Cortisol production rate in children by gas chromatography/mass spectrometry using [1,2,3,4-13C]cortisol

A urinary method of determining the cortisol production rate (CPR) in children was studied under physiologic conditions by administration of low amounts of [1,2,3,4-13C]cortisol. The CPR in three patients with multiple pituitary deficiency ranged from 7 to 16 mumoles d-1 m-2, and the CPR in three patients with congenital adrenal hyperplasia (CAH) due to 11 beta-hydroxylase deficiency (11 beta OHD) and 17 alpha-hydroxylase deficiency (17 alpha OHD) from 0.1 to 2.11 mumoles d-1 m-2. Results showed that with this method, very low CPRs can be reliably measured. The metabolism of [13C4]cortisol or [9,12,12-2H]cortisol was compared with that of native cortisol in adrenalectomized piglets. For the urinary cortisol metabolites, small to substantial differences in isotope dilution were noted relative to that in the original cortisol mixture. With [13C4]cortisol, the so-called secondary isotope effects were approximately 2% to 3% for tetrahydrocortisone (THE) and tetrahydrocortisol (THF), and about 10% for the cortolones, relative to the cortisol mixture. When [2H3]cortisol was used, the cortisol metabolites THE and THF contained only two deuterium atoms. Together with this apparent loss of one deuterium atom, the secondary isotope effects in these steroids amounted to 5% to 10%. It was concluded that [13C4]cortisol was the better tracer to use for the measurement of urinary CPR.     

Analysis of steroidal estrogens as pyridine-3-sulfonyl derivatives by liquid chromatography electrospray tandem mass spectrometry

Sulfonyl chlorides substituted with functional groups having high proton affinity can serve as derivatization reagents to enhance the sensitivity for steroidal estrogens in liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The most commonly used reagent for derivatization of estrogens for LC-ESI-MS/MS is dansyl chloride. In this study, we compared dansyl chloride, 1,2-dimethylimidazole-4-sulfonyl (DMIS) chloride, pyridine-3-sulfonyl (PS) chloride, and 4-(1H-pyrazol-1-yl)benzenesulfonyl (PBS) chloride for derivatization of 17beta-estradiol (E2) prior to LC-ESI-MS/MS. The product ion spectra of the dansyl and DMIS derivatives were dominated by ions representing derivatization reagent moieties. In contrast, the product ion spectrum of the PS derivative of E2 and, to a lesser extent, the PBS derivative, showed analyte-specific fragment ions. Derivatization with PS chloride was therefore chosen for further investigation. The product ion spectrum of the PS derivative of E2 showed intense ions at m/z 272, assigned to the radical E2 cation, and at m/z 350, attributed to the loss of SO(2) from the [M+H](+) ion. Third-stage mass spectrometry of the PS derivative of E2 with isolation and collisional activation of the m/z 272 ion resulted in steroid C and D ring cleavages analogous to those observed in electron ionization mass spectrometry. The product ion spectra of the PS derivatives of estrone, 17alpha-ethinylestradiol, equilin, and equilenin showed similar estrogen-specific ions. Using derivatization with PS chloride, we developed an LC-ESI-MS/MS method with multiple reaction monitoring of primary and confirmatory precursor-to-product ion transitions for the determination of E2 in serum.     

Gas chromatographic negative ion mass spectrometric assay of 2-dicyclopropylmethylamino-2-oxazoline (S-3341), a new antihypertensive drug

The quantification in plasma and urine of 2-dicyclopropylmethylamino-2-oxazoline (S-3341), a new antihypertensive drug is described using a sensitive gas chromatographic negative ion mass spectrometric method with ammonia as moderating gas. After a two-step extraction, derivatization is carried out with 3,5-bis(trifluoromethyl)benzoyl chloride and the abundance of the molecular ion (m/z 420) obtained is compared with that of the tetradeuterated standard (m/z 424). The low background due to the high mass and negative ion detection provides a detection limit of about 1 pg per injection. Oral administration of 1 or 2 mg S-3341 to patients gives a maximum concentration of 3.3 +/- 0.7 ng ml-1 and 7.6 +/- 2.0 ng ml-1 at 1.8 +/- 0.6 h and 1.4 +/- 0.7 h and an average elimination half-life of 6.7 h.     

