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L-CARNITINE

L-Carnitine=Levocarnitine

CAS Number: 541-15-1
Molecular Formula: C7H15NO3
Molecular Weight: 161.20

L-Carnitine is a quaternary ammonium compound involved in metabolism in most mammals, plants, and some bacteria.
In support of energy metabolism, carnitine transports long-chain fatty acids into mitochondria to be oxidized for energy production, and also participates in removing products of metabolism from cells.
Given its key metabolic roles, carnitine is concentrated in tissues like skeletal and cardiac muscle that metabolize fatty acids as an energy source.
Healthy individuals, including strict vegetarians, synthesize enough L-carnitine in vivo to not require supplementation.
Carnitine exists as one of two stereoisomers (the two enantiomers d-carnitine (S-(+)-) and l-carnitine (R-(-)-)).
Both are biologically active, but only l-carnitine naturally occurs in animals, and d-carnitine is toxic as it inhibits the activity of the l-form.
At room temperature, pure carnitine is a white powder, and a water-soluble zwitterion with low toxicity. Derived from amino acids, carnitine was first extracted from meat extracts in 1905, leading to its name from Latin, "caro/carnis" or flesh.
Some individuals with genetic or medical disorders (such as preterm infants) cannot make enough carnitine, requiring dietary supplementation.
Despite common carnitine supplement consumption among athletes for improved exercise performance or recovery, there is insufficient high-quality clinical evidence to indicate it provides any benefit.

Many eukaryotes have the ability to synthesize carnitine, including humans.
Humans synthesize carnitine from the substrate TML (6-N-trimethyllysine), which is in turn derived from the methylation of the amino acid lysine.
TML is then hydroxylated into hydroxytrimethyllysine (HTML) by trimethyllysine dioxygenase (TMLD), requiring the presence of ascorbic acid and iron. HTML is then cleaved by HTML aldolase (a pyridoxal phosphate requiring enzyme), yielding 4-trimethylaminobutyraldehyde (TMABA) and glycine.
TMABA is then dehydrogenated into gamma-butyrobetaine in an NAD+-dependent reaction, catalyzed by TMABA dehydrogenase.
Gamma-butyrobetaine is then hydroxylated by gamma butyrobetaine hydroxylase (a zinc binding enzyme) into l-carnitine, requiring iron in the form of Fe2+.

Carnitine is involved in transporting fatty acids across the mitochondrial membrane, by forming a long chain acetylcarnitine ester and being transported by carnitine palmitoyltransferase I and carnitine palmitoyltransferase II.
Carnitine also plays a role in stabilizing Acetyl-CoA and coenzyme A levels through the ability to receive or give an acetyl group.

Tissue distribution of carnitine-biosynthetic enzymes
The tissue distribution of carnitine-biosynthetic enzymes in humans indicates TMLD to be active in the liver, heart, muscle, brain and highest in kidney.
HTMLA activity is found primarily in the liver. The rate of TMABA oxidation is greatest in the liver, with considerable activity also in the kidney.

Carnitine shuttle system
The free-floating fatty acids, released from adipose tissues to the blood, bind to carrier protein molecule known as serum albumin that carry the fatty acids to the cytoplasm of target cells such as the heart, skeletal muscle, and other tissue cells, where they are used for fuel.
But before the target cells can use the fatty acids for ATP production and β oxidation, the fatty acids with chain lengths of 14 or more carbons must be activated and subsequently transported into mitochondrial matrix of the cells in three enzymatic reactions of the carnitine shuttle.

The first reaction of the carnitine shuttle is a two-step process catalyzed by a family of isozymes of acyl-CoA synthetase that are found in the outer mitochondrial membrane, where they promote the activation of fatty acids by forming a thioester bond between the fatty acid carboxyl group and the thiol group of coenzyme A to yield a fatty acyl–CoA.

In the first step of the reaction, acyl-CoA synthetase catalyzes the transfer of adenosine monophosphate group (AMP) from an ATP molecule onto the fatty acid generating a fatty acyl–adenylate intermediate and a pyrophosphate group (PPi).
The pyrophosphate, formed from the hydrolysis of the two high-energy bonds in ATP, is immediately hydrolyzed to two molecule of Pi by inorganic pyrophosphatase.
This reaction is highly exergonic which drives the activation reaction forward and makes it more favorable. In the second step, the thiol group of a cytosolic coenzyme A attacks the acyl-adenylate, displacing AMP to form thioester fatty acyl-CoA.

In the second reaction, acyl-CoA is transiently attached to the hydroxyl group of carnitine to form fatty acyl–carnitine.
This transesterification is catalyzed by an enzyme found in the outer membrane of the mitochondria known as carnitine acyltransferase 1 (also called carnitine palmitoyltransferase 1, CPT1).

The fatty acyl–carnitine ester formed then diffuses across the intermembrane space and enters the matrix by facilitated diffusion through carnitine-acylcarnitine translocase (CACT) located on inner mitochondrial membrane.
This antiporter return one molecule of carnitine from the matrix to the intermembrane space for every one molecule of fatty acyl–carnitine that moves into the matrix.

