Acetyl-carnitine

Short term L-acetyl carnitine treatment has shown symptomatic benefits in ATN, although it is unclear if this effect is long lasting because of neuronal regeneration or is merely an analgesic effect (Scarpini et al. 1997 Oslo et al. 2006). Longer term studies showed improvements in epidermal nerve fiber density (Hart et al. 2004) as well as the symptoms of neuropathy when patients were treated with L-acetyl carnitine (Hart et al. 2004 Herzmann et al. 2005). A short term randomized, double-blind, placebo-controlled study showed reduction in pain over a 2 week period in HIV patients with TNA (Youle and Oslo 2007). 

Carnitine is a vitamin-like quaternary ammonium salt, playing an important role in the human energy metabolism by facilitating the transport of long-chained fatty acids across the mitochondrial membranes. An easy, fast, and convenient procedure for the separation of the enantiomers of carnitine and 0-acylcarnitines has been reported on a lab-made teicoplanin-containing CSP [61]. The enantioresolution of carnitine and acetyl carnitine was enhanced when tested on a TAG CSP, prepared in an identical way [45]. Higher a values were reached also in the case of A-40,926 CSP [41]. 

ATP. The presence of acetyl-carnitine in mitochondria, at a concentration 400-fold greater than that of acetyl-CoA, along with the enzyme carnitine acetyltransferase, acts as a buffer to protect against large changes in the concentration of acetyl-CoA ... 

Fig. 3.2.8a-c Profiles of acylcarnitines as their methyl esters in cell culture medium (precursor of m/z 99 scan) following the in vitro probe assay in fibroblast cultures of a normal control (a) and a patient with the milder (b) and the more severe variant (c) of VLCAD deficiency. Note the more prominent elevation of dodecanoyl- (Ci2 m/z 358 peak 1) and myristoylcarnitine (Ci4 m/z 386 peak 2) compared to a relatively normal accumulation of palmitoylcarnitine ( , m/z 416 peak 3) in the milder VLCAD variant compared to the severe variant, where palmitoylcarnitine is markedly elevated. The asterisks represent the internal standards (from left to right) d3-acetyl-carnitine (C2 m/z 221), d9-isovalerylcarnitine (C5 m/z 269), d3-octanoylcarnitine (C8 m/z 305), d3-dodecanoylcarnitine (Ci2 m/z 361), and d3-palmitoylcarnitine ( m/z 419)... 

Acyl ester CoA Acetyl carnitine Carnitine + acetate -7.2... 

Knowles and co-workers observed (V/K) at C-1 of glyoxalate by analyzing the isotopic composition of the malate produced in the reaction at early and late stages (23). In order to measure this ratio accurately they developed a procedure to convert C-2 of malate to carbon dioxide. Through a series of enzymic reactions, C-2 was converted to the carbonyl carbon of the acetyl group of acetyl-carnitine (through the reaction sequence malate — pyruvate — acetyl-CoA - acetylcarnitine). The labeled carbon then was carried flirough another cycle back to malate, but in this case the label was in the carboxylate carbon at C-4 (acetyl-carnitine acetyl-CoA 4-[ 3C]malate). Malic enzyme converts this to pyruvate and labeled carbon dioxide, whose isotopic ratio is determined by mass spectrometry. 

Badiali De Giorgi, L., Bonvicini, F., Bianchi, D., Bossoni, G. and Laschi, R. (1987) Ultrastructural aspects of ageing rat hippocampus and effects of L-acetyl-carnitine treatment. Drugs Exp. Clin. Res. 13 185-189. 

Dolezal, V. and Tucek, S. (1981) Utilization of citrate, acetyl-carnitine, acetate, pyruvate and glucose for the synthesis of... 

The medium-chain 3-ketoacyl-CoA thiolase and the 3-ketoacyl-CoA thiolase activity of the trifimctional protein are inhibited by acetyl-CoA. " We have also demonstrated the sensitivity of the trifunctional protein to [acetyl-CoA]/[CoA] but at a fixed [acetyl-CoA + CoASHj. This was carried out by incubating isolated trifunctional protein with 2-hexadecenoyl-CoA, NAD, CoASH, carnitine acetyltransferase and a range of concentrations of carnitine and acetyl-carnitine to keep the total [CoA] constant. Results from a typical titration are shown in Fig. 3. 

