Polyneuropathy due to cobalamin deficiency in the rat

Electrophysiological profile of serum vitamin B12 levels, correlation with serum methylmalonic acid levels, and determination of subclinical peripheral nerve involvement

Background/Aim: Vitamin B12 is essential for normal neural conduction in peripheral nerves. This study aimed to investigate the electrophysiological profile for varying degrees of serum B12 levels and to determine whether a correlation existed between electrophysiological profiles and serum methylmalonic acid (MMA) levels. Also, determination of subclinical peripheral nerve involvement with cold administration was planned in serum B12 levels. Methods: A total of 101 (63 females, 38 males) subjects with known serum vitamin B12 levels were selected randomly from the neurology outpatient clinic for this study. The subjects were divided into three groups based on the serum total Vitamin B12 levels: (1) B12 deficiency (<126 pg/mL), (2) low B12 (126-250 pg/mL), and (3) normal B12 (250–500 pg/mL). Serum MMA and nerve conduction studies (NCS) were assessed and compared between the three groups. After the cooling procedure was applied to the ulnar and sural nerves, NCS was repeated. Results: There were 13 subjects in the B12 deficiency group, 44 subjects in the low B12 group, and 44 subjects in the normal group. We found that ulnar sensory nerve action potential amplitudes were significantly decreased (P = 0.009), ulnar F latency (P = 0.003; P < 0.001)) was prolonged, and peroneal combined muscle action potential amplitudes decreased (P = 0.026) in the B12 deficiency when compared with the low and normal B12 groups. Sural nerve amplitude and conduction velocities were found to be significantly abnormal after the cold application in all groups (P < 0.001). The increase in sural nerve sensory nerve amplitude potentials (SNAP) amplitudes was higher in the B12 deficiency group than in the other groups. Mean serum MMA levels were high in all groups. A correlation of nerve conduction study (NCS) changes with serum vitamin B12 and MMA was not observed in the groups after cold application. Conclusion: Vitamin B12 deficiency may cause subclinical sensorial and motor axonal nerve conduction changes. Nerve conduction changes may not always reach pathological values based on electrophysiological studies but may be detected after cooling administration even in the normal serum B12 levels. A correlation between serum MMA and vitamin B12 levels was found. Therefore, serum levels of vitamin B12, which is important for nerve conduction, should be carefully evaluated in clinical practice.

Evaluation of macular, retinal nerve fiber layer and choroidal thickness by optical coherence tomography in children and adolescents with vitamin B12 deficiency

PURPOSE

To investigate macular, Retinal Nerve Fiber Layer (RNFL) and choroidal thickness in children and adolescents with vitamin B₁₂ deficiency and no neurological examination finding.

METHODS

The study group includes of thirty-three children aged 8-17 years who were brought to the Pediatric outpatient clinic with the symptoms of fatigue and forgetfulness and whose Vitamin B₁₂ levels were detected < 200 pg/ml. The control group was the 30 children and adolescents applied to the same policlinic with various symptoms and whose Vitamin B₁₂ levels were found normal. Children and adolescents with chronic systemic/ocular disease history and myopia or hyperopia more than 4 diopters were not included in both groups. Spectral Domain-Optical Coherence Tomography (SD-OCT) was used for measurements.

RESULTS

Mean Macular thickness value was 261.2 ± 17.6 in the Vitamin B₁₂ deficiency group and 267.7 ± 17.4 in the control group. Mean value of Retinal Nerve Fiber Layer (RNFL) thickness was 103.5 ± 7.5 in the Vitamin B₁₂ deficiency group and 104.3 ± 8.9 in the control group. The mean values of Choroidal thickness were 360.1 ± 59.8 and 316.9 ± 95.4 in Vitamin B₁₂ deficiency and control groups, respectively. There was a statistically significant increase in choroidal thickness in Vitamin B₁₂ deficiency group compared to controls.

CONCLUSION

Statistically significant increase in the Choroidal thicknesses of children and adolescents with Vitamin B₁₂ deficiency is important in terms of shedding light on studies that will contribute to a better understanding of the relationship between vitamin B₁₂ and inflammation.

CLINICAL TRIAL REGISTRATION

This study is an observational study.

