Research on Cobalt Compounds
Methylcobalamin
Taniguchi H., Ejiri K., Baba
S., Clin Ther 1987;9(6):607-14
The effect of mecobalamin on
autonomic neuropathy was evaluated in 20 hemodialyzed uremic
patients; their mean age was 53 years and the duration of hemodialysis
was 6.5 years; 14 were women. The cardiac beat-to-beat variation
(BBV) was used as the measure of autonomic neuropathy. Twelve
patients with normal BBV test results were either given 1,500
micrograms of mecobalamin daily for three months (six patients)
or were untreated (six patients). The BBV test results did not
change significantly over the three months in either the treated
or untreated group, nor were there any significant between-group
differences. Eight patients with abnormal results on the BBV
test were given 1,500 micrograms of mecobalamin daily for six
months. The mean BBV values increased significantly from 3.3
beats/min before treatment to 5.8 beats/min at six months (P
less than 0.005); five of these patients (including three of
the four patients with diabetes) showed normal BBV values by
three months. It is concluded that mecobalamin can be used in
the treatment of autonomic and peripheral neuropathy in both
diabetic and nondiabetic patients with chronic renal failure.
Altern Med Rev 1998 Dec;3(6):461-3
Published erratum appears in Altern Med Rev 1999 Feb;4(1):9
Methylcobalamin is one of the
two coenzyme forms of vitamin B12. Evidence indicates this form
of vitamin B12, in addition to having a theoretical advantage
over cyanocobalamin, actually has some metabolic and therapeutic
applications not shared by the other forms of vitamin B12. This
monograph provides an overview of the pharmacokinetics of methylcobalamin,
and will highlight the potential therapeutic relevance for Bell's
palsy, cancer, diabetic neuropathy, eye function, heart rate
variability, HIV, homocysteinemia, male impotence, and sleep
disorders.
Kelly G.S., Altern Med Rev (1999
Aug) 4(4):249-65
Prolonged stress, whether a result
of mental/emotional upset or due to physical factors such as
malnutrition, surgery, chemical exposure, excessive exercise,
sleep deprivation, or a host of other environmental causes,
results in predictable systemic effects. The systemic effects
of stress include increased levels of stress hormones such as
cortisol, a decline in certain aspects of immune system function
such as natural killer cell cytotoxicity or secretory-IgA levels,
and a disruption of gastrointestinal microflora balance. These
systemic changes might be a substantial contributor to many
of the stress-associated declines in health. Based on human
and animal research, it appears a variety of nutritional and
botanical substances - such as adaptogenic herbs, specific vitamins
including ascorbic acid, vitamins B1 and B6, the coenzyme forms
of vitamin B5 (pantethine) and B12 (methylcobalamin), the amino
acid tyrosine, and other nutrients such as lipoic acid, phosphatidylserine,
and plant sterol/sterolin combinations - may allow individuals
to sustain an adaptive response and minimize some of the systemic
effects of stress.
Masson C., Presse Med (1999 Nov
27) 28(37):2048-9
RENEWED INTEREST: There are at
least three reasons for revisiting subacute combined degeneration.
DIAGNOSIS: There is evidence that diagnosis is too often differed
until a time when irreversible lesions of the spinal cord are
present. A high degree of suspicion is mandatory. CONTRIBUTION
OF MRI: Magnetic resonance imaging of the spine supplies interesting
information about the distribution of lesions and their course
under treatment. NO: Nitous oxide is an emerging cause of cobalamin
deficiency. Patients sometimes develop myeloneuropathy after
repeated or single exposure to nitrous oxide. This is explained
by inactivation of methylcobalamin as a result of irreversible
oxidation.
Institutional address:
Service de Neurologie
Hopital Beaujon
Clichy
Kapadia C.R., Gastroenterologist
(1995 Dec) 3(4):329-44
All of vitamin B12 in nature
is of microbial origin. Cobalamin, as vitamin B12 should correctly
be termed, is a large polar molecule that must be bound to specialized
transport proteins to gain entry into cells. Entry from the
lumen of the intestine under physiological conditions occurs
only in the ileum and only when bound to intrinsic factor. It
is transported into all other cells only when bound to another
transport protein, transcobalamin II. Congenital absence or
defective synthesis of intrinsic factor or transcobalamin II
result in megaloblastic anemia. The Immerslund-Graesbeck syndrome,
a congenital defect in the transcellular transport of cobalamin
through the ileal cell during absorption, also presents with
megaloblastic anemia, but with accompanying albuminuria. In
most bacteria and in all mammals, cobalamin regulates DNA synthesis
indirectly through its effect on a step in folate metabolism,
the conversion of N5-methyltetrahydrofolate to tetrahydrofolate,
which in turn is linked to the conversion of homocysteine to
methionine. This reaction occurs in the cytoplasm, and it is
catalyzed by methionine synthase, which requires methyl cobalamin
(MeCbl), one of the two coenzyme forms of the vitamin, as a
cofactor. Defects in the generation of MeCbl (cobalamin E and
G diseases) result in homocystinuria; affected infants present
with megaloblastic anemia, retardation, and neurological and
ocular defects. 5'-Deoxyadenosyl cobalamin (AdoCbl), the other
coenzyme form of cobalamin, is present within mitochondria,
and it is an essential cofactor for the enzyme Methylmalonyl-CoA
mutase, which converts L-methylmalonyl CoA to succinyl CoA.
