Browsing by Author "Ivaska, Vilma"

Statins are 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) inhibitors, and they are used in the treatment of hypercholesterolemia. Statins compete with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) for binding to HMG-CoA reductase and this way inhibit the cholesterol synthesis in the liver. Statins appear in lactone or hydroxy acid forms, and they are active in the acid form. Statins are usually administered with their hydroxy acid form except simvastatin and in this experiment only acid forms of statins were tested. The aim of this study was to compare the pharmacodynamic effects of statin acids and to determine their half maximal inhibitory concentration (IC50 value) towards their target, HMG-CoA reductase. These experiments were performed with atorvastatin, 2-hydroxyatorvastatin, 4-hydroxyatorvastatin, 3R,5S-fluvastatin, 3S,5R-fluvastatin, pitavastatin, pravastatin, rosuvastatin and simvastatin acid. To discover the optimal reaction conditions, first some preliminary experiments including time linearity and enzyme kinetics experiments were performed. In the inhibitory experiments different concentrations of the statins were incubated with HMG-CoA (20 µM), HMG-CoA reductase (0.9 µg/ml) and nicotinamide adenine dinucleotide phosphate (NADPH) in phosphate buffer (0.1 M). All samples were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS analysis). Results from the preliminary experiments and statin IC50 values were determined using nonlinear regression. Most of the statins inhibited HMG-CoA reductase with 50% inhibitory concentrations of 3-20 nM. These inhibition experiments also offered some new information about the metabolites of atorvastatin indicating that 2-hydroxyatorvastatin has similar inhibitory effects as atorvastatin while 4-hydroxyatorvastin seemed to be considerably less active. In the present experiment the IC50 value for 3R,5S-fluvastatin was much smaller than the IC50 value for 3S,5R-fluvastatin indicating that 3S,5R-fluvastatin is inactive. In conclusion, the results from these inhibitory experiments were mostly in line with the results from the previous measurements described in the literature.