Evidence for effective structure-based neuromodulatory effects of new analogues of neurosteroid allopregnanolone

The neurosteroid allopregnanolone (AP) modulates neuroendocrine/neurobiological processes, including hypothalamic-pituitary-adrenocortical activities, pain, anxiety, neurogenesis and neuroprotection. These observations raised the hope of developing AP-based therapies against neuroendocrine and/or neurodegenerative disorders. However, the pleiotropic actions of AP, particularly its cell-proliferation-promoting effects, hamper the development of selective/targeted therapies. For example, although AP-induced neurogenesis may serve to compensate neuronal loss in degenerative brains, AP-evoked cell-proliferation is contraindicated for steroid-sensitive cancer patients. To foster progress, we synthesised 4 novel AP analogues of neurosteroids (ANS) designated BR053 (12-oxo-epi-AP), BR297 (O-allyl-epi-AP), BR351 (O-allyl-AP) and BR338 (12-oxo-AP). First, because AP is well-known as allosteric modulator of GABAA receptors (GABAA-R), we used the electrophysiological patch-clamp technique to determine the structure-activity relationship of our ANS on GABAA-activated current in NCB20 cells expressing functional GABAA-R. We found that the addition of 12-oxo-group did not significantly change the respective positive or negative allosteric effects of 3α-AP or 3β-(epi)-AP analogues. Importantly, substitution of the 3α-hydroxyl-group by 3α-O-allyl highly modified the ANS activities. Unlike AP, BR351 induced a long-lasting desensitisation/inhibition of GABAA-R. Interestingly, replacement of the 3β-hydroxyl by 3β-O-allyl (BR297) completely reversed the activity from negative to positive allosteric action. In a second step, we compared the actions of AP and ANS on SH-SY5Y neuronal cell viability/proliferation using MTT-reduction assays. Different dose-response curves were demonstrated for AP and the ANS. By contrast to AP, BR297 was totally devoid of cell-proliferative effect. Finally, we compared AP and ANS abilities to protect against oxidative stress-induced neuronal death pivotally involved in neurodegenerative diseases. Both BR351 and BR297 had notable advantages over AP in protecting SH-SY5Y cells against oxidative stress-induced death. Thus, BR297 appears to be a potent neuroprotective compound devoid of cell-proliferative activity. Altogether, our results suggest promising perspectives for the development of neurosteroid-based selective and effective strategies against neuroendocrine and/or neurodegenerative disorders.

Toxicological potential of 2-alkylcyclobutanones – specific radiolytic products in irradiated fat-containing food – in bacteria and human cell lines

Food irradiation has been considered as a safe processing technology to improve food safety and preservation, eliminating efficiently bacterial pathogens, parasites and insects. This study aims to characterize the toxicological potential of 2-alkylcyclobutanones (2-ACBs), radiolytic derivatives of triglycerides, formed uniquely upon irradiation of fat-containing food. In irradiated food they are generated proportionally to fat content and absorbed radiation dose. The cyto- and genotoxic potentials of various highly pure synthetic 2-ACBs were studied in bacteria and human cell lines. While pronounced cytotoxicity was evident in bacteria, no mutagenic activity has been revealed by the Ames test in Salmonella strains TA 97, TA 98 and TA 100. In mammalian cells genotoxicity was demonstrated mainly by the induction of DNA base lesions recognized by the Fpg protein as determined by both the Comet Assay and the Alkaline Unwinding procedure. Formation of DNA strand breaks was observed by the Alkaline Unwinding procedure but not by the Comet Assay. The extent of cytotoxicity and genotoxicity were dependent on chain length and degree of unsaturation of the fatty acid chain. Further studies will have to clarify mechanisms of action and potential relevance for human exposure situation.

Different apoptotic mechanisms are involved in the antiproliferative effects of 7beta-hydroxysitosterol and 7beta-hydroxycholesterol in human colon cancer cells

Plant sterols are found in fruits and vegetables. Their cholesterol-lowering effect is well documented. Our study aimed at comparing antiproliferative effects of 7beta-hydroxysitosterol (7beta-OHsito) versus 7beta-hydroxycholesterol (7beta-OHchol) on the human colon cancer cell line Caco-2. When cells were exposed for 32 h to 60 microM 7beta-OHsito or to 30 microM 7beta-OHchol, both compounds caused 50% growth inhibition. Cells treated with 7beta-OHsito showed enhanced caspase-9 and -3 activities followed by DNA fragmentation. In contrast, 7beta-OHchol did not activate caspase-3 and activation of caspase-9 and DNA fragmentation were delayed. The treatment of cells with the caspase inhibitor Z-VAD.fmk retarded the 7beta-OHsito-induced apoptotic process but not that triggered by 7beta-OHchol. Our data suggest that the two compounds in spite of their structural similarities target different cellular pathways, which lead to cell death.

Detection of 2-alkylcyclobutanones, markers for irradiated foods, in adipose tissues of animals fed with these substances

Laboratory rats received a freshly prepared drinking fluid containing 0.005% 2-tetradecyl- or 2-tetradecenyl-cyclobutanones daily for 4 months. These two compounds were recovered in the adipose tissues of the animals that consumed them. Less than 1% of the 2-alkylcyclobutanones ingested daily were excreted in the feces. In addition, our data indicate that 2-alkylcyclobutanones are able to cross the intestinal barrier, to enter into the bloodstream, and to be stored in the adipose tissue of an animal. However, the amounts of these substances detected in the adipose tissues and in the feces were much smaller than the amounts ingested.

Unexpected reactivity of acetylenic omega-ketoesters toward TBAF and t-BuOK; new cascade reactions affording allene and oxetane derivatives

[reaction: see text]. The reactivity of acetylenic omega-ketoesters toward tetra-n-butylammonium fluoride and potassium tert-butoxide was studied. These cascade reactions proceeded smoothly and afforded either electrophilic allene derivatives or highly functionalized oxetane derivatives in moderate to high yields.

Supercritical fluid extraction of hydrocarbons and 2-alkylcyclobutanones for the detection of irradiated foodstuffs

Supercritical carbon dioxide can be used to carry out a selective and fast extraction (30 min) of volatile hydrocarbons and 2-alkylcyclobutanones contained in irradiated foods. After elimination of the traces of triglycerides still contained in the extracts on a silica column, the compounds were analysed by gas chromatography-mass spectroscopy (2-alkylcyclobutanones) and gas chromatography-flame ionization detection (volatile hydrocarbons). The present method was applied successfully to freeze-dried samples (1 g or less) of cheese, chicken, avocados and to various ingredients (chocolate, liquid whole eggs) included in non-irradiated cookies. It was faster (4-5 h) than the reference methods EN 1784 (volatile hydrocarbons) and EN 1785 (2-alkylcyclobutanones), which take 1.5 days each. The minimal dose detectable by this method is, in addition, slightly lower than those of the reference methods.

2-Alkylcyclobutanones as markers for irradiated foodstuffs. III. Improvement of the field of application on the EN 1785 method by using silver ion chromatography

The inclusion of a purification step by silver ion chromatography in the EN 1785 analytical protocol for 2-alkylcyclobutanones (validated by the European Committee for Standardization for the detection of ionizing radiation treatment) has considerably improved the quality of the chromatograms obtained, allowing the detection of food samples irradiated at very low doses (0.1 kGy) or irradiated ingredients included in low proportions in non irradiated foodstuffs. This analytical modification of the protocol EN 1785 ought thus to permit a very considerable extension of its current field of application.