This reaction is in the pathway for the metabolism of odd chain
fatty acids via propionic acid, as well as that of the amino
acids isoleucine, methionine, threonine, and valine. Impaired
synthesis of AdoCbl (cobalamin A or B disease) results in infants
with methylmalonic aciduria who are mentally retarded, hypotonic,
and who present with metabolic acidosis, hypoglycemia, ketonemia,
hyperglycinemia, and hyperammonemia. Megaloblastic anemia does
not develop in these children because adequate amounts of MeCbl
are present, but the effect of methylmalonic acid on marrow
stem cells may give rise to pancytopenia. Congenital absence
of reductases in the cytoplasm, which normally reduce the cobalt
atom in cobalamin from its oxidized to its reduced state (cobalamin
C and D diseases), results in impaired synthesis of both MeCbl
and AdoCbl. Both methylmalonic aciduria and homocystinuria therefore
develop in these children, and they present with megaloblastosis,
mental retardation, a host of neurological and ocular disorders,
and failure to thrive; however, they do not have hyperglycinemia
or hyperammonemia. A similar biochemical profile and clinical
presentation is also seen in cobalamin F disease, which results
from a defect in the release of cobalamin from lysosomes, following
receptor-mediated endocytosis of the transcobalamin II-cobalamin
complex into cells. It is important to recognize these inborn
errors of cobalamin absorption, transport, or function as soon
after birth as possible, because most respond (in some patients
more fully than others) to parenteral administration of cobalamin.
Delays in diagnosis can lead to grave clinical consequences.
Institutional address:
Department of Digestive Diseases
VA Medical Center
West Haven, CT 06516
USA
el Kholty S., Gueant J.L., Bressler
L., Djalali M., Boissel P., Gerard P. Nicolas J.P., Gastroenterology
(1991 Nov) 101(5):1399-408 ISSN: 0016-5085
The assimilation of labeled cobalamin
and the transport of corrinoids in portal blood, peripheral
venous blood, and bile were studied in eight cholecystectomized
patients, after ingestion of a dose of cyano[57Co]cobalamin
(0.5 microCi). The radioactivity appeared in the portal vein
after a delay of 1.5-2 hours and in the peripheral vein 1 hour
later. In bile, it reached a maximum at 24-72 hours; the excreted
cobalamin corresponded to 1.42% +/- 0.92% of the dose ingested.
The output of total corrinoids was 1.85 nmol/day. The high-performance
liquid chromatography analysis of bile showed the presence of
methylcobalamin, 5'-deoxyadenosylcobalamin, hydroxocobalamin,
and an unknown corrinoid. This corrinoid bound to R binder but
not to the intrinsic factor, and it had the same retention time
as cobinamide. The R binder was the single cobalamin-binding
protein found in bile. It was completely saturated in some periods
of bile secretion. The corrinoids corresponding to such a period
were eluted in Sephacryl S 300 gel filtration (Pharmacia Fine
Chemicals, Uppsala, Sweden) in two peaks corresponding to saturated
R binder and to free cobalamin. The mean level of total corrinoid
was significantly higher in the portal vein (593 +/- 238 pmol/L)
than in the peripheral vein (376 +/- 114 pmol/L) (P less than
0.01). This "cobalamin analogue" fraction was hypothetical
because it was calculated from the difference between total
corrinoid concentration and the so called "true cobalamin"
concentration. This difference corresponded to the cobalamin
analogue fraction. These data show that bile removes not only
cobalamin but also cobalamin analogues and that R binder is
the single carrier protein involved in their excretion.
Equipe de Biochemie-Immunologie
Unite INSERM 308
Faculte de Medecine
Vandoeuvre les Nancy
France
Fidanza A., Audisio M., Acta
Vitaminol Enzymol (1982) 4(1-2):105-14
Vitamins play an essential role
in lipid metabolism reactions and their presence is therefore
absolutely necessary for these reaction to occur. The effect
of pantothenic acid, niacin and riboflavin is here described.
By transformation into coenzymes these vitamins are involved
in fatty acid synthesis and oxidation reactions. Other vitamins,
like vitamin B12, folic acid, vitamin C, and essential fatty
acids influence lipid metabolism by different mechanisms. Coenzyme
B12 and folate coenzyme provide to balance, by methionine synthesis,
the pool of methyl radicals necessary for phospholipid biosynthesis.
