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The relationship between adiposity, bone density and microarchitecture is maintained in young women irrespective of diabetes status. Clin Endocrinol (Oxf) 2017; 87:327-335. [PMID: 28656591 DOI: 10.1111/cen.13410] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Revised: 05/31/2017] [Accepted: 06/24/2017] [Indexed: 12/26/2022]
Abstract
BACKGROUND The relationship between bone health and adiposity and how it may be affected in people with chronic metabolic conditions is complex. METHODS Seventeen women with type 1 diabetes mellitus (T1DM) and nine age-matched healthy women with a median age of 22.6 years (range, 17.4, 23.8) were studied by 3T MRI and MR spectroscopy to assess abdominal adiposity, tibial bone microarchitecture and vertebral bone marrow adiposity (BMA). Additional measures included DXA-based assessments of total body (TB), femoral neck (FN) and lumbar spine (LS) bone mineral density (BMD) and fat mass (FM). RESULTS Although women with T1DM had similar BMI and BMA to the controls, they had higher visceral and subcutaneous adiposity on MRI (P<.05) and total body FM by DXA (P=.03). Overall, in the whole cohort, a clear inverse association was evident between BMA and BMD at all sites (P<.05). These associations remained significant after adjusting for age, BMI, FM and abdominal adiposity. In addition, visceral adiposity, but not subcutaneous adiposity, showed a positive association with BMA (r, .4, P=.03), and a negative association with total body BMD (r, .5, P=.02). Apparent trabecular separation as assessed by MRI showed an inverse association to total body BMD by DXA (r, -.4, P=.04). CONCLUSION Irrespective of the presence of an underlying metabolic condition, young women display a negative relationship between MRI-measured BMA and DXA-based assessment of BMD. Furthermore, an association between BMA and visceral adiposity supports the notion of a common origin of these two fat depots.
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Abstract
BACKGROUND Type 4 renal tubular acidosis causes hyperkalaemia, for which diabetes and medications commonly used in this patient group are aetiological factors. Here we describe the novel use of fludrocortisone in this difficult condition. CASE REPORT A 55-year-old woman with complex co-morbidities, including Type 2 diabetes (HbA1c 37 mmol/mol 5.5%), was admitted with renal failure. Bloods on admission: eGFR 25 ml/min, creatinine 184 ?mol/L, urea 35.9 mmol/L, sodium 128 mmol/L, potassium 5.6 mmol/L, bicarbonate 15 mmol/L, and albumin 30 g/L. Her admission was prolonged, complicated by hospital-acquired sepsis (lower respiratory tract, urinary tract, and infected leg ulcers), poor venous access and severe depression. She had recurrent hyperkalaemia and deteriorating renal function, from presumed Type 4 renal tubular acidosis and excessive fluid losses from leg ulcers. Her renal function recurrently deteriorated, despite conventional treatment methods. After 69 days, she was commenced on fludrocortisone 50 mcg/day. Her renal function and serum potassium stabilized and she was discharged with potassium 4.3 mmol/L, eGFR 42 ml/min, and bicarbonate 23 mmol/L. She has remained stable on this treatment, without requiring further hospital admission for over 6 months, with eGFR 40 ml/min, and potassium 5.5 mmol/L, and albumin 26 g/L. CONCLUSION This woman was presumed to have Type 4 renal tubular acidosis and recurrent hyperkalaemia due to renal insufficiency, in the context of underlying diabetes and chronic kidney disease, which was poorly responsive to conventional management. There is limited evidence for using fludrocortisone in this setting. Our case suggests that fludrocortisone might offer a novel therapeutic strategy when conventional management is not working.
