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Biomedical subjects

Dirk O Stichtenoth

Publications and source records attributed to Dirk O Stichtenoth.

12 recordsLinked to original sources
PubMed2006

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.

Acetazolamide↗
PubMed2005

Determination of 3-nitrotyrosine in human urine at the basal state by gas chromatography-tandem mass spectrometry and evaluation of the excretion after oral intake.

3-Nitrotyrosine (NO(2)Tyr) is a potential biomarker of reactive-nitrogen species (RNS) including peroxynitrite. 3-Nitrotyrosine occurs in human plasma in its free and protein-associated forms and is excreted in the urine. Measurement of 3-nitrotyrosine in human plasma is invasive and associated with numerous methodological problems. Recently, we have described an accurate method based on gas chromatography (GC)-tandem mass spectrometry (MS) for circulating 3-nitrotyrosine. The present article describes the extension of this method to urinary 3-nitrotyrosine. The method involves separation of urinary 3-nitrotyrosine from nitrite, nitrate and l-tyrosine by HPLC, preparation of the n-propyl-pentafluoropropionyltrimethylsilyl ether derivatives of endogenous 3-nitrotyrosine and the internal standard 3-nitro-l-[(2)H(3)]tyrosine, and GC-tandem MS quantification in the selected-reaction monitoring mode under negative-ion chemical ionization conditions. In urine of ten apparently healthy volunteers (years of age, 36.5+/-7.2) 3-nitrotyrosine levels were determined to be 8.4+/-10.4 nM (range, 1.6-33.2 nM) or 0.46+/-0.49 nmol/mmol creatinine (range, 0.05-1.30 nmol/mmol creatinine). The present GC-tandem MS method provides accurate values of 3-nitrotyrosine in human urine at the basal state. After oral intake of 3-nitro-l-tyrosine by a healthy volunteer (27.6 microg/kg body weight) 3-nitro-l-tyrosine appeared rapidly in the urine and was excreted following a biphasic pharmacokinetic profile. Approximately one third of administered 3-nitro-l-tyrosine was excreted within the first 8 h. The suitability of the non-invasive measurement of urinary 3-nitrotyrosine as a method of assessment of oxidative stress in humans remains to be established.

Administration, Oral↗
PubMed2005

Effects of specific COX-2-inhibition on renin release and renal and systemic prostanoid synthesis in healthy volunteers.

BACKGROUND: The renin-angiotensin system plays a critical role in cardiovascular function, but little is known about the effects of specific cyclooxygenase 2 (COX-2) inhibition on this system in healthy humans under physiologic conditions. METHODS: Twenty-one healthy female volunteers received, in a randomized, double-blind, crossover study, celecoxib 200 mg twice a day, indomethacin 50 mg three times a day, or placebo for 4 days and a single dose, each, on day 5. On day 5 of each treatment, the following parameters were assessed with subjects in an upright position before and after administration of 20 mg furosemide intravenously: plasma renin activity (PRA), plasma aldosterone, serum and urine electrolytes, and creatinine. Index metabolites of prostanoids were analyzed by gas chromatography-tandem mass spectrometry in 24-hour urine on day 4 and in 2-hour urines before and after furosemide administration. RESULTS: Baseline and furosemide-stimulated PRA were reduced to a similar degree by celecoxib and indomethacin. Plasma aldosterone and urinary excretion of potassium showed changes consistent with the alteration of PRA. Urinary excretion rates of prostaglandin E(2), (PGE(2)), 7alpha-hydroxy-5, 11-diketotetranor-prosta-1,16-dioic acid (PGE-M), and 2,3-dinor-thromboxane B(2) (TxB(2)) were not reduced by celecoxib, whereas indomethacin led to a decrease of 40%, 45%, and 80%, respectively. Both active treatments inhibited urinary excretion of 2,3-dinor-6-keto-PGF(1alpha) and 6-keto-PGF(1alpha) by 60% and 40%, respectively. CONCLUSION: Renin-release in healthy humans with normal salt intake is COX-2 dependent. While COX-1 is critical for renal and systemic PGE(2) production, renal prostacyclin synthesis is apparently COX-2 dependent. Finally, the previously demonstrated shift of the thromboxane-prostacyclin balance toward prothrombotic thromboxane by specific COX-2 inhibition is confirmed.

6-Ketoprostaglandin F1 alpha↗
PubMed2004

Effects of carvedilol on oxidative stress in human endothelial cells and healthy volunteers.

