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Biomedical subjects

M J Mueller

Publications and source records attributed to M J Mueller.

At least 37 records · Page 2Linked to original sources
PubMed1998

Evidence for the formation of dinor isoprostanes E1 from alpha-linolenic acid in plants.

The free radical oxidation of arachidonic acid is known to generate complex metabolites, termed isoprostanes, that share structural features of prostaglandins and exert potent receptor-mediated biological activities. In the present study, we show that alpha-linolenic acid can undergo a similar oxidation process, resulting in a series of isomeric dinor isoprostanes E1. E-ring dinor isoprostane formation from linolenate was found to be catalyzed by soybean lipoxygenase. The main enzymatic products were 13- and 9-hydroperoxylinolenate but in addition, two dinor isoprostane E1 regioisomers were formed with a yield of 0.31%. Identification and quantification of two dinor isoprostane E1 regioisomers in plant cell cultures was achieved by a negative chemical ionization gas chromatography-mass spectrometry method using [18O]dinor isoprostanes E1 as internal standards. Endogenous levels of these compounds were determined in four taxonomically distant plant species and found to be in the range of 4.5 to 60.9 ng/g of dry weight. Thus analogous pathways in animals and plants exist, each leading to a family of prostaglandin-like compounds derived from polyunsaturated fatty acids. It remains to be shown whether the dinor isoprostanes exert biological activities in plants as has been demonstrated for their C20 congeners in mammals.

Alprostadil↗
PubMed1998

Transport of arachidonic acid across the neutrophil plasma membrane via a protein-facilitated mechanism.

Arachidonic acid is the rate-limiting substrate in the biosynthesis of leukotrienes in activated neutrophils. Liberation of arachidonate from intracellular membranes and uptake of exogenous arachidonate are the two principal mechanisms by which the cell can increase the level of this substrate. We investigated arachidonate uptake and export by using intact polymorphonuclear neutrophils and inside-out plasma membrane vesicles thereof. Here we show that the cellular uptake of arachidonate is energy dependent with an energy of activation (EA) of 10.0 kcal/mol and half-saturated at an arachidonate concentration of 4.8 nmol/mg of cell protein. Protein-facilitated transport of arachidonate across the plasma membrane in either direction is sensitive to proteases, chemical protein modifying reagents, anion transport inhibitors, and, most notably, toward several structurally unrelated leukotriene B4 receptor antagonists with IC50 values in the range of 16-44 microM. The inhibitors did not inhibit the diffusional uptake of methyl arachidonate into neutrophils and inside-out plasma membrane vesicles, indicating that a transport protein is required for the rapid uptake of the free acid but not for the uptake of the ester. Other long-chain fatty acids did compete with the uptake of arachidonate in both assay systems, whereas leukotriene B4 did not. This study documents a novel protein-facilitated transport mechanism for arachidonate in neutrophils, potentially involved in transcellular eicosanoid biosynthesis and sPLA2-mediated arachidonate signaling in neutrophils.

Animals↗
PubMed1998

Analysis of the molecular mechanism of substrate-mediated inactivation of leukotriene A4 hydrolase.

The bifunctional leukotriene A4 hydrolase catalyzes the final step in the biosynthesis of the proinflammatory leukotriene B4. During exposure to the substrate leukotriene A4, a labile allylic epoxide, the enzyme is gradually inactivated as a consequence of the covalent binding of leukotriene A4 to the active site. This phenomenon, commonly referred to as suicide inactivation, has previously been rationalized as a mechanism-based process in which the enzyme converts the substrate to a highly reactive intermediate within an activated enzyme-substrate complex that partitions between covalent bond formation (inactivation) and catalysis. To further explore the molecular mechanism of the self-inactivation of leukotriene A4 hydrolase by leukotriene A4, we prepared and analyzed mutated forms of the enzyme that were either catalytically incompetent or fully active but resistant toward substrate-mediated inactivation. These mutants were treated with leukotriene A4 and leukotriene A4 methyl and ethyl esters and subjected to differential peptide mapping and enzyme activity determinations, which showed that inactivation and/or covalent modification can be completely dissociated from catalysis. Our results, together with recent findings described in the literature, argue against a mechanism-based model for suicide inactivation. We conclude that the collected data on the substrate-mediated inactivation of leukotriene A4 hydrolase best conforms to an affinity-labeling mechanism.

