Glycerol Monolaurate Does Not Alter Rhesus Macaque ( Macaca mulatta ) Vaginal Lactobacilli and Is Safe for Chronic Use

Abstract

Glycerol monolaurate (GML) is a fatty acid monoester that inhibits growth and exotoxin production of vaginal pathogens and cytokine production by vaginal epithelial cells. Because of these activities, and because of the importance of cytokine-mediated immune activation in human immunodeficiency virus type 1 (HIV-1) transmission to women, our laboratories are performing studies on the potential efficacy of GML as a topical microbicide to interfere with HIV-1 transmission in the simian immunodeficiency virus-rhesus macaque model. While GML is generally recognized as safe by the FDA for topical use, its safety for chronic use and effects on normal vaginal microflora in this animal model have not been evaluated. GML was therefore tested both in vitro for its effects on vaginal flora lactobacilli and in vivo as a 5% gel administered vaginally to monkeys. In vitro studies demonstrated that lactobacilli are not killed by GML; GML blocks the loss of their viability in stationary phase and does not interfere with lactic acid production. GML (5% gel) does not quantitatively alter monkey aerobic vaginal microflora compared to vehicle control gel. Lactobacilli and coagulase-negative staphylococci are the dominant vaginal aerobic microflora, with beta-hemolytic streptococci, Staphylococcus aureus, and yeasts sporadically present; gram-negative rods are not part of their vaginal flora. Colposcopy and biopsy studies indicate that GML does not alter normal mucosal integrity and does not induce inflammation; instead, GML reduces epithelial cell production of interleukin 8. The studies suggest that GML is safe for chronic use in monkeys when applied vaginally; it does not alter either mucosal microflora or integrity.Glycerol monolaurate (GML), a fatty acid monoester, is generally recognized as safe by the Food and Drug Administration for topical skin and mucous membrane uses at doses up to 100 mg/ml; this is based on many years of experience with GML as an additive to cosmetics and foods. Previously, the compound was shown in vitro to inhibit exotoxin production by gram-positive bacteria, including production of staphylococcal toxic shock syndrome (TSS) toxin-1 and alpha-toxin, at concentrations of Ն20 g/ml, acting at the level of transcription (24,28,35). Streptococci and other gram-positive cocci, which do not produce glycerol ester hydrolases (lipases), are killed by GML at concentrations of Ն10 g/ml, but production of their exotoxins is inhibited at even lower GML doses (28). Staphylococcus aureus and coagulase-negative staphylococci secrete lipases, and thus, the organisms are resistant to killing by GML except at concentrations approaching 500 g/ml (28). Studies to assess the effect of GML on normal vaginal microflora lactobacilli have not been performed.Unlike gram-positive cocci, gram-negative Enterobacteriaceae are resistant to GML at even very high concentrations (Ͼ2,000 g/ml); however, rough mutants, lacking intact lipopolysaccharide (LPS), are highly susceptible to the bactericidal effects of GML (at concentrations of...

Glycerol Monolaurate Inhibits Candida and Gardnerella vaginalis In Vitro and In Vivo but Not Lactobacillus

“…on May 9, 2018 by guest http://aac.asm.org/ numbers of study participants, data for GML (0.5% and 5%) were evaluated individually but also pooled for determination of significant differences between visits. The prevalences of Lactobacillus between visit 1 and visit 2 for all treatment groups were not significantly different, consistent with the idea that the gels with or without GML have no effect on lactobacilli (24). Candida prevalences between visit 1 and visit 2 were not different in women given control gels (P ϭ 0.45) but were significantly reduced by treatment with GML gels (P ϭ 0.003).…”

“…Previous studies demonstrate that GML inhibits growth and production of exotoxins of various Gram-positive bacterial groups but does not inhibit the growth or metabolism of lactobacilli (23,24). GML does not inhibit Enterobacteriaceae unless LPS mutants, such as Re, are present (23).…”

“…GML (Cognis, Cincinnati, OH) was dissolved in gels made at the Fairview Compounding Pharmacy, Minneapolis, MN, by a pharmacist (M. L. Peterson) to mimic K-Y warming gel to achieve final concentrations of 0.5% or 5% and pHs of 4 to 4.5 (16,24). Vaginal applicators (Exacta-Med vaginal dispensers; Baxa Corporation, Englewood, CO) were filled with 5 ml of gels.…”

“…A critical exception is that lactobacilli are insensitive to GML. Long-term in vivo studies of monkeys show that 50 mg/ml of GML in intravaginal gels does not inhibit lactobacilli and is not proinflammatory (24). Gram-negative bacteria, such as Enterobacteriaceae, with intact lipopolysaccharide (LPS) are not susceptible to GML (23).…”

Staphylococcal and Streptococcal Superantigen Exotoxins

“…The studies suggest that GML, in addition to preventing TSST-1 production, stabilize the host mucosa to prevent outside-in signaling (109). GML is safe as used vaginally in 5% (50-mg/ml) gels for periods of up to 6 months, as tested in rhesus macaques (304). Studies suggest that GML can also be used to reduce simultaneously bacterial vaginosis pathogens and Candida infections vaginally (305).…”