Analysis and retention behaviour in high-performance liquid chromatography of terpenic plant constituents (Sideritis spp.) with pharmacological interest

Preparation and Evaluation of Siderol Amorphous Solid Dispersions: Selection of Suitable Matrix/Carrier

The present study investigates the preparation of amorphous solid dispersions (ASD) for the ent-kaurane diterpenoid siderol (SDR). Initially, evaluation of the pure drug (isolated from Sideritis scardica) revealed that the API is a non-stable glass former, and hence the selection of a suitable ASD's matrix/carrier needs special attention. For this reason, four commonly used polymers and copolymers, namely poly(vinylpyrrolidone), copovidone, hydroxypropyl cellulose, and Soluplus® (SOL), were screened via film casting and crystal growth rate measurements. Amongst them, SOL showed the highest SDR's crystal growth rate reduction, and, since it was also miscible with the drug, it was selected for further testing. In this direction, SDR-SOL ASDs were successfully prepared via melt-quench cooling. These formulations showed full API amorphization, while good physical stability (i.e., a stable SDR amorphous dispersions) were obtained after storage for several months. Finally, evaluation of molecular interactions (with the aid of ATR-FTIR spectroscopy) showed strong H-bonds between SOL and SDR, while the use of molecular dynamics (MD) simulations unraveled the nature of these interactions. Therefore, based on the findings of the present work, SOL seems to be an appropriate matrix/carrier for the preparation of SDR ASDs, although further studies are needed in order to explore its full potentials.

Kaurane diterpenes as mitochondrial alterations preventive agents under experimental oxidative stress conditions

CONTEXT

Foliol, linearol, and sidol are the most common diterpenes found in Sideritis L. spp. (Lamiaceae) with a wide range of demonstrated properties including anti-inflammatory, antioxidant, and anti-apoptotic effects.

OBJECTIVE

For the first time, the present work was studied for the potential protective role of these kaurane-type diterpenes on mitochondrial oxidative stress induced by H2O2 in the human astrocytoma U373-MG cell line and in the rat adrenal pheochromocytoma PC12 cell line.

MATERIALS AND METHODS

Mitochondrial protection was assayed at 5 and 10 µM concentrations for 24 h (for kaurane diterpenes) and H2O2 as oxidative stress inducer (0.1 mM for PC12 cells and 1 mM for U373-MG, for 30 min). ATP concentration was determined by high-performance liquid chromatography (HPLC), and changes in mitochondrial membrane potential, caspase-3 activity as well as in cytosolic and mitochondrial calcium levels were assessed by fluorometric techniques, by using specific fluorescent probes.

RESULTS

Pretreatments for 24 h with linearol and sidol, prior to H2O2 exposure, acted as mitochondrial alterations preventive agents by increasing membrane potential (over 40-60% in PC12 cells and over 10-20% in U373-MG), restoring both cytosolic and mitochondrial calcium homeostasis (linearol at 10 µM caused a 3.5-fold decrease in cytosolic calcium concentration in PC12 cells), decreasing caspase-3 activity (over 1.25-1.5-fold for linearol and sidol) and avoiding ATP depletion (linearol increased over 20% ATP level in both cell types).

CONCLUSION

Our results suggest that linearol and sidol could provide protective activity by targeting mitochondria in response to the deleterious changes induced by H2O2.

Kaurane diterpenes from Sideritis spp. exert a cytoprotective effect against oxidative injury that is associated with modulation of the Nrf2 system

Kaurane diterpenes have been shown to possess antioxidant properties. As a part of our ongoing studies on the identification of biologically active diterpenes from Sideritis spp., we have previously isolated and structurally elucidated the major kaurane diterpenes foliol, linearol and sidol, in a previous study from the aerial parts of Sideritis linearifolia and Sideritis leucantha. We have now examined the ability of these compounds to protect PC12 cells in an H2O2-induced oxidative stress model. Linearol and sidol (5 and 10 μM, 24 h) significantly attenuated loss of mitochondrial function (MTT assay) and membrane integrity (LDH assay) and morphological changes associated with H2O2-mediated cytotoxicity. Moreover, pretreatments with linearol and sidol effectively reduced intracellular ROS production, decreased MDA levels (lipid peroxidation product) and restored GSH/GSSG ratio. Furthermore, analysis of the effect of diterpenes on antioxidant enzymes showed that linearol and sidol induced the upregulation and protein expression of the main antioxidant enzymes CAT, SOD, GPx, GR and HO-1. Considering molecular mechanisms for maintaining cellular redox homeostasis by linearol and sidol, it would appear that the Nrf2 transcription factor seems to be involved. These results indicate that linearol and sidol are potential cytoprotective compounds, through antioxidant mechanisms, under H2O2-induced oxidative stress.