Vitamin B12 deficiency as a cause of severe neurological symptoms in breast fed infant - a case report

Background

Vitamin B₁₂ (cobalamin, cbl) deficiency in children is rare and may occurs in exclusively breast fed infants of mothers on vegetarian or vegan diet with lack of appropriate supplementation. The clinical manifestation of vitamin B12 deficiency include neurological disorders, megaloblastic anemia and failure to thrive. Routine and commonly used laboratory tests such as cell blood count (CBC) or serum vitamin B₁₂ level are sufficient for appropriate diagnosis. Typical therapy is based on intramuscular cobalamin injections. Early diagnosis and early onset of treatment are crucial factors for long-term prognosis of patients as the duration of deficiency may be correlated with the development of long lasting changes in the nervous system.

The purpose of this article is to present influence of maternal vitamin B₁₂ deficiency as a cause of infant psychomotor retardation.

Case presentation

We report the case of a 7 months old girl whose parents sought medical advice due to pathological somnolence and developmental regression of their daughter with onset approximately 2 months prior to the visit. Following several diagnostic tests it was determined that the infant’s symptoms were due to vitamin B₁₂ deficiency which was secondary to the mother’s latent Addison-Biermer disease. Apart from neurological symptoms the infant also showed megaloblastic anemia which is typical to cobalamin deficiencies. Intramuscular vitamin B₁₂ supplementation resulted in instant improvement of the patient’s general condition and blood morphology. Unfortunately, psychological examination indicated long-term psychomotor retardation due to delayed diagnosis of B₁₂ deficiency.

Conclusions

Vitamin B₁₂ levels should be considered during differential diagnosis of neurological symptoms in exclusively breast-fed infants especially if they co-exist with megaloblastic anemia and psychomotor retardation.

Vitamin B12 status does not influence central motor conduction time in asymptomatic elderly people: a transcranial magnetic stimulation study

INTRODUCTION

Vitamin B12 deficiency causes neurologic and psychiatric disease, especially in older adults. Subacute combined degeneration is characterized by damage to the posterior and lateral spinal cord affecting the corticospinal tract.

OBJECTIVE

To test corticospinal tract projections using motor evoked potentials (MEPs) by transcranial magnetic stimulation (TMS) in asymptomatic older adults with low vitamin B12 (B12) levels.

METHODS

Cross-sectional study of 53 healthy older adults (>70 years). MEPs were recorded in the abductor pollicis brevis and tibialis anterior muscles, at rest and during slight tonic contraction. Central motor conduction time (CMCT) was derived from the latency of MEPs and peripheral motor conduction time (PMCT). Neurophysiological variables were analyzed statistically according to B12 status.

RESULTS

Median age was 74.3 ± 3.6 years (58.5% women). Twenty-six out of the 53 subjects had low vitamin B12 levels (B12 < 221 pmol/l). MEPs were recorded for all subjects in upper and lower extremities. There were no significant differences in either latency or amplitude of MEPs and CMCT between low and normal B12 groups. There was a significant PMCT delay in the lower extremities in the low B12 group (p = 0.014).

CONCLUSIONS

No subclinical abnormality of the corticospinal tract is detected in asymptomatic B12-deficient older adults. The peripheral nervous system appears to be more vulnerable to damage attributable to this vitamin deficit. The neurophysiological evaluation of asymptomatic older adults with lower B12 levels should be focused mainly in peripheral nervous system evaluation.

Assessment of peripapillary retinal nerve fiber layer thickness in children with vitamin B12 deficiency

PURPOSE

Vitamin B(12) deficiency is a worldwide problem. It affects all ages, including children. It is one of the most common nutritional disorders and can cause harmful effects on the nervous system. In this study, we compared the peripapillary retinal nerve fiber layer thickness (RNFLT) in a healthy control group with children with vitamin B(12) deficiency. In our study, we aimed to evaluate the effect of vitamin B(12) deficiency on the RNFLT in children with the optical coherence tomography (OCT) method.

METHODS

Sixty-six children with a diagnosis of vitamin B(12) deficiency (patient group) and 66 age- and sex-matched healthy children (control group) were enrolled in this prospectively designed study. Blood counts, vitamin B(12) levels, folate levels, and full biochemical parameters were obtained for all the subjects in each group. Peripapillary RNFLT measurements were performed with Cirrus HD spectral domain OCT.

RESULTS

The thickness of the superior retinal nerve fiber layer (RNFL) in the vitamin B(12) deficiency group was significantly lower than that of the control group (p = 0.037). Although the average thickness of the RNFL was lower in the patient group, there was no statistically significant differences (p = 0.216). In the vitamin B(12) deficiency group, the average RNFL thickness and the superior RNFL thickness were significantly correlated with vitamin B(12) levels ((r1) = 0.353, (p1) < 0.004 and (r2) = 0.416, (p2) = 0.001, respectively).

