The bioactivity of Fynbos honey compared with Manuka honey in a salt- and enzyme-based synthetic saliva

Abstract

Candida albicans (C. albicans) is a common fungus that can cause oral candidiasis; especially in immune-compromised patients. Honey has previously shown anti-fungal, antioxidant and anti-inflammatory activities which may have beneficial effects in the oral cavity. The bioactivity of Fynbos honeys, a Manuka honey and oral digests was determined.

In this laboratory-based study, four Fynbos (FB) honey samples and a Manuka honey (MAN UMF10+) were incubated with a synthetic saliva for 2 min to simulate oral digestion. For each honey, three samples were generated; undigested, oral digest control and oral digest.

The ability of these samples to inhibit the growth of C. albicans (Strain 90028 (ATCC® 90028™)) was determined. Concentration ranges of 5 - 9% and 25 - 45% did not inhibit the growth of planktonic cells. Solutions of 7 - 9% FB1 and 45% FB2 and FB3, 40 and 45% FB4 as well as 30 - 35% MAN UMF 10+ honey inhibited the growth of C. albicans biofilms. With oral digestion, inhibition was unaltered. Although exposure did not alter viability, scanning electron microscopy analysis of cells in C. albicans biofilms exposed to 5% FB and MAN UMF10+ honey for 24 h revealed morphological changes with an increase in round/oval yeast cells instead of pseudohyphae or true hyphae associated with biofilms.

The ability to reduce the oxidative damage often associated with candidiasis firstly, the total polyphenolic content and then the antioxidant activity with the Trolox equivalent antioxidant capacity and oxygen radical absorbance capacity assays was determined. Nitric oxide (NO) scavenging activity was determined with the sodium nitroprusside assay. The ability of each honey to protect bovine serum albumin (BSA) and low density lipoprotein (LDL) against MGO and reactive oxygen species (ROS)-mediated oxidative damage was also determined. All honeys contained comparable amounts of polyphenols, scavenged ROS and reduced NO levels indicating antioxidant related bioactivity. Each honey protected BSA, but not LDL against oxidative damage. Oral digestion caused minor changes in the measured parameters.

Further studies were undertaken in cellular models. Honey solutions of 1.25 - 5% did not alter the cell number and viability of L929 (murine fibroblasts) and Caco-2 (human colon adenocarcinoma) cells following 24 h exposure, determined with the crystal violet and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H tetrazolium bromide assays, respectively. The cellular antioxidant activity (CAA) of 1.25% honey in both cell lines was determined using the dichlorofluorescein diacetate assay. All honey samples had CAA activity that was not affected with oral digestion. In the murine macrophages (RAW 264.7), the pro- and anti-inflammatory effects of each honey and oral digests was determined. Honeys, FB1, FB3 and MAN UMF10+ at a concentration of 1.25% were pro-inflammatory while in contrast, FB2 and FB4 were anti-inflammatory. All honeys and oral digests were to various degrees able to inhibit lipopolysaccharide-mediated NO formation in this cell line.

In conclusion, FB and MAN UMF10+ honeys reduced the growth of biofilms and at 5% caused changes in C. albicans morphology. The antioxidant properties of all honeys were retained following oral digestion. In cellular models, the honeys and oral digests showed no cytotoxicity, had cellular antioxidant activity and either a pro- or anti-inflammatory activity at the concentrations evaluated. Therefore, in this laboratory-based study, FB honeys had beneficial effects, that may translate into therapeutic benefits.