“Once you choose hope, anything’s possible.” Christopher Reeve
“Hope is like a road in the country; there was never a road, but when many people walk on it, the road comes into existence.” Lin Yutang
Introduction: N-Acetyl-Cysteine (or N-acetylcysteine, usually abbreviated NAC and frequently pronounced like the word ‘knack’) is an altered (modified by an N-acetyl-group) form of the sulfur-containing amino acid cysteine (Cys). NAC is one of the building blocks for the all important antioxidant substance glutathione (GSH). GSH is a powerful reagent that helps cells fight oxidative stress. One of the putative causes of Parkinson’s is oxidative stress on dopamine-producing neurons (see figure below). This post summarizes some of the biochemistry of NAC and GSH. Furthermore, NAC may provide some neuroprotective benefit as a complementary and alternative medicine (CAM) approach to treating Parkinson’s.
“Losing the possibility of something is the exact same thing as losing hope and without hope nothing can survive.” Mark Z. Danielewski
Glutathione (GSH): GSH is a 3-amino acid substance (tripeptide) composed of Cys linked to glutamate (Glu) and followed by glycine (Gly). NAC would need to be de-acetylated to provide Cys and that would feed in to the reaction synthesis. Importantly, Cys is the rate limiting reactant, which means without adequate amounts of Cys you do not make GSH. The schematic below gives the orientation and order of addition of the three amino acid components to give you GSH.
There are two advantages of NAC over Cys for making GSH: (i) the sulfhydryl group of NAC remains reduced (that is as an SH group) more so than the SH group of Cys; and (ii) the NAC molecule appears to transport itself through cell membranes much more easily than Cys. The reduced (i.e., free SH group) form of GSH, once synthesized within the cell, has several key functions that range from antioxidant protection to protein thiolation to drug detoxification in many different tissues. The key function of GSH is to provide what is known as “reducing equivalents” to the cell, which implies an overall key antioxidant effect.
The schematic below shows NAC transport from extracellular to intracellular (inside the cell), and the primary reactions for detoxification and thiolation from GSH. Implied by this figure below is that GSH is not easily transported into the cell. Furthermore, in a more toxic/hostile environment outside of the cell, you can easily oxidize 2 GSH molecules to become GSSG (the reduced SH group gets oxidized to form an S-S disulfide bond) and GSSG does not have the antioxidant effect of GSH. However, inside the cell, GSH is a very potent antioxidant/detoxifying substance. And the beauty of being inside the cell, there is an enzyme called GSH-reductase that regenerates GSH from GSSG.
To recap and attempt to simplify what I just said, NAC gets delivered into a cell, which then allows the cell to generate intracellular GSH. The presence of intracellular GSH gives a cell an enormous advantage to resist potentially toxic oxidative agents. By contrast, extracellular GSH has a difficult path into the cell; and is likely to be oxidized to GSSG and rendered useless to help the cell.
“Just remember, you can do anything you set your mind to, but it takes action, perseverance, and facing your fears.” Gillian Anderson
One of many biological functions of NAC: Perhaps the most important medical use of NAC is to help save lives in people with acetaminophen toxicity, in which the liver is failing. How does NAC do this? Acetaminophen is sold as Tylenol. It is also added to compounds that are very important for pain management ()analgesics), including Vicodin and Percocet. Acetaminophen overdose is the leading cause of acute liver failure in the USA. This excess of acetaminophen rapidly consumes the GSH in the liver, which then promotes liver death. NAC quickly restores protective levels of GSH to the liver, which hopefully reverses catastrophic liver failure to prevent death.
Systemically, when taken either orally or by IV injection, NAC would have 2 functions. First, NAC replenishes levels of Cys to generate the intracellular antioxidant GSH (see schemes above). Second, NAC has been shown to regulate gene expression of several pathways that link oxidative stress to inflammation. Since the primary goal of this post relates to NAC as a CAM in Parkinson’s, I will not expand further on the many uses of NAC in other disease processes. However, listed at the end are several review articles detailing the numerous medicinal roles of NAC.
“Love, we say, is life; but love without hope and faith is agonizing death.” Elbert Hubbard
Use of NAC as a CAM in Parkinson’s: This is what we know about oxidative stress in Parkinson’s and the potential reasons why NAC could be used as a CAM in this disorder, it goes as follows (it’s also conveniently shown in the figure at the bottom):
1. Substantia nigra dopamine-producing neurons die from oxidative stress, which can lead to Parkinson’s.
“You cannot tailor-make the situations in life but you can tailor-make the attitudes to fit those situations.” Zig Ziglar
Scientific and clinical support for NAC in treating Parkinson’s: Content presented here is meant for informational purposes only and not as medical advice. Please remember that I am a basic scientist, not a neurologist, and any use of these compounds should be thoroughly discussed with your own personal physician. This is not meant to be an endorsement because it would be more valuable and important for your neurologist to be in agreement with the interpretation of these papers.
To evaluate the use of NAC in Parkinson’s, Katz et al. treated 12 patients with Parkinson’s with oral doses of NAC twice a day for two days. They studied three different doses of 7, 35, and 70 mg per kilogram. For example, in a person weighing 170 pounds, from a Weight Based Divided Dose Calculator (click here), this would be 540, 2700, and 5400 mg/day of NAC for 7, 35, and 70 mg/kg, respectively. Using cerebral spinal fluid (CSF), they measured levels of NAC, Cys, and GSH at baseline and 90 minutes after the last dose. Their results showed that there was a dose-dependent range of NAC as detected by CSF. And they concluded that oral administration of NAC produce biologically relevant CSF levels of NAC at the three doses examined; the doses of oral NAC were also well-tolerated. Furthermore, the patients treated with NAC had no change in either motor or cognitive function. Their conclusions support the feasibility of using oral NAC as a CAM therapy for treatment of Parkinson’s.
