All reagents were procured from Panreac and Acros Organics at the highest grade available, and they were used without further purification. Anhydrous DMF was purchased from Sigma-Aldrich Co. Thin-layer chromatography (TLC) was performed on Merck TLC Silica gel 60 F254 plates by eluting with ethyl acetate or ethanol that was developed using a VL-6.LC UV lamp (Vilber). Yields refer to spectroscopically (1H and 13C NMR) homogeneous materials. The melting points were determined in glass capillaries on a Mel-Temp 3.0 apparatus (Laboratory Devices Inc., USA). The NMR spectra were recorded using Bruker Avance 400 (400 MHz for 1 H and 100 MHz for 13C) spectrometer in DMSO-d6 with tetramethylsilane used as an internal standard.
General procedure for synthesizing ester quinazolin-2,4(1 H,3H)-dione derivatives (2a-f)
A mixture of N1-substituted quinazolin-2,4(1H,3H)-dione 1 (20.0 mmol), ester of bromoacetic or 2-bromopropionic acid (21.0 mmol), and K2CO3 (7.0 g, 50.6 mmol) was stirred in a DMF solution (100 mL) at room temperature for 24 h. The reaction mass was filtered, evaporated to dryness in vacuo; the residue was treated with water (100 mL); the solid residue was filtered off, dried at room temperature, and recrystallized from ethyl acetate.
Esters of quinazolin-4(3H)-one derivatives 5a-c were synthesized similarly.
Benzyl (1-methyl-2,4-dioxo-1,4-dihydroquinazolin-3(2H)-yl)acetate (2a): white solid (EtOAc); mp 152–154 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.06 (1H, d, J = 8 Hz, H-5), 7.71 (1H, t, J = 8 Hz, H-7), 7.39 (1H, d, J = 8 Hz, H-8), 7.32–7.37 (5H, m, Ph), 7.29 (1H, t, J = 8 Hz, H-6), 5.21 (2H, s, NCH2C(O)), 5.05 (2H, s, CH2O), 3.30 (3H, s, CH3); 13C NMR (DMSO-d6, 100 MHz) δ 168.06, 161.00, 150.54, 139.44, 135.49, 135.17, 128.37, 128.12, 127.90, 127.86, 123.04, 114.58, 114.26, 66.55, 44.76, 28.02.
Benzyl 2-[2,4-dioxo-1-(prop-2-en-1-yl)-1,4-dihydroquinazolin-3(2H)-yl]propanoate (2b): white solid (EtOAc); mp 95–97 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.08 (1H, d, J = 8 Hz, H-5), 7.75 (1H, t, J = 8 Hz, H-7), 7.57 (1H, s, H-8), 7.23–7.33 (6H, m, H-6, Ph), 5.78–5.86 (1H, m, CH=), 5.60–5.62 (1H, m, CH), 5.05–5.15 (2H, m, =CH2), 4.52 (2H, s, CH2), 1.58 (3H, d, J = 7 Hz, CH3); 13C NMR (DMSO-d6, 100 MHz) δ 169.48, 160.42, 149.36, 139.23, 135.65, 135,54, 132.15, 128.42, 128.25, 127.94, 127.79, 123.15, 116.58, 114.87, 114.02, 66.32, 52.58, 42.88, 14.03.
Benzyl (1-benzyl-2,4-dioxo-1,4-dihydroquinazolin-3(2H)-yl)acetate (2c): white solid (EtOAc); mp 142–144 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.08 (1H, d, J = 8 Hz, H-5), 7.67 (1H, t, J = 8 Hz, H-7), 7.20–7.39 (12H, m, H-6, H-8, Ph, Ph), 5.39 (2H, s, NCH2C(O)), 5.21 (2H, s, CH2O), 4.88 (2H, s, CH2); 13C NMR (DMSO-d6, 100 MHz) δ 168.00, 160.79, 150.58, 139.52, 136.02, 135.75, 135.60, 128.75, 128.50, 128.22, 128.19, 127.98, 127.39, 126.45, 123.36, 115.25, 114.72, 66.55, 46.31, 42.65.
