Chronic oral toxicity of a synthetic antioxidant, 2,2'-methylenebis(4-ethyl- 6-tert-butylphenol), in rats

2,2'-Methylenebis (6-tert-butyl 4-methylphenol) enhances the antitumor efficacy of belotecan, a derivative of camptothecin, by inducing autophagy

Autophagy regulation is important for tumor cell survival. Activation and inhibition of autophagy can sensitize tumor cells to anticancer drugs. However, few autophagy-regulating small molecules are available to increase the efficacy of anticancer drugs. Here, we report that 2,2′-methylenebis (6-tert-butyl 4-methylphenol), hereafter referred to as methylenebis, is a novel autophagy-regulating small molecule that sensitizes tumor cells to belotecan, which is a derivative of camptothecin, a topoisomerase I inhibitor. Methylenebis activates autophagic flux by increasing the level of LC3-II and forming autolysosome puncta. Moreover, methylenebis enhances the antitumor efficacy of belotecan by activating both autophagy and apoptosis. Interestingly, methylenebis increased the level of LC3-II and belotecan independently decreased the level of p62, suggesting that methylenebis and belotecan target different steps of autophagy. Finally, we searched for compounds that are structurally similar to methylenebis. Our results imply that the specific structure of methylenebis contributes to its ability to activate autophagy.

A theoretical antioxidant pharmacophore for natural hydroxycinnamic acids

The structure-activity relationship analysis has been performed for trans- and cis-hydroxycinnamic acids, to determine their theoretical antioxidant pharmacophore. Based on the detailed conformational studies, the most stable rotamers have been selected. We have analyzed the descriptors of four antioxidant mechanisms important in free radical scavenging: hydrogen atom transfer, sequential proton loss electron transfer, single electron transfer - proton transfer and transition metal chelation, based on the B3LYP/6-311++G(2d,2p) calculations in vacuum and polar media. The results explain the activity difference between cinnamic acid and its derivatives. The descending order of antioxidant potential is as follows: caffeic > sinapinic ~ ferulic > p-coumaric > o-coumaric > m-coumaric ~ phenol. The results have shown that transisomers indicate higher reactivity than cis- and may be considered as good antioxidants. It has been determined that the highest antioxidant ability is related to the hydroxyl group in para position, supported by planar structure and stability of radical forms. π-Type delocalization of unpaired electron on aromatic ring, double bond and para O-atom is the key to radical stabilization. The ortho-dihydroxy substitution in benzene ring positively influences the ability to neutralize free radicals and makes caffeic acid the antioxidant pharmacophore of hydroxycinnamic acids.

Male reproductive toxicity of four bisphenol antioxidants in mice and rats and their estrogenic effect

Male mice and rats were fed a diet containing four bisphenol antioxidants, 2,2'-methylenebis(4-ethyl-6-tert-butylphenol) (ME), 2,2'-methylenebis(4-methyl -6-tert-butylphenol) (MM), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol) (BM), or 4,4'-thiobis(3-methyl-6-tert-butylphenol) (TM) at levels of 0.06-0.25% for 2 months. BM and TM decreased epididymal, seminal vesicular, prostate and preputial weights, and injured seminiferous tubules in mice in a dose-dependent fashion. BM and TM also reduced sex accessory organ weights and sperm production capacity in rats, but MM and ME were more toxic to rats than BM and TM. ME and MM did not bind ERalpha up to 10(-3) M, while BM and TM competitively bound ERalpha against beta-estradiol (E2). Fifty percent inhibitory concentrations (IC50 s) of BM, TM, and bisphenol A (positive control) against E2-binding were 7.3 x 10(-6) M, 1.8 x 10(-5) M, and 1.4 x 10(-5) M, respectively. When ovariectomized (OVX) mice were sc administered TM at doses of 60 and 300 mg/kg/day for 4 days, or when OVX mice were fed BM in the diet at a level of 0.25% for 2 months, uterine weight was significantly increased. These results suggest that BM and TM are weakly toxic, possibly through an estrogenic mechanism to male reproductive organs in mice as well as rats, while MM and ME may be the direct testicular toxins in rats but not mice.

ACUTE, SUBCHRONIC AND CHRONIC TOXICITY STUDIES OF A SYNTHETIC ANTIOXIDANT, 2,2'-ISOBUTYLIDENEBIS(4,6-DIMETHYLPHENOL) IN RATS

General toxicity studies on 2,2'-isobutylidenebis(4,6-dimethylphenol)(IBBMP) were conducted using male and female Wistar rats. In the acute test, the oral LD50 values were 119 mg/kg BW in males and 103 mg/kg BW in females. Hypersensitivity, loss of righting reflex and abdominal position were observed. In the subchronic test, rats were fed a diet containing IBBMP at levels of 0, 20, 100 or 500 ppm for 13 weeks with interim sacrifice at 4 weeks (equal to 0, 1.1, 5.5 or 27.9 mg/kg BW/day in males and 0, 1.1, 5.9 or 29.6 mg/kg BW/day in females). In both sexes, there were no changes in general condition, body weight gains and food intakes in all groups. No deaths were observed in all groups. Significant increase in AST was observed in 500 ppm males at Week 4. However, the change was not observed at Week 13. Slight but significant decreases in creatinine were also observed in 100 ppm females at Week 13 and 500 ppm males and females at Weeks 4 and 13. Total cholesterol (T-CHO) was significantly elevated in females of the 500 ppm group at Weeks 4 and 13. Absolute and relative liver weights were increased in 500 ppm of both sexes at Week 4. In females, the increases were also observed at Week 13. However, no remarkable histopathological findings were observed in all treated groups. In the chronic test, rats were fed a diet containing IBBMP at levels of 0, 100, 500 and 1500 ppm for 18 months with interim sacrifices at 6 and 12 months (equal to 0, 3.8, 19.4 or 59.4 mg/kg BW/day in males and 0, 4.3, 20.9 or 67.5 mg/kg BW/day in females). No remarkable changes in general appearance were observed in any rats. Body weight gains, food intakes and survival rates in all treated animals were comparable to those of the control. No remarkable changes in the hematological parameters were observed. T-CHO was significantly elevated in females of the 1500 ppm groups throughout the experiment. Significant increases or tendencies for increase in relative liver weights were observed in the 500 and 1500 ppm animals of both sexes. Increased incidences of swelling in liver cells were observed in 1500 ppm males at 6 months and 1500 ppm females at 12 and 18 months. At 18 months, dose-dependent increases in thickness of basement membrane of renal tubules and Bowman's capsule and cell infiltration to the interstitium of the kidney were observed in males. Significant increases of hyaline cast and basophilic change were also observed in 1500 ppm males. In females, increased incidences of hyaline cast were observed at 500 ppm and higher at 18 months. No other toxicity was apparent. No neoplastic lesions that could be attributed to IBBMP were observed in any organs of either sex. From the result of the chronic toxicity test, the no-observed-adverse-effect level (NOAEL) for IBBMP was concluded to be 100 ppm in the diet (4.26 mg/kg BW/day) in female rats on the basis of induction of hyaline cast in renal tubules at 500 ppm, whereas, in males, only a lowest-observed-adverse-effect level (LOAEL) was given as 100 ppm (3.84 mg/kg BW/day) on the basis of induction of thickening of basement membrane in renal tubules at 100 ppm.