The effects of new derivatives of caffeine-8-thioglycolic acid (100 µM) on isolated rat brain synaptosomes, human neuroblastoma cell line SH-SY5Y and human recombinant MAOB enzyme (hMAOB) (1 µM) were evaluated. Most of the compounds, administered alone, didn’t show statistically significant neurotoxic effects on SH-SY5Y, when compared to the control (non-treated cells). Of all studied structures JTA-2Ox, JTA-11, JTA-12 and JTA-13 decreased cell viability. In combination with 6-hydroxydopamine (6-OHDA) (100 µM), only JTA-1 and JTA-2 revealed neuroprotective effects, stronger than those of caffeine. All compounds administered alone revealed, neurotoxic effects on synaptosomes, as compared to non-treated synaptosomes. JTA-1, JTA-2 and JTA-3 showed lowest neurotoxic effects and were investigated in a model of 6-OHDA-induced oxidative stress. In this model of neurotoxicity, only JTA-1 and JTA-2 showed statistically significant neuroprotective effect, by preserving the synaptosomal viability and the level of reduced glutathione. Inhibition of hMAOB, was revealed by JTA-1 and JTA-2. They inhibited the enzyme by 23% and 25% respectively, thus approaching the selegiline activity, which was 42%. The possible mechanisms of neuroprotection of JTA-1 and JTA-2 might be a result from the inhibition of hMAOB, which catalyze the production of neurotoxic p-quinone from 6-OHDA.

ABSTRACT The present study reports a promising antioxidant protection by a recently developed micellar propolis formulation, against oxidative stress in in vitro and in vivo models of toxicity. The formulation, based on poplar propolis encapsulated in poly(ethylene oxide)–β-poly(propylene oxide)–β-poly(ethylene oxide) triblock copolymer (PEO26–PPO40–PEO26) micelles is characterized by small size (D h = 20 nm), enhances aqueous solubility and good colloidal stability. In vitro, propolis-loaded PEO26–PPO40–PEO26 micelles (20–100 µg/ml) significantly increased the cell viability of human hepatoma HepG2 cells, subjected to H2O2-induced cell injury (0.1 mM, 1 h). Antioxidant activity and protection of the micellar propolis were evaluated in a model of carbon tetrachloride-induced hepatotoxicity in rats (10% CCl4 solution, 1.25 ml/kg, p.o.) by measurement of non-enzyme (malondialdehyde and glutathione) and enzyme (catalase and superoxide dismutase) biomarkers of oxidative stress. Clinic observations, hematological, biochemical parameters and histological analysis were also performed. In vivo, micellar propolis (20 mg/kg b.w., p.o., 14 days) ameliorated CCl4-induced acute liver injury in rats. The oral administration of micellar propolis significantly prevented serum transaminase increases, as well as brought the levels of malondialdehyde, glutathione, and antioxidant enzymes catalase and superoxide dismutase toward the controls levels. Therefore, PEO26–PPO40–PEO26 micelles could be considered as a promising oral delivery system of propolis against oxidative stress injury in liver cells.