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Scott A Brown

Publications and source records attributed to Scott A Brown.

25 records · Page 2Linked to original sources
PubMed2003

The crystal structure of aminoglycoside-3'-phosphotransferase-IIa, an enzyme responsible for antibiotic resistance.

A major factor in the emergence of antibiotic resistance is the existence of enzymes that chemically modify common antibiotics. The genes for these enzymes are commonly carried on mobile genetic elements, facilitating their spread. One such class of enzymes is the aminoglycoside phosphotransferase (APH) family, which uses ATP-mediated phosphate transfer to chemically modify and inactivate aminoglycoside antibiotics such as streptomycin and kanamycin. As part of a program to define the molecular basis for aminoglycoside recognition and inactivation by such enzymes, we have determined the high resolution (2.1A) crystal structure of aminoglycoside-3'-phosphotransferase-IIa (APH(3')-IIa) in complex with kanamycin. The structure was solved by molecular replacement using multiple models derived from the related aminoglycoside-3'-phosphotransferase-III enzyme (APH(3')-III), and refined to an R factor of 0.206 (R(free) 0.238). The bound kanamycin molecule is very well defined and occupies a highly negatively charged cleft formed by the C-terminal domain of the enzyme. Adjacent to this is the binding site for ATP, which can be modeled on the basis of nucleotide complexes of APH(3')-III; only one change is apparent with a loop, residues 28-34, in a position where it could fold over an incoming nucleotide. The three rings of the kanamycin occupy distinct sub-pockets in which a highly acidic loop, residues 151-166, and the C-terminal residues 260-264 play important parts in recognition. The A ring, the site of phosphoryl transfer, is adjacent to the catalytic base Asp190. These results give new information on the basis of aminoglycoside recognition, and on the relationship between this phosphotransferase family and the protein kinases.

Adenosine Triphosphate↗
PubMed2003

Evaluation of the effects of inhibition of angiotensin converting enzyme with enalapril in dogs with induced chronic renal insufficiency.

OBJECTIVE: To determine whether the angiotensin converting enzyme inhibitor enalapril would lower systemic arterial and glomerular capillary pressure and reduce the magnitude of renal injury in a canine model of renal insufficiency. ANIMALS: 18 adult dogs that had renal mass reduced by partial nephrectomy. PROCEDURE: After surgical reduction of renal mass and baseline measurements, dogs in 2 equal groups received either placebo (group 1) or enalapril (0.5 mg/kg, PO, q 12 h; group 2) for 6 months. RESULTS: Values for systemic mean arterial blood pressure determined by indirect and direct measurement after 3 and 6 months of treatment, respectively, were significantly lower in group 2 than in group 1. During treatment, monthly urine protein-to-creatinine ratios were consistently lower in group 2 than in group 1, although values were significantly different only at 3 months. At 6 months, significant reduction in glomerular capillary pressure in group 2 was detected, compared with group 1, but glomerular filtration rate in group 2 was not compromised. Glomerular hypertrophy, assessed by measurement of planar surface area of glomeruli, was similar in both groups. Glomerular and tubulointerstitial lesions were significantly less in group 2, compared with group 1. CONCLUSIONS AND CLINICAL RELEVANCE: Data suggest that inhibition of angiotensin converting enzyme was effective in modulating progressive renal injury, which was associated with reduction of glomerular and systemic hypertension and proteinuria but not glomerular hypertrophy. Inhibition of angiotensin converting enzyme may be effective for modulating progression of renal disease in dogs.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2002

Effects of the calcium channel antagonist amlodipine in cats with surgically induced hypertensive renal insufficiency.

OBJECTIVE: To determine whether amlodipine besylate decreases systemic arterial blood pressure (BP) and reduces the prevalence of complications in cats with induced hypertensive renal insufficiency. ANIMALS: 20 cats with partial nephrectomy. PROCEDURE: Following reduction in renal mass, 10 cats were administered 0.25 mg of amlodipine/kg, PO, q 24 h (group A). Ten cats served as a control group (group C). Systolic BP (SBP), diastolic BP (DBP), and mean BP (MBP), physical activity, and pulse rate were measured continuously for 36 days by use of radiotelemetric devices. RESULTS: Compared with values for clinically normal cats, SBP, DBP, and MBP were significantly increased in cats of group C. Cats in group A had significant reductions in SBP, DBP, and MBP, compared with values for cats in group C. Albuminuria but not urine protein-to-creatinine ratio was significantly correlated (R2 = 0.317) with SBP in hypertensive cats. Prevalence of ocular lesions attributable to systemic hypertension in group C (7 cats) was greater than that observed in group A (2). Two cats in group C were euthanatized on day 16 because of nuerologic complications attributed to systemic hypertension. One normotensive cat in group A was euthanatized because of purulent enteritis of unknown cause on day 27. CONCLUSIONS AND CLINICAL RELEVANCE: Amlodipine had an antihypertensive effect in cats with coexistent systemic hypertension and renal insufficiency. Its use may improve the prognosis for cats with systemic hypertension by decreasing the risk of ocular injury or neurologic complications induced by high BP.

