Ternstroenols A - E: Undescribed pentacyclic triterpenoids from the Australian rainforest plant Ternstroemia cherryi

From the Bush to the Brain: Preclinical Stages of Ethnobotanical Anti-Inflammatory and Neuroprotective Drug Discovery-An Australian Example

The Australian rainforest is a rich source of medicinal plants that have evolved in the face of dramatic environmental challenges over a million years due to its prolonged geographical isolation from other continents. The rainforest consists of an inherent richness of plant secondary metabolites that are the most intense in the rainforest. The search for more potent and more bioavailable compounds from other plant sources is ongoing, and our short review will outline the pathways from the discovery of bioactive plants to the structural identification of active compounds, testing for potency, and then neuroprotection in a triculture system, and finally, the validation in an appropriate neuro-inflammatory mouse model, using some examples from our current research. We will focus on neuroinflammation as a potential treatment target for neurodegenerative diseases including multiple sclerosis (MS), Parkinson's (PD), and Alzheimer's disease (AD) for these plant-derived, anti-inflammatory molecules and highlight cytokine suppressive anti-inflammatory drugs (CSAIDs) as a better alternative to conventional nonsteroidal anti-inflammatory drugs (NSAIDs) to treat neuroinflammatory disorders.

Flavonoids and saponins: What have we got or missed?

BACKGROUND

Flavonoids and saponins are important bioactive compounds that have attracted wide research interests. This review aims to summarise the state of the art of the pharmacology, toxicology and clinical efficacy of these compounds.

METHODS

Data were retrieved from PubMed, Cochrane Library, Web of Science, Proquest, CNKI, Chongqing VIP, Wanfang, NPASS and HIT 2.0 databases. Meta-analysis and systematic reviews were evaluated following the PRISMA guideline. Statistical analyses were conducted using SPSS23.0.

RESULTS

Rising research trends on flavonoids and saponins were observed since the 1990s and the 2000s, respectively. Studies on pharmacological targets and activities of flavonoids and saponins represent an important area of research advances over the past decade, and these important resources have been documented in open-access specialised databases and can be retrieved with ease. The rising research on flavonoids and saponins can be attributed, at least in part, to their links with some highly investigated fields of research, e.g., oxidative stress, inflammation and cancer; i.e., 6.88% and 3.03% of publications on oxidative stress cited by PubMed in 1990 - 2021 involved flavonoids and saponins, respectively, significantly higher than the percentage involving alkaloids (1.88%). The effects of flavonoids concern chronic venous insufficiency, cervical lesions, diabetes, rhinitis, dermatopathy, prostatitis, menopausal symptoms, angina pectoris, male pattern hair loss, lymphocytic leukaemia, gastrointestinal diseases and traumatic cerebral infarction, etc, while those of saponins may have impact on venous oedema in chronic deep vein incompetence, erectile dysfunction, acute impact injuries and systemic lupus erythematosus, etc. The volume of in vitro research appears way higher than in vivo and clinical studies, with only 10 meta-analyses and systematic reviews (involving 290 interventional and observational studies), and 36 clinical studies on flavonoids and saponins. Data are sorely needed on pharmacokinetics, in vitro pan-assay interferences, purity of tested compounds, interactions in complex herbal extracts, real impact of anti-oxidative strategies, and mid- and long-term toxicities. To fill these important gaps, further investigations are warranted. On the other hand, drug interactions may cause adverse effects but might also be useful for synergism, with the goals of enhancing effects or of detoxifying. Furthermore, the interactions between phytochemicals and the intestinal microbiota are worth investigating as the field may present a promising potential for novel drug development.

Ternstroenol F: a new pentacyclic triterpenoid saponin isolated from the Australian rainforest plant Ternstroemia cherryi

A detailed close phytochemical investigation of the fruits of Ternstroemia cherryi led to the isolation and identification of the minor metabolite, ternstroenol F, which possessed the usual barrigenol-like terpenoid backbone. The notable difference was that this minor metabolite had the 2(E)-4(Z)-6(E)-decatrienoic acid forming an ester bond at C-22 of the oleanane backbone. Ternstroenol F was evaluated for its inhibitory effects on NO inhibition, cell viability and TNF- α release in RAW 264.7 macrophages, displaying an IC₅₀ values of 0.23, 0.81 and 1.84 µM respectively.

Eupomatenes A - E: Neolignans isolated from the leaves of Australian rainforest plant Eupomatia laurina

A detailed phytochemical investigation of the leaves of the Australian rainforest tree Eupomatia laurina, led to the discovery of five new neolignans, eupomatenes A - E and eight known compounds, eupomatenoid-2, trans-(2'S)-2-[1'-(4-methoxyphenyl)prop-2'-yl]anethol, chlorogenic acid, chlorogenic acid-methyl ester, tyrosol-1-O-β-xylopyranosyl-1(1 → 6)-O-β-glucopyranoside, leucoside, kaempferol-3-O-neohesperidoside, and pachypodol. The structures of all the compounds were determined by detailed spectroscopic analysis. All compounds were also evaluated for their anti-inflammatory properties by assessing their inhibitory effects on nitric oxide (NO) production and TNF- α release in RAW 264.7 macrophages. Whilst slight anti-inflammatory activity (in terms of inhibition of NO production) was observed with eupomatenes A - E, this was also associated with high levels of cell growth inhibition.

Potential anti-neuroinflammatory compounds from Australian plants - A review

Neuroinflammation is a complex response to brain injury involving the activation of glia, release of inflammatory mediators, such as cytokines and chemokines, and generation of reactive oxygen and nitrogen species. Even though it is considered an event secondary to neuronal death or dysfunction, neuro-inflammation comprises a majority of the non-neuronal contributors to the cause and progression of neurodegenerative diseases like Alzheimer's Disease (AD), Parkinson's Disease (PD), Multiple Sclerosis (MS), Chronic Traumatic Encephalopathy (CTE) and others. As a result of the lack of effectiveness of current treatments for neurodegenerative diseases, neuroinflammation has become a legitimate therapeutic target for drug discovery, leading to the study of various in vivo and in vitro models of neuroinflammation. Several molecules sourced from plants have displayed anti-inflammatory properties in the study of neurodegenerative diseases. A group of these anti-inflammatory compounds has been classified as cytokine-suppressive anti-inflammatory drugs (CSAIDs), which target the pro-inflammatory AP1 and nuclear factor-κB signaling pathways and inhibit the expression of many pro-inflammatory cytokines, such as interleukin IL-1, IL-6, TNF-α, or nitric oxide. Australian plants, thriving amid the driest inhabited continent of the world, are an untapped source of chemical diversity in the form of secondary metabolites. These compounds are produced in response to biotic and abiotic stresses that the plants are exposed to in the highly biodiverse environment. This review is an attempt to highlight anti-inflammatory compounds isolated from Australian plants.