ClinicalScience (1980)58. 101-103
SHORT COMMUNICATION
Long-term clearance of [57Co]cyanocobalaminin
vegans and pernicious anaemia
S. A M I N , T. S P I N K S , A. R A N I C A R , M. D . S H O R T
A N D A. V. H O F F B R A N D
Departmerits of Haeinatologr. Medical Physics and M R C Cyclotron Unit.Hammersmith Hospital. London
(Received 15 November 1978;accepted 29 August 1979)
Summary
I. Whole-body counting has been used to
monitor the clearance of [~7Colcyanocobalamin
in
normal subjects, vegans and patients with pernicious anaemia. After oral administration of T o labelled cyanocobalamin (1 pg/l &i), subjects
were counted for radioactivity monthly for a
maximum period of 1 year.
2. The results obtained were consistent with a
monoexponential clearance model and a leastsquares fit showed that there was no significant
difference between the mean clearance rates for the
vegans and normal subjects.
3. The patients with pernicious anaemia cleared
the vitamin significantly more quickly than the
normal control subjects.
4. This may be due to failure to reabsorb biliary
vitamin B,, in pernicious anaemia because of the
absence of intrinsic factor.
Key words: cyanocobalamin (vitamin B ,,), pernicious anaemia, vegans, whole-body counting.
Introduction
Vegans often have low serum vitamin B,, concentrations without showing clinical or haematological effects of the deficiency or progressing to
more severe deficiency. It has been suggested that
rate of loss of the vitamin from the body in vegans
or normal subjects may be slower than that in
Correspondence: Professor A. V. Hornrand, Department of Haematology, Royal Free Hospital, Pond Street,
London N.W.3.
patients with pernicious anaemia or other causes of
malabsorption of vitamin B,, because of the intact
entero-hepatic circulation for vitamin B,, in
subjects with normal absorption of the vitamin. It is
thus possible that vegans, despite low dietary intake
of vitamin B,,, may not become as severely
deficient of the vitamin as patients with pernicious
anaemia because of a slower body clearance of the
vitamin. To test this hypothesis, groups of vegans,
normal subjects and patients with pernicious
anaemia previously treated with vitamin B were
given an oral dose of vitamin B,, labelled with
J 7 cin~pernicious
;
anaemia, an active preparation
of intrinsic factor was given with the dose. A sensitive low-background whole-body monitor was used
to measure clearance of the vitamin.
,
Materials and methods
The whole-body monitor comprised a room of 6 inthick steel, containing ten 6 in x 4 in NaI (TI)
scintillation detectors. The detectors were arranged
in symmetrical linear arrays of five above and five
below a couch. Fixed distances between adjacent
detectors (30 cm) and opposed detectors (40 cm)
provided a counting geometry suitable for each
subject. Before administration of the dose, the
subject was positioned supine on the couch and the
basal radioactivity counts were recorded. Wide
energy-band counting conditions were used to provide maximum sensitivity after dosing and the
counting time was sufficient to ensure adequate
statistical accuracy in the net subject counts. An
oral dose of 1 pg (1 pCi of T o ) of cyanocobalamin (The Radiochemical Centre, Amersham,
101
0143-522 l/80/010101-03S
1.50/1
S.A i n h el al.
102
TABLE I . Cleararrce constaut ( A ) of 5’Co-labelled
Bucks, U.K.) was administered and whole-body
uitanriii B , , i/r uegarrs (1‘1-1‘4). rroniial subjects
counting was performed at 7 days and at approxi( N I-NS) and treated patients with perriicious arraemia
mately monthly intervals for a period of up to a
(PI-P5)
year. At least 100000 counts were recorded in a
Vegan VS was studied after vitamin B,, saturation and
counting time which was never longer than 10 min.
this result is omitted from the statistical analysis.
Retention counts were calculated according to the
method of Arimizu, Kakehi & Morris (1969)and
Subject
(Sex)
Clearance constant
Mean f SD
expressed as a ratio with a 57C0 standard source
(wcck)
counted in a fixed position on the couch before and
0.01 12
after each subject reading. This allowed for radio0.0097
active decay and any variations in instrumental
0.0104
sensitivity. These values were then normalized to a
0.0100
0.0103 k 0.0006
7 day reading. A monoexponential clearance
0.0080
characteristic for vitamin B,, was confirmed
0.0072
(Boddy & Adams, 1972) and the clearance
0.0080
constant 1 for each subject was determined by
0.0093
0.0091 f 04013
least-squares fitting. Results were expressed in the
0.0104
0.0107
form of mean SD for each subject group. In this
context 1 is defined by the equation C, = Ce-*‘
0.0099
where C = 7 day net count, and C,= net count at !
0.01 19
0.01 14 f O.ooo9
0.0110
weeks after the 7 day reading.
0.01 18
A total of 15 subjects were included in the study.
