Characteristics of neonicotinoid imidacloprid in urine following exposure of humans to orchards in China.

Imidacloprid (IMI) is a typical neonicotinoid with the largest usage in agricultural orchards in China. The long-term repeated use and the lack of proper protective measures may result in rural farmers and people living near orchards to be inevitably exposed to IMI. Excessive exposure may cause potential adverse effects on human health. To explore the characteristics of human exposure to IMI in urine, different groups of people, including pesticide applicators and their family members, and kindergarten children near IMI-applied orchards were investigated. The IMI and metabolite, 6-chloronicotinic acid (6-CNA), concentrations in urine were creatinine-adjusted to compensate for a possible dilution effect. Target analytes were detected in 100% of 1926 urine samples. The results showed that the IMI concentration in the 1-d urine from the rural residents significantly increased after a spraying event (p < 0.05) and reached the highest concentration (Geomean: 16.42 µg/g creatinine for IMI; 7.33 µg/g creatinine for 6-CNA) in the 2-d urine samples. The pesticide applicators of different genders had almost the same exposure environment (IMI Geomean of 13.25 µg/g creatinine for males and 14.71 µg/g creatinine for females) (p > 0.05). Females had higher exposure concentrations than that of males. People from different villages demonstrated diverse exposure levels with Geomean differences of 1.13-3.28 fold. For 3-6 years-old children, urinary concentrations from the rural group (Geomean: 3.73 µg/g creatinine for IMI; 3.95 µg/g creatinine for 6-CNA) were significantly higher than that of the urban group (Geomean: 1.13 µg/g creatinine for IMI; 0.88 µg/g creatinine for 6-CNA) (p = 0.00001), and the younger children tended to have higher exposure risk. Our findings showed that people in the Henan orchard areas were likely exposed to IMI to varying degrees. Further research on the health risk evaluation of IMI and controlling the exposure risks is needed.

Urinary Excretion of Niacin Metabolites in Humans After Coffee Consumption.

SCOPE: Coffee is a major natural source of niacin in the human diet, as it is formed during coffee roasting from the alkaloid trigonelline. The intention of our study was to monitor the urinary excretion of niacin metabolites after coffee consumption under controlled diet. METHODS AND RESULTS: We performed a 4-day human intervention study on the excretion of major niacin metabolites in the urine of volunteers after ingestion of 500 mL regular coffee containing 34.8 µmol nicotinic acid (NA) and 0.58 µmol nicotinamide (NAM). In addition to NA and NAM, the metabolites N1 -methylnicotinamide (NMNAM), N1 -methyl-2-pyridone-5-carboxamide (2-Py), and nicotinuric acid (NUA) were identified and quantified in the collected urine samples by stable isotope dilution analysis (SIVA) using HPLC-ESI-MS/MS. Rapid urinary excretion was observed for the main metabolites (NA, NAM, NMNAM, and 2-Py), with tmax values within the first hour after ingestion. NUA appeared in traces even more rapidly. In sum, 972 nmol h-1 of NA, NAM, NMNAM, and 2-Py were excreted within 12 h after coffee consumption, corresponding to 6% of the ingested NA and NAM. CONCLUSION: The results indicate regular coffee consumption to be a source of niacin in human diet.

Efficiency control of dietary pesticide intake reduction by human biomonitoring.

In spite of food safety controls for pesticide residues, a conventional diet still leads to a noticeable exposure of the general population to several pesticides. In a pilot study the response of exposure reduction by organic diet intervention on the urinary levels of pesticide metabolites was investigated. In the study two adult individuals were kept on a conventional diet for 11days and morning urine voids were collected at the last four days of the period. Afterwards, the participants switched to exclusively organic food intake for 18days and likewise morning urine samples were collected at the last four days of this period. In the urine samples six pyrethroid metabolites, six dialkylphosphates, four phenolic parameter for organophosphate pesticides and carbamates, 6-chloronicotinic acid (ClNA) as parameter for neonicotinoid insecticides, seven phenoxy herbicides, glyphosate and its metabolite AMPA were quantified using gas chromatographic mass spectrometric methods. Generally, the comparative analyses revealed greater shares as well as higher levels of the parameters in the samples taken during the common diet period compared to the organic diet period. Considerable decrease of the levels was found for almost all pyrethroid metabolites, dialkyphosphates and phenoxy herbicids, as well as for the phenolic metabolites 4-nitrophenol and 3,5,6-trichloropyridinol. In contrast, higher values were found for the organic diet period for ClNA and the metabolite of coumaphos in one of the volunteers. The present study confirms the results of former studies which indicated that an organic diet intervention results in considerable lower exposure to organophosphate pesticides and pyrethroids. It also verifies the former experience that monitoring of urinary parameters for non-persistent pesticides permits a reliable efficiency control of short-time effects by dietary interventions. Additionally to former studies, the results of the present study highlight the need of an extension of the parameter spectrum to all prominent pesticide groups.

