Search PubMed⌕ Search

Biomedical subjects

R W Nelson

Publications and source records attributed to R W Nelson.

At least 37 records · Page 2Linked to original sources
PubMed2000

Biosensor chip mass spectrometry: a chip-based proteomics approach.

Rapid advances in genomic sequencing, bioinformatics, and analytical instrumentation have created the field of proteomics, which at present is based largely on two-dimensional electrophoresis (2-DE) separation of complex protein mixtures and identification of individual proteins using mass spectrometry. These analyses provide a wealth of data, which upon further evaluation leads to many questions regarding the structure and function of the proteins. The challenge of answering these questions create a need for high-specificity approaches that may be used in the analysis of biomolecular recognition events and interacting partners, and thereby places great demands on general protein characterization instrumentation and the types of analyses they need to perform. Over the past five years we have been actively involved in interfacing two general, instrumental techniques, surface plasmon resonance-biomolecular interaction analysis (SPR-BIA) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, into a single concerted approach for use in the functional and structural characterization of proteins. Reviewed here is the recent progress made using biomolecular interaction analysis - mass spectrometry (BIA-MS) in the detailed characterization of proteins and protein-protein interactions and the development of biosensor chip mass spectrometry (BCMS) as a new chip-based proteomics approach.

Biosensing Techniques↗
PubMed2000

Oral medications for treating diabetes mellitus in dogs and cats.

Five classes of oral hypoglycaemic drugs and two trace minerals used to treat diabetes mellitus in humans are reviewed and current knowledge on the use of these drugs in diabetic dogs and cats is presented. Oral sulphonylurea drugs stimulate insulin secretion and have been used successfully to treat diabetes in cats but not dogs. Preliminary studies evaluating the efficacy of the biguanide, metformin, in diabetic cats have not been promising. Pharmacokinetic studies have been performed in healthy cats, but clinical studies evaluating the efficacy of the insulin-sensitising drugs, thiazolidinediones, have not been reported. Treatment with the alpha-glucosidase inhibitor, acarbose, improved control of glycaemia in diabetic dogs; similar studies have not been reported in cats. Although chromium picolinate did not improve control of glycaemia in diabetic dogs, vanadium has improved control of the abnormality in diabetic cats.

Administration, Oral↗
PubMed1999

Serum total and ionized magnesium concentrations and urinary fractional excretion of magnesium in cats with diabetes mellitus and diabetic ketoacidosis.

OBJECTIVE: To determine magnesium (Mg) status in cats with naturally acquired diabetes mellitus (DM) and diabetic ketoacidosis (DKA), evaluate changes in Mg status after treatment for DKA, and correlate Mg status with systemic blood pressure and degree of glycemic control. DESIGN: Case series and cohort study. ANIMALS: 12 healthy cats (controls), 21 cats with DM, and 7 cats with DKA. PROCEDURE: Serum total magnesium (tMg) and ionized magnesium (iMg) concentrations and spot urinary fractional excretion of magnesium (FEmg) were determined, using serum and urine samples obtained from all cats when they were entered in the study and from cats with DKA 12, 24, and 48 hours after initiating treatment. Indirect blood pressure and degree of glycemic control were determined in 10 and 21 cats with DM, respectively. RESULTS: Initially, 2 and 13 cats with DM and 1 and 4 cats with DKA had serum tMg and iMg concentrations, respectively, less than the low reference limit (mean-2 SD) determined for controls. In cats with DKA, serum tMg concentration decreased significantly over time after initiating treatment. Urinary FEmg was significantly higher in cats with DM or DKA, compared with controls. Systemic hypertension was not detected nor was there a correlation between Mg status and degree of glycemic control in cats with DM. CONCLUSIONS AND CLINICAL RELEVANCE: Hypomagnesemia was a common finding in cats with DM and DKA and was more readily identified by measuring serum iMg concentration than tMg concentration. The clinical ramifications of hypomagnesemia in such cats remain to be determined.

Animals↗
PubMed1999

A cell-free assay system for beta-catenin signaling that recapitulates direct inductive events in the early xenopus laevis embryo.

