2023 Volume 73 Issue 2 Pages 97-102
Curcumin is a polyphenol found in the rhizome of turmeric which has potential in oral care applications for the prevention of periodontal disease. In a previous study, a curcumin solution dissolved in dimethyl sulfoxide (DMSO) was used to evaluate the growth inhibitory effect against Porphyromonas gingivalis (P. gingivalis). However, due to its low level of safety, DMSO cannot be formulated into oral care products. In this study, the influences of different solvents on the growth inhibitory effect and their causes were investigated with curcumin dissolved in DMSO or dihydric alcohols.
To confirm the growth inhibitory effect, curcumin was dissolved in DMSO or dihydric alcohols and added to the liquid culture medium. P. gingivalis was cultured anaerobically, and the turbidity (OD600) of the medium was measured at the start of culture and after 6 to 36 hours. In addition, the growth inhibitory effect of curcumin dissolved in dihydric alcohols was determined by the presence or absence of turbidity in the medium after 36 hours of culture. In order to confirm the amount of curcumin dissolved in the solution, the curcumin solution was centrifuged followed by quantitative analysis of curcumin contained in the supernatant with HPLC.
The growth inhibition rates of curcumin dissolved in 0.1 and 1% DMSO were 77.5 and 79.1% and those dissolved in 0.1 and 1% propylene glycol were 40.8 and 56.8%, respectively. The differences in the growth inhibitory effect were considered to be due to differences in the amount of dissolved curcumin. Other studied solvents (e.g. butylene glycol and isoprene glycol) showed similar trends to propylene glycol.
To confirm the results further, the increase of the propylene glycol concentration was investigated. Differences due to solvents were confirmed; the amounts of curcumin dissolved in 0.1 and 1% DMSO was 1.7 were 2.5 µg/mL, and those in 0.1, 1, 5, and 10% propylene glycol were 0.4, 0.7, 2.2, and 2.7 µg/mL, respectively. From the results, effective growth inhibition is expected with a 10% dihydric alcohol concentration, which dissolves the same amount of curcumin as DMSO.
Since dihydric alcohols are safe, they may be useful as solvents when formulating curcumin into oral care products.
