May 1, 2001

Beehive Product May Inhibit Dental Caries

Centuries of folk medicine have made use of nature's bounty of plants, herbs, and other natural substances to combat diseases and infections. Now scientists are confirming in laboratory studies that one of these substances--propolis, a resinous product collected from beehives--may inhibit the development of tooth decay.

NIDCR-supported investigators at the University of Rochester, working collaboratively with researchers at the University of Campinas, Brazil, found that propolis significantly reduces dental plaque formation. Propolis is a potent inhibitor of glucosyltransferase (Gtf) enzymes, enzymes that synthesize glucans from sucrose and promote the binding of cariogenic bacteria to teeth, critical steps in the development of decay. Interestingly, the investigators also discovered that the effectiveness of propolis depends on the geographic area from which it was collected in Brazil.

Since early times, man has used propolis in a variety of ways. The word comes from the Greek and means "pro"--before, "polis"--city, or ''defender of the city." Ancient Greek texts refer to the substance as a cure for wounds and diseases. Hippocrates prescribed propolis for the healing of sores and ulcers, both internal and external. Records from12th century Europe show that medical preparations using propolis were used for treating mouth and throat infections.

This natural substance is actually used by bees to strengthen and protect their hive from germs and foreign invaders. Worker honeybees collect propolis from the buds of various poplar and conifer trees and bark lesions. The bees pack the propolis on their hind legs and carry it back to their colony where it is combined with beeswax and salivary secretions. Worker "hive" bees then use the substance to fill cracks in their hives and as a cleanser for cells prior to placing honey or pollen in them. Before the queen will lay her eggs in a cell, the bees clean it out and line it with a microscopic coating of propolis. Only then will the queen deposit her eggs in this sterile environment. Propolis also has antibacterial and antifungal effects that protect the colony against disease. It has been shown to kill Bacillus larvae, a bacterial disease that attacks bees.

In their research studies, the investigators tested ethanolic extracts of propolis (EEP) both on purified Gtf enzymes in solution and on the surface of saliva-coated hydroxyapatite (sHA) beads, designed to mimic the surface of a tooth. The Gtf enzymes that were tested included GtfB, GtfC, and GtfD, which are produced by Streptococcus mutans, the most common pathogen associated with dental caries. In addition, propolis was tested on Gtf from Streptococcus sanguis, which is also believed to be involved in the formation of dental plaque.

Results of the studies showed that overall, propolis inhibited 75-95 percent of Gtf activity in solution. There was a 45-95 percent inhibition in activity on the hydroxyapatite surfaces. The researchers tested propolis gathered from Minas Gerais in Southeastern Brazil and Rio Grande do Sul in Southern Brazil and discovered that the propolis samples differed in their effectiveness. This is likely caused by variability in the chemical composition of propolis due to the broad range of plants visited by honeybees when they collect the substance and variations in the contents of beeswax. In general, propolis from the Rio Grande do Sul region demonstrated significantly higher inhibitory activity on GtfB and GtfC, while propolis from Minas Gerais had a greater inhibitory effect on GtfD activity. Propolis from both regions inhibited S. sanguis Gtf equally well--more than 70-80 percent--as well as Gtf activity on hydroxyapatite surfaces.

Among the enzymes tested in this study, GtfB and GtfC appear to be the most important ones related to dental caries. Potential Gtf inhibitors tested in previous studies, including commercially available mouthrinses, have failed to inhibit GtfC activity significantly. The current study demonstrates that propolis is a potent inhibitor of GtfC, whether the enzyme is exposed to the substance before or after adsorption to a surface. This level of inhibition has not been observed before. Further characterization of the structure and function of the active component of propolis may lead to a new anti-caries product.

Findings from this study appeared in Caries Research. The research team included Drs. William H. Bowen and Anne M. Vacca Smith from the Center for Oral Biology, University of Rochester; Drs. Hyun Koo, Pedro L. Rosalen, Jaime A. Cury from the Faculty of Dentistry of Piracicaba, State University of Campinas, Piracicaba, Brazil; and Yong K. Park, School of Food Engineering, State University of Campinas, Brazil.