MANNITOL
EXPLANATION
Mannitol was evaluated for acceptable intake at the tenth,
eighteenth, twentieth, and twenty-ninth meetings of the Joint FAO/WHO
Expert Committee on Food Additives (Annex 1, references 13, 35, 41,
and 70). A toxicological monograph was published after the tenth
meeting (Annex 1, reference 12). At its twenty-ninth meeting, the
Committee extended the temporary ADI of 0-50 mg/kg b.w. to 1986
pending submission of the results of a number of long-term studies
completed but not submitted for evaluation. The previously-published
monograph has been expanded and is reproduced in its entirety below.
BIOLOGICAL DATA
Biochemical aspects
D-Mannitol occurs widely in nature in a variety of plants, algae,
fungi and certain bacteria. L-Mannitol does not occur naturally.
Traces of mannitol have been identified occasionally in human urine
(Pitkänen & Pitkänen, 1964).
When 14C-D-mannitol was given at a dose of 240 mg/rat orally to
non-fasted rats, about 50% of the radioactivity was recovered in the
expired 14CO2 (Wick et al., 1954).
In similar experiments, also using 14C-D-mannitol at 500 mg/kg
b.w., fasted rats oxidized 40% of the dose to 14CO2, non-fasted
rats oxidized 68%; 9.74% was stored in the carcass, 1.28% in the
liver, and 6.32% was excreted in the urine (Gongwer, 1963).
Feeding D-mannitol to rats and dogs led to a small but
significant increase of liver glycogen (Carr et al., 1933;
Todd et al., 1939; Silberman & Lewis, 1933; Carr & Krantz, 1938).
When 14C-D-mannitol was administered to rats by i.p. injection,
77-97% of the dose was excreted in the urine within 24 hours, and only
2-3% of the mannitol carbon was oxidized to 14CO2. Additional
experiments, in which mannitol was injected directly into the portal
vein, showed that mannitol could be oxidized only by the liver
(Wick et al., 1954).
D-Mannitol administered i.v. was completely cleared by the
kidneys of 2 dogs at rates identical to inulin and creatinine
(Smith et al., 1940).
Mannitol at a dose of 22.5 g/dog did not elevate the blood sugar
level of dogs after i.v. injection (Todd et al., 1939).
Toxicological studies
Special studies on carcinogenicity
Mice
Diets containing 0, 2.5, or 5% mannitol (0, 3750, or 7500 mg/kg
b.w., respectively) were fed to groups of 50 B6C3F1 mice of each sex
for 103 weeks. The mice were observed twice daily for clinical signs
of toxicity and body weights were recorded weekly. The body weights of
treated females were similar to those of controls, while those of the
treated males were slightly but not significantly higher than those of
controls; feed consumption was similar to controls in both dose
groups. There were no significant differences in survival rates nor in
tumour incidence between treated animals and controls. Mild nephrosis,
characterized by focal vacuolation of the tubular epithelium, was
observed in increased incidence in treated mice of both sexes (control
males 30%, low-dose males 58%, high-dose males 64%, control females
2%, low-dose females 6%, high-dose females 29%). The authors concluded
that this vacuolation was probably caused by osmotic imbalance. Under
the conditions of this bioassy, mannitol was noncarcinogenic to
B6C3F1 mice (NTP, 1982; Abdo et al., 1983).
Rats
Groups of 50 male and female F344 rats were fed diets containing
0, 2.5, or 5% mannitol for 103 weeks (corresponding to 0, 1250, or
2500 mg/kg b.w./day). The body weights of treated males were similar
to those of controls, while those of treated females were slightly but
not significantly lower than those of controls; feed consumption was
similar to controls in both dose groups. There were no significant
differences in survival rates nor in tumour incidence between treated
animals and controls. Retinopathy and cataracts occurred at increased
incidences in high-dose male and mid- and high-dose female rats
(retinopathy: males-17/50, 6/50, 42/50; females-10/50, 3/50, 33/50;
cataracts: males-15/50, 6/50, 40/50, females-9/50, 40/50, 32/50; all
for the controls, mid-, and high-dose groups respectively). This
increase appears to be associated with the distance of the animals
from sources of fluorescent light; however, a contributing effect of
mannitol cannot be discounted completely. Dilatation of the gastric
fundal gland was observed at increased incidences in dosed females
(control, 6/50 (12%); low-dose, 23/50 (46%); high-dose, 23/50 (46%)).
Under the conditions of the bioassay, mannitol was not carcinogenic to
F344 rats (NTP, 1982; Abdo et al., 1983).
