The effects of extracellular citric acid acidosis on the viability, cellular adhesion capacity and protein synthesis of cultured human gingival fibroblasts

Root surface demineralization is widely used as an adjunct to periodontal t reatment. To clarify the influence of citric acid root conditioning on peri odontal wound healing, the effects of citric acid and associated extracellu lar acidosis on the viability (MTT assay), attachment and protein synthesis ([H-3]-proline incorporation into trichloroacetic acid-precipitated protei ns) of human gingival fibroblasts (GF) were investigated. A concentration o f 47.6 mmol/L of citric acid (pH 2.3) in water led to total cell death with in three minutes of incubation. Media containing 23.8 mmol/L and 47.6 mmol/ L of citric acid exerted strong cytotoxicity (47 to 90 per cent of cell dea th) and inhibited protein synthesis (IC50=0.28 per cent) of GF within three hours of incubation. Incubation of cells in a medium containing 11.9 mmol/ L of citric acid also suppressed the attachment and spreading of fibroblast s on culture plates and Type I collagen, with 58 per cent and 22 per cent o f inhibition, respectively. Culture medium supplemented with 11.9, 23.8 and 47.6 mmol/L of citric acid also led to extracellular acidosis by decreasin g the pH value from 7.5 to 6.3, 5.2 and 3.8, respectively. In addition, it was confirmed that the toxic effect of media containing citric acid was due to their acidity rather than the citrate content. Most of the citric acid- induced cell death could be prevented by adjusting the pH value of the cult ure medium to pH 7.5. Sodium citrate, at a concentration of 47.6 mmol/L, al so exerted little cytotoxicity. The results suggested that toxicity of citr ic acid in specific stages of the healing process must be considered prior to its clinical application. Careful management of citric acid in order to avoid contact with tissue or the development of other demineralizing agents is important in enhancing periodontal wound healing.