A capillary liquid chromatographic/tandem mass spectrometric method for the quantification of gamma-aminobutyric acid in human plasma and cerebrospinal fluid

A sensitive and reliable method for the determination of gamma-aminobutyric acid (GABA), a major inhibitory neurotransmitter, in human plasma and cerebrospinal fluid (CSF) has been developed. The method is based on capillary liquid chromatography (LC)/tandem mass spectrometry (MS/MS) using deuterium-labeled GABA (gamma-aminobutyric acid-2,2-D(2), GABA-d(2)) as internal standard. Pre-column derivatization with 7-fluoro-4-nitrobenzoxadiazole (NBD-F) was deployed, allowing both effective in-line pre-concentration and sensitive tandem MS detection of the analyte. An extraction column (10 mm x 0.25 mm, 7 microm, C(18)) was used for preconcentrating and stacking the sample. Separation was carried out on an analytical column (50 mm x 0.25 mm, 5 microm, C(18)). Characteristic precursor-to-product ion transitions, m/z 267--> 249 (for NBD-GABA) and m/z 269--> 251 (for NBD-GABA-d(2)) were monitored for the quantification. A linear calibration curve from 10 to 250 ng/mL GABA with an r(2) value of 0.9994 was obtained. Detection limit was estimated to be 5.00 ng/mL GABA (S/N = 3). Human plasma and CSF samples were analyzed. The concentrations of GABA were found to be 98.6 +/- 33.9 ng/mL (mean +/- S.D., n = 12), and 44.3 +/- 10.0 ng/mL (n = 6) in plasma and CSF, respectively.     

Accurate quantification of dimethylamine (DMA) in human plasma and serum by GC-MS and GC-tandem MS as pentafluorobenzamide derivative in the positive-ion chemical ionization mode

Dimethylamine (DMA) circulates in human blood and is excreted in the urine. Major precursor for endogenous DMA is asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis. ADMA is hydrolyzed to DMA and L-citrulline by dimethylarginine dimethylaminohydrolase (DDAH). In previous work, we reported a GC-MS method for the quantification of DMA in human urine. This method involves simultaneous derivatization of endogenous DMA and the internal standard (CD(3))(2)NH by pentafluorobenzoyl chloride (PFBoylCl) and extraction of the pentafluorobenzamide derivatives by toluene. In the present work, we optimized this derivatization/extraction procedure for the quantitative determination of DMA in human plasma. Optimized experimental parameters included vortex time and concentration of PFBoylCl, carbonate and internal standard. The GC-MS method was thoroughly validated and applied to measure DMA concentrations in human plasma and serum samples. GC-MS quantification was performed by selected-ion monitoring of the protonated molecules at m/z 240 for DMA and m/z 246 for (CD(3))(2)NH in the positive-ion chemical ionization mode. Circulating DMA concentration in healthy young women (n=18) was determined to be 1.43+/-0.23 micaroM in serum, 1.73+/-0.17 microM in lithium heparin plasma, and 9.84+/-1.43 microM in EDTA plasma. DMA was identified as an abundant contaminant in EDTA vacutainer tubes (9.3+/-1.9 nmol/monovette, n=6). Serum and lithium heparin vacutainer tubes contained considerably smaller amounts of DMA (0.42+/-0.01 and 0.95+/-0.01 nmol/monovette, respectively, each n=6). Serum is recommended as the most appropriate matrix for measuring DMA in human blood. The present GC-MS method should be useful for the determination of systemic and whole body DDAH activity by measuring circulating and excretory DMA in experimental and clinical studies.     

Quantitation of positional isomers of deuterium-labeled glucose by gas chromatography/mass spectrometry.

