Urinary excretion of carnitine in multiply injured patients on different regimens of total parenteral nutrition

Plasma free carnitine in severe trauma: Influence of the association with traumatic brain injury

BACKGROUND

Metabolic response to severe trauma requires early nutritional resuscitation. Carnitine is essential for lipolysis, the energy source during this hypercatabolic phase. However l-carnitine is not present in nutritional replacement solutions. Furthermore, free carnitine depletion, defined as carnitine plasma level under 36μmol/L, was not adequately reported in adult patients with severe trauma. The aim of this study was to assess plasma free carnitine levels and factors of variation in severe trauma.

METHOD

Our observational study concerned 38 trauma patients including 18 with traumatic brain injury (TBI). On the third day after trauma, plasma free carnitine concentration was determined (by enzymatic method) while patients received artificial nutrition.

RESULTS

Low plasmatic free carnitine concentration was evidenced in 95% of the patients with a median value of 18μmol/L (11-47). Univariate analysis showed that mean arterial pressure, serum urea, CKD-EPI and patients with TBI were significantly associated with plasma free carnitine concentration less than 18μmol/L. Lower plasma free carnitine concentration was observed in the group of patients with TBI with 17.72μmol/L (11-36) versus 21.5μmol/L (11-47) for others patients (p=0.031). Logistic regression analysis showed that severe trauma with TBI and CKD-EPI above 94mL/min/1.73m2 appeared to be independent predictor of lower free carnitine plasmatic concentration (Goodness of fit=0.87 and AUC=0.89).

CONCLUSION

Our observations support hypotheses that plasma free carnitine concentration is lowered in severe injured patients especially for TBI patients and patients with estimated GFR above 94mL/min/1.73m².

Carnitine and septic shock: a review

Most studies have reported reduced carnitine levels in the tissues of patients with sepsis, probably due to increased urinary excretion. Because of the increased utilization of fatty acids and ketone bodies as sources of energy in sepsis, the carnitine deficiency can further impair the fuel metabolism and contribute to the unregulated lipid metabolism in these patients.

Recently, experimental and clinical studies have shown that carnitine and its congeners are able to: (a) downmodulate the spontaneous and endotoxin (LPS)-triggered overproduction of tumor necrosis factor (TNF)-alpha; (b) ameliorate the lipid metabolism; and (c) reduce the severity of illness, accelerate recovery, and, in some cases, improve survival in experimental septic shock.

Many questions concerning the ultimate molecular mechanism of action of these compounds in endotoxaemia are still unanswered. Yet, these compounds may be helpful in patients with sepsis, when associated with conventional therapy, in that they can effectively reduce TNF-alpha levels and ameliorate the host's metabolic processes.

The effect of carnitine supplemented total parenteral nutrition on lipid, energy and nitrogen metabolism in severely ill patients

To analyse the effects of L-carnitine supplemented TPN on lipid, energy and nitrogen metabolism, 16 severely injured patients were studied during the first 8 days after trauma. An L-carnitine solution (3g = 18.6mmol) was added to the fat emulsion and infused over 16h in a blind randomised fashion to half of the patients. Plasma triglyceride, free fatty acid and 3-OH-butyrate concentrations increased during the fat infusion, and fell to pre-infusion concentrations within 24h. There were no differences in plasma levels before, during or after infusion between the groups. ATP and phosphocreatine in muscle tissue were not influenced by carnitine supplementation. Glycogen, however, remained unchanged in the carnitine group and fell in the non-carnitine group. A cumulative N-balance measured from day 2 to day 8 was equally negative in both groups. Plasma carnitine levels were significantly higher in the supplemented group from day 3. The mean daily urinary carnitine excretion was increased 15-fold in the supplemented group. Muscle carnitine, however, remained unchanged in both groups and did not differ between them. The present results do not demonstrate any beneficial effects of parenterally administered L-carnitine on lipid, energy or nitrogen metabolism except for maintaining normal muscle glycogen levels in critically ill patients receiving TPN during the early phase after trauma.