Benzyl 2-(1-methyl-2,4-dioxo-1,4-dihydroquinazolin-3(2H)-yl)propanoate (2d): white solid (EtOAc); mp 100–103 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.07 (1H, d, J = 8 Hz, H-5), 7.73 (1H, t, J = 8 Hz, H-7), 7.53 (1H, s, H-8), 7.23–7.32 (6H, m, H-6, Ph), 5.60–5.64 (1H, m, CH), 5.07–5.21 (2H, m, CH2), 3.28 (3H, c, NCH3), 1.59 (3H, d, J = 7 Hz, CH3); 13C NMR (DMSO-d6, 100 MHz) δ 169.51, 160.96, 149.83, 139.06, 135.76, 135.33, 128.25, 127.97, 127.73, 123.02, 114.85, 113.91, 66.21, 52.58, 27.81, 14.04.
Benzyl (4-oxoquinazolin-3(4H)-yl)acetate (2e): white solid (Me2CHOH); mp 116–117 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.41 (1H, s, H-2), 8.16 (1H, d, J = 8 Hz, H-5), 7.85 (1H, t, J = 8 Hz, H-7), 7.71 (1H, d, J = 8 Hz, H-8), 7.57 (1H, t, J = 8 Hz, H-6), 7.30–7.38 (5H, m, Ph), 5.22 (2H, s, NCH2C(O)), 4.92 (2H, s, CH2O); 13C NMR (DMSO-d6, 100 MHz) δ 168.24, 160.52, 148.24, 148.21, 135.78, 135.04, 128.79, 128.56, 128.29, 127.70, 127.65, 126.35, 121.57, 66.93, 47.63.
Propan-2-yl (6-bromo-4-oxoquinazolin-3(4H)-yl)acetate (2f): light yellow solid (EtOAc); mp 114–116 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.41 (1H, s, H-2), 8.18 (1H, d, J = 2 Hz, H-5), 7.93 (1H, dd, J = 9 Hz, 2 Hz, H-7), 7.62 (1H, d, J = 9 Hz, H-8), 4.97 (1H, m, J = 6 Hz, CH), 4.81 (2H, s, NCH2C(O)), 1.20 (6H, d, J = 6 Hz, CH3); 13C NMR (DMSO-d6, 100 MHz) δ 170.56, 162.37, 151.83, 150.26, 140.79, 133.03, 131.45, 126.13, 123.16, 72.54, 50.86, 24.82.
General procedure for synthesizing guanidine quinazolin-2,4(1 H,3H)-dione derivatives (3a-d)
A mixture of N1-substituted quinazolin-2,4(1H,3H)-dione ester derivative (5.0 mmol), guanidine hydrochloride (0.5 g, 5.2 mmol), and KOH (0.3 g, 5.4 mmol) was refluxed in 95% ethanol solution (25 mL) for 10 min. The hot reaction mass was filtered and cooled. The solid residue was filtered off, dried at room temperature, and recrystallized from ethanol.
N -Carbamimidoyl-2-(1-methyl-2,4-dioxo-1,4-dihydroquinazolin-3(2 H )-yl)acetamide (3a): white solid (EtOH); mp 266–269 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.01 (1H, d, J = 7.5 Hz, H-5), 7.60–7.70 (5H, m, H-7, NH), 7.22 (1H, t, J = 7.5 Hz, H-6), 7.17 (1H, d, J = 8 Hz, H-8), 4.43 (2H, s, NCH2C(O)), 3.31 (3H, s, CH3); 13C NMR (DMSO-d6, 100 MHz) δ 171.01, 161.32, 158.80, 150.45, 140.44, 134.83, 127.40, 122.15, 114.77, 114.29, 47.08, 27.95; HRMS-ESI: MH+, found: C12H13N5O3 [M + H]+ 276.1091, requires: 276.1097.
