5-Aminosalicylic Acid Azo-Coupled with a GPR109A Agonist Is a Colon-Targeted Anticolitic Codrug with a Reduced Risk of Skin Toxicity.

To develop a 5-aminosalicylic acid (5-ASA)-based anticolitic drug with enhanced therapeutic activity, a colon-targeted codrug constituting 5-ASA and a GPR109A agonist was designed. 5-ASA azo-coupled with nicotinic acid (ASA-azo-NA) was synthesized, and the colon specificity and anticolitic effects were evaluated. Approximately 89% of ASA-azo-NA was converted to 5-aminonicotinic acid (5-ANA) and 5-ASA after 24 h of incubation in the cecal contents. 5-ANA was identified as a GPR109A agonist (concentration that gives half-maximal response (EC50): 18 µM) in a cell-based assay. Upon oral gavage of ASA-azo-NA (oral ASA-azo-NA) and sulfasalazine (oral SSZ), a colon-targeted 5-ASA prodrug, cecal accumulation of 5-ASA was comparable, and 5-ANA was barely detectable in the blood, while it was detected up to 62.7 µM with oral 5-ANA. In parallel, oral ASA-azo-NA did not elicit an adverse skin response. In murine macrophage and human colon carcinoma cells, activation of GPR109A by 5-ANA elevated the level of the anti-inflammatory cytokine IL-10, suppressed NF-κB activation, and potentiated the inhibitory activity of 5-ASA on NF-κB. Oral ASA-azo-NA ameliorated rat colitis and was more effective than oral SSZ, which were substantially blunted following cotreatment with the GPR109A antagonist, mepenzolate. In conclusion, ASA-azo-NA is a colon-targeted anticolitic codrug with a reduced risk of skin toxicity induced by the GPR109A agonist, therapeutically surpassing a current 5-ASA-based anti-inflammatory bowel disease drug in a rat colitis model.

Peroxisome Proliferator-Activated Receptor Activation is Associated with Altered Plasma One-Carbon Metabolites and B-Vitamin Status in Rats.

Plasma concentrations of metabolites along the choline oxidation pathway have been linked to increased risk of major lifestyle diseases, and peroxisome proliferator-activated receptors (PPARs) have been suggested to be involved in the regulation of key enzymes along this pathway. In this study, we investigated the effect of PPAR activation on circulating and urinary one-carbon metabolites as well as markers of B-vitamin status. Male Wistar rats (n = 20) received for 50 weeks either a high-fat control diet or a high-fat diet with tetradecylthioacetic acid (TTA), a modified fatty acid and pan-PPAR agonist with high affinity towards PPARα. Hepatic gene expression of PPARα, PPARß/δ and the enzymes involved in the choline oxidation pathway were analyzed and concentrations of metabolites were analyzed in plasma and urine. TTA treatment altered most biomarkers, and the largest effect sizes were observed for plasma concentrations of dimethylglycine, nicotinamide, methylnicotinamide, methylmalonic acid and pyridoxal, which were all higher in the TTA group (all p < 0.01). Hepatic Pparα mRNA was increased after TTA treatment, but genes of the choline oxidation pathway were not affected. Long-term TTA treatment was associated with pronounced alterations on the plasma and urinary concentrations of metabolites related to one-carbon metabolism and B-vitamin status in rats.

Simultaneous determination of tazarotene and its active metabolite tazarotenic acid in minipig plasma by LC-MS/MS and its application in pharmacokinetic study after topical administration of tazarotene gel.

To study the systemic exposure of tazarotene formulation after topical administration, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the simultaneous determination of tazarotene and tazarotenic acid in minipig plasma. Similar extraction recoveries for both analytes were obtained after the plasma samples were acidified by glacial acetic acid (5%) and extracted by ethyl ether-cyclohexane (4:1, v/v). Separation of the analytes was achieved within a short time by the addition of 0.1% formic acid to the mobile phase. Gradient elution was used to avoid the matrix effect. The method was linear over the concentration range of 10-600 pg/mL for both analytes. The data of intra- and inter-run precision and accuracy were lower than 5.2%, 7.3% and 7.3% for both analytes. The developed method can be applied to investigate the transdermal pharmacokinetics and the systemic exposure of tazarotene formulation after topical administration.

Comparative pharmacokinetics of norfloxacin nicotinate in common carp (Cyprinus carpio) and crucian carp (Carassius auratus) after oral administration.

