The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 12 No. 4 • August 2009

Emphysema, Pulmonary Fibrosis, and Lung Cancer: Quercetin and Curcumin Protect Against Nitric Oxide Modification of Lung Anti-Proteases

Lung diseases such as emphysema, pulmonary fibrosis, and lung cancer are believed to be caused by an imbalance between proteases (that break down proteins) and their natural inhibitors.1 A new study1 examined the effect on the function of cysteine proteases by modifications induced by nitrosative stress (excessive production of nitric oxide, as occurs in chronic/acute lung inflammation) and the ability of quercetin and curcumin to protect lung proteins from these effects.

In humans, the lung protease inhibitor alpha-1 antitrypsin provides important protection against the breakdown of lung proteins that contribute to the development of emphysema and COPD. This new study examined the effects of nitrosative stress on the structure and function of cystatins, noncovalent competitive inhibitors of cysteine proteinases (known as cathepsins B, H, I, and S), that are ubiquitously present in mammalian tissues1 and prevent excessive proteolysis (protein breakdown) that occurs in diseases such as bronchitis, rheumatoid arthritis, osteoporosis, Alzheimer’s disease, cancer metastasis, and microbial invasion.1

The new study reports on protective effects of curcumin and quercetin against nitrosative stress-induced dysfunction of the goat lung version of cystatin. The researchers found that “[t]he treatment of cystatin from goat lungs with the NO-generating compound SNP [sodium nitroprusside, which releases NO] causes concentration and time-dependent loss of enzyme [cystatin] activity.” This may be caused by the nitrosation of active amino acid sites in the cystatin molecule or the oxidation of critical tryptophan residues in the molecule.

Curcumin and quercetin provided significant protection against the functional and structural damage to goat lung cystatin, thus helping protect the molecule’s activity against excessive protein breakdown. Curcumin (50 µM) prevented this damage to cystatin, whereas for protection to a similar extent, quercetin at 5 times that concentration was required.1

The authors conclude: “The results of the study are of great significance. Proteins are the major targets of reactive species. … modification of proteins by reactive species (ROS, NO, RNS, etc.) render them more susceptible to enhanced proteolysis, inactivation and denaturation. The present study documents the suppression of NO-induced inactivation of GLC-1 [goat lung cystatin] by curcumin and quercetin. Also, structural changes in SNP-treated GLC-1 are minimized by curcumin and quercetin.” The authors suggest that curcumin and quercetin (as well as many other polyphenols) could provide “a rather inexpensive therapeutic option against oxidative injury.”

Food sources naturally rich in quercetin include black tea, apples, and tomatoes, while about 40% of the polyphenol content of the spice turmeric root powder consists of curcumin. We take turmeric root powder itself as a source of curcumin (rather than curcumin alone) as the whole root powder contains other related molecules (called curcuminoids) that have similar or even stronger protective effects. It is available in capsules (600 mg/capsule), which is nice because the taste of turmeric root powder by itself (not as it is found prepared in food) is rather unpalatable. Quercetin is also found in our new V-Shield™ (1000 mg in the recommended 2 capsules three times a day) and in our Personal Radical Shield™ (130 mg in the recommended 12 capsules per day).


  1. Shahnawaz et al. Preventive effect of curcumin and quercetin against nitric oxide mediated modification of goat lung cystatin. J Agric Food Chem 57:6055- 6059 (2009).

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