In a Western or Westernized diet, the abundant cholesterol is invariably associated with the presence of biochemically reactive oxysterols, the amount of which mainly depends upon the autoxidation degree of cholesterol itself, during food harvesting, production and storage. Oxysterols, in the average amount and composition detected in a high-cholesterol diet, display remarkable pro-inflammatory and cytotoxic effects on the gut epithelium. Moreover, in a low micromolar range, they may change the physiological level and membrane localization of tight junctions of the intestinal epithelial barrier, which then become leaky and permeable to microbiota. This combination of toxic effects possibly exerted by dietary oxysterols likely contributes to the impairment of the microbiota–gut–brain axis, through both direct and indirect mechanisms hereby reviewed. Importantly, dietary oxysterols are absorbed like cholesterol and circulate in the bloodstream, mainly within LDLs, rendering these micelles more oxidized and dangerous. Last but not the least, dietary oxysterols may deeply interfere with correct gut–brain signalling because of the redox pathways they are hyper-regulating and sustaining. In conclusion, protective dietary measures should be adopted, including restricted consumption of cholesterol-rich food and reduction of cholesterol autoxidation in food production and storage, for instance by supplementation of food with flavonoids and/or other bioactive substances with strong anti-oxysterol properties.
The side chain 27-hydroxycholesterol has been reported to inhibit the replication of several pathogen viruses, including herpes simplex virus, rhinovirus, rotavirus and SARS-CoV-2, in in vitro and ex vivo models.
In view of a future potential therapeutic use of 27-hydroxycholesterol, a pilot pharmacokinetic study was set up.
This active substance was complexed with 2-hydroxypropyl-β-cyclodextrin and orally administered in a single dose to CD1 male mice; its recovery in plasma and a few tissues up to 24 h post-treatment was evaluated.
The absorption of the oxysterol by the small intestine was moderate, due to its physicochemical properties, but still relevant and rapid, showing a peak at 1 h after supplementation and being almost completed 24 h after treatment. 27-Hydroxycholesterol appeared to be a high hepatic extraction drug, possibly with an extrahepatic component contributing to the total clearance.
Following the oral 25 mg/kg dosing, plasma levels of 27-hydroxycholesterol showed an average steady-state concentration similar to that shown to be able to inhibit the replication of all viruses tested so far in in vitro models.
The first pharmacokinetic data relative to a natural oxysterol administered p.o. are reported. Data should contribute to further elucidate oxysterol pathophysiology and guide non-clinical studies aiming at investigating possible therapeutic use of 27-hydroxycholesterol or its analogs.