Vitamin E shields lungs from smog effects

Many people develop a shortness of breath, wheezing or other forms of respiratory discomfort with rising concentrations of ozone, the primary irritant in smog. And a study in the March 12 New England Journal of Medicine has now reported that chronic exposure to ozone significantly raises an individual’s risk of dying from lung disease. Diet, however, can temper how lungs respond to air pollution, researchers reported this week. Among lung-guarding nutrients we all could use more of: gamma-tocopherol often referred to as the “other vitamin E.”

The typical American diet is actually ozone-friendly, meaning all too often it aids and abets pollution, noted researchers at the Society of Toxicology annual meeting in Baltimore, this week. But data they presented — mostly from animal studies — demonstrate how various dietary agents can boost the body’s defenses.

Take gamma-tocopherol.

Vitamin E consists of a mix of tocopherols and tocotrienols. Far and away the best known of these is alpha-tocopherol — the most potent fat-soluble antioxidant in the diet. However, gamma-tocopherol bests alpha big time when it comes to fighting inflammation, notes James Wagner of Michigan State University in East Lansing. And damaging inflammation is what smog-ozone triggers in lung tissue.

At least in rats, however, a heavy dose of gamma-tocopherol can prevent the aggravation by ozone of allergic airway disease, mucus production, nasal allergy symptoms and asthma. Wagner and his colleagues published a paper last year demonstrating these benefits. In animals that serve as a model of allergic airway disease, Wagner reported, ample gamma-tocopherol supplementation prevented almost every respiratory symptom that ozone worsened.

At this week’s SOT meeting, Wagner reviewed these data and described similar findings from brand new studies. These newer investigations involved animals breathing ozone-laden air after being first exposed to endotoxins. These are a family of bacterial poisons that can trigger fever and other symptoms of serious inflammatory disease in animals and people.

With allergic airway disease, including asthma, affected tissues develop inflammation. One symptom: the infiltration of inflammatory eosinophils — a type of white blood cell — within the tissue just beneath the surface of airways. In endotoxin-treated animals, a similar situation develops. In this case, however, different inflammatory white blood cells — neutrophils — set up housekeeping in the tissue just below the inner surfaces of airways.

And in animals exposed to high concentrations of endotoxin, airborne concentrations of 1 part per million ozone boosted mucus production in the animals’ airways 2- to 5-fold and triggered a roughly 10-fold buildup of neutrophils in the airway tissues. (That ozone concentration is about 10 times as high as might be encountered in very smoggy regions, such as Mexico City.)

If those same animals, however, had been treated with 30 milligrams per day of gamma-tocopherol in the four days leading up to their encountering the heavily ozone-polluted air, the mucus and neutrophil loading in their airways was elevated only slightly — about as much as was seen in ozone-exposed animals that had received no endotoxin.

Studies by Qing Jiang at Purdue University and Bruce N. Ames of Children’s Hospital of Oakland Research Institute have begun pointing to why gamma-tocopherol is so helpful. It inhibits key enzymes — the cyclooxygenases-1 and -2 that jumpstart a biochemical cascade that can unleash dramatic inflammation.

Wagner’s group has begun teaming up with Jiang and Ames. And “what our collaborative studies demonstrate is that gamma-tocopherol is much more effective than alpha-tocopherol at inhibiting COX-1 and 2,” Wagner says. “Inhibition of these COX enzymes is, in fact, the primary mechanism by which ibuprofen exerts its anti-inflammatory effects,” he explains.

Their new COX studies identified one metabolite of gamma-tocopherol that is every bit as potent as ibuprofen at tamping down inflammation. While test-tube data suggest alpha-tocopherol can inhibit some inflammatory enzymes in neutrophils, Wagner notes that “in side-by-side comparisons of animal studies of inflammation, gamma-tocopherol appears to be more effective than alpha.”

His co-moderator on an SOT panel where these data were reported, Monday, asked Wagner whether anyone could derive enough gamma-tocopherol from foods to protect their lungs from ozone. And his answer was succinct: “It is certainly NOT achievable with diet.”

To match the values of this gamma-tocopherol that proved protective in the nasal passages and lungs of ozone-exposed rats, people would have to consume between 0.7 and 2 grams of gamma-tocopherol per day. For comparison, even soybean oil — one of the richest sources of gamma-tocopherol — provides only 80 milligrams per 100 grams of oil. And 100 grams of oil is about half a cup.

So it’s likely, Wagner concludes, that if people need to down a gram of gamma-tocopherol a day, they will have to turn to dietary supplements.

Janet Raloff

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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