A method for determining the site and extent of deuterium (D) labeling of glucose by GC/MS and mass fragmentography was developed. Under chemical and electron impact ionization, ion clusters m/z 328, 242, 217, 212, and 187 of glucose aldonitrile pentaacetate and m/z 331 and 169 of pentaacetate derivative were produced. From the mass spectra of 13C- and D-labeled reference compounds, glucose carbon and hydrogen (C-H) positions included in these fragments were deduced to be m/z 328 = C1-C6, 2,3,4,5,6,6-H6; m/z 331 = C1-C6, 1,2,3,4,5,6,6-H7; m/z 169 = C1-C6, 1,3,4,5,6,6-H6; m/z 187 = C3-C6, 3,4,5,6,6-H5; m/z 212 = C1-C5, 2,3,4,5-H4; m/z 217 = C4-C6, 4,5,6,6-H4; and m/z 242 = C1-C4, 2,3,4-H3. After correction for isotope discrimination and deuterium-hydrogen exchange, the D enrichment of these fragments can be quantitated using selective ion monitoring, and the D enrichment of all C-H positions can be obtained by the difference in enrichment of the corresponding ion pairs. The validity of this approach was tested by examining D enrichment of known mixtures of 1-d1-, 2-d1-, 3-d1-, and 5,6,6-d3-glucose with unlabeled glucose and D enrichment of perdeuterated glucose using these fragments. This method was used to determine deuterium incorporation in C1 through C6 of blood glucose in fasted (24 h) rats infused with deuterated water. The distribution of deuterium was similar to that found by Postle and Bloxham (1980, Biochem. J. 192, 65-73). Approximately one deuterium atom was incorporated into C5 and only 75% deuterium atom was incorporated into C2. The enrichment of C2 and C6 of glucose relative to that of water indicated that 74 +/- 9% of plasma glucose was newly formed 4 h after the onset of deuterium infusion, and gluconeogenesis accounted for about 76 +/- 7% of the glucose 6-phosphate flux.     

Quantitative determination of circulating and urinary asymmetric dimethylarginine (ADMA) in humans by gas chromatography-tandem mass spectrometry as methyl ester tri(N-pentafluoropropionyl) derivative

Asymmetric dimethylarginine (ADMA; N(G),N(G)-dimethyl-L-arginine) is the most important endogenous inhibitor of nitric oxide synthase and a potential risk factor for cardiovascular diseases. This article describes a gas chromatographic-tandem mass spectrometric (GC-tandem MS) method for the accurate quantification of ADMA in human plasma or serum and urine using de novo synthesized [2H(3)]-methyl ester ADMA (d(3)Me-ADMA) as the internal standard. Aliquots (100 microl) of plasma/serum ultrafiltrate or native urine and of aqueous solutions of synthetic ADMA (1 microM for plasma and serum; 20 microM for urine) are evaporated to dryness. The residue from plasma/serum ultrafiltrate or urine is treated with a 100 microl aliquot of 2M HCl in methanol, whereas the residue of the ADMA solution is treated with a 100 microl aliquot of 2M HCl in tetradeuterated methanol. Methyl esters are prepared by heating for 60 min at 80 degrees C. After cooling to room temperature, the plasma or urine sample is combined with the d(3)Me-ADMA sample, the mixture is evaporated to dryness, the residue treated with a solution of pentafluoropropionic (PFP) anhydride in ethyl acetate (1:4, v/v) and the sample is incubated for 30 min at 65 degrees C. Solvent and reagents are evaporated under a stream of nitrogen gas, the residue is treated with a 200 microl aliquot of 0.4M borate buffer, pH 8.5, and toluene (0.2 ml for plasma, 1 ml for urine). Reaction products are extracted by vortexing for 1 min, the toluene phase is decanted, and a 1 microl aliquot is injected into the GC-tandem MS instrument. Quantitation is performed by selected reaction monitoring (SRM) of the common product ion at m/z 378 which is produced by collision-induced dissociation of the ions at m/z 634 for endogenous ADMA and m/z 637 for d(3)Me-ADMA. In plasma and urine of healthy humans ADMA was measured at concentrations of 0.39+/-0.06 microM (n=12) and 3.4+/-1.1 micromol/mmol creatinine (n=9), respectively. The limits of detection and quantitation of the method are approximately 10 amol and 320 pM of d(3)Me-ADMA, respectively.     