Special studies on mutagenicity
Mannitol was non-mutagenic in a host-mediated assay in mice using
Salmonella typhimurium G46 and TA1530 and Saccharomyces cerevisiae
strain D3, in a cytogenic assay in rat bone marrow, and in human W1-38
cells (Green, 1977).
Mannitol was not mutagenic in the Ames test using S. typhimurium
strains TA98, TA100, TA1535, and TA1537 (NTP, 1981).
Results of a dominant lethal assay in rats at doses of mannitol
of 0, 20, 200, 2000, and 5000 mg/kg b.w. by gavage were negative
(U.S. FDA, 1974).
Special study on renal reabsorption
Intravenous administration of mannitol at an initial dose of
0.3 g followed by hourly injections of 1 g to Sprague-Dawley rats
resulted in complete inhibition of salt and water reabsorption from
the medullary collecting system of the kidney (Sonnenberg, 1978).
Special studies on teratogenicity
Mannitol was tested for teratogenic effects in mice, rats, and
hamsters. Pregnant mice and rats given oral doses of mannitol up to
1.6 g per kg for 10 consecutive days and hamsters up to 1.2 g per kg
for 5 consecutive days showed no effects on maternal or fetal
survival. Mannitol was not teratogenic under the test conditions
(FDRL, 1972).
Acute toxicity
LD50
Animal Route (mg/kg b.w.) Reference
Mouse oral 22,000 Gongwer, 1960
i.v. 16,800 Robb, 1964
i.p. 14,000-16,000 Beck et al., 1936
Rat oral 17,300 Gongwer, 1960
Mice died with signs of central nervous system depression and
gastrointestinal tract mucosal damage; rats died with predominantly
gastrointestinal tract signs (Gongwer, 1960; Gongwer, 1961).
Short-term studies
Mice
Groups of five male and five female B6C3F1 mice were fed diets
containing 0.6, 1.25, 2.5, 5.0, or 10.0% mannitol for 14 days. No
control groups were used. Animals were killed on days 16-20 and
necropsies performed on all animals. All animals survived to the end
of the dosing periods and all groups had similar increases in body
weight. No compound-related effects were observed (NTP, 1952).
Groups of 10 male and 10 female B6C3F1 mice were fed diets
containing 0, 0.3, 0.6, 1.2, 2.5, or 5.0% mannitol for 13 weeks. On
one day animals from the 0.3 and 0.6% dose groups were accidently
given diets containing 0.3 or 0.6% Ziram. Animals were checked for
mortality/ morbidity twice daily. Each animal was subjected to
clinical examination and palpation weekly, and body weights and food
intake were recorded weekly. Necropsies were performed on animals in
the control and top two dose groups. Mean body-weight gain was higher
than controls in all dose groups except males of the top-dose group,
where weight gain was similar to controls. All animals survived to
termination and no compound-related effects were observed at necropsy
or on histopathological examination (NTP, 1982).
Rats
Groups of 20 rats were fed 35% sucrose plus 5% mannitol or 40%
sucrose (control group) over a period of 3 months. The growth curves
showed that mannitol was nutritionally inferior to sucrose (Ellis &
Krantz, 1941). These results are in accord with earlier findings that
mannitol is inferior to sucrose, as judged by weight gain of rats
(Ariyama & Takahasi, 1929).
Groups of 5 male and 5 female F344/N rats (6 weeks of age) were
fed diets containing 0.6, 1.2, 2.5, 5.0, or 10% mannitol for 14 days.
No control groups were used. Animals were killed on days 16-20 and
necropsies performed on all animals. All animals survived to the end
of the dosing period. Females fed diets containing 10% mannitol gained
less weight than did other groups. Two of 5 males in the top-dose
group developed diarrhoea from days 4 to 6. No gross lesions were
reported at autopsy (NTP, 1982).
Groups of 10 male and 10 female F344 rats were fed diets
containing 0, 0.3, 0.6, 1.25, or 5.0% mannitol for 13 weeks. On one
day, animals from the 0.3 and 0.6% dose groups were accidentally given
diets containing 0.3 or 0.6% Ziram. Animals were checked for
mortality/morbidity twice daily. Each animal was subjected to clinical
examination and palpation weekly, and body weights and food intake
were recorded weekly. Necropsies were performed at termination and
haematological and histopathological examinations were performed on
animals in the control and two highest-dose groups. Mean body-weight
gains of the top-dose group males were depressed by 9.6% relative to
controls; mean body-weight gains of other groups were similar to
controls. All animals survived and no compound-related clinical signs
or histopathologic effects were observed (NTP, 1982).
