Tsveta Stoyanova

Background/Objectives: Hemorphins, considered to be bioactive atypical oligopeptides, are products of hemoglobin metabolism. Recently, our team reported the synthesis and characterization of three N-modified analogs of hemorphin-4 (H4) with rhodamine B (Rh). In the present study, the Rh-1, Rh-2, and Rh-3 compounds were intracerebroventricularly infused at doses of 1, 2.5, 5, and 10 µg/5 µL, respectively, and evaluated for their antiseizure activity in 6-Hz and maximal electroshock (MES) tests and in a pentylenetetrazol (PTZ)-induced kindling model in mice. Phenytoin and diazepam were used as the reference drugs. The role of opioid receptors (ORs) underlying their mechanism of action was also evaluated in silico and pharmacologically. Results: The three Rh-H4 compounds showed a good safety profile at a concentration of 100 µg/mL in the mouse embryonic fibroblasts. They suppressed psychomotor seizures and seizure spreading as follows: Rh-1 at doses of 5 and 10 µg/5 µL, Rh-2 at the highest dose, and Rh-3 at doses of 1–10 µg/5 µL, respectively. Administered at doses of 5 µg/5 µL (Rh-1 and Rh-3) and 10 µg/5 µL (Rh-2), the compounds suppressed clonic seizures in the kindled mice comparable to the reference drug diazepam. A combination of selective delta (DOR), kappa (KOR), and mu (MOR) OR antagonists with the highest doses of the Rh-1, Rh-2, and Rh-3 compounds was used to elucidate the possible role of ORs in the underlying mechanism related to their protective activity against seizure spread. Only the selective DOR antagonist, natrindole, suppressed the effect of the Rh-1 peptide analog on seizures. The OR antagonist naloxone prevented the antiseizure activity of Rh-1 in the kindled mice. The results of docking analysis also showed the model-specific interaction of the three Rh-H4 compounds with the OR. Conclusions: Our results suggest that the antiseizure activity of Rh-1 is mediated by the OR, and in particular by the DOR, while the mechanism underlying the antiseizure effect of Rh-3 is more complex and may involve other receptors.

Recently, the four 5,5′-diphenylhydantoin Schiff bases, possessing different aromatic species (SB1-Ph, SB2-Ph, SB3-Ph and SB4-Ph) were synthesized, characterized, and evaluated for anticonvulsant activity in combination with phenytoin. In the present study, the SB1-Ph and SB4-Ph compounds were selected, based on their anticonvulsant potency, and compared with their cis isomers, prepared after a one-hour exposure to the UV source, for their anticonvulsant potency in the maximal electroshock (MES) test and the kainate (KA)-induced status epilepticus (SE) test in mice. In the MES test, the cis SB1-Ph compound exhibited superior to phenytoin and trans isomer activity in the three tested doses, while the cis SB4-Ph compound entirely suppressed the electroshock-induced seizure spread at the highest dose of 40 mg/kg. Pretreatment with the cis SB1-Ph compound and the cis SB4-Ph at the doses of 40 mg/kg, respectively, for seven days, significantly attenuated the severity of KA SE compared to the matched control group pretreated with a vehicle, while phenytoin was ineffective in this test. The cis SB4-Ph but not the cis SB1-Ph demonstrated an antioxidant effect against the KA-induced SE in the hippocampus. Our results suggest that trans–cis conversion of 5,5′-diphenylhydantoin Schiff bases has potential against seizure spread in the MES test and mitigated the KA-induced SE. The antioxidant potency of cis SB4-Ph might be associated with its efficacy in mitigating the SE.

Four 5,5′-diphenylhydantoin Schiff bases possessing different aromatic species (SB1–SB4) were recently synthesized and characterized using spectroscopic and electrochemical tools. The present study aimed to ascertain the anticonvulsant activity of the novel phenytoin derivatives SB1-Ph, SB2-Ph, SB3-Ph, and SB4-Ph, containing different electron-donor and electron-acceptor groups, and their possible mechanism of action. The SB2-Ph exhibited the highest potency to suppress the seizure spread with ED₅₀ = 8.29 mg/kg, comparable to phenytoin (ED₅₀ = 5.96 mg/kg). While SB2-Ph did not produce neurotoxicity and sedation, it decreased locomotion and stereotypy compared to control. When administered in combination, the four Schiff bases decreased the phenytoin ED₅₀ by more than 2× and raised the protective index by more than 7× (phenytoin+SB2-Ph). The strongest correlation between in-vivo and docking study results was found for ligands’ interaction energies with kappa and delta receptors. These data, combined with the worst interaction energies of our ligands with the mu receptor, suggest that the primary mechanism of their action involves the kappa and delta receptors, where the selectivity to the kappa receptor leads to higher biological effects. Our findings suggest that the four Schiff bases might be promising candidates with potential applications as a safe and effective adjuvant in epilepsy.

One of the pathological hallmarks of Alzheimer’s disease (AD) associated with its progression that contributes to β-amyloid (Aβ) generation is oxidative stress (OS). Clinical data suggest that melatonin is a potent antioxidant that might be effective in the adjunctive therapy of this neurodegenerative disease. The present study aimed to explore the role of melatonin on behavioral changes and markers of OS in three rat models, namely, pinealectomy (pin) model of melatonin deficit, intracerebroventricular (icv)Aβ_1-42 model of AD, and combination of both pin and Aβ_1-42 model (pin+icvAβ_1-42). The chronic injection with vehicle/melatonin (50 mg/kg, i.p. for 40 days) started on the same day of sham/pin and icv vehicle/Aβ_1-42 infusion procedures. Anxiety in the open field and the elevated plus-maze test and cognitive responses in the object recognition test were tested between the 30th–35th day after the surgical procedures. Markers of OS in the frontal cortex (FC) and hippocampus were detected by the ELISA method. Melatonin treatment corrected the exacerbated anxiety response only in the pin+icvAβ_1-42 model while it alleviated the cognitive impairment in the three models. Pinealectomy disturbed the antioxidant system via enhanced SOD activity and decreased GSH levels both in the FC and hippocampus. The Aβ_1-42 model decreased the SOD activity in the FC and elevated the MDA level in the two brain structures. The pin+icvAβ_1-42 model impaired the antioxidant system and elevated lipid peroxidation. Melatonin supplementation restored only the elevated MDA level of icvAβ_1-42 and pin+icvAβ_1-42 model in the hippocampus. In conclusion, our study reveals that the pin+icvAβ_1-42 rat model triggers more pronounced anxiety and alterations in markers of OS that may be associated with melatonin deficit concomitant to icvAβ_1-42-induced AD pathology.