0.0123
They comprised five normal volunteers, five vegans
and five patients with pernicious anaemia. One
vegan subject had been saturated with vitamin B,,
years. All patients ceased to receive intramuscular
over several months before administration of the
hydroxocobalamin 4-8 weeks before the study and
labelled dose and each patient with pernicious
did not receive further injections until the study was
anaemia, all of whom had been on treatment with
completed. Each subject had normal haemoglobin
1000 pg of hydroxocobalamin intramuscularly
and serum vitamin B,, concentrations at comevery 2 months for at least a year, was given two
mencement and termination of the study.
capsules of hog intrinsic factor with the radioactive vitamin B I Z The purpose of the study was
Results
explained to each subject, who gave informed
consent, and maintenance vitamin B,, injections
Table I shows the clearance values (as percentwere omitted during the period of the study. This
ages of dose/week) for the 15 subjects. Also shown
study had the approval of the Local Ethical
are the mean k 1 SD values for each group. There
Committee.
was no significant difference between the normal
Haemoglobin and serum vitamin B concentraand vegan group mean values ( P > 0.2)or between
tions (Euglena gracilis assay, normal range 160the vegan and pernicious anaemia patient values
925 ng/l) were performed on each subject before
( P > 0.5).as indicated by a standard I-test. On the
commencement of the study. The summary of the
other hand, clearance was significantly more rapid
findings in the three groups is given below.
in pernicious anaemia than in the normal group
Normal volunreer subjecls. There were two
(0.02 < P < 0.05).
males and three females with an age range of 20Since the vegan subjects V 1-V4 had low serum
35 years. Haemoglobin and serum vitamin B,,
vitamin B,, concentrations at the start of the clearconcentrations were normal in each case.
ance study, a fifth vegan (V5)was studied who had
Vegans. In this group all subjects were females
been saturated with vitamin B,, before the study.
from India, with an age range of 16-55 years.
Clearance in this subject was significantly slower
Haemoglobin and mean corpuscular volume were
than in the other vegans (>3 SD from mean).
normal in each, but serum vitamin B,, was subnormal (1 10,110, 127 and 142 ng/l respectively) in
Discussion
four subjects who had not received vitamin BIZ
Pernicious anaemia group. Comprised three
The results of this study show that vitamin B,, is
females and two males with an age range of 55-75
cleared from the body of patients with pernicious
,,
Clearance of cyanocobalamin
anaemia more rapidly than from normal subjects.
This rapid clearance could not be due to the 'washout' effect of maintenance hydroxocobalamin
injections, which were omitted during the period of
the study. Indeed, the normal subjects, absorbing
vitamin BIZ each day from the diet, might be
expected to clear the labelled vitamin from the
body more quickly than patients with malabsorption of the vitamin because of replacement of the
body labelled pool of vitamin B,, with newly
absorbed non-radioactive vitamin.
The observation that the vegan who had been
saturated with vitamin B 12 cleared the radioactive
oral dose more slowly than the other vegans
suggests that the increased clearance in the pernicious anaemia subjects is not due to increased
body stores due to prior vitamin B,, treatment and
is consistent with the concept that absolute loss
occurs as a percentage of body stores. Some
previous studies have suggested that vitamin BIZ
loss from the body occurs as a percentage of body
stores only after an equilibration period and
variously estimated between 70 and 200-300 days
for injected vitamin B,, (Heinrich, 1964; Heysell,
Bozian, Darby & Meneely, 1965; Reizenstein, Ek
& Matthews, 1966). On the other hand, Boddy
(197 1) and Boddy & Adams (1972) find that the
excretion rate did not change significantly after
about 1 week after administration and our findings
are in keeping with this more recent analysis.
Bozian, Ferguson, Heysell, Meneely & Darby
(1 963) did not find a difference in excretion rates
between pernicious anaemia and normal subjects.
However, only three normal subjects were studied
and they showed a mean loss of 0*12%/day; in
their study, the mean loss in 11 pernicious anaemia
subjects was somewhat higher, at 0*13%/day.
The most likely explanation for the increased
clearance of the vitamin from patients with
pernicious anaemia is failure to reabsorb biliary
vitamin BIZ and vitamin BIZ entering the small
intestine in other secretions, e.g. pancreatic. The
amount of vitamin BIZentering the bile every day
has been estimated to be from 0.5 to 5 ,ug
(Ardeman, Chanarin & Berry, 1965). In normal
103
subjects, or indeed in vegans, this vitamin BIZis
presumably attached to intrinsic factor and reabsorbed. On the other hand, in the absence of
intrinsic factor as in pernicious anaemia, and when
there is a small intestinal defect as after ileal
resection or with colonization of the upper small
intestine with colonic bacteria, it is likely that malabsorption of biliary vitamin B,, as well as of
dietary vitamin BIZwill occur. Whether any factor
is present in pernicious anaemia which leads to
excess loss of vitamin BIZis uncertain. Excess loss
of the vitamin in pancreatic juice and in sloughing
gastric and small intestinal cells may, however,
contribute. At all events, the present results provide
an explanation for the clinical observation that
vegans often seem to be able to maintain the status
quo at mild degrees of vitamin B,, deficiency
without progressing to severe deficiency.
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