Comparative pharmacokinetics of norfloxacin nicotinate (NFXNT) was investigated in common carp (Cyprinus carpio) and crucian carp (Carassius auratus) after a single oral dose of 10 mg/kg body weight (b.w.). Analyses of plasma samples were performed using ultra-performance liquid chromatography (UPLC) with fluorescence detection. After oral dose, plasma concentration-time curves of common carp and crucian carp were best described by a two-compartment open model with first-order absorption. The pharmacokinetic parameters of common carp were similar to those of crucian carp. The distribution half-life (t1/2α ), elimination half-life (t1/2ß ), peak concentration (Cmax ), time-to-peak concentration (Tmax ), and area under the concentration-time curve (AUC) of common carp were 1.58 h, 26.33 h, 6069.79 µg/L, 1.08 h, and 103072.36 h·µg/L, respectively, and those corresponding to crucian carp were 1.36 h, 26.55 h, 9586.06 µg/L, 0.84 h, and 126604.4 h·µg/L, respectively. These studies demonstrated that 10 mg NFXNT/kg body weight in common carp and crucian carp following oral dose presented good pharmacokinetic characteristics.

Comparison of the circulating metabolite profile of PF-04991532, a hepatoselective glucokinase activator, across preclinical species and humans: potential implications in metabolites in safety testing assessment.

A previous report from our laboratory disclosed the identification of PF-04991532 [(S)-6-(3-cyclopentyl-2-(4-trifluoromethyl)-1H-imidazol-1-yl)propanamido)nicotinic acid] as a hepatoselective glucokinase activator for the treatment of type 2 diabetes mellitus. Lack of in vitro metabolic turnover in microsomes and hepatocytes from preclinical species and humans suggested that metabolism would be inconsequential as a clearance mechanism of PF-04991532 in vivo. Qualitative examination of human circulating metabolites using plasma samples from a 14-day multiple ascending dose clinical study, however, revealed a glucuronide (M1) and monohydroxylation products (M2a and M2b/M2c) whose abundances (based on UV integration) were greater than 10% of the total drug-related material. Based on this preliminary observation, mass balance/excretion studies were triggered in animals, which revealed that the majority of circulating radioactivity following the oral administration of [¹4C]PF-04991532 was attributed to an unchanged parent (>70% in rats and dogs). In contrast with the human circulatory metabolite profile, the monohydroxylated metabolites were not detected in circulation in either rats or dogs. Available mass spectral evidence suggested that M2a and M2b/M2c were diastereomers derived from cyclopentyl ring oxidation in PF-04991532. Because cyclopentyl ring hydroxylation on the C-2 and C-3 positions can generate eight possible diastereomers, it was possible that additional diastereomers may have also formed and would need to be resolved from the M2a and M2b/M2c peaks observed in the current chromatography conditions. In conclusion, the human metabolite scouting study in tandem with the animal mass balance study allowed early identification of PF-04991532 oxidative metabolites, which were not predicted by in vitro methods and may require additional scrutiny in the development phase of PF-04991532.

Niacin in pharmacological doses alters microRNA expression in skeletal muscle of obese Zucker rats.

Administration of pharmacological niacin doses was recently reported to have pronounced effects on skeletal muscle gene expression and phenotype in obese Zucker rats, with the molecular mechanisms underlying the alteration of gene expression being completely unknown. Since miRNAs have been shown to play a critical role for gene expression through inducing miRNA-mRNA interactions which results in the degradation of specific mRNAs or the repression of protein translation, we herein aimed to investigate the influence of niacin at pharmacological doses on the miRNA expression profile in skeletal muscle of obese Zucker rats fed either a control diet with 30 mg supplemented niacin/kg diet or a high-niacin diet with 780 mg supplemented niacin/kg diet for 4 wk. miRNA microarray analysis revealed that 42 out of a total of 259 miRNAs were differentially expressed (adjusted P-value <0.05), 20 being down-regulated and 22 being up-regulated, between the niacin group and the control group. Using a biostatistics approach, we could demonstrate that the most strongly up-regulated (log2 ratio ≥0.5) and down-regulated (log2 ratio ≤-0.5) miRNAs target approximately 1,800 mRNAs. Gene-term enrichment analysis showed that many of the predicted target mRNAs from the most strongly regulated miRNAs were involved in molecular processes dealing with gene transcription such as DNA binding, transcription regulator activity, transcription factor binding and in important regulatory pathways such as Wnt signaling and MAPK signaling. In conclusion, the present study shows for the first time that pharmacological niacin doses alter the expression of miRNAs in skeletal muscle of obese Zucker rats and that the niacin-regulated miRNAs target a large set of genes and pathways which are involved in gene regulatory activity indicating that at least some of the recently reported effects of niacin on skeletal muscle gene expression and phenotype in obese Zucker rats are mediated through miRNA-mRNA interactions.

