Hi James,
I am very sorry to hear about your wife, the fact that you are here and looking for ways to slow or stop the progression of HD is awesome. I was moved by your story and decided to do some research on therapies for HD. I suffer from a much less serious serious inherited disease called psoriasis and hope that gene therapies become more available soon; obviously starting with serious disorders like HD. I certainly hope that you are able to find the best treatments for Jan, you seem like a sharp fellow!
I am not qualified to give medical advice and would like to remind anyone reading that it is their own responsibility to seek independent medical advice before taking any of the bellow mentioned substances. This does not constitute medical advice.
As you mentioned, Huntington's Disease (HD) is an inherited neurodegenerative disorder thought be caused by a CAG repeat expansion in the huntingtin gene, leading to polyglutamine expansion in the huntingtin protein [1]. The exact mechanism by which the mutant huntingtin causes HD remain illusive, but it is known that abnormalities in gene transcription, as well as mitochondrial function are involved and that these are accompanied by increases in oxidative damage. [1]
Targets for limiting degeneration = energy metabolism, inflammation, oxidative damage [1]
At this point therapies are being aimed at limiting the degenerative process, as you mentioned curing this disease will likely require gene therapy. In mouse models of HD small interfering RNA has however shown some promise for directly targeting the HD gene and its protein products [28][29].
Here are some of the methods under investigation for slowing degeneration:
Metabolic:
Evidence exists for a link between impaired metabolism and the pathogenesis of HD. Low expression of Peroxisome proliferator- activated receptor (PPAR) gamma coactivator PCG-1 alpha, is implicated in the mitochondrial dysfunction and oxidative damage in HD.[1][8] Haplotypes in the gene encoding HD PCG-1alpha influence the onset of HD, the mutant mHtt interferes with transcription of PCG-1aplha, leading to decreases of it and its targets, as well as BDNF[1]. This results in defective energy metabolism, antioxidant defence and ROS accumulation, leading to mitochondrial damage.[1] mHtt also disrupts the mitochondrial fission/fusion process, resulting in increased fission and vesicular transport interference.[1] This all results in decreased ATP production at nerve terminals and neuron death. [1]
Pharmacologic treatment with CoQ10, creatine, bezafibrate and nicotinamide increase PCG-1alpha and should improve neuron survival [1][9]. Thiazolidinediones, such as pioglitazone, have been used to increase PPARs and PCG-1 alpha and are neuroprotective in mouse models of HD. [1][10][11]. In mouse models of HD, pan-ppar agonist bezafibrate improved rotarod performance and survival also increased stratial atrophy and atrophy of stratial medium spiny neurons. [12] It also increased mitochondrial number and reduced malondialdehyde (MDA) in the stratium.[12]
NAD+ and the Sirtuins
Activation of SIRT1 results in the deacetylation of PGC-1alpha and increases activity[1]. Increased expression of SIRT1 has shown neuroprotective benefits in mouse models for HD and deficiency promotes the HD phenotype.[1][13][14].
Since sirtuins are NAD+ dependant deacetylases [13], one approach of activating them is by andminister NAD+ precursors. These include nicotinamide (Nam), nicotinic acid (NA), nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN). This also has the advantage of activating both SIRT1 and SIRT3, the latter induces superoxide dismutase 2 and mitochondrial reduced glutathione. [1] Increase Glutathione peroxidase expression has been shown to have neuroprotective effects in animal models of HD [1][23].
For further reading on the sirtuins and NAD+ in neurodegeneration and aging see [24], [25], [26], [27].
The Precursors
Nicotinamide, which is regular vitamin b3, may not be the best method for raising SIRT1 levels because at high doses it is inhibited by NAD+ in a negative feedback mechanism.[18] It has also been shown to inhibit SIRT1 at high concentrations and the rate limiting enzyme for its synthesis into NAD+ (NAMPT) declines with age [26]. That said, nicotinamide has been shown to increase BDNF and PCG-1 alpha in mouse models of HD.[19]
Nicotinamide mononucleotide has been used to increase NAD+ levels and aerobic metabolism in mice[17]. It is degraded into NR before it can enter cells[20] and NMN also seems to be less efficiently synthesized into NAD+ than NA or NR in muscle and liver tissues [16].
Nicotinamide riboside should 'in theory' be the most easily utilized by neurons because they are inefficient at de novo and salvage NAD+ synthesis [15]. However chronic NR administration failed to raise NAD+ levels significantly in the brain, which may be due to lower expression of Nrk2, which is responsible for NR metabolism into NAD+ [16].
Nicotinic acid has shown a 200 fold greater efficacy than Nam in raising NAD+ levels in glial cells.[15]. The rate limiting enzyme in NA biosynthesis to NAD+ is NAPRT, this enzyme is not inhibited by an NAD+ negative feedback bottleneck like NAMPT for Nam is [22]. Glial cells likely play a prominent role in supplying NAD+ to neurons.[15] Astrocytes (glial cells) outnumber neurons 5 fold and tile the entire central nervous system [21] Astrocystes can readily synthesize NAD+ from precursors like NA and Nam and transport NAD+ across the plasma membrane directly via the adenosine receptor P2XY7R [15]. Using precursors like NA gives the glia control of biosynthesis or restriction of NAD+. [15] It has shown efficacy in the treatment of pellagric dimentia and schizophrenia and increases brain NAD+ levels just 20 min after being injected into the brain.[15]
NA therefore seems like a promising NAD+ precursor and could possibly work in the brain. NR showed some disappointing results in the brain and is also more expensive than NA, costing close to $49.00 for 30 x 250mg, whereas NA cost about $5.00 for 100 x 250mg.
