-SEM) of urinary free and total carnitine excretion in normal adults were 162 +/- 19 and 328 +/- 28 micrometers/days, respectively. All of the patients exhibited protein-calorie malnutrition with a mean carnitine intake of 11.6 +/- 1.5 micrometers/day. Under this stringent carnitine economy with the adequate supply of lysine and methionine, urinary total carnitine excretion significantly reduced to 127 to 162 micrometers/day. This probably reflects the carnitine biosynthetic rate. However, during the periods of operation and/or infection, urinary total carnitine excretion significantly increased 2- to 7-fold that of normal levels. Significant positive correlation was found between the two forms of urinary carnitine and total nitrogen excretions. Serum free and total carnitine levels in patients were significantly higher than normal adults. Such findings can be explained by the endocrine responses to the stress phenomenon and indicate a catabolic response of skeletal muscle in which most of the body carnitine resides. This can impair their carnitine status.