Background:
Diets high in fibre protect against hypertension via the gut microbiota and gut-derived metabolites known as short-chain fatty acids (SCFAs). In a randomised clinical trial (RCT), SCFAs lowered 24-hour systolic blood pressure (BP) and reduced total peripheral resistance in untreated hypertensive patients compared to the placebo arm. SCFAs are known as anti-inflammatory molecules. It remains unclear if SCFAs change arterial function and if this is due to immune cell infiltration into the vasculature during hypertension.

Aim:
We aimed to investigate whether SCFAs lower BP by regulating the immune system.

Methods:
Six-week-old male C57BL/6 mice were subcutaneously implanted with minipumps containing saline or angiotensin II (Ang II, 0.75mg/kg/day) and received 0.9% sodium chloride water for four weeks (n=6-8/group). Mice were fed a control diet or the same high SCFA diet used in the RCT, called HAMSAB. Both diets were matched for all other nutrients. BP was measured weekly by tail-cuff. Flow cytometry at the endpoint determined immune cells in the aorta and spleen. Gut microbiome (16S rRNA sequencing), myography and aortic ultrasounds are being analysed. Data was analysed by 2-way ANOVA with adjustment by false discovery rate (q<0.05).

Results:
Ang II treatment increased the BP of control-fed mice relative to saline treatment (+57 mmHg, P<0.0001). Similarly to our observation in patients, HAMSAB-fed Ang II mice had significantly lower BP compared to control-treated Ang II mice (-21 mmHg, P=0.02). HAMSAB did not alter CD8 or CD4 T cells, B cells or monocytes in the aorta of hypertensive or normotensive mice, independent of diet. In contrast, Ang II increased the proportion of splenic B cells (Mean±SEM; 42.7%±1.81 Sham vs 50%±1.75 Ang, q=0.029), which was decreased in HAMSAB-fed Ang II-treated mice (42.5%±2.37, q=0.029). Other splenic immune cells, including monocytes, neutrophils, dendritic cells and T cell populations, were unaltered.

Conclusions:
While SCFAs lowered BP, our results suggest this was unlikely due to increased vascular immune cell infiltration. However, alterations to splenic B cells with SCFAs may implicate a role for the immune system in BP regulation elsewhere and warrant further investigation.

Background and aims: B cells are a heterogenous lymphocyte family with diverse immune functions. We have shown that murine angiotensin II-dependent hypertension is associated with B cell activation and that B cell depletion prevents increases in blood pressure (BP), cardiac and vascular remodelling. However, it is unclear which B cell subsets mediate these responses and whether their activation involves classical antigen recognition. Since specific immunoglobulin heavy chains (IGHVs) that form B cell receptors (BCRs) become more frequently expressed during an antigenic response, we used multiomic sequencing to characterise changes in B cell subsets and IGHVs in experimental hypertension. Methods: 8-11-week-old male and female C57BL6 mice were infused with angiotensin II (0.7 mg/kg/day, s.c.) for 28 days. Normotensive controls were infused with vehicle. Systolic BP was measured by tail-cuff plethysmography. Heart weight:body weight ratio (HW:BW) was used to assess cardiac hypertrophy. Splenic single cell suspensions were used for high-dimensional flow cytometry and single-cell RNA-sequencing (scRNAseq) to characterise B cell subsets while single-cell BCR sequencing (scVDJseq) was used to assess IGHVs. Results: In males, angiotensin II increased BP (166±3 vs 124±2 mmHg in veh) and HW:BW (6.0±0.2 vs 4.7±0.1 mg/g in veh). In females, angiotensin II similarly increased BP (164±4 vs 121±3 mmHg in veh), although the pressor response was slower and females had no change in HW:BW. Gene ontologies from scRNAseq showed activation of marginal zone (MZ) and follicular B cells, and an expansion of Sca-1+ MZ B cells in hypertensive mice (7% vs 4% in veh). Flow cytometry validated an increase in Sca-1+ MZ (Pang=0.0082) and interestingly females showed greater proportions of regulatory follicular (Psex=0.005) and MZ B cells (Psex=0.032), which are typically anti-inflammatory. Finally, scVDJseq revealed increases in IGHV1 BCR variants in follicular (effect size 95% CI [0.015, 0.061]) and MZ B cells (95% CI [0.013, 0.083]) from hypertensive mice, indicating an antigen-driven response. Conclusions: Hypertension is associated with activation of numerous B cell subsets, some via classical antigen recognition. The elevated regulatory/anti-inflammatory B cell profile in female mice may partially explain the temporal differences in pressor response and their protection against cardiac hypertrophy.

