WHO/Food Add./24.65 FAO Nutrition Meetings Report Series No. 38A SPECIFICATIONS FOR IDENTITY AND PURITY AND TOXICOLOGICAL EVALUATION OF SOME ANTIMICROBIALS AND ANTIOXIDANTS The content of this document is the result of the deliberations of the Joint FAO/WHO Expert Committee on Food Additives which met 8-17 December 1964a a Eighth Report of the Joint FAO/WHO Expert Committee on Food Additives, Wld Hlth Org. techn. Rep. Ser., 1965, 309; FAO Nutrition Meetings Report Series 1965, 38. NORDIHYDROGUAIARETIC ACID CHEMICAL NAMES Nordihydroguaiaretic acid; ß,gamma-dimethyl-alpha,delta-bis-(3,4- dihydroxyphenyl) butane; 4,4'-(2,3- dimethyltetramethylene) dipyrocatechol SYNONYM NDGA EMPIRICAL FORMULA C18H22O4 STRUCTURAL FORMULAMOLECULAR WEIGHT 302.37 DESCRIPTION Nordihydroguaiaretic acid is a white to greyish-white crystalline solid, which may be prepared from an evergreen desert shrub, Larrea divaricata. 1 g is soluble in 4 ml of ethanol. USE As an antioxidant in oils and foods. Biological Data Biochemical aspects There does not appear to be any information on the metabolism of NDGA.1 The effect of NDGA on enzyme systems has been studied. Specific inhibition of peroxidase, catalase, and ethyl alcohol dehydrogenase occurs with a concentration of 2x10-4 M of the antioxidant. Non-specific inhibition of ascorbic acid oxidase, D-amino-acid oxidase, the cyclophorase system and urease at a concentration of 2x10-3 M has been described.2 Acute toxicity Animal Route LD50 Reference (mg/kg body-weight) Rat oral 2000-5000 3 Mouse oral 2000-4000 3 Mouse intraperitoneal 550 3 Guinea-pig oral 830 3 Short-term studies Guinea-pig. NDGA was found to be among the more strongly reacting compounds among several antioxidants tested for their capacity to induce skin sensitivity in the guinea-pig.4 Dog. NDGA was fed to young mongrel dogs at dietary levels of 0.1% (3 dogs), 0.5% (4 dogs) and 1.0% (5 dogs) for 1 year. Adult dogs were fed the same range of dietary concentrations, the numbers in the groups being 2, 3 and 2 respectively, with 2 controls. The growth curves of the young dogs showed some impairment in weight gain at the 0.5% levels but not at the 0.1% and 1.0% levels. No significant pathological changes were found which were attributable to the treatment and all the dogs were in good physical condition at the time of sacrifice.5 Long-term studies Mouse. Long-term studies were carried out using 0.25% and 0.5% levels in mice. No deleterious effects on weight gain were observed, nor any important histological changes.6 Rat. Chronic toxicity experiments were conducted over a period of 2 years, in which NDGA was compared with phenol, catechol and gum guaiac in concentrations of 0.5% in rats. NDGA had little or no effect on growth or food intake, except in the highest concentration, where there was a temporary decrease in growth associated with a decreased food intake. Histological study of the liver, spleen and kidneys showed no significant effect. Necrosis of the liver was noted occasionally in all groups, including controls.6 Concentrations of 0.1%, 0.5% and 1.0% of NDGA were used in another series of rats. Haemorrhage into the caecum was observed in 50% of the animals. In a larger series of tests on rats at the same concentrations of NDGA, this haemorrhage did not occur. Cysts in the mesentery were found in several rats on the higher concentrations of NDGA. Two-year toxicity tests on groups of 10 male rats at 0%, 0.1%. 0.25%, 0.5% and 1% NDGA in the diet showed that 0.5% was the lowest level causing inflammatory caecal lesions and slight cystic enlargement of lymph nodes near the caecum. Growth inhibition occurred after the first 6 months at levels of 0.5% and 1%.3 In another experiment lasting 2 years, 0.5% of NDGA in the diet caused massive caecal haemorrhages, with single and multiple cysts in the mesentery in the angle of the junction between the small and large intestines. During the first 6 months, inhibition of the growth rate occurred only at the 1% level.3 (Work in progress) Groups of 20 rats (10 male and 10 female) were fed the following diets: 0.5% NDGA, 0.5% NDGA plus aspirin, 1% NDGA, 1% NDGA plus aspirin, and aspirin for 65 weeks. Growth has been retarded in all test groups compared with the controls.a Haemoglobin and haematocrit determinations were done at 16 and 23 weeks; all groups where NDGA was given had lower readings than those of the controls.a Two rats, one fed 0.5% NDGA plus aspirin, the other aspirin alone, showed some ulceration of the stomach after 42 and 50 weeks on test. Examination of faeces for occult blood was done after 49 weeks; the rats fed NDGA with no aspirin were all negative, but 5 rats fed aspirin alone or aspirin plus NDGA showed traces of occult blood.7 Hamster. (Work in progress) Hamsters (15 male and 15 female) were fed diets containing 0.1%, 0.5% and 1% NDGA for 65 weeks. Some deaths which occurred at the 1% level may be attributed to the effect of NDGA in the diet. Ulceration of the stomach was found in 3 hamsters at the 1% level after 48 weeks. At 22 weeks a marked decrease in haematocrit values was found for females, but not in males, on 1% NDGA. Examination of faeces for occult blood was negative in all groups. The investigator points out that 1% NDGA in the diet of hamsters produced a definite toxic effect, particularly in the female. Whether the lower level will prove to be the no-effect level will depend on the findings upon completion of the test, which is to he carried out over the lifetime of the animals.7 Comment on experimental studies reported The acute toxicity studies indicate that the guinea-pig is more sensitive than the rat but no long-term studies with the former species have been reported. The short-term studies in the dog suggest that a 1% dietary level is well tolerated in this species although there was some impairment of growth at the 0.5% level. The published long-term studies in the rat and mouse provide little detailed information and seem to have left some of the investigators in doubt a No statistical evaluation has yet been done as these experiments are not terminated; they are being carried out over the life span of the animals. about the acceptability of NDGA. The more recent long-term studies in rat and hamster are still in progress and cannot be evaluated until their completion. Evaluation Level causing no significant toxicological effect in the rat From the limited information available, it is not possible to evaluate the toxicological status of NDGA. No guidance can therefore be given at present on the use of NDGA as an antioxidant in food. Further Work Required 1. Further long-term studies in the rat and other species, including dog. 2. Metabolic studies in animals and man. References 1. Dacre. J. C. (1960) J. N.Z. Inst. Chem., 24, 161 2. Tappel, A. L. & Marr. A. G. (1954) J. Agr. Food Chem., 2, 554 3. Lehman, A. J., Fitzhugh, O. G., Nelson, A. A. & Woodard, G. (1951) Advanc. Food Res., 3, 197 4. Griepentrog, F. (1961) Arzneimittel-Forsch., 11, 920 5. Anderson, W. D., Bell, B. J. & Bieter, R. N. (1955) Unpublished report 6. Cranston, E. M., Jensen, M. J., Moren, A., Brey, T., Bell, E. T. & Bieter, R. N. (1947) Fed. Proc., 6, 318 7. Mannell, W. A., Canadian Food and Drug Directorate, Ottawa (Letter dated 23 September 1964)
See Also: Toxicological Abbreviations Nordihydroguaiaretic acid (FAO Nutrition Meetings Report Series 46a) Nordihydroguaiaretic acid (WHO Food Additives Series 5) NORDIHYDROGUAIARETIC ACID (JECFA Evaluation)