Aspirin is the one of the most popular drugs (more than 100 billions pills are taken every year). The range of diseases in case of those the therapy by aspirin and its derivations (salicylates) used is unbelievably wide. Aspirin is used as antiphlogistic, sedative analgesic, antipyretic and antiaggregant (i.e., decreasing the probability of congestion vessel) drugs. However far from everyone who uses these drugs think about that besides benefit salicylates do perceptible damage to the organisms. It is connected with the fact that aspirin and its derivations provoke stomach ulcer and have negative action to the liver and blood cells.

Scheme of TCA cycle with salicylate action

The lesion of liver is one of the most serious side effects which arise after using of aspirin. Negative influence on hepatocytes shows not only in case of overdose but also in curative doses which are prescribed for curing of several diseases (for example arthritis). One of the reasons of that is abnormality in regulation and functioning of the energetic metabolism of liver cells, particularly, Krebs cycle. Investigation of drug side effects mechanisms consists in two parts. Firstly, it is necessary to understand how is possible to decrease toxic effects of existed drugs. Secondly – to prognose new drug side effects that may significantly decrease production inputs and – in main - risk of their using. The strategy of complex research drugs action and their side effects was developed for that in our laboratory on the basis of kinetic modeling.

As a rule drugs are able to have a plural influence on the cell metabolism, i.e. there is several targets which are affected by drug. For example, several enzymes could be activated or inhibited by drug and, conversely, the others could be involved in the processes of biotransformation and elimination of drug from the organism. Moreover, apart from the main clinical action, the part of effects, produced by drug, may have negative, toxic consequences. All these facts significantly complicate experimental research of this problem and highlight systems methods, connected with metabolic modeling. Using this method it is possible to estimate experimentally the influence of one or another factor or process on the metabolism. Kinetic modeling allows not only doing that, but also comparing the model predictions with various types of experimental data.

As an example of this method using for drug side effects research we investigated the mechanisms of action of aspirin and other salicylates on the work of mitochondrion in liver cells, in particular, on the Krebs cycle.

Tricarboxylic acid cycle is the terminal step of organic substrates oxidation in the cell. Exactly this metabolic pathway collects the derivations of processing of proteins, fats, carbohydrates and carbonic gas forms there. The enzymes of Krebs cycle are located in the mitochondria and associated with respiration chain and ATP synthesis. Aspirin and their derivates are known to be able to influence the processes which take place in the mitochondria of liver cells playing the role of uncoupler of oxidative phosphorylation, decrease the coenzyme A concentration, inhibit α-ketoglutarate dehydrogenase and succinate dehydrogenase, inhibit β-oxidation of fatty acid, etc.

The α-ketoglutarate dehydrogenase and succinate dehydrogenase inhibition was shown to determine the negative effect of aspirin on energy metabolism whereas the uncoupling of oxidative phosphorylation and coenzyme A consumption just slightly decrease the rate of substrate oxidation in the cycle. Moreover we managed to show that inhibited by salicylates total flux in the Krebs cycle could be reconditioned by flux redistribution when glutamate and malate was added and by decrease of concentration of external α-ketoglutarate and glycine. This result might be explained in the following way. As it was shown above all the mechanisms of the salicylate influence, except the uncoupling, affect the lower segment of the Krebs cycle (reaction KGDH, STK, SDH, FUM on the scheme) and do not affect the upper segment (reaction AspAT, MDH и KMC). This means that redirection of flux in the Krebs cycle from its lower segment to the shunt which is realized by α-ketoglutarate-malate carrier could entail the increase of flux in the Krebs cycle which is inhibited by salicylates.

Thus, we have managed not only to model and estimate quantitatively the salicylate side effects on the energetic metabolism of mitochondria but also to develop the approach for these toxical processes compensation. It is possible to say that this project became visual illustration of Systems biology using for pharmaceutical tasks solution, as it contains the conclusion in two main questions - Drug side effects and Drug safety.

Publication

You could see this research results in more detail in the article - Mogilevskaya E., Demin O., Goryanin I. Kinetic Model of Mitochondrial Krebs Cycle: Unraveling the Mechanism of Salicylate Hepatotoxic Effects. Journal of Biological Physics, 2006, vol.32(3-4), pp.245-271..