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Mechanism of antitumoral activity of catechols in culture
Abstract:
Cell lines Raji and K 562, lacking tyrosinase, and two melanotic human melanoma cell lines (IRE 1 and IRE 2), were exposed to concentrations from 5 X 10(-3) M to 10(-5) M of different phenols which are substrates of tyrosinase, i.e. l-dopa, dopamine, hydroquinone, terbutylcatechol, and of phenols which are not substrates of the tyrosinase, i.e. resorcinol, butylated hydroxyanisole and hydroquinone dimethyl ether. Cultures were carried out in the presence or in the absence of oxygen radical scavenger enzymes superoxide dismutase, catalase and peroxidase. The stability of each substance in culture medium was assayed by high performance liquid chromatography (HPLC). Results showed that: catechols which are substrates of tyrosinase decompose fully after 24 hr in medium; they are equally toxic for melanoma and non-melanoma cell lines; their toxicity increases when they are preincubated in medium for 24 hr and 48 hr before addition of cells; their toxicity is significantly reduced by addition of scavenger enzymes; on the contrary, phenols not substrates of tyrosinase are stable in medium and their toxicity is not reduced by scavenger enzymes. It is concluded that tyrosinase does not play a major role in catechol toxicity in vitro, which is probably due to some products of catechol decomposition, especially oxygen radicals, acting outside the cells.
Insights
Tyrosinase substrates like catechols decompose rapidly and are toxic to cells, but this toxicity is reduced by antioxidants. This suggests oxygen radicals from catechol breakdown, not tyrosinase itself, cause cell damage in vitro.
Area of Science:
- Biochemistry
- Cell Biology
- Toxicology
Background:
- Tyrosinase is an enzyme involved in melanin production.
- Phenolic compounds can be substrates or non-substrates for tyrosinase.
- Cellular response to phenolic compounds requires investigation.
Purpose of the Study:
- To investigate the role of tyrosinase in the toxicity of phenolic compounds.
- To determine the mechanism of toxicity for tyrosinase substrates and non-substrates.
- To assess the influence of oxygen radical scavenger enzymes on phenolic compound toxicity.
Main Methods:
- Exposure of human melanoma and non-melanoma cell lines to various phenols.
- Assay of phenol stability in culture medium using high-performance liquid chromatography (HPLC).
- Evaluation of toxicity in the presence and absence of oxygen radical scavenger enzymes (superoxide dismutase, catalase, peroxidase).
Main Results:
- Tyrosinase substrates (catechols) decomposed fully within 24 hours in culture medium.
- Catechols exhibited similar toxicity to both melanoma and non-melanoma cell lines.
- Toxicity of catechols increased after preincubation and was significantly reduced by scavenger enzymes.
- Phenols not substrates for tyrosinase were stable and their toxicity was unaffected by scavenger enzymes.
Conclusions:
- Tyrosinase does not appear to be a major factor in the in vitro toxicity of catechols.
- The toxicity of catechols is likely mediated by decomposition products, particularly oxygen radicals.
- Oxygen radicals generated outside the cells contribute significantly to catechol-induced toxicity.