Recently, acetyl-L-carnitine has been the subject of numerous scientific studies showing this remarkable compound may be key in maintaining normal brain and nerve function during aging.
Acetyl-L-carnitine is a naturally occurring metabolite of L-carnitine, and both are present in the diet, particularly in foods of animal origin.
Traditionally, their main claim to fame lies in their role in fatty acid oxidation. L-carnitine and acetyl-L-carnitine are part of the so-called carnitine shuttle. L-carnitine shuttles fatty acids into the cell's mitochondria for oxidation and energy production. The main end products of fatty acid oxidation are energy (in the form of NADH), and acetyl groups. Most of these acetyl groups are further oxidized in the mitochondria's Krebs cycle, but some are needed in the cytosol for producing other important metabolites. Acetyl-L-carnitine provides a way to carry these acetyl groups through the mitochondrial membranes back out into the cytosol (the cell fluid).
In brain and other nerve tissues, this acetyl group export by acetyl-L-carnitine is important in maintaining normal levels of acetyl groups for the production of acetylcholine and other neurotransmitters that are so crucial for normal brain and nerve function.
Acetyl-L-carnitine also helps maintain normal activity of choline acetyl transferase. This important enzyme has a tendency to decline with age, causing suboptimal acetylcholine levels which in turn are thought to contribute to the impairment of brain function that is associated with aging.
Besides maintaining normal acetylcholine levels, several studies indicate other neuroprotective effects of acetyl-L-carnitine, which may be due to at least two modes of action. First, acetyl-L-carnitine has been shown to maintain cellular membrane stability, and to restore age-related membranal changes. Acetyl-L-carnitine can also act as an antioxidant, scavenging harmful superoxide anion radicals. Since superoxide anion can damage membrane lipids, this may explain acetyl-L-carnitine's membrane protective properties. Second, animal studies indicate that acetyl-L-carnitine preserves normal levels of nerve growth factor in brain tissue during aging. Moreover, human studies indicated that acetyl-L-carnitine increases cerebral blood flow.
In summary, acetyl-L-carnitine is a naturally occurring compound that supports normal brain and nerve function during aging through various mechanisms. These include its actions on acetylcholine synthesis, membrane stability, nerve growth factor production, and cerebral blood flow.
Acetyl-L-carnitine appears to be well absorbed and utilized by the body. Typically, daily amounts of 1,500 to 3,000 mg have been used for several months and were found to be adequate in human studies without adverse effects.
REFERENCES
Bowman BA; Acetyl-L-carnitine and Alzheimer's disease. Nutr Rev 1992;50:142-144.
Carta A et al: Acetyl-L-carnitine and Alzheimer's disease: pharmacological considerations beyond the cholinergic sphere. Ann N Y Acad Sci 1993;695:324-326.
Forloni G et al: Neuroprotective activity of acetyl-L-carnitine: studies in vitro. J Neurosci Res 1994;37:92-96.
Postiglione A et al: Cerebral blood flow in patients with chronic cerebrovascular disease: effect of acetyl-L-carnitine. Int J Clin Pharmacol Res 1990;10:129-132.
Salvioloi G, and Neri M: L-acetylcarnitine treatment of mental decline in the elderly. Drugs Exp Clin Res 1995;20:169-176.
Sano M et al: Double-blind parallel design pilot study of acetyl levocarnitine in patients with Alzheimer's disease. Arch Neurol 1992;49:1137-1141.
Spagnoli A et al: Long-term acetyl-L-carnitine treatment in Alzheimer's disease. Neurology 1991;41:1726-1732.
Taglialatela G et al: Acetyl-L-carnitine treatment increases nerve growth factor levels and choline acetyl transferase activity in the central nervous system of aged rats. Exp Gerontol 1994;29:55-66.
White HL, and Scates PW: Acetyl-L-carnitine as a precursor of acetylcholine. Neurochem Res 1990;15:597-601
