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Carnitine (β-hydroxy-γ-N-trimethylaminobutyric acid, 3-hydroxy-4-N,N,N- trimethylaminobutyrate) is a quaternary ammonium compound[1] involved in metabolism in most mammals, plants and some bacteria.[2] Carnitine may exist in two isomers, labeled D-carnitine and L-carnitine, as they are optically active. At room temperature, pure carnitine is a white powder, and a water-soluble zwitterion with low toxicity. Carnitine only exists in animals as the L-enantiomer, and D-carnitine is toxic because it inhibits the activity of L-carnitine.[3] Carnitine was discovered in 1905 as a result of its high concentration in muscle tissue. It was originally labeled vitamin BT; however, because carnitine is synthesized in the human body, it is no longer considered a vitamin.[2] Carnitine is involved in the oxidation of fatty acids, and involved in systemic primary carnitine deficiency. It has been studied for preventing and treating other conditions, and is used as a purported performance enhancing drug.[1]

Carnitine
Carnitine.svg
Carnitine-3D-structure.png
Clinical data
AHFS/Drugs.com Micromedex Detailed Consumer Information
Pregnancy
category
  • US: B (No risk in non-human studies)
Routes of
administration
Oral, intravenous
ATC code
Legal status
Legal status
Pharmacokinetic data
Bioavailability <10%
Protein binding None
Metabolism slightly
Excretion Urine (>95%)
Identifiers
CAS Number
PubChem CID
DrugBank
ChemSpider
UNII
KEGG
ChEBI
ChEMBL
Chemical and physical data
Formula C7H15NO3
Molar mass 161.199 g/mol
3D model (Jmol)
 NYesY (what is this?)  (verify)

Contents

Biosynthesis and metabolismEdit

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, requiring the presence of ascorbic acid. HTML is then cleaved by HTML aldose, 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 into L-carnitine, requiring iron in the form of Fe2+.[4]

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.[5] Carnitine also plays a role in stabilizing Acetyl-CoA and coenzyme A levels through the ability to receive or give an acetyl group.[6]

Physiological effectsEdit

DeficiencyEdit

Carnitine deficiency caused by a genetic defect in carnitine transport occurs in roughly 1 in 50,000 in the US. Systemic primary carnitine deficiency (SPDC) is characterized by various cardiological, metabolic and musculoskeletal symptoms that vary widely in age of onset and presentation. Prognosis is generally good with carnitine supplementation.[7]

Secondary carnitine deficiency may occur due to conditions such as malnutrition, poor absorption or access to only vegetables.[5]

SupplementationEdit

Some research has been carried out on carnitine supplementation in athletes, given its role in fatty acid metabolism; however, individual responses varied significantly in the 300 people involved in one study.[vague][6] Carnitine has been studied in various cardiometabolic conditions, with a bit of evidence pointing towards efficacy as an adjunct in heart disease and diabetes. However, there are insufficient trials to determine its efficacy.[8] Carnitine has no effect on preventing mortality associated with cardiovascular conditions.[9] Carnitine has no effect on serum lipids, except a possible lowering of LDL[10] Carnitine has no effect on most parameters in end stage kidney disease, however it possibly has an effect on c-reactive protein. The effects on mortality and disease outcome are unknown.[11]

AtherosclerosisEdit

An important interaction between diet and the intestinal microbiome brings into play additional metabolic factors that aggravate atherosclerosis beyond dietary cholesterol. This may help to explain some benefits of the Mediterranean diet. Hazen’s group from the Cleveland Clinic reported that carnitine[12] from animal flesh (four times as much in red meat as in fish or chicken), as well as phosphatidylcholine from egg yolk, are converted by intestinal bacteria to trimethylamine (the compound that causes uremic breath to smell fishy). Trimethylamine is oxidized in the liver to trimethylamine N-oxide (TMAO), which causes atherosclerosis in animal models. Patients in the top quartile of TMAO had a 2.5-fold increase in the 3-year risk of stroke, death, or myocardial infarction.