N -Carbamimidoyl-2-(1-methyl-2,4-dioxo-1,4-dihydroquinazolin-3(2 H )-yl)propanamide (3b): white solid (EtOH); mp 216–219 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.03 (1H, d, J = 8 Hz, H-5), 7.65 (1H, t, J = 8 Hz, H-7), 7.27 (1H, d, J = 7.5 Hz, H-8), 7.21 (1H, t, J = 7.5 Hz, H-6), 5,42 − 5,44 (1H, m, CH), 3.32 (3H, s, NCH3), 1.49 (3H, d, J = 7.5 Hz, CH3); 13C NMR (DMSO-d6, 100 MHz) δ 173.48, 161.28, 158.69, 150.53, 139.35, 134.25, 127.66, 122.02, 115.80, 114.85, 53.96, 28.13, 15.18; HRMS-ESI: MH+, found: C13H15N5O3 [M + H]+ 290.1248, requires: 290.1253; found: [М+Na]+ 312.1067, requires: 312.1073.
2-(1-Benzyl-2,4-dioxo-1,4-dihydroquinazolin-3(2 H )-yl)- N -carbamimidoylacetamide (3c): white solid (EtOH); mp 180–183 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.06 (1H, d, J = 8 Hz, H-5), 7.61–7.67 (5H, m, H-7, NH), 7.21–7.33 (7H, m, H-6, H-8, Ph), 5.38 (2H, s, NCH2), 4.38 (2H, s, NCH2C(O)); 13C NMR (DMSO-d6, 100 MHz) δ 171.25, 160.79, 158.80, 150.94, 139.47, 136.34, 134.93, 128.60, 127.99, 127.15, 126.50, 122.68, 115.28, 114.75, 45.96, 44.99; HRMS-ESI: MH+, found: C18H17N5O3 [M + H]+ 352.1404, requires: 352.1410; found: [М+Na]+ 374.1224, requires: 374.1229.
2-(6-Bromo-1-methyl-2,4-dioxo-1,4-dihydroquinazolin-3(2 H )-yl)- N -carbamimidoylacetamide (3d): light yellow solid (EtOH); mp 214–217; 1H NMR (DMSO-d6, 400 MHz) δ 8.03 (1H, s, H-5), 7.62 (1H, d, J = 9 Hz, H-7), 7.55 (4H, s, NH), 7.14 (1H, d, J = 9 Hz, H-8), 4.41 (2H, s, NCH2C(O)), 3.30 (3H, s, CH3); 13C NMR (DMSO-d6, 100 MHz) δ 170.62, 160.19, 158.72, 150.16, 139.70, 137.27, 129.17, 117.55, 115.99, 113.98, 47.22, 28.16; HRMS-ESI: MH+, found: C12H12BrN5O3 [M + H]+ 354.0196, requires: 354.0202; found: [М+Na]+ 376.0016, requires: 376.0021.
General procedure for synthesizing 5-amino-1,2,4-triazole quinazolin-2,4(1 H,3H)-dione derivatives (3e-i)
A mixture of N1-substituted quinazolin-2,4(1H,3H)-dione ester derivative (5.0 mmol), aminoguanidine carbonate (0.75 g, 5.5 mmol), and KOH (0.6 g, 10.7 mmol) was refluxed in 95% ethanol solution (25 mL) for 1 h. The hot reaction mass was filtered and cooled. The solid residue was filtered off, dried at room temperature, and recrystallized from ethanol. Quinazolin-4(3H)-one derivatives 6a-c were synthesized similarly.
3-[(5-Amino-4 H -1,2,4-triazol-3-yl)methyl]-1-methylquinazoline-2,4(1 H,3H)-dione (3e): white solid (EtOH); mp 351–354 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.01 (1H, d, J = 8 Hz, H-5), 7.66 (1H, t, J = 8 Hz, H-7), 7.21 (1H, t, J = 7.5 Hz, H-6), 7.16 (1H, d, J = 8.5 Hz, H-8), 4.36 (2H, s, NCH2), 3.31 (3H, s, CH3); 13C NMR (DMSO-d6, 100 MHz) δ 168.97, 161.43, 150.47, 140.70, 134.70, 127.26, 121.97, 115.09, 114.28, 47.64, 27.95; HRMS-ESI: MH+, found: C12H12N6O2 [M + H]+ 273.1095, requires: 273.1100; found: [М+Na]+ 295.0914, requires: 295.0919.