By its involvement in the microsomal respiratory chain, vitamin
C promotes cholesterol transformation into bile acids. The essential
fatty acids, mainly linoleic acid, are directly connected with
cholesterol transport and plasma cholesterol decrease. It is
suggested that many lipid metabolism disorders may be due to
primary and secondary hypovitaminosis. Nicotinic acid and its
derivatives have a particular pharmacological effect since they
cause a HDL increase with LDL decrease and improve cholesterol
transfer from LDL to HDL. Results of several experiments on
the influence of pantothenic acid on polyunsaturated fatty acid
metabolism are eventually reported, and these data are related
to the effect of the administration of vitamin C at high doses
on total cholesterol, triglyceride, lipoprotein, vitamin C and
fatty acids of the different plasma lipid fractions.
Scott J.M., Proc Nutr Soc (1999
May) 58(2):441-8
The folates are made up of a
pterdine ring attached to a p-aminobenzoate and a polyglutamyl
chain. The active form is tetrahydrofolate which can have C1
units enzymically attached. These C1 units (as a formly group)
are passed on to enzymes in the purine pathway that insert the
C-2 and C-8 into the purine ring. A methylene group (-CH2-)
attached to tetrahydrofolate is used to convert the uracil-type
pyrimidine base found in RNA into the thymine base found in
DNA. A further folate cofactor, i.e. 5-methyltetrahydrofolate,
is involved in the remethylation of the homocysteine produced
in the methylation cycle back to methionine. After activation
to S-adenosylmethionine this acts as a methyl donor for the
dozens of different methyltransferases present in all cells.
Folate deficiency results in reduction of purine and pyrimidine
biosynthesis and consequently DNA biosynthesis and cell division.
This process is most easily seen in a reduction of erythrocytes
causing anaemia. Reduction in the methylation cycle has multiple
effects less easy to identify. One such effect is certainly
on the nerve cells, because interruption of the methylation
cycle causing neuropathy can also happen in vitamin B12 deficiency
due to reduced activity of the vitamin B12-dependent enzyme
methionine synthase (EC 2.1.1.13). In vitamin B12 deficiency,
blocking of the methylation cycle causes the folate cofactors
in the cell to become trapped as 5-methyltetrahydrofolate. This
process in turn produces a pseudo folate deficiency in such
cells, preventing cell division and giving rise to an anaemia
identical to that seen in folate deficiency.
Institutional address:
Department of Biochemistry
Trinity College
Dublin, Ireland
Chen Z., Banerjee R., J Biol
Chem (1998 Oct 2) 273(40):26248-55
In mammals, methionine synthase
plays a central role in the detoxification of the rogue metabolite
homocysteine. It catalyzes a transmethylation reaction in which
a methyl group is transferred from methyltetrahydrofolate to
homocysteine to generate tetrahydrofolate and methionine. The
vitamin B12 cofactor cobalamin plays a direct role in this reaction
by alternately accepting and donating the methyl group that
is in transit from one substrate (methyltetrahydrofolate) to
another (homocysteine). The reactivity of the cofactor intermediate
cob(I)alamin renders the enzyme susceptible to oxidative damage.
The oxidized enzyme may be returned to the catalytic turnover
cycle via a reductive methylation reaction that requires S-adenosylmethionine
as a methyl group donor, and a source of electrons. In this
study, we have characterized an NADPH-dependent pathway for
the reductive activation of porcine methionine synthase. Two
proteins are required for the transfer of electrons from NADPH,
one of which is microsomal and the other cytoplasmic. The cytoplasmic
protein has been purified to homogeneity and is soluble cytochrome
b5. It supports methionine synthase activity in the presence
of NADPH and the microsomal component in a saturable manner.
In addition, purified microsomal cytochrome P450 reductase and
soluble cytochrome b5 reconstitute the activity of the porcine
methionine synthase. Identification of soluble cytochrome b5
as a member of the reductive activation system for methionine
synthase describes a function for this protein in non-erythrocyte
cells. In erythrocytes, soluble cytochrome b5 functions in methemoglobin
reduction. In addition, it identifies an additional locus in
which genetic polymorphisms may play a role in the etiology
of hyperhomocysteinemia, which is correlated with cardiovascular
diseases.
Institutional address:
Biochemistry Department
University of Nebraska
Lincoln, Nebraska 68588-0664
USA
Marsh E.N., Essays Biochem (1999)
34:139-54
The B12 or cobalamin coenzymes
are complex macrocycles whose reactivity is associated with
a unique cobalt-carbon bond. The two biologically active forms
are MeCbl and AdoCbl and their closely related cobamide forms.
MeCbl participates as the intermediate carrier of activated
methyl groups. During the catalytic cycle the coenzyme shuttles
between MeCbl and the highly nucleophilic cob(I)alamin form.
Examples of MeCbl-dependent enzymes include methionine synthase
and Me-H4-MPT: coenzyme M methyl transferase. AdoCbl functions
as a source of carbon-based free radicals that are unmasked
by homolysis of the coenzyme's cobalt-carbon bond. The free
radicals are subsequently used to remove non-acid hydrogen atoms
from substrates to facilitate a variety of reactions involving
cleavage of carbon-carbon, carbon-oxygen and carbon-nitrogen
bonds. Most reactions involve 1,2 migrations of hydroxy-, amino-
and carbon-containing groups, but there is also one class of
ribonucleotide reductases that uses AdoCbl. The structures of
two cobalamin-dependent enzymes, methionine synthase and methylmalonyl-CoA
mutase, have been solved. In both cases the cobalt is co-ordinated
by a histidine ligand from the protein. The significance of
this binding motif is presently unclear since in other cobalamin-dependent
enzymes spectroscopic evidence suggests that the coenzyme's
nucleotide 'tail' remains co-ordinated to cobalt when bound
to the protein.
