Phenolic acid phenethylesters and their corresponding ketones: Inhibition of 5-lipoxygenase and stability in human blood and HepaRG cells

5-lipoxygenase (5-LO) catalyzes the biosynthesis of leukotrienes, potent lipid mediators involved in inflammatory diseases, and both 5-LO and the leukotrienes are validated therapeutic targets. Caffeic acid phenethyl ester (CAPE) is an effective inhibitor of 5-LO and leukotriene biosynthesis but is susceptible to hydrolysis by esterases. In this study a number of CAPE analogues were synthesized with modifications to the caffeoyl moiety and the replacement of the ester linkage with a ketone. Several new molecules showed better inhibition of leukotriene biosynthesis than CAPE in isolated human neutrophils and in whole blood with IC50 values in the nanomolar (290-520 nmol/L) and low micromolar (1.0-2.3 µmol/L) ranges, respectively. Sinapic acid and 2,5-dihydroxy derivatives were more stable than CAPE in whole blood, and ketone analogues were degraded more slowly in HepaRG hepatocyte cultures than esters. All compounds underwent modification consistent with glucuronidation in HepaRG cultures as determined using LC-MS/MS analysis, though the modified sinapoyl ketone (10) retained 50% of its inhibitory activity after up to one hour of incubation. This study has identified at least one CAPE analogue, compound 10, that shows favorable properties that warrant further in vivo investigation as an antiinflammatory compound.

Leukotriene D4-induced Caco-2 cell proliferation is mediated by prostaglandin E2 synthesis

Leukotriene D₄ (LTD₄) is a pro-inflammatory mediator formed from arachidonic acid through the action of 5-lipoxygenase (5-LOX). Its biological effects are mediated by at least two G-coupled plasmatic cysteinyl LT receptors (CysLT_1-2R). It has been reported an upregulation of the 5-LOX pathway in tumor tissue unlike in normal colon mucosa. Colon tumors generally have an increased expression of CysLT₁R and colon cancer patients with high expression levels of CysLT₁R have poor prognosis. We previously observed that the cyclooxygenase pathway is involved in the control of intestinal epithelial cancer cell growth through PGE₂ production. The aim of this study was therefore to assess the effect of LTD₄ binding with CysLT₁R on Caco-2 cell growth. We note a number of key findings from this research. We observed that at a concentration similar to that found under inflammatory conditions, LTD₄ was able to induce Caco-2 cell proliferation and DNA synthesis. Moreover, with the use of a specific receptor antagonist this study has demonstrated that the effect of LTD₄ is a result of its interaction with CystLT₁R. We also note the possible participation of the PLC-IP₃-Ca²⁺/DAG-PKC signaling pathways in cytosolic PLA₂ and [³H]AA release induced by LTD₄-CystLT₁R interaction. Finally, we found that the resulting activation of the AA cascade and the production of PGE₂ eicosanoid could be related to the activation of cell signaling pathways such as ERK and CREB. These findings will help facilitate our understanding of how inflammatory mediators can affect the survival and dissemination of intestinal carcinoma cells.

Protection of mouse brain from aluminum-induced damage by caffeic acid

The natural product caffeic acid is a specific inhibitor of 5-lipoxygenase (5-LOX); it also possesses antioxidant and antiinflammatory properties. The current study was designed to determine whether the neuroprotective properties of caffeic acid are due to inhibition of 5-LOX. Cerebral damage was induced in mice by intracerebroventricular microinjection of aluminum (5.0 microg aluminum in 2.0 microL, once a day, for 5 days). Caffeic acid was administered intragastrically at 30 min prior to aluminum and repeated daily for an additional 10 days. The brain injury was determined by observation of behavioral changes in mice, as well as by measuring biochemical and pathological changes in the cerebral tissue. The levels of 5-LOX proteins and 5-LOX mRNA expression were measured in brain tissue. Aluminum impaired learning and memory in mice produced neuronal death in hippocampi, elevated brain malondialdehyde levels, increased protein expression of amyloid precursor protein (APP), amyloid beta, and 5-LOX. It also increased 5-LOX mRNA expression and decreased choline acetyl transferase (ChAT) protein expression in the brain tissue of mice. Caffeic acid prevented brain damage as well as behavioral and biochemical changes caused by aluminum overload. The results of this study suggest that overexpression of 5-LOX accompanies the cerebral injury induced by aluminum overload in mice, and that selective inhibitors of 5-LOX may have potential value in the treatment of aluminum neurotoxicity and conceivably of diseases associated with neuronal injury.