Albuminuria↗
PubMedDate not supplied

Evaluation of cystatin C as an endogenous marker of glomerular filtration rate in dogs.

Cystatin C is a cysteine protease inhibitor produced by all nucleated cells. It is freely filtered by the glomerulus and is unaffected by nonrenal factors such as inflammation and gender. Because of greater sensitivity and specificity, cystatin C has been proposed to replace creatinine as a marker of glomerular filtration rate (GFR) in humans. The aims of this study were to validate an automated assay in canine plasma and to evaluate the usefulness of cystatin C as a marker of GFR in dogs. Western blotting was used to demonstrate cross-reactivity of an anti-human cystatin C antibody. An immunoturbidimetric assay was used to detect cystatin C in 25 clinically healthy dogs and 25 dogs with renal failure. Mean cystatin C concentration in the healthy dogs and the dogs with renal failure was 1.08 +/- 0.16 mg/L and 4.37 +/- 1.79 mg/L respectively. Intra- and interassay variability was <5%. The assay was linear (r = .974) between 0.14 and 7.53 mg/L. Both cystatin C and creatinine concentrations were measured in banked, frozen serum from 20 remnant kidney model dogs and 10 volume-depleted dogs for which GFR measurements by exogenous creatinine clearance had been determined previously. In the remnant kidney model, cystatin C was better correlated with GFR than creatinine (r = .79 versus .54) but was less well correlated with GFR in volume-depleted dogs (r = .54 versus .95). GFR measurements were repeated in the remnant kidney model dogs 60 days after initial GFR measurements. At this time, cystatin C and creatinine concentrations correlated equally well with GFR (r = .891 versus .894, respectively). Cystatin C concentration is a reasonable alternative to creatinine for screening dogs with decreased GFR due to chronic renal failure.

Animals↗
PubMedDate not supplied

Assessment and management of proteinuria in dogs and cats: 2004 ACVIM Forum Consensus Statement (small animal).

Emerging data indicate that more attention should be given to the detection, evaluation, monitoring, and treatment of dogs and cats with proteinuria. The purposes of this consensus statement are to describe an appropriate approach for accomplishing these tasks and to provide specific recommendations for assessing and managing dogs and cats with proteinuria based on data that are currently available. Because proteinuria and albuminuria have numerous possible causes, they must be assessed appropriately to determine their implications for the patient. This assessment involves localization of the origin of the proteinuria as well as determination of its persistence and magnitude. Because persistent renal proteinuria usually indicates presence of chronic kidney disease, which sometimes is a progressive disorder, its detection identifies dogs and cats that have increased risk for adverse health outcomes. Thus, urine testing that will detect proteinuria should be a component of the clinical evaluations of dogs and cats under all circumstances that prompt their veterinarians to also perform comprehensive hematologic and serum biochemical evaluations. At a minimum, this testing should consist of a complete urinalysis that includes a satisfactorily accurate semiquantitative test for protein, and positive reactions should be properly followed with further testing. The appropriate response to persistent renal proteinuria depends on the magnitude of proteinuria and the status of the patient. The recommended response generally involves continued monitoring, further investigation, and therapeutic intervention, which should be implemented as an escalating series of inclusive, stepwise responses.

Animals↗
PubMedDate not supplied

Multilaboratory trial for determination of ceftiofur residues in bovine and swine kidney and muscle, and bovine milk.

A multilaboratory trial for determining ceftiofur-related residues in bovine and swine kidney and muscle, and bovine milk was conducted following regulatory guidelines of the U.S. Food and Drug Administration, Center for Veterinary Medicine. The methods convert all desfuroylceftiofur-related residues containing the intact beta-lactam ring to desfuroylceftiofur acetamide to establish ceftiofur residues in tissues. Four laboratories analyzed 5 sets of samples for each tissue. Each sample set consisted of a control/blank sample and 3 control samples fortified with ceftiofur at 0.5 Rm, Rm, and 2 Rm, respectively, where Rm is the U.S. tolerance assigned for ceftiofur residue in each tissue/matrix: 0.100 microg/mL for milk, 8.0 microg/g for kidney (both species), 1.0 microg/g for bovine muscle, and 2.0 microg/g for swine muscle. Each sample set also contained 2 samples of incurred-residue tissues (one > Rm and one < Rm) from animals treated with ceftiofur hydrochloride. All laboratories completed the method trial after a familiarization phase and test of system suitability in which they demonstrated > 80% recovery in pretrial fortified test samples. Results showed that the methods met all acceptable performance criteria for recovery, accuracy, and precision. Although sample preparation was easy, solid-phase extraction cartridge performance must be carefully evaluated before samples are processed. The liquid chromatography detection system was easily set up; however, the elution profile may require slight modifications. The procedures could clearly differentiate between violative (> Rm) and nonviolative (< Rm) ceftiofur residues. Participating laboratories found the procedures suitable for ceftiofur residue determination.

Animals↗