The potential role of hypocortisolism in the pathophysiology of PTSD and psoriasis

Different physical, chemical and psychological stressors can provoke a unique but different endocrine response involving activation of the hypothalamo-pituitary-adrenal (HPA) axis. Inability of adequate compensatory reaction can lead to many disorders. The aim of our study was comparison of cortisol values in diseases provoked by various stressors. Our investigation included 34 posttraumatic stress disorder (PTSD) patients, as an example of disorder caused by extremely strong, acute stressful stimulus, 19 psoriatic patients, as an example of chronic stress stimulus and 17 healthy volunteers. In each patient we determined 24-hour urinary cortisol, serum cortisol at 8 a.m. and 5 p.m., and cortisol in dexamethasone suppression test by the standard radioimmunoassay (RIA) method. PTSD patients showed lower urinary 24-hour cortisol values, (361 +/- 28 nmol/24 h), "stronger" circadian rhythm of serum cortisol (595 +/- 57 nmol/l at 8 a.m. and 242 +/- 23 nmol/l at 5 p.m.) and attenuated suppression of cortisol in dexamethasone suppression test (197 +/- 45 nmol/l) in comparison to healthy volunteers (590 +/- 87 nmol/24 h urine, 590 +/- 32 nmol/l at 8 a.m., 402 +/- 31 nmol/l, and < 86 nmol/l in dexa test). Psoriatic patients showed markedly lower 24-hour cortisol values (150 +/- 98 nmol/24 h), even in comparison to PTSD patients, then serum cortisol values (404 +/- 138 nmol/l at 8 a.m., 187 +/- 80 nmol/l at 5 p.m.) and enhanced suppression of cortisol (23 +/- 5 nmol/l). The model of attenuated feedback inhibition in PTSD patients shows that they are unusually reactive to stress and represents an alternative model of acute stress reaction to extremely strong stressful stimulus. Unusually low cortisol values in psoriatic patients correlate to our hypothesis that in chronic stress-related disease, as psoriasis is, exists, by still undefined mechanism, altered HPA axis function, which is obviously incompetent to realise its immunoregulatory function, so consequentially, clinical signs of psoriasis persist.     

Pancreatic B-cell function in non-insulin-dependent diabetes mellitus during successive periods of sulfonylurea and insulin treatment: serum C-peptide response to glucagon and urine C-peptide excretion

Serum C-peptide responses to glucagon and daily urine C-peptide excretion in successive periods of different treatment in two groups of patients with non-insulin-dependent diabetes mellitus (NIDDM) (mean interval between two tests less than 1 month) were compared. In group A patients (n = 8), the glycemic control was improved after transferring the treatment from sulfonylurea (SU) to insulin (fasting plasma glucose: SU: 192 +/- 47, insulin: 127 +/- 21 mg/dl, mean +/- S.D., p less than 0.01). Fasting serum C-peptide immunoreactivity (CPR) was significantly lower at the period of insulin treatment (SU: 1.93 +/- 1.01, insulin: 1.47 +/- 0.79 ng/ml, p less than 0.05), but there was no difference in the increase in serum CPR (maximal--fasting) (delta serum CPR) during glucagon stimulation in the two periods of treatment (SU: 1.70 +/- 0.72, insulin: 1.47 +/- 0.98 ng/ml). In group B patients (n = 7), there was no significant difference in glycemic control after transferring the treatment from insulin to SU (fasting plasma glucose: insulin: 127 +/- 24, SU: 103 +/- 13 mg/dl). Fasting serum CPR was significantly lower during the period of insulin treatment (insulin: 1.39 +/- 0.64, SU: 2.21 +/- 0.86 ng/ml, p less than 0.025), but delta serum CPR during glucagon stimulation still showed no significant difference between the two periods (insulin: 1.97 +/- 1.16, SU: 2.33 +/- 1.57 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)     

Measurement of the cortisol production rate in two sisters with 17 alpha-hydroxylase deficiency using [1,2,3,4-13C]cortisol and isotope dilution mass spectrometry

