RESUMEN
Extensive animal studies and a growing number of human clinical trials have now definitively demonstrated the central role of the renin-angiotensin-aldosterone system in the expression and modulation of cardiovascular disease. In contrast to the original hypothesis, the benefits of angiotensin antagonism do not emanate from the antihypertensive effect alone. Subsequent extensive investigations of angiotensin blockade suggest that the benefits of this approach may also result from the pharmacologic alteration of endothelial cell function and the ensuing changes in the biology of the vasculature. The more recent availability of direct antagonists of the AT(1) angiotensin receptor has introduced an element of doubt into this realm of clinical decision making. The receptor antagonists and the more widely studied converting-enzyme inhibitors share many endpoint attributes. Nevertheless, the partially overlapping mechanisms of action for the two classes of angiotensin antagonists confer distinct pharmacologic properties, including side effect profiles, mechanisms of action, and theoretic salutary effects upon the expression of cardiovascular disease. The current review will attempt to contrast the biology of angiotensin converting-enzyme inhibition with angiotensin II receptor antagonism. A discussion of the differential effects of these drug classes on endothelial cell function and on the modulation of vascular disease will be utilized to provide a theoretic framework for clinical decision making and therapeutics.
Asunto(s)
Antagonistas de Receptores de Angiotensina , Inhibidores de la Enzima Convertidora de Angiotensina/uso terapéutico , Angiotensinógeno/metabolismo , Enfermedades Cardiovasculares/tratamiento farmacológico , Sistema Renina-Angiotensina , Inhibidores de la Enzima Convertidora de Angiotensina/farmacología , Animales , Ensayos Clínicos como Asunto , Endotelio Vascular/efectos de los fármacos , Humanos , Sistema Renina-Angiotensina/efectos de los fármacos , Sistema Renina-Angiotensina/fisiologíaRESUMEN
In lower vertebrates, retinal ganglion cells (RGCs) can regenerate their axons and reestablish functional connections after optic nerve injury. We show here that in goldfish RGCs, the effects of several trophic factors converge on a purine-sensitive signaling mechanism that controls axonal outgrowth and the expression of multiple growth-associated proteins. In culture, goldfish RGCs regenerate their axons in response to two molecules secreted by optic nerve glia, axogenesis factor-1 (AF-1) and AF-2, along with ciliary neurotrophic factor. The purine analog 6-thioguanine (6-TG) blocked outgrowth induced by each of these factors. Previous studies in PC12 cells have shown that the effects of 6-TG on neurite outgrowth may be mediated via inhibition of a 47 kDa protein kinase. Growth factor-induced axogenesis in RGCs was accompanied by many of the molecular changes that characterize regenerative growth in vivo, e.g. , increased expression of GAP-43 and certain cell surface glycoproteins. 6-TG inhibited all of these changes but not those associated with axotomy per se, e.g., induction of jun family transcription factors, nor did it affect cell survival. Additional studies using RGCs from transgenic zebrafish showed that expression of Talpha-1 tubulin is likewise stimulated by AF-1 and blocked by 6-TG. The purine nucleoside inosine had effects opposite to those of 6-TG. Inosine stimulated outgrowth and the characteristic pattern of molecular changes in RGCs and competitively reversed the inhibitory effects of 6-TG. We conclude that axon regeneration and the underlying program of gene expression in goldfish RGCs are mediated via a common, purine-sensitive pathway.
