Lipoic Acid Protects Hearing Function
By Dr Gail Valentine
How often have you said, "I hear you," when it wasn't really a question of hearing but of understanding. For some of us, some of the time, and for others, all of the time, "hearing" is a necessity for successful communication. Think for a moment what it would be like if you couldn't hear. For certain, you'd be lacking a valuable sense ... the quality of your life would be poorer. Gone would be a leading-edge avenue for receiving information about the world. But also, your world would be without a needed ingredient of entertainment and pleasure. The "sound" of poetry, song, music, and the delicious uproar of life would be gone. I'm sure you get the idea. You may even "hear me." Did you also know that hearing loss is age-related? It's something we all suffer from, and it takes its toll day by day. As we age, we move closer to the "sounds of silence."
Specific nutrients can help protect and restore certain aspects of hearing function. Items such as magnesium, quercetin, ginkgo biloba, Vitamin D, calcium, niacin, and zinc can help preserve your ability to distinguish the many nuances of sound: timbre, balance, tone, pitch, bass and treble. Vinpocetine may help restore hearing function that has been lost due to age-related decline, exposure to noise pollution, or other various unknown causes.
Lipoic Acid Protects Against Antibiotic-Induced Hearing Loss
There's something more to be added to our nutritional armamentarium; it involves an old friend in new clothing. Sometimes known as thioctic acid to honor its sulphur (thio) component, we know this item also as the universal antioxidant alpha lipoic acid, or lipoic acid for short. Lipo indicates that there is a fat molecule in the alpha or first position, which is important because lipoic acid operates in fatty tissue as well as aqueous (water) tissue. Bound into the chemical composition of lipoic acid is the amino acid cysteine, which is connected to glutathione which we'll examine momentarily. First, the latest research.
At the Hearing Research Laboratories at Duke University, in Durham, North Carolina, researchers investigated what positive effect lipoic acid could have on aminoglycoside* antibiotic-induced damage to cochlear tissue of the ear.1 Recently, a number of studies have shown that gentamicin (a widely-used aminoglycoside antibiotic for infection of the cornea, conjunctiva, urinary tract, and other infections) expedites the generation of free radicals, strongly suggesting that this process plays an important role in aminoglycoside-induced ototoxicity (ear damage).2
* Aminoglycoside is a class of antibiotics. some examples are gentamicin and amikacin.
With the knowledge that certain nutrients operate as scavengers, possessing the ability to inactivate free radicals, the Duke researchers investigated the ability of alpha lipoic acid to reduce ear damage to the cochlea (see Fig 1) when damage is induced by the aminoglycoside antibiotic, amikacin. This antibiotic has been shown to be highly ototoxic to the cochlea, even more so than gentamicin.3 It causes damage to the inner hairs of the cochlea, which play a critical role in the mechano-electrical transduction of sound waves into mechanical bone movement and then into neuroelectrical pulses which are then sent to the brain.4
When the researchers measured electrical hearing threshold changes, the results showed that animals receiving alpha lipoic acid in combination with amikacin demonstrated significantly better hearing than the animals receiving amikacin alone. In effect, lipoic acid-protected animals did not have part of their hearing impaired compared with animals receiving the damaging antibiotic alone. The researchers thought that lipoic acid was particularly well suited to protect the ear because it is widely distributed in both aqueous and lipid tissues after administration.5 In addition, it crosses the blood-brain barrier quite readily, has low toxicity, and has excellent uptake in neural tissue. Furthermore, lipoic acid is delivered to both the intra- and extra-cellular environment.6 These data may help explain why lipoic acid is able to protect against aminoglucoside-induced hearing loss.
Lipoic Acid Succeeds Where Other Nutrients Fail
There has been a lot of research about the ability of glutathione (can be made from cysteine in the body) to act as a natural cochlear protectant by helping to prevent free radical damage to the cochlea.7 Yet glutathione supplementation has not been proven to be an effective route because it is poorly absorbed from the diet.8 Additionally, it has low ability to accumulate in brain tissue. However, lipoic acid has been shown to increase intracellular glutathione levels by as much as 70% in vivo.9 Several other benefits of lipoic acid regarding hearing protection involve its ability to regenerate and increase Vitamins C and E in the body. These vitamins are important naturally-occurring, free-radical scavengers.10 Also, lipoic acid chelates iron which appears to be catalyzed into mischievous activity by the antibiotic gentamicin. Iron operates as a pro-oxidant, greatly increasing free-radical activity.11 So lipoic acid's ability to disarm iron is of significant value.
Another report in the literature appeared eight years ago about a study finding that a certain vitamin regimen restored short-term hearing loss, especially hearing loss related to Meniere's disease.12 Meniere's disease is characterized by recurrent vertigo, ringing in the ears (tinnitus) and progressive hearing loss. The cause of Meniere's disease is unknown. The hearing-loss therapy involved the use of Vitamins B12, B1, B5, a steroid, a diuretic, and finally thioctic acid, a.k.a. alpha lipoic acid.