In the third and final reaction of the carnitine shuttle, the fatty acyl group is transferred from fatty acyl-carnitine to coenzyme A, regenerating fatty acyl–CoA and a free carnitine molecule. This reaction takes place in the mitochondrial matrix and is catalyzed by carnitine acyltransferase 2 (also called carnitine palmitoyltransferase 2, CPT2), which is located on the inner face of the inner mitochondrial membrane. The carnitine molecule formed is then shuttled back into the intermembrane space by the same cotransporter (CACT) while the fatty acyl-CoA enters β-oxidation.

Regulation of fatty acid β oxidation
The carnitine-mediated entry process is a rate-limiting factor for fatty acid oxidation and is an important point of regulation.

Inhibition
The liver starts actively making triglycerides from excess glucose when it is supplied with glucose that cannot be oxidized or stored as glycogen.
This increases the concentration of malonyl-CoA, the first intermediate in fatty acid synthesis, leading to the inhibition of carnitine acyltransferase 1, thereby preventing fatty acid entry into the mitochondrial matrix for β oxidation. This inhibition prevents fatty acid breakdown while synthesis occurs.

Activation
Carnitine shuttle activation occurs due to a need for fatty acid oxidation which is required for energy production. During vigorous muscle contraction or during fasting, ATP concentration decreases and AMP concentration increases leading to the activation of AMP-activated protein kinase (AMPK).
AMPK phosphorylates acetyl-CoA carboxylase, which normally catalyzes malonyl-CoA synthesis.
This phosphorylation inhibits acetyl-CoA carboxylase, which in turn lowers the concentration of malonyl-CoA. Lower levels of malonyl-CoA disinhibits carnitine acyltransferase 1, allowing fatty acid import to the mitochondria, ultimately replenishing the supply of ATP.

Transcription factors
Peroxisome proliferator-activated receptor alpha (PPARα) is a nuclear receptor that functions as a transcription factor.
It acts in muscle, adipose tissue, and liver to turn on a set of genes essential for fatty acid oxidation, including the fatty acid transporters carnitine acyltransferases 1 and 2, the fatty acyl–CoA dehydrogenases for short, medium, long, and very long acyl chains, and related enzymes.

PPARα functions as a transcription factor in two cases; as mentioned before when there is an increased demand for energy from fat catabolism, such as during a fast between meals or long-term starvation.
Besides that, the transition from fetal to neonatal metabolism in the heart. In the fetus, fuel sources in heart muscle are glucose and lactate, but in the neonatal heart, fatty acids are the main fuel which require the PPARα to be activated so it is able in turn to activate the genes essential for fatty acid metabolism in this stage.

Metabolic defects of fatty acids oxidation
More than 20 human genetic defects in fatty acid transport or oxidation have been identified. In case of Fatty acid oxidation defects, acyl-carnitines accumulate in mitochondria and are transferred into the cytosol, and then into the blood. Plasma levels of acylcarnitine in newborn infants can be detected in a small blood sample by tandem mass spectrometry.

When β oxidation is defective because of either mutation or deficiency in carnitine, the ω (omega) oxidation of fatty acids becomes more important in mammals. Actually, the ω Oxidation of Fatty Acids is another pathway for F-A degradation in some species of vertebrates and mammals that occurs in the endoplasmic reticulum of liver and kidney, it is the oxidation of the ω carbon—the carbon most far from the carboxyl group (in contrast to {displaystyle beta }beta  oxidation which occurs at the carboxyl end of fatty acid, in the mitochondria).

Physiological effects
As an example of normal synthesis, a 70 kilograms (150 lb) person would produce 11–34 mg of carnitine per day.[1] Adults eating mixed diets of red meat and other animal products ingest some 60–180 mg of carnitine per day, while vegans consume about 10–12 mg per day.
Most (54–86%) carnitine obtained from the diet is absorbed in the small intestine before entering the blood.
The total body content of carnitine is about 20 grams (0.71 oz) in a person weighing 70 kilograms (150 lb), with nearly all of it contained within skeletal muscle cells.
Carnitine metabolizes at rates of about 400 μmol per day, an amount less than 1% of total body stores.

Deficiency
Further information: Systemic primary carnitine deficiency
Carnitine deficiency is rare in healthy people without metabolic disorders, indicating that most people have normal, adequate levels of carnitine normally produced through fatty acid metabolism.
One study found that vegans showed no signs of carnitine deficiency.
Infants, especially premature infants, have low stores of carnitine, necessitating use of carnitine-fortified infant formulas as a replacement for breast milk, if necessary.

Two types of carnitine deficiency states exist.
Primary carnitine deficiency is a genetic disorder of the cellular carnitine-transporter system that typically appears by the age of five with symptoms of cardiomyopathy, skeletal-muscle weakness, and hypoglycemia.
Secondary carnitine deficiencies may happen as the result of certain disorders, such as chronic kidney failure, or under conditions that reduce carnitine absorption or increase its excretion, such as use of antibiotics, malnutrition, and poor absorption following digestion.