Institutional address:
Department of Chemistry
University of Michigan
Ann Arbor, MI 48109-1055
USA
Tamura J, Kubota K, Murakami
H, Sawamura M, Matsushima T, Tamura T, Saitoh T, Kurabayshi
H, Naruse T, Clin Exp Immunol 1999 Apr;116(1):28-32
Third Department of Internal
Medicine, Gunma University School of Medicine, Maebashi, Japan.
It has been suggested that vitamin
B12 (vit.B12) plays an important role in immune system regulation,
but the details are still obscure. In order to examine the action
of vit.B12 on cells of the human immune system, lymphocyte subpopulations
and NK cell activity were evaluated in 11 patients with vit.B12
deficiency anaemia and in 13 control subjects. Decreases in
the number of lymphocytes and CD8+ cells and in the proportion
of CD4+ cells, an abnormally high CD4/CD8 ratio, and suppressed
NK cell activity were noted in patients compared with control
subjects. In all 11 patients and eight control subjects, these
immune parameters were evaluated before and after methyl-B12
injection. The lymphocyte counts and number of CD8+ cells increased
both in patients and in control subjects. The high CD4/CD8 ratio
and suppressed NK cell activity were improved by methyl-B12
treatment. Augmentation of CD3-CD16+ cells occurred in patients
after methyl-B12 treatment. In contrast, antibody-dependent
cell-mediated cytotoxicity (ADCC) activity, lectin-stimulated
lymphocyte blast formation, and serum levels of immunoglobulins
were not changed by methyl-B12 treatment. These results indicate
that vit.B12 might play an important role in cellular immunity,
especially relativing to CD8+ cells and the NK cell system,
which suggests effects on cytotoxic cells. We conclude that
vit.B12 acts as an immunomodulator for cellular immunity.
Mayer G., Kroger M., Meier-Ewert
K., Neuropsychopharmacology 1996 Nov;15(5):456-64
Sleep Disorder Unit, Hephata
Klinik, Schwatmstadt-Treysa, Germany.
This preliminary study investigates
effects of methyl- and cyanocobalamin on circadian rhythms,
well-being, alertness, and concentration in healthy subjects.
Six women (mean age 35 years) and 14 men (mean age 37 years)
were randomly assigned to treatment for 14 days with 3 mg cyano-(CB12)
or methylcobalamin (MB12) after 9 days of pre-treatment observation.
Levels in the CB12 group increased rapidly in the first, then
slowly in the second treatment week, whereas increase in the
MB12 group was linear. Urinary aMT6s excretion was reduced by
both forms of vitamin B12 over 24 hours with a significant decrease
between 0700-1100 hours, whereas urinary excretion of potassium
was significantly increased between 0700-1100 hours. Activity
from 2300-0700 hours increased significantly under both forms
of vitamin B12. Sleep time was significantly reduced under MB12
intake. In this group the change in the visual analogue scales
items "sleep quality," "concentration,"
and "feeling refreshed" between pretreatment and the
first week of treatment showed significant correlations with
vitamin B12 plasma levels. Cortisol excretion and temperature
were not affected by either medication. We conclude that vitamin
B12 exerts a direct influence on melatonin. Only MB12 has a
positive psychotropic alerting effect with a distribution of
the sleep-wake cycle toward sleep reduction.
Yaqub B.A., Siddique A., Sulimani
R., Clin Neurol Neurosurg 1992;94(2):105-11
Division of Neurology, King Khalid
University Hospital, Riyadh, Saudi Arabia.
We studied the clinical and neurophysiological
effects of methylcobalamin on patients with diabetic neuropathy.
In a double-blind study, the active group showed statistical
improvement in the somatic and autonomic symptoms with regression
of signs of diabetic neuropathy. Motor and sensory nerve conduction
studies showed no statistical improvement after 4 months. The
drug was easily tolerated by the patients and no side effects
were encountered.
Kuwabara S., Nakazawa R., Azuma
N., Suzuki M., Miyajima K., Fukutake T., Hattori T., Intern
Med (1999 Jun) 38(6):472-5
OBJECT: To study the effects
of the intravenous administration of methylcobalamin, an analogue
of vitamin B12, for uremic or uremic-diabetic polyneuropathy
in patients who are receiving maintenance hemodialysis. An ultra-high
dose of vitamin B12 has been reported to promote peripheral
nerve regeneration in experimental neuropathy. METHODS: Nine
patients received a 500 microg methylcobalamin injection 3 times
a week for 6 months. The effects were evaluated using neuropathic
pain grading and a nerve conduction study. RESULTS: Serum concentrations
of vitamin B12 were ultra-high during treatment due to the lack
of urinary excretion. After 6 months of treatment, the patients'
pain or paresthesia had lessened, and the ulnar motor and median
sensory nerve conduction velocities showed significant improvement.
