Smoke from so-called harm-reduction cigarettes is just as dangerous to developing embryos as smoke from standard cigarettes, and may be even more toxic, new experiments with mouse embryo stem cells show.

The smoke issuing from the ends of these cigarettes is more harmful than the fumes inhaled through a filter, Dr. Prue Talbot of the University of California, Riverside and her colleagues report in the journal Human Reproduction.

There has been very little research on the chemicals remaining in cigarettes treated to remove certain toxic and cancer-causing substances and even less on how smoke from these cigarettes might affect developing embryos, Talbot told Reuters Health. “The caveat is there are many things in smoke besides the known carcinogens - smoke has somewhere between 4,000 and 6,000 chemicals in it,” she said.

To investigate, Talbot and her team grew mouse embryonic stem cells in mediums containing four different concentrations of smoke from Marlboro Reds and three harm-reduction brands: Marlboro Lights, which have multiple tiny holes placed in the filter to reduce the amount of smoke inhaled; Advance cigarettes, which are treated to reduce certain carcinogens; and Quest, a nicotine-free cigarette.

In one experiment, they measured the ability of cells to attach to a protein substrate (a stand-in for uterine implantation), and in the other they measured the ability of the cells to divide.

At all concentrations, and in both sets if experiments, all four types of cigarette smoke impaired the cells’ ability to attach, and the higher the concentration, the stronger the effect.

In every case, the non-filtered “sidestream” smoke was more toxic than the filtered “mainstream” smoke.

Similar effects were seen on the ability of attached cells to divide and survive. Smoke exposure also caused some of the attached cells to become detached, and again, the higher the concentration of smoke, the greater the effect.

Exposing pre-implantation mouse embryos to smoke solutions produced similar effects.

Based on the findings, Talbot said, any woman of reproductive age should not only not actively smoke, but should also do her best to avoid being exposed to cigarette smoke.

Women who are in the extremely early stages of pregnancy often don’t know it, she added, and the current findings suggest that this is when a developing embryo might be most vulnerable to exposure.

Talbot and her team are beginning to conduct similar work using human embryonic stem cells, and so far have seen similar results, she said.

SOURCE: Human Reproduction, January 2009.