Tazarotene foam versus tazarotene gel: a randomized relative bioavailability study in acne vulgaris.

BACKGROUND AND OBJECTIVE: Tazarotene, a retinoid pro-drug, is available in gel, cream and foam for the topical treatment of acne vulgaris. This single-centre, randomized, open-label study assessed relative bioavailability of its active metabolite tazarotenic acid after dosing of tazarotene foam or gel. STUDY DESIGN AND METHODS: Subjects with moderate-to-severe acne received a mean, once-daily dose of 3.7 g tazarotene foam or gel applied to face, chest, upper back and shoulders. Blood samples were collected pre-dose on multiple days and multiple time points over a 72-h period to measure plasma tazarotenic acid and tazarotene. RESULTS: Mean tazarotenic acid area under the plasma concentration-time curve (AUC) and maximum measured plasma concentration (Cmax) values were significantly higher for gel versus foam. Cmax occurred within 5-6 h after dosing, with an apparent terminal elimination half-life (t½) of 18-22 h. Accumulation was observed upon repeated dosing with steady-state conditions achieved at day 20. Mean tazarotene concentrations were also higher following gel application versus foam. Both foam and gel demonstrated an acceptable safety profile. CONCLUSION: Tazarotene foam, 0.1 % is an alternative to gel with less systemic exposure.

Biotransformation and pharmacokinetics of inositol hexanicotinate in rats.

Inositol hexanicotinate (IHN) is an ester of the anti-hyperlipidemic drug nicotinic acid (NA). This study assessed the hydrolysis rate of IHN in human and rat plasma, and pharmacokinetics of the drug using a rat animal model. IHN (10 or 50 µg/mL) was incubated in plasma at 37 °C for 72 h. Kinetic parameters were determined based on the disappearance of IHN and the appearance of NA. The mean IHN disappearance and NA appearance half-lives were 1.07 and 3.93 h in human plasma, and 0.152 and 2.68 h in rat plasma. Increasing the initial plasma concentration to 50 µg/mL increased the NA appearance half-life in human and rat plasma to 4.66 and 6.47 h, respectively. After single 50 or 100 mg/kg intravenous dose of IHN to Sprague-Dawley rats, the drug showed statistically significant dose-dependent alterations in systemic clearance, suggesting a non-linear saturable elimination of IHN. Dose-normalized mean plasma levels of NA increased by 30% with increasing IHN dose (p < 0.02). The mean metabolic ratio (i.e. NA/IHN AUC ratio) significantly increased with increasing IHN dose (p < 0.05). The results provide first indication of saturable elimination and rapid disappearance of IHN, while niacin was slowly formed.

Simultaneous quantification of niacin and its three main metabolites in human plasma by LC-MS/MS.

A sensitive and specific LC-MS/MS method for the simultaneous quantification of niacin (NA) and its three main metabolites nicotinamide (NAM), nicotinuric acid (NUA) and N-methyl-2-pyridone-5-carboxamide (2-Pyr) in human plasma has been developed and validated. Plasma samples (200 µL) were prepared by deproteinization with acetonitrile (500 µL), then the supernatant after centrifugation was evaporated and reconstituted. Chromatography was performed on a phenomenex synergi hydro-RP column with an isocratic elution of methanol-0.1% formic acid (5:95, v/v). The full separation of all analytes was achieved within 9 min. Multiple-reaction monitoring (MRM) using the fragmentation transitions of m/z 124.1 → 80.1, 123.1 → 80.0, 181.0 → 79.0 and 153.1 → 110.2 in positive electrospray ionization (ESI) mode was performed to quantify NA, NAM, NUA and 2-Pyr, respectively. The calibration curves were linear over the concentration range of 2.0-3000 ng/mL for NA and NUA, 10.0-1600 ng/mL for NAM and 50.0-5000 ng/mL for 2-Pyr. This method has been validated in accordance with the US FDA guidelines for bioanalytical method development and applied to the determination of NA and its three main metabolites in Chinese subjects following a single oral dose of niacin extended-release and simvastatin 1000 mg/20mg. In particular, because of the endogenous NAM and 2-Pyr in human plasma, the concentrations of NAM and 2-Pyr in human plasma after dosing were determined by subtracting blank values of them.

