Browsing Det helsevitenskapelige fakultet by Author "Sager, Georg"
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Browsing Det helsevitenskapelige fakultet by Author "Sager, Georg"
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Ravna, Aina W.; Sylte, Ingebrigt; Sager, Georg (Journal article; Tidsskriftartikkel; Peer reviewed, 04-Sep-2009)[+][-]
Abstract: The human ATP-binding cassette (ABC) transporters ABCB1, ABCC4 and ABCC5 are involved in resistance to chemotherapeutic agents. Here we present molecular models of ABCB1, ABCC4 and ABCC5 by homology based on a wide open inward-facing conformation of Escherichia coli MsbA, which were constructed in order to elucidate differences in the electrostatic and molecular features of their drug recognition conformations. As a quality assurance of the methodology, the ABCB1 model was compared to an ABCB1 X-ray crystal structure, and with published crosslinking and site directed mutagenesis data of ABCB1. Amino acids Ile306 (TMH5), Ile340 (TMH6), Phe343 (TMH6), Phe728 (TMH7), and Val982 (TMH12), form a putative substrate recognition site in the ABCB1 model, which is confirmed by both the ABCB1 X-ray crystal structure and the sitedirected mutagenesis studies. The ABCB1, ABCC4 and ABCC5 models display distinct differences in the electrostatic properties of their drug recognition sites. URI: http://hdl.handle.net/10037/2193 File(s) in this item: 1
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Ravna, Aina W.; Sylte, Ingebrigt; Sager, Georg (Journal article; Tidsskriftartikkel; Peer reviewed, 06-Sep-2007)[+][-]
Abstract: Background: Multidrug resistance is a particular limitation to cancer chemotherapy, antibiotic treatment and HIV medication. The ABC (ATP binding cassette) transporters human P-glycoprotein (ABCB1) and the human MRP5 (ABCC5) are involved in multidrug resistance. Results: In order to elucidate structural and molecular concepts of multidrug resistance, we have constructed a molecular model of the ATP-bound outward facing conformation of the human multidrug resistance protein ABCB1 using the Sav1866 crystal structure as a template, and compared the ABCB1 model with a previous ABCC5 model. The electrostatic potential surface (EPS) of the ABCB1 substrate translocation chamber, which transports cationic amphiphilic and lipophilic substrates, was neutral with negative and weakly positive areas. In contrast, EPS of the ABCC5 substrate translocation chamber, which transports organic anions, was generally positive. Positive-negative ratios of amino acids in the TMDs of ABCB1 and ABCC5 were also analyzed, and the positive-negative ratio of charged amino acids was higher in the ABCC5 TMDs than in the ABCB1 TMDs. In the ABCB1 model residues Leu65 (transmembrane helix 1 (TMH1)), Ile306 (TMH5), Ile340 (TMH6) and Phe343 (TMH6) may form a binding site, and this is in accordance with previous site directed mutagenesis studies. Conclusions: The Sav1866 X-ray structure may serve as a suitable template for the ABCB1 model, as it did with ABCC5. The EPS in the substrate translocation chambers and the positive-negative ratio of charged amino acids were in accordance with the transport of cationic amphiphilic and lipophilic substrates by ABCB1, and the transport of organic anions by ABCC5. URI: http://hdl.handle.net/10037/1251 File(s) in this item: 1
article.pdf (1.932Mb) -
Müller, Stig; How, Ole-Jakob; Hermansen, Stig Eggen; Stenberg, Thor Allan; Sager, Georg; Myrmel, Truls (Journal article; Tidsskriftartikkel; Peer reviewed, 21-Feb-2008)[+][-]
Abstract: Introduction: Arginine vasopressin (AVP) is increasingly used to restore mean arterial pressure (MAP) in low-pressure shock states unresponsive to conventional inotropes. This is potentially deleterious since AVP is also known to reduce cardiac output by increasing vascular resistance. The effects of AVP on blood flow to vital organs and cardiac performance in a circulation altered by cardiac ischemia are still not sufficiently clarified. We hypothesised that restoring MAP by low dose, therapeutic level AVP would reduce vital organ blood flow in a setting of experimental acute left ventricular dysfunction. Methods: Cardiac output (CO) and arterial blood flow to the brain, heart, kidney and liver were measured in nine pigs using transit-time flow probes. Left ventricular pressure-volume catheter and central arterial and venous catheters were used for haemodynamic recordings and blood sampling. Transient left ventricular ischemia was induced by intermittent left coronary occlusions resulting in a 17% reduction in cardiac output and a drop in MAP from 87 ± 3 to 67 ± 4 mmHg (p < 0.001). A low-dose therapeutic level of AVP (0.005 U/kg/min) was used to restore MAP to pre-ischemic values (93 ± 4 mmHg). Results: AVP further impaired systemic perfusion (CO and brain, heart and kidney blood flow reduced by 29, 18, 23 and 34%, respectively) due to a 2.0-, 2.2-, 1.9- and 2.1-fold increase in systemic, brain, heart and kidney specific vascular resistances. The hypoperfusion induced by AVP was associated with an increased systemic oxygen extraction. Oxygen saturation in blood drawn from the great cardiac vein fell from 29 ± 1 to 21 ± 3% (p = 0.01). Finally, these effects were reversed 40 min after AVP was withdrawn. Conclusion: Low dose AVP induced a pronounced reduction in vital organ blood flow in pigs after transient cardiac ischemia. This indicates a potentially deleterious effect of AVP in patients with heart failure or cardiogenic shock due to impaired coronary perfusion. URI: http://hdl.handle.net/10037/1422 File(s) in this item: 1
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