Supplementation
Despite widespread interest among athletes to use carnitine for improvement of exercise performance, inhibit muscle cramps, or enhance recovery from physical training, the quality of research for these possible benefits has been low, prohibiting any conclusion of effect.
At supplement amounts of 2–6 grams (0.071–0.212 oz) per day over a month, there was no consistent evidence that carnitine affected exercise or physical performance.
Carnitine supplements do not improve oxygen consumption or metabolic functions when exercising, nor do they increase the amount of carnitine in muscle.
There is no evidence that L-carnitine influences fat metabolism or aids in weight loss.

Male infertility
The carnitine content of seminal fluid is directly related to sperm count and motility, suggesting that the compound might be of value in treating male infertility.

Diseases
Carnitine has been studied in various cardiometabolic conditions, indicating it is under preliminary research for its potential as an adjunct in heart disease and diabetes, among numerous other disorders.
Carnitine has no effect on preventing all-cause mortality associated with cardiovascular diseases, and has no significant effect on blood lipids.
Although there is some evidence from meta-analyses that L-carnitine supplementation improved cardiac function in people with heart failure, there is insufficient research to determine its overall efficacy in lowering the risk or treating cardiovascular diseases.
There is only preliminary clinical research to indicate the use of L-carnitine supplementation for improving symptoms of type 2 diabetes, such as improving glucose tolerance or lowering fasting levels of blood glucose.
The kidneys contribute to overall homeostasis in the body, including carnitine levels.
In the case of renal impairment, urinary elimination of carnitine increasing, endogenous synthesis decreasing, and poor nutrition as a result of disease-induced anorexia can result in carnitine deficiency.
Carnitine has no effect on most parameters in end-stage kidney disease, although it may lower C-reactive protein, a biomarker for systemic inflammation.
Carnitine blood levels and muscle stores can become low, which may contribute to anemia, muscle weakness, fatigue, altered levels of blood fats, and heart disorders.
Some studies have shown that supplementation of high doses of l-carnitine (often injected) may aid in anemia management.

Drug interactions and adverse effects
Carnitine interacts with pivalate-conjugated antibiotics such as pivampicillin. Chronic administration of these antibiotics increases the excretion of pivaloyl-carnitine, which can lead to carnitine depletion.
Treatment with the anticonvulsants valproic acid, phenobarbital, phenytoin, or carbamazepine significantly reduces blood levels of carnitine.
When taken in the amount of roughly 3 grams (0.11 oz) per day, carnitine may cause nausea, vomiting, abdominal cramps, diarrhea, and body odor smelling like fish.
Other possible adverse effects include skin rash, muscle weakness, or seizures in people with epilepsy.

XLogP3-AA: -0.2
Hydrogen Bond Donor Count: 1
Hydrogen Bond Acceptor Count: 3
Rotatable Bond Count: 3
Exact Mass: 161.10519334    
Monoisotopic Mass: 161.10519334
Topological Polar Surface Area: 60.4 Ų
Heavy Atom Count: 11
Formal Charge: 0
Complexity: 134
Isotope Atom Count: 0
Defined Atom Stereocenter Count: 1
Undefined Atom Stereocenter Count: 0
Defined Bond Stereocenter Count: 0
Undefined Bond Stereocenter Count: 0
Covalently-Bonded Unit Count: 1
Compound Is Canonicalized    : Yes
InChI: InChI=1S/C7H15NO3/c1-8(2,3)5-6(9)4-7(10)11/h6,9H,4-5H2,1-3H3/t6-/m1/s1
InChIKey: InChIKey=PHIQHXFUZVPYII-ZCFIWIBFSA-N
SMILES: C([N+](C)(C)C)[C@@H](CC([O-])=O)O
Canonical SMILES: O=C([O-])CC(O)C[N+](C)(C)C

Uses
This medication is a diet supplement used to prevent and treat low blood levels of carnitine. Carnitine is a substance made in the body from meat and dairy products.
It helps the body use certain chemicals (long-chain fatty acids) for energy and to keep you in good health.
Low blood levels of carnitine may occur in people whose bodies cannot properly use carnitine from their diets, people on dialysis due to serious kidney disease, and people being treated with certain drugs (e.g., valproic acid, zidovudine).
Carnitine levels that are too low can cause liver, heart, and muscle problems.Carnitine comes in 2 forms, this medication (levocarnitine) and D-carnitine. An over-the-counter product called vitamin Bt contains a mixture of levocarnitine and D-carnitine. Vitamin Bt should not be used to treat serious carnitine deficiency since it can interfere with the body's use of levocarnitine.
Do not use levocarnitine to treat serious carnitine deficiency unless prescribed by your doctor.The form of levocarnitine taken by mouth is not recommended for treating people on dialysis due to serious kidney disease.
The injectable form should be used for this treatment. Consult your doctor for details.Some supplement products have been found to contain possibly harmful impurities/additives. Check with your pharmacist for more details about the brand you use.
The FDA has not reviewed this product for safety or effectiveness. Consult your doctor or pharmacist for more details.

