Callistemon genus- a review on phytochemistry and biological activities

Exploring the Anti-Inflammatory Potential of Australian Native Plants Based on their Ethnopharmacological Knowledge

Inflammation represents the inherent protective reaction of the human body to various harmful agents and noxious stimuli. Standard anti-inflammatory therapy including nonsteroidal anti-inflammatory drugs are associated with several side effects. In the past decades, people rely on medicinal plants for the treatment of inflammation. The traditional utilization of medicinal plants is regarded as a safe, cost-effective, and broadly accepted approach. In this study, anti-inflammatory activity of plants traditionally utilized by the D'harawal people in Australia has been assessed in vitro. Eighty Australian native plants were screened based on the Dharawal Pharmacopeia for their inhibitory effect on the nitric oxide (NO) production in lipopolysaccharides (LPS) and interferon (IFN)-γ stimulated RAW 264.7 murine macrophages for their anti-inflammatory activity. From the eighty ethanolic extracts screened, seventeen displayed potent NO inhibition with an IC50 recorded below 15 μg/mL. The aim of this review was to utilise the ethnopharmacological knowledge and to correlate the anti-inflammatory activity of the seventeen plants with either their known or unknown phytochemicals reported in the literature. In doing so, we have created a snapshot of Australian native plant candidates that warrant further chemical investigation associated with their anti-inflammatory activity.

Comparative Studies of Essential Oil Composition and Biological Activities of Callistemon citrinus from Western Himalaya

This work described a comprehensive study to estimate chemical constituents of essential oils (EOs) extracted from different parts of the Callistemon citrinus viz: fruits, leaves and aerial part. The EOs were characterized using physicochemical parameters, and GC-FID/MS. It was observed that among different parts, aerial part has the highest oil yield (0.90 %) followed by leaves and fruits. Further, seventeen compounds were characterized, and represented total amount (97.2-99.5 %) with domination of monoterpenes (12.5-34.6 %) and oxygenated monoterpenes hydrocarbon (61.8-86.8 %). α-pinene (11.8-24.7 %), α-phellandrene (1.2-3.0 %), p-cymene (3.3-3.9 %) and 1,8-cineole (58.3-85.1 %) were found as major compounds in C. citrinus samples. These major compounds are the quality chemical markers of C. citrinus oil. The findings revealed significant quantitative variations in EO composition of samples and were also clearly supported by multivariate statistical analysis. Moreover, EOs were evaluated for glucosidase and colon cancer cell lines inhibitory activities, which were found promising.

Melaleuca rugulosa (Link) Craven Tannins: Appraisal of anti-inflammatory, radical scavenging activities, and molecular modeling studies

ETHNOPHARMACOLOGICAL RELEVANCE

Genus Melaleuca or tea tree species are well known to be an important source of biological active oils and extracts. The biological significance appears in their usage for treatment of several clinical disorder owing to their traditional uses as anti-inflammatory, antibacterial, antifungal, and cytotoxic activities.

AIM OF THE STUDY

Our study aimed to investigate the metabolic profile of the M. rugulosa polyphenol-rich fraction along with determination of its anti-inflammatory potential, free radical scavenging and antiaging activities supported with virtual understanding of the mode of action using molecular modeling strategy.

MATERIALS AND METHODS

The anti-inflammatory activity of the phenolic rich fraction was investigated through measuring its inhibitory activity against inflammatory mediators viz tumor necrosing factor receptor-2 (TNF-α) and cyclooxygenases 1/2 (COX-1/2) in a cell free and cell-based assays. Moreover, the radical scavenging activity was determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH), oxygen radical absorbance capacity (ORAC) and β-carotene assays, while the antiaging activity in anti-elastase, anti-collagenase, and anti-tyrosinase inhibitory assays. Finally, the biological findings were supported with molecular docking study using MOE software.

RESULTS

The chromatographic purification of the polyphenol-rich fraction of Melaleuca rugulosa (Link) Craven afforded fourteen phytoconstituents (1-14). The anti-inflammatory gauging experiments demonstrated inhibition of inflammatory-linked enzymes COX-1/2 and the TNF-α at low μg/mL levels in the enzyme-based assays. Further investigation of the underlying mechanism was inferred from the quantification of protein levels and gene expression in the lipopolysaccharide (LPS)-activated murine macrophages (RAW264.7) in vitro model. The results revealed the reduction of protein synthesis of COX-1/2 and TNF-α with the down regulation of gene expression. The cell free in vitro radical scavenging assessment of the polyphenol-rich fraction revealed a significant DPPH reduction, peroxyl radicals scavenging, and β-carotene peroxidation inhibition. Besides, the polyphenol-rich fraction showed a considerable inhibition of the skin aging-related enzymes as elastase, collagenase, and tyrosinase. Ultimately, the computational molecular modelling studies uncovered the potential binding poses and relevant molecular interactions of the identified polyphenols with their targeted enzymes. Particularly, terflavin C (8) which showed a favorable binding pose at the elastase binding pocket, while rosmarinic acid (14) demonstrated the best binding pose at the COX-2 catalytic domain. In short, natural polyphenols are potential candidates for the management of free radicals, inflammation, and skin aging related conditions.

