An evaluation of 13 sexual lubricants has found that, while many are toxic to the cells that line the vagina and rectum, this does not lead to an increased rate of HIV infection – at least in test-tube experiments.
The researchers conclude that, while some of these commercially available compounds do cause damage to the epithelium (the layer of cells that lines the vagina and rectum), this may not in itself be sufficient to increase the likelihood of HIV infection. This means that although the 'lubes' that cause the most damage to cells are, in the main, water-based ones, they are unlikely to reduce the efficacy of the condoms they are designed to be used with. Some other water-based lubes, and the silicone-based ones, were not toxic to cells.
The researchers confirmed that the main reason some lubricants kill off tissue is because they contain more dissolved salts and other chemicals than the fluid inside cells: to use the technical term, they are hyperosmolar. This property means that they draw water out of the mucous membrane cells, drying them out and stripping them from the membrane surface. Two lubes tested were hypo-osmolar, meaning that instead the cells drew water out of the lube, which makes them swell and burst; one of these gels was toxic to cells too.
In contrast, the two gels that were iso-osmolar, meaning with the same fluid/salt balance as body fluids, did not damage mucous membranes; nor did the two lubes that were silicone- rather than water-based, and one of the hypo-osmolar ones.
While this property, osmolality, was the one most strongly associated with toxicity, preservatives found in some of the lubes were also toxic to cells, principally the compound chlorhexidine. This included K-Y Jelly, probably the most long-established lube and one that has been used as a ‘control’ in some microbicide trials. Chlorhexidine, and possibly other preservatives, also killed off some beneficial vaginal bacteria (Lactobacillus species) that guard against bacterial vaginosis and may protect against HIV infection.
Alarmingly, it found that the two lubes it tested that were oil-based – and specifically aimed at gay men who choose not to use condoms – were also likely to cause rectal membrane damage.
In the experiments, lubes did not prevent infection, but they also did not amplify infection – in other words, infected cells did not produce copies of HIV any faster than usual. This means that another process, such as active inflammation, may need to be there in order to increase the chance that a temporary, local infection of cells turns into a systemic, continuing one.
The research also found that cervicovaginal tissue was – contrary to what had previously been thought – just as likely to be damaged by some of the lubricants as rectal tissue.
Lead researcher Charlene Dezzutti and colleagues from the University of Pittsburgh, which has pioneered microbicides studies, were one of two teams who, in different papers presented at the 2010 International Microbicides Conference, first announced findings suggesting that many lubricants used in sex were toxic to cells and might possibly increase the risk of HIV transmission.
Previously it had been assumed that most lubes were neutral or even beneficial in terms of HIV transmission, partly because they reduce injury and soreness, and also because some of their ingredients have shown anti-HIV activity in the test tube. Although results showing the spermicide nonoxynol-9 and the candidate microbicide cellulose sulphate actually increased HIV transmission, this was not thought to be the case for other lubes.
Dezzutti and colleagues’ research seemed to show that it was the water-based lubes that were particularly associated with cell damage, which put prevention advocates into a dilemma: should the standard safer-sex advice still include using a water-based lube with condoms?
In the study, Charlene Dezzutti’s team took 14 lubricants commercially available in the USA and performed a number of tests on them.
Amongst the research team were Jim Pickett and Marc-André LeBlanc from International Rectal Microbicide Advocates (IRMA), who have urged more research into lubes. See here for IRMA's release on the study.
The lubes used in the present study were:
The researchers conducted a variety of tests:
The most important results were:
This research shows that the initial hunch that osmolality might be the cause of cellular toxicity was correct and that iso-osmolar water-based lubes and silicone-based ones are not toxic to vaginal or rectal cells.
It shows that, in the test tube at least, none of the lubes appear to increase the likelihood of HIV infection or replication, which is good news, but none decrease it either.
For obvious reasons, however, these studies cannot mimic whether lubes have protective or harmful effects when actually used in sex; explants are not the same as live tissue and no test can show whether lubes protect against HIV infection by protecting against the soreness, friction or injuries that might have occurred without them.
“Despite the lack of increased HIV infection in ... tissue,” the researchers write, “these results convey the importance of using condoms in conjunction with compatible lubricants.”
Charlene Dezzutti commented: “Much more work needs to be done to explore the safety of lubes. This was an early study; the jury is still out as to whether hyperosmolar lubes cause damage to the epithelium that, in conjunction with other processes like inflammation, could increase susceptibility to HIV.”
Dezzutti CS et al. Is wetter better? An evaluation of over-the-counter personal lubricants for safety and anti-HIV-1 activity. PLoS ONE 7(11): e48328, doi:10.1371/journal.pone.0048328, 2012. See open-access paper here.