Parenteral nutrition in the critically ill: use of a medium chain triglyceride emulsion

OBJECTIVES

The study investigated the use of an intravenous lipid emulsion containing medium chain triglycerides (MCTs) in critically ill patients, and compared the effects with those of a conventional long chain triglyceride (LCT) preparation.

DESIGN

Patients received a parenteral nutrition regime including either 500 ml 20% Lipofundin MCT/LCT (1/1) per day, or 500 ml 20% Lipofundin S (LCT) infused over 8 h each evening.

SETTING

The patients were receiving treatment, including assisted ventilation, in the Intensive Care Unit of a large teaching hospital. All patients on this unit for at least 3 days and who were likely to receive parenteral nutrition for at least a week were considered, unless they had severe renal or liver disease, or trauma/major surgery in the previous 3 days. Because ICU patients are a heterogenous group, subjects were randomised within clinical groups to receive either lipid. There were 24 patients entered into the study and the data on 20 matched patients is reported.

MEASUREMENTS AND RESULTS

Blood specimens were collected pre-TPN, daily at 0800 and after 5 h lipid infusion on days 1 and 6. Urine collections (24 h) were also performed. There were no apparent adverse effects due to the new MCT/LCT emulsion. Plasma ketone and glycerol concentrations were higher during MCT/LCT infusion, but 8 h post infusion plasma levels of ketones, triglycerides, non-esterified fatty acids and glucose were similar. Urinary carnitine excretion was high in all patients and was not significantly different between the groups. Nitrogen balance was less negative in patients receiving MCT/LCT on days 6 and 9.

CONCLUSION

MCTs are rapidly hydrolysed and oxidised to fatty acids and ketones which can be readily utilised. This study indicates that intravenous lipid emulsion containing MCT are safe in critically ill patients and may have advantages over LCT. The number and range of patients studied was, however, small and larger studies are needed.

Prevalence of carnitine depletion in critically ill patients with undernutrition

The aim of this study was to evaluate to what extent secondary carnitine deficiency may exist based on the prevalence of subnormal carnitine status in patients with critical illness and abnormal nutritional state. Healthy control patients (n = 12) were investigated and compared with patients with possible secondary carnitine deficiency, ie, patients with overt severe protein-energy malnutrition (PEM, n = 28), postoperative long-term (greater than 14 days) parenteral glucose feeding (250 g glucose/d, n = 7), severe liver disease (n = 10), renal insufficiency (n = 7), and sustained septicemia with increased metabolic rate (n = 8). Nutritional status, energy expenditure, creatinine excretion, and blood biochemical tests were measured in relationship to free and total carnitine concentrations in plasma and skeletal muscle tissue, as well as urinary excretion of free and total carnitine. The overall mortality rate was 48% within 30 days of the investigation in study patients with the highest mortality in liver disease (90%). The hospitalization range was 14 to 129 days in study patients. Most study patients had lost weight (4% to 19%) and had abnormal body composition. Patients with liver disease, septicemia, renal insufficiency, and those on long-term glucose feeding had significantly higher than predicted metabolic rate (+25% +/- 3%), while patients with severe malnutrition had decreased metabolic rate compared with controls. Patients with liver disease had increased plasma concentrations of free (96 +/- 16 mumol/L) and total (144 +/- 27 mumol/L) carnitine compared with controls (45 +/- 3, 58 +/- 7 mumol/L, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Serum carnitine levels in bone marrow transplant recipients