3-[1-(5-Amino-4 H -1,2,4-triazol-3-yl)ethyl]-1-methylquinazoline-2,4(1 H,3H)-dione (3f): white solid (EtOH, solvate 1:1); mp 91–93 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.06 (1H, d, J = 8 Hz, H-5), 7.75 (1H, t, J = 7.5 Hz, H-7), 7.53 (1H, t, J = 7.5 Hz, H-6), 7.30 (1H, d, J = 7.5 Hz, H-8), 5.50–5.53 (1H, m, NCH), 4.03–4.18 (2H, CH2, EtOH), 3.28 (3H, s, NCH3), 1.54 (3H, d, J = 7 Hz, CH3), 1.10 (3H, t, J = 7 Hz, CH3, EtOH); 13C NMR (DMSO-d6, 100 MHz) δ 169.53, 161.00, 149.76, 139.08, 135.32, 128.24, 122.99, 114.84, 113.91, 60.76, 52.45, 27.81, 13.95, 13.86; HRMS-ESI: MH+, found: C13H14N6O2 [M + H]+ 287.1251, requires: 287.1256; found: [М+Na]+ 309.1070, requires: 309.1076.
3-[(5-Amino-4 H -1,2,4-triazol-3-yl)methyl]-1-(prop-2-en-1-yl)quinazoline-2,4(1 H,3H)-dione (3g): white solid (EtOH); mp 275–277 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.01 (1H, d, J = 8 Hz, H-5), 7.67 (1H, t, J = 8 Hz, H-7), 7.22 (1H, t, J = 7.5 Hz, H-6), 7.17 (1H, d, J = 8.5 Hz, H-8), 5.83–5.92 (1H, m, CH=), 5.09–5.15 (2H, m, CH2=), 4.55 (2H, d, J = 5.5 Hz, CH2), 4.35 (2H, s, NCH2); 13C NMR (DMSO-d6, 100 MHz) δ 168.55, 160.94, 150.01, 140.92, 134.81, 132.6,5, 127.35, 122.02, 116.56, 115.26, 114.31, 47.73, 42.93; HRMS-ESI: MH+, found: C14H14N6O2 [M + H]+ 299.1251, requires: 299.1256; found: [М+Na]+ 321.1070, requires: 321.1076.
3-[1-(5-Amino-4 H -1,2,4-triazol-3-yl)ethyl]-1-(prop-2-en-1-yl)quinazoline-2,4(1 H,3H)-dione (3h): white solid (EtOH, solvate 1:1); mp 116–118; 1H NMR (DMSO-d6, 400 MHz) δ 8.07 (1H, d, J = 8 Hz, H-5), 7.77 (1H, t, J = 8 Hz, H-7), 7.54 (1H, d, J = 8 Hz, H-8), 7.31 (1H, t, J = 7.5 Hz, H-6), 5.82–5.91 (1H, m, CH=), 5.47–5.51 (1H, m, NCH), 5.03–5.12 (2H, m, CH2=), 4.48–4.56 (2H, m, NCH2), 4.00-4.15 (2H, m, CH2, EtOH), 1.53 (3H, d, J = 7 Hz, CH3), 1.09 (3H, t, J = 7 Hz, CH3, EtOH); 13C NMR (DMSO-d6, 100 MHz) δ 169.44, 160.44, 149,26, 139.27, 135.52, 132.17, 128.38, 123.09, 116.29, 114.84, 113.98, 60.76, 52.52, 42.78, 13.94, 13.81; HRMS-ESI: MH+, found: C15H16N6O2 [M + H]+ 313.1408, requires: 313.1413; found: [М+Na]+ 335.1227, requires: 335.1232.
3-[(5-Amino-4 H -1,2,4-triazol-3-yl)methyl]-1-benzylquinazoline-2,4(1 H,3H)-dione (3i): white solid (EtOH); mp 262–265 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.04 (1H, d, J = 8 Hz, H-5), 7.61 (1H, t, J = 8 Hz, H-7), 7.20–7.32 (7H, m, H-6, H-8, Ph), 5.37 (2H, s, NCH2), 4.33 (2H, s, CH2); 13C NMR (DMSO-d6, 100 MHz) δ 169.48, 166.46, 160.87, 151.03, 139.48, 136.43, 134.79, 128.60, 127.96, 127.13, 126.49, 122.56, 115.39, 114.76, 45.98, 45.56; HRMS-ESI: MH+, found: C18H16N6O2 [M + H]+ 349.1408, requires: 349.1413; found: [М+Na]+ 371.1227, requires: 371.1232.