In vertebrate embryos, signaling via the beta-catenin protein is known to play an essential role in the induction of the dorsal axis. In its signaling capacity, beta-catenin acts directly to affect target gene transcription, in concert with transcription factors of the TCF/LEF family. We have developed a cell-free in vitro assay for beta-catenin signaling activity that utilizes transcriptionally active nuclei and cytoplasm from cleavage-blocked Xenopus laevis embryos. Under these assay conditions, we demonstrate that either addition of beta-catenin protein or upstream activation of the beta-catenin signaling pathway can induce the expression of developmentally relevant target genes. Addition of exogenous beta-catenin protein induced expression of Siamois, XTwin, Xnr3, and Cerberus mRNAs in a protein synthesis independent manner, whereas a panel of other Spemann organizer-specific genes did not respond to beta-catenin. Lithium induction of the beta-catenin signaling pathway, which is thought to cause beta-catenin accumulation by inhibiting its proteasome-dependent degradation, caused increased expression of Siamois in a protein synthesis independent fashion. This result suggests that beta-catenin derived from a preexisting pool can be activated to signal, and that accumulation of this activated form does not require ongoing synthesis. Furthermore, activation of the signaling pathway with lithium did not detectably alter cytoplasmic beta-catenin levels and was insensitive to inhibition of the proteasome- dependent degradation pathway. Taken together, these results suggest that activation of beta-catenin signaling by lithium in this system may occur through a distinct activation mechanism that does not require modulation of levels through regulation of proteasomal degradation.

Animals↗
PubMed1999

BIA/MS of epitope-tagged peptides directly from E. coli lysate: multiplex detection and protein identification at low-femtomole to subfemtomole levels.

The use of biomolecular interaction analysis mass spectrometry to selectively isolate, detect, and characterize epitope-tagged peptides present in total cell lysates is demonstrated. Epitope-tagged tryptic peptides were captured via affinity interactions with either chelated Ni2+ or monoclonal antibodies and detected using surface plasmon resonance biomolecular interaction analysis (SPR-BIA). After SPR-BIA the tagged peptides were either eluted from the biosensor chips for mass spectrometric analysis or analyzed directly from the biosensor chip using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF). Protein database searches were performed using the masses of the tagged tryptic peptides, resulting in identification of the protein into which the epitope tag was inserted. Detection limits for both SPR-BIA and MALDI-TOF were at the low-femtomole to subfemtomole level. The approach represents a (multiplexed) high-sensitivity chip-based technique capable of identifying epitope-tagged proteins as they are present in complex mixtures.

Amino Acid Sequence↗
PubMed1999

Outcome of surgical versus medical treatment of dogs with beta cell neoplasia: 39 cases (1990-1997).

OBJECTIVE: To compare outcome of surgical versus medical treatment of dogs with beta cell neoplasia. DESIGN: Retrospective study. ANIMALS: 39 dogs with clinical signs of hypoglycemia and serum glucose and insulin concentrations consistent with a diagnosis of beta cell neoplasia. PROCEDURE: Information on signalment; clinical history; physical examination findings; results of CBC, serum biochemical analyses, and urinalysis; serum glucose and insulin concentrations; results of thoracic radiography and abdominal ultrasonography; treatment and treatment complications; survival time; and cause of death were obtained from medical records. RESULTS: 26 dogs underwent exploratory celiotomy and partial pancreatectomy; 13 dogs were treated medically (i.e., dietary change and prednisone). Median survival time was significantly longer for dogs treated surgically than for dogs treated medically. Significant differences were not found in mean age, body weight, duration of clinical signs prior to diagnosis, serum glucose and insulin concentration, or results of other serum biochemical tests between dogs treated surgically and dogs treated medically; also, there was no significant correlation between any of these parameters and survival time for either group of dogs. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that exploratory celiotomy and partial pancreatectomy are indicated once a tentative diagnosis of beta cell neoplasia is established in dogs.

Animals↗
PubMed1999

Comparison of serum fructosamine and blood glycosylated hemoglobin concentrations for assessment of glycemic control in cats with diabetes mellitus.

OBJECTIVE: To correlate serum fructosamine concentrations with established measures of glycemic control and to compare serum fructosamine and blood glycosylated hemoglobin (GHb) concentrations as a means for assessing glycemic control in diabetic cats. DESIGN: Longitudinal cohort study. ANIMALS: 26 healthy cats, 5 cats with stress-induced hyperglycemia, 15 untreated diabetic cats, and 36 treated diabetic cats. PROCEDURE: Control of glycemia was classified and monitored and serum fructosamine and blood GHb concentrations were measured for 12 poorly controlled diabetic cats before and after improving glycemic control, 8 well-controlled treated diabetic cats before and after glycemic control deteriorated, and 5 cats with diabetes mellitus before and after onset of stress-induced hyperglycemia. RESULTS: Mean serum fructosamine and blood GHb concentrations were significantly higher in untreated diabetic cats, compared with healthy cats, and in 24 poorly controlled diabetic cats, compared with 12 well-controlled diabetic cats. Mean serum fructosamine and blood GHb concentrations decreased significantly in 12 poorly controlled diabetic cats after improving glycemic control and increased significantly in 8 well-controlled diabetic cats after glycemic control deteriorated. A significant stress-induced increase in mean blood glucose concentration was evident 12 hours after insulin administration, but not in 5 docile diabetic cats that became fractious. CLINICAL IMPLICATIONS: Serum fructosamine and blood GHb concentrations are clinically useful tools for monitoring control of glycemia in cats with diabetes mellitus.