This study investigated plasma carnitine levels in patients undergoing allogenic bone marrow transplantation. The patients received fat-based TPN (50% fat, 50% CHO; calorie: nitrogen ratio 125:1) for an average of 33 +/- 7.5 days. TPN was started before transplantation and stopped when patients were able to eat. Caloric needs were estimated using the Harris-Benedict equation; 150% of the estimated BEE was given for the first two weeks after transplantation. The amount of TPN was gradually decreased as patients resumed their oral intake. All patients had low-normal serum carnitine levels before transplantation. There was no significant change in total or free serum carnitine levels during the course of TPN. However, in patients who had symptoms of graft vs. host reaction (GVH), the highest carnitine values during GVH (total 72.3 +/- 6.5 and free 61.2 +/- 12.4 mumol/l) were significantly higher (p < 0.001) than the baseline values (total 27.1 +/- 9.3 and free 24.9 +/- 9.6 mumol/l) or the highest non GVH values after transplantation (total 32.0 +/- 10.7 and free 29.0 +/- 10.7 mumol/l, respectively). The serum triglyceride, total cholesterol, and HDL cholesterol remained within normal range. In conclusion, bone marrow transplant patients receiving fat-based TPN have normal circulating levels of carnitine. GVH reaction caused an increase in the carnitine levels, which was probably due to increased tissue catabolism.

The effect of carnitine supplementation on carnitine balance in patients with persistent post-operative infection

The effect of L-carnitine (C) supplementation on body C balance, muscle C concentration, the leg exchange of C and some amino-acids was investigated in 8 patients with persistent post-operative infection. Before supplementation, total C concentration was 81 +/- 13 micromol/l plasma (SEM) and 15.4 +/- 1.5 micromol/g dry weight muscle, urinary excretion was 19 +/- 4 micromol/kg x 24 h and the arterial-femoral venous concentration difference over the leg (A-FV) of free C was -2.90 +/- 0.97 micromol/l, p < 0.05. Plasma-free C concentration correlated inversely with the A-FV of free C. The excretion of free C in urine was directly related to the plasma-free C concentration. A total C dose of 110 mg/kg during 4 days resulted in a 30% retention (range 12-48), a doubling of plasma C levels but no measurable alteration in either muscle C content or the arterial concentration and exchange of amino-acids over the leg. Plasma-free C concentration correlated inversely with the clearance of creatinine. In patients with persistent post-operative infection, muscle C concentration was normal and C was released from muscle as a consequence of muscle catabolism. The rate of C release was a major determinant of the plasma C concentration. At normal or low plasma C levels, the renal tubular reabsorption of C was a major determinant of body C balance. At elevated plasma concentrations of C, such as during C supplementation, the tubular capacity for reabsorption is exceeded and body carnitine balance is mainly dependent on the glomerular filtration.

Improved selenium, carnitine and taurine status in an enterally fed population

Ten adult, male, nonambulant and gastrostomy-fed individuals had received commercially available enteral feedings containing negligible amounts of selenium, carnitine, and taurine for an average of 59 months. Blood levels of these three nutrients were below published normal ranges as were the urinary excretions of carnitine and taurine. After 9 weeks on a product that was fortified with 23 micrograms of selenium, 39 mg of carnitine, and 38 mg of taurine per 8 ounces, blood levels were significantly increased with the levels of selenium and carnitine being normalized.

Effect of carnitine supplemented TPN on turnover and muscle utilisation of free fatty acids in patients with persistent post-operative infection

The effect of L-carnitine on FFA turnover and regional utilisation over the leg was investigated using infusion of 14C-oleic acid and measurement of the respiratory quotient (RQ) in eight artificially ventilated patients with severe post-operative infection and at least 2 weeks of carnitine free TPN. Carnitine or placebo was added to the daily infusion of lipid during two consecutive 4-day periods in a randomised cross-over fashion. The total dose of carnitine was 110 mg/kg over 4 days. Before carnitine supplementation, total plasma carnitine levels ranged between 39 and 152 micromol/l. The RQ was 0.87 +/- 0.02 (SEM). The turnover (185 +/- 64 micromol/min) and fractional turnover (0.39 +/- 0.04/min) of oleic acid as well as the uptake (31 +/- 10 micromol/min) and fractional uptake (0.46 +/- 0.05) over the leg were similar to previously reported values in healthy subjects. Carnitine supplementation, despite a doubling of the average plasma carnitine level, did not influence the RQ or the whole body turnover and regional exchange of oleic acid. The present results suggest that four days of carnitine supplementation in patients with persistent post-operative infection has no measurable effect on FFA utilisation, indicating that the patients' carnitine reserves were sufficient to maintain normal FFA utilisation.