3-[(5-Amino-4 H -1,2,4-triazol-3-yl)methyl]quinazolin-4(3 H )-one (6a): white solid (EtOH); mp 311–314 oC; 1H NMR (DMSO-d6, 400 MHz) δ 8.19 (1H, s, H-2), 8.12 (1H, d, J = 8 Hz, H-5), 7.78 (1H, t, J = 7.5 Hz, H-7), 7.64 (1H, d, J = 8 Hz, H-8), 7.49 (1H, t, J = 7.5 Hz, H-6), 4.32 (2H, s, CH2); 13C NMR (DMSO-d6, 100 MHz) δ 169.35, 160.15, 149.27, 148.11, 133.74, 126.91, 126.40, 125.98, 121.79, 49.32; HRMS-ESI: MH+, found: C18H17N5O3 [M + H]+ 352.1404, requires: 352.1410; found: [М+Na]+ 374.1224, requires: 374.1229.
3-[(5-Amino-1 H -1,2,4-triazol-3-yl)methyl]-6-bromoquinazolin-4(3 H )-one (6b): light yellow solid (EtOH); mp 321–324; 1H NMR (DMSO-d6, 400 MHz) δ 8.21 (1H, s, H-2), 8.20 (1H, s, H-5), 7.89 (1H, d, J = 8.5 Hz, H-7), 7.59 (1H, d, J = 8 Hz, H-8), 4.32 (2H, s, CH2); 13C NMR (DMSO-d6, 100 MHz) δ 168.97, 168.94, 159.05, 149,85, 147.11, 136.57, 129.39, 128.09, 123.33, 118.82, 49.48; HRMS-ESI: MH+, found: C11H9BrN6O [M + H]+ 321.0094, requires: 321.0099; found: [М+Na]+ 342.9913, requires: 342.9919.
Compound preparation
Test compounds were dissolved in 99% DMSO (stock concentration 40 mM) and stored at − 25°C. If sediment or opalescence was detected, 5% Tween 20 (Merck) was added. Serial dilutions were prepared ex tempore in a media suitable for the particular study. Final concentration in samples: DMSO < 0.25%, Tween 20 < 0.025% (were added to control samples in equal concentrations).
Animals
All procedures with animals in the study were carried out under the generally accepted ethical standards for the manipulations on animals adopted by the European Convention for the Protection of Vertebrate Animals used for Experimental and Other Scientific Purposes (1986) and taking into account the International Recommendations of the European Convention for the Protection of Vertebrate Animals used for Experimental research (1997). The study was approved by the Local Ethics Committee of the Volgograd State Medical University (registration No. IRB 00005839 IORG 0004900, OHRP), Certificate No. 2021/056, 15.06.2021. All sections of this study adhere to the ARRIVE Guidelines for reporting animal research29.
NHE-1 inhibition assay
Evaluation of NHE-1 inhibition was carried out on rabbit platelets by the known method30,31. The experiments were carried out on 15 male rabbits weighing 3.0–4.0 kg. Platelet-rich plasma (PRP) was obtained by centrifuging blood with 3.8% sodium citrate (1:10) at 1000 rpm for 12 min (Multi centrifuge CM 6M, Latvia). Platelet shapeshifting due to acidification was followed with a laser aggregometer BIOLA-220 LA (Russia). Test compounds (10 µl, 10 nM final concentration) were added to 200 µl of PRP 5 min in a cuvette before the addition of sodium propionate solution, incubated with constant stirring using a magnetic stirrer (800 rpm, 37°C). To control samples for NHE-1 activation, a buffer solution containing sodium propionate was added to 200 µL of PRP (600 µL, 135 mM sodium propionate, 20 mM HEPES, 1 mM CaCI2, 1 mM MgCI2, 10 mM glucose; pH 6.7). The change in light transmission at pH 7.4, 37°C was monitored in a Krebs solution (600 µL, 120 mM NaCl, 4.8 mM KCl, 1.2 mM KH2PO4, 2.5 mM MgSO4, 25 mM NaHCO3, 2.6 mM CaCl2, 5.4 mM glucose; pH 7.4). Test compounds were added to a final concentration of 10 nM to the cuvette into 200 µl of PRP 5 min before adding the sodium propionate solution, incubated with constant stirring using a magnetic stirrer (800 rpm, 37°C). NHE-1 inhibitors zoniporide, rimeporide, amiloride were used as reference drugs.
