Mechanisms of antibacterial action of three monoterpenes. (49/240)

In the present paper, we report the antimicrobial efficacy of three monoterpenes [linalyl acetate, (+)menthol, and thymol] against the gram-positive bacterium Staphylococcus aureus and the gram-negative bacterium Escherichia coli. For a better understanding of their mechanisms of action, the capability of these three monoterpenes to damage biomembranes was evaluated by monitoring the release, following exposure to the compounds under study, of the water-soluble fluorescent marker carboxyfluorescein from unilamellar vesicles with different lipidic compositions (phosphatidylcholine, phosphatidylcholine/phosphatidylserine [9:1], phosphatidylcholine/stearylamine [9:1], and phosphatidylglycerol/cardiolipin [9:1]). Furthermore, the interaction of the terpenes tested with dimyristoylphosphatidylcholine multilamellar vesicles as model membranes was monitored by means of differential scanning calorimetry. Finally, the results were related to the relative lipophilicity and water solubility of the compounds examined. Taken together, our findings lead us to speculate that the antimicrobial effect of (+)menthol, thymol, and linalyl acetate may result, at least partially, from a perturbation of the lipid fraction of microorganism plasma membrane, resulting in alterations of membrane permeability and in leakage of intracellular materials. Besides being related to physicochemical characteristics of the drugs (such as lipophilicity and water solubility), this effect seems to be dependent on lipid composition and net surface charge of microbial membranes. Furthermore, the drugs might cross the cell membranes, penetrating into the interior of the cell and interacting with intracellular sites critical for antibacterial activity.  (+info)

Permeation and reservoir formation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and benzo[a]pyrene (B[a]P) across porcine esophageal tissue in the presence of ethanol and menthol. (50/240)

Environmental influences may affect carcinogen absorption and residency in the tissues of the aero-digestive tract. We quantified the effect of ethanol and menthol on the rates of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and benzo[a]pyrene (B[a]P) absorption using a fully validated in vitro diffusion system, capable of accurately and precisely quantifying tobacco carcinogen permeation and reservoir formation in porcine esophageal mucosa. Confocal microscopy was employed to visualize the location of B[a]P in the exposed membranes. Markedly different extents of permeation and reservoir formation for the tobacco carcinogens were recorded in the presence of ethanol and menthol. The water-soluble NNK permeated the membrane rapidly, while the lipophilic B[a]P did not appreciably diffuse through the tissue. Significantly different extents of reservoir formation were observed for the different carcinogens and in the presence of the different penetration-enhancer solvents. Alcohol (at 5% concentration) did not influence the permeation or reservoir formation of NNK. A mentholated donor solution (0.08%) both decreased the flux of NNK and significantly increased the tissue reservoir formation. The magnitude of the reservoir formed by B[a]P was relatively extensive (even though membrane permeation rates were negligible), being greatest in the presence of both ethanol and menthol. This suggests synergy between the two penetration-enhancer species acting on this carcinogen. Confocal microscopy studies confirmed that there was an appreciable intra-cellular, and specifically nuclear, association of the B[a]P species during the reservoir formation process. The aqueous solubility of the diffusing species and the presence of penetration enhancers appeared to be key factors in the absorption and cellular binding processes. The results presented support the hypothesis that the use of mentholated cigarettes, or the concomitant consumption of alcohol while smoking, may have marked effects on the fate of tobacco chemicals. This finding may help to explain elevated rates of esophageal squamous cell carcinoma in African Americans.  (+info)

(-)-Menthol inhibits DNA topoisomerases I, II alpha and beta and promotes NF-kappaB expression in human gastric cancer SNU-5 cells. (51/240)

It has been reported that (-)-Menthol can inhibit the growth of rat liver epithelial tumor cells and is a potent chemopreventive agent. The purpose of the present experiment was to examine and identify cellular processes leading to cell death which are affected by (-)-Menthol in human gastric SNU-5 cancer cells. Cell death (cytotoxicity) was examined and analyzed by trypan blue stain and flow cytometric methods. It was shown that (-)-Menthol inhibited the proliferation of the cells in a dose- and time-dependent manner, inhibited topoisomerase I, IIa and IIbeta, but promoted the levels of NF-kappaB gene expression based on the Western blot and polymerase chain reaction (PCR) and cDNA microarray methods. These data suggest that (-)-Menthol may induce cytotoxicity through inhibiting gene expression of topoisomerase I, IIalpha and IIbeta and promoting the gene expression of NF-kappaB in SNU-5 cells.  (+info)

Novel role of cold/menthol-sensitive transient receptor potential melastatine family member 8 (TRPM8) in the activation of store-operated channels in LNCaP human prostate cancer epithelial cells. (52/240)

Recent cloning of a cold/menthol-sensitive TRPM8 channel (transient receptor potential melastatine family member 8) from rodent sensory neurons has provided the molecular basis for the cold sensation. Surprisingly, the human orthologue of rodent TRPM8 also appears to be strongly expressed in the prostate and in the prostate cancer-derived epithelial cell line, LNCaP. In this study, we show that despite such expression, LNCaP cells respond to cold/menthol stimulus by membrane current (I(cold/menthol)) that shows inward rectification and high Ca(2+) selectivity, which are dramatically different properties from "classical" TRPM8-mediated I(cold/menthol). Yet, silencing of endogenous TRPM8 mRNA by either antisense or siRNA strategies suppresses both I(cold/menthol) and TRPM8 protein in LNCaP cells. We demonstrate that these puzzling results arise from TRPM8 localization not in the plasma, but in the endoplasmic reticulum (ER) membrane of LNCaP cells, where it supports cold/menthol/icilin-induced Ca(2+) release from the ER with concomitant activation of plasma membrane (PM) store-operated channels (SOC). In contrast, GFP-tagged TRPM8 heterologously expressed in HEK-293 cells target the PM. We also demonstrate that TRPM8 expression and the magnitude of SOC current associated with it are androgen-dependent. Our results suggest that the TRPM8 may be an important new ER Ca(2+) release channel, potentially involved in a number of Ca(2+)- and store-dependent processes in prostate cancer epithelial cells, including those that are important for prostate carcinogenesis, such as proliferation and apoptosis.  (+info)

