GLUCOSE ISOMERASE (non-immobilized and immobilized)
from STREPTOMYCES RUBIGINOSIS
EXPLANATION
These enzymes preparations have not been previously reviewed by
the Joint FAO/WHO Expert Committee on Food Additives.
BIOLOGICAL DATA
Biochemical aspects
No information available.
Toxicological studies
Special studies on reproduction
Rats
Groups of 10-12 male Wistar-derived rats were fed diets for
60 days containing 0, 0.4, or 1.6% of an enzyme preparation
(non-immobilized), in use prior to 1973 (designated HFE), or 0.125 or
1.25% of an enzyme preparation immobilized to DEAE-cellulose
(designated DCI), which has been used since 1973. Females kept on the
same diets for 14 days were mated on a one-to-one basis with the dosed
males. After one week the first set of females were replaced with a
new set and mated with the males. One set of females was allowed to
cast their litters normally and nurse the young until weaning at 21
days. The second set of females was sacrificed on day 13 of pregnancy
and the uterine contents examined. The fertility was slightly
depressed in all dosed groups as compared to the control values and
the response was characterised as not unusual in animals fed semi-
purified diets. Resorptions were increased as compared to controls in
the high-dose HFE and DCI groups, but the magnitude of the effect was
not regarded as significant. There were no compound-related effects on
gestation, viability, or lactation indices, nor on corpora lutea,
total implants, or live fetuses (Cox et al., 1973).
Groups of 24-29 pregnant Wistar rats were fed diets which
provided 0, 200, or 800 mg/kg b.w./day of HFE, or 62.5 or 625 mg/kg
b.w./day of DCI. The test compounds were fed beginning at day 14 of
pregnancy and continued through parturition and lactation until
weaning at day 21. No compound-related changes were observed on
fertility, gestation, viability, or lactation indices (Cox et al.,
1973).
Special studies on teratology
Rats
Groups of 22 pregnant female Wistar-derived rats were given doses
of 0, 200, or 800 mg/kg b.w. of HFE, or doses of 62.5 or 625 mg/kg
b.w. of DCI by gavage daily from days 6 through 15 of pregnancy. The
animals were sacrificed and their uterine contents examined 1 day
prior to the full term of pregnancy. One-third of the foetuses were
subjected to visceral examination and two-thirds were processed for
skeletal examination. No compound-related effects were observed on
soft tissue or skeletal abnormalities, nor on number of implant sites,
resorption sites, or live and dead foetuses (Cox et al., 1973).
Rabbits
Groups of 13-17 female Dutch-belted rabbits were artificially
inseminated and dosed daily with 0, 200, or 800 mg/kg b.w. HFE or with
62.5 or 625 mg/kg b.w. DCI by gavage on days 6-18 of pregnancy. On day
28 the animals were subjected to Ceasarean section and the uterine
contents examined. The pups were placed in an incubator for 24 hours
for evaluation of neonatal survival, then examined for visceral
abnormalities and processed for skeletal examination. There was a
small increase in number of resorptions and/or foetal deaths in the
high-dose HFE groups. There were no compound-related effects on
corpora lutea, implant sites, live foetuses, or soft tissue or
skeletal anomalies (Cox, et al., 1973).
Acute toxicity
No information available.
Short-term studies
Rats
Groups of 20 weanling rats/sex/dose were fed diets containing 0,
3, 6, or 12% of an enzyme "cake" of a glucose isomerase preparation
for 90 days. Pathology studies were conducted on 10 animals of each
sex in the high-dose and control groups. No adverse effects were found
with respect to body-weight gain, clinical chemistry, haematology,
relative and absolute organ weights, or gross and microscopic
pathology (Oser, 1969).
