Determination of Menthol in Plasma and Urine by Gas Chromatography/Mass Spectrometry (GC/MS).

Menthol, a monoterpene, is a principal component of peppermint oil and is used extensively in consumer products as a flavoring aid. It is also commonly used medicinally as a topical skin coolant; to treat inflammation of the mucous membranes, digestive problems, and irritable bowel syndrome (IBS); and in preventing spasms during endoscopy and for its spasmolytic effect on the smooth muscle of the gastrointestinal tract. Menthol has a half life of 3-6 h and is rapidly metabolized to menthol glucuronide which is detectable in urine and serum following menthol use. We describe a method for the determination of total menthol in human plasma and urine using liquid/liquid extraction, gas chromatography/mass spectrometry (GC/MS) in selected ion monitoring mode and menthol-d4 as the internal standard. Controls are prepared with menthol glucuronide and all samples undergo enzymatic hydrolysis for the quantification of total menthol. The method has a linear range of 5-1000 ng/mL, and coefficient of variation <10%.

The inhibition of bone resorption in rats treated with (-)-menthol is due to its metabolites.

(-)-Menthol, a monoterpene from Mentha species (Lamiaceae), has been shown to inhibit bone resorption in vivo by an unknown mechanism. In the present study, plasma and urine profiling in rats determined by GC/MS demonstrate that (-)-menthol is extensively metabolized, mainly by hydroxylation and carboxylation, and excreted in the urine, in part as glucuronides. In plasma, very low concentrations of (-)-menthol metabolites were detected after a single dose of (-)-menthol, whereas after repeated treatment, several times higher concentrations and long residence times were measured. In contrast, the elimination of unchanged (-)-menthol was increased by repeated treatment. (-)-Menthol, at concentrations found in plasma, did not inhibit bone resorption in cultured mouse calvaria (skull). However, the neutral metabolites of (-)-menthol, extracted from urine of rats fed with (-)-menthol, inhibited bone resorption in vitro, the concentrations being at plasma level or higher. These results suggest that not (-)-menthol itself, but one or several of its neutral metabolites inhibit the bone resorbing cells in vivo.

Simple measurement of gluconeogenesis by direct 2H NMR analysis of menthol glucuronide enrichment from 2H2O.

The contribution of gluconeogenesis to fasting glucose production was determined by a simple measurement of urinary menthol glucuronide (MG) 2H enrichment from 2H2O. Following ingestion of 2H2O (0.5% body water) during an overnight fast and a pharmacological dose (400 mg) of a commercial peppermint oil preparation the next morning, 364 micromol MG was quantitatively recovered from a 2-h urine collection by ether extraction and a 125 micromol portion was directly analyzed by 2H NMR. The glucuronide 2H-signals were fully resolved and their relative intensities matched those of the monoacetone glucose derivative. The pharmacokinetics and yields of urinary MG after ingestion of 400 mg peppermint oil as either gelatin or enteric-coated capsules 1 h before breakfast were quantified in five healthy subjects. Gelatin capsules yielded 197 +/- 81 micromol of MG from the initial 2-h urine collection while enteric-coated capsules gave 238 +/- 84 micromol MG from the 2- to 4-h urine collection.

Disposition kinetics and effects of menthol.

BACKGROUND: Menthol is widely used in a variety of commercial products and foods, but its clinical pharmacology is not well studied. To determine the disposition kinetics and to examine subjective and cardiovascular effects of menthol, we conducted a crossover placebo-controlled study that compared pure menthol versus placebo, along with an uncontrolled exposure to menthol in food or beverage. A novel assay for the measurement of menthol in biological fluids was also developed. METHODS: Twelve subjects were studied; each received a 100 mg l-menthol capsule, a placebo capsule, and 10 mg menthol in mint candy or mint tea on three different occasions. Plasma and urine levels of menthol and conjugated menthol (glucuronide), cardiovascular measurements, and subjective effects were measured at frequent intervals. RESULTS: Menthol was rapidly metabolized, and only menthol glucuronide could be measured in plasma or urine. The plasma half-life of menthol glucuronide averaged 56.2 minutes (95% confidence interval [CI], 51.0 to 61.5) and 42.6 minutes (95% CI, 32.5 to 52.7) in menthol capsule and mint candy/mint tea conditions, respectively (P < .05). The plasma area under the plasma concentration-time curve ratios for menthol capsule to mint candy/mint tea treatment averaged 9.2 (95% CI, 8.2 to 10.1). Urinary recovery of menthol as the glucuronide averaged 45.6 and 56.6% for menthol capsule and mint candy/tea, respectively (difference not significant). After menthol capsule dosing, the decrease in heart rate was less than the decrease after placebo administration (P < .05). Menthol reduced subjective vigor value at 30 minutes. CONCLUSIONS: We conclude that pure menthol and menthol in food or beverages have a similar systemic bioavailability and that menthol has a small cardioaccelerating effect.

Hepatoprotective effect of C-phycocyanin: protection for carbon tetrachloride and R-(+)-pulegone-mediated hepatotoxicty in rats.

Effect of C-phycocyanin (from Spirulina platensis) pretreatment on carbontetrachloride and R-(+)-pulegone-induced hepatotoxicity in rats was studied. Intraperitoneal (i.p.) administration (200 mg/kg) of a single dose of phycocyanin to rats, one or three hours prior to R-(+)-pulegone (250 mg/kg) or carbontetrachloride (0.6 ml/kg) challenge, significantly reduced the hepatotoxicity caused by these chemicals. For instance, serum glutamate pyruvate transaminase (SGPT) activity was almost equal to control values. The losses of microsomal cytochrome P450, glucose-6-phosphatase and aminopyrine-N-demethylase were significantly reduced, suggesting that phycocyanin provides protection to liver enzymes. It was noticed that the level of menthofuran, the proximate toxin of R-(+)-pulegone was nearly 70% more in the urine samples collected from rats treated with R-(+)-pulegone alone than rats treated with the combination of phycocyanin and R-(+)-pulegone. The possible mechanism involved in the hepatoprotection is discussed.