Increased spinal cord NGF levels in rats with cobalamin (vitamin B12) deficiency

Vitamin B12 Deficiency and the Nervous System: Beyond Metabolic Decompensation-Comparing Biological Models and Gaining New Insights into Molecular and Cellular Mechanisms

Vitamin B12 (VitB12) is a micronutrient and acts as a cofactor for fundamental biochemical reactions: the synthesis of succinyl-CoA from methylmalonyl-CoA and biotin, and the synthesis of methionine from folic acid and homocysteine. VitB12 deficiency can determine a wide range of diseases, including nervous system impairments. Although clinical evidence shows a direct role of VitB12 in neuronal homeostasis, the molecular mechanisms are yet to be characterized in depth. Earlier investigations focused on exploring the biochemical shifts resulting from a deficiency in the function of VitB12 as a coenzyme, while more recent studies propose a broader mechanism, encompassing changes at the molecular/cellular levels. Here, we explore existing study models employed to investigate the role of VitB12 in the nervous system, including the challenges inherent in replicating deficiency/supplementation in experimental settings. Moreover, we discuss the potential biochemical alterations and ensuing mechanisms that might be modified at the molecular/cellular level (such as epigenetic modifications or changes in lysosomal activity). We also address the role of VitB12 deficiency in initiating processes that contribute to nervous system deterioration, including ROS accumulation, inflammation, and demyelination. Consequently, a complex biological landscape emerges, requiring further investigative efforts to grasp the intricacies involved and identify potential therapeutic targets.

Recreational Nitrous Oxide Abuse: Prevalence, Neurotoxicity, and Treatment

Nitrous oxide (N₂O), also known as "laughing gas," is a colorless, nonirritating gas. Clinically, it is widely used as an inhaled anesthetic, analgesic, and anxiolytic. In recent years, recreational abuse of N₂O has become increasingly common, especially among young adults and adolescents, but many of them lack awareness of the possible side effects associated with this drug. N₂O abuse can damage multiple systems, especially the nervous system, but the exact mechanism of N₂O toxicity remains controversial. At present, an increasing number of cases of nervous system damage caused by N₂O abuse have been reported both at home and abroad. Discontinuation of N₂O use and timely supplementation with vitamin B12 are essential for a good prognosis. Long-term abuse without timely treatment will eventually lead to irreversible neurological damage. In this article, we discuss the epidemiology of N₂O abuse, neurotoxicity mechanisms, clinical manifestations, relevant auxiliary examinations, treatments, and prognosis to improve social awareness of N₂O exposure risk, especially among users and clinicians.

Neurological disorders in vitamin B12 deficiency

The review discusses thesteps of vitamin B12 metabolism and its role in maintaining of neurological functions. The term "vitamin B12 (cobalamin)" refers to several substances (cobalamins) of a very similar structure. Cobalamin enters the body with animal products. On the peripherу cobalamin circulates only in binding with proteins transcobalamin I and II (complex cobalamin-transcobalamin II is designated as "holotranscobalamin"). Holotranscobalamin is absorbed by different cells, whereas transcobalamin I-binded vitamin B12 - only by liver and kidneys. Two forms of cobalamin were identified as coenzymes of cellular reactions which are methylcobalamin (in cytoplasm) and hydroxyadenosylcobalamin (in mitochondria). The main causes of cobalamin deficiency are related to inadequate intake of animal products, autoimmune gastritis, pancreatic insufficiency, terminal ileum disease, syndrome of intestinal bacterial overgrowth. Relative deficiency may be seen in excessive binding of vitamin B12 to transcobalamin I. Cobalamin deficiency most significantly affects functions of blood, nervous system and inflammatory response. Anemia occurs in 13-15% of cases; macrocytosis is an early sign. The average size of neutrophils and monocytes is the most sensitive marker of megaloblastic hematopoiesis. The demands in vitamin B12 are particularly high in nervous tissue. Hypovitaminosis is accompanied by pathological lesions both in white and gray brain matter. Several types of neurological manifestations are described: subacute combined degeneration of spinal cord (funicular myelinosis), sensomotor polyneuropathy, optic nerve neuropathy, cognitive disorders. The whole range of neuropsychiatric disorders with vitamin B12 deficiency has not been studied well enough. Due to certain diagnostic difficulties they are often regarded as "cryptogenic", "reactive", "vascular» origin. Normal or decreased total plasma cobalamin level could not a reliable marker of vitamin deficiency. In difficult cases the content of holotranscobalamin, methylmalonic acid / homocysteine, and folate in the blood serum should be investigated besides carefully analysis of clinical manifestations.