There were no side effects. CONCLUSION: Intravenous methycobalamin
treatment is a safe and potentially beneficial therapy for neuropathy
in chronic hemodialysis patients.
Institutional address:
Department of Neurology
Chiba University School of Medicine.
Yagihashi S., Tokui A., Kashiwamura
H., Takagi S., Imamura K., Horm Metab Res (1982 Jan Jan) 14(1):10-3
To study in vivo effect of methylcobalamin
(CH3-B12) on the peripheral nerve structures, rats with experimental
diabetes induced by streptozotocin were administered with daily
intramuscular injection of CH3-B12 (500 microgram/kg) for 16
weeks. By isolated nerve fiber studies, CH3-B12-treated diabetic
rats showed less incidence of paranodal demyelination as an
early sign of segmental demyelination than non-treated diabetic
rats. From morphometrical analysis on sural nerves, the reduction
in the density of myelinated nerve fibers, nerve fiber size
and axon size of myelinated fibers was definitely protected
in treated diabetic rats. The results suggested that continuous
treatment with CH3-B12 had an ameliorative effect on the peripheral
nerve lesions in experimental diabetic neuropathy.
Watanabe T., Kaji R., Oka N.,
Bara W., Kimura J., J Neurol Sci 1994 Apr;122(2):140-3
Department of Neurology, Kyoto
University Hospital, Japan.
Despite intensive searches for
therapeutic agents, few substances have been convincingly shown
to enhance nerve regeneration in patients with peripheral neuropathies.
Recent biochemical evidence suggests that an ultra-high dose
of methylcobalamin (methyl-B12) may up-regulate gene transcription
and thereby protein synthesis. We examined the effects of ultra-high
dose of methyl-B12 on the rate of nerve regeneration in rats
with acrylamide neuropathy, using the amplitudes of compound
muscle action potentials (CMAPs) after tibial nerve stimulation
as an index of the number of regenerating motor fibers. After
intoxication with acrylamide, all the rats showed equally decreased
CMAP amplitudes. The animals were then divided into 3 groups;
rats treated with ultra-high (500 micrograms/kg body weight,
intraperitoneally) and low (50 micrograms/kg) doses of methyl-B12,
and saline-treated control rats. Those treated with ultra-high
dose showed significantly faster CMAP recovery than saline-treated
control rats, whereas the low-dose group showed no difference
from the control. Morphometric analysis revealed a similar difference
in fiber density between these groups. Ultra-high doses of methyl-B12
may be of clinical use for patients with peripheral neuropathies.
Kira J., Tobimatsu S., Goto I.,
Intern Med 1994 Feb;33(2):82-6
Department of Neurology, Faculty
of Medicine, Kyushu University, Fukuoka.
Serum vitamin B12 levels and
unsaturated vitamin B12 binding capacities were measured in
24 patients with multiple sclerosis (MS), 73 patients with other
neurological disorders and 21 healthy subjects. There was no
decrease in the vitamin B12 levels, however, a significant decrease
in the unsaturated vitamin B12 binding capacities was observed
in patients with MS when compared with other groups. A massive
dose of methyl vitamin B12 (60 mg every day for 6 months) was
administered to 6 patients with chronic progressive MS, a disease
which usually had a morbid prognosis and widespread demyelination
in the central nervous system. Although the motor disability
did not improve clinically, the abnormalities in both the visual
and brainstem auditory evoked potentials improved more frequently
during the therapy than in the pre-treatment period. We therefore
consider that a massive dose methyl vitamin B12 therapy may
be useful as an adjunct to immunosuppressive treatment for chronic
progressive MS.
Reynolds E.H., J Neuroimmunol
1992 Oct;40(2-3):225-30
Maudsley Hospital, London, UK.
Multiple sclerosis (MS) is occasionally
associated with vitamin B12 deficiency. Recent studies have
shown an increased risk of macrocytosis, low serum and/or CSF
vitamin B12 levels, raised plasma homocysteine and raised unsaturated
R-binder capacity in MS. The aetiology of the vitamin B12 deficiency
in MS is often uncertain and a disorder of vitamin B12 binding
or transport is suspected. The nature of the association of
vitamin B12 deficiency and MS is unclear but is likely to be
more than coincidental. There is a remarkable similarity in
the epidemiology of MS and pernicious anaemia. Vitamin B12 deficiency
should always be looked for in MS. The deficiency may aggravate
MS or impair recovery. There is evidence that vitamin B12 is
important for myelin synthesis and integrity but further basic
studies are required.
