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BackgroundCallistemon citrinus (Curtis.) (Family- Myrtaceae) is a popular evergreen shrub in Bangladesh. In the present study, the leaves of this plant have been assessed comprehensively for free radical scavenging, thrombolytic and membrane stabilizing activities.MethodsThe leaves were collected, powdered and extracted with methanol. The extract was then concentrated and successively fractionated into petroleum ether, carbon tetrachloride, chloroform and aqueous soluble fractions. The extractives were investigated for free radical scavenging, thrombolytic and membrane stabilizing activities.ResultsIn case of 1,1 diphenyl-2-picrylhydrazyl (DPPH) and hydrogen peroxide radical scavenging assays, the crude methanol extract of the leaves showed the highest free radical scavenging activity among the tested materials including standard ascorbic acid (p = 0.0000). Besides, this extract was also found significantly rich (p = 0.0000) in phenolics and flavonoids compared to other organic fractions. In thrombolytic study, the petroleum ether fraction exhibited significantly stronger thrombolysis (p = 0.024) than other leaf extractives but was weaker than the standard streptokinase. In membrane stabilizing assay, the activity of chloroform fraction was similar to that of standard acetylsalicylic acid (p = 1.000) in hypotonic solution induced hemolysis. However, membrane stabilization activity of this chloroform fraction was found significantly stronger than that of the standard (p = 0.0000) in heat induced hemolysis.ConclusionThis study has revealed the medicinal capabilities of different organic fractions of C. citrinus displaying free radical scavenging, thrombolysis and membrane stabilizing antiinflammatory potentials. Further bioactivity guided isolation is required to obtain pharmacologically secondary metabolites.

A preliminary study was conducted to demonstrate fate of the bacterial storage compound poly‐β‐hydroxybutyrate (PHB) once ingested and degraded in vivo in crustaceans. The 2% supplementation of 13C‐labeled Ralstonia eutropha DSM545 containing 75% PHB on dry weight in postlarval whiteleg shrimp, Litopenaeus vannamei resulted in consistent enrichment of two fatty acids (containing 14–24 carbons [C] in length) pentadecanoic acid (15:0) and palmitic acid (16:0) in all lipid fractions. This could indicate that 13C signal may not only originate from the PHB but partly from the structural components of the bacterial cell. There was a trend of lower 13C enrichment in various lipid fractions of the postlarvae as compared to the diet. These findings may have important implications as to potential of PHB as energy source rather than as building block. There was a rapid transfer of 13C in the postlarvae as seen by the significant 13C enrichment in the tissues 4 hr after feeding with labeled bacterial cells. Overall, the assimilation of PHB in crustacean tissues is demonstrated for the first time. Our results indicate that PHB once ingested is rapidly assimilated in the tissues and could probably act as an energy source rather than as a building block.

In marine invertebrates, lipids are the predominant organic reserve (Sánchez-Paz et al., 2006). It has energetic and structural functions during embryonic and early larval development (Mourente, Medina, Gonzalez, & Rodriguez, 1995). Aside from these, lipids are also known to act as energy reserve and are needed for the maintenance and integrity of cellular membranes and serve as precursors for metabolic regulators such as prostaglandins, thromboxans and prostacyclins, hormones that promote maturation and moulting

The analgesic potential of the leaves of Callistemon citrinus was reported earlier but no active principle for this analgesia was explored. To identify the major analgesic metabolite(s), the leaves were extracted with methanol and fractionated into petroleum ether, carbon tetrachloride, chloroform and aqueous soluble fractions. Based on the thin layer chromatography, the carbon tetrachloride fraction was subjected to gel permeation chromatography and a compound (1) was isolated, which was characterized as β-amyrin. Compound (1) displayed significant peripheral analgesia (p < 0.05) on mice model at an oral dose 200 mg/kg body weight. It also showed noticeable anti-inflammatory membrane stabilizing activity. In silico docking study of β-amyrin with cyclooxygenase (COX)-2 showed a good binding affinity (–9.1 Kcal/mol). Virtual pharmacokinetics and toxicity studies explore its potentials as a lead molecule having no extreme lethality.