Are transcription factors NF-κB and AP-1 involved in the ANG II-stimulated production of proinflammatory cytokines induced by LPS in dehydrated rats?

The Effects of Angiotensin II or Angiotensin 1-7 on Rat Pial Microcirculation during Hypoperfusion and Reperfusion Injury: Role of Redox Stress

Renin-angiotensin systems produce angiotensin II (Ang II) and angiotensin 1-7 (Ang 1-7), which are able to induce opposite effects on circulation. This study in vivo assessed the effects induced by Ang II or Ang 1-7 on rat pial microcirculation during hypoperfusion-reperfusion, clarifying the mechanisms causing the imbalance between Ang II and Ang 1-7. The fluorescence microscopy was used to quantify the microvascular parameters. Hypoperfusion and reperfusion caused vasoconstriction, disruption of blood-brain barrier, reduction of capillary perfusion and an increase in reactive oxygen species production. Rats treated with Ang II showed exacerbated microvascular damage with stronger vasoconstriction compared to hypoperfused rats, a further increase in leakage, higher decrease in capillary perfusion and marker oxidative stress. Candesartan cilexetil (specific Ang II type 1 receptor (AT₁R) antagonist) administration prior to Ang II prevented the effects induced by Ang II, blunting the hypoperfusion-reperfusion injury. Ang 1-7 or ACE2 activator administration, preserved the pial microcirculation from hypoperfusion-reperfusion damage. These effects of Ang 1-7 were blunted by a Mas (Mas oncogene-encoded protein) receptor antagonist, while Ang II type 2 receptor antagonists did not affect Ang 1-7-induced changes. In conclusion, Ang II and Ang 1-7 triggered different mechanisms through AT₁R or MAS receptors able to affect cerebral microvascular injury.

Vitamin D receptor activation and downregulation of renin-angiotensin system attenuate morphine-induced T cell apoptosis

Opiates have been reported to induce T cell loss. We evaluated the role of vitamin D receptor (VDR) and the activation of the renin-angiotensin system (RAS) in morphine-induced T cell loss. Morphine-treated human T cells displayed downregulation of VDR and the activation of the RAS. On the other hand, a VDR agonist (EB1089) enhanced T cell VDR expression both under basal and morphine-stimulated states. Since T cells with silenced VDR displayed the activation of the RAS, whereas activation of the VDR was associated with downregulation of the RAS, it appears that morphine-induced T cell RAS activation was dependent on the VDR status. Morphine enhanced reactive oxygen species (ROS) generation in a dose-dependent manner. Naltrexone (an opiate receptor antagonist) inhibited morphine-induced ROS generation and thus, suggested the role of opiate receptors in T cell ROS generation. The activation of VDR as well as blockade of ANG II (by losartan, an AT(1) receptor blocker) also inhibited morphine-induced T cell ROS generation. Morphine not only induced double-strand breaks (DSBs) in T cells but also attenuated DNA repair response, whereas activation of VDR not only inhibited morphine-induced DSBs but also enhanced DNA repair. Morphine promoted T cell apoptosis; however, this effect of morphine was inhibited by blockade of opiate receptors, activation of the VDR, and blockade of the RAS. These findings indicate that morphine-induced T cell apoptosis is mediated through ROS generation in response to morphine-induced downregulation of VDR and associated activation of the RAS.

Angiotensin II AT1 blockade reduces the lipopolysaccharide-induced innate immune response in rat spleen

ANG II AT(1) receptor blockade reduces inflammation in hypertension. To determine whether ANG II AT(1) receptor blockers (ARBs) influence the innate immune inflammatory response in normotensive rats, we studied rat plasma and spleen after a 3-day subcutaneous pretreatment with the ARB candesartan followed by a single dose of the bacterial endotoxin LPS (50 microg/kg ip). Peripheral administration of LPS to rodents produced a generalized inflammatory response with increased release of TNF-alpha, IL-1beta, and IL-6 into the circulation. Candesartan pretreatment reduced the LPS-induced release of TNF-alpha, IL-1beta, and IL-6 into the circulation. The red pulp of rat spleen expressed large numbers of AT(1) receptors and the LPS receptors Toll-like receptor 4 and CD14. Candesartan administration significantly blocked AT(1) receptors. The ARB reduced the LPS-induced upregulation of CD14 gene expression; expression of TNF-alpha and IL-6 mRNA and protein; expression of IL-1beta and IkappaB-alpha mRNA; COX-2 mRNA and protein expression and PGE(2) concentration; inducible nitric oxide synthase (iNOS) gene and protein expression and iNOS activity; and Nox2 gene expression and 8-isoprostane levels. In addition, candesartan reduced the CD14 protein expression in saline- and LPS-treated rats. Our results suggest that AT(1) receptors are essential for the development of the full innate immune response to bacterial endotoxin. The ARB decreased the general peripheral inflammatory reaction to LPS and partially decreased the inflammatory response in the spleen. An unrestricted innate immune response to the bacterial endotoxin may have deleterious effects for the organism and may lead to development of chronic inflammatory disease. We postulate that ARBs may have therapeutic effects on inflammatory conditions.