Effects of encapsulated niacin on metabolism and production of periparturient dairy cows.

Nicotinic acid (niacin) can suppress lipolysis, but responses to dietary niacin have been inconsistent in cattle. Our aim was to determine if 24 g/d of encapsulated niacin (EN; providing 9.6g/d of bioavailable nicotinic acid) alters lipid metabolism and productivity of transition cows. Beginning 21 d before expected calving, primiparous (n = 9) and multiparous (n = 13) cows (body condition score of 3.63 ± 0.08) were sequentially assigned within parity to EN (12 g provided with ration twice daily) or control through 21 d postpartum. Liver biopsies were collected on d -21, -4, 1, 7, and 21 relative to parturition. Blood samples were collected on d -21, -14, -7, -4, 1, 4, 7, 14, and 21 relative to parturition. On d 7 postpartum, a caffeine clearance test was performed to assess liver function, and on d 21 to 23 postpartum, blood samples were collected every 8h to monitor posttreatment nonesterified fatty acid (NEFA) responses. Data were analyzed using mixed models with repeated measures over time. A treatment × time × parity effect was observed on prepartum dry matter intake (DMI), which was caused by a 4 kg/d decrease in DMI of EN-treated multiparous cows compared with control multiparous cows during the final 4 d prepartum. A significant increase in plasma nicotinamide concentration occurred in EN-treated cows on d -7 and 21 relative to parturition. Prepartum glucose concentration decreased in treated animals, with no difference in plasma insulin concentration. Treatment × time × parity effects were detected for NEFA and ß-hydroxybutyrate concentrations during the postpartum period. Plasma NEFA peaked at 1,467 ± 160 µM for control animals compared with 835 ± 154 µM for EN-treated animals. After treatments ended on d 21, no evidence was found for a plasma NEFA rebound in either parity group. A treatment × parity × time interaction was detected for liver triglyceride content, indicating a tendency for less liver triglyceride in EN-treated primiparous cows, but caffeine clearance rates were not affected by treatment. No treatment effects were observed for body condition score, body weight, energy balance, or milk or milk component production. A high dose of EN can decrease postpartum plasma NEFA concentration, but may also decrease prepartum DMI.

Simultaneous determination of niacin and its metabolites--nicotinamide, nicotinuric acid and N-methyl-2-pyridone-5-carboxamide--in human plasma by LC-MS/MS and its application to a human pharmacokinetic study.

An LC-MS/MS method for the simultaneous quantitation of niacin (NA) and its metabolites, i.e. nicotinamide (NAM), nicotinuric acid (NUA) and N-methyl-2-pyridone-5-carboxamide (2-Pyr), in human plasma (1 mL) was developed and validated using nevirapine as an internal standard (IS). Extraction of the NA and its metabolites along with the IS from human plasma was accomplished using a simple liquid-liquid extraction. The chromatographic separation of NA, NAM, NUA, 2-Pyr and IS was achieved on a Hypersil-BDS column (150 x 4.6 mm, 5 microm) column using a mobile phase consisting of 0.1% formic acid : acetonitrile (20:80 v/v) at a flow rate of 1 mL/min. The total run time of analysis was 2 min and elution of NA, NAM, NUA, 2-Pyr and IS occurred at 1.37, 1.46, 1.40, 1.06 and 1.27 min, respectively. A detailed validation of the method was performed as per the FDA guidelines and the standard curves were found to be linear in the range of 100-20000 ng/mL for NA; 10-1600 ng/mL for NUA and NAM and 50-5000 ng/mL for 2-Pyr with mean correlation coefficient of ≥ 0.99 for each analyte. The method was sensitive, specific, precise, accurate and suitable for bioequivalence and pharmacokinetic studies. The developed assay method was successfully applied to a pharmacokinetic study in humans.

[Determination of nicacid and its metabolites in human plasma by HPLC-MS/MS].

