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Biomedical subjects

Michael J Dunn

Publications and source records attributed to Michael J Dunn.

At least 37 records · Page 2Linked to original sources
PubMed2005

The utility of N,N-biotinyl glutathione disulfide in the study of protein S-glutathiolation.

Glutathione disulfide (GSSG) accumulates in cells under an increased oxidant load, which occurs during neurohormonal or metabolic stimulation as well as in many disease states. Elevated GSSG promotes protein S-glutathiolation, a reversible post-translational modification, which can directly alter or regulate protein function. We developed novel strategies for the study of protein S-glutathiolation that involved the simple synthesis of N,N-biotinyl glutathione disulfide (biotin-GSSG). Biotin-GSSG treatment of cells mimics a defined component of oxidative stress, namely a shift in the glutathione redox couple to the oxidized disulfide state. This induces widespread protein S-glutathiolation, which was detected on non-reducing Western blots probed with streptavidin-horseradish peroxidase and imaged using confocal fluorescence microscopy and ExtrAvidin-FITC. S-Glutathiolated proteins were purified using streptavidin-agarose and identified using proteomic methods. We conclude that biotin-GSSG is a useful tool in the investigation of protein S-glutathiolation and offers significant advantages over conventional methods or antibody-based strategies. These novel approaches may find widespread utility in the study of disease or redox signaling models where GSSG accumulation occurs.

Amino Acid Sequence↗
PubMed2005

A method for the determination of minoxidil in hair-regrowth formulations by micellar electrokinetic capillary chromatography.

A method based on micellar electrokinetic capillary chromatography (MEKC) was developed for determination of minoxidil in Rogaine and competing products. The original intent of the work was to offer an orthogonal means to HPLC for testing illicit imitations of Rogaine. However, because the patent has since expired, we offer the procedure as a confirmatory measure to HPLC for assay of generic minoxidil products. The MEKC procedure complements an earlier method based on free solution capillary electrophoresis (FSCE), designed to the same end. Validation was carried out on both a Dionex CES-1, which utilizes gravity injection, and a PE-ABI 270HT, which employs vacuum injection. The procedure was validated for both active pharmaceutical ingredient and for minoxidil solutions. The run buffer is pH 7.0, 20 mM sodium phosphate, 20 mM sodium dodecyl sulfate, with 10% isopropanol; the internal standard is dl-tryptophan. The method bears the attributes of simplicity, ease of use, and short analysis time (12 min). It is selective with respect to known process and degradation impurities. High efficiency was achieved on the CES-1, with a plate count exceeding 200,000 for minoxidil at an elution time of 9 min. Although slight differences in performance were noted across the two instruments, results on both were in conformance with modern day validation expectations. Comparison of MEKC with HPLC resulted in slightly higher values for the former, but all results met registration specifications and internal targets.

Chromatography, High Pressure Liquid↗
PubMed2005

A quantitative investigation into the losses of proteins at different stages of a two-dimensional gel electrophoresis procedure.

We report the results of a systematic investigation to quantify the losses of protein during a well-established two-dimensional polyacrylamide gel electrophoresis (2-DE) procedure. Radioactively labelled proteins ([(14)C]bovine serum albumin and a homogenate prepared from the liver of a rat that had been injected with [(35)S]methionine) were used, and recovery was quantified by digesting pieces of gel in H(2)O(2) and subjecting the digests to liquid scintillation counting. When samples were loaded onto the first dimension immobilised pH gradient strips by in-gel rehydration, recovery of protein from the strips was 44-80% of the amount of protein loaded, depending on the amount of protein in the sample. Most of the unrecovered protein appeared to have adhered to the reswelling tray. Losses during isoelectric focusing (IEF) were much smaller (7-14%), although approximately 2% of the protein appeared to migrate from sample strips to adjacent blank strips in the focussing apparatus. A further 17-24% of the proteins were lost into the buffers during equilibration prior to running in the second dimension. Losses during the second dimension run and subsequent staining with SYPRO Ruby amounted to less than 10%. The overall loss during 2-DE was reduced by approximately 25% when proteins were loaded onto the IEF strips using sample cups instead of by in-gel rehydration. These extensive and variable losses during the 2-DE procedure mean that spot intensities on 2-DE gels cannot be used to derive reliable, quantitative information on the amounts of proteins present in the original sample.

