Background: Dietary intake of fruit and vegetables is associated with lower incidence of hypertension, but the mechanisms involved have not been elucidated. Here, we evaluated the effect of a high-fiber diet and supplementation with the short-chain fatty acid acetate on the gut microbiota and the prevention of cardiovascular disease. Methods: Gut microbiome, cardiorenal structure/function, and blood pressure were examined in sham and mineralocorticoid excess–treated mice with a control diet, high-fiber diet, or acetate supplementation. We also determined the renal and cardiac transcriptome of mice treated with the different diets. Results: We found that high consumption of fiber modified the gut microbiota populations and increased the abundance of acetate-producing bacteria independently of mineralocorticoid excess. Both fiber and acetate decreased gut dysbiosis, measured by the ratio of Firmicutes to Bacteroidetes, and increased the prevalence of Bacteroides acidifaciens . Compared with mineralocorticoid-excess mice fed a control diet, both high-fiber diet and acetate supplementation significantly reduced systolic and diastolic blood pressures, cardiac fibrosis, and left ventricular hypertrophy. Acetate had similar effects and markedly reduced renal fibrosis. Transcriptome analyses showed that the protective effects of high fiber and acetate were accompanied by the downregulation of cardiac and renal Egr1 , a master cardiovascular regulator involved in cardiac hypertrophy, cardiorenal fibrosis, and inflammation. We also observed the upregulation of a network of genes involved in circadian rhythm in both tissues and downregulation of the renin-angiotensin system in the kidney and mitogen-activated protein kinase signaling in the heart. Conclusions: A diet high in fiber led to changes in the gut microbiota that played a protective role in the development of cardiovascular disease. The favorable effects of fiber may be explained by the generation and distribution of one of the main metabolites of the gut microbiota, the short-chain fatty acid acetate. Acetate effected several molecular changes associated with improved cardiovascular health and function.

To determine whether differential release of nitric oxide underlies the diversity of regional kidney blood flow responses to vasoactive agents, this study examined how nitric oxide synthase blockade with IV N(G)-nitro-L-arginine (L-NNA), and also IV L-NNA plus co-infusion of glyceryl trinitrate, affected responses to renal arterial boluses and infusions of vasoactive agents. L-NNA, but not vehicle, or L-NNA plus glyceryl trinitrate, increased mean arterial pressure (35%) and reduced renal blood flow (20%), cortical perfusion (11%), and medullary perfusion (54%). L-NNA plus glyceryl trinitrate, but not L-NNA alone, blunted renal vasodilatation in response to boluses of bradykinin and acetylcholine, abolished increased medullary perfusion after bolus angiotensin II, and enhanced reductions in medullary perfusion, and to a lesser extent those in renal blood flow and cortical perfusion, during norepinephrine infusion. Neither L-NNA, nor L-NNA plus glyceryl trinitrate, affected responses to infusions of angiotensin II, [Phe(2),Ile(3),Orn(8)]-vasopressin, or endothelin-1. The data indicate roles for nitric oxide in angiotensin II-induced increases in medullary perfusion and in protecting medullary perfusion from norepinephrine-induced vasoconstriction. However, differential engagement of nitric oxide synthase cannot completely account for the diversity of responses of regional kidney perfusion to vasoactive agents. Effects of nitric oxide synthase blockade on renal vascular responses to vasoactive agents were revealed only when glyceryl trinitrate was co-infused to restore resting nitrergic vasodilator tone. This may reflect interactions between nitric oxide and other vasodilator mediators, in modulating renal hemodynamic responses to vasoactive agents.

Tissue hypoxia has been demonstrated, in both the renal cortex and medulla, during the acute phase of reperfusion after ischemia induced by occlusion of the aorta upstream from the kidney. However, there are also recent clinical observations indicating relatively well preserved oxygenation in the nonfunctional transplanted kidney. To test whether severe acute kidney injury can occur in the absence of widespread renal tissue hypoxia, we measured cortical and inner medullary tissue Po2 as well as total renal O2 delivery (Do2) and O2 consumption (Vo2) during the first 2 h of reperfusion after 60 min of occlusion of the renal artery in anesthetized rats. To perform this experiment, we used a new method for measuring kidney Do2 and Vo2 that relies on implantation of fluorescence optodes in the femoral artery and renal vein. We were unable to detect reductions in renal cortical or inner medullary tissue Po2 during reperfusion after ischemia localized to the kidney. This is likely explained by the observation that Vo2 (-57%) was reduced by at least as much as Do2 (-45%), due to a large reduction in glomerular filtration (-94%). However, localized tissue hypoxia, as evidence by pimonidazole adduct immunohistochemistry, was detected in kidneys subjected to ischemia and reperfusion, particularly in, but not exclusive to, the outer medulla. Thus, cellular hypoxia, particularly in the outer medulla, may still be present during reperfusion even when reductions in tissue Po2 are not detected in the cortex or inner medulla.

4. Low NO bioavailability is central to the development and maintenance of hypertension and to related endothelial dysfunction and target organ damage. We propose that L-arginine can interrupt the vicious cycle that initiates and maintains low NO in hypertension by increasing the formation of NO.