Pharmacophore modeling
Compound structures were characterized with a matrix of QL-descriptors of the 2nd rank of the 5th type using IT Microcosm system32. QL-descriptor matrix and experimental values of NHE-1 inhibitory activity served as an initial training set. We used a two-layer perceptron with a bottleneck MLP k-m-1 for neural network modeling of regression dependence, where the number of input neurons k > > m is the number of hidden neurons; calculations were performed in the Statistica program33. Iterative training of networks was performed with the division of the initial dataset into training and test sets in a ratio of 60/40% with an automatic selection of neural networks with high values of the correlation coefficients. For the best performing neural network, sensitivity analysis (Sens) of input neurons was performed, low-sensitivity neurons were removed, and iterative neural network modeling was performed. In the best neural network, the most sensitive input neurons were identified. By superposition of the found significant QL-descriptors, a pharmacophore was formed that defines a high level of NHE-1 inhibitory activity of the tested compounds.
Platelet aggregation assay
Functional activity of platelets was determined on a two-channel laser analyzer of platelet aggregation "BIOLA-220 LA" (Russia) as described previously34. The experiments were carried out on male 6 rabbits weighing 3.5–4 kg. To prepare platelet-rich plasma (PRP) venous blood was taken from the ear marginal vein of a rabbit, stabilized with a 3.8% sodium citrate solution in a ratio of 9:1 and centrifuged for 10 min at 1500 rpm. PRP (300 µL) and a solution of the test compound at a concentration of 100 µM were sequentially introduced into the cell of the aggregometer. The samples were incubated in thermostated cells of the aggregometer at 37°C for 5 min. To induce aggregation adenosine-5-diphosphoric acid (ADP, Sigma, USA) at a final concentration of 5 µM, was added to the cuvette. Acetylsalicylic acid (Shandong Xinhua Pharmaceutical Co., Ltd., China) was used as a reference drug.
Isolation and treatment of peritoneal macrophages
Peritoneal macrophages (PM) were isolated from the peritoneal exudate of C57bl/6j mice. To accumulate PM, 1 ml of 3% peptone solution was injected intraperitoneally. After 3 days the mice were euthanized by cervical dislocation. Cells of peritoneal exudate were obtained by aseptically washing the abdominal cavity with 5 ml of sterile Hanks’s solution (+ 4–6°C) without calcium and magnesium ions. The total number and viability of cells were assessed in a Goryaev counting chamber (Russia) with a 0.4% trypan blue staining (Sigma-Aldrich, USA). The cell concentration was adjusted to 1.0×106 cells/ml in DMEM (Gibco) supplemented with 2 mM L-glutamine (Gibco), 10% heat-inactivated fetal bovine serum (BioClot, Germany), 100 U/ml penicillin and 100 mg/ml streptomycin (Gibco) and plated 200 µl/well in 96-well transparent plates (SPL Life Sciences Co., Ltd., Korea). It was left for 2 h at 37°C in a humidified atmosphere with 5% CO2, after which the wells were washed to remove non-adherent cells. After 24 hours of incubation, 20 µl of the supernatant was removed and 20 µl of solutions of test compounds were added 30 min before E. coli O127:B8 LPS (100 ng/ml final concentration).
Assay of nitric oxide (NO)
The accumulation of nitrite anion (a stable end product of NO decomposition produced by iNOS) in supernatants was determined using a standard Griess reagent. Briefly, 50 µl of supernatants collected 22 hours after incubation of PM with test and control compounds were mixed with 50 µl of 1% sulfonamide in 2.5% H3PO4 and 50 µl of 0.1% N-(1-naphthyl) ethylenediamine in 2,5% H3PO4. After incubation at 23°C for 10 min in an orbital shaker, the optical density was determined at a wavelength of 550 nm with a microplate reader Infinite M200 PRO (Tecan, Austria).