In a separate study, Monti at al presented some preliminary evidence for the use of NAC in Parkinson’s. The first part of their study consisted of a neuronal cell system that was pre-treated with NAC in the presence of the pesticide rotenone as a model of Parkinson’s. These results showed that with NAC there was more neuronal cell survival after exposure to rotenone compared to the rotenone-treated cells without NAC. The second part of the study was a small scale clinical evaluation using NAC in Parkinson’s. These patients were randomized and given either NAC or nothing and continued to use their traditional medical care. The patients were evaluated at the start and after three months of receiving NAC; they measured dopamine transporter binding and performed the unified Parkinson’s disease rating scale (UPDRS) to measure clinical symptoms. The clinical study revealed an increase in dopamine transporter binding in the NAC treatment group and no measurable changes in the control group. Furthermore UPDRS scores were significantly improved in the NAC treatment group compared to the control patient group. An interesting feature of this study was the use of pharmaceutical NAC, which is an intravenous (IV) medication and they also used 600 mg NAC tablets. The dose used was 50 mg per kg mixed into sterile buffer and infused over one hour one time per week. In the days they were not getting the IV NAC treatment, subjects took 600 mg NAC tablets twice per day.
Okay, what did I just say? I will try to summarize both of these studies in a more straightforward manner. The results above suggest that NAC crosses the blood brain barrier and does offer some anti-oxidative protection. In one study, this was shown by increased levels of both GSH and Cys dependent on the NAC dose. In another study, they directly measured dopamine transporter binding, which was increased in the presence of NAC. In the second study using a three month treatment strategy with NAC, there was a measurable positive effect on disease progression as measured by UPDRS scores.
“Our greatest weakness lies in giving up. The most certain way to succeed is always to try just one more time.” Thomas A. Edison
Potential for NAC in treating Parkinson’s: Overall, both studies described above suggest the possibility that NAC may be useful in treating Parkinson’s. However, in both cases these were preliminary studies that would require much larger randomized double-blind placebo-controlled trials to definitively show a benefit for using NAC in treating Parkinson’s. On a personal note, I have been taking 600 mg capsules of NAC three times a day for the past year with the hope that it is performing the task as outlined in this post. Using information from the first study that would be a NAC dose of 24 mg per kilogram body weight. In conclusion, the information described above suggests that NAC may be useful in regulating oxidative stress, one of the putative causes of Parkinson’s. As with all studies, time will tell if ultimately there is a benefit for using NAC in Parkinson’s.
“I am not an optimist, because I am not sure that everything ends well. Nor am I a pessimist, because I am not sure that everything ends badly. I just carry hope in my heart. Hope is the feeling that life and work have a meaning. You either have it or you don’t, regardless of the state of the world that surrounds you. Life without hope is an empty, boring, and useless life. I cannot imagine that I could strive for something if I did not carry hope in me. I am thankful to God for this gift. It is as big as life itself.” Vaclav Havel
Katz M, Won SJ, Park Y, Orr A, Jones DP, Swanson RA, Glass GA. Cerebrospinal fluid concentrations of N-acetylcysteine after oral administration in Parkinson’s disease. Parkinsonism Relat Disord. 2015;21(5):500-3. doi: 10.1016/j.parkreldis.2015.02.020. PubMed PMID: 25765302.
Martinez-Banaclocha MA. N-acetyl-cysteine in the treatment of Parkinson’s disease. What are we waiting for? Med Hypotheses. 2012;79(1):8-12. doi: 10.1016/j.mehy.2012.03.021. PubMed PMID: 22546753.
Monti DA, Zabrecky G, Kremens D, Liang TW, Wintering NA, Cai J, Wei X, Bazzan AJ, Zhong L, Bowen B, Intenzo CM, Iacovitti L, Newberg AB. N-Acetyl Cysteine May Support Dopamine Neurons in Parkinson’s Disease: Preliminary Clinical and Cell Line Data. PLoS One. 2016;11(6):e0157602. doi: 10.1371/journal.pone.0157602. PubMed PMID: 27309537; PMCID: PMC4911055.
Mosley RL, Benner EJ, Kadiu I, Thomas M, Boska MD, Hasan K, Laurie C, Gendelman HE. Neuroinflammation, Oxidative Stress and the Pathogenesis of Parkinson’s Disease. Clin Neurosci Res. 2006;6(5):261-81. doi: 10.1016/j.cnr.2006.09.006. PubMed PMID: 18060039; PMCID: PMC1831679.
Nolan YM, Sullivan AM, Toulouse A. Parkinson’s disease in the nuclear age of neuroinflammation. Trends Mol Med. 2013;19(3):187-96. doi: 10.1016/j.molmed.2012.12.003. PubMed PMID: 23318001.
Rushworth GF, Megson IL. Existing and potential therapeutic uses for N-acetylcysteine: the need for conversion to intracellular glutathione for antioxidant benefits. Pharmacol Ther. 2014;141(2):150-9. doi: 10.1016/j.pharmthera.2013.09.006. PubMed PMID: 24080471.
Taylor JM, Main BS, Crack PJ. Neuroinflammation and oxidative stress: co-conspirators in the pathology of Parkinson’s disease. Neurochem Int. 2013;62(5):803-19. doi: 10.1016/j.neuint.2012.12.016. PubMed PMID: 23291248.