CONCLUSION

Our study showed that a deficiency in vitamin B(12), elsewhere it is important for the development of the central nervous system, is associated with a reduction in the thickness of the superior RNFL.

Clinical, nerve conduction and nerve biopsy study in vitamin B12 deficiency neurological syndrome with a short-term follow-up

OBJECTIVE

The frequency and type of neuropathy in vitamin B12 deficiency neurological syndrome (VBDNS) is controversial. This study reports the frequency and type of nerve dysfunction in VBDNS using nerve conduction and sural nerve biopsy and its response to treatment.

METHOD

Sixty-six patients with VBDNS diagnosed on the basis of low serum vitamin B12 level and/or megaloblastic bone marrow were subjected to clinical evaluation, hemoglobin, mean corpuscular volume, thyroid function test, HIV serology, and vasculitic profile. Peroneal motor and sural sensory nerve conduction studies were done. Sural nerve biopsy was done in six patients. The patients were treated with cyanocobalamin injection and followed up clinically and with nerve conduction study at 3 and 6 months.

RESULTS

The median age of the patients was 46 (12-80) years and 11 patients were females. The duration of symptoms was 1-96 (median 7) months. Clinical features of neuropathy were present in 46 (69.7%) patients and nerve conduction was abnormal in 36 (54.5%) patients. On nerve conduction study, 8 (22.2%) patients had axonal, 4 (11.1%) had demyelinating, and 24 (66.7%) had mixed features. Nerve biopsy revealed acute axonal degeneration in early stage and chronic axonopathy with demyelination in the late stages of disease. The nerve conduction parameters improved at 6 months along with clinical recovery.

CONCLUSION

Nearly 70% patients with VBDNS had evidence of neuropathy which is mainly axonal with some demyelinating features.

[Metabolic and nutritional neuropathies: update in diabetes, vitamin B12 and copper deficiency]

Metabolic and deficiency neuropathies retain a growing interest because of their important prevalence. The dismemberment of diabetic neuropathies is proceeded, letting distinct pathophysiological mechanisms appear. So, even if glycaemic control remains determining for preventing the neuropathy associated with type 1 diabetes, it seems to have a restricted role with type 2 diabetes in which other metabolic factors are involved. The diagnosis of neuropathy due to B12 vitamin deficiency remains a real challenge for the clinician. Indeed, positive and negative predictive values of serum B12 and metabolites assay are weak, only a good therapeutic response allows a reliable diagnostic. It is so recommended to know the clinical and contextual particularities of this etiology in order to not delay the vitamin substitution, determining for the functional outcome. Finally, copper deficiency remains an unknown cause of neuropathy which is suitable to raise in case of malabsorption but also and especially in case of abuse of dental adhesive rich in zinc.

Assessment of peripapillary retinal nerve fiber layer thickness in children with vitamin B12 deficiency

PURPOSE

Vitamin B(12) deficiency is a worldwide problem. It affects all ages, including children. It is one of the most common nutritional disorders and can cause harmful effects on the nervous system. In this study, we compared the peripapillary retinal nerve fiber layer thickness (RNFLT) in a healthy control group with children with vitamin B(12) deficiency. In our study, we aimed to evaluate the effect of vitamin B(12) deficiency on the RNFLT in children with the optical coherence tomography (OCT) method.

METHODS

Sixty-six children with a diagnosis of vitamin B(12) deficiency (patient group) and 66 age- and sex-matched healthy children (control group) were enrolled in this prospectively designed study. Blood counts, vitamin B(12) levels, folate levels, and full biochemical parameters were obtained for all the subjects in each group. Peripapillary RNFLT measurements were performed with Cirrus HD spectral domain OCT.

RESULTS

The thickness of the superior retinal nerve fiber layer (RNFL) in the vitamin B(12) deficiency group was significantly lower than that of the control group (p = 0.037). Although the average thickness of the RNFL was lower in the patient group, there was no statistically significant differences (p = 0.216). In the vitamin B(12) deficiency group, the average RNFL thickness and the superior RNFL thickness were significantly correlated with vitamin B(12) levels ((r1) = 0.353, (p1) < 0.004 and (r2) = 0.416, (p2) = 0.001, respectively).

CONCLUSION

Our study showed that a deficiency in vitamin B(12), elsewhere it is important for the development of the central nervous system, is associated with a reduction in the thickness of the superior RNFL.

