New Delhi, July 4: A Calcutta University scientist who had nearly two decades ago proposed that vitamin C may protect the lungs from cigarette smoke has now unravelled the molecular mechanisms of smoke-induced lung injury and the vitamin's protective effect.

Kaustubh Panda, coordinator of biotechnology at the university, asserts that his research is not intended to play down the myriad health risks of tobacco but highlights an inexpensive way of protecting smokers from emphysema, or lung damage.

Panda and his colleagues have shown, through experiments on human lung cells in test tubes and guinea pigs in the laboratory, how compounds called oxidants generated from cigarette smoke damage lung proteins, while vitamin C can neutralise these oxidants.

Their findings were published today in the US journal Proceedings of the National Academy of Sciences.

Public health specialists cautioned that the findings should not give smokers a false sense of protection.

"It is plausible that vitamin C may provide some protection from emphysema, but tobacco and smoking also lead to cardiovascular deaths and cancer, which are bigger killers," said K. Srinath Reddy, senior cardiologist and president of the New Delhi-based Public Health Foundation of India.

"Smoking is an addictive and suicidal exercise," Panda said. "Our results clearly show the dangers of smoking, which means there are benefits of quitting. But despite legislative steps and health warnings, many tobacco users are unable to bail themselves out. Vitamin C may help such people."

Medical researchers have long been agreed that smoking damages the lungs but there's been debate about the mechanisms leading to emphysema: the destruction of the elastic architecture of the lungs, leading to enlargement of their air spaces.

Smoking is a key cause of emphysema, a condition that leads to breathlessness and can progress to chronic obstructive pulmonary disease, projected by the World Health Organisation to become the third greatest cause of death by the year 2030.

Norbert Weissmann, a senior scientist at the University of Giessen Lung Centre, Germany, and his colleagues had suggested five years ago that even when lung damage was triggered by smoke, it was also associated with internal mechanisms involving lung cells.

The scientists had proposed that an enzyme that catalyses the formation of nitric oxide in the lungs is the primary cellular factor for cigarette smoke-induced lung injury.

"It has not been very clear what causes the disease and there has been no therapy to stop or reverse lung destruction in emphysema," Weissmann had said in a media release in 2011. "There have been no new concepts about therapy over the past 20 years."

The Calcutta University study has now provided strong experimental evidence that oxidants in cigarette smoke are primarily responsible for changing the structure of lung proteins, causing them to lose structural features and elasticity.

"This work (gives) a more accurate and detailed picture of the chemistry of cigarette smoke-induced lung damage and clearly proves that oxidants from cigarette smoke are the primary causative factors for the emphysema," wrote a scientist not involved in the study but familiar with its design and findings.

Panda began exploring the effects of vitamin C on lung cells in the mid-1990s, as a doctoral scholar.

"But at that time, we did not have the sophisticated tools for experiments to differentiate between the effects of oxidants and internal cellular processes," he said.

Panda worked with research scholars Indranil Gupta and Souradipto Ganguly in his department and collaborators in New York and Cleveland in the US for the latest experiments to examine the mechanisms underlying lung damage and vitamin C's effects.

Cigarette smoke has been claimed to be a mixture of over 4,700 compounds, among which a significant proportion are oxidants -- electron-hungry molecules that have been known to have adverse effects on biological tissues.

The Calcutta experiments suggest that oxidants from smoke may directly interact with lung tissue to cause damage to proteins, leading to emphysema.

In one set of experiments, the scientists gave vitamin C in a dose of 20mg per kg body weight to guinea pigs for about seven days before they were exposed to cigarette smoke.

Guinea pigs that had received vitamin C showed less damage to their lungs than guinea pigs that did not receive the vitamin.