Monkeys
Three rhesus monkeys were fed 3 g mannitol daily for 3 months.
Two animals were employed as controls. No toxic signs nor pathological
changes were observed (Ellis & Krantz, 1941).
Long-term studies
Rats
Wistar-derived SPF albino rats were fed 0, 1, 5, or 10% mannitol
in their diets for 94 weeks (40 males and 40 females/group).
Decreasing amounts of corn starch (10, 9, 5, or 0% respectively) were
added to each diet. Body weights were generally decreased by
approximately 5-7% in the medium- and high-dose male rats. Food
consumption, haematology, haemochemistry, histopathology, and most
urinalyses were unaffected by mannitol administration. Total urinary
calcium and magnesium were elevated in a dose-related manner, but
these were not considered to be pathological changes.
Histopathological evaluation revealed that most neoplasms were
unrelated to treatment, but a low incidence of benign thymomas in
female rats was apparently treatment-related (2 benign thymic tumours
in female controls, 6 in each of the 1 and 5% mannitol groups, and 10
in the 10% mannitol group). No significant group differences occurred
for thymomas in male rats (0 in controls, 3 at 1%, 1 at 5%, and 0 at
10% of mannitol in the diet). No additional treatment-related
neoplasms occurred in other lymphopoietic tissues (Saatman
et al., 1978).
Female rats of the Sprague-Dawley strain were administered
mannitol at dose levels of 0, 1, 5, or 10% of the diet. All surviving
rats were killed after 27 months of treatment, when mortality of the
rats receiving 10% mannitol was 68%. Evaluation of mortality, general
health and behaviour, body weight, food consumption, urinary
chemistry, organ weights, and subcutaneous tissue masses observed
in-life did not indicate any effects due to the administration of
mannitol. In addition, evaluation of all gross necropsy findings, as
well as histopathological evaluations of the thymus of all rats, and
histomorphology of all other tissues of those rats with thymic
abnormalities, resulted in the conclusion that there was no effect of
mannitol on Sprague-Dawley rats in this study (Gongwer et al.,
1978).
Female rats of the Wistar strain (100 animals/group) were
administered mannitol at dose levels of 0, 1, 5, or 10% of the diet
for 30 months. Histopathological evaluations of the thymus of these
rats revealed no effect of mannitol on the development of primary
thymic neoplasms. Other findings in the thymus, and in other tissues
examined histopathologically in those rats with thymic abnormalities,
were not attributable to the administration of mannitol. There was no
indication that the incidences of gross necropsy findings were related
to the administration of mannitol. Slightly increased incidences of
tissue masses in the cervix and/or uterus noted in the compound-
treated groups as compared to the control were considered of
no biological importance because of their low overall incidence. Mean
adjusted body-weight values of the group which received 10% mannitol
in the diet were lower (and occasionally statistically significant)
than in the concurrent control group when all animals were weighed at
weeks 26 and 52, and when rats of selected replicates were weighed at
weeks 88-120. Most mean values of the rats receiving 1% of the
compound in the diet were slightly lower than those of controls
throughout the study; mean body weights of rats receiving 5% mannitol
were slightly lower than control weights from approximately weeks
88-120. Differences in these two groups, however, were slight and not
statistically significant. Evaluation of mortality, general health and
behaviour, food consumption, urinary chemistry and volume, terminal
organ and body weights, and subcutaneous tissue masses observed
in-life did not indicate any effects which could be attributed to the
administration of mannitol at levels of 1, 5, and 10% of the diet
(Gongwer et al., 1978).
Female Fischer rats (100 animals/group) were administered
mannitol at dose levels of 0, 1, 5, or 10% of the diet for 30 months.
Histopathological evaluation of the thymus of these rats revealed no
effect of mannitol on the development of primary thymic neoplasms.
Other findings in the thymus, and in other tissues examined
histopathologically in those rats with thymic abnormalities, were not
attributable to the administration of mannitol. The incidences of
gross necropsy findings were not related to the administration of
mannitol.
Slightly increased incidences of tissue masses in the anogenital
area, cervix, and uterus were noted in the 10% Fischer rat group as
compared to the control group. These findings were not considered to
be of biological importance; the incidence of uterine masses in this
study were well within the expected spontaneous incidence rate for
this strain of rats. The combined incidence of focal medullary
hyperplasia and medullary pheochromocytoma was higher in the high-dose
group than in the control or other test groups. However, there
was no clear dose response of focal medullary hyperplasia and
pheochromocytoma, and the investigating pathologists concluded that
this increased incidence was probably a chance occurrence unrelated to
the administration of mannitol.