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A "Diabetes Acute Care Day" for medical students increases their knowledge and confidence of diabetes care: a pilot study. BMC MEDICAL EDUCATION 2016; 16:88. [PMID: 26956764 PMCID: PMC4784451 DOI: 10.1186/s12909-016-0600-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Accepted: 02/23/2016] [Indexed: 06/05/2023]
Abstract
BACKGROUND Evidence suggests that junior doctors lack the confidence and skills to manage acute/inpatient diabetes. We investigated the impact of the introduction of a "Diabetes Acute Care Day" on undergraduate medical students' knowledge and confidence in acute/inpatient diabetes. METHODS Participants attended four short lectures on the basics of diabetes, diabetic emergencies, inpatient diabetes management and peri-operative/procedure care followed by case-based learning tutorials on diabetic ketoacidosis (DKA), hyperosmolar hyperglycaemic state (HHS) and hypoglycaemia using capillary blood glucose charts to interpret and practice subsequent insulin prescription and adjustment. Participants were asked to complete multiple-choice questions and confidence questionnaires using a visual analogue score pre and post participation. RESULTS One hundred forty-four students completed the pre-course survey and 196 completed the post-course survey. Mean confidence using a visual analogue score increased in all areas with a mean at baseline of 46.9 mm rising to 71.2 mm post-participation (p < 0.001). The largest increases were in the management of HHS, patients on subcutaneous and intravenous insulin and perioperative/procedure care. The mean mark obtained in the pre-test multiple choice questions (MCQs) was 2.72 (27.2 %) and increased to 4.74 (47.4 %) on the post-score MCQs (p < 0.001). 56.9 % of participants answered all 10 pre-test MCQs with the mean number of questions answered = 4.71 rising to 82.0 % of students answered all ten questions and the mean number of questions answered = 9.56 in the post-test MCQs. CONCLUSIONS An intensive "Diabetes Acute Care Day" consisting of themed live lectures and case-based learning tutorials is an effective way to increase medical students' knowledge and confidence in acute/inpatient diabetes. Further development and evaluation of this educational intervention is required to assess the impact of on patient care in the clinical setting post graduation.
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Use of metformin in chronic kidney disease should continue to be based on common sense in the absence of an evidence base. Diabet Med 2015; 32:981-2. [PMID: 25645049 DOI: 10.1111/dme.12709] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 01/19/2015] [Indexed: 11/30/2022]
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Abstract
A 54-year-old lady being investigated at the medical clinic for back pain and weight loss, was diagnosed with idiopathic retroperitoneal fibrosis on the basis of CT imaging, biopsy findings and absence of known secondary causes. After lengthy discussions with the patient during several clinic visits she declined the use of corticosteroid treatment due to concerns for the potential side effects. Serial monitoring of inflammatory markers and interval imaging suggested a spontaneous remission in the inflammatory process. We describe the case and discuss the management of retroperitoneal fibrosis.
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Patient education on the benefit and risks of medications goes beyond metformin. Diabet Med 2012; 29:1471-2. [PMID: 22817327 DOI: 10.1111/j.1464-5491.2012.03754.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Abstract
Hypertensive disorders in pregnancy are common and can occur as a result of pre-existing hypertension or as new onset hypertension usually in the second half of pregnancy. In either situation there is potential for considerable perinatal and maternal morbidity and mortality. This review article aims to compare therapeutic options outlined in a selection of national guidelines and to look in more detail at the most commonly prescribed drugs - labetalol, methyldopa and nifedipine - with respect to their pharmacology and the evidence for their use in pregnancy. We will also consider the rationale for identifying and treating hypertension in pregnancy and the effect this can have on short- and long-term maternal and neonatal outcomes.
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Lack of confidence among trainee doctors in the management of diabetes: the Trainees Own Perception of Delivery of Care (TOPDOC) Diabetes Study. QJM 2011; 104:761-6. [PMID: 21511736 PMCID: PMC3158855 DOI: 10.1093/qjmed/hcr046] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
BACKGROUND There is an increased prevalence of diabetes. Doctors in training, irrespective of specialty, will have patients with diabetes under their care. AIM To determine levels of confidence of doctors in training in the management of diabetes and establish their training needs in this area of clinical practice. DESIGN A national online survey of trainee doctors in the UK using a pre-validated questionnaire. METHODS A four-point confidence rating scale was used to rate confidence in the management of diabetes and comparators. A six-point scale was used to quantify how often trainees would contribute to the management of patients with diabetes and trainees were asked about their training in managing diabetes. RESULTS A total of 2149 doctors completed the survey. The percentage 'fully confident' in diagnosing diabetes was 27%, diagnosing and managing hypoglycaemia 55%, diagnosing and managing diabetic ketoacidosis 43%, managing intravenous (IV) insulin 27%, prescribing IV fluids for patients with diabetes 39% and altering diabetes therapy prior to surgery/other procedure 18%. In comparison, 66% and 65% were 'fully confident' in the management of angina and asthma, respectively (P < 0.05). Forty-one percent would take the initiative to optimize glycaemic control for patients under their care >80% of the time. Respectively, 19% and 35% of respondents reported that their undergraduate and postgraduate training had prepared them adequately to optimize treatment of diabetes. The majority (>70%) wanted further training in managing all aspects of diabetes care. CONCLUSIONS Trainee doctors in the UK lack confidence in the management of diabetes, are unlikely to take the initiative to optimize glycaemic control and report a need for further training.
