Chemistry and Biochemistry Aspects of the 4-Hydroxy-2,3-trans-nonenal

4-hydroxy-2,3-trans-nonenal (C9H16O2), also known as 4-hydroxy-2E-nonenal (C9H16O2; HNE) is an alpha,beta-unsaturated hydroxyalkenal. HNE is a major aldehyde, formed in the peroxidation process of omega-6 polyunsaturated fatty acids (omega-6 PUFAs), such as linoleic and arachidonic acid. HNE is not only harmful but also beneficial. In the 1980s, the HNE was regarded as a "toxic product of lipid peroxidation" and the "second toxic messenger of free radicals". However, already at the beginning of the 21st century, HNE was perceived as a reliable marker of oxidative stress, growth modulating factor and signaling molecule. Many literature data also indicate that an elevated level of HNE in blood plasma and cells of the animal and human body is observed in the course of many diseases, including cancer. On the other hand, it is currently proven that cancer cells divert to apoptosis if they are exposed to supraphysiological levels of HNE in the cancer microenvironment. In this review, we briefly summarize the current knowledge about the biological properties of HNE.