Mean body weights of Fischer rats receiving mannitol at dietary
levels of 5 and 10% were slightly lower than concurrent control
weights from weeks 13 and 60, respectively, through termination of the
study (with the exception of week 108 in the 5% group). These
differences were generally small (less than 9%), and the majority were
not statistically significant. No consistent dose relationship was
evident. Evaluation of mortality, general health and behaviour, food
consumption, urinary chemistry and volume, terminal organ and
body-weights, and subcutaneous tissue masses observed in-life did not
indicate any effects which could be attributed to the administration
of mannitol at levels of 1, 5, and 10% of the diet (Gongwer et al.,
1978).
Observations in man
mannitol has a slow rate of absorption from the intestinal tract
and exerts laxative properties. The laxative threshold for man was
found to lie between 10 and 20 g of mannitol per single dose (Ellis &
Krantz, 1941).
In man, i.v. administration of mannitol is practiced for
induction of diuresis in oliguria, for forced diuresis in poisoning
cases, or to measure the extracellular fluid compartment. There is an
extensive literature available on these aspects (Milde, 1965;
Widdowson & Dickerson, 1964).
Following the i.v. injection of 10 g mannitol into man, 81% of
the dose was excreted unchanged in the urine and up to 80 g produced
no toxic effect (Smith et al., 1940).
Administration of 25 g mannitol on 3 subsequent days did not
significantly influence either the blood-sugar level or the
respiratory quotient (Ellis & Krantz, 1941).
When 100 g mannitol was fed, the maximum increase in blood sugar
level was 10 mg/dl (Field, 1919).
The i.v. injection of 10 g of mannitol daily over a period of 1
month produced no significant changes in non-protein nitrogen,
CO2-combining power of blood, red cell count, or renal function
(Ellis & Krantz, 1941).
Ten patients fasted overnight were administered 28 to 100 g of
(U-14C)-mannitol orally as a 5% aqueous solution. Within this dose
range, about 20% of the mannitol ingested was excreted unchanged in
the urine, indicating appreciable absorption. The level of
radioactivity in the blood rose for the first 2 hours and remained at
a plateau for 2 to 4 hours; the radioactive compounds present in blood
were not identified and data on blood glucose levels were not
reported. Expired 14CO2 increased for 8 hours after mannitol
ingestion; however, (U-14C)-mannitol administered i.v. produced very
little radioactive CO2. Oral doses of 40 g or more generally caused
frequent bowel movements, diarrhoea, and excretion in the stool of a
higher percentage of the dose. Only traces of radioactivity occurred
in the urine and stools after 48 hours. It was concluded that within
an oral dose range of 40 to 100 g, approximately 65% of ingested
mannitol was absorbed; about one-third of the absorbed mannitol was
excreted in the urine, the remainder being metabolized presumably in
the liver (Nasrallah & Iber, 1969).
Based on the above study, the caloric value of dietary mannitol
was considered to be about 2 kcal per g (Dwivedi, 1977).
Comments
Mannitol is dehydrogenated to fructose and then metabolized
through the mammalian glycolytic pathway; it occurs endogenously in
humans.
No mutagenic or cytotoxic effect was found when mannitol was
tested in vitro and in vivo. Teratogenic studies in several
species did not reveal any compound-related adverse effects.
Mannitol, when fed to rats and mice at up to 5% of the diet, was
not carcinogenic. Retinopathy and cataract formation occurred at
increased incidences in male rats in the earliest carcinogenicity
study, but these effects were not seen in four subsequent studies. An
increase in the number of benign thymomas was noted in female Wistar
rats, observed in a lifetime feeding study, and this was not
reproduced in three other studies designed to evaluate the species
specificity of this finding. One of the species tested (female Fischer
rats) had an increased incidence of adrenal medullary hyperplasia plus
pheochromocytoma (for a discussion of adrenal medullary lesions
produced by polyols, see Annex 1, reference 62, section 2.5).
Clinical experience with this substance as a therapeutic agent in
man has indicated no adverse effects. Mannitol is poorly absorbed and
exerts a laxative effect on man and animals, a common feature of all
polyols.
EVALUATION
Estimate of acceptable daily intake for man
ADI "not specified". The fact that high doses of mannitol exert a
laxative effect in man, which is common feature of all polyols, should
be taken into account when considering appropriate levels of use of
polyols, alone and in combination.
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