Toxicological evaluation of L-proline in a 90-day feeding study with Fischer 344 rats.

L-proline (L-Pro) is a non-essential amino acid, and has become widely used as supplements and health foods, recently. A subchronic oral toxicity study of L-Pro was conducted with groups of 10 male and 10 female Fischer 344 rats fed a powder diet containing 0%, 0.625%, 1.25%, 2.5% and 5.0% of L-Pro for 90 days. No treatment-related clinical signs and mortality were noted. We observed no clear treatment-related effects with regard to body weight, food intake or urinalysis data. The average daily water intakes of the treated female groups were significantly increased compared to the controls. The hematology (red blood cell parameter) and serum biochemistry (glucose, blood urea nitrogen, creatinine or uric acid) of the treated male and/or female groups were lower than those of the control groups. However, these changes were lacked dose-dependence, and no abnormalities were found in corresponding pathological findings. In conclusion, the no-observed-adverse-effect-level (NOAEL) for L-Pro was determined to be a dietary dose of 5.0% (2772.9 mg/kg body weight/day for males and 3009.3mg/kg body weight/day for females) under the present experimental conditions.

Toxic effects of l-aspartic acid at high dose levels on kidneys and salivary glands in Fischer 344 rats detected in a 90-day feeding study.

A subchronic oral toxicity study of l-aspartic acid (l-Asp) was conducted with groups of 10 male and 10 female Fischer 344 rats fed a powder diet containing 0%, 0.05%, 1.25%, 2.5% and 5.0% concentrations for 90 days. Serum biochemistry showed treatment-related decreases of blood urea nitrogen, creatinine and uric acid levels in both sexes. In addition, incidences of urinary ketone and protein were significantly increased in treated both sexes, while relative kidney weight was significantly increased in the 5.0% male rat, and regenerative renal tubules with tubular dilation were histopathologically observed in male rats of the 2.5% or greater groups. The observed renal injury was confirmed not to be due to accumulation of alpha2u-globulin. Acinar cell hypertrophy of salivary glands was histopathologically evident in male and female rats of the 2.5% or greater groups. The present results indicate that l-Asp causes toxic effects on kidneys and possibly salivary glands at high dose levels in male and female Fischer 344 rats. Such toxic effects were observed only in animals given 2.5% and/or higher doses of l-Asp. In conclusion, the no-observed-adverse-effect-level (NOAEL) for l-Asp is 1.25% (696.6 mg/kg body weight/day for males and 715.2 mg/kg body weight/day for females) under the present experimental conditions.

Chronic toxicity of thiabendazole (TBZ) in CD-1 mice.

Male and female CD-1 mice (50 mice per group) were administered thiabendazole (TBZ) in diet at levels of 0 (control), 0.031, 0.125 and 0.5% for 78 weeks. A life time study was terminated after 78 weeks due to enhanced strain specific mortality. There were no significant differences in mortality between the control and treated groups. Mean body weights of high-dose groups showed significant decreases compared with the controls. The bladder weights of male and female mice of the 0.5% group were significantly higher than those of the control mice. Gross findings in treated mice included the renal atrophy, hydronephrosis, calculi in renal pelvis and/or bladder and ovarian atrophy. Microscopic findings in the kidneys of treated mice included the nephrosis, hydronephrosis or hyperplasia of transitional epithelium of renal pelvis or papilla. In the bladder of treated mice, hyperplasia or squamous metaplasia of transitional epithelium and one transitional cell papilloma were observed. Dose-dependent decreases in the incidence of spontaneous lesion in the male or female reproductive system were recognized. It is concluded that TBZ is not carcinogenic to CD-1 mice of both sexes. However, caution should be exercised in the long-term application of high TBZ doses.

Goitrogenic effects of green tea extract catechins by dietary administration in rats.

The effects of green tea extract catechins on the rat thyroid were examined in a 13-week feeding study and subsequent 2-,4- and 8-week studies. Commercially available polyphenon-60 (P-60) which contains green tea extract catechins at 66.2% was used as a source of catechins. A basic diet containing different concentrations of P-60 was used for experiments. In the 13-week study, 10 rats of each sex were administered diets containing P-60 at 0 (control), 0.625, 1.25, 2.5 and 5.0%. Goiters were observed in the 13-week test. The mean thyroid weight of rats fed a diet containing 5.0% of P-60 (5.0% group) significantly increased to 444% of the control in males and to 304% of the control in females. Histological examinations of the thyroid of the 5.0% group revealed marked hypertrophy and/or hyperplasia of the follicles, some with depletion of colloid and some with rich colloid, and formation of a fibrous capsule. Slight hypertrophy of follicular cells was observed in male rats fed a diet containing 1.25% of P-60 (1.25% group) and female rats fed a diet containing 2.5% of P-60 (2.5% group). Degree and incidence of thyroid lesions were higher in males than in females in the 1.25, 2.5 and 5.0% groups. In the 2-8-week studies, five rats of each sex were given diets containing 0 (control) and 5.0% of P-60. In the 5.0% group, the mean thyroid weight in males significantly increased to 161% of the control as early as 2 weeks and increased to 357% of the control at 8 weeks. Histologically, these goiters were also associated with follicular cell hypertrophy/hyperplasia as in the 13-week study. The degree and incidence of thyroid lesions were higher in males than in females. These results indicate that dietary administration of the green tea extract catechins at high doses induced goiters in rats, and this may be due to antithyroid effects of catechins. In the 13-week study, the no-observed effect level (NOEL) of green tea extract catechins for F344 rats based on histological changes of the thyroid was considered to be 0.625% in males and 1.25% in females in the diet, respectively.

Inhibitory action of (-)-epigallocatechin gallate on radiation-induced mouse oncogenic transformation.

The anticarcinogenic activity of a major component of green tea, (-) epigallocatechin gallate (EGCg) was examined by using the radiation-induced oncogenic transformation in C3H10T1/2 cells. EGCg substantially suppressed the radiation-induced transformation so that the transformation frequency with 15 microM of EGCg was reduced nearly to spontaneous levels. This effect of EGCg was in a dose-dependent manner and significant suppression of transformation was observed even in treatment of cells with 5 microM of EGCg concentration where the cytotoxicity was mild. The inhibitory effect of EGCg was maximal when it was present during the entire incubation period. However, neither treatment prior to nor concurrent with radiation was effective, suggesting that EGCg action is mainly involved in the promotional stage of C3H10T1/2 cell transformation.