Chemoprevention of tongue carcinogenesis in rats

Final report on the safety assessment of BHT(1)

BHT is the recognized name in the cosmetics industry for butylated hydroxytoluene. BHT is used in a wide range of cosmetic formulations as an antioxidant at concentrations from 0.0002% to 0.5%. BHT does penetrate the skin, but the relatively low amount absorbed remains primarily in the skin. Oral studies demonstrate that BHT is metabolized. The major metabolites appear as the carboxylic acid of BHT and its glucuronide in urine. At acute doses of 0.5 to 1.0 g/kg, some renal and hepatic damage was seen in male rats. Short-term repeated exposure to comparable doses produced hepatic toxic effects in male and female rats. Subchronic feeding and intraperitoneal studies in rats with BHT at lower doses produced increased liver weight, and decreased activity of several hepatic enzymes. In addition to liver and kidney effects, BHT applied to the skin was associated with toxic effects in lung tissue. BHT was not a reproductive or developmental toxin in animals. BHT has been found to enhance and to inhibit the humoral immune response in animals. BHT itself was not generally considered genotoxic, although it did modify the genotoxicity of other agents. BHT has been associated with hepatocellular and pulmonary adenomas in animals, but was not considered carcinogenic and actually was associated with a decreased incidence of neoplasms. BHT has been shown to have tumor promotion effects, to be anticarcinogenic, and to have no effect on other carcinogenic agents, depending on the target organ, exposure parameters, the carcinogen, and the animal tested. Various mechanism studies suggested that BHT toxicity is related to an electrophillic metabolite. In a predictive clinical test, 100% BHT was a mild irritant and a moderate sensitizer. In provocative skin tests, BHT (in the 1% to 2% concentration range) produced positive reactions in a small number of patients. Clinical testing did not find any depigmentation associated with dermal exposure to BHT, although a few case reports of depigmentation were found. The Cosmetic Ingredient Review Expert Panel recognized that oral exposure to BHT was associated with toxic effects in some studies and was negative in others. BHT applied to the skin, however, appears to remain in the skin or pass through only slowly and does not produce systemic exposures to BHT or its metabolites seen with oral exposures. Although there were only limited studies that evaluated the effect of BHT on the skin, the available studies, along with the case literature, demonstrate no significant irritation, sensitization, or photosensitization. Recognizing the low concentration at which this ingredient is currently used in cosmetic formulations, it was concluded that BHT is safe as used in cosmetic formulations.

Effects of dietary N-(4-hydroxyphenyl)retinamide on N-nitrosomethylbenzylamine metabolism and esophageal tumorigenesis in the Fischer 344 rat

BACKGROUND

9-cis-Retinoic acid (9-cis-RA) and N-(4-hydroxyphenyl)retinamide (4-HPR) are effective chemopreventive agents against epithelial tumors in the oral cavity, breast, and prostate. We tested the inhibitory activity of these retinoids against N-nitrosomethylbenzylamine (NMBA)-induced tumorigenesis in the rat esophagus.

METHODS

Male Fischer 344 rats were randomly assigned to receive diets either lacking or containing 9-cis-RA or 4-HPR for 1 week before tumor initiation with NMBA and then for the duration of the study. NMBA metabolism, O(6)-methylguanine adduct formation, and cytochrome P450 messenger RNA (mRNA) expression in the esophagi of the rats were studied to investigate the mechanisms by which dietary 4-HPR affects tumorigenesis. All statistical tests were two-sided.

RESULTS

Dietary 4-HPR resulted in a dose-dependent and statistically significant enhancement (P<.05) of tumorigenesis in response to NMBA. In two different tumor bioassays, the mean tumor multiplicity for rats fed the highest concentration of dietary 4-HPR (0.8 g/kg diet) was increased by 5.9 tumors (95% confidence interval [CI] = 1.7 to 10.1 tumors) and 6.7 tumors (95% CI = 5.6 to 7.8 tumors) compared with the mean tumor multiplicity for rats that received the control diet lacking 4-HPR. Animals fed diets containing 9-cis-RA displayed no statistically significant increase in tumorigenesis. Compared with animals fed a diet lacking 4-HPR, animals fed 4-HPR had increased NMBA metabolism in esophageal explant cultures and had higher levels of O(6)-methylguanine DNA adducts and CYP2A3 mRNA in their esophagi.

CONCLUSIONS

Dietary 4-HPR enhances tumorigenesis in response to NMBA in the rat esophagus by increasing tumor initiation events. Dietary 4-HPR may exert paradoxical effects at some sites, such as the aerodigestive tract, by modulating the bioactivation of carcinogens in target tissues.

Thiobarbituric acid reactive substances in patients with laryngeal cancer

The purpose of this study was to measure the level of thiobarbituric acid reactive substances (TBARS), which are products of lipid peroxidation, as a reflection of oxidative status in 30 patients with laryngeal cancer. The TBARS were measured 1 day before surgery and 3 weeks after laryngectomy compared to 30 normal control subjects by the thiobarbituric acid (TBA) test using spectrophotometry. The TBARS levels were significantly elevated in patients with laryngeal cancer compared to the controls (18.4 +/- 3.13 mumol/l versus 7.75 +/- 1.9 mumol/l; P < 0.05). There were no differences in the TBARS levels in relation to T staging, N staging, or degree of differentiation. Among patients with laryngeal cancer smokers had slightly higher TBARS levels. Comparison of the paired observations of laryngeal cancer larynx before and after operation revealed a significant rise in the TBARS levels after laryngectomy. Tissue damage resulting from surgery is the most probable explanation for this rise. The state of altered lipid peroxidation detected in our patients might be related to a deficient antioxidant status. The role of antioxidants in the prevention of laryngeal cancer among high risk patients is worth studying.

