Computational studies on statins photoactivity

Statins are popular drugs widely prescribed to control hypercholesterolaemia and to prevent cardiovascular diseases. Synthetic statins constitute a group of pharmaceuticals which are very sensitive to exposure to light in both UVA and UVB ranges. Light, by causing drugs degradation, can essentially change their pharmaceutical properties leading even to the loss of therapeutic activity and/or to the formation of deleterious photoproducts. Drugs which exhibit photochemical reactivity may elicit undesired adverse effects. A detailed understanding of mechanisms involved in molecular basis of these effects origin is very important for evaluating the photobiological risk associated with therapy in which drugs prone to exposure to light are involved. In this work we critically discussed finding regarding the mechanisms of synthetic statins phototransformation. We showed inconsistency of some previously reported facts and revised earlier presented studies. We also completed the lack of information on pitavastatin photobehaviour. This all together resulted in proposal of new schemes for the statins photodecomposition. We reviewed data derived from both experimental and computational methods. Studies of photochemical problems by the use of theoretical methods enable getting insight into areas of some fascinating events that experimental techniques can touch only indirectly. Besides effect of light, phenomenon of statins’ sensitivity to pH and resulting implications were discussed. Statins undergo pH-dependent interconversion between their pharmacologically active hydroxy acid and inactive lactone forms, and it was shown that for both forms, drugs’ interactions should be considered. Knowledge of the statins interconversion mechanisms is important for understanding how differences in the structures of their molecules can affect the drugs’ activity.

Experimental and theoretical studies on fluvastatin primary photoproduct formation

Fluvastatin (FLV) belongs to the group of compounds referred to as statins, also known as 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors. Statins act as cholesterol-lowering agents and are among the most frequently prescribed drugs. They upregulate low-density lipoprotein receptors in the liver by binding to the active site of HMG-CoA reductase, which is the key enzyme in cholesterol biosynthesis. Statins have been detected as contaminants in natural waters and are susceptible to degradation upon exposure to light. Fluvastatin is extremely sensitive to light; upon irradiation it forms a range of photoproducts. In this study the fluvastatin molar absorption coefficient and the quantum yield of the drug photodegradation were determined. The FLV photodegradation quantum yield value determined in this work (Φ = 0.13 ± 0.02) was found to be significantly larger than that previously reported in the literature. Our results also showed that the generation of singlet oxygen is not involved in the drug photodecomposition indicating that the excited triplet state of fluvastatin is not populated efficiently. Moreover, experimental methods and DFT calculations were applied to get insight into the possible mechanisms of fluvastatin primary photoproduct formation. Using the transient absorption spectroscopy technique, the transient species formed immediately after the drug excitation were followed, and the scheme for fluvastatin primary photochemistry was suggested. The primary photoproducts were identified on the basis of spectroscopic and spectrometric methods. A new mechanism for photooxygenation leading to the formation of one of the identified photoproducts (FP2) was proposed and a new approach to the formation of the other photoproduct (FP1) was provided. The theoretical mechanistic explanation of the photoproduct formation is in excellent agreement with the experimental data.