How to use L-CARNITINE
If you are taking the over-the-counter product, read all directions on the product package before taking this medication.
If you have any questions, consult your pharmacist. If your doctor has prescribed this medication, take it as directed.
This medication is best taken with or just after meals to lessen stomach upset.
If you are taking more than 1 dose a day, take the doses at evenly spaced times throughout the day (usually at least 3 to 4 hours apart).
If you are taking the liquid form, use a medication-measuring device to carefully measure the prescribed dose.
Do not use a household spoon.
The liquid form may be taken alone or mixed in a drink or other liquid food.To prevent stomach upset, drink your dose slowly or mix the liquid form with more fluids or liquid food.
Chewable forms of this medication should be chewed thoroughly before swallowing.
The dosage is based on your medical condition and response to therapy. Do not increase your dose or take this medication more often than recommended by your doctor or the package instructions without your doctor's approval.
Take this medication regularly in order to get the most benefit from it.
To help you remember, take it at the same time(s) each day.
If your condition persists or worsens, or if you think you may have a serious medical problem, seek immediate medical attention.

Summary
Our body produces L-carnitine from the essential amino acid lysine via a specific biosynthetic pathway. Healthy individuals, including strict vegetarians, generally synthesize enough L-carnitine to prevent deficiency.
However, certain conditions like pregnancy may result in increased excretion of L-carnitine, potentially increasing the risk for deficiency.
Because of its role in the transport of long-chain fatty acids from the cytosol to the mitochondrial matrix, L-carnitine is critical for mitochondrial fatty acid β-oxidation. (More information)
L-Carnitine supplementation is indicated for the treatment of primary systemic carnitine deficiency, which is caused by mutations in the gene that codes for the carnitine transporter, OCTN2.
L-Carnitine is also approved for the treatment of carnitine deficiencies secondary to inherited diseases, such as propionyl-CoA carboxylase deficiency and medium chain acyl-CoA dehydrogenase deficiency, and in patients with end-stage renal disease undergoing hemodialysis.
Evidence from randomized controlled trials suggests that L-carnitine or acylcarnitine esters may be useful adjuncts to standard medical treatment in individuals with cardiovascular disease.
Routine administration of L-carnitine to people with end-stage renal disease undergoing hemodialysis is not recommended unless it is to treat carnitine deficiency.
Acetyl-L-carnitine (ALCAR) may help reduce the severity of chemotherapy-induced peripheral neuropathy. High-quality evidence is needed to evaluate whether ALCAR may benefit the treatment of peripheral neuropathies associated with diabetes or caused by antiretroviral therapy.
There is some low-quality evidence to suggest that supplemental L-carnitine or ALCAR may be beneficial as adjuncts to standard medical therapy of depression, Alzheimer's disease, and hepatic encephalopathy. (More information)
There is little evidence that L-carnitine supplementation improves cancer-related fatigue, low fertility, or overall physical health. (More information)
If you choose to take L-carnitine supplements, the Linus Pauling Institute recommends acetyl-L-carnitine at a daily dose of 0.5 to 1 g. Note that supplemental L-carnitine (doses, 0.6-7.0 g) is less efficiently absorbed compared to smaller amounts in food. (More information)
Introduction
L-Carnitine (β-hydroxy-γ-N-trimethylaminobutyric acid) is a derivative of the amino acid, lysine (Figure 1). It was first isolated from meat (carnus in Latin) in 1905. Only the L-isomer of carnitine is biologically active.
L-Carnitine appeared to act as a vitamin in the mealworm (Tenebrio molitor) and was therefore termed vitamin BT (2). Vitamin BT, however, is a misnomer because humans and other higher organisms can synthesize L-carnitine (see Metabolism and Bioavailability).
Under certain conditions, the demand for L-carnitine may exceed an individual's capacity to synthesize it, making it a conditionally essential nutrient.

Metabolism and Bioavailability
In healthy people, carnitine homeostasis is maintained through endogenous biosynthesis of L-carnitine, absorption of carnitine from dietary sources, and reabsorption of carnitine by the kidneys.

Endogenous biosynthesis
Humans can synthesize L-carnitine from the amino acids lysine and methionine in a multi-step process occurring across several cell compartments (cytosol, lysosomes, and mitochondria). Across different organs, protein-bound lysine is methylated to form ε-N-trimethyllysine in a reaction catalyzed by specific lysine methyltransferases that use S-adenosyl-methionine (derived from methionine) as a methyl donor.
ε-N-Trimethyllysine is released for carnitine synthesis by protein hydrolysis.
Four enzymes are involved in endogenous L-carnitine biosynthesis.
They are all ubiquitous except γ-butyrobetaine hydroxylase is absent from cardiac and skeletal muscle.
This enzyme is, however, highly expressed in human liver, testes, and kidney.
L-carnitine is primarily synthesized in the liver and transported via the bloodstream to cardiac and skeletal muscle, which rely on L-carnitine for fatty acid oxidation yet cannot synthesize it.
The rate of L-carnitine biosynthesis in humans was studied in strict vegetarians (i.e., in people who consume very little dietary carnitine) and estimated to be 1.2 µmol/kg of body weight/day.
The rate of L-carnitine synthesis depends on the extent to which peptide-linked lysines are methylated and the rate of protein turnover.
There is some indirect evidence to suggest that excess lysine in the diet may increase endogenous L-carnitine synthesis; however, changes in dietary carnitine intake level or in renal reabsorption do not appear to affect the rate of endogenous L-carnitine synthesis.