Kaji R., Kodama M., Imamura A.,
Hashida T., Kohara N., Ishizu M., Inui K., Kimura J., Muscle
Nerve 1998 Dec;21(12):1775-8
To develop a symptomatic treatment
for amyotrophic lateral sclerosis, we compared the effects of
ultrahigh-dose and low-dose (25 and 0.5 mg/day, intramuscularly,
for 14 days) methylcobalamin on averaged compound muscle action
potential amplitudes (CMAPs) in a double-blind trial. No significant
changes in CMAP amplitude were found in 12 patients who had
the low-dose treatment at either 2 or 4 weeks after start of
treatment. By contrast, 12 patients assigned to the ultrahigh-dose
group demonstrated a significant increase at 4 weeks. This method
may provide a clinically useful measure to improve or retard
muscle wasting, if a larger extended trial fulfills its promise.
Yamazaki K., Oda K., Endo C.,
Kikuchi T., Wakabayashi T., Neurosci Lett 1994 Mar 28;170(1):195-7
Laboratory Animal Research Center,
Tsukuba Research Laboratories, Eisai Co., Ltd., Ibaraki, Japan.
We examined the effects of methylcobalamin
(methyl-B12, mecobalamin) on degeneration of motor nerve terminals
in the anterior gracile muscle of gracile axonal dystrophy (GAD)
mutant mice. GAD mice received orally methyl-B12 (1 mg/kg body
wt/day) from the 40th day after birth for 25 days. In the distal
endplate zone of the muscle, although most terminals were degenerated
in both the untreated and methyl-B12-treated GAD mice, sprouts
were more frequently observed in the latter. In the proximal
endplate zone, where few degenerated terminals were seen in
both groups of the mice, the perimeter of the terminals was
increased and the area of the terminals was decreased significantly
in the methyl-B12-treated GAD mice. These findings indicate
that methyl-B12 promotes regeneration of degenerating nerve
terminals in GAD mice.
Yamatsu K., Kaneko T., Kitahara
A., Ohkawa I., Nippon Yakurigaku Zasshi 1976 Mar;72(2):259-68
Experiments were performed to
investigate the effects of Vitamin B12, i.e., methylcobalamin
and cobamide, on the neural degeneration and regeneration. Male
Wistar rats (140 to 150 g) under conditions of experimental
unilateral sciatic nerve crushing were treated consecutively
with methylcobalamin (50 and 500 mug/kg/day i.p.), cobamide
(50 and 500 mug/kg/day i.p.) or saline. EMG recordings were
periodically carried out and rats of each group were sacrificed
to determine the weight-loss of denervated muscles 1, 2, 3 and
4 weeks after crush. Neither methylcobalamin nor cobamide exerted
any significant effect on body-weight gain of the nerve-crushed
rats with a daily injection of 50 and 500 mug/kg i.p.. The EMG
pattern of the denervated biceps femoris muscle showed a total
lack of fibrillation for 2 days after the nerve-crush. Thereafter,
the fibrillation appeared and continued for 10 to 14 days until
the nerve had regenerated, as evidenced by the appearance of
a complex NMU voltage. The occurrence of fibrillation voltage
was slightly delayed in methylcobalamin group (500 mug/kg/day)
as compared with the saline control group. The re-appearance
of normal NMU voltage was more rapid in the methylcobalamin
500 mug/kg group than in controls and other experimental groups.
Neither methylcobalamin nor cobamide had any significant effect
on the weight-loss of the gastrocnemius and tibialis anterior
muscles following crush of the sciatic nerve. However, a daily
injection of 500 mug/kg of methylcobalamin produced a significant
increase in the weight of the soleus muscle which recovered
to the extent of being the same weight of the contralateral
4 weeks after the nerve-crush. These results suggest that methylcobalamin
may have an inhibitory effect on Wallerian degeneration and
also a facilitatory effect on the neural regeneration of the
crushed sciatic nerve of rats.
Steen M.T., Boddie A.M., Fisher
A.J., Macmahon W., Saxe D., Sullivan K.M., Dembure P.P., Elsas
L.J., Prenat Diagn (1998 Jun) 18(6):545-55
While folate supplementation
reduces the risk of recurrent neural-tube defects (NTD), both
folate and cobalamin deficiencies may be independent risk-factors
for neural-tube defects. Folate-dependence and impaired remethylation
of homocysteine are implicated as mechanisms for NTD. There
are few references reported for folate, cobalamin, homocysteine
and methionine in the fetal compartment. This case-controlled
pilot study of amniotic fluid (AF) samples derived from 16 NTD
pregnancies and 64 age-matched controls quantities total homocysteine
(tHcy), total cysteine (tCys), folate, cobalamin (B12), and
methionine. Only decreased AF B12 concentrations were found
(150 pg/ml versus 540 pg/ml, P < 0.02). Since cobalamin,
folate and homocysteine participate in the remethylation of
homocysteine, via methyl transfer from 5-methyltetrahydrofolate
to B12, to methionine, we compared ratios of these methionine
synthase (EC 2.1.1.13)-related intermediates. The ratio of B12/folate
for NTD versus controls was 48 (34-90) versus 126 (123-182),
P < 0.001. The ratio of methionine/(folate x tHcy) was 1.4
(1.2-2.2) versus 2.7 (2.4-3.3), P < 0.001. We conclude that
AF from pregnancies with NTD have lower B12 concentrations,
and that ratios of product to substrate(s) of homocysteine remethylation
suggest impaired methionine synthase in the fetal compartment
through the early second trimester.
