2-Hydroxyisocaproic acid is bactericidal in human dental root canals ex vivo.

AIM: To compare the activity of 2-hydroxyisocaproic acid (HICA), calcium hydroxide (Ca(OH)2 ) and chlorhexidine digluconate (CHG) against Enterococcus faecalis T-75359 (root canal isolate) in the root canals of extracted human teeth. METHODOLOGY: Bacterial suspensions (108  cfu mL-1 ) were incubated in root canals with 0.9 mm diameter root blocks (n = 73) for 21 days. Bacterial penetration into dentine was analysed by the Brown and Brenn method (n = 5). Canals (n = 17/group) were medicated with 40% of HICA paste, 40% of Ca(OH)2 paste, 2% of CHG solution or 0.9% of saline solution for 7 days. Samples taken from the inner (first 0.1 mm) and deeper (second 0.1 mm) dentine, and residual roots were cultured in broth for 24 h. Bacterial growth was detected by spectrophotometry (optical density, OD) and confirmed by culture on agar. The OD data were analysed with Kruskal-Wallis and Friedman with Wilcoxon signed-rank test between and within groups, respectively, and agar culture data with Pearson chi-square with Mann-Whitney and Cochran with McNemar tests, respectively (P < 0.05). RESULTS: Bacterial invasion into dentine tubules was confirmed. In deeper dentine, HICA inhibited >90% of bacterial growth in comparison with saline. No bacterial growth was observed in 82-100% of inner and deeper dentine samples. CHG prevented the growth in 88%, Ca(OH)2 in 59-76% and saline in 65-71%, respectively. HICA was significantly more active than Ca(OH)2 (P = 0.008) in the residual roots. The viability testing on agar showed essentially the same result. CONCLUSION: HICA paste exerted superior activity against E. faecalis and could have potential for root canal medication.

Antimicrobial 2-hydroxyisocaproic acid and chlorhexidine resist inactivation by dentine.

AIM: To compare the antibacterial activity of 2-hydroxyisocaproic acid (HICA) with currently used root canal medicaments and to examine their interactions with potential inhibitors in nutrient-deficient and nutrient-rich conditions. METHODOLOGY: First, the antibacterial activity of single concentrations of HICA, calcium hydroxide solution or slurry, chlorhexidine digluconate or acetate was tested against Enterococcus faecalis with and without potential inhibitors: dentine powder (DP), hydroxyapatite or bovine serum albumin, in a low concentration of peptone water. Relative viable counts were determined by culture at 1, 24 and 48 h. In the second set of experiments, the activity of three concentrations of HICA was evaluated against two isolates of E. faecalis with and without potential inhibitors in nutrient-rich thioglycollate broth using a modification of a standard microdilution method. The minimum bactericidal concentration was determined by culture at 1, 24 and 48 h. RESULTS: Concentrations of ≥33 mg mL(-1) of HICA were found to be bactericidal against E. faecalis in both nutrient-deficient and nutrient-rich environments at 24- to 48-h incubation, whereas the initial activity of Ca(OH)2 slurry was lost at 48-h incubation. HICA tolerated well all tested potential inhibitors up to 19 mg mL(-1) . DP concentrations higher than this inhibited its activity in a dose-dependent manner in both environments. DP demonstrated moderate antibacterial activity, and it enhanced the otherwise limited activity of Ca(OH)2 slurry and solution. DP did not impact on the activity of chlorhexidine. CONCLUSIONS: These results support the long-term antibacterial activity of HICA and indicate its tolerance to clinically relevant concentrations of dentine and other inhibitors commonly present in the root canal system. Therefore, HICA may have potential as an interappointment medication in the treatment of root canal infections.

2-hydroxyisocaproic acid is fungicidal for Candida and Aspergillus species.

The amino acid derivative 2-hydroxyisocaproic acid (HICA) is a nutritional additive used to increase muscle mass. Low levels can be detected in human plasma as a result of leucine metabolism. It has broad antibacterial activity but its efficacy against pathogenic fungi is not known. The aim was to test the efficacy of HICA against Candida and Aspergillus species. Efficacy of HICA against 19 clinical and reference isolates representing five Candida and three Aspergillus species with variable azole antifungal sensitivity profiles was tested using a microdilution method. The concentrations were 18, 36 and 72 mg ml(-1) . Growth was determined spectrophotometrically for Candida isolates and by visual inspection for Aspergillus isolates, viability was tested by culture and impact on morphology by microscopy. HICA of 72 mg ml(-1) was fungicidal against all Candida and Aspergillus fumigatus and Aspergillus terreus isolates. Lower concentrations were fungistatic. Aspergillus flavus was not inhibited by HICA. HICA inhibited hyphal formation in susceptible Candida albicans and A. fumigatus isolates and affected cell wall integrity. In conclusion, HICA has broad antifungal activity against Candida and Aspergillus at concentrations relevant for topical therapy. As a fungicidal agent with broad-spectrum bactericidal activity, it may be useful in the topical treatment of multispecies superficial infections.