OBJECTIVE: To develop a sensitive HPLC-MS/MS method for the determination of nicacid and its metabolites in human plasma. METHODS: The assay was conducted with an API 3000 LC-MS/MS system comprising of a Genimi C18 column (50 x 3.00 mm, 3 microm), and an eluate of 0.1% acetic acid-methanol-isopropyl alcohol (98: 1:1), and flow rate was 0.2 mL/min. Acetonitrile was used to precipitate protein from the plasma samples. The loading samples contained the residue from the supernatant that were dissolved in the eluate solution and rinsed by dichloromethane was used as the loading samples. The ion pairs of m/z 124.1-->80.0, m/z 123.1-->80.0, m/z 181.1-->135.0 and m/z 138.1-->92.0 were used to quantify nicacid, niacinamide, nicotinuric acid and 6-methyl nicotinic acid (IS), respectively. RESULTS: The standard curves of nicacid, niacinamide and nicotinuric were linear in the range of 1.25-320 microg/L, 1.25-1280 microg/L and 1.25-1280 microg/L, respectivly. All with a low determination limits of 1.25 microg/L and a less than 9% within-day and inter-day RSD. The recovery rates reached 89% to 105%. CONCLUSION: The method is simple, rapid, sensitive, and suitable for the determination of nicacid and its metabolites in human plasma.

Quantitative investigation of trigonelline, nicotinic acid, and nicotinamide in foods, urine, and plasma by means of LC-MS/MS and stable isotope dilution analysis.

A straightforward stable isotope dilution analysis (SIDA) for the quantitative determination of trigonelline, nicotinic acid, and nicotinamide in foods such as coffee, as well as in biological samples by means of LC-MS/MS (MRM) has been developed. The coefficients of variation for their quantitative analysis in a coffee sample were 2.1% for trigonelline, 1.1% for nicotinic acid, and 3.1% for nicotinamide, and recovery experiments showed good results between 98.5 and 104.5%. Application of this SIDA for the quantification of trigonelline, nicotinic acid, and nicotinamide in coffee samples of different roasting degrees revealed a drastic degradation of trigonelline as well as the generation of nicotinic acid accounting for 4-6% of the initial trigonelline content, whereas nicotinamide remained rather constant at a low level. Besides the analysis of coffee samples, the feasibility of the developed SIDA was verified by analysis of other foods including breakfast cereals, rice, liver, and herring, as well as human urine and plasma samples.

Estimation of serum protein binding of compounds metabolized in serum using matrix inhibition.

It is difficult to evaluate the serum protein binding of compounds that are metabolized in rat serum, even when using ultrafiltration. Protein binding was estimated using matrix inhibition, a method that uses the change in metabolic velocity achieved by changing the free fraction of a compound in the incubation mixture by diluting the serum with phosphate buffered saline. The T(1/2) of phenyl nicotinate, benzyl nicotinate, octyl nicotinate, hexyl nicotinate, butyl nicotinate and [(3)H] compound A were 0.165, 0.780, 2.62, 3.94, 5.22 and 135 min, respectively, with protein binding values of 82.1%, 91.6%, 98.8%, 98.5%, 85.5% and 96.9%. The protein binding value of compound A estimated by ultrafiltration was 93.4%, indicating that the two methods give similar values. The matrix inhibition method is thus applicable for the evaluation of compounds metabolized in serum, and provides a simple, useful method to determine protein binding.

Determination of inositol hexanicotinate in rat plasma by high performance liquid chromatography with UV detection.

A HPLC method with UV detection at 262nm was developed to analyze inositol hexanicotinate in rat plasma. Plasma samples were extracted with an equal volume of acetonitrile, followed by dilution with mobile phase buffer (5mM phosphate buffer, pH 6.0) to eliminate any solvent effects. Inositol hexanicotinate and the internal standard (mebendazole) were separated isocratically using a mobile phase of acetonitrile/phosphate buffer (35:65, v/v, pH 6.0) at a flow rate of 1.0mL/min and a reverse-phase XTerra MS C(18) column (4.6mmx150mm, 3.5microm). The standard curve was linear over a concentration range of 1.5-100.0microg/mL of inositol hexanicotinate in rat plasma. The HPLC method was validated with intra- and inter-day precisions of 1.55-4.30% and 2.69-21.5%, respectively. The intra- and inter-day biases were -0.75 to 19.8% and 2.58-22.0%, respectively. At plasma concentrations of 1.5-100microg/mL, the mean recovery of inositol hexanicotinate was 99.6%. The results of a stability study indicated that inositol hexanicotinate was unstable in rat plasma samples, but was stable in acetonitrile extracts of rat plasma for up to 24h at 4 degrees C. The assay is simple, rapid, specific, sensitive, and reproducible and has been used successfully to analyze inositol hexanicotinate plasma concentrations in a pharmacokinetic study using the rat as an animal model.

