Long chain acylcamitines

Yamada KA, McHowat J, Yan GX, Donahue K, Peirick J, Richer AG, Corr PB Cellular uncoupling induced by accumulation of long-chain acylcamitine during ischemia. Circ Res 1994 74 83-95. 

Lecluyse EL, Sutton SC, Fix JA. In vitro effects of long-chain acylcamitines on the permeability, transepithelial electrical resistance and morphology of rat colonic mucosa. J Pharmacol Exp Ther 1993 265 955-962. 

A Arduini, A Peschechera, S Dottori, AF Sciarroni, F Seraflni, M Calvani. High performance liquid chromatography of long-chain acylcamitine and phospholipids in fatty acid turnover studies. J Lipid Res 37 684-689, 1996. 

Several changes in ion membrane homeostasis also occur from fatty acid and long chain acylcamitines (LCAC) accumulation or from the formation of lysophosphadyl-choline (LPC) and arachidonic acid (AA) due to phospholipid breakdown by lipases. In fact, fatty acids and AA favor activation of K+ outward current while LCAC and LPC favor inward over outward current, reviewed by Carmeliet.55... 

One property of the translocase is specially noteworthy its affinity for long-chain acylcamitine is very much higher than for carnitine itself. This suggests a basic role for carnitine, additional to the acetylation buffer already mentioned. Every fourth reaction of the P-oxidation spiral (the excision of an acetyl unit by a thiolase enz5mie) requires free CoASH, so that if the CoA of the mitochondrial matrix became over-acy-lated the whole process would come to a halt. If acyl-CoA were formed directly from fatty acids in the same compartment (the matrix) as oxidation this might readily happen. However, the carnitine system guards against this fail-nonsafe situation, because if the acyl-CoA/CoASH ratio (and hence the acylcamitine/camitine ratio) rises the translocase will selectively export acylcamitine from the matrix and import carnitine this will lower the ratio and restore P-oxidation. It remains (I think ) to be seen if this effect can be conclusively demonstrated. 

Bartlett, K., Bhuiyan, A.K., Aynsley Green, A., Butler, P.C. Alberti, K.G. (1989) Clin. Sci. 77, 413 16. Human forearm arteriovenous differences of carnitine, short-chain acylcarnitine and long-chain acylcamitine. 

VLCAD deficiency is identified on acylcamitine profile by elevations of long-chain acylcamitines C12, C12 l, C14, C14 l, C14 2, C16, andC18 l. 

Acylcamitine profiles indicate elevated long-chain acylcamitines C12, C14, C18, and C18 l, but they also show elevated 3-hydroxyacylcamitines hydroxy-C14, hydroxy-C16, and hydroxy-C 18 1. Urine organic acid analysis shows dicarboxylic acids and 3-hydroxydicarboxylic acids. These latter metabolites can rarely also be observed in certain patients with respiratory chain enzyme deficiencies. Lactate and the lactate to pyruvate ratio are often elevated. The incidence of TCHAD deficiency on newborn screening is estimated at 1 60,000. The diagnosis is usually confirmed by mutation analysis of the genes for the a-chain HADHA and the p-chain HADHB. Enzyme assays are nowadays rarely available. 

Su, X., Han, X., Mancuso, D.J., Abendschein, D.R. and Gross, R.W. (2005) Accumulation of long-chain acylcamitine and 3-hydroxy acylcamitine molecular species in diabetic myocardium Identification of alterations in mitochondrial fatty acid processing in diabetic myocardium by shotgun lipidomics. Biochemistry 44, 5234-5245. 

Htilsmann, W.C., Schneijdenberg, C.T.W.M. Verkleij, A.J. (1991) Accumulation and excretion of long-chain acylcamitine by rat hearts studies with aminocarnitine. Biochim. Biophys. Acta 1097 263-269. 