Nrf2-dependent neuroprotective activity of diterpenoids isolated from Sideritis spp

ETHNOPHARMACOLOGICAL RELEVANCE

The species of the genus Sideritis are extensively used in the Mediterranean area in folk medicine for their digestive, antimicrobial, anti-inflammatory and antioxidant properties, among others. Moreover, Sideritis species as tea infusions are popularly known for improving memory function and cognitive ability. Diterpenoids are one of the most abundant and important pharmacological interest of the classes of natural products presented in these medicinal plants.

AIM OF THE STUDY

To determine for the first time the neuroprotective effects, based on their antioxidant properties, of the three isolated major diterpenoids andalusol, conchitriol and lagascatriol in an oxidative stress model.

MATERIALS AND METHODS

H2O2 was used as oxidant inductor and rat adrenal pheochromocytoma PC12 cells as cellular model. Cell viability was measured using MTT and LDH assays, lipid peroxidation was determined by HPLC, GSH and GSSG levels assessed by fluorometric techniques, enzymatic activity and protein expression were determined by spectrofometric techniques and Western blot, respectively.

RESULTS

Pretreatments with the three diterpenoids significantly attenuated H2O2-induced changes in mitochondrial integrity and activity (MTT assay), in cell membrane integrity (LDH assay) and in cell morphology. Moreover, these diterpenoids inhibited intracellular ROS production H2O2-induced, reduced lipid peroxidation and counteracted GSH/GSSG changes. Furthermore, both activities and protein expression of the endogenous antioxidant enzymes (CAT, SOD, GR, GPx and HO-1) were increased. The Nrf2 pathway was involved, at least in part, in the protective effects of these diterpenoids.

CONCLUSION

These findings suggest that these natural compounds provide significant antioxidant effects in PC12 under for counteracting the oxidative damage H2O2-induced and their potential role as useful agents for the prevention of those oxidative stress-mediated dementia disorders. Andalusol was the most active compound among the studied diterpenoids.

Chemical Characterization, Mineral Content and Radical Scavenging Activity of Sideritis scardica and S. raeseri from R. Macedonia and R. Albania

Chemical characterization was made of over-ground flowering parts of Sideritis scardica from R. Macedonia and S. raeseri from both R. Macedonia and R. Albania. GC/FID/MS investigation of the n-hexane extracts revealed more than 90 components, dominated by diterpenes and hydrocarbons. The most abundant components were hentriacontane, nonacosane and heptacosane, and two other components both with MW=286, probably diterpenes, which were not fully identified. In addition, the content of total phenols, made by the Folin-Cioclateu method, ranged up to 50.8 and up to 48.9 mg gallic acid/g for S. scardica and S. raeseri, respectively. Free radical scavenging activity was evaluated by DPPH assay and the activity, presented as IC50 values, ranged from 3.2-8.9 mg/mL and 7.6-12.6 mg/mL for S. scardica and S. raeseri, respectively. The content of twenty minerals in dried over-ground parts of the plants and in water tea-infusions were determined by the ICP-AES method and some of them alternatively by ETAAS. The most abundant minerals were K > Ca > Mg > P > Fe > Al > Na. The microelements and toxic elements contents were represented in the following order: Zn > Mn > B > Ba > Cu > Sr > Li > Ni > Cr > Co, and Cd > Pb > As, respectively. Water tea-infusions contained a large portion of the total K, P, Na, Cu and Pb, but smaller amounts of the other elements.

Diterpenoids isolated from Sideritis species protect astrocytes against oxidative stress via Nrf2

Andalusol (1), conchitriol (2), and lagascatriol (3) are diterpenoids produced by Sideritis species. Hydrogen peroxide-induced oxidative stress in U373-MG cells was used as an in vitro model to evaluate the cytoprotective potential, based on antioxidant properties, of these isolated compounds and to investigate the underlying mechanisms. Experimental results revealed that pretreatment with compounds 1 and 3 restored H₂O₂-induced oxidative changes by increasing cell viability, attenuating morphological changes, inhibiting intracellular ROS production and lipid peroxidation, and enhancing the antioxidant defense system. Furthermore, nuclear factor E2-related factor 2 (Nrf2) signaling was involved in the protective mechanisms of 1-3. The present findings suggest that two of the compounds studied (1 and 3) might play a preventive role in neurodegenerative diseases associated with oxidative stress.