Plasma and urine pharmacokinetics of niacin and its metabolites from an extended-release niacin formulation.

OBJECTIVE: To characterize plasma and urine pharmacokinetics of niacin and its metabolites after oral administration of 2,000 mg of extended-release (ER) niacin in healthy male volunteers. METHODS: Niacin ER was administered to 12 healthy male subjects following a low-fat snack. Plasma was collected for 12 h post dose and was analyzed for niacin, nicotinuric acid (NUA), nicotinamide (NAM) and nicotinamide-N-oxide (NNO). Urine was collected for 96 h post dose and analyzed for niacin and its metabolites, NUA, NAM, NNO, N-methylnicotinamide (MNA) and N-methyl-2-pyridone-5-carboxamide (2PY). RESULTS: Mean niacin Cmax and AUC(0-t) values were 9.3 microg/ml and 26.2 microg x h/ml and were the highest of all analytes measured. Peak niacin and NUA levels occurred at 4.6 h (median) while tmax for NAM and NNO were 8.6 and 11.1 h, respectively. The mean plasma terminal half-life for niacin (0.9 h) and NUA (1.3 h) was shorter as compared to NAM (4.3 h). Urine recovery of niacin and metabolites accounted for 69.5% of the administered dose; only 3.2% was excreted as niacin. The highest recovery was for 2PY (37.9%), followed by MNA (16.0%) and NUA (11.6%). Mean half-lives for 2PY and MNA calculated in urine were 12.6 and 12.8 h, respectively. CONCLUSIONS: Niacin was extensively metabolized following oral administration, and about 70% of the administered dose is recovered in urine in 96 h as niacin, NUA, MNA, NNO, NAM and 2PY. The plasma levels of the parent niacin were higher than its metabolites though only about 3% of the unchanged drug is recovered in urine.

Effect of the rate of niacin administration on the plasma and urine pharmacokinetics of niacin and its metabolites.

The metabolic profile of niacin is influenced by the rate of niacin administration. This study characterizes the effect of administration rate on the pharmacokinetics of niacin and its metabolites. Twelve healthy males were enrolled in an open-label, dose-rate escalation study and received 2000 mg niacin at 3 different dosing rates. Plasma was analyzed for niacin, nicotinuric acid, nicotinamide, and nicotinamide-N-oxide. Urine was analyzed for niacin and the metabolites nicotinuric acid, nicotinamide, nicotinamide-N-oxide, N-methylnicotinamide, and N-methyl-2-pyridone-5-carboxamide. C(max) and AUC(0-t) for niacin and nicotinuric acid increased with an increase in dosing rate. The changes observed in plasma nicotinamide and nicotinamide-N-oxide parameters, however, did not correlate to dosing rate. The total amount of niacin and metabolites excreted in urine was comparable for all 3 treatments. However, with the increase in dosing rate, urine recovery of niacin and nicotinuric acid showed a significant increase, whereas N-methyl-2-pyridone-5-carboxamide and N-methylnicotinamide showed a significant decrease.

Functional map and age-related differences in the human face: nonimmunologic contact urticaria induced by hexyl nicotinate.

Variation in human skin reactivity to various irritants in association with age and body region has been reported. Hexyl nicotinate (HN), a lipophilic nicotinate ester, was used to induce nonimmunologic contact urticaria in human volunteers of 2 age groups: 10 young subjects [24-34 years, mean +/- standard deviation (SD) 29.8 +/- 3.9 years] and 10 older volunteers (66-83 years, mean +/- SD 73.6 +/- 17.4 years); and to define skin function and potential age-related differences in various facial areas. About 5 mM of HN in ethanol was applied to 8 locations on the face, neck, and volar forearm. A laser Doppler flowmeter was used to determine baseline blood flow and to monitor the skin blood flow changes after HN application. In the contralateral areas, stratum corneum turnover was determined using 5% dansyl chloride in petrolatum. In the young group, the perioral area exhibited the strongest reaction to HN. In the older group, the chin was the most sensitive site. In both the groups, the forearm was the least responsive. The older group demonstrated a stronger reaction than the younger group in 3 sites (forehead, cheek, and nasolabial area). Stratum corneum turnover was slower in the nasolabial area and in the forearm in both age groups, whereas the fastest was in the perioral area and the chin in the younger group and in the chin and the forehead in the older group. Compared to the older group, the younger group showed a slower stratum corneum turnover in the nose and the neck. This study demonstrates the regional and the age-related variability of the stratum corneum turnover and the skin reactions to HN. These observations may help explain some aspects of the cutaneous intolerance in skin care of the face.