Animals↗
PubMed1999

Effect of magnesium-deficient diet on serum and urine magnesium concentrations in healthy cats.

OBJECTIVE: To evaluate the efficacy of using serum total and ionized magnesium (Mg) concentrations and urine Mg concentrations to identify Mg deficiency in cats. ANIMALS: 6 healthy castrated male cats. PROCEDURE: A Mg-replete diet was fed for 37 days, followed by a Mg-deficient diet for 37 days. On days 1, 3, and 7 of the last week of each diet, serum ionized and total Mg concentrations were determined; in addition, urine Mg concentration was determined each day of the last week. Serum total and ionized Mg concentrations were compared with urine Mg concentration, amount of Mg excreted during 24 hours (24-hour urine Mg excretion), ratio of urine Mg concentration to urine creatinine concentration (Umg:Ucr), and urinary fractional excretion of Mg (FEmg) to determine which variable best predicted Mg status. RESULTS: Cats fed Mg-deficient diets had significantly lower serum total and ionized Mg concentrations and 24-hour urine Mg excretion values, compared with cats fed Mg-replete diets. Serum total Mg concentration was the best predictor of Mg status. Twenty-four-hour urine Mg excretion was a repeatable, reliable measurement and had the best correlation with serum total Mg concentration. Serum total Mg concentration also correlated with urine Mg concentration, Umg:Ucr, and FEmg. CONCLUSIONS AND CLINICAL RELEVANCE: Serum total and ionized Mg concentrations can be used to identify cats with dietary-induced Mg deficiencies. Twenty-four-hour urine Mg excretion and urine Mg concentration correlated best with serum total Mg concentration and, therefore, may be the most useful urine variables for identifying Mg deficiency.

Animal Feed↗
PubMed1998

Change in serum thyroid-stimulating hormone concentration in response to administration of thyrotropin-releasing hormone to healthy dogs, hypothyroid dogs, and euthyroid dogs with concurrent disease.

OBJECTIVE: To determine whether measuring change in serum thyroid-stimulating hormone (TSH) concentration in response to thyrotropin-releasing hormone (TRH) administration can be used as a test of thyroid function in dogs suspected of having hypothyroidism. DESIGN: Case-cohort study. ANIMALS: 13 healthy dogs, 20 hypothyroid dogs, and 18 euthyroid dogs with concurrent diseases. PROCEDURE: Blood samples were collected before and 30 minutes after TRH administration, and serum TSH concentration was measured. The 13 healthy dogs were used to establish a reference range for change in TSH concentration after TRH administration. The remaining 38 dogs were categorized as hypothyroid or euthyroid on the basis of baseline total thyroxine (T4) and TSH concentrations, T4 concentration 4 hours after TRH administration, and clinical response to administration of sodium levothyroxine. RESULTS: Median baseline TSH concentration was 0.25 ng/ml (range, 0.03 to 0.44 ng/ml) in healthy dogs, 0.93 ng/ml (0.21 to 3.5 ng/ml) in hypothyroid dogs, and 0.21 ng/ml (0.03 to 0.63 ng/ml) in euthyroid dogs with concurrent diseases. Median percentage change in TSH concentration after TRH administration was 207% (range, 25 to 2,200%) in healthy dogs, 24% (-21 to 134%) in hypothyroid dogs, and 167% (69 to 1,800%) in euthyroid dogs with concurrent diseases. Overall accuracy of using the TRH-induced change in TSH concentration to identify hypothyroid dogs was 90%. CLINICAL IMPLICATIONS: Although percentage change in TSH concentration in response to TRH administration can be used to differentiate euthyroid from hypothyroid dogs, the test has little advantage over measurement of baseline TSH and total or free T4 concentration.

Animals↗
PubMed1998

Beta-catenin directly induces expression of the Siamois gene, and can initiate signaling indirectly via a membrane-tethered form.