Absorption of exogenous L-carnitine
Dietary L-carnitine
The bioavailability of L-carnitine from food can vary depending on dietary composition.
For instance, one study reported that bioavailability of L-carnitine in individuals adapted to low-carnitine diets (i.e., vegetarians) was higher (66%-86%) than in those adapted to high-carnitine diets (i.e., regular red meat eaters; 54%-72%).
The remainder is degraded by colonic bacteria.

L-carnitine supplements
While bioavailability of L-carnitine from the diet is quite high (see Dietary L-carnitine), absorption from oral L-carnitine supplements is considerably lower. The bioavailability of L-carnitine from oral supplements (doses, 0.6 to 7 g) ranges between 5% and 25% of the total dose (5). Less is known regarding the metabolism of the acetylated form of L-carnitine, acetyl-L-carnitine (ALCAR); however, the bioavailability of ALCAR is thought to be higher than that of L-carnitine. The results of in vitro experiments suggested that ALCAR might be partially hydrolyzed upon intestinal absorption.
In humans, administration of 2 g/day of ALCAR for 50 days increased plasma ALCAR concentrations by 43%, suggesting that either ALCAR was absorbed without prior hydrolysis or that L-carnitine was re-acetylated in the enterocytes (5).

Elimination and reabsorption
L-Carnitine and short-chain acylcarnitine derivatives (esters of L-carnitine; are excreted by the kidneys. Renal reabsorption of free L-carnitine is normally very efficient; in fact, an estimated 95% is thought to be reabsorbed by the kidneys.
Therefore, carnitine excretion by the kidney is usually very low.
However, several conditions can decrease the efficiency of carnitine reabsorption and, correspondingly, increase carnitine excretion.
Such conditions include high-fat, low-carbohydrate diets; high-protein diets; pregnancy; and certain disease states (see Primary systemic carnitine deficiency).
In addition, when circulating L-carnitine concentration increases, as in the case of oral supplementation, renal reabsorption of L-carnitine may become saturated, resulting in increased urinary excretion of L-carnitine.
Dietary or supplemental L-carnitine that is not absorbed by enterocytes is degraded by colonic bacteria to form two principal products, trimethylamine and γ-butyrobetaine. γ-Butyrobetaine is eliminated in the feces; trimethylamine is efficiently absorbed and metabolized to trimethylamine-N-oxide, which is excreted in the urine.

Biological Activities
Mitochondrial oxidation of long-chain fatty acids
L-Carnitine is synthesized primarily in the liver but also in the kidneys and then transported to other tissues.
It is most concentrated in tissues that use fatty acids as their primary fuel, such as skeletal and cardiac muscle.
In this regard, L-carnitine plays an important role in energy production by conjugating to fatty acids for transport from the cytosol into the mitochondria.

L-Carnitine is required for mitochondrial β-oxidation of long-chain fatty acids for energy production.
Long-chain fatty acids must be esterified to L-carnitine (acylcarnitine) in order to enter the mitochondrial matrix where β-oxidation occurs.
On the outer mitochondrial membrane, CPTI (carnitine-palmitoyl transferase I) catalyzes the transfer of medium/long-chain fatty acids esterified to coenzyme A (CoA) to L-carnitine.
This reaction is a rate-controlling step for the β-oxidation of fatty acid.
A transport protein called CACT (carnitine-acylcarnitine translocase) facilitates the transport of acylcarnitine across the inner mitochondrial membrane.
On the inner mitochondrial membrane, CPTII (carnitine-palmitoyl transferase II) catalyzes the transfer of fatty acids from L-carnitine to free CoA. Fatty acyl-CoA is then metabolized through β-oxidation in the mitochondrial matrix, ultimately yielding propionyl-CoA and acetyl-CoA.
Carnitine is eventually recycled back to the cytosol.

Description
L-Carnitine is a conditionally essential nutrient.
It is obtained from dietary sources or through the metabolism of lysine and methionine.
L-Carnitine facilitates the transport of long-chain fatty acids into the mitochondrial matrix for β-oxidation, has other diverse roles on metabolism, and is involved in the maintenance of coenzyme A stores.
Plasma and/or tissue levels of L-carnitine are decreased in primary L-carnitine deficiency, a disorder characterized by impaired fatty acid oxidation, with symptoms varying depending on whether it is systemic or muscle-specific.1 Serum and tissue levels of L-carnitine are also reduced in secondary L-carnitine deficiencies caused by a variety of hereditary defects or acquired disorders.

