Biotransformation of [3 H]serotonin by cultured hamster skin to 3 H-metabolites corresponding to N-acetylserotonin (NAS), melatonin, and 5-methoxytryptamine (5-MT) was demonstrated. This process was time-dependent, with the highest production of radioactive NAS and melatonin metabolites after 3 and 5 h of incubation followed by a decrease in the rate of metabolite release into the media. Conversely, the formation of radioactive metabolite corresponding to 5-MT increased gradually during skin culture, reaching the highest level after 24 h of incubation. The production of 3 H-metabolites, corresponding to NAS, melatonin, and 5-MT, was stimulated by forskolin with a maximum effect of forskolin at 10 M concentration. The gas chromatographic/mass spectroscopy analysis of the fraction eluting at the retention time of NAS standard material showed that it contained NAS, further confirming production and release of NAS into the media by hamster skin. Therefore, we conclude that mammalian skin can acetylate serotonin to NAS and postulate that the NAS is further metabolized by the skin to form melatonin which is subsequently transformed to 5-MT.Melatonin serves as the main signal molecule which links the photoperiod to metabolic, endocrine, and immunological changes and which is mainly synthesized in the pineal gland, retina, brain, and Harderian gland (1). Depending of the site of production and target organ it can act as a hormone, neurotransmitter, cytokine, and biological modifier (2).Melatonin is a product of a two-step conversion of serotonin, which involves the acetylation of serotonin (3) and subsequent methylation by hydroxyindole-O-methyltransferase (4). The majority of melatonin released into the bloodstream is metabolized in the liver and kidneys (5, 6), mainly by 6-hydroxylation and conjugation to glucuronate or sulfate (5, 6), and to a minor degree by deacetylation to 5-methoxytryptamine (5-MT), 1 which is further deaminated (5-7). In contrast, melatonin bioconversion at the organ site of synthesis appears to be different from the metabolism of circulating melatonin (8 -10). For example, in the retina melatonin is first deacetylated to 5-MT, which can then be deaminated, producing 5-methoxyindoleacetic acid and 5-methoxytryptophol (8, 9). Melatonin deacetylation to 5-MT was also detected in retinal pigment epithelium and non-mammalian skin that are target sites for melatonin bioregulation (8 -10). Extracranial sites of both synthesis and metabolism of melatonin have also been demonstrated in the peripheral blood mononuclear leukocytes (11), and according to some authors in the gastrointestinal tract (12).Melatonin production has not previously been demonstrated in skin, which is the largest body organ that can react to external and internal stimuli via the skin immune system (13), the pigmentary system (14), and the skin endocrine system (15, 16). In lower verterbrates skin is a recognized target for melatonin action, e.g. melatonin has lightening activity on the skin (17). In mammals, it has been reported th...

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. Validation of our model was performed in 13 patients, and the predictive performance was highly favorable (R 2 was 0.9, and bias and precision were 0.18 and 0.18, respectively). Prediction models such as ours can be utilized in future pharmacokinetics and pharmacodynamics studies evaluating the exposure-response profile and to determine the pharmacodynamic target of interest as it relates to the free concentration.Antimicrobial pharmacodynamics describes the relationship between drug exposure and antimicrobial activity. The past 25 years have witnessed tremendous advances in understanding the relationship between antimicrobial pharmacodynamics and microbiological response, and the pharmacodynamic targets associated with maximal effect have been identified for many antimicrobials (8,9,14,16). For vancomycin, the ratio of the area under the serum drug concentration-versus-time curve (AUC) and the MIC, or the AUC/MIC ratio, appears to be the best predictor of response based in part on data from animal models, in vitro studies, and limited human studies (22,27). Collectively, these data suggest that microbiological success is optimized when the vancomycin total drug AUC/MIC ratio exceeds 400 (22,26). In clinical practice, since it is not practical to obtain serial vancomycin concentrations within a dosing interval to estimate the AUC, many clinicians use vancomycin trough concentrations as a surrogate for the AUC when optimizing the vancomycin dosing regimen.One commonality of these vancomycin pharmacodynamic studies is that they examined total vancomycin concentrations (total [vanco]) rather than free or unbound drug (22,27). While these studies demonstrated a positive correlation between the total vancomycin AUC/MIC ratio and response, there are data that indicate only free drug or unbound drug is pharmacologically active and is most predictive of the response (3,5,10,11,15,19,21,24,33). We are not aware of any studies that have assessed whether free vancomycin concentrations (f[vanco]) are predictive of outcomes.In the absence of pharmacodynamic studies that delineate the relationship between drug exposure and response, it is common practice to multiply the total drug exposure by the extent of protein binding to determine the amount of free drug necessary for response. In order to do this, it is critical to have a reasonable point estimate of the extent of protein binding. While it is assumed that vancomycin is approximately 50% bound (25), protein binding for the agent has not been well characterized in the literature, and estimates have varied considerably (1,2,12,18,23,31,35). In particular, a recent analysis reported a range of percent protein binding to be 12% to 100% in 15 hospitalized adults (4).Given the variability surrounding the extent of vancomycin protein binding, the purpose of this study was 2-fold: (i) to determine the extent to which vancomycin is protein bound in the blood and (ii) to identify factors that modulate vancomycin protein binding to create and validate a prediction tool for estimat...