Beta-catenin is shown to directly induce the expression of siamois (a homeobox-containing gene involved in axial patterning) in a cell-autonomous, protein synthesis independent manner. Siamois can thus be considered a direct target of beta-catenin signaling in Xenopus. Expression of a portion of the armadillo repeat region of beta-catenin via a membrane-tethered fusion protein is shown to give similar levels of siamois induction and axis duplication as a free, untethered form. Reduction of endogenous free beta-catenin levels by overexpression of C-cadherin leads to complete inhibition of signaling by the membrane-tethered repeat region. Since the membrane-tethered repeat region is unlikely to be bound up by C-cadherin, these results show that the membrane-tethered beta-catenin relies on endogenous beta-catenin for signaling. We propose that the membrane-tethered construct acts by titrating a cytoplasmic inhibitor of beta-catenin signaling.

Animals↗
PubMed1998

Systemic hypertension and proteinuria in dogs with diabetes mellitus.

OBJECTIVE: To determine prevalence and severity of systemic arterial hypertension and proteinuria in dogs with naturally developing diabetes mellitus (DM) and to determine whether these abnormalities were related to age, sex, duration of DM, or degree of control of glycemia. DESIGN: Case series and cohort study. ANIMALS: Fifty dogs with naturally developing DM. PROCEDURES: Blood pressure was measured in all 50 dogs. Thirty-eight dogs were evaluated once, and 12 were evaluated sequentially. Thirty-five were evaluated for proteinuria by determining protein-to-creatinine ratio in urine (n = 35) or by electrophoresis of urine (33). RESULTS: Hypertension was detected in 23 on the basis of a systolic pressure > 160 mm HG (12 dogs), a diastolic pressure > 100 mm HG (21), or a mean pressure > 120 mm HG (23). All dogs with systolic hypertension had concurrent diastolic and mean hypertension, and 19 of 21 dogs with diastolic hypertension had concurrent high mean pressure. Ten of 12 dogs reevaluated at subsequent visits had no change in blood pressure. Blood pressure remained consistent in 3 dogs tested at different times during the day on a single visit. Duration of DM and presence of proteinuria were significant predictors of hypertension. Seven of 35 (20%) dogs had an increased protein-to-creatinine ratio in their urine. Albumin concentration and albumin-to-creatinine ratio were significantly higher in urine from diabetic dogs, compared with healthy, nondiabetic dogs. Hypertension was associated with an increased albumin-to-creatinine ratio. CLINICAL IMPLICATIONS: Systemic hypertension and proteinuria may be common in diabetic dogs, but the clinical importance of these findings are, as yet, unknown.

Age Factors↗
PubMed1998

Cobalt 60 irradiation of pituitary gland tumors in three cats with acromegaly.

Acromegaly was diagnosed in 3 cats with insulin-resistant diabetes mellitus (DM) on the basis of history and physical examination findings, which ruled out other causes of insulin-resistant DM, and by documenting high plasma concentrations of growth hormone. Computed tomography revealed a mass in the area of the pituitary gland in each cat. Pituitary gland tumors were irradiated with cobalt 60, and none of the cats developed complications to radiotherapy. Each cat received a total dose of 48 Gy of cobalt 60 during 12 treatments. After completion of radiotherapy, insulin requirements were less for all cats, although in 1 cat, this improvement was transient. Diabetes mellitus resolved in 2 of 3 cats. After treatment, decreases in insulin requirements correlated with decreases in plasma growth hormone concentrations in 2 of 3 cats in which DM resolved. On the basis of these findings, irradiation of pituitary gland tumors appears to be a treatment option for cats with acromegaly.

Acromegaly↗
PubMed1998

Effect of dietary insoluble fiber on control of glycemia in dogs with naturally acquired diabetes mellitus.

