Obesity and smoking reduces abilityto fight cancer

HOW ARE those New Year's resolutions shaping up? If they involved kicking cigarettes and slimming down to a healthy weight, then a new study led by University College Dublin should provide a bit of extra motivation, writes CLAIRE O'CONNELL

UCD researchers have shown that cigarette smokin’g dampens down immune cells that help protect the body from viruses and cancer. And the stifling effects are even more pronounced in obesity.

The study, published on Monday in the journal PLoS ONE, looked at cells of the immune system called "natural killer cells" (NK cells).

They sound fierce, but thankfully they are batting for our side – seeking out and destroying potential dangers to health such as viruses and circulating tumour cells.

“Natural killer cells are really good,” explains Dr Lydia Lynch, a post-doctoral researcher with the obesity research group at St Vincent’s University Hospital in Dublin. “They go after viruses and abnormal cells like tumour cells, you don’t even realise it’s happening.”

Previous work by the group showed that the number and potency of NK cells in the blood goes down in obesity, and the new study wanted to see whether smoking affected the ability of NK cells to kill cancer cells. So they set up a smoking machine to puff through cigarettes and mimic the effects of tobacco smoke on the blood.

“It smokes cigarettes into the media , and what you get back is the equivalent of what would be in your blood if you smoked 20 a day,” says Lynch, who is working both at UCD and Harvard Medical School.

The team then took NK cells from 40 severely obese people and 20 lean people and challenged them with cancer cells in the lab.

“We take the cells straight out of lean and obese people and we added the tumour cells just as we usually would to see if they can kill them,” explains Lynch. “Then we added a bit of this ‘smoke’ media.”

Adding the smoking extract reduced the ability of the NK cells to kill the cancer cells, and the immune cells from obese people appeared to be more susceptible to the effects of the cigarettes.

NK cells from obese people showed a 33 per cent reduction in killing ability, while NK cells from lean people showed a 28 per cent reduction.

THE FINDINGS AREintriguing against the backdrop of other studies that show obesity increases the risk of certain cancers, and that losing weight brings the risk back down again. Meanwhile, obese smokers aged 40 have a 14-year reduction in life expectancy compared to lean non-smokers.

The research team, which included Prof Donal O’Shea at UCD and Prof Cliona O’Farrelly in Trinity, also looked into the molecular mechanism behind the effects they saw in the lab and found the smoking extract seemed to interfere with the NK cells attacking their targets.

“One of the ways NK cells can work is when they see a cancer cell they attach on and release toxic granules into the cell, which then dies,” explains Lynch. “But when you add the ‘smoke’ it stops these toxic granules coming out.”

The study, which was funded by the Diabetes Federation of Ireland and the Health Research Board, also found that adding the hormone adiponectin helped protect NK cells from the smoke extract. Could this be a potential treatment to boost compromised immune cells?

“The best thing to do is get your body mass index down and stop smoking. But you can’t do that quickly, so if adiponectin was potent – and further studies are required – that might be something you could in the future give to patients,” says Lynch. “We already know from studies that obese people have less of it. So if it can be protective of the immune system it could be a road we could go down in the future.”