New research in Israel suggests a new preventive treatment of asthma. The results, published this week in the journal ”Bioorganic and Medicinal Chemistry” by Professor Ehud Keinan, Dean of Chemistry, and his coworkers, confirm that asthma-like symptoms were prevented in an animal model following inhalation of limonene, which a potent ozone scavenger.
Natural ozone scavengers may prevent asthma
New Technion research suggests a new preventive treatment of asthma. The results, published this week in the journal ”Bioorganic and Medicinal Chemistry” by Professor Ehud Keinan, Dean of Chemistry, and his coworkers, confirm that asthma-like symptoms were prevented in an animal model following inhalation of limonene, which a potent ozone scavenger.
”Ozone in the outer atmosphere is essential for life on earth because it absorbs the destructive ultra violet radiation emitted by the sun,” explains Prof. Keinan. ”On earth, however, ozone is a notoriously known dangerous component of air pollution. Numerous studies on the pulmonary toxicity of environmental ozone have demonstrated that exposure to ozone, even at low levels, induces airway inflammation and lung injury in both humans and animals.”
”Therefore, we were quite surprised by a 2002 report from The Scripps Research Institute, by Prof. Lerner and coworkers, who reported that ozone could be formed endogenously in our body. Their results supported the possibility that ozone is formed in inflammatory tissues by neutrophils, suggesting that ozone is formed as a part of the body’s defence against pathogens. That discovery led us to assume that inflammation in asthma could involve formation of ozone not only by neutrophils, but also by other white blood cells, and that ozone itself could recruit and activate more white blood cells, which, in turn, would produce more ozone. A vicious circle involving white blood cells recruitment and ozone production, could account for the fact that inflammation in asthma is persistent.”
Following this assumption, the Technion researchers hypothesized that electron-rich olefins, which are known to react readily with ozone, could be used for prophylactic treatment of asthma. Inhalation of volatile, hydrophobic olefins, could allow their accumulation in the lung membranes, thereby equipping the airways with local ozone scavenging capability. Naturally occurring monoterpenes, for example, which are produced ubiquitously by plants, could provide us not only with pleasant smells but more importantly, with chemical protection against either exogenous or endogenous ozone. The unsaturated monoterpene limonene, which is the main component in the essential oil of citrus fruits, could thus function as an ozone scavenger. In contrast, eucalyptol, a saturated monoterpene, which is an essential oil of the eucalyptus tree, cannot scavenge ozone.
The experiments involved exposing rats with asthma-like symptoms to either limonene or eucalyptol for a couple of days before examining their lung function. The pulmonary function of sick rats showed that limonene inhalation significantly prevented the asthmatic symptoms while eucalyptol inhalation did not alleviate the disease. The anti-inflammatory effect of limonene was also confirmed by pathological evidence.
”The high environmental concentration of natural ozone scavengers in agricultural areas could possibly now explain why the prevalence of asthma in rural population is significantly lower than its prevalence in urban population,” proposes Professor Keinan.
The research was carried out with graduate student Aaron Alt, Dr. David Shoseyov of the Hadassah Mount Scopus University hospital, Dr. Haim Bibi of the Barzilai Medical Center, Ashkelon, Dr. Gail Amir of the Hadassah University hospital and Dr. Lea Bentur of the Technion Medical School.