Used in sport and infant nutrition. Carnitine is a quaternary ammonium compound biosynthesized from the amino acids lysine and methionine. In living cells, it is required for the transport of fatty acids from the cytosol into the mitochondria during the breakdown of lipids (or fats) for the generation of metabolic energy. It is often sold as a nutritional supplement. Carnitine was originally found as a growth factor for mealworms and labeled vitamin Bt. Carnitine exists in two stereoisomers: its biologically active form is L-carnitine, while its enantiomer, D-carnitine, is biologically inactive.; Carnitine is not an essential amino acid; Levocarnitine is a carrier molecule in the transport of long chain fatty acids across the inner mitochondrial membrane. It also exports acyl groups from subcellular organelles and from cells to urine before they accumulate to toxic concentrations. Lack of carnitine can lead to liver, heart, and muscle problems. Carnitine deficiency is defined biochemically as abnormally low plasma concentrations of free carnitine, less than 20 µmol/L at one week post term and may be associated with low tissue and/or urine concentrations. Further, this condition may be associated with a plasma concentration ratio of acylcarnitine/levocarnitine greater than 0.4 or abnormally elevated concentrations of acylcarnitine in the urine. Only the L isomer of carnitine (sometimes called vitamin BT) affects lipid metabolism. The "vitamin BT" form actually contains D,L-carnitine, which competitively inhibits levocarnitine and can cause deficiency. Levocarnitine can be used therapeutically to stimulate gastric and pancreatic secretions and in the treatment of hyperlipoproteinemias.; There is a close correlation between changes in plasma levels of osteocalcin and osteoblast activity and a reduction in osteocalcin plasma levels is an indicator of reduced osteoblast activity, which appears to underlie osteoporosis in elderly subjects and in postmenopausal women. Administration of a carnitine mixture or propionyl-L-carnitine is capable of increasing serum osteocalcin concentrations of animals thus treated, whereas serum osteocalcin levels tend to decrease with age in control animals.; it can be synthesized in the body. However, it is so important in providing energy to muscles including the heart-that some researchers are now recommending carnitine supplements in the diet, particularly for people who do not consume much red meat, the main food source for carnitine. Carnitine has been described as a vitamin, an amino acid, or a metabimin, i.e., an essential metabolite. Like the B vitamins, carnitine contains nitrogen and is very soluble in water, and to some researchers carnitine is a vitamin (Liebovitz 1984). It was found that an animal (yellow mealworm) could not grow without carnitine in its diet. However, as it turned out, almost all other animals, including humans, do make their own carnitine; thus, it is no longer considered a vitamin. Nevertheless, in certain circumstances-such as deficiencies of methionine, lysine or vitamin C or kidney dialysis--carnitine shortages develop. Under these conditions, carnitine must be absorbed from food, and for this reason it is sometimes referred to as a "metabimin" or a conditionally essential metabolite. Like the other amino acids used or manufactured by the body, carnitine is an amine. But like choline, which is sometimes considered to be a B vitamin, carnitine is also an alcohol (specifically, a trimethylated carboxy-alcohol). Thus, carnitine is an unusual amino acid and has different functions than most other amino acids, which are most usually employed by the body in the construction of protein. Carnitine is an essential factor in fatty acid metabolism in mammals. It's most important known metabolic function is to transport fat into the mitochondria of muscle cells, including those in the heart, for oxidation. This is how the heart gets most of its energy. In humans, about 25% of carnitine is synthesized in the liver, kidney and brain from the amino acids lysine and methionine. Most of the carnitine in the body comes from dietary sources such as red meat and dairy products. Inborn errors of carnitine metabolism can lead to brain deterioration like that of Reye's syndrome, gradually worsening muscle weakness, Duchenne-like muscular dystrophy and extreme muscle weakness with fat accumulation in muscles. Borurn et al. (1979) describe carnitine as an essential nutrient for pre-term babies, certain types (non-ketotic) of hypoglycemics, kidney dialysis patients, cirrhosis, and in kwashiorkor, type IV hyperlipidemia, heart muscle disease (cardiomyopathy), and propionic or organic aciduria (acid urine resulting from genetic or other anomalies). In all these conditions and the inborn errors of carnitine metabolism, carnitine is essential to life and carnitine supplements are valuable. carnitine therapy may also be useful in a wide variety of clinical conditions.
Carnitine supplementation has improved some patients who have angina secondary to coronary artery disease. It may be worth a trial in any form of hyperlipidemia or muscle weakness.
Carnitine supplements may be useful in many forms of toxic or metabolic liver disease and in cases of heart muscle disease. Hearts undergoing severe arrhythmia quickly deplete their stores of carnitine.
Athletes, particularly in Europe, have used carnitine supplements for improved endurance.
Carnitine may improve muscle building by improving fat utilization and may even be useful in treating obesity. carnitine joins a long list of nutrients which may be of value in treating pregnant women, hypothyroid individuals, and male infertility due to low motility of sperm.
Even the Physician's Desk Reference gives indication for carnitine supplements as "improving the tolerance of ischemic heart disease, myocardial insufficiencies, and type IV hyperlipoproteinemia.
Carnitine deficiency is noted in abnormal liver function, renal dialysis patients, and severe to moderate muscular weakness with associated anorexia." (http://www.dcnutrition.com).
Carnitine is a biomarker for the consumption of meat. L-carnitine is found in pulses and common pea.

