Washington, Dec 9 : They might be considered safe, but harm-reduction cigarettes can be even more toxic than traditional cigarettes, according to a new study.

Researchers from University of California - Riverside have found that smoke from the "light" or "low-yield" harm-reduction cigarettes retains toxicity, and that this can have an adverse impact on prenatal development.

"Many chemicals found in harm-reduction cigarette smoke have not been tested, and some are listed by manufacturers as safe," said lead researcher Prue Talbot and a professor of cell biology.

"But our tests on mice clearly show that these chemicals adversely affect reproduction and associated development processes.

"The effects are likely to be the same in humans, in which case pregnant women would be particularly vulnerable to the effect of smoke from these cigarettes," she added.

During the study, the researchers used mouse embryonic stem cells (mESCs) as a model for pre-implantation embryos-embryos that have not yet implanted in the wall of the uterus-and compared the toxicity on these cells of cigarette smoke emanating from traditional and harm-reduction brands.

They analysed the effects of two kinds of cigarette smoke: mainstream smoke, which is smoke actively inhaled by smokers; and sidestream smoke, which is smoke that burns off the end of a cigarette.

The results showed that both kinds of smoke from traditional and harm-reduction cigarettes were toxic to pre-implantation embryos and could retard growth or kill embryonic cells at the stage of development.

Moreover, mainstream smoke and sidestream smoke from harm-reduction cigarettes were found to be more potent than the corresponding smoke from traditional brands of cigarettes.

"This result was unexpected since harm reduction brands purportedly have lower concentrations of toxicants," Talbot said.

"Clearly, the tobacco companies have not eliminated all toxins from harm-reduction brands of cigarettes," said Talbot, who also is the director of the UCR Stem Cell Center.

"We found that both mainstream and sidestream smoke from traditional and harm-reduction cigarettes hindered the attachment of mESCs to extracellular materials.

"Such attachment is crucial to normal embryonic development. Moreover, cell survival and proliferation-also necessary for embryonic growth-were hindered as well.

"This may be because sidestream smoke is produced at a lower temperature and therefore contains higher concentrations of toxicants," Talbot added.

The study appears in the journal Human Reproduction. (ANI)