A 33-week feeding study was carried out in Wistar rats. Groups of
30 males and 30 females were fed diets containing 0.4 or 4.0% HFE or
0.125 or 1.25% DCI. The animals in the high-dose HFE group showed a
marked decrease in food intake and began losing weight by the ninth
week. Four animals/sex in the high-dose HFE group were sacrificed and
necropsied at 10 weeks. The remaining animals in the high-dose group
were removed from the 4% diet and separated into 2 equal groups. One
group received a basal (control) diet and one received 2% of the HFE
preparation. An immediate resumption of food intake and growth ensued,
and after a 2-week period all of the original animals on the high-dose
diet were recombined and put on the 2% diet. An interim sacrifice of 5
animals/sex/group was conducted at week 16 for pathological
examination. Laboratory analyses for haematology, clinical chemistry,
and urinalysis were conducted on 10 animals/sex/group at 6, 12, and 26
weeks. The results of these analyses indicated no compound-related
effects. Gross and microscopic pathology studies and studies on organ
weights at 16 and 33 weeks showed no compound-related effects of
either enzyme preparation.
An additional study was conducted to determine if palatability
was the cause of the weight loss exhibited in the high-dose (4%) HFE
animals. Groups of 10 rats/sex were given 0 or 2000 mg/kg b.w. of the
HFE preparation daily by gavage in a water vehicle (both groups
received a control diet). Decreased weight gain was observed in the
treated rats, more markedly in the males. However, the magnitude of
the effect was much less than seen in the dietary study, indicating
that palatability was likely a factor in that study (Cox et al.,
1973).
Dogs
Groups of 5 dogs/sex were given diets containing 0.4 or 4.0% HFE,
or 0.125 or 1.25% DCI, for 30 weeks. An interim sacrifice of 1
animal/group/sex was carried out at 11 weeks in the high-dose group
and 14 weeks in the remaining groups. There were palatability problems
in dogs at the 4% level of the HFE preparation. After 2 weeks, 0.1%
dried garlic was added to their diet in an attempt to mask the odor of
HFE. At 12 weeks, because of reduced-weight gain and palatability
difficulties, the high-dose HFE diet was reduced to 2.0%. Other than
reduced-weight gain in the high-dose HFE dogs there were no compound-
related effects on weight gain, haematology, clinical chemistry,
urinalysis, organ weights, or gross or microscopic pathology
(Cox et al., 1973).
Long-term studies
No information available.
Observations in man
No information available.
Comments
Decreased weight gain, due in part at least to reduced dietary
palatability, was seen when high doses of the non-immobilized (HFE)
form of the enzyme was fed to rats and dogs. A suggestion of a
possible foetotoxic response was also seen when high doses of the
enzyme were given to rats and rabbits. No gross or microscopic
pathology was associated with this form of the enzyme.
The immobilized form of the enzyme showed no adverse effects in
short-term feeding studies in rats and dogs, teratology studies in
rats, dogs, and rabbits, or in reproduction studies in rats except for
a small increase in resorptions, which was of uncertain significance,
in animals given high doses of the substance.
EVALUATION
Level causing no toxicological effect
Non-immobilized enzyme
Rats: 2% (20,000 ppm) in the diet, equivalent to 2000 mg/kg
b.w./day.
Immobilized enzyme
Rats: 1.25% (12,500 ppm) in the diet, equivalent to 1250 mg/kg
b.w./day.
Estimate of acceptable daily intake for man
Non-immobilized enzyme
No ADI allocated, because no information was available on the food use
of the non-immobilized enzyme.
Immobilized enzyme
Acceptable for use in food processing when used as a component in an
immobilized system.
REFERENCES
Cox, G.E., Bailey, D.E., & Morareidge, K. (1973). Sub-acute feeding
studies in rats and dogs with glucose isomerase enzyme
preparations. Unpublished report of Food and Drug Research
Laboratories, Inc., Waverly, NY, USA. Submitted to WHO by Nabisco
Brands, Inc.
Oser, B.L. (1969). Subacute (90 day) feeding studies with enzyme cake
and isomerase 100 (converted starch). Unpublished report of Food
and Drug Research Laboratories, Inc., Waverly, NY, USA. Submitted
to WHO by Nabisco Brands, Inc.