We tested for regional differences in perfusion responses, within the renal medulla and cortex, to renal nerve stimulation in pentobarbital sodium-anesthetized rabbits. Laser-Doppler flux (LDF) was monitored at various depths below the cortical surface (1–15 mm). Basal cortical LDF (1–3 mm, ∼200–450 U) was greater than medullary LDF (5–15 mm, ∼70–160 U), but there were no statistically significant differences in basal LDF within these regions. The background LDF signal during aortic occlusion was similar in the cortex (2 mm, 31 U) and outer medulla (7 mm, 31 U), but slightly greater in the inner medulla (12 mm, 44 U). During electrical stimulation of the renal nerves (0.5–8 Hz), cortical LDF and total renal blood flow were similarly progressively reduced with increasing stimulus frequency. Medullary LDF (measured between 5 and 15 mm) was overall less responsive than cortical LDF. For example, 4-Hz stimulation reduced inner medullary LDF (9 mm) by 19 ± 6% but reduced cortical LDF (1 mm) by 54 ± 11%. However, medullary LDF responses to nerve stimulation were similar at all depths measured. Our results indicate that while the vascular elements controlling medullary perfusion are less sensitive to the effects of electrical stimulation of the renal nerves than are those controlling cortical perfusion, sensitivity within these vascular territories appears to be relatively homogeneous.

1. To determine whether differential release of products of arachidonic acid metabolism, via the cyclo-oxygenase pathway, underlies the diversity of responses of regional kidney perfusion to vasoactive agents, we tested the effects of intravenous indomethacin on responses to renal arterial bolus doses of vasoactive agents in pentobarbitone-anaesthetized rabbits. 2. Total renal blood flow (RBF) and regional kidney perfusion were determined by transit time ultrasound flowmetry and laser-Doppler flowmetry, respectively. 3. Responses of regional kidney blood flow to vasoactive agents were diverse: noradrenaline reduced cortical but not medullary perfusion, [Phe 2,Ile 3,Orn 8]-vasopressin reduced medullary perfusion more than cortical perfusion, endothelin-1 and angiotensin II increased medullary perfusion in the face of reduced cortical perfusion, while acetylcholine, bradykinin and the nitric oxide donor methylamine hexamethylene methylamine (MAHMA) NONOate all increased both cortical and medullary perfusion. 4. Indomethacin administration was followed by reductions in total RBF (17 +/- 6%), cortical perfusion (13 +/- 5%) and medullary perfusion (40 +/- 8%). Angiotensin II- and endothelin-1-induced increases in medullary perfusion were abolished by indomethacin, but indomethacin had no significant effects on responses of regional kidney perfusion to acetylcholine, bradykinin, MAHMA NONOate, noradrenaline and [Phe 2,Ile 3,Orn 8]-vasopressin. 5. Our results suggest that vasodilator cyclo-oxygenase products contribute to the maintenance of resting renal vascular tone, particularly in vascular elements controlling medullary perfusion. Cyclo-oxygenase products also appear to mediate endothelin-1- and angiotensin II-induced increases in medullary perfusion. However, regionally specific engagement of cyclo-oxygenase-dependent arachidonic acid metabolism does not appear to contribute to the differential effects of noradrenaline and [Phe 2,Ile 3,Orn 8]-vasopressin on cortical and medullary perfusion.

Coronavirus disease-2019 (COVID-19) is primarily a respiratory disease, however, an increasing number of reports indicate that SARS-CoV-2 infection can also cause severe neurological manifestations, including precipitating cases of probable Parkinson’s disease. As microglial NLRP3 inflammasome activation is a major driver of neurodegeneration, here we interrogated whether SARS-CoV-2 can promote microglial NLRP3 inflammasome activation. Using SARS-CoV-2 infection of transgenic mice expressing human angiotensin-converting enzyme 2 (hACE2) as a COVID-19 pre-clinical model, we established the presence of virus in the brain together with microglial activation and NLRP3 inflammasome upregulation in comparison to uninfected mice. Next, utilising a model of human monocyte-derived microglia, we identified that SARS-CoV-2 isolates can bind and enter human microglia in the absence of viral replication. This interaction of virus and microglia directly induced robust inflammasome activation, even in the absence of another priming signal. Mechanistically, we demonstrated that purified SARS-CoV-2 spike glycoprotein activated the NLRP3 inflammasome in LPS-primed microglia, in a ACE2-dependent manner. Spike protein also could prime the inflammasome in microglia through NF-κB signalling, allowing for activation through either ATP, nigericin or α-synuclein. Notably, SARS-CoV-2 and spike protein-mediated microglial inflammasome activation was significantly enhanced in the presence of α-synuclein fibrils and was entirely ablated by NLRP3-inhibition. Finally, we demonstrate SARS-CoV-2 infected hACE2 mice treated orally post-infection with the NLRP3 inhibitory drug MCC950, have significantly reduced microglial inflammasome activation, and increased survival in comparison with untreated SARS-CoV-2 infected mice. These results support a possible mechanism of microglial innate immune activation by SARS-CoV-2, which could explain the increased vulnerability to developing neurological symptoms akin to Parkinson’s disease in COVID-19 infected individuals, and a potential therapeutic avenue for intervention.

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