Affinity Labels↗
PubMed1998

Radically novel prostaglandins in animals and plants: the isoprostanes.

Animal prostaglandins and plant jasmonates are well-known enzymatically formed cyclopentanoic lipids that have regulatory functions and serve as inducible mediators of host defense reactions. A novel group of prostaglandin-like compounds, the isoprostanes, generated in animals and plants by a nonenzymatic, free radical-catalyzed process, are now suspected to be mediators of oxidant injury in vivo.

Animals↗
PubMed1998

A "step-to" gait decreases pressures on the forefoot.

Physical therapists use various gait training strategies to reduce stress on the lower extremities, but we could find no description or evaluation of the step-to gait using a cane. The purpose of this study was to evaluate the effect of a step-to gait pattern and a cane on peak plantar pressures on the forefoot and the heel. Ten healthy subjects were evaluated (five females, five males, mean age = 24.6 +/- 4.9 years). In addition, one subject with peripheral neuropathy was tested to determine if a patient could be trained to use the step-to walking pattern and show similar results. All subjects were instructed in four walking conditions; step-to with and without a cane and step-through with and without a cane. Walking speed during the step-through pattern (normal walking) was matched to the speed of the step-to pattern. For the 10 healthy subjects, peak plantar pressures and walking speed of each of the four conditions were compared using a 2 x 2 repeated measures analysis of variance. One factor was gait pattern and one factor was use of a cane. Peak plantar pressures decreased an average of 53% on the forefoot but increased an average of 14% on the heel when subjects walked using step-to gait compared with a step-through gait. There was no effect due to use of a cane or walking speed between the conditions. The patient with peripheral neuropathy demonstrated a similar pattern but greater magnitude of changes compared with the healthy subjects. The foot initiating the step-to pattern showed a reduction in peak plantar pressures on the forefoot, probably because the foot remained flat during stance phase and a large push-off was not required. The step-to pattern, however, results in a slower and less symmetrical gait. The use of a step-to gait may be beneficial for patient populations that need to reduce plantar pressures on the forefoot.

Adult↗
PubMed1997

Protein-facilitated export of arachidonic acid from pig neutrophils.

Activated neutrophils release a variety of eicosanoids into the extracellular medium including arachidonic acid, 5-hydroxyicosatetraenoic acid, and leukotriene A4 and B4. In this study, the mechanism of arachidonic acid export has been examined using inside-out plasma membrane vesicles from pig polymorphonuclear leukocytes. Tritiated arachidonic acid associated rapidly with the membrane vesicles and crossed the membrane into the intravesicular space in a time-dependent and saturable manner. Half the maximal influx rate was measured at an arachidonate concentration of 5.7 microM, and a maximal influx velocity of 3.0 nmol/mg x min was determined at pH 6.8. Influx into vesicles was sensitive to a number of common anion transport inhibitors including pentachlorophenol, phloretin, diiodosalicylic acid, and quercetin as well as to the proteases trypsin and Pronase, suggesting a protein-dependent process. Furthermore, influx was temperature-sensitive with an energy of activation of 11.6 kcal/mol. Varying extravesicular concentration of ATP, Na+, or K+ had no impact on arachidonate influx, whereas changes in pH had a profound effect; optimum transport activity was observed at an extravesicular pH of 6, whereas raising the pH to 9.5 essentially abolished uptake. These results indicate and initially characterize a novel protein-facilitated arachidonate export mechanism in pig neutrophils.

Adenosine Triphosphate↗
PubMed1997

Therapeutic footwear: enhanced function in people with diabetes and transmetatarsal amputation.