Downregulation of transient receptor potential melastatin 8 by protein kinase C-mediated dephosphorylation. (53/240)

Transient receptor potential melastatin 8 (TRPM8) and transient receptor potential vanilloid 1 (TRPV1) are ion channels that detect cold and hot sensations, respectively. Their activation depolarizes the peripheral nerve terminals resulting in action potentials that propagate to brain via the spinal cord. These receptors also play a significant role in synaptic transmission between dorsal root ganglion (DRG) and dorsal horn (DH) neurons. Here, we show that TRPM8 is functionally downregulated by activation of protein kinase C (PKC) resulting in inhibition of membrane currents and increases in intracellular Ca2+ compared with upregulation of TRPV1 in cloned and native receptors. Bradykinin significantly downregulates TRPM8 via activation of PKC in DRG neurons. Activation of TRPM8 or TRPV1 at first sensory synapse between DRG and DH neurons leads to a robust increase in frequency of spontaneous/miniature EPSCs. PKC activation blunts TRPM8- and facilitates TRPV1-mediated synaptic transmission. Significantly, downregulation is attributable to PKC-mediated dephosphorylation of TRPM8 that could be reversed by phosphatase inhibitors. These findings suggest that inflammatory thermal hyperalgesia mediated by TRPV1 may be further aggravated by downregulation of TRPM8, because the latter could mediate the much needed cool/soothing sensation.  (+info)

Chemical and cold sensitivity of two distinct populations of TRPM8-expressing somatosensory neurons. (54/240)

The cold- and menthol-sensing TRPM8 receptor has been proposed to have both nonnociceptive and nociceptive functions. However, one puzzle is how this single type of receptor may be used by somatosensory neurons to code for two distinct sensory modalities. Using acutely dissociated rat dorsal root ganglion (DRG) neurons without culture, we show that TRPM8 receptors are expressed on two distinct classes of somatosensory neurons. One class is sensitive to menthol and features nonnociceptive neuron properties, including capsaicin-insensitive, ATP-insensitive, transient acid response, and expression of TTX-sensitive sodium channels only. This class is termed the menthol-sensitive/capsaicin-insensitive neuron class (MS/CIS). The other class is also sensitive to menthol but has characteristics of nociceptive neurons including capsaicin-sensitive, ATP-sensitive, prolonged acid response, and expression of both TTX-sensitive and TTX-resistant sodium channels. This class is termed the menthol-sensitive/capsaicin-sensitive neuron class (MS/CS). The presence of these two neuron classes in acutely dissociated DRG neurons support the idea that TRPM8 receptors can have both nonnociceptive and nociceptive functions. While both neuron classes respond to menthol and cold, the overall responses induced by menthol and cold are significantly larger in MS/CIS than in MS/CS neurons. Furthermore, low concentrations of menthol produce strong selection of the MS/CIS neuron population over the MS/CS neuron population. On the other hand, the population selection becomes weaker with higher concentrations of menthol. TRPM8 current density shows significant higher in MS/CIS neurons than in MS/CS neurons, suggesting different expression levels of TRPM8 receptors between the two neuron populations, and this difference may provide a mean of selective activation of MS/CIS neurons at low stimulation intensity.  (+info)

The role of Ca2+ in (-)-menthol-induced human promyelocytic leukemia HL-60 cell death. (55/240)

A human promyelocytic leukemia HL-60 cell line was selected to examine the effect of (-)-Menthol on cell death. Based on the results from morphological changes and the percentage of viable cells in HL-60 cells after treatment with various concentrations of (-)-Menthol, it was shown that (-)-Menthol induced cell death through necrosis, not apoptosis. No cell cycle arrest was found in HL-60 cells examined by flow cytometry analysis. Also, the DNA gel electrophoresis method showed that (-)-Menthol did not induce apoptosis in HL-60 cells. However, it was found that (-)-Menthol induced the production of Ca2+ in these examined cells, dose-dependently. When HL-60 cells were pretreated with the chelator (BAPTA) of Ca2+ for 3 hours before addition of (-)-Menthol to the culture, a decrease of Ca2+ production was observed. Under the same conditions, the percentage of viable HL-60 cells was increased. Apparently Ca2+ production is associated with the induction of (-)-Menthol-induced cell death.  (+info)

Metallophosphite-catalyzed asymmetric acylation of alpha,beta-unsaturated amides. (56/240)

The l-menthone-derived TADDOL phosphite 6b catalyzes highly enantioselective conjugate additions of acyl silanes to alpha,beta-unsaturated amides. p-Methoxybenzoyl cyclohexyldimethylsilane adds to a variety of N,N-dimethyl acrylamide derivatives in the presence of the lithium salt of 6b. In many instances the alpha-silyl-gamma-ketoamide product undergoes facile enantioenrichment (to 97-99% ee) upon recrystallization. Desilylation with HF.pyr affords the formal Stetter addition products. Baeyer-Villiger oxidation of the desilylated gamma-ketoamides affords useful ester products. An X-ray diffraction study of 6b reveals that the isopropyl group of the menthone ketal influences the position of the syn-pseudoaxial phenyl group in the TADDOL structure. Through a crossover experiment, the silicon migration step in the reaction mechanism is shown to be strictly intramolecular.  (+info)