Occurrence and Profile Characteristics of the Pesticide Imidacloprid, Preservative Parabens, and Their Metabolites in Human Urine from Rural and Urban China.

Knowledge of human exposure to imidacloprid, the most extensively used insecticide, and para-hydroxybenzoic acid esters (parabens), the most extensively used preservative, is insufficient. In this study, 295 urine samples collected from subjects in rural and urban areas in China were analyzed for imidacloprid and four parabens (namely, methyl paraben, ethyl paraben, propyl paraben, and butyl paraben) as well as their major metabolites (namely, 6-chloronicotinic acid (6-ClNA) and para-hydroxybenzoic acid (p-HB)). Imidacloprid was detected in 100% of the urine samples from rural Chinese subjects and 95% of the urine samples from urban Chinese subjects. Concentrations of urinary imidacloprid detected in rural Chinese subjects (geometric mean (GM) = 0.18 ng/mL) were slightly higher than those detected in urban Chinese subjects (GM = 0.15 ng/mL) when the effect of pesticide spraying was excluded. However, concentrations of urinary imidacloprid detected in rural adults increased significantly in the subsequent days of pesticide spraying (GM = 0.62 ng/mL), which could return to the normal levels within 3 days. In contrast, concentrations of urinary parabens detected in rural Chinese subjects (GM = 6.90 ng/mL) were lower than that in urban Chinese subjects (GM = 30.5 ng/mL). In addition, the metabolism characteristics of imidacloprid to 6-ClNA and parabens to p-HB were discussed preliminarily.

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.

Disposition and acute toxicity of imidacloprid in female rats after single exposure.

Single dose of imidacloprid (IMI-20mg/kg bodyweight) was orally administered in female rats. Its disposition along with two metabolites 6-chloro nicotinic acid (6-CNA) and 6-hydroxy nicotinic acid (6-HNA) was monitored in organs (brain, liver, kidney, and ovary) and bodily fluids (blood, urine) at 6, 12, 24 and 48h and faeces at 24 and 48h. Maximum concentration (Cmax) of IMI and metabolites in each organ and bodily fluid occurred after 12h. Area under curve (AUC) of IMI ranged from 35 to 358µg/ml/h; 6-CNA: 27.12-1006.42µg/ml/h and 6-HNA: 14.98-302.74µg/ml/h in different organs and bodily fluids. Clearance rate of IMI was maximum in ovary followed by kidney, liver, brain, faeces, blood and urine. Percent inhibition of acetyl-cholinesterase (AChE) was comparable in brain and Red Blood Cells (RBC) at 6-48h which suggests the RBC-AChE as valid biomarker for assessing IMI exposure. It is evident that IMI was absorbed, metabolized, and excreted showing increased level of serum enzymes like Glutamic oxaloacetic transaminase (GOT), Glutamic pyruvic transaminase (GPT) and biochemical constituents like billirubin and Blood Urea Nitrogen (BUN) at 48h. These data suggest that IMI is widely distributed, metabolized and induced toxicology effects at 20mg/kg bodyweight to female rats.

Nicotinuric acid: a potential marker of metabolic syndrome through a metabolomics-based approach.

