Angiotensin II subtype AT1 and AT2 receptors regulate microvascular hydraulic permeability via cAMP and cGMP

A hitchhiker's guide through the COVID-19 galaxy

Numerous reviews have summarized the epidemiology, pathophysiology and the various therapeutic aspects of Coronavirus disease 2019 (COVID-19), but a practical guide on "how to treat whom with what and when" based on an understanding of the immunological background of the disease stages remains missing. This review attempts to combine the current knowledge about the immunopathology of COVID-19 with published evidence of available and emerging treatment options. We recognize that the information about COVID-19 and its treatment is rapidly changing, but hope that this guide offers those on the frontline of this pandemic an understanding of the host response in COVID-19 patients and supports their ongoing efforts to select the best treatments tailored to their patient's clinical status.

Scavengers of reactive oxygen species, paracalcitol, RhoA, and Rac-1 inhibitors and tacrolimus inhibit angiotensin II-induced actions on glomerular permeability

Systemic infusions of ANG II rapidly induce large, dynamic increases in the permeability of the glomerular filtration barrier (GFB) in rats. After binding to its receptor(s), ANG II generates reactive oxygen species (ROS) and produces Ca2+ influx into cells, leading to activation of a plethora of signaling cascades, including, e.g., calcineurin and small GTPases, such as Rac-1 and RhoA. In the present study we sought to interact with some of these cascades to test potential novel antiproteinuric agents. In anesthetized Wistar rats, the left urether was cannulated for urine collection, and blood access was achieved. Rats were infused with ANG II (16 ng·kg−1·min−1) alone, or together with the ROS scavengers tempol or dimethylthiourea (DMTU) or the D-vitamin analog paracalcitol, the RhoA-kinase inhibitor Y-27632, the Rac-1 inhibitor NSC-23766, or the calcineurin inhibitor tacrolimus. FITC-Ficoll-70/400 (mol.radius 10–80 Å) and 51Cr-EDTA were infused throughout the experiment. Plasma and urine samples were taken during baseline and at 5 and 15 min after the start of the infusions and analyzed by high-performance size-exclusion chromatography for determination of glomerular sieving coefficients (θ) for Ficoll10–80Å. ANG II infusion into rats caused marked increases in glomerular permeability to large Ficoll molecules (Ficoll50–80Å), which were abrogated by the ROS scavenger tempol and partly by DMTU. Paracalcitol, RhoA, and Rac-1 inhibition, and, to some extent tacrolimus, but not prostacyclin, could also inhibit the glomerular permeability actions of ANG II. Our data suggest that cellular ROS generation and active Ca2+ signaling are involved in ANG II-induced increases in glomerular permeability.

Ibudilast inhibits cerebral aneurysms by down-regulating inflammation-related molecules in the vascular wall of rats

OBJECTIVE

Phosphodiesterase-4 (PDE-4) is a cyclic adenosine monophosphate-specific enzyme involved in various inflammatory diseases. We studied its role in and the effect of ibudilast, which predominantly blocks PDE-4, on rat cerebral aneurysms.

METHODS

Cerebral aneurysms were induced at the anterior cerebral artery-olfactory artery bifurcation of female rats subjected to hypertension, increased hemodynamic stress, and estrogen deficiency. The effect of ibudilast (30 or 60 mg/kg/d for 3 months) on their cerebral aneurysms was studied by morphological and immunohistochemical assessment and quantitative real-time polymerase chain reaction assay. In our in vitro study, we grew endothelial cells stimulated by angiotensin II under estrogen-free conditions and examined the effect of ibudilast on PDE-4 activation and the cyclic adenosine monophosphate level.

RESULTS

Morphological evaluation using vascular corrosion casts showed ibudilast significantly suppressed cerebral aneurysms in a dose-dependent manner. In rats with induced cerebral aneurysms, the gene and protein expression of PDE-4 was high, and endothelial leukocyte adhesion molecules (P-selectin, intracellular adhesion molecule 1, and vascular adhesion molecule 1), matrix metalloproteinase-9, and tumor necrosis alpha were expressed. Macrophage migration was also increased. Treatment with ibudilast down-regulated these molecules, suppressed macrophage migration into the aneurysm wall, and inhibited PDE-4 activation and the elevation of cyclic adenosine monophosphate in endothelial cells.