General description
Enzymatic UV-Test with a linearity in the range of 5.6 - 112 μM L-carnitine in the test solution.

Application
Determination of L-carnitine in seminal plasma, serum, or urine in life science research applications.

Biochem/physiol Actions
L-carnitine is an abundant amino acid present in red meat. Its trimethylamine structure has similarity to that of choline. The major source of this amino acid is by dietary ingestion. In mammals, it is also endogenously produced from lysine. It participates in the transport of fatty acids into the mitochondrial compartment. It produces trimethylamine-N-oxide (TMAO) and promotes atherosclerosis.

Principle
L-Carnitine is acetylated to acetyl carnitine by acetyl coenzyme A (acetyl CoA) in the presence of the enzyme carnitine acetyl transferase (CAT).
The resulting coenzyme A (CoA) is acetylated back to acetyl CoA in the presence of adenosine-5′-triphosphate (ATP) and acetate, catalyzed by the enzyme acetyl CoA synthetase (ACS).
This results in the formation of adenosine-5′-monophosphate (AMP) and inorganic pyrophosphate (PPi).
In the presence of ATP, supported by myokinase (MK), AMP forms twice the amount of adenosine-5′-diphosphate (ADP).
This is converted in the following reaction with phosphoenol pyruvate (PEP) in the presence of pyruvate kinase (PK).
The pyruvate formed is reduced to L-lactate by reduced nicotinamide adenine dinucleotide (NADH) in the presence of lactate dehydrogenase (LDH).
The amount of NADH consumed during the reaction is equivalent to half the amount of L-carnitine. NADH is measured spectroscopically at 340 nm.

A gravimetric method was used to determine the solubility of L-carnitine in different pure solvents and ethanol–acetone solvent mixture.
The solubility in different pure solvents were then correlated by the modified Apelblat equation, λh equation and the modified van’t Hoff equation, with the modified van’t Hoff equation presenting the best consistence.
Meanwhile, to illustrate the effect of ethanol or acetone on the change of the solubility, a new parameter defined as influence coefficient was introduced and the coefficient of acetone depending on temperature and molar faction of acetone was depicted.
In addition, the changes for enthalpy, entropy and Gibbs free energy were calculated by the modified van’t Hoff equation.
It can be drawn that the changes for enthalpy and entropy in a solvent mixture decrease to a minimum before consequent increasing with increasing molar faction of acetone.
Furthermore, the change for Gibbs free energy shows a linear relationship with natural logarithm of the solubility.

L-Carnitine (Levocarnitine) is an endogenous molecule involved in fatty acid metabolism, biosynthesized within the human body using amino acids: L-lysine and L-methionine, as substrates. L-Carnitine functions to transport long chain fatty acyl-CoAs into the mitochondria for degradation by β-oxidation. L-carnitine can ameliorate metabolic imbalances in many inborn errors of metabolism.

L-carnitine is a very small molecule that weighs 161.21 Da; and it is produced through the biosynthesis of the essential amino acids lysine and methionine.
L-carnitine is found in our muscle cells (mainly "skeletal muscle" and "myocardium"), and it is an essential substance for lipid metabolism (conversion of lipids to energy), which takes place in the mitochondria of cells.
However, lipids cannot cross the membranes of mitochondria alone.
When lipids enter the body, they are broken down into fatty acids, which are transported into mitochondria by the combination of “fatty acids” + “L-carnitine”.
Thus, lipids are converted into energy and used in the body. While sugar is responsible for instantaneous energy production, fatty acid is responsible for sustainable energy production and effectively operating the muscles and the heart.
In other words, L-carnitine is the component that transports fatty acid into mitochondria.

L-carnitine has indispensable functions in intermediary metabolism and is received by endogenous synthesis and from exogenous sources.
It plays an obligate role in fatty acid metabolism by directing fatty acids into the mitochondrial oxidative pathway through the action of specialised acyltransferases.
In poultry production, L-carnitine has a multi functional purpose, which includes: growth promotion, strengthening the immune system, antioxidant effects and improving semen quality. The concentration of L-carnitine in animals varies widely across species, tissue type, and nutritional status of the animal. It has been suggested that the L-carnitine requirement may be increased under certain circumstances such as via higher performance, various stress conditions and where the diet is deficient in animal protein sources. The review of L-carnitine functions uniquely includes the main aspects of this consequential feed supplementary inclusion in poultry nutrition.