OBJECTIVE: Patients with diabetes mellitus (DM) and a transmetatarsal amputation (TMA) have considerable deficits in function compared with age-matched controls. The purpose of this study was to determine if therapeutic footwear could improve the functional mobility of patients with DM and TMA. STUDY DESIGN: Repeated-measures design. SETTING: Academic medical center. PATIENTS: Thirty subjects (10 women, 20 men) with DM and a TMA, with a mean age of 61.7 +/- 4.0 yrs. INTERVENTIONS: Six types of footwear evaluating the following components: length of shoe (full-length or short shoe), a rigid rocker-bottom sole, and an ankle-foot-orthosis. OUTCOME MEASURES: Physical Performance Test (PPT), functional reach, and walking speed. Measurements in each footwear condition occurred after a 1-month adjustment period. RESULTS: Patients wearing full-length custom-made shoes with a total-contact insert, a rigid rocker-bottom sole or a short shoe with a rigid rocker-bottom sole (with or without an ankle-foot-orthosis) had similar and significantly higher scores in the PPT and faster walking speed than when wearing regular shoes with a toe filler (p < .05). The short shoe and the ankle-foot-orthosis, however, generated many patient complaints about cosmesis and restriction at the ankle, respectively. There were no differences in any of the measures of functional reach. CONCLUSION: Although there are individual exceptions, we recommend the full-length shoe, total-contact insert, and a rigid rocker-bottom sole for most patients with DM and a TMA.

Activities of Daily Living↗
PubMed1997

Functional limitations in patients with diabetes and transmetatarsal amputations.

BACKGROUND AND PURPOSE: Reports in the surgical and rehabilitation literature suggest that patients with transmetatarsal amputations (TMAs) function well with regular shoes and a toe filler. Functional limitations, however, have not been documented in this population. The purpose of this study was to compare the function of patients with diabetes mellitus (DM) and TMA with that of age- and gender-matched control subjects. SUBJECTS: Thirty subjects (15 subjects with DM and TMAs and 15 control subjects), with a mean age of 62.3 years (SD = 9.2, range = 43-83), were studied. METHODS: Function was measured using the Functional Reach Test (FRT), the Physical Performance Test (PPT), walking speed for 15.2 m (50 ft), and the Sickness Impact Profile (SIP). Subjects in the TMA-DM group wore standard shoes with a toe filler. RESULTS: The TMA-DM group scored lower (mean +/- standard deviation) than did the control group on all tests (FRT: 19.1 +/- 8.6 vs 31.5 +/- 9.1 cm [7.5 +/- 3.4 vs 12.4 +/- 3.6 in]; PPT: 18.7 +/- 4.8 vs 24.1 +/- 2.2 points [28 points possible]; walking speed: 51.5 +/- 13.2 vs 75.6 +/- 9.3 m/min; SIP: 17.0 +/- 12.7 vs 3.7 +/- 4.7). CONCLUSION AND DISCUSSION: Persons with DM and TMAs have considerable functional limitations. Research is needed to determine whether therapeutic footwear or other forms of rehabilitation can improve their function.

Activities of Daily Living↗
PubMed1997

Induction of 12-oxo-phytodienoic acid in wounded plants and elicited plant cell cultures.

Jasmonic acid (JA) is rapidly biosynthesized from alpha-linolenic acid in plants upon contact with pathogens or wounding, and triggers gene activation, leading to the synthesis of defensive secondary metabolites and proteins. Despite the recent finding that its precursor, 12-oxo-phytodienoic acid (PDA), is a more powerful inducer of gene activation, interest has focused so far almost exclusively on JA. A validated negative chemical ionization-gas chromatography-mass spectrometry method has been developed that allows the simultaneous quantification of endogenous 12-oxo-PDA and JA in plant tissues. In six out of eight plant species tested maximal levels of 12-oxo-PDA exceeded peak levels of JA by approximately 3- to 5-fold after elicitation with a yeast cell wall preparation or when plants were wounded. These experiments support the hypothesis that 12-oxo-PDA acts as the predominant jasmonate signal in most plants, whereas JA remains an active metabolite of its precursor. Furthermore, JA but not 12-oxo-PDA was shown to be secreted into the medium from cultured plant cells, suggesting that JA may also act as an intercellular signal.

Cells, Cultured↗
PubMed1997

Relationships between measures of function, strength and walking speed in patients with diabetes and transmetatarsal amputation.