Hence, were disposal of acetyl-CoA to keh enesis, the tricarhoxylic acid cycle or to acetyl-carnitine inhibited, feedback inhibition of P-oxidation would result and it has been suggested that this may control p-oxidation in cardiac mitochondria. However, although 3-ketoacyl-CoA esters are readily observed as intermediates of peroxisomal P-oxidation, we have never observed accumulation of 3-ketoacyl-CoA esters in mitochondrial incubations even at maximal P-oxidation flux and under conditions in which acetyl-CoA accumulates. Therefore, the accumulation of 3-ketoacyl-CoA esters may be strongly prevented and an excess of thiolase activity puBs P-oxidation as the... 

One of the functions of hepatic P-oxidation is to provide ketone bodies, acetoac-etate and p-hydroxybutyrate, to the peripheral circulation. These can then be utilized by peripheral tissues such as brain and heart. Beta-oxidation itself produces acetyl-CoA which then has three possible fates entry to the Krebs cycle via citrate S5mthase keto-genesis or transesterification to acetyl-carnitine by the action of carnitine acetyltrans-ferase (CAT). Intramitochondrial acetyl-carnitine then equilibrates with plasma via the carnitine acyl-camitine translocase and presumably via the plasma membrane carnitine transporter. Human studies have shown that acetyl-carnitine may provide up to 5% of the circulating carbon product from fatty acids and can be taker and utilized by muscle and possibly brain." In addition, acyl-camitines are of important with regard to the diagnosis of inborn errors of P- oxidation. For these reasons, we wished to examine the production of acetyl-carnitine and other acyl-camitine esters by neonatal rat hepatocytes. 

Calibration curves were obtained for free carnitine in the range of 5-lOOpmol/L, 2-40pmol/L for acetyl-carnitine and from 0.25-6pmol/L for all other available acyl-camitines by adding standards to a normal plasma pool. All calibration curves were linear (r > 0.99, data not shown). For unsaturated and hydroxylated acyl-camitines an identical response as for their saturated counterparts was assumed. 

Figure I. Acyl-carnitine profiles in fatly acid uxidatiun defects. Acyl-carnitine profiles were obtained from plasma or serum samples as described in materials and methods. In the upper left panel normal control the positions of the deutcrated internal standards (IS) arc indicated. For comparison the profiles were printed with the - Hj-CS-IS at SO iiof full scale in all panels, The ion at m/z 218 corresponds to free carnitine m/z 260, acetyl-carnitine nifz 274, propionyl-carniline m/z 288, butyryl-carnitine m/z 302, iso-C5-carnitinc (isovalcryl-carnitine) m/z 316, hexanoyI-carnitine m/z. 344, octanoyl-carnitine m/z 370, C 10 1-carnitine m/z 400, C12-camitinc m/z 426. CT 4 1-carnitine m/z 444, hydroxy-C 14-carmtine m/z 4,36, Cl 6-carnitine m/z 472, hydroxy-C16-carnitine m/z 482, Cl8 1-carnitine m/z 498, hydroxy-C 18 1-carnitine.

Calabrese, V, Scapagnini, G., Latteri, S., Colombrita, C., Ravagna, A., Catalano, C., Pennisi, G., Calvani, M., and Butterfield, D.A. (2002). Long-term ethanol administration enhances age-dependent modulation of redox state in different brain regions in the rat protection by acetyl carnitine. Int. J. Tissue React. 24 97-104. 

Szutowicz et al. 1996 Tucek 1993). However, it is known that non-excitable cells in the mitochondrial inner membrane are relatively impermeable to acetyl-CoA. Therefore, acetyl-CoA has to be transported out of mitochondria by indirect pathways involving citrate, acetate or acetyl-carnitine, which in the cytoplasm are converted back to acetyl-CoA by pathways driven by ATP-citrate lyase (ACL EC 2.3.3.8), acetyl-CoA synthase (EC 6.2.1.3) and carnitine acetyltransferase (EC 2.3.1.7), respectively (Szutowicz et al. 1996). 

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