Global Burden Related to Nitrous Oxide Exposure in Medical and Recreational Settings: A Systematic Review and Individual Patient Data Meta-Analysis

The risk of adverse effects of nitrous oxide (N₂O) exposure is insufficiently recognized despite its widespread use. These effects are mainly reported through case reports. We conducted an individual patient data meta-analysis to assess the prevalence of clinical, laboratory, and magnetic resonance findings in association with N₂O exposure in medical and recreational settings. We calculated the pooled estimates for the studied outcomes and assessed the potential bias related to population stratification using principal component analysis. Eighty-five publications met the inclusion criteria and reported on 100 patients with a median age of 27 years and 57% of recreational users. The most frequent outcomes were subacute combined degeneration (28%), myelopathy (26%), and generalized demyelinating polyneuropathy (23%). A T2 signal hyperintensity in the spinal cord was reported in 68% (57.2–78.8%) of patients. The most frequent clinical manifestations included paresthesia (80%; 72.0–88.0%), unsteady gait (58%; 48.2–67.8%), and weakness (43%; 33.1–52.9%). At least one hematological abnormality was retrieved in 71.7% (59.9–83.4%) of patients. Most patients had vitamin B12 deficiency: vitamin B12 <150 pmol/L (70.7%; 60.7–80.8%), homocysteine >15 µmol/L (90.3%; 79.3–100%), and methylmalonic acid >0.4 µmol/L (93.8%; 80.4–100%). Consistently, 85% of patients exhibited a possibly or probably deficient vitamin B12 status according to the cB12 scoring system. N₂O can produce severe outcomes, with neurological or hematological disorders in almost all published cases. More than half of them are reported in the setting of recreational use. The N₂O-related burden is dominated by vitamin B12 deficiency. This highlights the need to evaluate whether correcting B12 deficiency would prevent N₂O-related toxicity, particularly in countries with a high prevalence of B12 deficiency.

White matter changes in chronic alcoholic liver disease: Hypothesized association and putative biochemical mechanisms

Advanced liver disease has long been associated with cerebral abnormalities. These abnormalities, termed acquired hepatocerebral degeneration, are typically visualized as T1 weighted hyperintensity on MRI in the deep gray matter of the basal ganglia. Recent reports, however, have demonstrated that a subset of patients with chronic alcoholic liver disease may also develop white matter abnormalities. Thus far, the morphology of these changes is not well characterized. Previous studies have described these changes as patchy, sporadic white matter abnormalities but have not posited localization of these changes to any particular white matter tracts. This paper hypothesizes that the white matter findings associated with advanced alcoholic liver disease localize to the corticocerebellar tracts. As an initial investigation of this hypothesis, 78 patients with a diagnosis of liver cirrhosis and an MRI showing clearly abnormal T1 weighted hyperintensity in the bilateral globus pallidus, characteristic of chronic liver disease, were examined for white matter signal abnormalities in the corticocerebellar tracts using FLAIR and T2 weighted images. The corticocerebellar tracts were subdivided into two regions: periventricular white matter (consisting of the sum of the centrum-semiovale and corona radiata), and lower white matter (consisting of the corona radiata, internal capsules, middle cerebral peduncles, middle cerebellar peduncles and cerebellum). As compared to matched controls, significantly greater signal abnormalities in both the periventricular white matter and lower white matter regions of the corticocerebellar tracts were observed in patients with known liver cirrhosis and abnormal T1 W hyperintensity in the globi pallidi. This difference was most pronounced in the lower white matter region of the corticocerebellar tract, with statistical significance of p<0.0005. Furthermore, the pathophysiologic mechanism underlying these changes remains unknown. This paper hypothesizes that the etiology of white matter changes associated with advanced liver disease may resemble that of white matter findings in subacute combined degeneration secondary to vitamin B12 deficiency. Specifically, significant evidence suggests that dysfunctional methionine metabolism as well as dysregulated cytokine production secondary to B12 deficiency play a major role in the development of subacute combined degeneration. Similar dysfunction of methionine metabolism and cytokine regulation is seen in alcoholic liver disease and is hypothesized in this paper to, at least in part, lead to white matter findings associated with alcoholic liver disease.