Asunto(s)
Axones/metabolismo , Proteínas de Peces , Regeneración Nerviosa/genética , Purinas/metabolismo , Células Ganglionares de la Retina/metabolismo , Transducción de Señal/fisiología , Molécula de Adhesión Celular del Leucocito Activado/biosíntesis , Animales , Antígenos de Superficie , Axones/efectos de los fármacos , Unión Competitiva/efectos de los fármacos , Moléculas de Adhesión Celular Neuronal/biosíntesis , Células Cultivadas , Factor Neurotrófico Ciliar/metabolismo , Factor Neurotrófico Ciliar/farmacología , Proteína GAP-43/biosíntesis , Expresión Génica/efectos de los fármacos , Carpa Dorada , Sustancias de Crecimiento/metabolismo , Sustancias de Crecimiento/farmacología , Nucleótidos de Guanina/farmacología , Inosina/metabolismo , Inosina/farmacología , Proteínas de la Membrana/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Neuritas/efectos de los fármacos , Neuritas/metabolismo , Proteínas Proto-Oncogénicas c-jun/metabolismo , Purinas/farmacología , Células Ganglionares de la Retina/citología , Células Ganglionares de la Retina/efectos de los fármacos , Transducción de Señal/efectos de los fármacos , Tionucleótidos/farmacología , Tubulina (Proteína)/biosíntesisRESUMEN
Although purinergic compounds are widely involved in the intra- and intercellular communication of the nervous system, little is known of their involvement in the growth and regeneration of neuronal connections. In dissociated cultures, the addition of adenosine or guanosine in the low micromolar range induced goldfish retinal ganglion cells to extend lengthy neurites and express the growth-associated protein GAP-43. These effects were highly specific and did not reflect conversion of the nucleosides to their nucleotide derivatives; pyrimidines, purine nucleotides, and membrane-permeable, nonhydrolyzable cyclic nucleotide analogs were all inactive. The activity of adenosine required its conversion to inosine, because inhibitors of adenosine deaminase rendered adenosine inactive. Exogenously applied inosine and guanosine act directly upon an intracellular target, which may coincide with a kinase described in PC12 cells. In support of this, the effects of the purine nucleosides were blocked with purine transport inhibitors and were inhibited competitively with the purine analog 6-thioguanine (6-TG). In PC12 cells, others have shown that 6-TG blocks nerve growth factor-induced neurite outgrowth and selectively inhibits the activity of protein kinase N, a partially characterized, nerve growth factor-inducible serine-threonine kinase. In both goldfish and rat retinal ganglion cells, 6-TG completely blocked outgrowth induced by other growth factors, and this inhibition was reversed with inosine. These results suggest that axon outgrowth in central nervous system neurons critically involves an intracellular purine-sensitive mechanism.
Asunto(s)
Axones , Nucleósidos de Purina/metabolismo , Nucleótidos de Purina/metabolismo , Células Ganglionares de la Retina/fisiología , Adenosina/metabolismo , Animales , Proteínas Quinasas Dependientes de Calcio-Calmodulina/metabolismo , Carpa Dorada , Hidrólisis , Inosina/metabolismo , Fosfatidilinositol 3-Quinasas/metabolismo , Antagonistas de Receptores Purinérgicos P1 , Ratas , Ratas Sprague-Dawley , Tioguanina/farmacologíaRESUMEN
Previous work has demonstrated the existence of regulatory circuitry that controls response to the dominant determinant Ac1-9 of myelin basic protein (MBP) which is highly restricted in TCR V gene usage to V beta 8.2 and V alpha 2.3. In particular, a CD4+ V beta 14+ regulatory T cell was shown to be a vital component of this circuit. In our work presented here, the peptide specificity of the response to V beta 8.2 peptides was examined. Five overlapping peptides, B1 through B5, were studied for their ability to induce a proliferative response: B2 (21-50), B4 (61-90), and B5 (76-101) each had this capacity in the B10.PL or (SJL x B10.PL)F1 mice. The determinant within the TCR peptide B5 appears dominant, whereas determinants within the B2 and B4 peptides are physiologically cryptic. Furthermore, only B5 could down-regulate the response to MBP Ac1-9 and significantly protect mice from MBP- or Ac1-9-induced EAE, whereas B2 or B4 treatment had no significant effect. Treatment of mice with B5 did not result in generalized deletion or inactivation of V beta 8.2+ T cells. The core residues of the B5 determinant lie within framework region 3 of the V beta 8.2 chain and do not include residues from the joining CDR3 region. Response to B5 was restricted by the I-Au MHC molecule. Furthermore, B5 only induced responses in mice with certain MHC alleles. It is evident that by specifically down-regulating the initial dominant response to Ac1-9, Ag-induced disease can be prevented. These data have implications for understanding induction of TCR-based regulation, as well as relevance to possible therapeutic approaches for oligoclonal responses in human autoimmune diseases.