Supercritical‑CO2 extraction, identifcation and quantifcation of polyprenol as a bioactive ingredient from Irish trees species

Abstract

Plants are a staple of balanced diet and also an important remedial source for various ailments1,2 . Plants are essential for pharmacological research and drug development, where they are sources of direct therapeutic drugs, precursor materials for drug synthesis, and models for pharmacologically active compounds3 . One such compound class exploited for the aforementioned reasons are that of polyisoprenoids4,5 . Polyisoprenoids (polymers of isoprene unit) are linear hydrophobic, branched chains of fatty alcohol6 . Polyisoprenoids are divided into two main subgroups found in nature difering based on the hydrogenation status of α-terminal double bond in the molecule, polyprenols (α-unsaturated) and dolichols (α-saturated)4,7,8 (Supplementary Fig. S17 ). Polyprenols are long-chain isoprenoid polymers with the formula (C5H8)nOH, that can be found in a wide range of natural sources, including bacteria and plants. In mammals, the mono-saturated dolichols are dominant4,9,10. Plants represent the widest range of polyprenols diversity, containing both poly-cis/trans-prenols6 . Polyprenols are always found as a mixture of homologues difering in the number of isoprene units11. Te degree of polymerization of polyprenols is specifc to plant species, growth stages and cultivation/growth conditions8 . In the human body polyprenols are metabolised into dolichols and dolichyl phosphate by enzymatic catalysis11. In humans, dolichols regulate the permeability and stability of membranes, partaking in the biosynthesis of human glycoproteins11,12. Both dolichols and polyprenols are found in the form of esters, carboxylic acids and free alcohol in the cell13, while a small portion is found in the form of phosphates14. Polyprenols have non-carcinogenic, non-mutagenic, non-teratogenic and non-toxic efects in humans15–17, while also providing signifcant anti-tumour, anti-anaemia, anti-HIV and anti-hepatitis C efects18,19. Polyprenols have also been found to positively afect conditions such as hypertension, high cholesterol, gout, lupus and diabetes, along with other disorders disturbing proper immune functionality13,20,21. Moreover, polyprenols serve as a chemotaxonomic marker for systematic families in botanic taxonomy22, and also act as a scavenger against oxygen species generated by chemicals or accumulated upon ageing or UV light23. Polyprenols extracted from Ginkgo biloba leaves showed anti-bacterial efects against Escherichia coli, Salmonella enterica, Bacillus subtilis24. More studies are required on researching plant sources of polyprenol compounds and their derivatives as suggested in a review by Zhang et al. for developing plant extracts into products for therapeutic use5 .