Animals↗
PubMed2004

Attenuation of d-amphetamine-induced disruption of conditional discrimination performance by alpha-flupenthixol.

RATIONALE: Previous evidence suggests that manipulation of forebrain dopamine (DA) systems may impair the use of conditional information to inform goal-directed performance, and this may be related to impairments in the ability to use task-setting cues in schizophrenia. OBJECTIVE: To investigate, using the indirect DA agonist d-amphetamine and the D1/D2 receptor antagonist alpha-flupenthixol, the influence of DAergic manipulation on discrimination performance that requires the use of conditional information to inform goal-directed performance. METHODS: Both instrumental and Pavlovian conditional discriminations were employed in which rats learned to respond appropriately according to the presence of auditory conditional stimuli, and results from these experiments were contrasted with a control Pavlovian-instrumental transfer task. RESULTS: Experiment 1 showed a disruption of instrumental conditional discrimination performance by d-amphetamine at 1.5 mg/kg and attenuation of correct responding following 1.0 mg/kg. Disruption with both doses was observed in experiment 2 using a conditional discrimination based on Pavlovian, conditioned responding. Results from a control Pavlovian-instrumental transfer task (experiment 3) revealed that d-amphetamine (0.5, 1.0 and 1.5 mg/kg) did not have any detrimental effect on subjects' basic sensory, motor or motivational processes. Experiment 4 showed that d-amphetamine disruption of instrumental conditional discrimination was attenuated by pre-treatment with the D1/D2 receptor antagonist alpha-flupenthixol. CONCLUSION: These results demonstrate that tasks dependent on conditional relationships are highly sensitive to manipulation of DAergic systems.

Animals↗
PubMed2004

Detection and mapping of widespread intermolecular protein disulfide formation during cardiac oxidative stress using proteomics with diagonal electrophoresis.

Regulation of protein function by reversible cysteine-targeted oxidation can be achieved by multiple mechanisms, such as S-glutathiolation, S-nitrosylation, sulfenic acid, sulfinic acid, and sulfenyl amide formation, as well as intramolecular disulfide bonding of vicinal thiols. Another cysteine oxidation state with regulatory potential involves the formation of intermolecular protein disulfides. We utilized two-dimensional sequential non-reducing/reducing SDS-PAGE (diagonal electrophoresis) to investigate intermolecular protein disulfide formation in adult cardiac myocytes subjected to a series of interventions (hydrogen peroxide, S-nitroso-N-acetylpenicillamine, doxorubicin, simulated ischemia, or metabolic inhibition) that alter the redox status of the cell. More detailed experiments were undertaken with the thiol-specific oxidant diamide (5 mm), a concentration that induces a mild non-injurious oxidative stress. This increase in cellular oxidation potential caused global intermolecular protein disulfide formation in cytosolic, membrane, and myofilament/cytoskeletal compartments. A large number of proteins that undergo these associations were identified using liquid chromatography-mass spectrometry/mass spectrometry. These associations, which involve metabolic and antioxidant enzymes, structural proteins, signaling molecules, and molecular chaperones, were confirmed by assessing "shifts" on non-reducing immunoblots. The observation of widespread protein-protein disulfides indicates that these oxidative associations are likely to be fundamental in how cells respond to redox changes.

Animals↗
PubMed2004

The Rac/Cdc42 guanine nucleotide exchange factor beta1Pix enhances mastoparan-activated Gi-dependent pathway in mast cells.

