Estudio de las vías moleculares y celulares moduladas por la minociclina en su aplicación como farmaco neuroprotector

Resumen

Minocycline is a second-generation semi-synthetic antibiotic belonging to the tetracycline family, indicated for the treatment of acne vulgaris, some sexually transmitted diseases, and rheumatoid arthritis. Minocycline displays neuroprotective actions in several models of neurodegenerative diseases, including ischemia, Huntington disease, amyotrophic lateral sclerosis, and stroke. However, recent evidence indicates that minocycline does not always present beneficial actions, even though some results show the apparition of deleterious effects. The mechanisms by which minocycline exerts its citoprotective properties remain poorly understood. In this Thesis we have investigated the cellular and molecular pathways involved in this process in several models including isolated mitochondria, granular cell cultures, SH-SY5Y cell line, primary cultures of hippocampal neurons and synaptosomes. Minocycline is effective in blocking mitochondrial swelling induced by Ca2+; this effect might be mediated through dissipation of the mitochondrial transmembrane potential and the blockade of mitochondrial Ca2+ uptake. Moreover, minocycline was able to interact with the glutamatergic neurotransmission in order to decrease the release of this neurotransmitter and subsequent receptor activation. This effect provokes a diminution in the cytosolic Ca2+ concentration. These results support the hypothesis that minocycline affords cytoprotection through mitigation of neuronal excitability and Ca2+ overloading at the mitochondrial and cellular levels. Other members of the minocycline antibiotic family like tetracycline failed to induce these effects. In our model, minocycline exerted no antioxidant actions. It was not able to modify intracellular NAD(P)H and GSH levels by itself. Additionally, this antibiotic did not prevent ROS-induced cell death due to malonate (mitochondrial complex II inhibitor), and it did not block mitochondrial swelling induced either by this toxin or KO2. Also, minocycline was unsuccessful in avoiding the oxidation of the phospholipid cardiolipin and the depletion of GSH levels. On the other hand, we studied the aging process in an animal model denominated senescence accelerated mouse (SAMP8) which has been attributed to cholinergic impairment. We analyzed the expression of two ChE genes AChE and BuChE and did not observe any difference. Nevertheless, BuChE activity in SAMP-8 brains was two fold increased versus SAMR-1 brains, and AChE activity remained unchanged in both strains.