Comparison of medium and long chain triglyceride metabolism in intensive care patients on parenteral nutrition

The metabolic effects of an intravenous lipid emulsion containing medium chain triglycerides (MCTs) were studied in eleven critically ill, ventilated patients receiving parenteral nutrition. The effects were compared in a cross-over study with those of a conventional emulsion containing only long chain triglycerides (LCTs). The lipid was well tolerated, but there were differences in the metabolic effects with a significantly greater increase in the plasma concentrations of glycerol and ketones during MCT/LCT infusion compared to LCT. The plasma concentration of non esterified fatty acids was also higher. This fell rapidly post infusion. Since non esterified fatty acids and ketones are readily available energy sources for tissues lipid emulsions containing MCT may prove valuable for catabolic, critically ill patients.

Alterations of serum and urinary carnitine profiles in cancer patients: hypothesis of possible significance

The present study examined the serum and urinary carnitine concentrations of 21 cancer patients with metastatic disease and 13 healthy age-matched controls by taking three consecutive samples during an 8-week period. The serum concentrations of all fractions of carnitine were significantly lower in the female cancer patients than in the female controls. The concentrations of urinary carnitine fractions were relatively higher in the total cancer population; however, only acid-insoluble acylcarnitine (AIAC) was statistically significant. The renal clearance of acid-soluble acylcarnitine (ASAC) and AIAC was significantly greater in cancer subjects than in controls. Significant inverse relationships were established between the ASAC and AIAC clearances and their respective serum concentrations. The renal tubular reabsorption of AIAC was significantly less in cancer patients than in control subjects as indicated by the fractional excretion of carnitine. The increased clearance of acylcarnitine and excretion of large amounts of AIAC are proposed to be a response to chemotherapy and represent a loss of energy to the cancer patient.

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.

[Effect of L-carnitine supplemented total parenteral nutrition on postoperative lipid and nitrogen utilization]

During episodes of trauma carnitine-free total parenteral nutrition (TPN) may result in a reduction of the total body carnitine pool, leading to a diminished rate of fat oxidation. Sixteen patients undergoing esophagectomy were equally and randomly divided and received isonitrogenous (0.2 gN/kg.day) and isocaloric (35 kcal/kg.day TPN over 11 days without and with L-carnitine supplementation (12 mg/kg.day). Compared with healthy controls, the total body carnitine pool was significantly reduced in both groups prior to the operation. Without supplementation carnitine concentrations were maintained, while daily provision of carnitine resulted in an elevation of total carnitine mainly due to an increase of the free fraction. Without supplementation the cumulative urinary carnitine losses were 11.5 +/- 6.3 mmol corresponding to 15.5% +/- 8.5% of the estimated total body carnitine pool. Patients receiving carnitine revealed a positive carnitine balance in the immediate postoperative phase, 11.1% +/- 19.0% of the infused carnitine being retained. After 11 days of treatment comparable values for respiratory quotient, plasma triglycerides, free fatty acids, ketone bodies, and cumulative nitrogen balance were observed. It is concluded that in the patient population studied here carnitine supplementation during postoperative TPN did not improve fat oxidation or nitrogen balance.