Carbachol stimulates granule exocytosis, phospholipase C (PLC), and phospholipase D (PLD) in RBL-2H3hm1 mast cells by a mechanism that involves Galphaq. However, mastoparan stimulates the same responses through Gi protein. Both Gi and Galphaq pathways are suppressed by Clostridium difficile toxin B, suggesting that Rac and Cdc42 small GTPases are also involved. Over-expression of beta1Pix, a guanine nucleotide exchange factor for Rac and Cdc42, enhances mastoparan-but not carbachol-induced hexosaminidase secretion and PLC and PLD activation. Furthermore, cells expressing beta1Pix exhibit elevated levels of mastoparan-stimulated IP3 production. Taken together, these findings implicate beta1Pix in regulating hexoasaminidase secretion and IP3 production in early stage upon mastoparan stimulation.

Animals↗
PubMed2004

Androgens target prohibitin to regulate proliferation of prostate cancer cells.

Proteins involved in the growth response of prostate cancer cells to androgen were investigated by comparing the proteomes of LNCaP cells treated with vehicle or androgen. Whole-cell lysates were separated by two-dimensional PAGE, and HPLC-MS/MS was used to identify androgen-regulated proteins. Prohibitin, a protein with cell-cycle regulatory activity, was shown to be downregulated by 50% following androgen stimulation. Western blot and reverse transcription-PCR experiments confirmed the result and showed that regulation occurs at the level of transcription. To determine the importance of prohibitin in androgen-stimulated growth, we used transient transfection to overexpress the protein and RNA interference to knock down the protein. Subsequent FACS analysis showed that cells with reduced levels of prohibitin showed a slight but reproducible increase in the percentage of population in cell cycle, while cells with increased prohibitin levels showed a clear reduction in the percentage entering cell cycle, following dihydrotestosterone stimulation, when compared to untransfected controls. Confocal microscopy showed localization of prohibitin in the nucleus as well as the mitochondria of LNCaP cells. It therefore seems that the regulation of prohibitin is a vital part of the cellular growth response to androgen stimulation in LNCaPs and prohibitin may have a nuclear regulatory role in cell-cycle progression.

Amino Acid Sequence↗
PubMed2004

A systematic investigation into the recovery of radioactively labeled proteins from sodium dodecyl sulfate-polyacrylamide gels.

We report the results of a systematic investigation designed to optimize a method for quantifying radioactivity in proteins in sodium dodecyl sulfate-polyacrylamide gels. The method involves dissolving appropriately sized pieces of gel in hydrogen peroxide and heating to 70 degrees C overnight followed by liquid scintillation counting. H(2)O(2) had no effect on the count rates of [(14)C]bovine serum albumin (BSA) when counted in a conventional liquid scintillation system, and the count rates remained stable for several days. Temperatures below 70 degrees C resulted in incomplete extraction of radioactivity from gels containing [(14)C]BSA, but there was also a significant reduction in count rates in samples incubated at 80 degrees C. At 70 degrees C recovery was not affected by the amount of sample loaded onto the gel or by the staining procedure (Coomassie Brilliant Blue or SYPRO Ruby). Recoveries were in the range of 89-94%, and the coefficient of variation for five replicate samples was 5-10%. This method offers a reliable way of measuring the amount of radioactivity in proteins that have been separated by electrophoresis. It may be useful, for example, in quantitative metabolic labeling experiments when it is necessary to know precisely how much tracer has been incorporated into a particular protein.

Animals↗
PubMed2004

Optimization of the first dimension for separation by two-dimensional gel electrophoresis of basic proteins from human brain tissue.

A major cause of poor resolution in the alkaline pH range of two-dimensional electrophoresis (2-DE) gels is unsatisfactory separation of basic proteins in the first dimension. We have compared methods for the separation of basic proteins in the isoelectric focusing dimension of human brain proteins. The combined use of anodic cup-loading and the hydroxyethyldisulphide containing solution (DeStreak) produced better resolution in both analytical and micropreparative protein loaded 2-DE gels than the other methods investigated.

Brain Chemistry↗