A key issue is that vegans who consumed L-carnitine did not produce TMAO because they did not have the intestinal bacteria that produce TMA from carnitine.[13]

SourcesEdit

FoodEdit

The highest concentrations of carnitine are found in red meat.[14][15] It can be found at significantly lower levels in many other foods including nuts and seeds (e.g. pumpkin, sunflower, sesame), legumes or pulses (beans, peas, lentils, peanuts), vegetables (artichokes, asparagus, beet greens (young leaves of the beetroot), broccoli, brussels sprouts, collard greens, garlic, mustard greens, okra, parsley, kale), fruits (apricots, bananas), cereals (buckwheat, corn, millet, oatmeal, rice bran, rye, whole wheat, wheat bran, wheat germ) and other foods (bee pollen, brewer's yeast, carob).[citation needed]

Product Quantity Carnitine
Lamb 100 g 190 mg
Beef steak 100 g 95 mg
Ground beef 100 g 94 mg
Pork 100 g 27.7 mg
Bacon 100 g 23.3 mg
Tempeh 100 g 19.5 mg
Cod 100 g  5.6 mg
Chicken breast 100 g  3.9 mg
American cheese 100 g  3.7 mg
Ice cream 100 mL  3.7 mg
Whole milk 100 mL  3.3 mg
Avocado one medium 2 mg[16]
Cottage cheese 100 g  1.1 mg
Whole-wheat bread 100 g  0.36 mg
Asparagus 100 g  0.195 mg
White bread 100 g  0.147 mg
Macaroni 100 g  0.126 mg
Peanut butter 100 g  0.083 mg
Rice (cooked) 100 g  0.0449 mg
Egg 100 g  0.0121 mg
Orange juice 100 mL  0.0019 mg
Lentil 100 g 2.1 mg[17]
Potato 100 g 2.4 mg[17]
Sweet Potato 100 g 1.1 mg[17]
Banana 100 g 0.2 mg[17]
Carrot 100 g 0.3 mg[17]
Apple (without skin) 100 g 0.2 mg[17]
Raisin 100 g 0.8 mg[17]

In general, 20 to 200 mg are ingested per day by those on an omnivorous diet, whereas those on a strict vegetarian or vegan diet may ingest as little as 1 mg/day.[citation needed] However, even strict vegetarians (vegans) show no signs of carnitine deficiency, despite the fact that most dietary carnitine is derived from animal sources.[14][15] No advantage appears to exist in giving an oral dose greater than 2 g at one time, since absorption studies indicate saturation at this dose.[18]

Health CanadaEdit

Other sources may be found in over-the-counter vitamins, energy drinks and various other products. Products containing L-carnitine can now be marketed as "natural health products" in Canada. As of 2012, Parliament has allowed carnitine products and supplements to be imported into Canada (Health Canada). The Canadian government did issue an amendment in December 2011 allowing the sale of L-carnitine without a prescription.[19]

HistoryEdit

Levocarnitine was approved by the U.S. Food and Drug Administration as a new molecular entity under the brand name Carnitor on December 27, 1985.[20]