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Metformin action on AMP-activated protein kinase: a translational research approach to understanding a potential new therapeutic target. Diabet Med 2010; 27:1097-106. [PMID: 20854376 DOI: 10.1111/j.1464-5491.2010.03098.x] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Clinical studies in Type 2 diabetes mellitus have shown that the effects of metformin go beyond improving HbA(1c) and include reductions in cardiovascular endpoints. Metformin therapy has been widely used in the treatment of Type 2 diabetes for many years, yet the precise mode of action remains uncertain. It has recently been proposed that metformin-mediated stimulation of hepatic AMP-activated protein kinase (AMPK) underlies the hypoglycaemic effects of metformin. AMPK is a heterotrimeric enzyme that is expressed in many tissues and plays a central role in the regulation of energy homoeostasis. Furthermore, there is increasing evidence that AMPK is implicated in the pathophysiology of cardiovascular and metabolic diseases. The generation of more specific and potent activators of AMPK, however, could have additional metabolic and vascular benefits for patients with Type 2 diabetes.
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Time-kill kinetics of oritavancin and comparator agents against Staphylococcus aureus, Enterococcus faecalis and Enterococcus faecium. J Antimicrob Chemother 2009; 63:1191-9. [DOI: 10.1093/jac/dkp126] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
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Long term treatment with rifampicin for pruritis has implications for warfarin use. Scott Med J 2009. [DOI: 10.1258/rsmsmj.54.1.58g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Warfarin is an established treatment method for anticoagulating patients following diagnosis of deep vein thrombosis (DVT). We present a patient who was on rifampicin treatment for pruritis, secondary to primary biliary cirrhosis (PBC), who was diagnosed with a DVT post operatively. A therapeutic INR was not obtained following fourteen days of warfarin treatment due to a drug interaction with rifampicin. We review the use of rifampicin for pruritis in PBC and the mechanism of interaction between warfarin and rifampicin.
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Non Hodgkin's lymphoma presenting with bone pain and no lymphadenopathy. Scott Med J 2009. [DOI: 10.1258/rsmsmj.54.1.58b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
A 40-year-old female who was an ex-intravenous drug user on methadone presented to the Emergency department reporting all over body pain and was subsequently found to have a diagnosis of non-Hodgkin's B cell lymphoma in the absence of lymphadenopathy. She did not respond to chemotherapy and pain management was difficult. This case demonstrates three things. Firstly, clinicians should be aware that ex- or current intravenous drug users presenting with pain may have significant pathology. Secondly, pain management in patients on methadone can be difficult. Lastly, the case describes an atypical but recognised presentation of lymphoma with bone involvement but no lymphadenopathy.
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Establishing pragmatic estimated glomerular filtration rate thresholds to guide metformin prescribing: careful assessment of risks and benefits is required. Diabet Med 2008; 25:636-7. [PMID: 18346163 DOI: 10.1111/j.1464-5491.2008.02411.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Abstract
Diabetes is a risk factor for cancer and specifically colorectal cancer. It is also associated with increased cancer mortality. Aspirin, non-steroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase 2 (Cox-2) inhibitors have been shown to decrease the incidence of colorectal cancer. This effect may be mediated by inhibiting prostaglandin synthesis. Long-term use of high-dose aspirin and NSAIDs is associated with significant gastrointestinal side effects. Unfortunately, the use of Cox-2 inhibitors is associated with an increased incidence of acute myocardial infarction and death from cardiovascular disease. The increased risk of cardiovascular disease in patients with diabetes results in the loss of the potential to use Cox-2 inhibitors for cancer chemoprophylaxis. Until a safer type of Cox-2 inhibitor is available, or low-dose aspirin is evaluated for chemoprophylaxis, a more intense screening programme for colorectal cancer may be appropriate for patients with diabetes, especially men. Healthcare professionals managing patients with diabetes should be aware of the increased risk of this type of cancer.