Institutional address:
Department of Pediatrics
Emory University School of Medicine
Atlanta, GA 30322
USA
Weir D.G., Scott J.M., Br Med
Bull (1999) 55(3):669-82
Vitamin B12 (cobalamin) deficiency
associated neuropathy, originally called subacute combined degeneration,
is particularly common in the elderly. The potential danger
today is that with supplementation with folic acid of dietary
staples such as flour, that the incidence of this disease could
rise as folic acid, as opposed to natural folate (N5CH3HFGlu1),
enters the cell and the metabolic cycle by a cobalamin independent
pathway. This chapter briefly describes the clinical presentation
of the disease, which unless treated will induce permanent CNS
damage. The biochemical basis of the interrelationship between
folate and cobalamin is the maintenance of two functions, nucleic
acid synthesis and the methylation reactions. The latter is
particularly important in the brain and relies especially on
maintaining the concentration of S-adenosylmethionine (SAM)
which, in turn, maintains the methylation reactions whose inhibition
is considered to cause cobalamin deficiency associated neuropathy.
SAM mediated methylation reactions are inhibited by its product
S-adenosylhomocysteine (SAH). This occurs when cobalamin is
deficient and, as a result, methionine synthase is inhibited
causing a rise of both homocysteine and SAH. Other potential
pathogenic processes related to the toxic effects of homocysteine
are direct damage to the vascular endothelium and inhibition
of N-methyl-D-aspartate receptors.
Institutional address:
Department of Clinical Medicine
Trinity College
Dublin, Ireland.
Ueda Y., Murakawa Y., Takeno
M., Miki T., Sakane T., Ryumachi (1990 Oct) 30(5):350-5
We have previously shown that
when patients with active rheumatoid arthritis (RA) were examined
for the ability of their lymphocytes to respond in the autologous
mixed lymphocyte reaction (AMLR), profoundly reduced AMLR responses
were found in the RA patients. The defects were mainly due to
the impaired response of CD8+ and CD4+ Law8- subsets; however,
both CD4+Leu8+ and CD4+ + Leu8- cells functioned normally as
responding cells. The present study demonstrated that the abnormalities
of RA CD8+ T cells in the AMLR were corrected when the AMLR
cultures were set up in the presence of methyl-B12. In addition,
a main target of the methyl-B12 effect observed was both CD8+Leu8+
and CD8+Leu8- cells. Thus, methyl-B12 may become a potential
agent that would be able to control the pathophysiology of RA.
Institutional address:
Department of Internal Medicine
Shimane Medical University
Izumo-shi, Japan
Funada U., Wada M., Kawata T.,
Tanaka N., Tadokoro T., Maekawa A., Biosci Biotechnol Biochem
2000 Oct;64(10):2053-8
Department of Applied Biology
and Chemistry, Faculty of Applied Bioscience, Tokyo University
of Agriculture, Japan.
Cyanocobalamin, deoxyadenosylcobalamin
and methylcobalamin were separately administered to mice sensitized
with the ovalbumin antigen to investigate the allergic response.
The serum IgE and pulmonary histamine concentrations were significantly
lower in all cobalamin (Cbl)-administered groups. The production
of interleukin (IL)-2 and IL-4 in splenocytes was also lower
in all Cbl-administered groups. These results show that Cbls
were effective in mitigating allergic reactions and IL-2 production.
CD3+ CD28+ (CD28 is an accessory molecule related to IL-2 production)
and CD4+ CD28+ in splenocytes were higher in all the Cbl-administered
groups. However, CD3+ CD28-, CD4+ CD28- and CD5+ CD25- (CD25:
IL-2 R alpha/p55) were lower in the Cbl-administered groups.
In addition, Cbl specifically inhibited the cellular phosphorylation
of tyrosine induced by ovalbumin sensitization. These results
indicate that the signal in a cell by CD 28 was restrained by
Cbl. We infer that Cbl administration significantly reduced
the IL-2 concentration, and secondarily the IL-4, IgE and histamine
concentrations.
Mathe G., Biomed Pharmacother
(1999 Dec) 53(10):484-6
We detected in 1989, with the
inhibitor test of proviral insertion into c-erb B erythroblastosis,
two retrovirus integrase inhibitors: hydroxy-methyl-ellipticine
and acriflavine. They have been used for ten years in AIDS patients
with high efficacy and no toxicity. Since vitamin B12 and cobalt,
which it contains, have been detected as HIV1-integrase inhibitors
by an in-vitro test, we have also used vitamin B12 (combined
with folic acid), whose clinical action has been remarkable.
Ten or so other compounds have been detected by such in-vitro
tests, among which there are many compounds (such as flavones)
which are used in many conditions and are not toxic.