Cobalamin and normal prions: a new horizon for cobalamin neurotrophism

It is known that cobalamin (Cbl) deficiency damages myelin by increasing tumor necrosis factor (TNF)-α and decreasing epidermal growth factor (EGF) levels in rat central nervous system (CNS), and affects the peripheral nervous system (PNS) morphologically and functionally. It is also known that some polyneuropathies not due to Cbl deficiency are connected with increased TNF-α levels, and that various cytokines (including TNF-α) and growth factors regulate the in vitro synthesis of normal prions (PrP(C)s). Given that there is extensive evidence that PrP(C)s play a key role in the maintenance of CNS and PNS myelin, we investigated whether the PrP(C) octapeptide repeat (OR) region is involved in the pathogenesis of rat Cbl-deficient (Cbl-D) polyneuropathy. After intracerebroventricularly administering antibodies (Abs) against the OR region (OR-Abs) to Cbl-D rats to prevent myelin damage and maximum nerve conduction velocity (MNCV) abnormalities, and PrP(C)s to otherwise normal rats to reproduce PNS Cbl-D-like lesions, we measured PrP(C) levels and MNCV of the sciatic and tibial nerves. PrP(C) and TNF-α levels were increased in sciatic and tibial nerves of Cbl-D and saline-treated rats, and the OR-Abs normalized the myelin ultrastructure, TNF-α levels, and MNCV values of the sciatic and tibial nerves of Cbl-D rats. The same peripheral nerves of the otherwise normal PrP(C)-treated rats showed typical Cbl-D myelin lesions, significantly increased TNF-α levels, and significantly decreased MNCV values. These findings demonstrate that Cbl deficiency induces excess PrP(C)s and thereby excess OR regions, which seem to be responsible for the PNS myelin damage, as has recently been found in the case of CNS myelin damage [66]. Furthermore, excess TNF-α is also involved in the pathogenesis of Cbl-D polyneuropathy. In conclusion, we have extended the list of prion diseases by adding one caused by excess PrP(C)s and the polyneuropathies related to excess TNF-α.

Interrelationships of undernutrition and neurotoxicity: food for thought and research attention

The neurotoxic actions of chemical agents on humans and animals are usually studied with little consideration of the subject's nutritional status. States of protein-calorie, vitamin and/or mineral undernutrition are associated with a range of neurodevelopmental, neurological and psychiatric disorders, commonly with involvement of both the central and the peripheral nervous system. Undernutrition can modify risk for certain chemical-induced neurologic diseases, and in some cases undernutrition may be a prerequisite for neurotoxicity to surface. In addition, neurologic disease associated with undernutrition or neurotoxicity may show similarities in clinical and neuropathological expression, especially in the peripheral nervous system. The combined effects of undernutrition and chemical neurotoxicity are most relevant to people with low incomes who experience chronic hunger, parasitism and infectious disease, monotonous diets of plants with neurotoxic potential (notably cassava), environmental pollution from rapid industrial development, chronic alcohol abuse, or prolonged treatment with certain therapeutic drugs. Undernutrition alone or in combination with chemical exposure is also important in high-income societies in the setting of drug and alcohol abuse, old age, food faddism, post-bariatric surgery, and drug treatment for certain medical conditions, including cancer and tuberculosis. The nutritional demands of pregnancy and lactation increase the risk of fetal and infant undernutrition and chemical interactions therewith.

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.

Activation of the liver X receptor increases neuroactive steroid levels and protects from diabetes-induced peripheral neuropathy

Neuroactive steroids act in the peripheral nervous system as physiological regulators and as protective agents for acquired or inherited peripheral neuropathy. In recent years, modulation of neuroactive steroids levels has been studied as a potential therapeutic approach to protect peripheral nerves from damage induced by diabetes. Nuclear receptors of the liver X receptor (LXR) family regulate adrenal steroidogenesis via their ability to control cholesterol homeostasis. Here we show that rat sciatic nerve expresses both LRXα and β isoforms and that these receptors are functional. Activation of liver X receptors using a synthetic ligand results in increased levels of neurosteroids and protection of the sciatic nerve from neuropathy induced by diabetes. LXR ligand treatment of streptozotocin-treated rats increases expression in the sciatic nerve of steroidogenic acute regulatory protein (a molecule involved in the transfer of cholesterol into mitochondria), of the enzyme P450scc (responsible for conversion of cholesterol into pregnenolone), of 5α-reductase (an enzyme involved in the generation of neuroactive steroids) and of classical LXR targets involved in cholesterol efflux, such as ABCA1 and ABCG1. These effects were associated with increased levels of neuroactive steroids (e.g., pregnenolone, progesterone, dihydroprogesterone and 3α-diol) in the sciatic nerve, and with neuroprotective effects on thermal nociceptive activity, nerve conduction velocity, and Na(+), K(+)-ATPase activity. These results suggest that LXR activation may represent a new pharmacological avenue to increase local neuroactive steroid levels that exert neuroprotective effects in diabetic neuropathy.