This "vitamin" therapy was compared against what was described as conventional therapy, consisting of a steroid, Vitamin B, dextran, and a local anesthetic (to nerves distributed to the head). All told, 454 ears were treated for sudden deafness and 354 cases for perceptive hearing loss from other causes. Both treatments were equally efficacious; but in newer cases of hearing loss, treated within a four-week period of onset, the "vitamin" therapy gave significantly better cure and effectiveness rates. Also, in cases with severe hearing loss or vestibular symptoms (vertigo, loss of balance, nausea, among others), the "vitamin" treatment was more effective. This was also true for cases of Meniere's patients in this study. Remember that the "vitamin" therapy also contained lipoic acid at a level of 200 mg per dose, a respectable level.
Fig 1. The outer, middle and inner ear (where the cochlea resides).
Lipoic Acid Protects Against Noise-Induced Hearing Loss
In another very recent paper, lipoic acid combined with Vitamin E protected against exposure to high-energy impulse noise caused by explosions, which resulted in structural and functional damage to the hollow organs, especially to the respiratory and auditory (hearing) systems.13 Using rats in the study, the researchers examined whether a short period of pre-exposure supplementation with antioxidants could protect against the damage of the blast. The rats received either 800 iu of Vitamin E, 1,000 mg of Vitamin C, or 25 mg of lipoic acid. All items were given for three days. On the fourth day the rats were deeply anesthetized and exposed to a simulated blast wave. Supplementation with Vitamin E or lipoic acid - but not Vitamin C - reversed hearing loss. The amount of lipoic acid used was quite low compared to the amount of Vitamin E used. Typical human use of Vitamin E might be 800 iu/day, but typical lipoic acid intake might be 400 mg/day. Therefore, it can be concluded that a relatively small amount of lipoic acid can help protect against hearing damage.
Taking Lipoic Acid Makes Good Sense
Hearing impairment can occur due to aging and can be compounded by a multitude of other external conditions often beyond our control. If you live or work in a noise-pollution environment, or are subjected to high-energy impulse sounds (such as sudden sirens or unpredictable loud noises); if you listen to loud music (even a Walkman can injure hearing); if you use any antibiotics or other drugs which may produce excessive free radicals in the ear; or if you are already experiencing hearing decline, it would be wise to consider lipoic acid. Given the positive safety profile of lipoic acid and the promise of a significant degree of auditory protection, it makes good sense to add lipoic acid to your supplement program.
See The Resurrection of Sound - October 1998 for more on protecting and improving hearing function.
- Conlon BJ, Aran JM, Erre JP, Smith DW Attenuation of aminoglycoside-induced cochlear damage with the metabolic antioxidant alpha-lipoic acid. Hear Res 1999 Feb;128(1-2):40-44.
- Lima da Costa D, Erre JP, Aran JM. Aminoglycoside ototoxicity and the medial efferent system: I. Comparison of acute and chronic gentamicin treatments. Audiology 1998 May-Jun;37(3):151-6.
- Aran JM, Chappert C, Dulon D, Erre JP, Aurousseau C. Uptake of amikacin by hair cells of the guinea pig cochlea and vestibule and ototoxicity: comparison with gentamicin. Hear Res 1995 Feb;82(2):179-183.
- Patuzzi R, Moleirinho A. Automatic monitoring of mechano-electrical transduction in the guinea pig cochlea. Hear Res 1998 Nov;125(1-2):1-16.
- Packer L, Tritschler HJ. Alpha-lipoic acid: the metabolic antioxidant. Free Radic Biol Med 1996;20(4):625-626.
- Panigrahi M, Sadguna Y, Shivakumar BR, Kolluri SV, Roy S, Packer L, Ravindranath V. Alpha-lipoic acid protects against reperfusion injury following cerebral ischemia in rats. Brain Res 1996 Apr 22;717(1-2):184-188.
- Garetz SL, Rhee DJ, Schacht J.Sulfhydryl compounds and antioxidants inhibit cytotoxicity to outer hair cells of a gentamicin metabolite in vitro. Hear Res 1994 Jun 15;77(1-2):75-80.
- Anderson ME, Powrie F, Puri RN, Meister A. Glutathione monoethyl ester: preparation, uptake by tissues, and conversion to glutathione. Arch Biochem Biophys 1985 Jun;239(2):538-548.
- Bast A, Hansen GR. Interplay between lipoic acid and glutathione in the protection against microsomal lipid peroxidation. Biochem Biophys Acta.963;558:561.
- Kagan VE, Shvedova A, Serbinova E, Khan S, Swanson C, Powell R, Packer L. Dihydrolipoic acid - a universal antioxidant both in the membrane and in the aqueous phase. Reduction of peroxyl, ascorbyl and chromanoxyl radicals. Biochem Pharmacol 1992 Oct 20;44(8):1637-49.
- Ou P, Tritschler HJ, Wolff SP. Thioctic (lipoic) acid: a therapeutic metal-chelating antioxidant? Biochem Pharmacol 1995 Jun 29;50(1):123-126.
- Konishi K, Nakai,Yamane H. The efficacy of lasix-vitamin therapy (l-v therapy) for sudden deafness and other sensorineural hearing loss. Acta OtoLaryngol. 1991;486:78-91.
- Armstrong KL, Cooper MF, Williams MT, Elsayed NM Vitamin E and lipoic acid, but not vitamin C improve blood oxygenation after high-energy IMPULSE noise (BLAST) exposure. Biochem Biophys Res Commun 1998 Dec 9;253(1):114-118.
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