Carbonyl Stress In Aging Process

With the epistemological advance in field of aging research, the gerontologist has recognized that the aging mechanism is a negative and stochastic process rather than active or programmed one. Now, the free radical theory of aging has been considered as "the first theory of aging" in the field of gerontology. Considering non-enzymatic glycation as well as free radical oxidation is another critical part of energy metabolism related side-reactions, and it has also been proved participated in the mechanisms of many age-related diseases, even aging process. Unsaturated carbonyls, intermediates of free radical oxidation and non-enzymatic glycation, have been reported very reactive and toxic to almost all cellular and extracellular biomacromolecules, leads us to raise a very intriguing question: whether the carbonyl stress underlaid the processes of free radical oxidation and the non-enzymatic glycation? Hence we come to this study—carbonyl stress in aging process.Accoding to the topic, we have investigated from two aspects: carbonyl stress and detoxification of carbonyl stress.Firstly, we proved the carbonyl stress played key roles in the formation of age pigment at the biochemical level. By extending the front-surface 3D-fluorescence technique to estimate age pigments, we attained the entire spectra of it, and both bluish and yellowish fluorophores had been detected, which clarified the color controversy in the field of age pigments research. In this study, the rat-tail collagen showed significant red-shift according to the "mature" process of age pigments. The fluorescent value of age pigments increased with theenhancement of carbonyl stress, and decreased with the addition of carbonyl inhibitor. All these data demonstrated that the carbonyl, especially carbonyl-amine crosslink, is at the core of formation of age pigment.Secondly, we found malondialdehyde (MDA), one of the representative carbonyls, decreased human bone marrow mesenchymal stem cells (MSC) proliferation and prolonged its population doubling time in cell culture conditions. Advanced investigation showed that the MDA induced S phase delay followed by a G2/M arrest and apoptosis acceleration of MSC accounted for the effects of above mentioned. As carbonyls can react readily, even at neutral pH and room temperature, with important biochemical groups, such as amino and thiol, we deduced that MDA might cause the alteration of cellular membrane receptor or excite any other signalling pathway, which impaired the MSC under the cell culture conditions and disordered the cellular functions.Thirdly, we discovered the carbonyl stress might be responsible for the blood viscosity increase during the storage. It was reported the inevitable side-reactions, including the free radical oxidation and the non-enzymatic glycation, were the key contributors of hemorheological alteration. They decreased the deformability of erythrocytes, activated the adhesive properties of platelets, and even resulted in vessel wall stiffness. Results from our investigation showed that the viscosity and TBARS level of blood were enhanced remarkably during blood storage and long-distance transport, and the increase of viscosity mainly resulted from carbonyl stress mediated oxidative stress of erythrocytes.Finally, we explored the detoxification of carbonyl stress. Melatoninwas well known as a natural "sleep hormone" and an effective antioxidant. Considering its characteristic diurnal rhythm of synthesis and secretion with the highest levels at night and low levels during daytime in blood, it was reasonable to conjecture that the elimination of free radicals by melatonin may not attribute to detoxify the oxidative stress. We studied the effects of melatonin on carbonyl stress both in biochemical level and blood viscosity system. We found melatonin reacted readily with MDA, and induced recovery from MDA-related blood viscosity increase directly or excited some factors in plasma to decrease viscosity. All these data suggested that the elimination of MDA might implicate the molecular mechanism of melatonin's antioxidant activities. The model of streptozotocin-diabetic mouse was also established and serum levels of TBARS were measured, which would helpful for the following researches of melatonin in vivo.In summary, our investigation on carbonyl stress and carbonyl detoxification in models at the biochemical, cellular and tissue levels clearly demonstrated that the carbonyl stress was the core of free radical oxidation and the non-enzymatic glycation. All these results casted new light on free radical oxidation and the non-enzymatic glycation research, and provided important information and wide space to inspire its pathophysiological exploration.