OBJECTIVE: Metabolic syndrome is a multiplex disorder and puts patients on the road to type 2 diabetes and atherosclerotic cardiovascular diseases. However, a surrogate biomarker in plasma or urine in fully reflecting features of metabolic syndrome has not been explored. RESEARCH DESIGN AND METHODS: Urine metabolomics has potential utility in metabolic profiling because urine metabolites analysis reflects global outflux of metabolic change. Accordingly, we collected data on subjects (n = 99) with overweight, dyslipidemia, hypertension or impaired glucose tolerance and took a metabolomics approach to analyze the metabolites of urine revealed in metabolic syndrome by high-performance liquid chromatography-time-of-flight mass spectrometry and elicit potential biomarkers to picture metabolic syndrome. RESULTS: Our results revealed that the urine nicotinuric acid value of subjects with diabetes (HbA1c ≥ 6.5% or those receiving diabetes medications) (n = 25) was higher than subjects without diabetes (n = 37) (221 ± 31 vs. 152 ± 13 × 10(3) mAU, P = 0.0268). Moreover, urinary nicotinuric acid level was positively correlated with body mass index, blood pressure, total cholesterol, low-density lipoprotein cholesterol, triacylglycerol and high sensitivity C-reactive protein, but negatively correlated with high-density lipoprotein cholesterol. CONCLUSIONS: This is the first study, to our knowledge, to propose that nicotinuric acid represents an important pathogenic mechanism in process from metabolic syndrome to diabetes and atherosclerotic cardiovascular disease.

[Detection of chloropyridinyl neonicotinoid insecticide metabolite 6-chloronicotinic acid in the urine: six cases with subacute nicotinic symptoms].

Neonicotinoid is a recently developed insecticide with worldwide use that has been increasing. It acts as a nicotinic acetylcholine receptor agonist. Chloropyridinyl neonicotinoid is a subgroup of neonicotinoid, and are commercially available as imidacloprid, nitenpyram, acetamiprid, and thiacloprid. The maximum residue limits of acetamiprid for fruits and tea leaves are high in Japan, e.g. 5 ppm for grapes and 30 ppm for tea leaves. 6-chloronicotinic acid (6 CNA) is a common metabolite in animals after exposure to chloropyridinyl neonicotinoids, but has not yet been detected in human urine. 'Spot' urine samples on the first visit and after were collected from eleven patients 6-52 years-old, who visited X-clinic from August to December in 2008, within 24 hours after symptom onset with unknown origin. Urinary 6 CNA was detected in six out of the eleven patients (IC positive group), by ion chromatography and identified in twenty specimens of these six patients by liquid chromatography-mass spectrometry (LC/MS), maximum 84.8 microg/L from the first visit to the 20th visit. The sensitivity of ion chromatography for LC/MS was 45%, and the specificity was 100%. The IC positive group showed headache, general fatigue, finger tremor, and short time memory disturbance in 100%, fever (> 37.0 degrees C), cough, palpitation, chest pain, stomachache, myalgia/muscle spasm/muscle weakness in 83%, heart rate abnormality (sinus tachycardia, sinus bradycardia, or intermittent WPW syndrome) in 83%, high domestic fruits intake (> 500 g/day) in 83%, high tea beverage intake (> 500 mL/day) in 66%. Five patients who were not among the IC positive group showed < 80%, < 40%, 60%, 60%, 20%, respectively. The patients gradually recovered through supportive therapy and the restriction of fruits and tea intake within several days to two months. In conclusion, urinary 6-chloronicotinic acid, a common metabolite of chloropyridinyl neonicotinoid insecticide, was detected for the first time, from six patients with subacute nicotinic symptoms.

Development of fluorescence polarization immunoassay for the rapid detection of 6-chloronicotinic acid: main metabolite of neonicotinoid insecticides.

A fluorescence polarization immunoassay (FPIA) for the quantitative determination of 6-chloronicotinic acid (6-CNA) using polyclonal antibody was developed. The 6-CNA-protein (bovine serum albumin and soybean trypsin inhibitor) conjugates and fluorescein-labeled 6-CNA derivative (tracer) were prepared and used as the immunogens and tracer, respectively. The synthesized tracer was purified by thin layer chromatography (TLC) and showed a good binding to antiserum (73/5) which was obtained from the immunized rabbit (No. 73) with 6-CNA-BSA conjugate. The detection limit (10% inhibition) of FPIA was 4 microg/mL, and IC(50) value was 32 microg/mL. The FPIA showed a cross-reaction for 5-amino-2-chloropyridine (60%), but no cross-reaction for other pesticides was observed. Recoveries for spiked apple, urine, soil, and water samples (5, 50, and 500 ppm) averaging between 78.6 +/- 8.8 and 114 +/- 18% were reasonable and in good agreement with the amounts spiked. Although the developed FPIA possesses low sensitivity, this assay is more simple and quick than other analytical methods, such as high performance liquid chromatography and gas chromatography. Thus, the developed FPIA method could be a useful tool for express screening 6-CNA in agricultural, environmental, and biological samples.

