Background:  Lemon and lime juices have recently been proposed as potential topical microbicides to prevent sexual transmission of HIV. Based on encouraging results from preliminary in vitro efficacy studies and reports that some women are already using lemon or lime juices as a microbicide, these juices are currently being evaluated in clinical safety trials. This study was initiated to evaluate lemon and lime juice in a wide range of preclinical assays routinely used to identify potential topical microbicides.

Methods:  Freshly prepared lemon and lime juices were evaluated for efficacy against R5- and X4-tropic HIV using co-receptor engineered cell lines, cervical cell lines, cervical explant tissue, and primary cells. Cytotoxicity determinations were conducted in parallel with efficacy assays. The juices were also tested for effect on viability of Lactobacillus species that are associated with vaginal health. All cell-based assays included three replicates per sample and at least three different experimental set-ups.

Results:  The therapeutic index (TI = TC₅₀/IC₅₀) for transformed cell lines or primary cells exposed to lemon or lime juice for 3 hours to 6 days are shown below. Viability of cervical explant tissue was reduced by 69 to 84% following 2-hour exposure to lemon or lime juice respectively. Lemon or lime juice also exhibited some toxicity to Lactobacillus crispatus (average MIC₅₀ 18.45±4.8%) and L. jensenii (average MIC₅₀ 16.09±5.55%). For comparison, TI values for non-cytotoxic, active antiviral control compounds such as T-20 or dextran sulfate were generally >100 and these compounds did not inhibit viability of Lactobacillus species.

Conclusions:  In this study, lemon and lime juices exerted marked cytotoxicity across a variety of pre-clinical assays in transformed and primary cells as well as explant tissue. The cytotoxicity observed dominated the activity profiles of the juices, providing minimal separation of antiviral efficacy from nonspecific effects on cells and explant tissue. Thus, our preclinical assays of cytotoxicity and efficacy for lemon and lime juices have identified potential safety concerns for this microbicide strategy.