Oxidation long-chain fatty adds

The release of H20 from [9,10- H]myristate and/or [9,10- I palmitate has been used extensively for detecting medium- and long-chain fatty add oxidation defects, both in cultured fibroblasts and in fresh lymphocytes. Over the past 10 years we have used both substrates to screen routinely for fatty acid oxidation defects in over 1,200 patients and have identified 113 individuals with specific fatty acid oxidation disorders (Table 1). More recently we have examined the use of a third substrate, [9,10- oleate, to improve discrimination of long-chain defects. ... 

Spiekerkoetter U, et al. Treatment recommendations in long-chain fatty add oxidation defects consensus from a workshop. J Inherit Metab Dis. 2009 32(4) 498-505. 

In both long-chain fatty add oxidation disorders (LCFAOD) and medium-chain fatty acid oxidation disorders (MCAD), emergency management of acute illness and the avoidance of prolonged fasting are key treatment strategies. 

Olpin, S.E., Manning, N.J., Pollitt, R.J. Clark, S. (1997). J. Inherited Metab. Dis. 20, 415 19. Improved detection of long-chain fatty add oxidation defects in intact cells using [9,10-Tl]oleate. Vianey-Saban, C., Divry, C., Biivet, M., Nada, M., Zabot, M.T., Mathieu, M. Roe, C. (1998) Clin. Chim. Acta, 269, 43-62. Mitochondrial very-long-chain acyl-coenzyme A dehydrogenase defidency clinical characteristics and diagnostic considerations in 30 patients. 

Figure 19.6 indicates the oxidation of palmitoyl-CoA to myristoyl-CoA with the production of an acetyl-CoA molecule. The myristoyl-CoA molecule can undergo another oxidative cycle, and so on. Note that the /3-hydroxyacyl-CoA dehydrogenase is specific for the l isomer of /3-hydroxyacyl-CoA. Also note that at least three acetyl-CoA dehydrogenases exist, one favoring short-chain fatty acids, another intermediate-length fatty adds, and the third long-chain fatty adds. 

Carnitine is required for transport of longoxidative metabolism as well as in the formation of ketone bcidies, The concentration of free carnitine in muscle is about 4,0 mmol/kg. The concentration of carnitine bound to long-chain fatty adds (fatty acyl-camitine) is lower, about 0,2 mmol/kg. Short-chain fatty adds, including acetic, are also esterified to carnitine, but the functions of these complexes are not clear. There is some indication that keto forms of BCAAs (BCKAs) can also be esterified to carnitine. These complexes can then be transported into the mitochondria for complete oxidation of the BCKAs, The importance of this mode of BCKA transport is not dear (Takakura et ai., 1997). 

The nature of a fatty add influences its fate. Short- and medium-tdiain fatty adds tend to be oxidised immediately to carbon dioxide, rather than deposited as TGs or phospholipids. The presence of double bonds ("unsaturations") in long-chain fatty adds influences the immediate fate of the add. Some evidence suggests that unsaturated fatty acids, such as 18 2, tend to be oxidized at a slightly faster rate in the hours following a meal than saturated fatty acids, such as 18 0 (Jones et al., 1985, Jones and Schoeller, 1988). More specifically, about 2% of a test meal of 18 0 may be oxidized in the 9 hours toUowing Ingestion, whereas about 10% of a test meal of 18 2 may be oxidized in the same period, The mechanisms that influence the fates of unsahirated and saturated fatty adds are only beginning to be understood. 

FIGURE 5.7 One cycle in the oxidation of a long-chain fatty add. 

Wanders, R.J., van Roermund, C.W., van Wijland, M.J., Schulgens, RB., van den Bosch, H., Schram, A.W. Tagcr, J.M. (1988) Biochem. Biopl s. Res. Commun. 153, 618 24. Direct demonstration that the deficient oxidation of very long chain fatty acids in X-linked adrenoleukodystrophy is due to an impaired ability of peroxisomes to activate very long chain fatty adds. 

