Wendy Pearson

Horses don’t normally drink tea, mint-flavoured or not. But U of G tests have found that feeding horses a souped-up mint supplement developed on campus might help counter joint inflammation. As a result, Guelph researchers may soon investigate spearmint as a possible treatment for human arthritis.

They’re not promising a cure for the disease. But results of in vitro tests and last year’s horse study hold promise for using mint extract to reduce inflammation and pain and perhaps to slow the progression of arthritis, says Wendy Pearson, a three-time Guelph grad now studying medicinal plants for horses as a post-doc in the Department of Plant Agriculture.

Pearson says arthritis is common among horses. Veterinarians use oral and injected drugs — including phenylbutazone, or “aspirin for horses” — to treat joint pain, but those products can speed up cartilage breakdown and cause side effects, including stomach ulcers. Pearson, a longtime rider who keeps horses on her Milton, Ont., hobby farm, says finding alternative therapies might benefit animals.

It might also help people who suffer from various forms of the disease. Arthritis affects some 4.5 million Canadians at an estimated cost of $18 billion a year.

“For diseases like osteoarthritis, this is a great opportunity for people with interest in medicinal plants to focus their work,” says Pearson. “It’s a chronic disease, and we do not have a drug cure.”

Last year, she fed two horses mint containing high amounts of an anti-inflammatory substance called rosmarinic acid (Ros-A). Those animals produced lower levels of pain molecules associated with joint inflammation than two horses eating a control diet. She plans to repeat the study this year with four more animals.

Found in spearmint and other plants, rosmarinic acid is a phenol with antioxidant and anti-inflammatory properties. More than a decade ago, Laima Kott, a research scientist in the Department of Plant Agriculture, developed a mint clone that contains up to 20 times more of the substance than ordinary Mentha spicata.

Three years ago, she hoped to study its use in treating allergies and asthma. Now, based on Pearson’s work with horses, Kott plans to investigate the use of high RosA spearmint tea for slowing cartilage damage and reducing inflammation and pain in people with rheumatoid arthritis. She’s principal investigator for a team of researchers on a proposed project involving Pearson and other Guelph plant scientists, as well as researchers in the Department of Human Health and Nutritional Sciences and U of G’s Human Nutraceuticals Research Unit.

Besides looking for disease treatments, Kott hopes their work will help Ontario farmers develop the high-RosA spearmint as a new crop to feed a growing functional food industry.

Pearson’s horse trial using that “super-mint” followed her earlier study of high Ros-A mint in tissue culture models. For that earlier work, she made a “simulated stomach” using gastric, intestinal and liver cells to test anti-inflammatory properties of rosmarinic acid and three of its breakdown products on pig cartilage. Only the high Ros-A mint inhibited production of compounds associated with pain, inflammation and cartilage damage.

A paper on that in vitro study by Pearson and her collaborators — Kott; Ron Fletcher, a plant agriculture research associate; and clinical studies professor Mark Hurtig — has been accepted by BMC Complementary and Alternative Medicine. They have also discussed their work with a Guelph-based feed supplement maker and a company that makes human natural health products.

Pearson says using medicinal plants for treating ailments in horses and in livestock animals like cattle and poultry makes sense. Just look in your medicine cabinet: about 25 per cent of products dispensed by pharmacists come directly from plants. That creates an unusual niche for her between plants and horses.

“I fit in this weird place. I’m in plant agriculture, but I have an office at Equine Guelph,” says Pearson, who worked in research and development in veterinary natural health products before returning to campus last year.

After completing her undergrad here, she studied nutrition and toxicology for graduate degrees in animal and poultry science and in biomedical sciences.