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Type 1 (distal) renal tubular acidosis in a patient with Type 1 diabetes mellitus--not all cases of metabolic acidosis in Type 1 diabetes mellitus are due to diabetic ketoacidosis. Diabet Med 2008; 25:114-5. [PMID: 18199141 DOI: 10.1111/j.1464-5491.2007.02334.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Comparison of the Effects of Thioridazine and Mesoridazine on the QT Interval in Healthy Adults After Single Oral Doses. Clin Pharmacol Ther 2007; 82:548-54. [PMID: 17410120 DOI: 10.1038/sj.clpt.6100194] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We compared the effects of single doses of thioridazine and mesoridazine on the heart rate-corrected QT (QTc) interval in healthy adult volunteers. QTc intervals and plasma concentrations of thioridazine, mesoridazine, and metabolites were measured after single oral doses of thioridazine hydrochloride 50 mg, mesoridazine besylate 50 mg, or placebo in a double-blind, crossover study. Mean maximum increases in the QTc interval following thioridazine (37.3+/-4.1 ms, P=0.023) and mesoridazine (46.6+/-7.4 ms, P=0.021) were similar and significantly greater than following placebo (12.9+/-8.1 ms). The area under the effect-time curve over 8 h following drug administration was similar between the two drugs (129.3+/-22.1 vs 148.3+/-43.0 ms h). In conclusion, thioridazine and mesoridazine are associated with similar effects on the QTc interval.
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Effect of a pocket-size tablet-dispensing device on glycaemic control in Type 2 diabetic patients. Diabet Med 2007; 24:101-2; author reply 102. [PMID: 17227335 DOI: 10.1111/j.1464-5491.2007.2010_1.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Low molecular weight heparins--a safer option than unfractionated heparin? ADVERSE DRUG REACTIONS AND TOXICOLOGICAL REVIEWS 2001; 20:256-76. [PMID: 11770172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
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Abstract
BACKGROUND Bacterial resistance to aminoglycoside antibiotics occurs primarily through the expression of modifying enzymes that covalently alter the drugs by O-phosphorylation, O-adenylation or N-acetylation. Aminoglycoside phosphotransferases (APHs) catalyze the ATP-dependent phosphorylation of these antibiotics. Two particular enzymes in this class, APH(3')-IIIa and AAC(6')-APH(2"), are produced in gram-positive cocci and have been shown to phosphorylate aminoglycosides on their 3' and 2" hydroxyl groups, respectively. The three-dimensional structure of APH (3')-IIIa is strikingly similar to those of eukaryotic protein kinases (EPKs), and the observation, reported previously, that APH(3')-IIIa and AAC(6')-APH(2") are effectively inhibited by EPK inhibitors suggested the possibility that these aminoglycoside kinases might phosphorylate EPK substrates. RESULTS Our data demonstrate unequivocally that APHs can phosphorylate several EPK substrates and that this phosphorylation occurs exclusively on serine residues. Phosphorylation of Ser/Thr protein kinase substrates by APHs was considerably slower than phosphorylation of aminoglycosides under identical assay conditions, which is consistent with the primary biological roles of the enzymes. CONCLUSIONS These results demonstrate a functional relationship between aminoglycoside and protein kinases, expanding on our previous observations of similarities in protein structure, enzyme mechanism and sensitivity to inhibitors, and suggest an evolutionary link between APHs and EPKs.