See alsoEdit

ReferencesEdit

  1. ^ a b Karlic, Heidrun; Lohninger, Alfred (1 July 2004). "Supplementation of l-carnitine in athletes: does it make sense?". Nutrition. 20 (7-8): 709–715. doi:10.1016/j.nut.2004.04.003. ISSN 0899-9007. 
  2. ^ a b Bremer, J. (1 October 1983). "Carnitine--metabolism and functions". Physiological Reviews. 63 (4): 1420–1480. ISSN 0031-9333. PMID 6361812. 
  3. ^ Harmeyer, J. "The Phystiological Role of L-Carntine" (PDF). Lohmann Information. 
  4. ^ Strijbis, Karin; Vaz, Frédéric M.; Distel, Ben (1 May 2010). "Enzymology of the carnitine biosynthesis pathway". IUBMB Life. 62 (5): 357–362. doi:10.1002/iub.323. ISSN 1521-6551. 
  5. ^ a b Flanagan, Judith L; Simmons, Peter A; Vehige, Joseph; Willcox, Mark DP; Garrett, Qian (16 April 2010). "Role of carnitine in disease". Nutrition & Metabolism. 7: 30. doi:10.1186/1743-7075-7-30. ISSN 1743-7075. PMC 2861661 . 
  6. ^ a b Cite error: The named reference sport was invoked but never defined (see the help page).
  7. ^ Magoulas, Pilar L.; El-Hattab, Ayman W. (1 January 2012). "Systemic primary carnitine deficiency: an overview of clinical manifestations, diagnosis, and management". Orphanet Journal of Rare Diseases. 7: 68. doi:10.1186/1750-1172-7-68. ISSN 1750-1172. 
  8. ^ Mingorance, Carmen; Rodríguez-Rodríguez, Rosalía; Justo, María Luisa; Álvarez de Sotomayor, María; Herrera, María Dolores (1 January 2011). "Critical update for the clinical use of L-carnitine analogs in cardiometabolic disorders". Vascular Health and Risk Management. 7: 169–176. doi:10.2147/VHRM.S14356. ISSN 1176-6344. PMC 3072740 . 
  9. ^ Shang, Ruiping; Sun, Zhiqi; Li, Hui (21 July 2014). "Effective dosing of L-carnitine in the secondary prevention of cardiovascular disease: a systematic review and meta-analysis". BMC cardiovascular disorders. 14: 88. doi:10.1186/1471-2261-14-88. ISSN 1471-2261. PMID 25044037. 
  10. ^ Huang, Haohai; Song, Lijun; Zhang, Hua; Zhang, Hanbin; Zhang, Jiping; Zhao, Wenchang (1 January 2013). "Influence of L-carnitine supplementation on serum lipid profile in hemodialysis patients: a systematic review and meta-analysis". Kidney & Blood Pressure Research. 38 (1): 31–41. doi:10.1159/000355751. ISSN 1423-0143. PMID 24525835. 
  11. ^ Chen, Yizhi; Abbate, Manuela; Tang, Li; Cai, Guangyan; Gong, Zhixiang; Wei, Ribao; Zhou, Jianhui; Chen, Xiangmei (1 February 2014). "L-Carnitine supplementation for adults with end-stage kidney disease requiring maintenance hemodialysis: a systematic review and meta-analysis". The American Journal of Clinical Nutrition. 99 (2): 408–422. doi:10.3945/ajcn.113.062802. ISSN 1938-3207. PMID 24368434. 
  12. ^ Koeth, RA; Wang, Z; Levison, BS; et al. (2013). "Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis". Nat Med. 19 (5): 576–85. 
  13. ^ Spence, J. David (Last updated: 28 JUL 2016). "REVIEW, Recent advances in pathogenesis, assessment, and treatment of atherosclerosis [version 1; referees: 3 approved]" (PDF). F1000Research 2016. 5(F1000 Faculty Rev):1880. ISSN 1938-3207.  Check date values in: |date= (help)
  14. ^ a b "L-Carnitine – Linus Pauling Institute – Oregon State University". 
  15. ^ a b Lombard, K. A.; Olson, A. L.; Nelson, S. E.; Rebouche, C. J. (1989-08-01). "Carnitine status of lactoovovegetarians and strict vegetarian adults and children". The American Journal of Clinical Nutrition. 50 (2): 301–306. ISSN 0002-9165. PMID 2756917. 
  16. ^ Rebouche CJ. Carnitine. In: Shils ME, Olson JA, Shike M, Ross AC, eds. Modern Nutrition in Health and Disease. 9th ed. Philadelphia: Lippincott, Williams & Wilkins; 1999:505-512. Cited by Jane Higdon (2002), see Oregon State U, accessed 12 January 2016
  17. ^ a b c d e f g Demarquoy, Jean; Georges, Béatrice; Rigault, Caroline; Royer, Marie-Charlotte; Clairet, Amélie; Soty, Maud; Lekounoungou, Serge; Le Borgne, Françoise (2004-06-01). "Radioisotopic determination of l-carnitine content in foods commonly eaten in Western countries". Food Chemistry. 86 (1): 137–142. doi:10.1016/j.foodchem.2003.09.023. 
  18. ^ Bain, Marcus A.; Milne, Robert W.; Evans, Allan M. (2006-10-01). "Disposition and metabolite kinetics of oral L-carnitine in humans". Journal of Clinical Pharmacology. 46 (10): 1163–1170. doi:10.1177/0091270006292851. ISSN 0091-2700. PMID 16988205. 
  19. ^ "Regulations Amending the Food and Drug Regulations". 
  20. ^ FDA approval letter

Further readingEdit

The following are good secondary sources on the subject of this article.

External linksEdit