[1,2,3,4-13C]cortisol was i.v. administered to two sisters aged 11 yr (patient I) and 3 yr (patient II) who suffer from 17 alpha-hydroxylase deficiency. This is the first time that the cortisol production rate (CPR) in patients with 17 alpha-hydroxylase deficiency has been measured with a stable labelled tracer using the urinary method. The urine was collected for 3 days. High-performance liquid chromatography (HPLC) of approximately 100 ml urine extracts was carried out to isolate the small amount of cortisol metabolites excreted. The cortisol metabolites were oxidized to 11-oxo-aetiocholanolone. The isotope dilution in the methyl oxime tert-butyldimethylsilyl ether derivatives was measured by selected ion monitoring gas chromatography/mass spectrometry (GC/MS). The CPR calculated from tetrahydrocortisone (THE) and the cortolones was 765 and 536 nmol/day, respectively in patient I. The CPR in patient II was only calculated from THE and was 62 nmol/day. If radioactive labelled cortisol had been used, much larger quantities of urine would have been needed for isolation of sufficient mass of metabolites, even then purification may have been difficult. Steroid profiling of 1 ml urine samples by GC and identification by GC/MS revealed high concentrations of pregnenolone, progesterone, 11 beta-hydroxy progesterone and corticosterone metabolites. Tetrahydrocorticosterone and 5 alpha-tetrahydrocorticosterone were found in urine at elevated excretions of 2.5 and 5.7, 0.9 and 2.0 mumols/24 h, in patients I and II respectively. No cortisol metabolites were detected by routine GC or GC/MS as the low amounts excreted co-eluted with the relatively abundant corticosterone metabolites.     

Simultaneous determination of endogenous and 13C-labelled thyroid hormones in plasma by stable isotope dilution mass spectrometry

This study describes a capillary gas chromatography-mass spectrometry (GC-MS) method for the simultaneous determination of endogenous thyroid hormone (thyroxine, T4) and its 13C-labelled analogue (13C6-thyroxine) in plasma. 13C9-thyroxine was used as analytical internal standard. A double derivatization (CH3OH/HCl and HFBA) inducing good GC mobility was used for the GC-MS analysis of the thyroid hormones. Quantification was carried out by selected ion monitoring (SIM) of specific ions of the fragment ions (m/z 970/976/979). The detection limit of the present GC-MS-SIM method was found to be 100 pg per injection for thyroxine (S/N=3.0). A first implementation in in vivo tests of 13C6-T4 like metabolic tracer was carried out under veterinary control on one cat and one rabbit. The thyroxine follow-up was done by GC-MS and based on double isotopic dilution with two different regio-selective 13C-labelled molecules of the same hormone. The present paper discusses the possibilities and limitations of this methodology. The in vivo experiment demonstrated that the use of stable isotopes and mass spectrometry provide a reliable methodology for hormonal monitoring.     

Characterization of a novel hemoglobin-glutathione adduct that is elevated in diabetic patients.

BACKGROUND: Typically, a diagnosis of diabetes mellitus is based on elevated circulating blood glucose levels. In an attempt to discover additional markers for the disease and predictors of prognosis, we undertook the characterization of HbA1d3 in diabetic and normal patients. MATERIAL AND METHODS: PolyCAT A cation exchange chromatography and liquid chromatography-mass spectroscopy was utilized to separate the alpha- and beta-globin chains of HbA1d3 and characterize their presence in normal and diabetic patients. RESULTS: We report the characterization of HbA1d3 as a glutathionylated, minor hemoglobin subfraction that occurs in higher levels in diabetic patients (2.26 +/- 0.29%) than in normal individuals (1.21 +/- 0.14%, p < 0.001). The alpha-chain spectrum displayed a molecular ion of m/z 15126 Da, which is consistent with the predicted native mass of the HbA0 alpha-globin chain. By contrast, the mass spectrum of the beta-chain showed a mass excess of 307 Da (m/z = 16173 Da) versus that of the native HbA0 beta-globin chain (m/z = 15866 Da). The native molecular weight of the modified beta-globin chain HbA0 was regenerated by treatment of HbA1d3 with dithiothreitol, consistent with a glutathionylated adduct. CONCLUSIONS: We propose that HbA1d3 (HbSSG) forms normally in vivo, and may provide a useful marker of oxidative stress in diabetes mellitus and potentially other pathologic situations.     