Weinberg J.B., Sauls D.L., Misukonis
M.A., Shugars D.C., Blood (1995 Aug 15) 86(4):1281-7
Various cobalamins act as important
enzyme cofactors and modulate cellular function. We investigated
cobalamins for their abilities to modify productive human immunodeficiency
virus-1 (HIV-1) infection of hematopoietic cells in vitro. We
show that hydroxocobalamin (OH-Cbl), methylcobalamin (Me-Cbl),
and adenosylcobalamin Ado-Cbl (Ado-Cbl) inhibit HIV-1 infection
of normal human blood monocytes and lymphocytes. The inhibitory
effects were noted when analyzing the monocytotropic strains
HIV-1-BaL and HIV-1-ADA as well as the lymphocytotropic strain
HIV-1-LAI. Cobalamins did not modify binding of gp120 to CD4
or block early steps in viral life cycle, inhibit reverse transcriptase,
inhibit induction of HIV-1 expression from cells with established
or latent infection, or modify monocyte interferon-alpha production.
Because of the ability to achieve high blood and tissue levels
of cobalamins in vivo and the general lack of toxicity, cobalamins
should be considered as potentially useful agents for the treatment
of HIV-1 infection.
Institutional address:
Department of Medicine
VA Medical Center
Durham, NC 27705
USA
Drummond J.T., Matthews R.G.,
Biochemistry (1994 Mar 29) 33(12):3732-41
Cobalamin-dependent methionine
synthase catalyzes the remethylation of homocysteine to form
methionine, using methyltetrahydrofolate as the primary methyl
donor. The enzyme is susceptible to inactivation by the anaesthetic
gas, nitrous oxide, through either short-term exposure to high
levels or chronic exposure to low levels of this agent. We have
studied the chemical reaction wherein the bound cobalamin prosthetic
group of the enzyme from Escherichia coli catalyzes the degradation
of nitrous oxide. By poising the enzyme at low ambient potentials
in an electrochemical cell, the concentration of enzyme in the
highly reactive cob(I)alamin state can be controlled, and the
observed rate of inactivation is directly dependent upon the
amount of enzyme in this redox state. The inactivation consumes
both nitrous oxide and electrons, while nitrogen gas is evolved.
The inactivation process is also directly dependent upon the
proton concentration, but the effect of pH was found to be on
the enzyme, revealing a redox-linked base presumed to be on
or near the cobalamin. The chemical reaction between enzyme-bound
cob(I)alamin and nitrous oxide that leads to inactivation is
therefore independent of pH. In a single turnover experiment,
where enzyme-bound cob(I)alamin is generated from methylcobalamin
by methyl transfer to the substrate homocysteine, the cob(I)alamin
decays to cob(II)alamin, suggesting that the degradation of
nitrous oxide involves one-electron reduction of nitrous oxide.
We propose that the inactivation chemistry is likely to be a
one-electron reduction of nitrous oxide, which leads to the
formation of a highly reactive oxidant, such as hydroxyl radical,
and subsequent enzyme damage.
Institutional address:
Biophysics Research Division
University of Michigan
Ann Arbor, MI 48109
Chanarin I., Crit Rev Toxicol
(1982 Sep) 10(3):179-213
The anaesthetic gas nitrous oxide
(N2O), when inhaled for longer than 6 hr, produces megaloblastic
anemia in man. Longer term inhalation, as in addicts, produces
a syndrome similar to that due to B12 neuropathy, and long term
exposure to low concentrations results in an increased abortion
rate and neuropathy, particularly in dental personnel. N2O acts
by oxidizing vitamin B12 from the active reduced cob[I]alamin
form to the inactive cob[III]alamin form. In turn, this inactivates
the enzyme methionine synthetase which requires both B12 and
folate as cofactors. In the rat, hepatic methionine synthetase
is completely inactivated after 3 hr exposure to a mixture of
equal parts of N2O/O2. There is an impared uptake of folate
analogues by the liver so that the plasma folate level rises
and thereafter there is a considerable loss of folate into the
urine. Hepatic folate concentration falls to 25% within 10 days
of N2O exposure. There is a failure to synthesize folate polyglutamate
(the active folate coenzyme) from all other than formyltetrahydrofolate.
As oxidization of the methyl of methionine is an important source
of formyl, the failure of methionine synthesis in turn appears
to lead to the failure in supply of formate and, hence, a lack
of the formylfolate substrate.
Kano Y., Sakamoto S., Sakuraya
K., Kubota T., Taguchi H., Miura Y., Takaku F., J Lab Clin Med
(1984 Nov) 104(5):711-7
Results of the deoxyuridine suppression
test, a good marker for defining biochemical megaloblastosis
caused by deficiency of folate and vitamin B12, became abnormal
(greater than 10%) after 6 hours of administration of nitrous
oxide anesthesia. 5-Formyltetrahydrofolate and methylcobalamin
administration during nitrous oxide anesthesia have no remarkable
effect on the correction of deoxyuridine suppression test values.
On the other hand, 5-formyltetrahydrofolate and methylcobalamin
administrated at the end of nitrous oxide anesthesia corrected
the abnormal deoxyuridine suppression test values nearly to
normal range within 1 hour.
