Editing Homocysteine

[[Key concepts in ALS]]

''Plasma homocysteine (Hcy) levels were significantly increased in patients with amyotrophic lateral sclerosis (ALS) compared with healthy controls. ALS cases with shorter time to diagnosis presented higher Hcy levels, suggesting that higher Hcy may be linked to faster progression of the disease.'' {{#pmid:18195267|zoccolella2008}}

''Homocysteine (Hcy) exerts multiple neurotoxic mechanisms that have also been shown to be relevant in the pathogenesis of amyotrophic lateral sclerosis (ALS). We reviewed the published evidence to assess possible correlations between Hcy and ALS. A Medline literature search was performed to identify all studies on Hcy and ALS or motor neurons published from 1 January 1966 through 28 February 2009. Twelve studies (one in vitro, eight in vivo, and three studies on human subjects) were reviewed. The in vitro and in vivo animal studies showed that Hcy can damage motor neurons by inducing oxidative stress and stimulating excitotoxic receptors. In preliminary studies on human subjects, ALS subjects had higher median Hcy levels compared to age- and sex-matched controls. Higher Hcy levels were also correlated with a possible marker of disease progression. Finally, a short-term treatment with a high dose of methylcobalamin, which reduces Hcy levels, was effective in improving compound motor action potentials in patients with ALS. '''In conclusion, several types of evidence show that accumulation of Hcy may increase the risk and progression of motoneuronal degeneration. If this is confirmed, early interventions to decrease Hcy levels may be useful to modify ALS progression and possibly onset.''''' {{#pmid:19551535|zoccolella2010}}

''Homocysteine (HCY) is a pro-inflammatory sulphur-containing redox active endogenous amino acid, which concentration increases in neurodegenerative disorders including amyotrophic lateral sclerosis (ALS). A widely held view suggests that HCY could contribute to neurodegeneration via promotion of oxidative stress. However, the action of HCY on motor nerve terminals has not been investigated so far. We previously reported that oxidative stress inhibited synaptic transmission at the neuromuscular junction, targeting primarily the motor nerve terminals. In the current study, we investigated the effect of HCY on oxidative stress-induced impairment of transmitter release at the mouse diaphragm muscle. The mild oxidant H2O2 decreased the intensity of spontaneous quantum release from nerve terminals (measured as the frequency of miniature endplate potentials, MEPPs) without changes in the amplitude of MEPPs, indicating a presynaptic effect. Pre-treatment with HCY for 2 h only slightly affected both amplitude and frequency of MEPPs but increased the inhibitory potency of H2O2 almost two fold. As HCY can activate certain subtypes of glutamate N-methyl D-aspartate (NMDA) receptors we tested the role of NMDA receptors in the sensitizing action of HCY. Remarkably, the selective blocker of NMDA receptors, AP-5 completely removed the sensitizing effect of HCY on the H2O2-induced presynaptic depressant effect. Thus, '''at the mammalian neuromuscular junction HCY largely increases the inhibitory effect of oxidative stress on transmitter release, via NMDA receptors activation.''' This combined effect of HCY and local oxidative stress can specifically contribute to the damage of presynaptic terminals in neurodegenerative motoneuron diseases, including ALS.'' {{#pmid:26500495|bukharaeva2015}}

''BBB permeability was measured by Evans blue dye permeation and was found to be 25% greater in the Cbs(+/-) cortex compared with wild-type controls. Our study suggests an important toxic effect of elevated Hcy on brain microvessels and implicates Hcy in the disruption of the BBB.'' {{#pmid:16189268|kamath2006}}

''Hyperhomocysteinemia (HHcy) is a risk factor for neuroinflammatory and neurodegenerative diseases. '''Homocysteine (Hcy) induces redox stress, in part, by activating matrix metalloproteinase-9 (MMP-9), which degrades the matrix and leads to blood-brain barrier dysfunction. Hcy competitively binds to gamma-aminbutyric acid (GABA) receptors, which are excitatory neurotransmitter receptors.''' However, the role of GABA-A receptor in Hcy-induced cerebrovascular remodeling is not clear. '''We hypothesized that Hcy causes cerebrovascular remodeling by increasing redox stress and MMP-9 activity via the extracellular signal-regulated kinase (ERK) signaling pathway and by inhibition of GABA-A receptors, thus behaving as an inhibitory neurotransmitter.''' Hcy-induced reactive oxygen species production was detected using the fluorescent probe, 2'-7'-dichlorodihydrofluorescein diacetate. Hcy increased nicotinamide adenine dinucleotide phosphate-oxidase-4 concomitantly suppressing thioredoxin. Hcy caused activation of MMP-9, measured by gelatin zymography. The GABA-A receptor agonist, muscimol ameliorated the Hcy-mediated MMP-9 activation. In parallel, Hcy caused phosphorylation of ERK and selectively decreased levels of tissue inhibitors of metalloproteinase-4 (TIMP-4). Treatment of the endothelial cell with muscimol restored the levels of TIMP-4 to the levels in control group. ''';Hcy induced expression of iNOS and decreased eNOS expression, which lead to a decreased NO bioavailability.''' Furthermore muscimol attenuated Hcy-induced MMP-9 via ERK signaling pathway. '''These results suggest that Hcy competes with GABA-A receptors, inducing the oxidative stress transduction pathway and leading to ERK activation.''''' {{#pmid:19308943|tyagi2009}}

''Homocysteine also induced NF-kappaB activation that seemed associated with transglutaminase 2 up-regulation'' {{#pmid:18594946|curro2009}}

''Plasma thiols were significantly reduced during treatment with NAC: homocysteine by 45% (P < 0.0001), cysteinyl glycine by 24% (P < 0.0001) and cysteine by 11% (P = 0.0002). The high dose of NAC was well tolerated. In conclusion NAC has no effect on plasma Lp(a) levels while the reduction in homocysteine is considerable and-might be of clinical significance in cases with high plasma homocysteine levels.'' {{#pmid:8929261|wiklund1996}}


== References ==

[https://www.mendeley.com/community/alstuttu-homocysteine/documents/ Mendeley group]

[[Category:Lab abnormalities]]