Quantification of steroid conjugates using fast atom bombardment mass spectrometry

Fast atom bombardment/mass spectrometry or liquid secondary ion mass spectrometry provides the capability for direct analysis of steroid conjugates (sulfates, glucuronides) without prior hydrolysis or derivatization. During the analysis of biologic extracts, limitations on the sensitivity of detection arise from the presence of co-extracted material which may suppress or obscure the analyte signal. A procedure is described for the quantitative determination of dehydroepiandrosterone sulfate in serum which achieved selective isolation of the analyte using immunoadsorption extraction and highly specific detection using tandem mass spectrometry. A stable isotope-labeled analog [( 2H2]dehydroepiandrosterone sulfate) was used as internal standard. Fast atom bombardment of dehydroepiandrosterone sulfate yielded abundant [M-H]- ions that fragmented following collisional activation to give HSO4-; m/z 97. During fast atom bombardment/tandem mass spectrometry of serum extracts, a scan of precursor ions fragmenting to give m/z 97 detected dehydroepiandrosterone sulfate and the [2H2]-labeled analog with a selectivity markedly superior to that observed using conventional mass spectrometry detection. Satisfactory agreement was observed between quantitative data obtained in this way and data obtained by gas chromatography/mass spectrometry of the heptafluorobutyrates of dehydroepiandrosterone sulfate and [2H2]dehydroepiandrosterone sulfate obtained by direct derivatization.     

Accurate quantification of dimethylamine (DMA) in human urine by gas chromatography-mass spectrometry as pentafluorobenzamide derivative: evaluation of the relationship between DMA and its precursor asymmetric dimethylarginine (ADMA) in health and disease

Dimethylamine [DMA, (CH(3))(2)NH)] is abundantly present in human urine. Main sources of urinary DMA have been reported to include trimethylamine N-oxide, a common food component, and asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis. ADMA is excreted in the urine in part unmetabolized and in part after hydrolysis to DMA by dimethylarginine dimethylaminohydrolase (DDAH). Here we describe a GC-MS method for the accurate and rapid quantification of DMA in human urine. The method involves use of (CD(3))(2)NH as internal standard, simultaneous derivatization with pentafluorobenzoyl chloride and extraction in toluene, and selected-ion monitoring of m/z 239 for DMA and m/z 245 for (CD(3))(2)NH in the electron ionization mode. GC-MS analysis of urine samples from 10 healthy volunteers revealed a DMA concentration of 264+/-173 microM equivalent to 10.1+/-1.64 micromol/mmol creatinine. GC-tandem MS analysis of the same urine samples revealed an ADMA concentration of 27.3+/-15.3 microM corresponding to 1.35+/-1.2 micromol/mmol creatinine. In these volunteers, a positive correlation (R=0.83919, P=0.0024) was found between urinary DMA and ADMA, with the DMA/ADMA molar ratio being 10.8+/-6.2. Elevated excretion rates of DMA (52.9+/-18.5 micromol/mmol creatinine) and ADMA (3.85+/-1.65 micromol/mmol creatinine) were found by the method in 49 patients suffering from coronary artery disease, with the DMA/ADMA molar ratio also being elevated (16.8+/-12.8). In 12 patients suffering from end-stage liver disease, excretion rates of DMA (47.8+/-19.7 micromol/mmol creatinine) and ADMA (5.6+/-1.5 micromol/mmol creatinine) were found to be elevated, with the DMA/ADMA molar ratio (9.17+/-4.2) being insignificantly lower (P=0.46). Between urinary DMA and ADMA there was a positive correlation (R=0.6655, P<0.0001) in coronary artery disease, but no correlation (R=0.27339) was found in end-stage liver disease.     

Kinetics of cortisol metabolism and excretion. A hypothetic model based on the cumulative urinary radioactivity in eight multiple pituitary deficient patients.