Carnitine excretion: a catabolic index of injury

In patients with trauma or sepsis, carnitine is known to be produced to a greater extent; deficient production could impair the energy management that is required in such patients. To clarify the requirements of carnitine after injury, we studied carnitine elimination (in 10 critically ill injured patients) both during fasting and early parenteral nutrition. Increased carnitine (mainly, free) output after injury (9.36 +/- 1.63 mumol/kg p less than 0.02 vs reference) was negatively related to nitrogen balance (p less than 0.05) and positively to 3-methyl-histidine output (p less than 0.01), acting as a market of body mass catabolism. The output of both total and free carnitine progressively decreased (p less than 0.01) throughout the course of total parenteral nutrition. In conclusion, our data definitively suggest that carnitine loss after injury reflects body cell mass wastage and does not necessarily mean an increased need.

Effects of L-carnitine infusion on intralipid clearance and utilization. Study carried out in septic patients of an intensive care unit

Endogenous and exogenous supplies of carnitine are decreased in septic patients under total parenteral nutrition, while carnitine urinary elimination is increased. But the increase of lipid role in the energetic cover requires a greater intervening role of tissue carnitine. So one may hope that in septic patients additional supply of L-carnitine would increase the catabolism of infused lipids. Twenty-eight septic patients, admitted in an intensive care unit were given parenteral nutrition (200 g of glucose, 12.5 g of N/24 hr). On the day of the study, 250 ml of Intralipid 20% (Kabi Vitrum) were administered in 4 hr. During the same period 13 patients were infused with 2 g of L-carnitine (Sigma-Tau). The remaining 15 patients constituted the control group. Basic plasma levels of triglycerides, nonesterified fatty acids, free glycerol, phospholipids, and ketone bodies remained within physiological limits. They increased during the lipid infusion and returned to initial values, 4 hr after the end of the infusion. Free and total carnitine levels and free/total carnitine ratio were comparable to healthy subjects' reference values. These parameters increased during L-carnitine infusion. This infusion had no effect on exogenous lipid clearance. However, it seemed to increase the uptake and the hepatic oxidation of circulating fatty acids. It invalidated the increase of lactate and pyruvate that had been noticed when lipids were solely infused.

Carnitine levels in skeletal muscle of malnourished patients before and after total parenteral nutrition

Carnitine is necessary for the transport of long-chain fatty acids across the mitochondrial membrane. Carnitine is derived from the diet and from endogenous synthesis from lysine and methionine. About 98% of the body's carnitine pool is located in skeletal muscle tissue. Skeletal muscle carnitine levels were determined in two groups of malnourished patients, eight patients with anorexia nervosa with a weight loss of 32.4% +/- 1.8 (mean +/- SEM) and six surgical patients with major gastrointestinal disorders and a weight loss of 15.2% +/- 2.7. Their hepatic and kidney functions were normal. On admission, the muscle carnitine levels were 16.9 +/- 4.0 mumol/g dry weight (mean +/- SD) for the surgical patients and 20.8 +/- 5.0 mumol/g dry weight for the anorexia nervosa patients, which corresponded to carnitine levels seen in healthy subjects. No statistical significance was found between the two groups. Total parenteral nutrition was given to the surgical patients for 2 weeks and to the anorexia nervosa patients for 3-5 weeks. No statistical difference in muscle carnitine levels was found in either group after nutritional support. These malnourished patients had no decreased muscle carnitine levels on admission and maintained them during several weeks of total parenteral nutrition.