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Abstract
Bacterial resistance to the aminoglycoside antibiotics is manifested primarily through the expression of enzymes which covalently modify these drugs. One important mechanism of aminoglycoside modification is through ATP-dependent O-phosphorylation, catalyzed by a family of aminoglycoside kinases. The structure of one of these kinases, APH(3')-IIIa has recently been determined by x-ray crystallography, and the general fold is strikingly similar to eukaryotic protein kinases (Hon, W. C., McKay, G. A., Thompson, P. R., Sweet, R. M., Yang, D. S. C., Wright, G. D., and Berghuis, A. M. (1997) Cell 89, 887-895). Based on this similarity, we have examined the effect of known inhibitors of eukaryotic protein kinases on two aminoglycoside kinases, APH(3')-IIIa and the enzyme AAC(6')-APH(2") which also exhibits acetyl-CoA-dependent aminoglycoside modification activity. We report that several known protein kinase inhibitors are also good inhibitors of aminoglycoside kinases. Compounds belonging to the isoquinolinesulfonamide group are especially effective in this regard, giving competitive inhibition in the micromolar range with respect to ATP and noncompetitive inhibition versus the aminoglycoside substrate. This study provides the basis for future aminoglycoside kinase inhibitor design and for the development of compounds which could reverse antibiotic resistance in the clinic.
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Structure of an enzyme required for aminoglycoside antibiotic resistance reveals homology to eukaryotic protein kinases. Cell 1997; 89:887-95. [PMID: 9200607 DOI: 10.1016/s0092-8674(00)80274-3] [Citation(s) in RCA: 195] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Bacterial resistance to aminoglycoside antibiotics is almost exclusively accomplished through either phosphorylation, adenylylation, or acetylation of the antibacterial agent. The aminoglycoside kinase, APH(3')-IIIa, catalyzes the phosphorylation of a broad spectrum of aminoglycoside antibiotics. The crystal structure of this enzyme complexed with ADP was determined at 2.2 A. resolution. The three-dimensional fold of APH(3')-IIIa reveals a striking similarity to eukaryotic protein kinases despite a virtually complete lack of sequence homology. Nearly half of the APH(3')-IIIa sequence adopts a conformation identical to that seen in these kinases. Substantial differences are found in the location and conformation of residues presumably responsible for second-substrate specificity. These results indicate that APH(3') enzymes and eukaryotic-type protein kinases share a common ancestor.
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Recognition of aminoglycoside antibiotics by enterococcal-staphylococcal aminoglycoside 3'-phosphotransferase type IIIa: role of substrate amino groups. Antimicrob Agents Chemother 1996; 40:2648-50. [PMID: 8913482 PMCID: PMC163593 DOI: 10.1128/aac.40.11.2648] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The interactions of the aminoglycoside 3'-phosphotransferase IIIa with aminoglycoside antibiotics lacking specific amino groups were examined by steady-state kinetic analyses. The results demonstrate that an amino group on C-1 and either an amino or a hydroxyl group at the 2' and 6' positions are important for detoxification of aminoglycosides by this enzyme.
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Catalytic mechanism of enterococcal kanamycin kinase (APH(3')-IIIa): viscosity, thio, and solvent isotope effects support a Theorell-Chance mechanism. Biochemistry 1996; 35:8680-5. [PMID: 8679630 DOI: 10.1021/bi9603884] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Bacterial resistance to the aminoglycoside antibiotics is manifested primarily through the production of enzymes which covalently modify these drugs. The Enterococci and Staphylococci produce an ATP-dependent kinase, APH(3')-IIIa, which phosphorylates such antibiotics as kanamycin, amikacin, and neomycin, and this enzyme shows a Theorell-Chance kinetic mechanism by traditional product and analogue inhibitor analysis and by the alternative substrate diagnostic [McKay, G. A., & Wright, G. D. (1995) J. Biol. Chem. 270, 24686-24692]. We report that the APH(3')-IIIa exhibits small solvent (VH/VD approximately equal to 1.50) and thio effects (VATP/VATP gamma S = 2) indicating hydroxyl group deprotonation and nucleophilic attack on ATP do not significantly contribute to the overall steady-state rate. The enzymatic rates were determined with the viscogens PEG 8000, glycerol, and sucrose, and these experiments demonstrate that ATP binding and ADP release are diffusion controlled and that ADP release is solely rate limiting for APH(3')-IIIa. In addition, the slope of V/K for ATP vs relative viscosity is greater than the theoretical limit of 1, suggesting a possible enzyme conformational change upon binding of ATP. This new experimental evidence supports a Theorell-Chance mechanism for APH(3')-IIIa.