The lanthaninn teehnique was used to study the epithelial permeability in the rat small intestine (Madara and Trier 1982). Dense lanthanum precipitates in TJ and paracellular spaces were restricted to a subpopulation of villous goblet cells and were not found between villous absorptive cells. These TJ were also permeable to barium, but not to macromolecular tracers such as microperoxidase, eytochrome c and horseradish peroxidase. It was also shown that palmitoylcamitine (PCC) opens TJ in a monolayer of Caco-2 colon carcinoma cells this phenomenon appears to be responsible for the significant enhancement of the absorption of hydrophilic drugs across intestinal mucosa caused by PCC and other long-chain acylcamitines (Hochman, Fix et al. 1994).In an experiment on rats, it was demonstrated that immobilisation stress induced a significant (but reversible) increase in epithelial permeability to the lanthanum tracer (Mazzon, Stumiolo et al. 2002). 

Long-chain acyl-CoA esters are then converted to acylcamitine esters by readily reversible reactions with L-camitine catalyzed by carnitine palmitoyltransferase I (CPT I). 

Figure 3. Mitochondrial fatty acid oxidation. Long-chain fatty acids are converted to their CoA-esters as described in the text, and their fatty-acyl-groups transferred to CoA in the matrix by the concerted action of CPT 1, the acylcarnitine/carnitine exchange carrier and CPT (A) as described in the text. Medium-chain and short-chain fatty acids (Cg or less) diffuse directly into the matrix where they are converted to their acyl-CoA esters by a acyl-CoA synthase. The mechanism of p-oxidation is shown below (B). Each cycle of P-oxidation removes -CH2-CH2- as an acetyl unit until the fatty acids are completely converted to acetyl-CoA. The enzymes catalyzing each stage of P-oxidation have different but overlapping specificities. In muscle mitochondria, most acetyl-CoA is oxidized to CO2 and H2O by the citrate cycle (Figure 4) some is converted to acylcamitine by carnitine acetyltransferase (associated with the inner face of the inner membrane) and exported from the matrix. Some acetyl-CoA (if in excess) is hydrolyzed to acetate and CoASH by acetyl-CoA hydrolase in the matrix. Enzymes ...

As many as 1 in 10,000 persons may inherit such prob-lems.48 50a Tire proteins that may be defective include a plasma membrane carnitine transporter carnitine palmitoyltransferases camitine/acylcamitine trans-locase long-chain, medium-chain, and short-chain acyl-CoA dehydrogenases 2,4-dienoyl-CoA reductase (Eq. 17-1) and long-chain 3-hydroxyacyl-CoA dehydrogenase. Some of these are indicated in Fig. 17-2. 

Recovery of radiolabeled acylcamitines after incubation of isolated rat liver mitochondria was greatest for a-Unolenoyl Co A than for various other long-chain acyl-Co As (Gavino Gavino, 1991 Table 1). Their data are in agreement with those of Clouet et al. (1989) and Emmison et al. (1995), both of whom evaluated recovery of p-oxidized tracer on the basis of its appearance in acid-extractable products, mainly ketones (Tables 1 and 2). 

In order to be metabolized, long-chain fatty acids must first undergo conjugation to carnitine for transport by the acylcamitine-camitine carrier across the mitochondrial inner membrane [139]. Short-chain fatty acids enter the mitochondria through monocarboxylic acid transporters [139]. Studies were carried out to assess the effects cephaloridine, cephaloglydn and cephalexin on the mitochondrial oxidative metabolism of fatty adds such as butyrate and pahnitate [67]. 

Carnitine serves as the carrier that transports activated long chain fatty acyl groups across the inner mitochondrial membrane (Fig. 23.4). Carnitine acyl transferases are able to reversibly transfer an activated fatty acyl group from CoA to the hydroxyl group of carnitine to form an acylcamitine ester. The reaction is reversible, so that the fatty acyl CoA derivative can be regenerated from the carnitine ester. 

Carnitine palmitoyltransferase I (CPTI also called carnitine acyltransferase I, CATI), the enzyme that transfers long-chain fatty acyl groups from CoA to carnitine, is located on the outer mitochondrial membrane (Fig. 23.5). Fatty acylcamitine crosses the inner mitochondrial membrane with the aid of a translocase. The fatty acyl group is transferred back to CoA by a second enzyme, carnitine palmitoyl-transferase II (CPTII or CATII). The carnitine released in this reaction returns to the cytosolic side of the mitochondrial membrane by the same translocase that brings fatty acylcamitine to the matrix side. Long-chain fatty acyl CoA, now located within the mitochondrial matrix, is a substrate for (3-oxidation. 

