Effects of annulatophenone, annulatophenonoside, and acetylannulatophenonoside on brain synaptosomes and small cerebral vessels

Pharmacia 73: e193535 DOI 10.3897/pharmacia.73.e193535 Research Article Effects of annulatophenone, annulatophenonoside, and acetylannulatophenonoside on brain synaptosomes and small cerebral vessels Magdalena Kondeva-Burdina1 , Boris Kadinov2, Zlatina Kokanova-Nedialkova3 , Paraskev Nedialkov3 1 Department of Pharmacology, Pharmacotherapy and Toxicology, Faculty of Pharmacy, Medical University of Sofia, Dunav str. 2, 1000 Sofia, Bulgaria 2 Institute of Neurobiology, Bulgarian Academy of Sciences, Acad. Georgi Bonchev str., bl. 23, 1113 Sofia, Bulgaria 3 Department of Pharmacognosy, Faculty of Pharmacy, Medical University of Sofia, Dunav str. 2, 1000 Sofia, Bulgaria Corresponding author: Paraskev Nedialkov () Received 29 March 2026 ♦ Accepted 16 April 2026 ♦ Published 4 May 2026 Citation: Kondeva-Burdina M, Kadinov B, Kokanova-Nedialkova Z, Nedialkov P (2026) Effects of annulatophenone, annulatophenonoside, and acetylannulatophenonoside on brain synaptosomes and small cerebral vessels. Pharmacia 73: e193535. https://doi. org/10.3897/pharmacia.73.e193535 Abstract Three benzophenones (annulatophenone Hd15, annulatophenonoside Hd21, and acetylannulatophenonoside Hd22) isolated from the aerial parts of Hypericum annulatum Moris were evaluated for their neuroprotective properties. All compounds demonstrated significant neuroprotection in an in vitro 6-hydroxydopamine model using isolated rat brain synaptosomes. Annulatophenone Hd15 exhibited the strongest effect, enhancing synaptosomal viability and GSH levels by 35% and 25%, respectively, surpassing the positive control, silybin (25% and 15%). The lower activity of annulatophenonoside Hd21 is attributed to its sugar moiety, while acetylation in acetylannulatophenonoside Hd22 further reduced efficacy. The effects of the benzophenones on the contractility of the rat basilar artery (a. basilaris) were also evaluated, with only Hd22 increasing vascular tone. Keywords a. basilaris, benzophenones, contractility, Hypericum annulatum, neuroprotection, synaptosomes Introduction Representatives of the genus Hypericum (family Hypericaceae) comprise nearly 500 species classified into 36 intrageneric taxonomic sections. Its representatives range from trees and shrubs to annual and perennial herbaceous plants, adapted to habitats from semi-desert and dry areas to moderately moist and marshy environments. The genus is nearly worldwide in distribution, absent from regions such as southern Chile and Argentina, Antarctica, south- ern oceanic islands, most tropical lowlands (except H. japonicum), and Arctic, subarctic, and alpine zones (Robson 1984). In Bulgaria, the genus Hypericum is represented by 22 species (Jordanov and Kožucharov 1970). Hypericum annulatum Moris (sect. 27. Adenosepalum Spach) is a herbaceous perennial species native to the Balkan Peninsula, Sardinia, North Africa, and Arabia (Robson 1996). The earliest studies on the chemical composition of Hypericum annulatum date back to the late 1970s, when the xanthone gentisein and several fla- Copyright Kondeva-Burdina M et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 2 Kondeva-Burdina M et al.: Effects of benzophenones on brain synaptosomes and small cerebral vessels vonoids, including hyperoside, quercitrin, rutin, kaempferol, quercetin, and myricetin, were identified (Kitanov and Achtardjiev 1979). About two decades later, the 3-O-glucoside of gentisein (xanthohypericoside) was discovered—the first xanthone O-glycoside reported in the genus Hypericum—along with norathyriol, isomangiferin, isoquercitrin, and 1–3,II–8-biapigenin (Kitanov and Nedialkov 2000). Further studies have also established the presence of hypericin and pseudohypericin, with a total content of 0.066% of the dry mass of the aerial parts (Kitanov 2001). In 2001, the benzophenone O-glycoside hypericophenoside was isolated, together with annulatophenone. These compounds represent the first examples of simple oxygenated benzophenones identified in species of the genus Hypericum (Kitanov and Nedialkov 2001). Subsequent studies on this plant led to the isolation of three annulatophenone glycosides: annulatophenoside and acetylannulatophenoside (Nedialkov and Kitanov 2002) and neoannulatophenoside (Momekov et al. 2006). In addition to the simple oxygenated benzophenones, the aerial parts of Hypericum annulatum have also yielded 5,7-dihydroxy-3-methylchromone (Nedialkov and Kitanov 2002), pinocembrin-7-O-glucoside (Momekov et al. 2006), and annulatomarin (Nedialkov et al. 2007). In other studies, benzophenone glycosides (neoannulatophenonoside, hypericophenonoside, annulatophenone, annulatophenonoside, and acetylannulatophenonoside) isolated from H. annulatum demonstrated cytoprotective potential in a K-562 cell model of epirubicin-induced toxicity (Momekov et al. 2006) and a protective effect against carbon tetrachloride-induced toxicity in isolated rat hepatocytes (Mitcheva et al. 2006). From the aerial parts of this plant, the prenylated phloroglucinol hyperatomarin has also been isolated, which has demonstrated antibacterial and cytotoxic activity (Šavikin-Fodulović et al. 2003; Momekov et al. 2008). Additionally, analysis of the essential oil from the aerial parts of Hypericum annulatum revealed that its main constituents are α-pinene, (E)β-ocimene, undecane, myrcene, and β-pinene (Radulović et al. 2010). The benzophenones annulatophenone, annulatophenonoside, and acetylannulatophenonoside were also found in the methanolic extract of the aerial parts of Hypericum mannulatum (Zheleva-Dimitrova et al. 2012). Parkinson’s disease (PD) is a neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra, leading to a dopamine deficiency. Extensive biochemical evidence from human autopsies and animal models indicates that oxidative stress (OS) in the substantia nigra may drive dopaminergic neurodegeneration, though it remains unclear whether this stress is a primary cause or a secondary effect. Studies employing the neurotoxins 6-OHDA (6-hydroxydopamine) and MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), which reliably produce oxidative stress and parkinsonian syndromes in multiple animal models, have greatly contributed to understanding dopaminergic neurodegeneration and the development of neuroprotective strategies (Grünblatt et al. 2000). It is well established that 6-OHDA is a highly reactive neurotoxin that readily undergoes au- to-oxidation and monoamine oxidase–mediated deamination, generating hydrogen peroxide and reactive oxygen species (ROS). Its neurodegenerative effects are thought to be mediated by OS, leading to increased ROS generation and subsequent lipid peroxidation of neuronal membranes (Glinka et al. 1997; Grünblatt et al. 20 (...truncated)