A new model is proposed to study the kinetics of [3H]cortisol metabolism by using urinary data only. The model consists of 5 pools, in which changes of the fractions of dose are given by a system of 5 ordinary differential equations. After i.v. administration of [3H]cortisol to 8 multiple pituitary deficient (MPD) patients (group I) the urines from each patient were collected in 9-15 portions during the following 3 days. From the urinary data the rate constants of cortisol metabolism were calculated. A published set of urinary data from patients with a normal cortisol metabolism (group II) was used for comparison. The overall half-life of the label in the circulation was 30 min for both groups; the half-life of the label excretion by both groups was 6 h and the time of maximal activity in the main metabolizing pool was 1.8 h in group I and 1.5 h in group II. The 20% of normal cortisol production rate (CPR) in the 8 MPD patients amounted to 7.2 +/- 1.9 mumol/(m2*d). Therefore, the low CPR but normal rate constants, i.e. a normal metabolic clearance rate of cortisol, in the MPD patients suggest a sensitive adjustment of the cortisol response in the target organs.     

Candidate definitive method for the determination of cortisol in human serum

As a substantial part in the development of a reference material in clinical chemistry, a highly accurate and precise isotope dilution mass spectrometric method has been worked out for the determination of cortisol in human serum. The candidate definitive method consists of addition of 4-[14C]cortisol and, following equilibration, solvent extraction of cortisol and its internal standard from the serum matrix. After conversion into methoxime-trimethylsilyl derivatives, the extract is purified by gel chromatography. Measurements are made by combined capillary gas chromatography mass spectrometry. The ratio of peak heights at m/z 605 and 607 for each sample and calibration mixtures is used for quantification. To ensure maximum accuracy each set of calibration mixtures was composed from two stock solutions and closely bracketed the anticipated serum concentration. An analysis of variance, involving comparison of within-run and between-run variability, gave a total coefficient of variation (CV) of 0.38% for a serum pool containing 90.79 ng cortisol ml-1 serum.     

Determination of the redox properties of human NADPH-cytochrome P450 reductase

Midpoint reduction potentials for the flavin cofactors in human NADPH-cytochrome P450 oxidoreductase were determined by anaerobic redox titration of the diflavin (FAD and FMN) enzyme and by separate titrations of its isolated FAD/NADPH and FMN domains. Flavin reduction potentials are similar in the isolated domains (FAD domain E(1) [oxidized/semiquinone] = -286 +/- 6 mV, E(2) [semiquinone/reduced] = -371 +/- 7 mV; FMN domain E(1) = -43 +/- 7 mV, E(2) = -280 +/- 8 mV) and the soluble diflavin reductase (E(1) [FMN] = -66 +/- 8 mV, E(2) [FMN] = -269 +/- 10 mV; E(1) [FAD] = -283 +/- 5 mV, E(2) [FAD] = -382 +/- 8 mV). The lack of perturbation of the individual flavin potentials in the FAD and FMN domains indicates that the flavins are located in discrete environments and that these environments are not significantly disrupted by genetic dissection of the domains. Each flavin titrates through a blue semiquinone state, with the FMN semiquinone being most intense due to larger separation (approximately 200 mV) of its two couples. Both the FMN domain and the soluble reductase are purified in partially reduced, colored form from the Escherichia coli expression system, either as a green reductase or a gray-blue FMN domain. In both cases, large amounts of the higher potential FMN are in the semiquinone form. The redox properties of human cytochrome P450 reductase (CPR) are similar to those reported for rabbit CPR and the reductase domain of neuronal nitric oxide synthase. However, they differ markedly from those of yeast and bacterial CPRs, pointing to an important evolutionary difference in electronic regulation of these enzymes.     