OBJECTIVE: To determine the correlation between strength and functional measures, and the intercorrelation between the functional measures themselves, in a group of subjects with diabetes mellitus (DM) and transmetatarsal amputation (TMA). DESIGN: Correlational study. SETTING: The subjects were tested in the Applied Kinesiology Laboratory of the Program in Physical Therapy at Washington University School of Medicine, St Louis, MO, USA. SUBJECTS: Thirty subjects with DM and TMA (mean age 61.7 +/- 11.3 years) were studied. MAIN OUTCOME MEASURES: Function was measured using the Functional Reach Test (FR), the Physical Performance Test (PPT), the Sickness Impact Profile (SIP), and walking speed (WS) for 15.24 m. Strength measurements were taken using a hand-held dynamometer. RESULTS: Highest correlations were found between hip extension strength and PPT: r = 0.69, FR: r = 0.45, and WS: r = 0.76, between knee extension strength and PPT: r = 0.48, and WS: r = 0.51, between hip flexion strength and PPT: r = 0.51, FR: r = 0.47, and WS: r = 0.59, between knee flexion strength and PPT: r = 0.57, and WS: r = 0.63, and between dorsiflexion strength and PPT: r = 0.49, and WS: r = 0.63. The following intercorrelations between functional measures were significant; PPT and FR: r = 0.66, PPT and SIP: r = -0.54, PPT and WS: r = 0.77, FR and WS: r = 0.54, SIP and WS: r = -0.47. CONCLUSIONS: The relationship between measures of hip and knee muscle strength and function provides some evidence that rehabilitation should focus on strengthening hip and knee extensors and flexors to improve function. The relationships between walking speed and strength, PPT, FR and SIP suggest that the simple measure of walking speed is a useful functional test in the clinic.

Aged↗
PubMed1997

Therapeutic footwear can reduce plantar pressures in patients with diabetes and transmetatarsal amputation.

OBJECTIVE: To compare how footwear (full-length shoe or short shoe), a total contact insert, a rigid rocker-bottom (RRB) sole, and an ankle-foot orthosis (AFO) affect peak plantar pressure (PPP) on the distal residuum and contralateral extremity of patients with diabetes and transmetatarsal amputation (TMA). RESEARCH DESIGN AND METHODS: Thirty patients with diabetes and TMA participated (mean age 62 +/- 4 years). In-shoe plantar pressures during walking were measured in six types of footwear. Each measurement occurred after a 1-month adjustment period. Repeated measure analysis of variance (ANOVA) was used to compare treatments. RESULTS: All five types of therapeutic footwear reduced plantar pressures compared with regular shoes with a toe-filler (P < 0.05). A full-length shoe, total contact insert, and RRB sole resulted in lower pressures on the distal residuum (222 vs. 284 kPa) and forefoot of the contralateral extremity (197 vs. 239 kPa), compared with a regular shoe and toe-filler. Footwear with an AFO showed reduced PPP on the residuum, but most patients complained of reduced ankle motion during walking. A short shoe reduced pressures on the residuum, but not on the contralateral extremity, and many patients had complaints regarding cosmesis of the shoe. CONCLUSIONS: The full-length shoe, total contact insert, and an RRB sole provided the best pressure reduction for the residuum and contralateral foot, with the optimal compromise for cosmetic acceptance and function.

Adult↗
PubMed1997

Therapeutic footwear helps protect the diabetic foot.

There is evidence to indicate that therapeutic footwear can help prevent lower extremity amputation in patients with diabetes. The primary means of preventing amputation is to protect the insensitive foot from unnoticed trauma and excessive plantar pressures that occur during walking. The specific prescription of the shoe will depend on many foot risk criteria, but particularly on the patient's level of sensation, history of ulceration, and the amount of foot deformity. This article describes the type of footwear recommended for each of these increasing levels of foot risk categories.

Diabetic Foot↗
PubMed1996

Leukotriene A4 hydrolase, mutation of tyrosine 378 allows conversion of leukotriene A4 into an isomer of leukotriene B4.

