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Oxidative stress has been implicated in pathophysiology of different human stress- and age-associated disorders, including osteoporosis for which antioxidants could be considered as therapeutic remedies as was suggested recently. The 1,4-dihydropyridine (DHP) derivatives are known for their pleiotropic activity, with some also acting as antioxidants. To find compounds with potential antioxidative activity, a group of 27 structurally diverse DHPs, as well as one pyridine compound, were studied. A group of 11 DHPs with 10-fold higher antioxidative potential than of uric acid, were further tested in cell model of human osteoblast-like cells. Short-term combined effects of DHPs and 50 µM H2O2 (1-h each), revealed better antioxidative potential of DHPs if administered before a stressor. Indirect 24-h effect of DHPs was evaluated in cells further exposed to mild oxidative stress conditions induced either by H2O2 or tert-butyl hydroperoxide (both 50 µM). Cell growth (viability and proliferation), generation of ROS and intracellular glutathione concentration were evaluated. The promotion of cell growth was highly dependent on the concentrations of DHPs used, type of stressor applied and treatment set-up. Thiocarbatone III-1, E2-134-1 III-4, Carbatone II-1, AV-153 IV-1, and Diethone I could be considered as therapeutic agents for osteoporosis although further research is needed to elucidate their bioactivity mechanisms, in particular in respect to signaling pathways involving 4-hydroxynoneal and related second messengers of free radicals.

The effects of eleven 1,4-dihydropyridine derivatives (DHPs) used alone or together with prooxidant anticancer drug doxorubicin were examined on two cancer (HOS, HeLa) and two nonmalignant cell lines (HMEC, L929). Their effects on the cell growth (3H-thymidine incorporation) were compared with their antiradical activities (DPPH assay), using well-known DHP antioxidant diludine as a reference. Thus, tested DHPs belong to three groups: (1) antioxidant diludine; (2) derivatives with pyridinium moieties at position 4 of the 1,4-DHP ring; (3) DHPs containing cationic methylene onium (pyridinium, trialkylammonium) moieties at positions 2 and 6 of the 1,4-DHP ring. Diludine and DHPs of group 3 exerted antiradical activities, unlike compounds of group 2. However, novel DHPs had cell type and concentration dependent effects on 3H-thymidine incorporation, while diludine did not. Hence, IB-32 (group 2) suppressed the growth of HOS and HeLa, enhancing growth of L929 cells, while K-2-11 (group 3) enhanced growth of every cell line tested, even in the presence of doxorubicin. Therefore, growth regulating and antiradical activity principles of novel DHPs should be further studied to find if DHPs of group 2 could selectively suppress cancer growth and if those of group 3 promote wound healing.

Biosynthesis of hydrogen sulfide (H2S), a key signalling molecule in human (patho)physiology, is mostly accomplished by the human enzymes cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (MST). Several lines of evidence have shown a close correlation between increased H2S production and human diseases, such as several cancer types and amyotrophic lateral sclerosis. Identifying compounds selectively and potently inhibiting the human H2S-synthesizing enzymes may therefore prove beneficial for pharmacological applications. Here, the human enzymes CBS, CSE and MST were expressed and purified from Escherichia coli, and thirty-one pyridine derivatives were synthesized and screened for their ability to bind and inhibit these enzymes. Using differential scanning fluorimetry (DSF), surface plasmon resonance (SPR), circular dichroism spectropolarimetry (CD), and activity assays based on fluorimetric and colorimetric H2S detection, two compounds (C30 and C31) sharing structural similarities were found to weakly inhibit both CBS and CSE: 1 mM C30 inhibited these enzymes by approx. 50% and 40%, respectively, while 0.5 mM C31 accounted for CBS and CSE inhibition by approx. 40% and 60%, respectively. This work, while presenting a robust methodological platform for screening putative inhibitors of the human H2S-synthesizing enzymes, highlights the importance of employing complementary methodologies in compound screenings.

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