Lageweg, W. Wanders, R.J.A. (1993) Biochem. Pharmacol. 46, 79-85. Studies on the effect of fenoprofen on the activation and oxidation of long chain and very long chain fatty adds in hepatocytes and subcellular fractions from rat liver. 

Other fatty acids including long-chain fatty adds were normal, provided the first clue that the mitochondrial and peroxisomal P-oxidation systems might have different substrate spedfidties. Subsequent studies indeed revealed that peroxisomes are the primary site of oxidation of very-long-chain fatty acids whereas oxidation of long-chain fatty acids occurs predominantly in mitochondria. Later studies showed that oxidation of pristanic add and the bile acid intermediates di- and trihydroxycholestanoic acid is also primarily peroxisomal. 

As discussed above, the peroxisomal fatty acid P-oxidation system is specifically involved in the degradation of a specific group of fatty acids including very-long-chain fatty acids, pristanic acid and di- and trihydroxycholestanoic acid. Several inherited diseases in man have been described in which peroxisomal P-oxidationis impaired at some level as reflected in the differential accumulation of very-long-chain fatty adds, pristanic acid and the bile acid intermediates in plasma from patients. The following disorders can be distinguished ... 

Brivet, M., Slama, A., Saudubray, J-M. Lemonnier, A. (1995). Ann. Clin. Biochem. 32, 293-297. Rapid diagnosis of long and medium chain fatty add oxidation disorders using lymphocytes. 

We recently identified a new peroxisomal disorder in a patient showing signs and symptoms comparable to those observed in Zellweger syndrome. In the patients plasma, very-long-chain fatty adds, pristanic acid, and di- and trihydroxycholestanoic add were elevated suggesting a defect in the peroxisomal P-oxidation system. Subsequent studies identified the defect in this patient at the level of the 3-hydroxyacyl-CoA dehydrogenase component of the newly identified D-bifunctional protein. 

Lysine, like most other AAs, is a building block of body protdns. Among the indispensable AAs, lysine is present in the greatest amounts, at 93.0 and 38 mmol/dl in tissues and serum, respectively (see Table 15.3). Carnitine, a compound responsible for transport of long-chain fatty adds into the mitochondria for oxidation, is synthesized in the liver and kidneys from lysine and methionine. Lysine is also required for collagen synthesis and may be central to bone health. - Lysine s effects... 

In mitochondria, there are four fatty acyl CoA dehydrogenase species, each of which has a specificity for either short-, mediurr-long-, or very-long-chain fatty acids. MCAD deficiency, an autos mal, recessive disorder, is one of the most common inborn errors of metabolism, and the most common inborn error of fatty add oxidation, being found in 1 in 12,000 births in the west, and 1 in 40,000 worldwide. It causes a decrease in fatty acid oxidation and severe hypoglycemia (because the tissues cannot obtain full ener getic benefit from fatty acids and, therefore, must now rely on glu cose). Treatment includes a carbohydrate-rich diet. [Note Infants are particularly affected by MCAD deficiency, because they rely for their nourishment on milk, which contains primarily MCADs. 

The study reported in Table 4.12 illustrates the role of carnitine in fatty add oxidation and introduces the topic of medium-chain fatty acids. This study, conducted before the role of carnitine in fatty acid transport was realized, involved addition of radioactive fatly acids to suspensions of liver mitochondria. The fatty acids used iriduded [ "Cjoctanoic acid (medium-chain) and [ " Clpalmitic add (long-chain). The susperisions were incubated for 30 minutes to permit uptake of the fatty acids, their subsequent oxidation, and discharge of radioactive carbon dioxide. The produced in the Krebs cycle diffuses out of the mitochondria into the surrounding fluid-... 

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]. 

To study the oxidation of these long-chain fatty acids we prepared their carnitine esters and tested them as substrates for isolated mitochondria from heart and other tissues. These experiments showed that the C22 fatty adds, both mono- and polyunsaturated indeed are poorly oxidized by mitochondria compared with ordinary fatty acids. Also, the presence of these very long-chain fatty acids interferes with the oxidation of the shorter-chain acids, e.g., palmitate [3,4]. 

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