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Kinetic mechanism of aminoglycoside phosphotransferase type IIIa. Evidence for a Theorell-Chance mechanism. J Biol Chem 1995; 270:24686-92. [PMID: 7559583 DOI: 10.1074/jbc.270.42.24686] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Bacterial resistance to aminoglycoside-aminocyclitol antibiotics is mediated primarily by covalent modification of the drugs by a variety of enzymes. One such modifying enzyme, the 3'-aminoglycoside phosphotransferase, which is produced by Gram-positive cocci such as Enterococcus and Streptococcus inactivates a broad range of aminoglycosides by ATP-dependent phosphorylation of specific hydroxyl residues on the antibiotics. Through the use of dead-end and product inhibitor studies, we present the first detailed examination of the kinetic mechanism for the 3'-aminoglycoside phosphotransferase-IIIa. Initial velocity patterns deduced from steady-state kinetics indicate a sequential mechanism with ordered binding of ATP first followed by aminoglycoside. Dead-end inhibition by AMP and adenylyl-imidodiphosphate is competitive versus ATP and noncompetitive versus kanamycin A. Dead-end inhibition by tobramycin, a kanamycin analogue lacking a 3'-OH, is competitive versus both kanamycin A and uncompetitive versus ATP, indicative of ordered substrate binding where ATP must add prior to aminoglycoside addition. Product inhibition by kanamycin phosphate is noncompetitive versus ATP when kanamycin A is held at subsaturating concentrations (Km(kanA)), whereas no inhibition is observed when the concentration of kanamycin A is held at 10Km(kanA). This is consistent with kanamycin phosphate being the first product released followed by ADP release. The patterns of inhibition observed support a mechanism where ATP binding precedes aminoglycoside binding followed by a rapid catalytic step. Product release proceeds in an ordered fashion where kanamycin phosphate is released quickly followed by a slow release of ADP. Aminoglycoside substrates, such as kanamycin A, show substrate inhibition that is uncompetitive versus ATP. This indicates binding of the aminoglycosides to the slowly dissociating (E-ADP) complex at high drug concentrations. These experiments are consistent with a Theorell-Chance kinetic mechanism for 3'-aminoglycoside phosphotransferase-IIIa.
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Abstract
The aminoglycoside antibiotics are inactivated by modifying enzymes that are now widely distributed in many pathogenic bacteria. This situation threatens the continued use of these clinically important drugs. We have undertaken studies to understand the molecular mechanism of aminoglycoside resistance, and we report the affinity labeling of the enterococcal aminoglycoside 3'-phosphotransferase, APH(3')-IIIa, with an electrophilic ATP analogue, 5'-[p-(fluorosulfonyl)benzoyl]adenosine (FSBA). Incubation of purified APH(3')-IIIa with FSBA resulted in time-dependent irreversible inactivation of enzyme activity with a binding constant, Ki, of 0.406 mM and a rate of maximal inactivation, kmax, of 0.086 min-1. Addition of ATP completely protected the enzyme from inactivation, consistent with labeling of the ATP binding site. Reaction of APH(3')-IIIa with [14C]FSBA showed that inactivated APH(3')-IIIa incorporates 1 mol of FSBA/mol of enzyme. Peptide mapping of FSBA-inactivated APH(3')-IIIa resulted in the identification of two peptide peaks with highly increased absorbance at 260 nm, indicative of covalent labeling with FSBA. Analysis by electrospray ionization mass spectrometry and Edman degradation revealed two tryptic peptides, Val31-Lys44 and Leu34-Arg49, which incorporated the FSBA label at Lys33 and Lys44, respectively. This establishes the importance of the N-terminal region of APHs in ATP binding, a region of these enzymes which has heretofore not been considered for involvement in substrate binding.
