INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
WORLD HEALTH ORGANIZATION
TOXICOLOGICAL EVALUATION OF SOME
FOOD COLOURS, ENZYMES, FLAVOUR
ENHANCERS, THICKENING AGENTS, AND
CERTAIN FOOD ADDITIVES
WHO FOOD ADDITIVES SERIES 6
The evaluations contained in this publication were prepared by the
Joint FAO/WHO Expert Committee on Food Additives which met in Rome,
4-13 June 19741
World Health Organization Geneva 1975
1 Eighteenth Report of the Joint FAO/WHO Expert Committee on
Food Additives, Wld Hlth Org. techn. Rep. Ser., 1974, No. 557.
FAO Nutrition Meetings Report Series, 1974, No. 54.
GUANYLIC ACID, CALCIUM AND DISODIUM SALTS
BIOLOGICAL DATA
BIOCHEMICAL ASPECTS
GMP is widely distributed as a component of RNA in living
organisms. GMP is dephosphorylated to guanosine, hydrolyzed further to
guanine, deaminated to xanthine and oxidized finally to uric acid or
allantoin in mammals. Two-thirds of this is excreted in the urine, the
rest is excreted and further broken down in the gut. Digestion appears
to take place mainly in the duodenum, the nucleosides being probably
absorbed actively, the purines probably by diffusion across the
intestinal wall. The greater portion of GMP in the body is derived
from de novo purine bio-synthesis, the rest derived from preformed
dietary purines. Biosynthesized IMP is the precursor of GMP to which
it is converted by oxidation to xanthosine-5 mono-phosphate and
amination. Dietary or endogenous purine bases and ribo-nucleosides are
also converted to the 5'-ribonucleotides by phosphorylation (Kojima,
1973).
500 mg/kg i.v. GMP produced in mice abdominal postures, slight
respiratory depression and slight depression of avoidance response
after 15 minutes. There was no muscular relaxation but depression of
rotating activity for one hour, no modification of electroshock
convulsion but a decrease, dose-dependent, of the convulsive dose of
metrazole as well as increased loss of righting reflex (Kojima, 1973).
100 mg/kg GMP intragastric in mice did not affect intestinal transport
as measured by charcoal transportation. Concentrations below 10-4g/ml
had no effect on the contractile response of isolated guinea-pig ileum
to acetylcholine, histamine or barium chloride. 100 mg/kg GMP s.c. in
rats did not affect gastric juice secretion but slightly increased pH
and depressed total acidity. 100 mg/kg s.c. GMP in mice depressed
salivary secretion (Kojima, 1973).
Rapid intracarotid injection increased the cerebral blood flow
but did not affect the oxygen consumption and glucose uptake of the
perfused cat brain (Otsuki et al., 1968). Intravenous GMP had no
significant effect on the B.P. heart-rate and ECG of the anaesthetized
rabbit (Yabo, 1964). Parenteral GMP produced transient changes in the
EEG of rabbits (Hirayama, 1968) and i.p. GMP had no marked effect on
the conditioned avoidance response of the rat (Hirayama, 1968).
Topical GMP enhanced the electrical response of the chordatympani to
topical MSG in the rat (Sato et al., 1965).
25 mg/kg GMP intragastrically had no diuretic effect in rats.
Oral 500 mg/kg GMP in mice did not affect the analgesic response of
mice or carrageenin oedema in rats (Kojima, 1973). Male and pregnant
(day 10 or 18 of gestation) rats were given by gavage 25 mg/kg bw of
8-14C GMP. Plasma radioactivity reached a maximum within 30 minutes
after ingestion and decreased abruptly to practically zero within 24
hours, the half life being about one hour. About 84% of total activity
appeared in urine, 0.2% in faeces, none in expired air, between 0-0.6%
remained in organs, about 12% in organ-free carcass of males and 18
day pregnant females 24 hours after treatment. The foetus contained
about 0.01% activity 24 hours after treatment (Ohara et al., 1973).
Groups of five male rats (control group 10) were given 0%, 1% and 4%
GMP for five or 10 days in a purine free basal diet. Levels of uric
acid in serum and urine were hardly affected, most of the exogenously
ingested GMP was rapidly excreted in urine as allantoin. Only liver
hypoxanthine-guamine phosphoribosyl transferase and adenine
phosphoribosyl transferase activities were increased and also the
ratio of liver uricase/xanthine oxidase activity suggesting metabolism
by shunt pathways for exogenously ingested GMP (Hashimoto et al.,
1973).
TOXICOLOGICAL STUDIES
Special studies on teratogenicity
Rat
One group of nine pregnant rats was given daily 100 mg/kg bw of
GMP during days 9-15 of pregnancy. No significant effects on fetuses
were noted (Kaziwara et al., 1971).