[Effect of Panax ginseng components on the differentiation of mouse embryonic stem cells into cardiac-like cells]

Bioactive compounds that may control the specific differentiation from mouse embryonic stem (ES) cells into cardiac-like cells have been screened from herbal medicines. Among seven preparations, Panax ginseng was found to promote the differentiation into beating cells and to sustain their beating for longer than the control. Active compounds were found in its water-soluble fraction. Although they were not isolated, their candidates were surveyed in 42 compounds selected from the database of P. ginseng. Finally we found that vitamin B12 (VB12) and methionine were active. VB12 accelerated the differentiation into beating cells and made the beating rate constantly 100%. Moreover, VB12 was effective in the recovery of beating that was inhibited by spermine action. The mechanism of action of VB12 is discussed in termo of the relevance of intercellular electrical signal transduction.

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.

Morphometric analysis of the fiber populations of the rat sciatic nerve, its spinal roots, and its major branches

Correspondence between the nerve composition and the functional characteristics of its fiber populations is not always evident. To investigate such correspondence and to give a systematic picture of the morphology of the rat hind limb nerves, extensive morphometric study was performed on the sciatic nerve, its founding dorsal and ventral spinal roots, and its major branches. Nerve histology was examined in semithin sections via microscopic image analysis. Variation in the density of myelinated fibers, fiber interspace, and nerve cross-sectional area was studied in individual roots and nerves. In the dorsal roots, fiber numbers and cross-sectional areas were directly linearly proportional to the spinal root level number. Constituent fiber populations were identified using multicomponent lognormal models, and an optimal model for every nerve or root was selected by using an information theoretic approach. For the dorsal and ventral roots and the sciatic and peroneal nerves, optimal fiber population models consisted of three components, whereas, for the tibial and sural nerves, two components were optimal. Functional identities of the revealed fiber populations were established by using calculations of corresponding conduction velocities according to Arbuthnott et al. (J. Physiol. [1980] 308:125-157) and anatomical considerations. It is anticipated that morphological parameters established in this study would advance the development of neural prostheses in humans. The proximodistal correspondences among the fiber populations of different nerves were established by parametric statistical comparisons. The proposed approach provides a conceptual framework for understanding the comparative anatomy of the peripheral nerves and spinal roots and can be further applied in other species.

Increased levels of the CD40:CD40 ligand dyad in the cerebrospinal fluid of rats with vitamin B12(cobalamin)-deficient central neuropathy

The levels of the soluble (s) CD40:sCD40 ligand (L) dyad, which belongs to the tumor necrosis factor (TNF)-alpha:TNF-alpha-receptor superfamily, are significantly increased in the cerebrospinal fluid (CSF), but not the serum of cobalamin (Cbl)-deficient (Cbl-D) rats. They were normalized or significantly reduced after treatment with Cbl, transforming growth factor-beta1 or S-adenosyl-L-methionine, and the normal myelin ultrastructure of the spinal cord was concomitantly restored. The concomitance of the two beneficial effects of these treatments strongly suggests that the increases in CSF sCD40:sCD40L levels may participate in the pathogenesis of purely myelinolytic Cbl-D central neuropathy in the rat. In keeping with this, an anti-CD40 treatment prevented myelin lesions.