Assay of interleukin 6
Cell supernatant was collected and centrifuged at 1000 g for 20 min in a 2-16PK Sigma centrifuge (Germany). The concentration of (IL-6) was determined by ELISA using a commercial kit (Cloud-clone ELISA kit) with a microplate reader Infinite M200 PRO (Tecan, Austria).
Cytotoxicity study
The activity of lactate dehydrogenase (LDH) in a cell culture medium served as a marker of membrane permeability and cell death. Aliquotes of supernatants were taken after 24 h of inoculation with test compounds, mixed with 250 µl of 0.194 nM NADH solution in 54 mM phosphate buffered saline (pH 7.5). Then, 25 µl of a 6.48 mM pyruvate solution was added to the mixture. The optical density was followed at a wavelength of 340 nm for 20 min. Conversion of optical density into cell viability was carried out according to a standard curve (DMSO treated cells − 100%, 0.01% Triton X-100–0% viable cells).
Intraocular pressure studies
The experiments were carried out on adult outbred intact rats of both sexes, which were kept in standard cages at a temperature of 25°C and a standard light regime. Before the start of the experiment, the rats had free access to food and water. Intraocular pressure (IOP) was measured with a TonoVet device (Finland)35 which measures IOP with a short touch of a small disposable tip in the center of the cornea, no corneal anesthesia is required. The study was carried out according to the published method36. One drop (50 µl) of a test 0.4% solution of the compound was instilled into the right eye, and deionized water was added to the left eye. IOP was measured in both eyes. The left eye, in turn, serves to assess the possible systemic exposure of the test compounds. Drugs with NHE-inhibitory activity were instilled in concentrations suggested in therapeutic practice − 0.2% zoniporide, 0.4% amiloride. IOP was measured at five time points (0, 1, 2, 3, and 4 hrs), where 0 hour is the baseline value. IOP-lowering activity was assessed as the maximum decrease in IOP from the initial values. The control and experimental groups of 5 animals were formed. At 9:00 am, baseline IOP was measured in animals of all groups.
Study of antiglycating activity
The glycation reaction was modeled using 1 mg/ml bovine serum albumin (Chemmed, Russia) and 0.36 M glucose (Vekton, Russia) in 50 mM phosphate buffer solution (PBS, pH 7.4) at 60°C. After 24 hrs, albumin was precipitated using trichloroacetic acid (10% final concentration) and centrifugation (15 000 rpm, 4 min). The supernatant was removed by aspiration, and the residue was dissolved in 50 mM PBS (pH 10.5). Aliquots of 300 µl were transferred to a black flat-bottom 96-well microplate. AGE fluorescence was registered using Infinite M200 Pro (Tecan, Austria) microplate reader at excitation/emission wavelengths of 370/440 nm. Signals were normalized using blank samples containing BSA and the test compound in the appropriate concentration without the glucose. When normalized, the activity is expressed as the AGE fluorescence coefficient, determined by the formula:
,
where A and B correspond to the absolute fluorescence values of the glucose-containing and mean glucose-free sample.
Activity s expressed as a percentage using the formula:
,
where fly(sample) and fly(control) correspond to the normalized fluorescence coefficients of experimental and control samples.
Tail suspension test
The experiment was carried out on male mice weighing 22–25 g, divided into groups of 6 animals each under room lighting (300 lux). Tail suspension test37 was performed using the Panlab LE808 apparatus, suspended by the tail with a piece of adhesive tape (painless method), instinctively tries to free itself from an unpleasant situation, after unsuccessful attempts to escape, the animal begins to demonstrate the behavior of despair - immobilization. At the same time, it is believed that the severity of despair, determined by immobility, directly depends on depressive disorders in the subjects, and is significantly reduced when taking antidepressants. In experiments, test substances were administered intragastrically 30 min before the start of the test. Experimental groups received test compounds in an equimolar dose to the comparison drug amiloride. Animals of the remaining groups were treated with 2.6 mg/kg amiloride, 10 mg/kg amitriptyline, or 8 mg/kg imipramine. Distilled water was administered to the control group. The time of immobilization of the animals was recorded.