Rabbit
Three groups of 9-10 pregnant rabbits were fed diets containing
either normal diet (12 animals), or 0.2 g/kg bw or 2.0 g/kg bw GMP
from days 6-18 of gestation. All except four dams in each group
were sacrificed on day 29, the remainder was allowed to litter
spontaneously, pups being observed until 30 days of age. No adverse
effects were noted on body weight and food consumption except the
group on 2.0 g/kg which had reduced food consumption. Implantation
numbers did not differ from controls but mortality of fetuses in the
2.0 g/kg group was lower than in controls. All groups showed some
delay in ossification, but no treatment - specific skeletal
abnormalities. There were no effects on number of delivered fetuses,
survival rate of the 0.2 g/kg group was greater at weaning. Mean pup
body weights were normal and no significant malformations were found
in the pups of both dosage groups (Jojima et al., 1973).
Chick embryo
GMP was neither highly toxic nor teratogenic in this system
(Karnofsky et al., 1961).
Acute toxicity
LD50
Animal Route (mg/kg bw) References
Mouse Oral 10 000 Usui et al., 1971
Oral (male) 15 000 Ichimura & Muroi, 1973
Oral (female) 16 300 " " "
s.c. (male) 5 050 " " "
s.c. (female) 5 050 " " "
i.p. (male) 6 800 " " "
i.p. (female) 5 010 " " "
i.v. (male) 3 580 " " "
i.v. (female) 3 950 " " "
Rat Oral 10 000 Usui et al., 1971
Oral (male) 17 300 Ichimura & Muroi, 1973
Oral (female) 17 300 " " "
s.c. (male) 3 550 " " "
s.c. (female) 3 400 " " "
i.p. (male) 4 750 " " "
i.p. (female) 3 880 " " "
i.v. (male) 2 720 " " "
i.v. (female) 2 850 " " "
Short-term studies
Rat
Three groups of 10 male and 10 female rats were given 0%,
0.1% and 1% of GMP in their diet daily for three and six months.
No significant abnormalities were noted as regards spontaneous
behaviour, body weight gain, food intake, haematology, urinalysis,
macroscopic and histological examination (Usui et al., 1971).
Long-term studies
None available.
Comments:
Inosinates, guanylates and ribonucleotides are substances
normally present in all tissues and their role in purine metabolism
as well as their breakdown in the majority of mammals, but not man,
to uric acid and allantoin is well known. The various products have
been studied adequately in long-term, reproduction and teratology
tests. Ingestion of large amounts of these compounds by man can
increase the serum uric acid level and urinary uric acid excretion
and this needs to be considered in relation to people with gouty
diathesis and those taking uric-acid retaining diuretics. Hence
specific mention of the addition of these substances on the level may
be indicated. The changes in dietary purine intake from the use of
flavour enhancers are no greater than those likely to be occasioned
by changes in consumption of those dietary items which are the main
contributors of purine.
EVALUATION
Acceptable daily intake not specified1.
1 The statement "ADI not specified" means that, on the basis of
the available data (toxicological, biochemical, and other), the total
daily intake of the substance, arising from its use or uses at the
levels necessary to achieve the desired effect and from its acceptable
background in food, does not, in the opinion of the Committee,
represent a hazard to health. For this reason, and for the reasons
stated in individual evaluations, the establishment of an acceptable
daily intake (ADI) in mg/kg bw is not deemed necessary.
REFERENCES
Hashimoto, S. et al. (1973) Life Sciences Laboratories, Ajinomoto Co.,
Japan
Hirayama, H. (1968) Folia pharmacol, jap., 64, 279
Ichimura, M. & Muroi, K. (1973) Report of Life Sciences Laboratories,
Ajinomoto Co. Japan
Jojima, M. et al. (1973) Report of Life Sciences Laboratories,
Ajinomoto Co. Japan
Karnofsky, D. A. & Lacon, C. R. (1961) Biochem. Pharmacol., 7, 154
Kaziwara, K., Mizutani, M. & Ihara, T. (1971) J. Takeda Res. Lab.,
30(2), 314-321
Kojima, K. (1973) Safety evaluation of IMP, GMP and DSRN, Toxicology,
2, (in press)
Ohara, V., Matsuzawa, V. & Takeda, J. (1973) Report of Life Sciences
Laboratories, Ajinomoto Co. Japan.
Otsuki, S. et al. (1968) Med and Biol., 76, 107
Sato, M. et al. (1965) Jap. J. Physiol., 15, 53
Usui, T. et al. (1971) J. Takeda Res. Lab., 30(3), 614-635
Yabo, S. (1964) Folia pharmacol, jap., 60, 194
See Also:
Toxicological Abbreviations