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

We have recently demonstrated that the neuropathological morphological alterations caused by cobalamin (Cbl) deficiency in the rat central nervous system are related to the vitamin's inability to modulate the synthesis of some neurotoxic and neurotrophic agents in opposite directions. In the present study, we measured nerve growth factor (NGF) levels in the spinal cord (SC) and cerebrospinal fluid (CSF) of rats made Cbl-deficient (Cbl-D) by means of total gastrectomy (TG) or a Cbl-D diet. In both cases, Cbl deficiency increased SC and CSF NGF levels after the appearance of myelinolytic lesions in the SC white matter (SCWM) (i.e. after the second post-TG month), and these changes were normalised by Cbl treatment in the 4-month-totally-gastrectomised (TGX) rats. Intracerebroventricular (i.c.v.) anti-NGF-antibody treatment prevented the onset of the myelinolytic SCWM lesions in the 2-month-TGX rats (i.e. when SC and CSF NGF levels are still normal) and normalised the ultrastructure of the SCWM in the 4-month-TGX rats, which was however worsened by the i.c.v. administration of NGF. These findings demonstrate that: (i) Cbl deficiency increases SC and CSF NGF levels; and (ii) endogenous NGF seems to play a noxious role in the progression of rat Cbl-D central neuropathy.

Cobalamin (vitamin B12) in subacute combined degeneration and beyond: traditional interpretations and novel theories

Subacute combined degeneration (SCD) is a neuropathy due to cobalamin (Cbl) (vitamin B(12)) deficiency acquired in adult age. Hitherto, the theories advanced to explain the pathogenesis of SCD have postulated a causal relationship between SCD lesions and the impairment of either or both of two Cbl-dependent reactions. We have identified a new experimental model, the totally gastrectomized rat, to reproduce the key morphological features of the disease [spongy vacuolation, intramyelinic and interstitial edema of the white matter of the central nervous system (CNS), and astrogliosis], and found new mechanisms responsible for the pathogenesis of SCD: the neuropathological lesions in TGX rats are not only due to mere vitamin withdrawal but also to the overproduction of the myelinolytic tumor necrosis factor (TNF)-alpha and the reduced synthesis of the two neurotrophic agents, epidermal growth factor (EGF) and interleukin-6. This deregulation of the balance between TNF-alpha and EGF synthesis induced by Cbl deficiency has been verified in the sera of patients with pernicious anemia (but not in those with iron-deficient anemia), and in the cerebrospinal fluid (CSF) of SCD patients. These new functions are not linked to the coenzyme functions of the vitamin, but it is still unknown whether they involve genetic or epigenetic mechanisms. Low Cbl levels have also been repeatedly observed in the sera and/or CSF of patients with Alzheimer's disease or multiple sclerosis, but whether Cbl deficit plays a role in the pathogenesis of these diseases is still unclear.

Effects of vitamin B12 and folate deficiencies on DNA methylation and carcinogenesis in rat liver

Deficiencies of the major dietary sources of methyl groups, methionine and choline, lead to the formation of liver cancer in rodents. The most widely investigated hypothesis has been that dietary methyl insufficiency results in abnormal DNA methylation. Vitamin B12 and folate also play important roles in DNA methylation since these two coenzymes are required for the synthesis of methionine and S-adenosyl methionine, the common methyl donor required for the maintenance of methylation patterns in DNA. The aim of this study was to review the effects of methyl-deficient diets on DNA methylation and liver carcinogenesis in rats, and to evaluate the role of vitamin B12 status in defining carcinogenicity of a methyl-deficient diet. Several studies have shown that a methyl-deficient diet influences global DNA methylation. Evidence from in vivo studies has not clearly established a link between vitamin B12 and DNA methylation. We reported that vitamin B12 and low methionine synthase activity were the two determinants of DNA hypomethylation. Choline- or choline/methionine-deficient diets have been shown to cause hepatocellular carcinoma in 20-50% of animals after 12-24 months. In contrast, the effect of vitamin B12 withdrawal, in addition to choline, methionine and folate, induced hepatocellular carcinoma in less than 5% of rats.

New Basis of the Neurotrophic Action of Vitamin B12

Over the last few years we have reproduced all of the key morphological and biochemical features of human subacute combined degeneration in the central nervous system and peripheral nervous system of rats made cobalamin-deficient by means of total gastrectomy or a chronic cobalamin-deficient diet. We have also recently clarified the pathogenesis of experimental subacute combined degeneration induced in the rat by cobalamin deprivation. The results of our studies strongly support the notion that cobalamin plays a pivotal role in regulating the balance of the network of cytokines and growth factors in the central nervous system of the rat. We have demonstrated that cobalamin tightly regulates the central nervous system synthesis and/or the cerebrospinal fluid level of two cytokines, tumor necrosis factor-alpha and interleukin-6, and a growth factor, epidermal growth factor. Of these neuroactive agents, one, tumor necrosis factor-alpha, is neurotoxic, whereas the others are neurotrophic. Therefore, it becomes clear that cobalamin-deficient central neuropathy is caused not by the withdrawal of the vitamin, but reflects a locally increased production of neurotoxic agents, combined with the locally decreased production of neurotrophic agents.