Decreased serum level of NGF in alcohol-dependent patients with declined executive function

The role of neurotrophic factors has been highlighted as a cause of decline in the cognitive function of alcohol-dependent patients. It is known that nerve-growth factor (NGF), one of the neurotrophins, is related to the growth and differentiation of nerve cells, as well as to a decline in cognitive function. The purpose of this study was to investigate the relationship between decreased NGF levels and cognitive decline in alcohol-dependent patients. The serum concentration of NGF was measured in 38 patients with chronic alcohol dependence, and several neuropsychological tests were also performed for cognitive function assessment. The results indicated a significant correlation between serum NGF level and the trail-making test part B, which evaluates executive function, but did not show a significant correlation with other cognitive function tests. An increased serum level of NGF was associated with a decreased completion time in the trail-making test B, and this finding indicates that a high serum level of NGF is related to greater executive function. This finding may imply a protective role of NGF in preventing neuron damage among patients with alcohol dependence. Larger controlled studies will be necessary in the future to investigate this issue further.

Molecular mechanisms of cognitive impairment in iron deficiency: alterations in brain-derived neurotrophic factor and insulin-like growth factor expression and function in the central nervous system

OBJECTIVE

The present review examines the relationship between iron deficiency and central nervous system (CNS) development and cognitive impairment, focusing on the cellular and molecular mechanisms related to the expression and function of growth factors, particularly the insulin-like growth factors I and II (IGF-I/II) and brain-derived neurotrophic factor (BDNF), in the CNS.

METHODS

Nutritional deficiencies are important determinants in human cognitive impairment. Among these, iron deficiency has the highest prevalence worldwide. Although this ailment is known to induce psychomotor deficits during development, the precise molecular and cellular mechanisms underlying these alterations have not been properly elucidated. This review summarizes the available information on the effect of iron deficiency on the expression and function of growth factors in the CNS, with an emphasis on IGF-I/II and BDNF.

RESULTS AND DISCUSSION

Recent studies have shown that specific growth factors, such as IGF-I/II and BDNF, have an essential role in cognition, particularly in processes involving learning and memory, by the activation of intracellular-signaling pathways involved in cell proliferation, differentiation, and survival. It is known that nutritional deficiencies promote reductions in systemic and CNS concentrations of growth factors, and that altered expression of these molecules and their receptors in the CNS leads to psychomotor and developmental deficits. Iron deficiency may induce these deficits by decreasing the expression and function of IGF-I/II and BDNF in specific areas of the brain.

Mechanistic Studies on the Reaction of Nitrocobalamin with Glutathione: Kinetic evidence for formation of an aquacobalamin intermediate

The essential but also toxic gaseous signaling molecule nitric oxide is scavenged by the reduced vitamin B12 complex cob(II)alamin. The resulting complex, nitroxylcobalamin (NO--Cbl(III)), is rapidly oxidized to nitrocobalamin (NO2Cbl) in the presence of oxygen; however it is unlikely that nitrocobalamin is itself stable in biological systems. Kinetic studies on the reaction between NO2Cbl and the important intracellular antioxidant, glutathione (GSH), are reported. In this study, a reaction pathway is proposed in which the β-axial ligand of NO2Cbl is first substituted by water to give aquacobalamin (H2OCbl+), which then reacts further with GSH to form glutathionylcobalamin (GSCbl). Independent measurements of the four associated rate constants k1, k-1, k2, and k-2 support the proposed mechanism. These findings provide insight into the fundamental mechanism of ligand substitution reactions of cob(III)alamins with inorganic ligands at the β-axial site.