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.

Identification of urinary modified nucleosides and ribosylated metabolites in humans via combined ESI-FTICR MS and ESI-IT MS analysis.

The physiological response of the human body to several diseases can be reflected by the metabolite pattern in biological fluids. Cancer, like other diseases accompanied by metabolic disorders, causes characteristic effects on cell turnover rate, activity of modifying enzymes, and RNA/DNA modifications. This results in an altered excretion of modified nucleosides and biochemically related compounds. In the course of our metabolic profiling project, we screened 24-h urine of patients suffering from lung, rectal, or head and neck cancer for previously unknown ribosylated metabolites. Therefore, we developed a sample preparation procedure based on boronate affinity chromatography followed by additional prepurification with preparative TLC. The isolated metabolites were analyzed by ion trap mass spectrometry (IT MS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS). IT MS was applied for LC-auto MS(3) screening runs and MS(n(n=4-6)) syringe pump infusion experiments, yielding characteristic fragmentation patterns. FTICR MS measurements enabled the calculation of corresponding molecular formulae based on accurate mass determination (mass accuracy: 1-5 ppm for external and sub-ppm values for internal calibration). We were able to identify 22 metabolites deriving from cellular RNA metabolism and related metabolic pathways like histidine metabolism, purine biosynthesis, methionine/polyamine cycle, and nicotinate/nicotinamide metabolism. The compounds 1-ribosyl-3-hydroxypyridinium, 1-ribosyl-pyridinium, and 3-ribosyl-1-methyl-l-histidinium as well as a series of ribosylated histamines, conjugated to carboxylic acids at the N(omega)-position were found as novel urinary constituents. The occurrence of the modified nucleosides 2-methylthio-N(6)-(cis-hydroxyisopentenyl)-adenosine, 5-methoxycarbonylmethyl-2-thiouridine, N(6)-methyl-N(6)-threonylcarbamoyladenosine, and 2-methylthio-N(6)-threonylcarbamoyladenosine in human urine is verified for the first time.

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.

Pattern recognition analysis for classification of hypertensive model rats and diurnal variation using 1H-NMR spectroscopy of urine.

Urine samples were collected during the daytime and nighttime from spontaneously hypertensive model rats and normal rats without dosing. The 1H NMR spectra were measured for their urine samples, and analyzed by a pattern recognition method, known as Principal Component Analysis (PCA) and Soft Independent Modeling of Class Analogy (SIMCA). The separation of urinary data due to the diurnal variation (daytime and nighttime) and also to the difference between the two strains of rat was achieved in the PCA score plot. Differences of the urinary profiles in the respective separation were effectively extracted as marker variables by the SIMCA method. NMR measurements coupled with pattern recognition methods provide a straightforward approach to inspect the disease metabolic status and the preliminary screening tool of marker candidates for further development.

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.

Effects of excess nicotinamide administration on the urinary excretion of nicotinamide N-oxide and nicotinuric acid by rats.

We investigated a useful chemical index for an excessive nicotinamide intake and how this excessive nicotinamide intake affects the tryptophan-nicotinamide metabolism in rats. Weaning rats were fed on a tryptophan-limited and nicotinic acid-free diet containing no, 0.003%, 0.1%, 0.2%, or 0.3% nicotinamide for 21 days. Urine samples were collected on the last day and analyzed the intermediates and metabolites on the tryptophan-nicotinamide pathway. Nicotinamide N-oxide, nicotinic acid and nicotinuric acid, metabolites of nicotinamide, were detected when nicotinamide at more than 0.1% had been taken. An intake of nicotinamide of more than 0.1% increased the urinary excretion of quinolinic acid, an intermediate on the pathway. Nicotinamide N-oxide and nicotinuric acid increased with increasing dietary concentration of nicotinamide. These results show that the measurements of nicotinamide N-oxide and nicotinuric acid in urine would be useful indices for an excessive nicotinamide intake.

