Role of oxidative stress in Alzheimer's disease

Abstract

Alzheimer's disease (AD) is the most common cause of disability in individuals aged >65 years worldwide. AD is characterized by the abnormal deposition of amyloid β (Aβ) peptide, and intracellular accumulation of neurofibrillary tangles of hyperphosphorylated τ protein and dementia. The neurotoxic oligomer Aβ peptide, which is the neuropathological diagnostic criterion of the disease, together with τ protein, are mediators of the neurodegeneration that is among the main causative factors. However, these phenomena are mainly initiated and enhanced by oxidative stress, a process referring to an imbalance between antioxidants and oxidants in favour of oxidants. This imbalance can occur as a result of increased free radicals or a decrease in antioxidant defense, free radicals being a species that contains one or more unpaired electrons in its outer shell. The major source of potent free radicals is the reduction of molecular oxygen in water, that initially yields the superoxide radical, which produces hydrogen peroxide by the addition of an electron. The reduction of hydrogen peroxide produces highly reactive hydroxyl radicals, termed reactive oxygen species (ROS) that can react with lipids, proteins, nucleic acids, and other molecules and may also alter their structures and functions. Thus, tissues and organs, particularly the brain, a vulnerable organ, are affected by ROS due to its composition. The brain is largely composed of easily oxidizable lipids while featuring a high oxygen consumption rate. The current review examined the role of oxidative stress in AD.

Reactive Oxygen Species and Sperm Cells

“…Moreover, tyrosine phosphorylation leads to binding the spermatozoon to the zona pellucida and is necessary for the acrosome reaction [4,5]. On the contrary, oxidative stress caused by high levels of ROS has various adverse effects in a living body, such as cranial nerve disease (e.g., Alzheimer's disease and Parkinson's disease), arteriosclerosis, diabetes, and inflammatory bowel disease (e.g., ulcerative colitis and Crohn's disease) [22][23][24][25]. Similarly, ROS in semen function as an essential second messenger in the fertilization process at low levels, including capacitation, hyperactivation, acrosome reaction, and sperm-oocyte fusion [4,5].…”

Analyzing Nootropic Effect of <i>Phyllanthus reticulatus</i> Poir. on Cognitive Functions, Brain Antioxidant Enzymes and Acetylcholinesterase Activity against Aluminium-Induced Alzheimer’s Model in Rats: Applicable for Controlling the Risk Factors of Alzheimer’s Disease

“…Enzyme mainly glutamine synthetase and creatine kinase are sensitive to oxidative modification and noticeably reduced in the brains of Alzheimer's patients [19]. Higher levels of lipid peroxidation take place in the brain in AD and are most well-known where degenerative changes are most noticeable [20]. Polyunsaturated fatty acids (PUFAs) of the brain membrane phospholipids are particularly susceptible to free radical attack because their double bonds permit easy withdrawal of hydrogen ions [21].…”

Dieta mediterránea y sus efectos benéficos en la prevención de la enfermedad de Alzheimer

“…Los radicales libres y las especies reactivas del oxígeno que se generan en el organismo son neutralizados normalmente por moléculas endó-genas 33 , sin embargo, este balance antioxidante se altera en patologías relacionadas con la edad 40 , como la EA, favoreciendo una mayor producción de especies oxidativas las cuales se asocian con daño neuronal 32 , peroxidación lipídica y oxidación de enzimas relacionadas con la mantención de funciones de las neuronas y la glia 41 .…”

“…El efecto antioxidante del vino tinto se debería a la gran cantidad de polifenoles que contiene, entre ellos destaca el resveratrol que protegería a los vasos sanguíneos de los procesos inflamatorios, oxidativos, la agregación plaquetaria y formación de trombos, propias de la aterosclerosis 39 . Algunos estudios han logrado concluir que la vitamina E, presente en semillas, nueces y vegetales de hojas verdes, podría reducir el riesgo de padecer demencia o EA 43 , además, esta vitamina combatiría el estrés oxidativo mediante la disminución de la lipoperoxidación y la apóptosis, en base a lo observado en estudios in vitro 32 , ya que los fosfolípidos son los principales afectados por la presencia de radicales libre y la vitamina E, por su carácter liposoluble, es más afín con estos componentes celulares pudiendo prevenir su oxidación 41,44 . Mediante estudios in vitro e in vivo se confirmó que previene la hiperfosforilación de tau debido a que es capaz de interferir con la actividad de enzimas relacionadas con este proceso.…”