Carnitine

What is Carnitine?

Carnitine is a conditionally essential metabolite that transports fatty acids into the mitochondria to be used in fatty acid metabolism. Fatty acids that are ingested from lipids, form a complex with coenzyme A that is called an acyl-CoA.  Carnitine transports fatty acids into the mitochondria by accepting acyl groups from acyl-CoA.  This process is catalyzed by an enzyme called carnitine palmitoyltransferase I (CPT1). This yields the final mololecule called an acylcarnitine and free coenzyme A.  The hydroxyl group in L-carnitine (free carnitine) is esterified this way in order to transport fatty acyl groups of any size into the inner mitochondrial matrix. Carnitine is found in all mammalian cells in either the free or acylated form and can also be obtained through the diet from meat and dairy sources (Jones 2010).

Each carboxylic acid reacts with carnitine to form a specific acylcarnitine species. Nomenclature for acylcarnitines is based on the molecule to which L-carnitine has bonded. For example, acetic acid can react with coenzyme A to form acetyl-CoA, which in turn reacts with L-carnitine to form the ester acetylcarnitine. Other examples of acylcarnitines include palmitoylcarnitine, from palmitic acid, linoleoylcarnitine, from linoleic acid and arachidonoylcarnitine, from arachidonic acid.

What Does This Mean?

Changes in metabolites may be a response to altered biochemical pathways due to disease (Jones 2010). We believe that a change in our patients’ acylcarnitine profiles is a useful indicator of changes in their metabolic states. Monitoring these changes in our patients could be an opportunity to advance understanding of the mechanism of their diseases, finding new biomarkers, or new therapies.

The formation of acylcarnitines is important not only in the metabolism of fatty acids but is also an important pathway in the mechanism of the ketogenesis.  Carnitine could also be involved in a host of other pathways by consequence of its free hydroxyl group.  It has been suggested that L-carnitine can complex with various other metabolites and carboxylic acids of varying lengths to transport them throughout the body for a variety of functions (Jones 2010).

Our Focus

In some research circles it is believed that changes in the concentration of carnitine can be used to identify changes in metabolism.  Ketosis under the ketogenic diet gradually changes the main source of energy for the body to lipids, and may subsequently lead to a more prominent role for carnitine in the body.  By monitoring the levels of carnitine and related metabolites on a regular basis the mechanism by which the ketogenic diet works can be better elucidated.  Changes in carnitine have already been connected to several disease states such as celiac disease, ulcerative colitis, and diabetes (Jones 2010).

The metabolomic assay is an analytical technique used by our team to isolate carnitine species and other metabolites present in various compartments throughout the body (i.e. RBCs, plasma, and organ tissues). The first step of the assay is to release carnitine and other metabolites from the cellular components of the sample. For example, a sample of red blood cells must be first hemolyzed through addition of water and then frozen. This process will lyse cellular membranes and in doing so will release the metabolites that are present within the erythrocytes. Next, the cellular constituents and large proteins are precipitated using an acetonitrile/methanol solvent. Subsequent centrifugation isolates the cellular proteins and membranes in the form of a pellet which is discarded. The supernatant is then transferred to vials and are evaporated with nitrogen gas. The samples are then sent to the UF Chemistry Department’s Mass Spectrometry Services where they are injected into a high performance liquid chromatography-electrospray ionization-time of flight-mass spectrometry (HPLC-ESI-TOF-MS) to acquire data.  Retention time and mass-to-charge ratio are received from the assay. Our laboratory and the Carnitine Team are then involved with the interpretation of the data acquired from the assay.

Making Biological Conclusions and Future Plans

Our lab employs an iterative process of global and targeted metabolomics to identify masses received from the results of the metabolomic assay. That is, mass spectrometry is performed on samples and analyzed at a global level to determine masses of interest, these masses then become the focus of a targeted approach. These masses are also used to identify specific acylcarnitines, fatty acids, and amino acids that are of biological importance and interest. The possible metabolite masses received from chemistry are identified by use of online databases such as the Human Metabolome Database (HMDB) and METLIN. Biological information can then be interpreted and used to address important questions about carnitine’s role in our patient populations. Analysis of the concentrations of different acylcarnitine species may provide us with a glimpse into the mechanism of disease. Below is an outlined depiction of our research process.

References

Jones LL, McDonald DA, Borum PR. Acylcarnitines: role in brain. Prog Lipid Res. 2010 Jan;49(1):61-75.

 

Ketogenic Therapy

Our Program

KetoGator Fund

Databases

Family Resources

Therapy Timeline

The Ketobuddy System

Shands Clinic

Meal Making

Newsletter

Ketogenic Links

 

Dr. Peggy R. Borum
University of Florida
FSHN Department
P. O. Box #110370
Gainesville, FL 32611-0370

409A FSHN Bldg
Newell Drive
UF Campus

prb@ufl.edu
Phone: 352-392-7553
Fax: 352-392-8957

 

Contact Webmaster