Identification of N1-methyl-2-pyridone-5-carboxamide and N1-methyl-4-pyridone-5-carboxamide as components in urine extracts of individuals consuming coffee.

Caffeine metabolites were extracted from urine samples collected 4 h after consumption of a cup of coffee and were separated by high-performance liquid chromatography (HPLC) on a C18 (5 microm) reverse-phase column using an acetonitrile (5%), acetic acid (0.05%) solution as the mobile phase. The elution profiles indicated the constant presence of a major and a minor components eluting between the caffeine metabolites 5-acetamido-6-formyl-3-methyluracil (AFMU) and 7-methylxanthine (7X) in an approximate nine. A procedure was developed for the isolation of the major component in an apparent pure form, and the yield was 10-20 mg from 400 ml of urine. The minor component was isolated in an apparent pure form by this procedure as well, and the yield was 0.5 mg from 200 ml of urine. The average ratio of the two components in urine, UV absorption and 1H-NMR spectra of the two components, and 13C-NMR spectrum, mass spectrum and elemental analysis of the major component identified the major and minor components as N(1)-methyl-2-pyridone-5-carboxamide and N(1)-methyl-4-pyridone-5-carboxamide, respectively, two major metabolites of the vitamin niacin present in a significant amount in coffee beans. The two metabolites were present in the same average amount in urine extracts of individuals irregardless of coffee consumption. The findings are briefly discussed in relation to the nutritional sources of niacin and to current procedures for measuring amounts of the two metabolites in urine samples.

Monitoring of 6-chloronicotinic acid in human urine by gas chromatography-tandem mass spectrometry as indicator of exposure to the pesticide imidacloprid.

A new analytical method for determining 6-chloronicotinic acid (6-ClNA) in human urine is proposed. 6-ClNA is the main metabolite in warm-blooded animals after exposure to the insecticide imidachloprid. 6-ClNA was extracted from human urine using solid phase extraction (SPE) with laboratory-made cartridges of Amberlite XAD-4. A clean-up step and a derivatization process were carried out prior to gas chromatography-tandem mass spectrometric (GC-MS-MS) determination. A study on the influence of pH in the extraction process revealed that it affects the analyte extraction efficiency. A working pH zone was defined between 0.8 and 2.8. Calibration curves were studied in the concentration range of 0.5-100 ng mL(-1) and showed good linearity. Limits of detection and determination of the method were 16 and 56 pg mL(-1) respectively. The mean recovery at 10 and 100 ng mL(-1) was between 97.2 and 102.1% and the repeatability was lower than 5.4% in all cases. The analysis of urine samples of five agricultural workers from Almería (Spain) did not detect the metabolite.

Acute dose-dependent disposition studies of nicotinic acid in rats.

The pharmacokinetics of nicotinic acid (NiAc) and nicotinuric acid (NiUAc), the major metabolite of NiAc, and the dose dependency of these pharmacokinetics were determined in rats. Intravenous injections of 2, 5, 15, and 45 mg/kg of NiAc and 5 and 15 mg/kg of NiUAc were administered, and plasma and urine samples were assayed for NiAc and NiUAc by HPLC. The plasma concentration-time profiles of NiAc showed a typical characteristic of capacity-limited elimination after higher doses. When the NiAc dose was elevated, the total plasma clearance of NiAc decreased dramatically, and the normalized area under the plasma concentration-curve increased markedly. There was no change in the volume of distribution at steady state. After the administration of NiUAc, however, the pharmacokinetics of NiUAc were linear, at least up to a dose of 15 mg/kg. With increasing doses of NiAc, the ratio for NiUAc to unchanged drug excreted in urine decreased markedly from 4.54 +/- 0.93 at 2 mg/kg to 0.37 +/- 0.12 at 45 mg/kg while the renal clearance of NiAc remained constant. An in vitro study of the plasma protein binding of NiAc showed no saturability, with a 40 to 50% bound fraction, when total NiAc concentrations were 1 to 130 micrograms/ml. Plasma NiAc profiles after the iv administration of NiAc were adequately described by the two-compartment model including the "pooled" Michaelis-Menten elimination process. The present results suggest that the nonlinear disposition of NiAc can be attributed in part to the saturation of glycine conjugation, and also, probably to amidation.