Limonene, lungs and the Biblical citron

(Another guest blogging by Dr. Jim Duke)

Israeli scientists (Keinan et al, 2005) suggest that the monoterpene limonene which constitutes more than half of the Biblical citron's essential oil might help asthmatics, especially those aggravated by ozone pollution. I posed a few questions to the good doctor. Could poor children here in our inner cities, where asthma is increasing dramatically, reduce their asthma attacks and or symptoms, especially when around ozone pollution, as on school buses in inner cities, by squeezing citrus peels (apparently all contain limonene) and inhaling the pleasant aroma periodically. Since the sedative antiinflammatory limonene is also absorbed thru the skin, rather rapidly I might add, I'd also try adding crushed citrus peels to bath water which might help as well, say at the end of the days commute. Keinan's group predicted that electron-rich olefins, which are known ozone scavengers, could be used for prophylactic treatment of asthma. Volatile, unsaturated monoterpenes, like limonene, could saturate the pulmonary membranes equipping the airways with local chemical protection against either exogenous or endogenous ozone. In his experimental rats, limonene inhalation significantly prevented bronchial obstruction (eucalyptol, alias cineole, saturated and inert to ozone, did not). I doubt I can convince our government to compare citrus-inhalation in clinical trials as a third arm against placebo and some expensive pharmaceuticals. As a gray-headed botanist, I cannot and do not prescribe. But if I had a hundred asthmatic grandchildren, you could bet half of them would be trying citrus peel and others would not, followed by a vice versa cross-over, recording the frequency and severity of their attacks for old grandpa. Faith-based types might best be praying too, and using the peel of the Biblical citron, called ethrog or etrog in some versions of the Bible. Without praying to improve my odds, I'll still bet the citrus peel would score well along side the pharmaceuticals. I know it would be cheaper and bet it'll be safer, possibly as efficacious. We'll never know until there are unbiassed clinical trials.

That asthmatic possibility is relatively new; it's been known for a decade that limonene could also prevent cancers as well. Mondello et al (1995) found that limonene was the most frequent monoterpene component in all the citrus oils that they examined, varying from 50% in lime oil to about 97% in grapefruit oil. Its about 52% in the etrog. d-Limonene works in preclinical models of breast cancer, causing > 80% of carcinomas to regress with little host toxicity. (Crowell et al, 1994). More reecently Tsuda et al (2004) singled out as promising cheoipreventive anticancer phytochemicals vitamin derivatives, phenolic and flavonoid agents, fatty acids, organic sulfur compounds, isothiocyanates, curcumins, and d-limonene. Those last four suggest a Biblical chutney. the garlic and onion for organic sulfur compounds; watercress and horseradish for isothiocyanates, turmeric for curcumin, and citrus peels for limonene. Lu et al (2003) showed that D-limonene exerts its cytotoxic effect on gastric cancer cells by inducing apoptosis. Parija et al (2003) and Kaji et al (2001) reiterate the well known anticarcinogenic activity of d-limonene mentioning also is chemopreventive nature in hepatocarcinogenesis.

But this is the month when we focus our blogs on lung cancer. PubMed only has 11 citations re limonene and lung cancer. But if I were diagnosed with lung cancer today, Id be ingesting more garlic and more citrus too. I might even be inhaling limonene-containing essential oils as I squeezed citrus peels. Raphaeol et al (2003) note that several naturally occurring monoterpenes, like carvone, limonene and perillic acid, inhibit experimental lung metastasis. Limonene at 100 uM/kg body wt. 10 doses ipr remarkably reduced metastatic tumor nodule formation. Limonene and perillic acid just might even inhibit the metastatic progression of melanoma cells.

I doubt that Witschi (2000) would join me in judiciously inhaling citrus essential oils. Under the catchy title, "Successful and not so successful chemoprevention of tobacco smoke-induced lung tumors." Wirschi notes that none of the following "chemopreventive" agents: green tea, phenethyl isothiocyanate, acetylsalicylic acid, N-acetylcysteine, 1,4-phenylenebis[methylene]selenocyanate and THE d-limonene reduced lung tumor multiplicity or incidence. I'd still be eating my garlic and brazilnuts and inhaling my citrus, even though no clincial trials have indicated their safety or efficacy, if I feared lung cancer. I suspect they will do as much good and less harm at a much lower cost, economically, mentally and physically, than the chemotherapeutic cocktails being offered by the allopaths and their covert sponsors, the pharmaceutical firms. Many people believe more in the faith-based botanical herbs than they do in the allopathic ACS and NCI chemotherapeutic poisons. Such people have a better chance of being helped by these safer food farmacy items, also improving their odds against the other diseases of modern man, cardiopathy and diabetes and iatrogenesis.