Chemotaxonomic implications of the absence of alkaloids in Psychotria gitingensis

Neuroblastoma SH-SY5Y cytotoxicity, anti-amyloidogenic activity and cyclooxygenase inhibition of Lasianthus trichophlebus (Rubiaceae)

The anti-amyloidogenic potential and cyclooxygenase anti-inflammatory activity of Lasianthus trichophlebus extracts were evaluated. The MeOH extract (LTM) and chloroform extract (LTC) exhibited significant cytotoxic inhibition against the neuroblastoma SH-SY5Y cell with an IC₅₀ of 17.52 μg/mL and 12.28 μg/mL, respectively. Thioflavin T assay indicated the LTC extract inhibition (70.56% at 50 μg/mL) to be statistically comparable (p < 0.05) to the positive control. Cyclooxygenase inhibition against COX-1 and COX-2 enzymes gave IC₅₀ values for the LTM extract to be 18.20 and 29.60 µg/mL, respectively; while, the LTC extract showed 4.11 and 2.78 µg/mL, respectively. LC-MS of the LTM extract identified 22 putative compounds, which may prove to be pharmacologically relevant. This study has provided potential insights into the utilization of L. trichophlebus to develop safer plant-based agents for anti-inflammatory or neurodegenerative diseases.

Isolation and Characterization of Cyclotides from Brazilian Psychotria: Significance in Plant Defense and Co-occurrence with Antioxidant Alkaloids

Plants from the genus Psychotria include species bearing cyclotides and/or alkaloids. The elucidation of factors affecting the metabolism of these molecules as well as their activities may help to understand their ecological function. In the present study, high concentrations of antioxidant indole alkaloids were found to co-occur with cyclotides in Psychotria leiocarpa and P. brachyceras. The concentrations of the major cyclotides and alkaloids in P. leiocarpa and P. brachyceras were monitored following herbivore- and pathogen-associated challenges, revealing a constitutive, phytoanticipin-like accumulation pattern. Psyleio A, the most abundant cyclotide found in the leaves of P. leiocarpa, and also found in P. brachyceras leaves, exhibited insecticidal activity against Helicoverpa armigera larvae. Addition of ethanol in the vehicle for peptide solubilization in larval feeding trials proved deleterious to insecticidal activity and resulted in increased rates of larval survival in treatments containing indole alkaloids. This suggests that plant alkaloids ingested by larvae might contribute to herbivore oxidative stress detoxification, corroborating, in a heterologous system with artificial oxidative stress stimulation, the antioxidant efficiency of Psychotria alkaloids previously observed in planta. Overall, the present study reports data for eight novel cyclotides, the identification of P. leiocarpa as a cyclotide-bearing species, and the absence of these peptides in P. umbellata.

Iridoids and a Norsesquiterpenoid from the Leaves of Villaria odorata

Phytochemical investigation of Villaria odorata, a Philippine endemic Rubiaceae species, led to the identification of three iridoids, morindolide (1), hydrophylinA (2), hydrophylin B (3) and a norsesquiterpenoid, vomifoliol (4). This is the first report of compounds 1–4 from the genus Villaria. These classes of compounds proved to be important chemotaxonomic markers in the Rubiaceae family in combination with morphology and molecular data.