Gas chromatographic-mass spectrometric determination of isotopic enrichment of 6-15NH2 in adenine nucleotides

A gas chromatographic-mass spectrometric method for the determination of isotopic abundance in [6-15NH2]adenine nucleotides is described. The method involves formation of the di-t-butyldimethylsilyl (TBDMS) derivative of adenine following isolation of the nucleotide fraction with solid-phase ion-exchange chromatography and subsequent acid hydrolysis of nucleotides to free base. Mass spectra for both adenine-diTBDMS and [6-15NH2]adenine-diTBDMS were obtained to identify those ions containing the 6-NH2 moiety. The base peak (m/z 306) was formed by loss of C4H9 (57) and constitutes approximately one-third of the total ion current. Using selected ion monitoring of the m/z 306/m/z 307 ratio, levels of isotopic abundance of 1.0-50.0 mol% excess could be measured reproducibly with the injection of 10-20 pmol of the adenine-diTBDMS derivative obtained from isolated rat hepatocytes. Confirmation that measured isotopic abundance was referable to labeling of the 6-15NH2 group was obtained by oxidation of adenine to hypoxanthine and determination of enrichment in the hypoxanthine-diTBDMS derivative. The method was used to study the formation of [6-15NH2]adenine nucleotides during the incubation of isolated rat hepatocytes with [15N]alanine. A level of approximately 6.0 mol% excess was observed at 60 min incubation.     

The time-course of ACTH stimulation of cortisol synthesis by the immature ovine foetal adrenal gland.

The aim of this study was to establish the time-course of foetal adrenal gland activation by ACTH at a period of intra-uterine development during which adrenal function is minimal (100-120 days of gestation). Blood samples for cortisol analysis were collected at 6-h intervals during the 24 h ACTH (0.05, 0.5 and 5.0 micrograms/h) infusion and during the subsequent 24-h period following cessation of the infusion. Plasma cortisol concentrations were measured using a newly developed radioimmunoassay, whose sensitivity was found to be comparable to that of the validated double-isotope dilution derivative method. There was a significant increase in foetal plasma cortisol concentration, from 3.9 +/- 1 to 17.8 +/- 1.9 nmol/l, within 12 h of commencement of the 2 higher doses of ACTH. Values are mean +/- SEM; n = 5. Following termination of the infusion, cortisol levels fell significantly by the first 6 h, returning to basal levels thereafter. An increase in plasma ACTH from 4.6 +/- 0.6 to 8.4 +/- 1.0 pmol/l was sufficient to initiate a significant increase in cortisol production. The results suggest that the normal low values of cortisol at this period of gestation result from inadequate endogenous ACTH production at this stage.     

Hydroxysteroid dehydrogenase transformations of 5β-scymnol and identification of oxoscymnol transformation products by liquid chromatography-tandem mass spectroscopy

A new and sensitive high performance liquid chromatography (HPLC) separation procedure coupled with tandem mass spectroscopy (MS and MS(2)) detection was developed to identify for the first time the oxidation products of 5β-scymnol [(24R)-(+)-5β-cholestan-3α,7α,12α,24,26,27-hexol] catalysed by bacterial hydroxysteroid dehydrogenase (HSD) reactions in vitro. The authentic scymnol (MW 468) standard yielded a protonated molecular ion [M+H](+) at m/z 469 Da, and higher mass adduct ions attributed to [M+NH(4)](+) (m/z 486), [M+H+CH(3)OH](+) (m/z 501) and [M+H+CH(3)COOH](+) (m/z 530). (24R)-(+)-5β-Cholestan-3-one-7α,12α,24,26,27-pentol (3-oxoscymnol, m/z 467 Da, relative retention time (RRT)=0.89) was identified as the principle molecular species of scymnol in the reaction with 3α-HSD pure enzyme. [S](0.5) for the reaction of 3α-HSD with scymnol as substrate was 0.7292 mM. (24R)-(+)-5β-cholestan-7-one-3α,12α,24,26,27-pentol (7-oxoscymnol, m/z 467 Da, RRT=0.79) and (24R)-(+)-5β-cholestan-12-one-3α,7α,24,26,27-pentol (12-oxoscymnol, m/z 467 Da, RRT=0.81) were similarly identified as principle molecular species in the respective 7α-HSD and 12α-HSD reactions. Polarity of the oxoscymnol species was established as 7-oxoscymnol>12-oxoscymnol>3-oxoscymnol>scymnol (in order from most polar to least polar). Confirmation that 5β-scymnol is an oxidative substrate for steroid-metabolising enzymes was made possible by the use of sophisticated liquid chromatography-mass spectrometry (LC-MS) techniques that will likely provide the basis for further exploration of scymnol as a therapeutic compound.