Metabolic Effects of Methacrylic Monomers on HL-60 Cell Line

Objective: The incomplete auto- or photo-polymerization of methacrylic monomers present in dental composite resins leads to a release of these molecules in the oral cavity and in biological fluids causing possible local and systemic adverse effects through intracellular mechanisms still not completely clarified. Aim of this work is therefore the in vitro evaluation of the biochemical interactions between urethane dimethacrylate (UDMA) and 1,4-butanediol dimethacrylate (BDDMA) – two monomers present in dental resins – and the well characterized promyelocytic HL-60 cell line. This type of cells was selected because of the good sensitivity to cytotoxic, metabolic and differentiating agents which may be present in dental materials.

Methods: The monomers concentrations able to induce cell differentiation, although in presence of an increased mortality, have been selected through experiments of proliferation and differentiation (0.40 mmol/L BDDMA and 0.055 mmol/L UDMA). The oxidative burst recovery has been further utilized as differentiation marker. Experiments were performed using, as control, cells untreated or treated with a differentiating agent (All-trans retinoic acid).

The effects of UDMA and BDDMA on HL-60 cells were evaluated analyzing:

1. the energetic cellular metabolism through the determination of oxygen consumption rate (by oxygraphy), glucose consumption, glucose 6-phosphate dehydrogenase activity (by spectrophotometry) and lactate production (by NMR spectrometry).

2. cellular redox status through the analysis of GSH concentration and enzymatic activity of glutathione reductase, superoxide dismutase and catalase (by spectrophotometry).

Results: Data show that examined molecules induce on HL-60 cells a decrease of oxygen consumption rate (index of mitochondrial damage) and consequent glucose consumption increase. A GSH depletion with no changes in the activity of analyzed enzymes is also observed.

Conclusions: The observed metabolic alterations can partially explain the cytotoxic effects induced by UDMA and BDDMA. This type of investigations can be therefore considered as an useful backup for the biocompatibility studies of dental materials.