Decreased GFAP-mRNA expression in spinal cord of cobalamin-deficient rats

We have demonstrated previously that chronic vitamin B12 [cobalamin (Cbl)] deficiency preferentially affects glial cells in the rat central nervous system (CNS) and severely affects peripheral glial cells independently of and concomitantly with the central neuropathy. In this study, we determined the mRNA levels for myelin basic protein (MBP) and glial fibrillary acidic protein (GFAP) in different CNS areas of rats made Cbl-deficient by total gastrectomy, as well as the mRNA levels for glycoprotein Po and peripheral myelin protein (PMP)22 in the sciatic nerve. GFAP-mRNA levels were significantly decreased in the spinal cord (SC) and hypothalamus, but not in the cortex, hippocampus, or striatum of totally gastrectomized (TGX) rats. No differences in GFAP protein levels were found in the SC and hypothalamus of the TGX rats treated or not with Cbl. MBP-mRNA levels were significantly decreased only in the hypothalamus, and the levels of mRNA for both glial markers returned to normal with Cbl replacement therapy. The levels of mRNA for the various myelin proteins in the sciatic nerve were not modified by Cbl deficiency. These results demonstrate that: a) the neurotrophic action of Cbl in rat CNS occurs in a zonal manner; and b) Cbl deficiency does not affect myelin synthesis (with the sole exception of the hypothalamus).

Cobalamin (vitamin B(12)) positively regulates interleukin-6 levels in rat cerebrospinal fluid

We have previously demonstrated that the repeated intracerebroventricular (i.c.v.) microinjection of interleukin-6 (IL-6) prevented the myelinolytic lesions of cobalamin-deficient (Cbl-D) central neuropathy [or subacute combined degeneration (SCD)] in totally gastrectomized (TGX) rats. We therefore hypothesized that cobalamin (Cbl) may actually regulate IL-6 levels in rat cerebrospinal fluid (CSF). We measured IL-6 levels in the CSF of rats made Cbl-D by means of total gastrectomy (TG) or chronic feeding with a Cbl-D diet and killed at different times from the beginning of the experiment, and found that IL-6 levels significantly and progressively decreased over time. Chronic 2-month Cbl administration started 1 week after surgery prevented the decrease in IL-6 levels and, when it was started 2 months after surgery, it significantly increased IL-6 levels, but not to presurgical values. We also investigated whether IL-6 decrease might be ultimately due to the Cbl-deficiency-linked decrease in epidermal growth factor (EGF) synthesis. Repeated i.c.v. administrations of EGF to TGX rats did not modify CSF IL-6 levels. These results, together with those of a previous study showing the preventive effect of IL-6 treatment on SCD lesions, demonstrate that: (i) Cbl selectively regulates CSF IL-6 levels; and (ii) decreased IL-6 availability plays a role in the pathogenesis of the experimental SCD, in which no evidence of inflammatory and/or immunological reaction has been observed.

Human cobalamin deficiency: alterations in serum tumour necrosis factor-alpha and epidermal growth factor

OBJECTIVES

We have previously demonstrated that vitamin B12 (cobalamin)-deficient central neuropathy in the rat is associated with local overexpression of neurotoxic tumour necrosis factor (TNF)-alpha combined with locally decreased synthesis of neurotrophic epidermal growth factor (EGF). The aims of this study were to investigate whether a similar imbalance also occurs in the serum of adult patients with clinically confirmed cobalamin deficiency and whether it can be corrected by vitamin B12 replacement therapy.

PATIENTS AND METHODS

We studied 34 adult patients with severe cobalamin deficiency, 12 patients with pure iron deficiency anaemia and 34 control subjects. Haematological markers of cobalamin deficiency and serum TNF-alpha and EGF levels were measured using commercial kits. Thirteen cobalamin-deficient patients were re-evaluated after 3 and 6 months of parenteral vitamin B12 treatment.

RESULTS

TNF-alpha was significantly higher (p < 0.01) and EGF significantly lower (p < 0.01) in the patients with cobalamin deficiency, but both were unchanged in patients with pure iron deficiency anaemia. In cobalamin-deficient patients the serum TNF-alpha levels correlated significantly with plasma total homocysteine levels (r = 0.425; p < 0.02). In the treated patients TNF-alpha and EGF levels normalised concomitantly with clinical and haematological disease remission.