Background: Renal denervation (RDN) is guideline recommended adjunct treatment for complex or resistant hypertension in the 2023 ESC guidelines. Recent sham-controlled trials have consistently reported clinically significant blood pressure reductions in the absence of adverse renal consequences. Likewise, long-term follow-up data indicates the antihypertensive effect of RDN is robust out to 10 years, without significantly impacting renal function. Previous long-term follow up work however has been limited by single-centre experiences and relatively small samples. We aimed to assess the renal safety in patients having received RDN for complex hypertension at various interventional centres across Australia.

Methods: 101 patients (69.8±13.1 years, 71.2% male) who underwent RDN, on average 10.4±1.1 years prior, were enrolled for follow-up. Patients provided blood samples for measurement of eGFR and underwent ambulatory blood pressure measurement (ABPM) alongside seated office blood pressures.

Results: BP was significantly reduced with SBP reduced by 12.97mmHg (95%CI:18.1, 7.9) at 10-year follow-up (p<0.0001). DBP was reduced by 9.9mmHg (95%CI: 12.9, 6.8, p<0.0001). This coincides with a reduction of 0.6 antihypertensive drug classes prescribed at long-term follow-up (p=0.0002). eGFR was reduced by 5.6±15.7ml/min/1.73m2 (p=0.001) at long-term follow-up, within age-related declines. Serum sodium (p=0.63) and potassium (p=0.7) however remain stable between time points. Site-specific analyses revealed no significant eGFR fall across the follow-up period (p=0.8479; BSL: 67.72ml/min v LTFU:68.33ml/min). Change in eGFR in this subcohort between baseline and long-term follow-up did not correlate with treatment response (p=0.78, r=0.005, measured by SBP change over the study visits, baseline SBP (p=0.32, r=-0.19) or change in absolute number of antihypertensive drug classes (p=0.71, r=0.0008).

Conclusions: Renal function appears to remain stable out to ~10 years of follow-up after RDN, well within age-associated decline over this period, alongside significant reductions in BP. A population of patients was identified which lacked an eGFR fall relative to baseline at 10-year follow-up irrespective of treatment response or medication changes implying a possible renoprotective effect of RDN.

Background: Intraoperative hypotension is common during cardiac surgery requiring cardiopulmonary bypass (CPB) and can result in tissue hypoxia. Renal medullary tissue hypoxia has been implicated in the pathogenesis of postoperative acute kidney injury which occur in approximately 30% of patients. Vasopressors are used clinically to treat hypotension during CPB; however, their effects on the kidney microcirculation are unknown.
Aim: To determine the effects of 4 commonly used vasopressors (metaraminol, noradrenaline, phenylephrine and vasopressin) on renal microcirculatory perfusion and oxygenation in sheep undergoing CPB when used to maintain a target mean arterial pressure (MAP) of 75–85 mmHg.
Methods: Under general anaesthesia, we inserted laser Doppler and oxygen-sensing probes in the renal cortex and medulla in 16 sheep to measure tissue microcirculatory perfusion and oxygenation continuously. Animals were then studied for over 3 hours of CPB. After commencing CPB at a pump flow of 2.4 L.min-1, animals were studied for a baseline period with a MAP of 50–60 mmHg, after which a MAP of 75–85 mmHg was targeted using a continuous infusion of different vasopressors (metaraminol [n=8], noradrenaline [n=8], phenylephrine [n=8] or vasopressin [n=7]) over 2 further study periods. The primary outcome was renal medullary tissue oxygen tension. This study employed a within-animal crossover design, and sheep were allocated randomly to receive 2 vasopressors sequentially over separate study periods to achieve target MAP.
Results: Compared with the conscious state, CPB was associated with renal medullary tissue hypoxia at MAP 50–60 mmHg (mean ± SD: 35.2 ± 12.9 vs. 11.8 ± 12.6 mmHg; P=0.005). This was exacerbated when a MAP of 75–85 mmHg was attained with noradrenaline compared with metaraminol (−14.2 ± 24.8 vs +2.9 ± 21.6 mmHg; P=0.02), phenylephrine (1.4 ± 5.0 mmHg; P=0.03), and vasopressin (5.1 ± 0.6 mmHg; P=0.03).

Conclusion: Restoring a blood pressure during CPB using noradrenaline exacerbated renal medullary hypoxia relative to other commonly used vasopressors. These findings underscore the importance of selecting vasopressor drugs that do not compromise the renal microcirculation during cardiac surgery, which may mitigate the incidence of postoperative acute kidney injury.