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Dietary Broccoli Can Help Protect Against Airway Oxidative Stress

By Shweta Trivedi
April 2009

Photo of Marc Riedl, M.D.
Lead author Marc Riedl, UCLA assistant professor of clinical immunology and allergy, is shown in the Hart and Louise Lyon Laboratory where the study was conducted. (Photo courtesy of UCLA)

Researchers at the David Geffen School of Medicine at the University of California, Los Angeles (UCLA) and the Environmental Protection Agency (EPA) report that orally administered sulforaphane (SFN) - a compound that is found in cruciferous vegetables and is especially high in broccoli sprouts - can enhance Phase II antioxidant enzyme levels in human airways. According to the authors, their study provides the first data to clearly demonstrate this biological effect of SFN in the human airway and may have therapeutic implications in regard to asthma and other conditions associated with airway oxidative stress.

The study ( Exit NIEHS, funded by NIEHS, NIH and EPA and published in Clinical Immunology, explores an important endogenous protective mechanism whereby cellular damage can be prevented by dietary intake of a vegetable rich in a reactive oxygen species (ROS) scavenging compound. This placebo-controlled clinical study demonstrated the positive in vivo effects of oral SFN administration on up-regulation of a variety of antioxidant enzymes. Inflammation caused during oxidative stress has also been linked to allergic rhinitis and other respiratory diseases such as chronic obstructive pulmonary disease.

Lead author Marc Riedl, M.D., Exit NIEHS and Andrew Saxon, M.D., Exit NIEHS of the Hart and Louise Lyon Laboratory at David Geffen School of Medicine at UCLA co-authored the study with David Diaz-Sanchez, Ph.D., a principal investigator with the Human Studies Division at U.S. Environmental Protection Agency at UNC- Chapel Hill.

Endogenous Phase II enzymes are known to abrogate oxidative stress by scavenging ROS and free radicals. Previous in vitro and animal studies had shown that SFN is a potent inducer of Phase II enzymes. Findings of the new study support the hypothesis that oral SFN is capable of elevating Phase II enzymes in human airway cells.

"This study provides support for the concept that we can enhance the body's own natural antioxidant and cytoprotective mechanisms," Diaz-Sanchez commented. "Oxidative stress is a critical pathway in asthma, airway inflammation and air pollution health effects. Interventions using exogenous antioxidants [in supplement form] have been disappointing, perhaps due to bioavailability. This study takes a novel approach by encouraging the body to increase its own antioxidants by the use of dietary intervention."

Sixty-five healthy non-smoking volunteers were enrolled for the study at UCLA campus and from neighboring communities. Study design involved assessment of baseline Phase II enzyme expression in day 1 nasal lavage. Different groups of subjects were then given a measured amount - 25, 50, 75, 100, 125, 150, 175 and 200 grams - of broccoli sprout homogenate (BSH) once daily for three days. The control subjects received a placebo, alfalfa sprout homogenate, which is similar in taste and appearance to the BSH but does not have high levels of sulforaphane glucosinolates. There was no apparent toxicity in administering BSH orally, and it was well tolerated by the subjects.

Nasal lavage samples for Phase II enzyme expression analysis were collected on day three, and on day four blood was drawn for assessing serum SFN levels. RNA from cells in pellets of nasal lavage was analyzed with quantitative real-time PCR.

At doses of 100g daily, BSH induced expression of Phase II enzyme genes - glutathione s-transferase M1 (GSTM1), glutathione S-transferase P1 (GSTP1), heme-oxygenase-1 (HO-1) and NADPH quinone oxidoreductase 1 (NQO1) - in the cells. There was also a dose-dependent increase in the expression of the enzymes. The maximum BSH dosage of 200 grams generated a 101 percent increase in GSTP1 and a 199 percent increase in NQO1. Expression of GSTM1 and HO-1 also increased by more than 100 percent at the maximum dosage.

Citation: Riedl MA, Saxon A, Diaz-Sanchez D. 2009. Oral sulforaphane increases Phase II antioxidant enzymes in the human upper airway. Clin. Immunol. 130(3):244-251.

(Shweta Trivedi, Ph.D., is a postdoctoral fellow in the Laboratory of Respiratory Biology Environmental Genetics Group.)

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