Discovery of anti-inflammatory compounds from Australian rainforest plants

Inflammation is an important biological process for maintaining the body’s homeostasis and is essential for successfully fighting pathogens as well as the repair of damaged tissue in the body. However, inflammatory processes are also involved in the onset and maintenance of diseases like rheumatoid arthritis, asthma, chronic inflammatory bowel diseases, type 2 diabetes, cancer and neurodegenerative diseases. The currently available list of approved anti-inflammatory agents mainly consists of nonsteroidal anti-inflammatory drugs, steroidal anti-inflammatory drugs, and anti-inflammatory biologics. Despite this arsenal, therapy is often not effective enough or is hampered by severe side effects including stomach ulcers, renal toxicity, and increase in the risk of thrombotic events. Thus, the discovery of safer anti-inflammatory agents with less severe side effects is still extremely desirable for the treatment of inflammatory diseases. This thesis describes the screening of crude ethanolic extracts of 100 Australian rainforest plant samples from the Northern Queensland region of Australia. It goes on to explore the chemical diversity of three selected plants samples with potent anti-inflammatory activity. This study led to the isolation of 14 pure compounds, out of which 7 are reported for the first time. The anti-inflammatory activity of these compounds have been demonstrated as their potential to downregulate nitric oxide production in LPS/IFN-γ activated RAW 264.7 macrophage cell line

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

Anti-inflammatory activity of prenyl and geranyloxy furanocoumarins from Citrus garrawayi (Rutaceae)

Anti-inflammatory activity guided isolation from Citrus garrawayi (Rutaceae) led to the discovery of five new garracoumarins A – E (1 - 5), and five known (6 – 10) isoprenylated furanocoumarins and the known sterol bourjotinolone A (11). Discussed herein is the anti-inflammatory structure activity relationship of the ten furanocoumarins and a detailed spectroscopic analysis leading to the structure elucidation of the new and known isoprenylated furanocoumarins

Costatamins A - C, new 4-phenylcoumarins with anti-inflammatory activity from the Australian woodland tree Angophora costata (Myrtaceae)

The bioassay guided isolation of new anti-inflammatory metabolites from the Australian Indigenous plant Angophora costata, led to the discovery of three new 4-phenylcoumarins, costatamins A – C (1–3). The structures were determined by detailed spectroscopic analysis. Costatamins A – C were evaluated for their inhibitory effects on (a) NO production and (b) downregulation of TNF-α in RAW 264.7 macrophages, displaying an inhibitory range of 20–30 μg/mL for both the inflammatory markers

[In Press] Acronyols A and B, new anti-inflammatory prenylated phloroglucinols from the fruits of Acronychia crassipetala

Two new phloroglucinols, acronyols A (1) and B (2) along with the four known (3–6) pholoroglucinols were identified following anti-inflammatory activity guided fractionation from the fruits of Acronychia crassipetala (family Rutaceae). The pholoroglucinols (1–6) were evaluated for their inhibitory effects on NO production and downregulation of TNF-a in RAW 264.7 macrophage cell lines

The reciprocal EC50 value as a convenient measure of the potency of a compound in bioactivity-guided purification of natural products

Identification of potent natural products is a challenging task in which sophisticated separation processes including HPLC are employed. The bioactivity of HPLC fractions is determined with a bioassay, and the most potent compounds are progressed to structural elucidation. In pharmacology, the potency of a compound is expressed as the half-maximal effective concentration (EC50), which refers to the concentration of a drug that induces a response halfway between the baseline and maximum. While expressing the potency of a compound by its EC50 value makes sense in a clinical context, it is counterintuitive in the context of bioactivity-guided purification, as the potency of a compound is inversely related to its EC50 value, and the most potent compound is the one with the lowest EC50. In natural products chemistry, it would be more logical if an increase in potency would be reflected by an increase of a parameter reflecting the potency. In this study, we introduce the term “effective dilution volume (EDV50)” as the reciprocal of the EC50 (1/EC50). We show how the EDV50 can be used to identify potent compounds in chromatographic separations, allowing to easily graph and identify anti-inflammatory compounds. We show two examples of this approach by overlaying an HPLC chromatogram with the EDV50 to point out the most potent compounds. We hope that the EDV50 will make the illustration of active fractions containing potent compounds in a chromatogram obvious for the reader and will become a useful graphic tool in the natural products literature in the future

Mulgravanols A and B, rare oxidized xanthenes and a new phloroglucinol isolated from the Australian rainforest plant Waterhousea mulgraveana (Myrtaceae)

Phytochemical investigation of the Australian rainforest plant leaves Waterhousia mulgraveana, yielded two rare oxidized xanthenes, mulgravanols A (1) and B (2) along with a new phloroglucinol, mulgravanol C (3). Mulgravanol A (1) is the first reported example of a complex xanthene flanked by a methine bridged phloroglucinol unit. All the compounds displayed moderate inhibitory effects on nitric oxide production and TNF-α release in RAW 264.7 macrophages (IC50) 42–55 μM. The structures of the new compounds were assigned based on a detailed spectroscopic interpretation

Diarylheptanoids with anti-inflammatory activity from the rhizomes of Pleuranthodium racemigerum (Zingiberaceae)

Three new metabolites, 1-(4′′-Methoxyphenyl)-7-(3′,4′-di-hydroxyphenyl)-(E)-hept-2-ene (1), 1-(4′′- Methoxyphenyl)-7-(3′,4′-di-methoxyphenyl)-(E)-hept-2-ene (2), 1-(4′′-Methoxyphenyl)-7-(4′-methoxyphenyl)- (E)-hept-2-ene (3), and the known diaryl heptanoid (4) were identified following anti-inflammatory activity guided fractionation from the rhizomes of Pleuranthodium racemigerum (Zingiberaceae). These diaryl heptanoids (1 – 4) were evaluated for their inhibitory effects on NO production and downregulation of TNF-α in RAW 264.7 macrophages and N-11 microglial cell lines)

A new anti-inflammatory phenolic monosaccharide from the Australian native rainforest plant Elaeocarpus eumundi

Chemical analysis of the ethanolic extract of the Australian rainforest plant Elaeocarpus eumundi yielded a new phenolic monosaccharide (1) and the known dihydropieceid (2). The structures of both compounds were elucidated based on the spectroscopic methods including UV, HR-ESIMS and 1D, 2D NMR data. Compounds 1 and 2 exhibited good anti-inflammatory activity in LPS and IFN-γ activated RAW 264.7 macrophage cells