Leukotriene A4 hydrolase catalyzes the final step in the biosynthesis of the proinflammatory compound leukotriene B4, a reaction which is accompanied by suicide inactivation of the enzyme by leukotriene A4. We have recently reported that Tyr-378 is a major structural determinant for suicide inactivation and that mutation of Tyr-378 into Phe or Gln protects leukotriene A4 hydrolase from this catalytic restriction (Mueller, M. J., Blomster, M., Opperman, U. C. T., Jörnvall, H., Samuelsson, B., and Haeggström, J. Z. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 5931-5935). In the present study, we show that both [Y378F]- and [Y378Q]leukotriene A4 hydrolase converts leukotriene A4 not only into leukotriene B4 but also into a second, previously unknown, product of the enzyme. From biophysical analyses and comparison with a synthetic standard, the structure of this product was determined to 5S,12R-dihydroxy-6,10-trans-8, 14-cis-eicosatetraenoic acid, i.e. Delta6-trans-Delta8-cis-leukotriene B4. The relative formation of Delta6-trans-Delta8-cis-leukotriene B4 versus leukotriene B4 by [Y378F]- and [Y378Q]leukotriene A4 hydrolase, was 18% and 32%, respectively. For [Y378F]leukotriene A4 hydrolase, the turnover of leukotriene A4 into leukotriene B4 or Delta6-trans-Delta8-cis-leukotriene B4 was calculated to 2.5 s-1 which is almost three times the kcat value of the wild type enzyme. Taken together, these findings indicate that Tyr-378 is located at the active site where it assists in the formation of the correct double-bond geometry in the product leukotriene B4.

Binding Sites↗
PubMed1996

Leukotriene A4 hydrolase: protection from mechanism-based inactivation by mutation of tyrosine-378.

Leukotriene A4 (LTA4) hydrolase [(7E,9E,11Z,14Z)-(5S,6S)-5,6-epoxyicosa-7, 9,11,14-tetraenoate hydrolase; EC 3.3.2.6] is a bifunctional zinc metalloenzyme that catalyzes the final step in the biosynthesis of the potent chemotactic agent leukotriene B4 (LTB4). LTA4 hydrolase/aminopeptidase is suicide inactivated during catalysis via an apparently mechanism-based irreversible binding of LTA4 to the protein in a 1:1 stoichiometry. Previously, we have identified a henicosapeptide, encompassing residues Leu-365 to Lys-385 in human LTA4 hydrolase, which contains a site involved in the covalent binding of LTA4 to the native enzyme. To investigate the role of Tyr-378, a potential candidate for this binding site, we exchanged Tyr for Phe or Gln in two separate mutants. In addition, each of two adjacent and potentially reactive residues, Ser-379 and Ser-380, were exchanged for Ala. The mutated enzymes were expressed as (His)6-tagged fusion proteins in Escherichia coli, purified to apparent homogeneity, and characterized. Enzyme activity determinations and differential peptide mapping, before and after repeated exposure to LTA4, revealed that wild-type enzyme and the mutants [S379A] and [S380A]LTA4hydrolase were equally susceptible to suicide inactivation whereas the mutants in position 378 were no longer inactivated or covalently modified by LTA4. Furthermore, in [Y378F]LTA4 hydrolase, the value of kcat for epoxide hydrolysis was increased 2.5-fold over that of the wild-type enzyme. Thus, by a single-point mutation in LTA4 hydrolase, catalysis and covalent modification/inactivation have been dissociated, yielding an enzyme with increased turnover and resistance to mechanism-based inactivation.

Base Sequence↗
PubMed1996

Generalizability of in-shoe peak pressure measures using the F-scan system.

In-shoe pressure analysis can be useful in the management of a variety of foot and ankle problems, but guidelines are needed to determine the practical limitations of the measures. The primary purpose of this study was to determine the reliability of peak plantar pressures taken with the F-Scan system over multiple steps, sensors, and days, and using a force platform for additional calibration. Data were collected on 10 healthy subjects as they walked across a force platform for a minimum of three trials on four separate sessions that were 1 week apart. Using a mean of three steps with a single sensor on 1 day, generalizability coefficients were 0.75 for manufacturer calibration and 0.82 with force platform calibration; reliability coefficients for absolute decisions (index of dependability) were 0.60 for manufacturer calibration and 0.76 with force platform calibration. Force measures from the F-Scan and force platform were highly correlated (r = 0.93), but the absolute difference between the measures varied between sensors and over time. RELEVANCE:--Peak pressure measures taken from a mean of three steps with procedures outlined by the F-Scan manufacturer provide pressure values that demonstrate adequate reliability for clinical and research purposes when rank ordering of measures is indicated. If measures are to be used for making absolute decisions (e.g., identifying a threshold for injury), calibration from a stable source such as a force platform is recommended.

Journal Article↗