OBJECTIVE: To evaluate the effect of a high insoluble-fiber (HF) diet containing 12% cellulose in dry matter and a low insoluble-fiber (LF) diet on control of glycemia in dogs with naturally acquired insulin-dependent diabetes mellitus. DESIGN: Prospective randomized crossover controlled trial. ANIMALS: 11 dogs with naturally acquired diabetes mellitus. PROCEDURE: Dogs were fed HF and LF diets for 8 months each in 1 of 2 randomly assigned diet sequences. Caloric intake and insulin treatment were adjusted as needed to maintain stable body weight and control of glycemia, respectively. After a 2-month adaptation period, control of glycemia was evaluated every 6 weeks for 6 months. Variables assessed included serum glucose concentration measured during the preprandial state, blood glycosylated hemoglobin concentration, serum glucose concentration measured every 2 hours for 24 hours beginning at the time of the morning insulin injection, 24-hour mean serum glucose concentration, mean serum glucose concentration fluctuation from the 24-hour mean serum glucose concentration, and 24-hour urinary excretion of glucose. RESULTS: Significant differences in mean daily caloric intake, body weight, or daily insulin dosage among dogs fed HF and LF diets were not found. Mean preprandial serum glucose concentration, most postprandial serum glucose concentrations, 24-hour mean serum glucose concentration, and 24-hour urinary excretion of glucose were significantly lower in dogs fed the HF diet, compared with the LF diet. CLINICAL IMPLICATIONS: Results of this study support feeding of commercially available insoluble fiber diets to dogs with naturally acquired diabetes mellitus.

Animals↗
PubMed1998

Comparison of serum concentrations of thyroid-stimulating hormone in healthy dogs, hypothyroid dogs, and euthyroid dogs with concurrent disease.

OBJECTIVE: To evaluate use of an assay for measuring serum concentration of canine thyroid-stimulating hormone (cTSH) as an aid for diagnosing thyroid disease in a population of dogs suspected of having hypothyroidism. DESIGN: Case-cohort study. ANIMALS: 62 healthy dogs and 49 dogs with clinical signs consistent with hypothyroidism (16 were hypothyroid and 33 were euthyroid with concurrent disease). PROCEDURE: Samples from healthy dogs were used to establish a reference range for serum cTSH concentration. The 49 dogs were categorized as hypothyroid or euthyroid with concurrent disease on the basis of clinical signs, results of additional diagnostic and thyroid-stimulating hormone (TSH) response tests, and response to administration of levothyroxine sodium. Function of the thyroid gland was considered normal when serum total thyroxine (T4) concentration 6 hours after TSH administration was > 2.5 micrograms/dl. Hypothyroidism was diagnosed when serum T4 concentration after TSH administration was < or = 1.5 microgram/dl. RESULTS: Serum cTSH concentration differed significantly among all 3 groups. Four of 33 (12%) euthyroid dogs had cTSH concentrations that were greater than the reference range, whereas 6 of 16 (38%) hypothyroid dogs had cTSH concentrations within the reference range. Specificity for serum cTSH concentration was 0.88 and sensitivity was 0.63. When interpreted in combination with serum T4 concentration, specificity increased to 1.0. CLINICAL IMPLICATIONS: cTSH assay had good specificity for use in the diagnosis of hypothyroidism in dogs. Because this assay had low sensitivity, a diagnosis of hypothyroidism could not be excluded on the basis of a serum cTSH concentration that was within the reference range.

Animals↗
PubMed1998

Mass spectrometric methods for evaluating point mutations.

Two methods for internally calibrating spectra resulting from the matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry analysis of partially digested proteins are described. Partial digestion of proteins results in a large number of ion signals present in the MALDI-TOF mass spectrum, which in turn represent a significant over-sampling of each amino acid present in the analyte. This over-sampling allows ion signals of undisputed origin to be used as internal calibrants for the evaluation of fragments suspected to contain point mutations. Correlated with the correct amino acid sequence, the mass values of all ion signals (calibrants and analytes) are observed to fall into a single low-error data set. Conversely, empirically derived data applied to an incorrect sequence split the data into subsets of different errors. The methods take advantage of the self-consistent nature of data generated during the enzymatic mass mapping of proteins using MALDI-TOF, and they aid in the rapid, sensitive and accurate evaluation of point mutations present in proteins.

Amino Acid Sequence↗
PubMed1997

Surface plasmon resonance biomolecular interaction analysis mass spectrometry. 2. Fiber optic-based analysis.

Fiber optic probe-based surface plasmon resonance (SPR) detection has been used in combination with matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry for the rapid, sensitive, and selective detection of biomolecules. SPR was used to monitor the covalent immobilization of a polyclonal antibody to the surface of a fiber optic probe. The derivatized probe was then used for the selective detection (from solution) of the corresponding antigen and a secondary antibody directed toward the antigen. Species retained during the SPR detection process were next analyzed by direct MALDI-TOF analysis of the probe surface (after exposed to the MALDI matrix and introduction into the mass spectrometer). The combined approach allowed for the two-dimensional detection of biomolecules, with SPR analysis yielding quantitative information pertinent to the binding events and MALDI-TOF providing details on the qualitative nature of the binding partners.

Animals↗