Liver fibrosis: a balance of ACEs?

There is an increasing body of evidence to suggest that the RAS (renin–angiotensin system) contributes to tissue injury and fibrosis in chronic liver disease. A number of studies have shown that components of a local hepatic RAS are up-regulated in fibrotic livers of humans and in experimental animal models. Angiotensin II, the main physiological effector molecule of this system, mediates liver fibrosis by stimulating fibroblast proliferation (myofibroblast and hepatic stellate cells), infiltration of inflammatory cells, and the release of inflammatory cytokines and growth factors such as TGF (transforming growth factor)-β1, IL (interleukin)-1β, MCP (monocyte chemoattractant protein)-1 and connective tissue growth factor. Furthermore, blockade of the RAS by ACE (angiotensin-converting enzyme) inhibitors and angiotensin type 1 receptor antagonists significantly attenuate liver fibrosis in experimental models of chronic liver injury. In 2000 ACE2 (angiotensin-converting enzyme 2), a human homologue of ACE, was identified. ACE2 efficiently degrades angiotensin II to angiotensin-(1–7), a peptide which has recently been shown to have both vasodilatory and tissue protective effects. This suggests that ACE2 and its products may be part of an alternate enzymatic pathway in the RAS, which counterbalances the generation and actions of angiotensin II, the ACE2–angiotensin-(1–7)–Mas axis. This review focuses on the potential roles of the RAS, angiotensin II and ACE2 in chronic liver injury and fibrogenesis.

Thermoregulation: some concepts have changed. Functional architecture of the thermoregulatory system

While summarizing the current understanding of how body temperature (Tb) is regulated, this review discusses the recent progress in the following areas: central and peripheral thermosensitivity and temperature-activated transient receptor potential (TRP) channels; afferent neuronal pathways from peripheral thermosensors; and efferent thermoeffector pathways. It is proposed that activation of temperature-sensitive TRP channels is a mechanism of peripheral thermosensitivity. Special attention is paid to the functional architecture of the thermoregulatory system. The notion that deep Tb is regulated by a unified system with a single controller is rejected. It is proposed that Tb is regulated by independent thermoeffector loops, each having its own afferent and efferent branches. The activity of each thermoeffector is triggered by a unique combination of shell and core Tbs. Temperature-dependent phase transitions in thermosensory neurons cause sequential activation of all neurons of the corresponding thermoeffector loop and eventually a thermoeffector response. No computation of an integrated Tb or its comparison with an obvious or hidden set point of a unified system is necessary. Coordination between thermoeffectors is achieved through their common controlled variable, Tb. The described model incorporates Kobayashi’s views, but Kobayashi’s proposal to eliminate the term sensor is rejected. A case against the term set point is also made. Because this term is historically associated with a unified control system, it is more misleading than informative. The term balance point is proposed to designate the regulated level of Tb and to attract attention to the multiple feedback, feedforward, and open-loop components that contribute to thermal balance.

Effects of central injection of angiotensin-converting-enzyme inhibitor and angiotensin type 1 receptor antagonist on the brain NF-kappaB and AP-1 activities of rats given LPS

Angiotensin II (ANG II) activation of the angiotensin type 1 (AT1) receptor facilitates the production of brain interleukin-1beta (IL-1beta) and contributes to the induction of the fever following the intracerebroventricular (i.c.v.) injection of lipopolysaccharide (LPS). The purpose of the present study was to investigate whether proinflammatory transcription factors [nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1)] contribute to the ANG II-dependent production of cytokines within the brain. Interestingly, we found that a single i.c.v. injection of LPS had no effect on NF-kappaB and AP-1 activities in the hypothalamus, hippocampus, and cerebellum at either 1 or 3 h post-injection (except for a decrease in hypothalamic AP-1 activity at 1 h). Furthermore, both an angiotensin-converting-enzyme (ACE) inhibitor and an AT1 receptor antagonist enhanced (rather than reduced) the NF-kappaB and AP-1 activities in the hippocampus and/or cerebellum of rats given LPS. In contrast, an i.c.v. injection of ANG II increased the NF-kappaB activity in the hypothalamus. These results suggest that while "endogenous" ANG II exerts (via AT1 receptors) inhibitory effects on the activation of transcription factors in the brain of rats given LPS, a large dose of exogenous ANG II produces effects opposite to those induced by the presumably small amount of endogenous ANG II released locally by LPS. Our results seem not to support the idea that NF-kappaB and AP-1 play key roles in the ANG II-induced enhancement of the production of proinflammatory cytokines that is induced by LPS in the rat's brain.