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Broad spectrum aminoglycoside phosphotransferase type III from Enterococcus: overexpression, purification, and substrate specificity. Biochemistry 1994; 33:6936-44. [PMID: 8204627 DOI: 10.1021/bi00188a024] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The aminoglycoside phosphotransferases (APHs) are responsible for the bacterial inactivation of many clinically useful aminoglycoside antibiotics. We report the characterization of an enterococcal enzyme, APH(3')-IIIa, which inactivates a broad spectrum of aminoglycosides by ATP-dependent O-phosphorylation. Overproduction of APH(3')-IIIa has permitted the isolation of 30-40 mg of pure protein/(L of cell culture). Purified APH(3')-IIIa is a mixture of monomer and dimer which is slowly converted to dimer only over time. Dimer could be dissociated into monomer by incubation with 2-mercaptoethanol, suggesting that dimerization is mediated by formation of disulfide bond(s). Both monomer and dimer show Km values in the low micromolar range for good substrates such as kanamycin and neomycin, and kcat values of 1-4 s-1. All aminoglycosides show substrate inhibition except amikacin and kanamycin B. Determination of minimum inhibitory concentrations indicates a positive correlation between antibiotic activity and kcat/Km, but not with Km or kcat. NMR analysis of phosphorylated kanamycin A has directly demonstrated regiospecific phosphoryl transfer to the 3'-hydroxyl of the 6-aminohexose ring of the antibiotic. Analysis of structure-activity relationships with a variety of aminoglycosides has revealed that the deoxystreptamine aminocyclitol ring plays a critical role in substrate binding. This information will form the basis for future design of inhibitors of APH(3')-IIIa.
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A note on cardiovascular diseases and physical aspects of the environment. INTERNATIONAL JOURNAL OF BIOMETEOROLOGY 1984; 28:17-27. [PMID: 6715069 DOI: 10.1007/bf02193511] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
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A comparison of maximum oxygen uptake determination by bicycle ergometry at various pedaling frequencies and by treadmill running at various speeds. EUROPEAN JOURNAL OF APPLIED PHYSIOLOGY AND OCCUPATIONAL PHYSIOLOGY 1976; 35:191-200. [PMID: 954738 DOI: 10.1007/bf02336193] [Citation(s) in RCA: 60] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Tests of performance on a bicycle ergometer have routinely been standardized with pedaling frequencies of up to 60 rpm. Only rarely have higher speeds been used. It may be hypothesized than a higher VO2, more closely approximating the maximum attainable by treadmill running, may be achieved in bicycle ergometry if higher pedal frequencies are used so that premature fatigue of the leg musculature does not obscure the comparison. Even in treadmill running it remains equivocal which combination of speed and grade of running will produce a maximum VO2. Five male subjects performed maximally at pedal frequencies of 60, 80, 100 and 120 rpm and running speeds of 6.0, 6.5, 7.0, and 7.5 mph, on a bicycle and treadmill respectively. Power output on the bicycle and increasing grade sequence on the treadmill were maintained constant for each speed investigated. The highest VO2 attained in each test was measured and compared both within and between the modes of testing. It was confirmed that peak VO2 during bicycle ergometry is significantly less than VO2 max attained in treadmill running. Pedal frequencies of 80 and 100 rpm produced optimal VO2's in ergometry. No differences were noted between VO2's determined at any speed of treadmill running. Subjects preferred 60 or 80 rpm in ergometry and 6.0 and 7.0 mph in treadmill running; 120 rpm and 7.5 mph in bicycling and treadmill running, respectively, were generally disliked.
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Breccias from the lunar highlands: preliminary petrographic report on apollo 16 samples 60017 and 63335. Science 1973; 179:71-4. [PMID: 17731632 DOI: 10.1126/science.179.4068.71] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Lunar samples 60017,4 and 63335,14 are composed of microbreccias and devitrified glass. These components are predominantly anorthositic, with the exception of a cryptocrystalline clast found in the microbreccia portion of 63335,14 which contains 2.7 percent potassium oxide and 66.7 percent silicon dioxide. The samples have been subjected to extreme shock and thermal metamorphism. The parent materials of the microbreccias include both a coarse-grained anorthosite and a fine-grained subophitic anorthositic gabbro.
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Abstract
All phases in a thin section of sample 10022 have been analyzed by electron microprobe. Augite grains show strong iron enrichment in the outer 15 to 20 microns. Pigeonite cores occur within augite grains. The plagioclase has an anorthite content of between 73 and 81 mole percent and is high in Si and low in Al compared to stoichiometric feldspar. Residual phases include microcrystalline Fe-rich "pyroxene," plagioclase, K-rich alkali feldspar, silica, and rare areas rich in P and Zr with concentrations of Ba, Y, and rare earth elements. The density, viscosity, and crystallization history of the lava of sample 10022 are discussed.
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