CONCLUSIONS

In humans, as in rats, cobalamin concentration appears to be correlated with the synthesis and release of TNF-alpha and EGF in a reciprocal manner, because cobalamin deficiency is accompanied by overproduction of TNF-alpha and underproduction of EGF.

Effect on the peripheral nervous system of systemically administered dimethylsulfoxide in the rat: a neurophysiological and pathological study

The issue of dimethylsulfoxide (DMSO) neurotoxicity is an important one, given its wide use in experimental toxicology as a solvent for hydrophobic substances. We examined the effect of the intraperitoneal administration of different DMSO solutions (1.8-7. 2%) on the peripheral nervous system of Wistar rats treated for 10 consecutive days and followed-up for an additional 45 days. DMSO administration induced a dose-dependent reduction in nerve conduction velocity, with complete recovery occurring in the follow-up. No structural changes were found in the sciatic nerve at 1.8% and 3.6% DMSO concentrations, suggesting that the mechanism of action of DMSO involves a functional impairment (i.e. conduction block) similar to that already described for this substance in isolated systems. However, when DMSO was administered at the 7.2% concentration, evident structural changes were observed in the sciatic nerve, with myelin disruption and uncompacted myelin lamelle. The neurophysiological and pathological changes observed in our study are severe enough to merit careful consideration in the course of experimental studies involving DMSO as a solvent for drugs which are under evaluation for their potential neurotoxicity.

Epidermal growth factor as a local mediator of the neurotrophic action of vitamin B(12) (cobalamin) in the rat central nervous system

We have recently demonstrated that the myelinolytic lesions in the spinal cord (SC) of rats made deficient in vitamin B(12) (cobalamin) (Cbl) through total gastrectomy (TG) are tumor necrosis factor-alpha (TNF-alpha)-mediated. We investigate whether or not permanent Cbl deficiency, induced in the rat either through TG or by chronic feeding of a Cbl-deficient diet, might modify the levels of three physiological neurotrophic factors-epidermal growth factor (EGF), vasoactive intestinal peptide (VIP), and somatostatin (SS)-in the cerebrospinal fluid (CSF) of these rats. We also investigated the ability of the central nervous system (CNS) in these Cbl-deficient rats to synthesize EGF mRNA and of the SC to take up labeled Cbl in vivo. Cbl-deficient rats, however the vitamin deficiency is induced, show a selective decrease in EGF CSF levels and an absence of EGF mRNA in neurons and glia in various CNS areas. In contrast, radiolabeled Cbl is almost exclusively taken up by the SC white matter, but to a much higher degree in totally gastrectomized (TGX) rats. Chronic administration of Cbl to TGX rats restores to normal both the EGF CSF level and EGF mRNA expression in the various CNS areas examined. This in vivo study presents the first evidence that the neurotrophic action of Cbl in the CNS of TGX rats is mediated by stimulation of the EGF synthesis in the CNS itself. It thus appears that Cbl inversely regulates the expression of EGF and TNF-alpha genes in the CNS of TGX rats.

Myelinolytic lesions in spinal cord of cobalamin-deficient rats are TNF-alpha-mediated

Repeated intracerebroventricular (i.c.v.)microinjection of tumor necrosis factor-alpha (TNF-alpha) into normal rats causes intramyelin and interstitial edema in the white matter of the spinal cord (SC). This response is identical to that observed in the SC white matter of rats made cobalamin (Cbl) deficient by total gastrectomy (TG). Immunoblot analysis showed that: 1) the level of the biologically active form of the TNF-alpha protein (17 kDa) is higher in the SC of totally gastrectomized (TGX) rats 2 months after TG, i.e., at the postoperative time when edema is observed; 2) SC levels of TNF-alpha protein (17 kDa) in 2-mo-TGX-, Cbl-treated rats are reduced to control. Repeated i.c.v. microinjections of anti-TNF-alpha antibodies, transforming growth factor-beta1 (TGF-beta1) or interleukin-6 (IL-6) into TGX rats, begun shortly after TG, substantially reduced both intramyelin and interstitial edema in the SC white matter. This study provides the first evidence that the hallmark myelin damage of Cbl-deficient central neuropathy, which is a pure myelinolytic disease, is not caused directly by the withdrawal of the vitamin itself, but reflects enhanced production of the biologically active form of TNF-alpha by SC cells. This study thus supports the view that TGF-beta1 and IL-6 may act as neuroprotective agents in Cbl deficiency central neuropathy.