Before long-chain fatty acids can enter the mitochondria and get access to the P-oxidation pathway, they must first be activated to acyl-CoA in a reaction that requires ATP and coenzyme-A. The acyl-CoA still cannot cross the mitochondrial inner membrane and must react with carnitine to form the corresponding carnitine ester. This reaction is catalyzed by the enzyme carnitine palmitoyltransferase (CPT). The acylcamitine itself is also unable to diffuse into the mitochondrial matrix so that the transport is achieved by a specific protein, the carnitine acylcamitine translocase. Following transport across the mitochondrial inner membrane, acylcamitines are converted back to the corresponding acyl-CoA and carnitine. This reaction is catalyzed by another carnitine palmitoyltransferase which is a different enzyme than that involved in the formation of the acylcamitine outside the mitochondria. Hence, there are two CPTs, one associated with the inner aspect of the mitochondrial inner membrane, CPT-lP and one that lies... 

Having CATa and CATb on either side of the microsomal membrane appears to serve no obvious purpose unless, by analogy with the well-characterized mitochondrial system,these are linked to some form of transport system to move fatty acylcamitines across the membrane. It is impractical to study directly the transport of radiolabelled long-chain fatty acylcamitines into or out of sealed microsomal vesicles because these metabolites bind non-specifically to many cellular proteins. We, therefore, devised a way to do this indirectly, based on the use of the lumenal enzyme ethanol acyltransferase (EAT) as a reporter . In the endoplasmic reticulum EAT ° catalyzes the reaction ... 

Mitochondrial P-oxidation of long-chain fatty acids is the major source of energy production in man. The mitochondrial inner membrane is impermeable to long chain fatty acids or their CoA esters whereas acylcamitines are transported. Three different gene products are involved in this carnitine dependent transport shuttle carnitine palmi-toyl transferase I (CPT I), carnitine acyl-camitine carrier (CAC) and carnitine palmitoyl transferase II (CPT II). The first enzyme (CPT I) converts fatty acyl-CoA esters to their carnitine esters which are subsequently translocated across the mitochondrial inner membrane in exchange for free carnitine by the action of the carnitine acyl-camitine carrier (CAC). Once inside the mitochondrion, CPT II reconverts the carnitine ester back to the CoA ester which can then serve as a substrate for the P-oxidation spiral. 

II or Pompe disease. Tyrosinemia type I, which mainly affects the liver and kidney, also manifests with hypertrophic cardiomyopathy. Conduction defects predisposing to arrhythmia are typically found in disorders of fatty acid oxidation (especially long-chain disorders, CPTII, and camitine-acylcamitine translocase deficiency), Keams-Sayre, and other primary mitochondrial defects. 

L-camitine is given in many metabohc disorders as a supplement or to correct a carnitine deficiency. The dose of carnitine can vary between 50 and 100 mg/kg/day, and in some organic acidurias, as much as 200-300 mg/kg/24 days may be necessary, hi some of the long-chain fatty acid oxidation disorders, use of carnitine is controversial, and in the view of potential adverse effects (formation of car-diotoxic acylcamitines), supplementation at time of metabolic decompensation should be avoided [18]. 

In the heart, fatty acid oxidation defects can cause cardiomyopathy. The cardiomyopathy is usually associated with a degree of hypertrophy. Cardiomyopathy is typical for severe fatty acid oxidation defects of long-chain fatty acids. Cardiomyopathy in those with carnitine transporter defect is typically dilated in nature without hypertrophy. Severe ventricular arrhythmias (ventricular tachycardia, ventricular fibrillation, torsades de pointes) occur in fatty acid oxidation defects. They are frequent in severe fatty acid oxidation defects of long-chain fatty acids and particularly prominent in camitine-acylcamitine translocase deficiency but can also occur in MCAD deficiency during decompensation. Atrioventricular block can occur but is rare. 

Shen JJ, et al. Acylcamitines in fibroblasts of patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency and other fatty acid oxidation disorders. J Inherit Metab Dis. 2(XX) 23(l) 27-44. 

Plasma acylcamitine profiles improve when dietary long-chain fat is restricted and MCT is supplemented. 

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