Chemoselective hydrazone formation between HYNIC-functionalized peptides and (18)F-fluorinated aldehydes.

INTRODUCTION: Since the demand for (18)F-fluorinated peptides for quantitative in vivo receptor imaging using PET has increased, a new chemoselective two-step (18)F-labeling strategy based on hydrazone formation between an unprotected hydrazine-functionalized peptide and an (18)F-labeled aldehyde was developed. METHODS: First, 4-[(18)F]fluorobenzaldehyde ([(18)F]FB-CHO) was prepared from 4-formyl-N,N,N-trimethylanilinium triflate via direct no-carrier-added (18)F-fluorination (dimethyl sulfoxide, 90 degrees C, 5 min) and purified by RP-HPLC. Hydrazone formation between [(18)F]FB-CHO and 6-hydrazinonicotinic acid (HYNIC) and the unprotected HYNIC-functionalized peptides (HYNIC-d-Phe(1))-Tyr(3)-Thr(8)-octreotide and (HYNIC-Arg(1))-substance P was evaluated with respect to the dependence of radiochemical yield on pH, precursor concentration and temperature. The stability of [(18)F]FB-CH=N-HYNIC-Tyr(3)-Thr(8)(NH(2))-octreotide in aqueous solution at various pH (4.0, 5.5 and 7.5) as well as the in vivo stability of [(18)F]FB-CH=N-HYNIC-Tyr(3)-Thr(8)-octreotide in mouse blood (30 min p.i.) was investigated. RESULTS: Yields of the hydrazone formation were independent of pH between pH 0.5 and 5.5. Optimal labeling yields of 85% were obtained with a precursor concentration of 2.1 mM at 70 degrees C for 10 min. The labeling products were stable at pH 7.5 at 37 degrees C, while in more acidic media (pH 4.0) the product slowly decomposed to form up to 31+/-2% [(18)F]FB-CHO within 5 h. Metabolite studies showed no detectable degradation of [(18)F]FB-CH=N-HYNIC-Tyr(3)-Thr(8)-octreotide in mouse blood (30 min p.i.). CONCLUSIONS: In conclusion, chemoselective hydrazone formation between unprotected HYNIC-functionalized peptides and [(18)F]FB-CHO is a fast and straightforward radiolabeling method leading to high yields under mild acidic conditions. In addition, it represents a powerful and versatile radiolabeling strategy that is applicable to a variety of radionuclides and peptide precursors already available for (99m)Tc labeling.

Disposition and biotransformation of the acetylenic retinoid tazarotene in humans.

Oral tazarotene, an acetylenic retinoid, is in clinical development for the treatment of psoriasis. The disposition and biotransformation of tazarotene were investigated in six healthy male volunteers, following a single oral administration of a 6 mg (100 microCi) dose of [14C]tazarotene, in a gelatin capsule. Blood levels of radioactivity peaked 2 h postdose and then rapidly declined. Total recovery of radioactivity was 89.2+/-8.0% of the administered dose, with 26.1+/-4.2% in urine and 63.0+/-7.0% in feces, within 7 days of dosing. Only tazarotenic acid, the principle active metabolite formed via esterase hydrolysis of tazarotene, was detected in blood. One major urinary oxidative metabolite, tazarotenic acid sulfoxide, accounted for 19.2+/-3.0% of the dose. The majority of radioactivity recovered in the feces was attributed to tazarotenic acid representing 46.9+/-9.9% of the dose and only 5.82+/-3.84% of dose was excreted as unchanged tazarotene. Thus following oral administration, tazarotene was rapidly absorbed and underwent extensive hydrolysis to tazarotenic acid, the major circulating species in the blood that was then excreted unchanged in feces. A smaller fraction of tazarotenic acid was further metabolized to an inactive sulfoxide that was excreted in the urine.