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Ethyl glucuronide (EtG) is a direct ethanol biomarker and U.S. Department of Health and Human Services has advised that specificity studies at low EtG levels are needed for distinction of ethanol consumption and incidental exposure. The authors report urinary EtG excretion with ethanol abstinence, dermal exposure and oral consumption. EtG concentration by sensitive liquid chromatography-tandem mass spectrometry measurement in 39 urine specimens from adult alcohol abstainers (< 10-62 microg/L) and in urine from 13 children (< 10-80 microg/L) indicates either unrecognized ethanol exposure or endogenous ethanol metabolism. With repetitive daily dermal exposure to hand sanitizer (60% ethanol) by 9 adults, EtG concentration ranged from < 10 to 114 microg/L in 88 first-morning void specimens. EtG excretion following a 24 g ethanol drink by 4 adults revealed maximum urine EtG concentration (12,200-83,200 microg/L) at 3 to 8 h postdose and an EtG detection window up to 25-39 h, compared to an ethanol window of only 2 to 4 h. Oral ethanol use also showed an increase in the percent (molar equivalent) ethanol excreted as EtG with increasing oral ethanol doses. Human excretion studies show 1. EtG detectable at low concentration (< 100 microg/L) when ethanol use or exposures is not evident, 2. EtG concentration less than 120 microg/L in first morning specimens from adults with repeated dermal exposure to ethanol, 3. EtG levels maximally elevated within 3-8 h and above baseline for up to 39 h after a 24 g ethanol drink, and 4. a dose-dependent increase in the percentage of ethanol excreted as EtG with increasing oral ethanol use.

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Assessment of catecholamine production and excretion is important in the laboratory detection of pheochromocytoma, a rare but curable cause of hypertension. Advances in catecholamine and metabolite methodologies have enhanced the diagnostic acumen by increasing analytical sensitivity and eliminating many of the interferences observed with earlier methods. Estimation of urinary catecholamines metanephrine and vanillylmandelic acid is routinely used in the biochemical detection of pheochromocytoma and in monitoring the completeness of tumor excision as well as the possibility of recurrence. Traditional spectrophotometric and fluorometric methods for urinary catecholamines and their metabolites are being replaced by highly sensitive and selective chromatographic methods. The ability to quantify individual catecholamines and metanephrines by high-performance liquid chromatography is of particular value for detecting familial forms of the tumor that may secrete epinephrine. Plasma norepinephrine and epinephrine measurements are of additional diagnostic value in determining recent catecholamine release and response to clonidine suppression. For either urine or plasma measurements, appropriate patient preparation, sample collection, and method validation along with an understanding of the variable pattern of catecholamine secretion and metabolism in pheochromocytoma are essential. Advances in laboratory methodology and reference intervals for catecholamines for clinical interpretation are reviewed.

The lysosomal acidic protease cathepsin D, a recognized independent predictor of prognosis in human breast cancer, has not been studied widely in patients with endometrial adenocarcinoma. Cathepsin D levels (52-kD precursor plus 48-kD intermediate and 34/14-kD mature form) were measured in tumor cytosols from 26 hysterectomy specimens by immunoradiometric assay. Significant correlation between cathepsin D levels and tumor differentiation was noted with linear increase in cathepsin D from 8 pmol/mg (standard error of the mean [SEM], 1.73 pmol/mg) for Grade I tumors to 28 pmol/mg (SEM, 3.91 pmol/mg) for Grade III tumors. A group of four papillary serous carcinomas showed relatively high cathepsin D levels reaching 39 pmol/mg. A significant stepwise increase in cathepsin D levels was associated with increased depth of myometrial invasion. Noninvasive tumors averaged 7 pmol/mg (SEM, 4.0 pmol/mg); intramural tumors averaged 15 pmol/mg (SEM, 2.45 pmol/mg); and transmural invasive tumors averaged 30 pmol/mg (SEM, 3.72 pmol/mg). There was no significant correlation of cathepsin D levels with age, estrogen/progesterone receptor hormone status, clinical stage, and lymph node metastasis. Cathepsin D levels correlate significantly with tumor differentiation and myometrial invasiveness and may show promise as a clinically useful adjunct to prognosis assessment and the planning of therapy for patients with endometrial adenocarcinoma.