Subacute Combined Degeneration of the Spinal Cord due to Different Etiologies and Improvement of MRI Findings

Subacute combined degeneration (SCD) is a rare neurological complication of vitamin B12 deficiency, characterized by demyelination of the dorsal and lateral spinal cord. Herein, we describe three cases, who presented with SCD, one related to reduced intake of vitamin B12 because of a vegetarian diet and two related to nitrous oxide exposure during surgery. MR images of our patients revealed symmetrical hyperintense signals in dorsal and lateral columns in T2 weighted series. After treatment with intramuscular B12 injections (1 mg daily for 2 weeks, once weekly thereafter for three months) all patients showed improvement of their symptoms. Abnormalities of the spinal cord on MRI resolved in three months. In conclusion, SCD either due to nitrous oxide exposure or due to reduced intake of vitamin B12 is a reversible condition, when detected and treated early.

Mechanistic studies on the reaction between cob(II)alamin and peroxynitrite: evidence for a dual role for cob(II)alamin as a scavenger of peroxynitrous acid and nitrogen dioxide

Peroxynitrite/peroxynitrous acid (ONOO(-)/ONOOH; pK(a(ONOOH)) =6.8) is implicated in multiple chronic inflammatory and neurodegenerative diseases. Both mammalian B(12)-dependent enzymes are inactivated under oxidative stress conditions. We report studies on the kinetics of the reaction between peroxynitrite/peroxynitrous acid and a major intracellular vitamin B(12) form, cob(II)alamin (Cbl(II)), using stopped-flow spectroscopy. The pH dependence of the reaction is consistent with peroxynitrous acid reacting directly with Cbl(II) to give cob(III)alamin (Cbl(III)) and (.)NO(2) , followed by a subsequent rapid reaction between (.)NO(2) and a second molecule of Cbl(II) to primarily form nitrocobalamin. In support of this mechanism, a Cbl(II)/ONOO(H) stoichiometry of 2:1 is observed at pH 7.35 and 12.0. The final major Cbl(III) product observed (nitrocobalamin or hydroxycobalamin) depends on the solution pH. Analysis of the reaction products in the presence of tyrosine-a well-established (.)NO(2) scavenger-reveals that Cbl(II) reacts with (.)NO(2) at least an order of magnitude faster than tyrosine itself. Given that protein-bound Cbl is accessible to small molecules, it is likely that enzyme-bound and free intracellular Cbl(II) molecules are rapidly oxidized to inactive Cbl(III) upon exposure to peroxynitrite or (.)NO(2).

Unexplained chronic cough and vitamin B-12 deficiency

BACKGROUND

Chronic cough is characterized by sensory neuropathy. Vitamin B-12 (cobalamin) deficiency (Cbl-D) causes central and peripheral nervous system damage and has been implicated in sensory neuropathy and autonomic nervous system dysfunction.

OBJECTIVE

We evaluated whether Cbl-D has a role in chronic, unexplained cough.

DESIGN

Laryngeal threshold (histamine concentration that provokes a 25% decrease in the midinspiratory flow), bronchial threshold (histamine concentration that provokes a 20% decrease in the forced expiratory volume in 1 s), and cough threshold (histamine concentration that causes ≥5 coughs) in response to an inhaled histamine were assessed in 42 patients with chronic, unexplained cough [27 Cbl-D patients and 15 patients without Cbl-D (Cbl-N)] before and after intramuscular injections of cobalamin for 2 mo. Laryngeal, bronchial, and cough hyperresponsiveness was diagnosed when histamine concentration thresholds were ≤8 mg/mL. Seven Clb-D and 3 Cbl-N patients underwent an oropharyngeal biopsy before treatment.

RESULTS

Cbl-D patients had a higher prevalence of laryngeal hyperresponsiveness than did Cbl-N patients (92.6% compared with 66.7%; P = 0.03), a thinner oropharyngeal epithelium [133.7 μm (95% CI: 95, 172 μm) compared with 230.8 μm (95% CI: 224, 237 μm); P = 0.002], a lower number of myelinated nerve fibers [2.25/mm(2) (95% CI: 1.8, 2.7/mm(2)) compared with 3.44/mm(2) (95% CI: 3, 3.8/mm(2)); P = 0.05], and a higher immunoreactive score for nerve growth factor (NGF) [6.7 (95% CI: 6, 7.3) compared with 2.8 (95% CI: 2.5, 3.1); P = 0.02]. After cobalamin supplementation, symptoms and laryngeal, bronchial, and cough thresholds were significantly improved in Cbl-D but not in Cbl-N patients.