Oxidative Damage
CoQ10 – works within the electron transport chain and is a scavenger of free radicals. [1] It blocks 3-nitropropionic acid (3-NP) mediated striatal lesions and blocks DNA and lipid oxidation.[1] In a clinical trial for HD patients (CARE-HD), 600mg/day CoQ10 and ramacemide slowed progression of the disease.[6] A second clinical trial (2CARE) is currently underway using 2,400 mg /day doses, after an earlier study (Pre2care) showed that plasma CoQ10 levels plateau at levels above this dose [7].
MitoQ is a form of coenzyme Q linked to triphosphonium ions, this modification allows it to selectively accumulate within the mitochondria. [1]
SS31 and SS20 are novel peptide antioxidants which bind to the inner mitochondria and have been shown to be neuroprotective in mice [1] [2] [3].
Ways of activating the nuclear factor erythroid 2 related factor 2 / antioxidant response element (Nrf2/ARE) transcriptional pathway are also under investigation [1]. This mediates the expression of the antioxidant enzymes hemeoxygenase 1, NADPH-oxidoreductase, heat shock proteins, as well as enzymes that produce glutathione.[1] 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO)-methylamide was investigated for this purpose and did yield some positive results [2]. CDDO-methylamide and CDDO-trifluoroethylamide improved motor function in a mouse model of Hd [4] Dimethylfumarate, had some positive results in phase III clinical trials for multiple sclerosis and is approved for clinical use. [5]
Good luck with your research, what is your rational for using Dihexa?
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[9] Maat-Kievit A, Losekoot M, Van Den Boer-Van Den Berg H, et al. New problems in testing for
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[14] Jeong H, Cohen DE, Cui L, et al. Sirt1 mediates neuroprotection from mutant huntingtin by activation of the TORC1 and CREB transcriptional pathway. Nat Med 2012;18:159-165.
[15] Penberthy et al., The Importance of NAD in Multiple Sclerosis, Curr Pharm Des. PMC Mar 5, 2009.
[16] Canto et al., The NAD+ Precursor Nicotinamide Riboside Enhances Oxidative Metabolism and Protects against High-Fat Diet-Induced Obesity, Cell Metabolism 2012, Volume 15, Issue 6, p838–847.
[17] Sinclair et al., Declining NAD+ Induces a Pseudohypoxic State Disrupting Nuclear-Mitochondrial Communication during Aging, Cell 2013 155, Issue 7, p1624–1638.
[18] Bitterman et al., Inhibition of Silencing and Accelerated Aging by Nicotinamide, a Putative Negative Regulator of Yeast Sir2 and Human SIRT1, The Journal of Biological Chemistry 2002, 277, 45099-45107.
[19] Hathorn T, Snyder-Keller A, Messer A. Nicotinamide improves motor deficits and upregulates PGC-1alpha and BDNF gene expression in a mouse model of Huntington’s disease. Neurobiol Dis 2011;41:43-50.
[20] Nikiforov et al., Pathways and subcellular compartmentation of NAD biosynthesis in human cells: from entry of extracellular precursors to mitochondrial NAD generation, J Biol Chem. 2011 Jun 17;286(24):21767-78.
[21] Vinters et al., Astrocytes: Biology and Pathology, Acta Neuropathol. 2010 119(1): 7-35.
[22] Hara et al., Elevation of Cellular NAD Levels by Nicotinic Acid and Involvement of Nicotinic Acid Phosphoribosyltransferase in Human Cells, J. Biol. Chem. 2007, 282:24574-24582.
[23] Mason RP, Casu M, Butler N, et al. Glutathione peroxidase activ- ity is neuroprotective in models of Huntington’s disease. Nat Genet 2013;45:1249-1254.
[24] Wiley et al., NAD+ controls neural stem cell fate in the aging brain, The EMBO JournalVolume 33, Issue 12, pages 1289–1291, 17 June 2014.
[25] Guarente et al., Sirtuin deacetylases in neurodegenerative diseases of aging, Cell Research (2013) 23:746–758. 21 May 2013
[26] Imai et al., NAD+ and sirtuins in aging and disease, Volume 24, Trends in Cell Biology, Issue 8, August 2014, Pages 464–471
[27] Herskovitis et al., SIRT1 in Neurodevelopment and Brain Senescence, Neuron Volume 81, Issue 3, 5 February 2014, Pages 471–483
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[29] Godinho BM, Ogier JR, Darcy R, O’Driscoll CM, Cryan JF. Self- assembling modified b-cyclodextrin nanoparticles as neuronal siRNA delivery vectors: focus on Huntington’s disease. Mol Pharm 2013;10:640-649.
Edited by Phoenicis, 02 August 2014 - 10:19 PM.