L-carnitine
Levocarnitine
541-15-1
(R)-Carnitine
vitamin BT
Carnitor
(-)-Carnitine
(-)-L-Carnitine
Karnitin
L-(-)-Carnitine
Carnitene
bicarnesine
Levocarnitina
Metina
L-Carnitine inner salt
Levocarnitinum
Carniking
Carnilean
Carnitine, (-)-
L(-)-Carnitine
Levocarnitinum [Latin]
Levocarnitina [Spanish]
Carniking 50
(3R)-3-hydroxy-4-(trimethylammonio)butanoate
gamma-Trimethyl-beta-hydroxybutyrobetaine
gamma-Trimethyl-ammonium-beta-hydroxybutirate
1-CARNITINE
(3R)-3-hydroxy-4-(trimethylazaniumyl)butanoate
3-Carboxy-2-hydroxy-N,N,N-trimethyl-1-propanaminium hydroxide, inner salt
DRG-0211
UNII-0G389FZZ9M
(R)-(3-Carboxy-2-hydroxypropyl)trimethylammonium hydroxide
R-(-)-3-hydroxy-4-trimethylaminobutyrate
3-carboxy-2-hydroxy-N,N,N-trimethyl-1-propanaminium
L-gamma-trimethyl-beta-hydroxybutyrobetaine
1-Propanaminium, 3-carboxy-2-hydroxy-N,N,N-trimethyl-, inner salt, (R)-
(R)-3-hydroxy-4-(trimethylammonio)butanoate
(3-Carboxy-2-hydroxypropyl)trimethyl-ammonium hydroxide, inner salt
(L-3-Carboxy-2-hydroxypropyl)trimethylammonium hydroxide, inner salt
CHEMBL1149
Ammonium, (3-carboxy-2-hydroxypropyl)trimethyl-, hydroxide, inner salt, L-
Carnicor
1-Propanaminium, 3-carboxy-2-hydroxy-N,N,N-trimethyl-, hydroxide, inner salt, (R)-
0G389FZZ9M
(R)-3-Hydroxy-4-(trimethylammonio)butyrate
Carnitolo
Carnovis
Carrier
CHEBI:16347
Lefcar
(-)-(R)-3-Hydroxy-4-(trimethylammonio)butyrate
L-carnitine Base
1-Propanaminium, 3-carboxy-2-hydroxy-N,N,N-trimethyl-, hydroxide, inner salt
1-Propanaminium, 3-carboxy-2-hydroxy-N,N,N-trimethyl-, inner salt, (2R)-
44985-71-9
L(-)-Carnitine, 99+%
Levocarnitine [USAN:INN]
L Carnitine
MFCD00038747
vitamin B T
Carnitor (TN)
SMR000112475
carnitine (L-form)
gamma-Trimethyl-hydroxybutyrobetaine
(3R)-3-hydroxy-4-(trimethylamino)butanoic acid
3-hydroxy-4-trimethylammoniobutanoate
EINECS 208-768-0
Carnipass
delta-carnitine
Levocarnitine (JAN/USP/INN)
L-Carnitin
Malonyl-Carnitin
HSDB 7588
Carnipass 20
Carnitine, L-
L-Carnitine,(S)
Car-O
Levocarnitine [USAN:USP:INN:BAN]
PubChem5901
(R)-3-Hydroxy-4-trimethylammoniobutyrate
bmse000211
L-carnitine (Levocarnitine)
SCHEMBL21970
MLS001332549
MLS001332550
ARONIS24315
BIDD:GT0603
1-Propanaminium,3-carboxy-2-hydroxy-N,N,N-trimethyl-
GTPL4780
DTXSID4023208
HMS2093J13
HMS2267H24
Pharmakon1600-01505437
HY-B0399
(R)-(3-Carboxy-2-hydroxypropyl)trimethylammonium hydroxide, inner salt
ABP000696
Ammonium, (3-carboxy-2-hydroxypropyl)trimethyl-, hydroxide,inner salt
ANW-31960
BDBM50037268
c0049
CC0198
NSC741806
NSC759132
s2388
SBB058880
AKOS005267245
BCP9000830
CCG-213241
DB00583
KS-1422
NSC 759132
NSC-741806
NSC-759132
6-CHLORO-3-HYDROXY(1H)INDAZOLE
3-hydroxy-4-trimethylammoniobutanoic acid
AS-11974
gamma-L-trimethyl-beta-hydroxybutyrobetaine
L-Carnitin 100 microg/mL in Acetonitrile
L-Carnitine inner salt, synthetic, >=98%
N1935
ST50824805
C00318
D02176
(3R)-3-oxidanyl-4-(trimethylazaniumyl)butanoate
(R)-3-Hydroxy-4-(trimethylammonio)butanoic acid
AB00919083_05
AB00919083_06
(R)-(-)-3-Hydroxy-4-(trimethylammonio)butyrate
A829968
(3R)-(-)-3-Hydroxy-4-(trimethylammonio)butanoate
Q20735709
(3R)-(-)-3-Hydroxy-4-(trimethylammonio)butanoate 99+%
L-carnitine(Levocarnitine)/Carnitor, vitamin BT, Karnitin
UNII-S7UI8SM58A component PHIQHXFUZVPYII-ZCFIWIBFSA-N
Levocarnitine, European Pharmacopoeia (EP) Reference Standard
Levocarnitine, United States Pharmacopeia (USP) Reference Standard
1-Propanaminium, 3-carboxy-2-hydroxy-N,N,N-trimethyl-, inner salt, (2R)- (9CI)
Ammonium, (3-carboxy-2-hydroxypropyl)trimethyl-, hydroxide, inner salt, L- (8CI)

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