Rhododendrons are evergreens that belong to the same family as azaleas, with 800 species that grow around the world from Nepal to West Virginia. Parts of certain rhododendron species are toxic to both humans and animals; people have become ill just from eating honey made by bees feeding on the flowers. However, scientists are finding that extracts from other rhododendrons have properties that show promise in treating diseases.
Italian researchers at the University of Padova studied the composition of an essential oil from the Rhododendron anthopogon species. They were able to isolate compounds that showed a significant killing effect against strains of bacteria like Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis and Mycobacterium tuberculosis and fungi like Candida. These antimicrobial effects were found with doses as low as 0.04 percent solution.
The same Italian study that discovered antimicrobial properties in rhododendron also determined that the essential oil reduced cancer cell growth independently of either the cell line or the treatment protocols used. Additional research published in the April 2010 issues of “Organic Letters” reported that a compound isolated from the flower buds of the Rhododendron molle species showed selective cytotoxic activity against a human hepatoma carcinoma cell line.
Patients with atopic dermatitis, a type of skin disorder similar to eczema, often have increased levels of eosinophils and pro-inflammatory factors. Researchers at China’s Chung-Ang University College of Medicine used extracts from the roots of Rhododendron mucronulatum that were either applied topically or injected into laboratory animals that had an atopic dermatitis condition. The mice exhibited measurable reduced levels of eosinophils and other inflammatory markers after treatment with the extract.
In December 2009, the journal “Molecular Pain” published a study that looked at efforts to mediate persistent inflammatory pain. The experiment used Hyperoside, one of the flavonoids isolated from Rhododendron ponticum L., which significantly reversed the effects of NMDA pain receptors in the spinal cord and exhibited analgesic activities against persistent inflammatory stimuli in mice.
Kidney and Liver Function
A study at China’s Tongji Medical College found that rhododendron root extracts were able to regulate kidney function. Two follow-up studies in India wanted to see whether extracts from Rhododendron arboreum had a similar positive role in the liver. An ethanol-based extract from the leaves was given to rats with induced liver damage in varying doses for five days, with results showing a definitely hepatoprotective property, possibly because of its reported antioxidant activity from the quercetin related flavonoids present in the plant.