OBJECTIVE: Carvedilol is a nonselective beta- and alpha(1)-receptor antagonist with additional antioxidant properties in vitro. In this study, we assessed the antioxidative potential of carvedilol in cell culture and in antihypertensive doses in healthy men. METHODS: In vitro, human cultured endothelial cells were treated with native low-density lipoprotein (LDL), oxidized LDL or tumor necrosis factor (TNF)alpha in the absence and in the presence of carvedilol (40 micro M); 8-iso-prostaglandin (PG)F(2alpha), as parameter of oxidative stress, was determined in the supernatants. In a double-blind, randomized, cross-over study, 17 healthy men received 25 mg carvedilol b.i.d., 100 mg metoprolol b.i.d. or placebo for 6 days. After each treatment, systemic oxidative stress was assessed by measuring urinary excretion of 8-iso-PGF(2alpha) and 2,3-dinor-5,6-dihydro-8-iso-PGF(2alpha), and the plasma concentration of 3-nitrotyrosine by means of gas chromatography-tandem mass spectrometry. In addition, thiobarbituric acid-reactive substances (TBARS) in plasma were assessed using spectrophotometry. RESULTS: Native LDL and oxidized LDL induced 8-iso-PGF(2alpha) production in endothelial cells. Carvedilol significantly reduced this effect (e.g., for oxidized LDL: 2.66+/-0.22 pg vs 1.46+/-0.14 pg 8-iso-PGF(2alpha) per micro g protein, P<0.05). In healthy volunteers, carvedilol and metoprolol markedly decreased blood pressure and heart rate, but had no statistically significant effect on any indicator of oxidative stress measured. Remarkably, a trend toward reduction of urinary isoprostanes and 3-nitrotyrosine in plasma by both active treatments was observed, suggesting a non-specific antioxidative effect by beta blockade. CONCLUSIONS: In vitro, the antioxidative potential of carvedilol was confirmed. In healthy men, antihypertensive doses of carvedilol exert no specific inhibition of oxidative stress.

Adrenergic Antagonists↗
PubMed2003

Temporal profiles of cerebrospinal fluid leukotrienes, brain edema and inflammatory response following experimental brain injury.

The post-traumatic changes of leukotrienes LTC4, LTD4, LTE4, and LTB4 in cerebrospinal fluid of rats from 10 min to 7 days were investigated after controlled cortical impact in relation to brain edema and cellular inflammatory response. LTC4 increased five-fold at 4 h, normalized at 24 h, and showed another four-fold increase at 7 days. The same pattern was observed for LTD4 and LTE4. LTB4 however, behaved differently: concentrations were lower and levels peaked two-fold at 24 h. Edema in the injured hemisphere increased continuously up to 24 h without change contralaterally. Leukocyte infiltration, macrophage presence and microglia activation were most prominent at 24 h, 7 days and 24 h respectively. Leukotriene changes in CSF seem to reflect those in the affected tissue, with a time delay and in lower concentrations, and were not linearly correlated to brain edema. The initially high leukotriene levels are rather likely to contribute to the cytotoxic edema than to enhance a vasogenic edema component. The profile of LTB4 was parallel to the time course of leukocyte infiltration, indicating initiation of infiltration as well as prolonged production by leukocytes themselves. The second leukotriene peak at 7 days is likely to follow a different pathway and might be related to a production in macrophages or activated glia.

Animals↗
PubMed2003

The second generation of COX-2 inhibitors: what advantages do the newest offer?

The discovery of two cyclooxygenase (COX)-isoenzymes, a constitutive COX-1, serving homeostatic prostanoid synthesis, and an inducible COX-2, responsible for proinflammatory prostanoid production, led to the development of new non-steroidal anti-inflammatory drugs (NSAIDs), the selective COX-2 inhibitors, promising minimal NSAID-typical toxicity with full anti-inflammatory efficacy. So far, the strategy of selective COX-2 inhibition has been successful. Selective COX-2 inhibitors have significantly less gastrotoxicity and no effects on platelet aggregation. However, with regard to renal adverse events, selective COX-2 inhibitors do not offer a clinically relevant advantage over non-selective inhibitors. Moreover, concerns over the cardiovascular risk of selective COX-2 inhibitors have recently been raised. The second generation of COX-2 inhibitors with higher COX-2 selectivity was developed with the promise of further reduction of NSAID-typical adverse effects. The leading compounds are valdecoxib, parecoxib, etoricoxib and lumaricoxib. At the present time they have proven efficacy for the treatment of pain and inflammation. Parecoxib as a parenteral, highly selective COX-2 inhibitor has the potential to become the NSAID of choice for treatment of postoperative pain. In clinical trials, valdecoxib, parecoxib, etoricoxib and lumaricoxib have caused no more endoscopic ulcers than placebo. However, to date, no data on the clinically relevant endpoints perforation, symptomatic ulcer and bleeding are available. Furthermore, no definite conclusions on renal and cardiovascular safety are possible. Current evidence points to a marginal, if any, gain of safety compared with the first generation of COX-2 inhibitors. However, trials with the new COX-2 inhibitors offer the chance to address these open questions of highly selective COX-2 inhibition; that is, thrombogenic risk, sodium and water retention, and interference with tissue repair, in particular, healing of mucosal damage.

Clinical Trials as Topic↗