CONCLUSIONS

This study suggests that Cbl-D may contribute to chronic cough by favoring sensory neuropathy as indicated by laryngeal hyperresponsiveness and increased NGF expression in pharyngeal biopsies of Cbl-D patients. Cbl-D should be considered among factors that sustain chronic cough, particularly when cough triggers cannot be identified.

Loss of epidermal growth factor regulation by cobalamin in multiple sclerosis

We investigated whether the physiological regulation of cerebrospinal fluid (CSF) levels of tumor necrosis factor (TNF)-alpha, epidermal growth factor (EGF), and nerve growth factor (NGF) by cobalamin (Cbl) that is observed in rat and human central nervous system (CNS) is retained in the CSF of patients with multiple sclerosis (MS). The study involved 158 MS patients grouped on the basis of the different clinical courses (relapsing-remitting (RR), secondary-progressive (SP), and primary-progressive (PP)), and 76 gender- and age-matched control patients with other non-inflammatory and non-neoplastic neurological diseases. The MS patients were therapy-free at the time of lumbar puncture. CSF Cbl and EGF were blindly measured by means of radioimmunoassays, and CSF TNF-alpha, and NGF by means of highly sensitive enzyme-linked immunosorbent assays. Serum EGF was also measured in 38 of the MS patients and 20 healthy controls. CSF Cbl levels were significantly higher (RR patients 27.9+/-9.7 pg/ml, p<0.0001 vs. C; SP patients 25.4+/-8 pg/ml, p<0.02 vs. C), and CSF TNF-alpha and EGF levels significantly lower in the patients with the RR (TNF-alpha 28.3+/-23.4 x 10(-3) pg/ml, p<0.0001 vs. C; EGF 129.9+/-44.8 pg/ml, p<0.02 vs. C) or SP (TNF-alpha 20.5+/-20.5 x 10(-3) pg/ml, p<0.001 vs. C; EGF 116.5+/-24.8 pg/ml, p<0.05 vs. C) clinical course than in controls (Cbl 21+/-4.6 pg/ml; TNF-alpha 75.6+/-34.7 x 10(-3) pg/ml; EGF 170.2+/-54.8 pg/ml). There were no differences in CSF NGF or serum EGF levels between any of the MS clinical courses and controls. Our results indicate that: (a) the positive Cbl-mediated regulation of myelino- and oligodendrocyte-trophic EGF is lost in the CSF of RR- or SP-MS patients; (b) the decrease in EGF levels in the CSF may be one factor impeding CNS remyelination in MS; and (c) the PP clinical course may have different pathogenetic mechanism(s) also on the basis of the molecules investigated in this study.

Vitamin-regulated cytokines and growth factors in the CNS and elsewhere

There is a growing awareness that natural vitamins (with the only exception of pantothenic acid) positively or negatively modulate the synthesis of some cytokines and growth factors in the CNS, and various mammalian cells and organs. As natural vitamins are micronutrients in the human diet, studying their effects can be considered a part of nutritional genomics or nutrigenomics. A given vitamin selectively modifies the synthesis of only a few cytokines and/or growth factors, although the same cytokine and/or growth factor may be regulated by more than one vitamin. These effects seem to be independent of the effects of vitamins as coenzymes and/or reducing agents, and seem to occur mainly at genomic and/or epigenetic level, and/or by modulating NF-kappaB activity. Although most of the studies reviewed here have been based on cultured cell lines, but their findings have been confirmed by some key in vivo studies. The CNS seems to be particularly involved and is severely affected by most avitaminoses, especially in the case of vitamin B(12). However, the vitamin-induced changes in cytokine and growth factor synthesis may initiate a cascade of events that can affect the function, differentiation, and morphology of the cells and/or structures not only in the CNS, but also elsewhere because most natural vitamins, cytokines, and growth factors cross the blood-brain barrier. As cytokines are essential to CNS-immune and CNS-hormone system communications, natural vitamins also interact with these circuits. Further studies of such vitamin-mediated effects could lead to vitamins being used for the treatment of diseases which, although not true avitaminoses, involve an imbalance in cytokine and/or growth factor synthesis.

