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Top1. Introduction
Iridoids represent a large group of cyclopenta[c]pyran monoterpenoids found in a number of folk medicinal plants and used as hypotensives, cough medicines, bitter tonics, sedatives, antipyretics, remedies for wound sand skin disorders (Tietze et al., 1983). This fact encouraged scientists to investigate the bioactivities of these plant compounds. Additional studies during recent years revealed that iridoids exhibit a wide range of bioactivity: neuroprotective, antitumor, anti-inflammatory, antioxidant, cardiovascular, antihepatotoxic, choleretic, hypoglycemic, hypolipidemic, antispasmodic, antiviral, antimicrobial, immunomodulator, antiallergic, anti-leishmanial and molluscicidal effects (Ghisalberti et al., 1998, Usmanov et al., 2019). Naturally occurring iridoid compounds were classified into different sub-groups on the basis of their demonstrated or postulated biosynthesis pathway as well as on the basis of chemical properties. According to Hegnauer’s classification (Hegnauer, 1986), natural iridoids in the broadest sense are represented by nine structural groups, consisting of cyclopentanoid monoterpenes and secoiridoids in general characterized by the structural feature of a 7,8-seco ring including pseudo alkaloids, as well as complex indole- and isoquinoline-type alkaloids. In another study, the iridoid glycosides were summarized (El-Naggar et al., 1980), which are mainly containing a glucose, secoiridoid glucosides and non-glycosidic compounds, while all nitrogen-containing iridoids were omitted. Also, simple pseudoalkaloids were considered as artefacts, where they were formed by replacement of oxygen by nitrogen in iridoids, during ammonia treatment at extraction.
Oxidative stress, chronic liver inflammation from viral and chemical toxicity, and accumulation of fats in liver from insulin resistance are the key factors for liver diseases. Several pro-inflammatory cytokines such as TNF-a, IL-1b, and IL-6 and endothelial growth factors are over-expressed by liver kupffer cells in the inflammation site, which in turn initiate an inflammation cascade to produce TGF-b1 and other growth factors and chemokines for remedial measure. The growth factor TGF-b1 induces the activation of hepatic stellate cells for transformation into myfibroblasts, which initiate apoptosis of hepatocytes in liver tissues. The pro-inflammatory genes, TNF-a, IL-1b, IL-6, IL-8, and IL-17 are considered as key players to elevate obesity and fat-related inflammation in liver (Andrade et al., 2015; Czaja et al., 2014; Tilg et al., 2010). Therefore, search for new effective medicinal compounds with hepatoprotective properties is an important task. Pathology and functional disorders of the liver are almost always combined with pathology of the gallbladder and biliary tract, and therefore the most successful therapy is aimed at improving the metabolic processes in the liver, increasing its resistance to pathogenic effects, accelerating the recovery of its functions during various injuries and to eliminate dysfunctional disorders of the biliary tract.