Carnitine: an overview of its role in preventive medicine

Carnitine (beta-hydroxy-gamma-N-trimethylaminobutyric acid) is required for transport of long-chain fatty acids into the inner mitochondrial compartment for beta-oxidation. Widely distributed in foods from animal, but not plant, sources, carnitine is also synthesized endogenously from two essential amino acids, lysine and methionine. Human skeletal and cardiac muscles contain relatively high carnitine concentrations which they receive from the plasma, since they are incapable of carnitine biosynthesis themselves. Since the discovery of a primary genetic carnitine deficiency syndrome in 1973, carnitine has become the subject of extensive research. It is now recognized that carnitine deficiency may also occur secondary to genetic disorders of intermediary metabolism as well as to a variety of clinical disorders, including renal disease treated by hemodialysis, the renal Fanconi syndrome, cirrhosis, untreated diabetes mellitus, malnutrition, Reye's syndrome, and certain disorders of the endocrine, neuromuscular, and reproductive systems. Administration of the anticonvulsant valproic acid and total parenteral nutrition may also induce hypocarnitinemia. In many instances, the physiological implications of secondary carnitine deficiency have not been resolved. However, evidence for a specific carnitine requirement for the newborn, especially if preterm, is accumulating. Moreover, carnitine administration may have a favorable effect on some forms of hyperlipoproteinemia. Carnitine, now recognized as a conditionally essential nutrient, is a significant factor in preventive medicine.

Parenteral nourishment of patients undergoing surgical or traumatic stress

Severe surgical or other traumatic stress initiates an integrated central nervous system and metabolic response characterized by catabolism which selectively preserves vital organs, drawing on peripheral tissue proteins for required amino acids. When oral intake is prohibited adequate intravenous nutritional support hastens convalescence and may be life-saving. Intravenous nutrients routinely consist of amino acids for replacement of lost protein, a nonprotein calorie source--usually glucose, and vitamins and minerals. Lipid, infrequently used in routine surgery as part of the calorie source, supplies essential fatty acids and prevents side effects resulting with large amounts of intravenous glucose. Lipid has other benefits. Stress-induced hormones stimulate lipid catabolism. When lipid is used for part of the calorie requirement in intravenous feedings, the plasma insulin level is reduced and peripheral amino acids become available for synthesis of critically needed visceral proteins. Recent work has shown that the branched chain amino acids carnitine and some species of lipid added to intravenous nutrient formulations postoperatively affect the nitrogen retention and may hasten convalescence. Further work should be directed at understanding the unique biochemical changes occurring after injury, devising objective assay procedures to measure the severity of the response and improving intravenous formulations for the acutely ill surgical patient.

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.

Fat metabolism following an intravenous bolus dose of a fat emulsion and carnitine

Intravenous fat tolerance tests were performed with (carboxyl-14C)-triolein labelled Intralipid in four normal subjects with and without L-carnitine administration, 20 and 25 mg/kg body weight. The pharmacokinetics of L-carnitine was studied simultaneously with measurements of variables reflecting fat metabolism during 4 h. 3-OH-butyrate concentration in plasma was higher in all subjects when carnitine was given. No effect of carnitine was found in elimination of the exogenous triglycerides, the 14CO2 activity in expired air, concentration and specific radioactivity of non- esterified fatty acids or glucose in plasma. The data suggest that carnitine may slightly increase fatty acid oxidation in normal subjects provided that increase of 3-OH-butyrate concentration in plasma is the most sensitive variable reflecting fatty acid oxidation of the variables applied in this study.

Muscle and plasma carnitine levels and urinary carnitine excretion in multiply injured patients on total parenteral nutrition

Carnitine is necessary for the transport of long-chain fatty acids across the mitochondrial membrane. Thirteen severely injured patients on total parenteral nutrition were studied during days 2-8 post injury. Initially plasma and skeletal muscle carnitine values were within the range earlier found for normal subjects, whereas the urinary carnitine excretion was markedly increased. On day 4 there was a simultaneous decrease in the carnitine concentration in plasma (alpha < 0.01) and urine (alpha < 0.05) as well as in skeletal muscle tissue (alpha < 0.05 using only the values that could be paired i.e. from eight subjects), whereas no difference was found between day 2 and 8. One explanation of this pattern might be that a redistribution of carnitine occurs to other organs not measured, for example the liver. In skeletal muscle tissue, statistically significant positive correlations were found between the carnitine level and ATP (alpha < 0.01) and phosphocreatine (alpha < 0.02) as well as between carnitine and glycogen (alpha < 0.05).