Cobalamin in inflammation III - glutathionylcobalamin and methylcobalamin/adenosylcobalamin coenzymes: the sword in the stone? How cobalamin may directly regulate the nitric oxide synthases

Several mysteries surround the structure and function of the nitric oxide synthases (NOS). The NOS oxygenase domain structure is unusually open with a large area of solvent that could accommodate an unidentified ligand. The exact mechanism of the two-step five-electron monoxygenation of arginine to N(G)-hydroxy-L-arginine, thence to citrulline and nitric oxide (NO), is not clear, particularly as arginine/N(G)-hydroxy-L-arginine is bound at a great distance to the supposed catalytic heme Fe [III], as the anti-stereoisomer. The Return of the Scarlet Pimpernel Paper proposed that cobalamin is a primary indirect regulator of the NOS. An additional direct regulatory effect of the 'base-off' dimethylbenzimidazole of glutathionylcobalamin (GSCbl), which may act as a sixth ligand to the heme iron, promote Co-oriented, BH(4)/BH(3) radical catalysed oxidation of L-arginine to NO, and possibly regulate the rate of inducible NOS/NO production by the NOS dimers, is further advanced. The absence of homology between the NOS and methionine synthase/methylmalonyl CoA mutase may enable GSCbl to regulate both sets of enzymes simultaneously by completely separate mechanisms. Thus, cobalamin may exert central control over both pro-and anti-inflammatory systems.

Cobalamin-mediated regulation of transcobalamin receptor levels in rat organs

Total gastrectomy (TG) causes cobalamin (Cbl) deficiency followed by increases in tumor necrosis factor (TNF)-alpha levels in the spinal cord (SC) of the rat. In order to understand how Cbl deficiency may influence cell Cbl transport, we have measured by immunoblotting protein levels of the receptor for the Cbl-transcobalamin (TC) complex (TC-R) in both animal and cell models. TC-R protein levels were elevated in the total membranes of duodenal mucosa, kidneys, liver, and SC of rats made Cbl-deficient (Cbl-D) by means of TG or feeding with a Cbl-D diet. Postoperative Cbl-replacement treatment normalized the TC-R protein levels in each of the tested organs, regardless of whether this treatment was given during the first two post-TG or during the third and fourth post-TG mo. In Caco-2 cells, progressively increasing TNF-alpha concentrations supplemented to culture medium induced an up-regulation of TC-R protein levels. We provide the first evidence of the regulation of a Cbl-specific receptor by the vitamin itself in some rat organs.

Cobalamin deficiency-induced down-regulation of p75-immunoreactive cell levels in rat central nervous system

We investigated immunoreactivity for p75 neurotrophin receptor (NTR) in the spinal cord white matter and septum of rats made cobalamin-deficient (Cbl-D) by means of total gastrectomy or a Cbl-D diet. Cbl deficiency down-regulates p75NTR-immunoreactive cell levels in spinal cord white matter and septum with different time courses. On the whole, the spinal cord white matter seems to be more affected in terms of p75NTR-immunoreactive cells, most of which are astrocytes. The p75NTR-immunoreactive cell levels in the spinal cord white matter and septum normalized in rats treated with Cbl (scheme b) and killed 4 months after total gastrectomy. However, Western blot analysis of p75NTR in the spinal cords of Cbl-D rats shows increased p75NTR protein levels, which are resistant to Cbl replacement. These findings demonstrate that a neurotrophic vitamin (Cbl) positively regulates the levels of a neurotrophic receptor (p75NTR) (at least in terms of immunohistochemistry) in rat central nervous system, although the underlying mechanism(s) are still unknown.

New insights into the pathophysiology of cobalamin deficiency

Cobalamin-deficient (Cbl-D) central neuropathy in the rat is associated with a locally increased expression of neurotoxic tumour necrosis factor-alpha (TNF-alpha) and a locally decreased expression of neurotrophic epidermal growth factor (EGF). These recent findings suggest that cobalamin oppositely regulates the expression of TNF-alpha and EGF, and raise the possibility that these effects might be independent of its coenzyme function. Furthermore, adult Cbl-D patients have high levels of TNF-alpha and low levels of EGF in the serum and cerebrospinal fluid. Serum levels of TNF-alpha and EGF of cobalamin-treated patients normalize concomitantly with haematological disease remission. These observations suggest that cobalamin deficiency induces an imbalance in TNF-alpha and EGF levels in biological fluids that might have a role in the pathogenesis of the damage caused by pernicious anaemia.