Use of antioxidant supplements in the treatment of human oral leukoplakia

An increasing public awareness of antioxidants may prompt a patient's request to be treated without surgery if a leukoplakic lesion is discovered. However, surgical excision remains the treatment of choice for oral leukoplakia. The use of antioxidant supplements has shown some promise, but the predictability of success remains uncertain and long-term results are unavailable. Before the decision to use any antioxidant is made, it is critical to obtain a histopathologic diagnosis of the lesion. When dealing with a lesion diagnosed as hyperkeratosis, it may be appropriate to choose an antioxidant that may take some time for clinical improvement to occur. However, as the grade of epithelial dysplasia becomes more severe, consideration must be given to the possibility of malignant transformation during antioxidant treatment. We do not recommend the use of antioxidant supplements in the treatment of any carcinoma. The therapeutic use of antioxidant supplements outside of clinical trials conducted at academic medical centers should be done with considerable caution by practitioners in private practice. It should be emphasized that in these clinical trial patients were seen at frequent intervals to monitor their progress and to intervene if there was a noticeable deterioration in the clinical appearance of the lesion. In spite of the uncertainty with respect to antioxidant treatment, there are circumstances in which it should be considered. Recurrence after surgical excision when there is little reason to believe that a second surgical excision would be any more successful is an ideal candidate. Also, patients with widespread leukoplakia that involves a large area of the oral mucosa might be suitable for treatment with antioxidants, as well as patients who have extensive medical problems that make them surgical risks. The choice of which antioxidant(s) to use is complex because thus far there is no combination that is superior to the others. Beta-carotene with ascorbic acid or alpha-tocopherol is attractive because of a lack of side effects, but the range in reported values for lesion improvement has been broad and the clinical improvement typically takes several months. Clinical response with 13-cRA is faster but requires baseline and periodic serologic testing, as well as close monitoring for side effects. In those circumstances in which time is an important consideration, 13-cRA might be useful because clinical improvement can be evaluated within a matter of weeks as compared with beta-carotene. The group from M.D. Anderson Hospital has shown the value of an induction dose of 13-cRA that is followed by a lower maintenance dose. Unfortunately, the problem of recurrence after discontinuation of 13-cRA is quite common. One aspect that has not been evaluated is the combination of conventional surgical excision and the administration of postoperative antioxidants. This would have the obvious advantage of conventional treatment of surgery together with the possible protective effect of the antioxidants. Although this is an attractive hypothesis, we do not know of any studies that have proven this to be beneficial.

Inhibitory effects of selenium, vitamin A and butylated hydroxytoluene on growth of human maxillary cancer cells in vitro

The effects of vitamin A, selenium, and butylated hydroxytoluene (BHT) on the growth of a human maxillary cancer cell line were examined in monolayer cell cultures. The colony-forming assay showed a 50% reduction in the survival rate of the cell line at a concentration of 3.6 micrograms/ml of selenium, 28 micrograms/ml of vitamin A, and 74 micrograms/ml of BHT. Flow cytometric analysis with both FITC-labeled bromodeoxyuridine monoclonal antibody and propidium iodide demonstrated an increase of the S-phase fraction in the presence of selenium, an increase of the G0/G1-phase fraction in the presence of vitamin A, and an increase of the G2-M-phase fraction 1 day followed by an increase of G0/G1-phase fraction from the 3rd to 7th day when BHT was added. These results suggest that the mechanisms of inhibition of DNA synthesis by these compounds are different.

Inhibitory effects of selenium, vitamin A and butylated hydroxytoluene on in vitro growth of human tongue cancer cells

The effects of vitamin A, selenium and butylated hydroxytoluene (BHT) on the growth of a human tongue cancer cell line were examined in monolayer cell cultures. A colony-forming assay showed a 50% reduction in the survival rate of the cell line at a concentration of 2.6 micrograms/ml selenium, 60 micrograms/ml vitamin A and/or 38 micrograms/ml BHT. Relatively low concentrations of selenium markedly inhibited glucose consumption. Flow cytometric analysis with both fluorescein-isothiocyanate-labelled bromodeoxyuridine monoclonal antibody and propidium iodide demonstrated an increase in S-phase fractions 1 day after the addition of selenium, increased G0/G1 phase fractions in the presence of vitamin A and increased G2-M phase fractions when BHT was added. These results suggest that these compounds inhibit DNA synthesis of in vitro human tongue cancer cells by different mechanisms.

Surgical treatment of stage I and II oral squamous cell carcinomas: analysis of causes of failure

Sixty-one patients with stage I and II squamous cell carcinomas of the oral cavity treated by surgery alone were analysed to investigate treatment outcome, pattern of failure, and occurrence of second malignant neoplasms. The disease recurred or developed lately in 11 patients. The ipsilateral neck was the most common site of failure. Salvage treatment was successful in only three of these patients. Occult neck metastasis was found in 31% of patients with T2 tumours. Second malignant neoplasms developed in 20 patients and were the cause of death in 8 patients. In conclusion, locoregional control of stage I and II oral carcinomas is achieved by surgery alone. Elective neck dissection is required for patients with stage II tumours, showing a high risk of lymph node metastasis in histology.