CONCLUSION

These results suggest that blocking of PDE4 is associated with the reduction of inflammation-related molecules and macrophage migration, thereby reducing the progression of cerebral aneurysms. It may represent a new conservative therapy to treat patients with cerebral aneurysms.

AT(1) receptor blockers increase insulin-like growth factor-I production by stimulating sensory neurons in spontaneously hypertensive rats

Insulin-like growth factor-I (IGF-I) is an important cardioprotective substance. We previously reported that sensory neuron stimulation increases IGF-I production by releasing calcitonin gene-related peptide (CGRP) in spontaneously hypertensive rats (SHRs). Because angiotensin II (Ang II) inhibits sensory neuron activation by interacting with Ang II type 1 (AT(1)) receptors, it is possible that AT(1) receptor blockers (ARBs) increase IGF-I production in SHRs. We examined this possibility in the current study, using the ARBs olmesartan, valsartan, losartan, and telmisartan. Plasma, renal, and cardiac levels of CGRP and IGF-I in SHRs were significantly lower than those in normotensive Wistar Kyoto rats (WKYs) (P < 0.01), which increased to levels found in WKYs after the administration of ARBs. These ARB-induced increases in SHRs were completely reversed by pretreatment with capsazepine (CPZ), which is a specific vanilloid receptor-1 (VR-1) antagonist. The mean arterial blood pressure (MABP) was decreased after administration of ARBs in SHRs, and those decreases were reversed by pretreatment with CPZ. The administration of nifedipine decreased MABP but did not increase CGRP or IGF-I levels in SHRs. Baseline CGRP release and cellular cyclic adenosine 3',5'-monophosphate (cAMP) levels in dorsal root ganglion neurons (DRG) isolated from SHRs were significantly lower than those in DRG isolated from WKYs (P < 0.01). Although ARBs reversed decreases in CGRP release and cAMP levels in the presence of Ang II in DRG isolated from WKYs, they increased CGRP release and cAMP levels in the absence of Ang II in DRG isolated from SHRs. Cellular levels of Ang II were not detected in DRG isolated from WKYs or SHRs, but messenger RNA (mRNA) levels for angiotensin-converting enzyme in DRG were significantly higher in SHRs than in WKYs (P < 0.01). The expression of AT(1) receptors in DRG was not different between WKYs and SHRs. Thus, it is likely that decreases in CGRP release and cAMP levels in DRG isolated from SHRs are mainly caused by AT(1) receptor activation by Ang II through an autocrine mechanism. These observations suggest that ARBs might increase CGRP release from sensory neurons by sensitizing VR-1 activation through increases in cAMP levels, which thereby increased the production of IGF-I in SHRs. These activities of ARBs might at least partly explain their therapeutic effects in areas such as improving insulin resistance in patients with diabetes and hypertension.

Adiponectin protects against angiotensin II or tumor necrosis factor alpha-induced endothelial cell monolayer hyperpermeability: role of cAMP/PKA signaling

OBJECTIVE

Angiotensin II (Ang II) and tumor necrosis factor (TNF)-alpha levels increase endothelial permeability, and we hypothesized that adiponectin suppressed these responses in a cAMP-dependent manner.

METHODS AND RESULTS

The effect of adiponectin on transendothelial electric resistance (TEER) and diffusion of albumin through human umbilical vein and bovine aortic endothelial cell monolayers induced by Ang II (100 nmol/L) or TNF-alpha (5 ng/mL) was measured. Treatment with the globular domain of adiponectin (3 mug/mL) for 16 hours abrogated the adverse TEER effect of TNF-alpha (-35 versus -12 Omega/cm(2) at 45 minutes, P<0.05) and Ang II (-25 versus -5 Omega/cm(2) at 45 minutes, P<0.01) and partially suppressed the increased diffusion of albumin with Ang II (40% versus 10% change, P<0.05) or TNF-alpha (40% versus 20% change, P<0.05). Full-length adiponectin also suppressed Ang II-induced monolayer hyperpermeability. Adiponectin treatment also suppressed Ang II-induced increased actin stress fiber development, intercellular gap formation, and beta-tubulin disassembly. Adiponectin increased cAMP levels, and its effects were abrogated by inhibition of adenylyl cyclase or cAMP-dependent protein kinase signaling.

CONCLUSIONS

Adiponectin protects the endothelial monolayer from Ang II or TNF-alpha-induced hyperpermeability by modulating microtubule and cytoskeleton stability via a cAMP/ PKA signaling cascade.