CONCLUSION

Natural polyphenols are potential candidates for the management of free radicals, inflammation, and skin aging related conditions.

Pharmacological action and underlying molecular mechanism of Callistemon: A genus of promising medicinal herbs

INTRODUCTION

The genus Callistemon belongs to a group of medically significant plants which have found tremendous use in traditional medicine across the globe. They are reported for anti-cancer, neuroprotective, anti-inflammatory, antioxidant, anti-microbial, and many other significant medicinal attributes. However, the current use of this genus is limited mainly to ornamental and recreational purposes. Recent studies have reported several novel compounds like phloroglucinol derivatives, terpenes, phenolics, etc., from Callistemon spp., which have great medical significance. Further, there is a surge of recent studies reporting novel pharmacological properties of Callistemon. The number of review studies discussing the underlying molecular mechanism behind the pharmacological action of Callistemon is quite limited.

METHODS

The literature search for studies published from 1991 to 2021 using Google scholar and PubMed were selected. The review documented relevant literature focused on Callistemon spp exhibiting significant pharmacological effects.

RESULTS

This review deals with the pharmacological properties of Callistemon and the underlying molecular mechanism responsible for protective effect in several pathophysiological conditions. This study updated the current information regarding the medicinal importance of Callistemon spp. for research and the public community.

DISCUSSION AND CONCLUSIONS

The preliminary studies, interrogating pharmacological properties of Callistemon spp., hold great promise and demand further research to decipher the mode of action. More and more research are needed in this direction to explore the full potential of the genus Callistemon as a medicinal herb.

The phloroglucinol calcitrinone A, a novel mitochondria-targeting agent, induces cell death in breast cancer cells

Breast cancer is the most common cancer and the leading cause of cancer-related mortality among females worldwide. From the leaves of Callistemon citrinus, we have isolated a novel phloroglucinol dimer, calcitrinone A, and analyzed its potential anticancer activity using the triple-negative breast cancer cell line MDA-MB-231. Calcitrinone A decreased the total intracellular ATP levels, inhibited proliferation, and induced apoptosis in MDA-MB-231 cells, but was less toxic to peripheral blood mononuclear cells. The antiproliferative and apoptosis-inducing effects of calcitrinone A were confirmed in vivo using breast cancer xenografts grown on chick chorioallantoic membranes. Mechanistic analysis showed mitochondrial membrane-potential dissipation and interference with energy-yielding processes resulting in cell accumulation in the S phase of the cell cycle. Seahorse assay analysis revealed an early inhibition of mitochondrial oxidative phosphorylation (OXPHOS). At the molecular level, calcitrinone A inhibited activity of the succinate-coenzyme Q reductase (SQR) (mitochondrial complex II). In silico docking identified the coenzyme Q binding pocket as a possible high affinity binding site for calcitrinone A in SQR. Inhibition of complex II was accompanied by strong elevation of mitochondrial superoxide and cytoplasmic ROS. Calcitrinone A might be a promising anticancer lead compound acting through the interference with the mitochondrial complex II activity.

In silico and in vitro studies of isolated constituents from Callistemon citrinus leaves: Anti-microbial potential and inhibition of iNOS activity

Phytochemical investigation of Callistemon citrinus (Curtis) Skeels (syn. Callistemon lanceolatus (Sm.) Sweet and Melaleuca citrina (Curtis) Dum.Cours.) leaves resulted in the isolation of five undescribed compounds, including one acylphloroglucinol derivative and four monoterpene galloylglucosides, in addition to 29 known diverse secondary metabolites. Interestingly, this study reports chemosystematically significant isolation of the monoterpene galloylglucosides from the genus for the first time. Furthermore, exploration of the isolated compounds as inhibitors of inflammation-related molecular targets, molecular docking studies targeting human adipocyte lipid-binding protein FABP4 (3P6H) and human nitric oxide synthase (3E7G) were carried out in order with the in vitro evaluation of the isolated compounds for their anti-microbial and inhibitory of inducible nitric oxide synthase (iNOS) activities. Molecular docking studies revealed that eighteen compounds showed lower docking scores than ibuprofen, the native ligand in the crystal structure 3P6H, and nine compounds showed lower docking scores than AR-C95791, the native ligand in the binding site of 3E7G. Additionally, in vitro studies revealed that seven compounds showed moderate iNOS inhibitory activity. They also were moderately cytotoxic to HepG2, LLC-PK₁ and Vero cells. Pulverulentone A showed moderate antibacterial activity against MRSA (IC₅₀ 22.2 μM) and antifungal activity against C. neoformans, while corosolic acid showed strong antibacterial activity against VRE (IC₅₀ 15.9 μM).Thus, the in silico and in vitro studies indicated that some isolated compounds hold potentials as inhibitors of iNOS activity and anti-microbial agents.