Type-2 diabetes imparts an increased risk of eye disorders such as glaucoma, cataracts and retinopathies, however a team of researchers led by Dingbo "Daniel" Lin, PhD, research assistant professor of human nutrition, Kansas State University in Manhattan, KS, have been studying how Chinese wolfberries (the bright orange-red, oblong-shaped fruit also referred to as Goji berries) can play a role in lowering oxidative stress, one of the factors that occurs in diabetic retinopathy, a common complication of diabetes and the leading cause of blindness in American adults diagnosed with type-2 diabetes.
The nature of the research was nutrigenomic, the study of how food nutrients can affect gene expression and disease. “Wolfberry bioactive components dually function as super powerful antioxidants and signaling molecules which in turn alter gene expression, including genes involving cell growth and death processes,” said Dr. Lin.
He went on to note that wolfberries have high levels of zeaxanthin, lutein, polysaccharides and polyphenolics, which have been shown to improve vision, including the prevention of age-related macular degeneration and diabetic retinopathy. Wolfberries have long been associated with helping to rebalance homeostasis, boost the immune system, nourish the liver and kidneys and improve vision.
Dr. Lin’s research bridges his experience in biochemistry, eye research, and his recent work in nutrition as it relates to vision. This current study began in July of 2008 and was inspired by a conversation Dr. Lin had with his father, a traditional medical doctor in China, regarding the eye and phytochemicals.
"In our culture's history, we have traditional medicine literature that describes things like the wolfberry and its functions," Dr. Lin said. "I would not say that wolfberries are a medicine, but they can be used as a dietary supplement to traditional treatments to improve vision. Wolfberries have high antioxidant activity and are very beneficial to protect against oxidative stress caused by environmental stimuli and genetic mutations. Oxidative stress is known as cell impairment of the production of reactive oxygen. Cellular oxidative stress is involved in many human diseases, such as diabetes, vision impairment and blindness."
Specifically, the researchers involved in the NIH-funded study examined the wolfberries’ effects on the retina pigment epithelial cell layer in type-2 diabetic mice. "It's the only cell layer in the far back of the retina, and it provides a fundamental support to the whole retina, just like the base of a building," explained Dr. Lin. "All of the nutrients pass through that cell layer.
“Wolfberry is such a unique, food type of fruits containing relatively high polysaccharides, polyphenolics and carotenoids,” he continued. “The unique character indicates that wolfberry may have impact on hyperglycemia through multiple molecular signaling pathways.”
The researchers also examined the endoplasmic reticulum, which is where the folding process of proteins occurs in a cell. When the accumulation of unfolded protein aggregates occurs persistently, the endoplasmic reticulum is under stress. Prolonged stress will eventually cause cell deaths, Dr. Lin said.
The research team’s in vitro and in vivo studies demonstrated that the wolfberry's phytochemicals protected the retinal pigment epithelial cells from hyperglycemia, or high glucose. The findings further showed that the fruit had local effects on oxidative stress, reactivates the enzyme AMPK and reduces endoplasmic reticulum stress.
"AMPK is a key enzyme in the balance of cell energy homeostasis," Dr. Lin said. "The outcome of the current research will lead to the development of dietary regimens in prevention of an eye disease."
Though the team’s research was presented at the 2009 Experimental Biology conference and 2009 American Society of Cell Biology Conference, they are continuing to study wolfberries and their health benefits, trying to identify anti-hyperglycemia fractions, using in vitro and in vivo models.
Dr. Lin acknowledged the potential use of wolfberries as a dietary supplement, but given the ongoing interest in “super fruits,” he said he was concerned about wolfberry’s inclusion in the super fruit vernacular and its related impact on consumer buying habits. “Personally I do not like the term ‘super fruits’ because we still know very little about the nature,” he said. “We have to let consumers know about this. What is the side effect? We have to work hard on this kind of question as well. For example, beta-carotene had been considered as a powerful antioxidant, but now we know it may cause cancer. Therefore I would suggest that food source should be diverse and balanced.”