## 4 Discussion
[PERSON]'s research noted that anethole dithiolethione, often used in treating neurodegenerative diseases, has an inhibitory effect on MAO-B, while it has no inhibitory effect on MAO-A [38]. [PERSON] and co-authors also indicated the effect of anethole on the MAO-B enzyme [39]. This was confirmed in our studies, because anethod itself (**3a**) did not show MAO-A inhibitory properties, while the corresponding diol (**3b**) and hydroxy ketone (**3c**) showed MAO-A inhibition activity at an IC\({}_{50}\) concentration of approx. 3 umol/L in a competitive manner; for **3b**, K\({}_{i}\) was <0.001 umol/L, whereas for **3c**, it amounted to 12.91 umol/L. The same relationship was observed for **4a**, but in this case, only compound **4b** showed an inhibitory effect with K\({}_{i}\) = 0.65 umol/L. For compounds **1a** and **2a**, no studies concerning MAO-A inhibition were found. However, it can be observed that both **1b** and **2b** interacted with MAO-A in the active site, while hydroxy ketones did so only in the case of compound **2b**. It can be concluded that the best family of MAO-A inhibitors tested in this work are the hydroxy ketones, which protect serotonin against deamination. ITC is a technique that measures the heat of different reactions, not only binding. In the case of enzyme-substrate reactions, the device measured the heat released as a result of substrate binding to the enzyme. This can lead to a substrate reaction, e.g., its oxidation, as it was in the case of monoaminoxidase. The \"Michaelis constant\" mode was used to mathematically describe such a reaction. In the case of enzyme-inhibitor reactions alone, the device measured the heat of binding of the inhibitors to the enzyme. The \"binding to one site\" mode was used to describe the reaction. Importantly, in the case of enzyme-substrate reactions in the presence of an inhibitor, the \"inhibition constant\" mode was used. On that basis, IC50 was calculated. This showed that the ITC method is adjusted to characterize enzymatic reactions. The limitation of the ITC method is that the inhibitor may bind to the enzyme not only in the active site, giving an additional small heat release signal. For this reason, it is complementary to perform docking simulations, which allows us to describe the binding only in the active site. Therefore, molecular modeling was used to compare affinity of inhibitors to the enzyme [40; 41; 42]. It could be observed that both methods (ITC and molecular docking) showed similar trends for compounds **1b** and **5b** interacting with the enzyme. In both tests, compound **5b** was shown to be the best inhibitor of MAO-A, which binds to the active site competitively (Table 1). Molecular modeling was performed using two methods: AD and LF. In most cases, higher affinity for the enzyme was demonstrated by LF docking (Table 2). 5-HT binds to MAO-A through the amino acids ILE335 and TYR326 [43]. MAO-A forms covalent bonds with the substrate by cysteine residues, e.g., CYS406 [44]. An example of an effective inhibitor is compound **5b**, which showed high affinity for the enzyme in a docking procedure by binding to the enzyme through the amino acid residue TYR407 adjacent to CYS406, blocking access to the substrate. Adding aromatic compounds such as propenylbenzene derivatives (hydroxy ketones and diols) to food can not only enrich it with an attractive aroma, but also be an additive, giving food functional properties. Preparations of aromatic compounds can also be used in pharmacy in the future. Both directions of potential application require many studies related to their safe use in the diet. The nearest planned studies will include adding the tested aromatic compounds to different types of food and assessing their bioavailability during simulated digestion and absorption in Caco-2 cells.