Sideritis spp.: uses, chemical composition and pharmacological activities--a review

The genus Sideritis (Lamiaceae) comprises more than 150 perennial and annual vegetal species widely distributed in the Mediterranean area, together with Canary and Madeira islands. It is a controversial botanic genus, with a complex taxonomical classification due to the high number of hybridizations that occur between species; their study requires a deep research experience. Sideritis species have been traditionally used as teas for feeding, flavoring agents and in folk medicine as antiinflammatory, antiulcerative, antimicrobial, vulnerary, antioxidant, antispasmodic, anticonvulsant, analgesic and carminative agents. The chemical components found in Sideritis genus include terpenes, flavonoids, essential oil, iridoids, coumarins, lignanes and sterols, among others. Diterpenes, flavonoids and essential oil occur in almost every species and are the main compounds responsible for the observed in vivo and in vitro pharmacological activities. The aim of this review is to provide a comprehensive overview on the botanical, phytochemical and pharmacological aspects from the genus Sideritis, with the objective of establishing scientific basis that explains its ethnopharmacological use.

Differential antioxidant effects of consuming tea from Sideritis clandestina subsp. peloponnesiaca on cerebral regions of adult mice

Oxidative stress is involved in the pathophysiology of neurodegenerative diseases and aging. Many species of the genus Sideritis (mountain tea) are widely consumed in the Mediterranean region as herbal tea. This study evaluated the effect of supplementation of mice with herbal tea from Sideritis clandestina subsp. peloponnesiaca on the antioxidant status of different brain regions. To select the most bioactive herbal tea, the polyphenolic content (Folin-Ciocalteu method) and the antioxidant properties (ferric reducing antioxidant power [FRAP] and 2,2-diphenyl-1-picrylhydrazyl assays) of several taxa and different populations of the S. clandestina infusions were measured in vitro. Male adult mice had ad libitum access to water (control) or the herbal tea (4% w/v) for 6 weeks. At the end of the treatment period we assessed the total antioxidant power (FRAP assay) and the levels of malondialdehyde (indicator of lipid peroxidation) and reduced glutathione in the cerebral cortex, cerebellum, and midbrain. These biochemical measures have also been determined in liver samples used as a comparative reference peripheral tissue. Consumption of 4% herbal tea increased the total antioxidant power of the midbrain by 72% (P<.05); a significant (P<.05) decrease in malondialdehyde levels and increase in reduced glutathione content of the cerebellum (78% and 27%, respectively) and midbrain (59% and 32%, respectively) were also observed. These findings indicate that mountain tea consumption enhances the antioxidant defense of the adult rodent brain in a region-specific manner.

Chemical composition of ultrasonic-assisted n-hexane extracts of Sideritis scardica Grieseb. and Sideritis raeseri Boiss. & Heldr. (Lamiaceae) from Macedonia and Albania

Chemical composition of n-hexane extracts obtained from dried over-ground parts of two species of Sideritis, S. scardica Grieseb. and S. raeseri Boiss. & Heldr. (Lamiaceae) was analyzed using GC/FID/MS. The collection of plants was made on different locations in the western part of Macedonia and the southern part of Albania, comprising twelve different samples of plant material. The ultrasonic-assisted extraction process was used for preparation of the n-hexane extracts yielded 0.73-3.33 % and 9.11-10.44 % of extracts for S. scardica and S. raeseri, respectively. Over one hundred constituents of the extracts were identified, belonging to several classes of components: diterpenes, hydrocarbons, dominantly present in each of the extracts, followed by fatty acids, aliphatic and aromatic alcohols, sterols, triterpene alcohols, and monoterpenes and sesquiterpenes, which were found in much smaller amounts or only in traces. The most abundant constituents of the extracts of both species of Sideritis were two diterpene components, both with M=286, which were not fully identified. Large percentages of nonacosane (1.71-12.22% and 7.46-19.68% for S. scardica and S. raeseri, respectively) and hentriacontane (4.48-20.79% and 8.09-30.31 % for S. scardica and S. raeseri, respectively) were also found in the extracts of both species.