An update on the relationship between the kidney, salt and hypertension

TRPV1 signaling of perirenal adipose tissue promotes DOCA-Salt-induced hypertension and kidney injury

BACKGROUND

Denervation of renal or perirenal adipose tissue (PRAT) can reduce arterial blood pressure in various hypertensive experimental models. Trpv1 (transient receptor potential vanillin 1) channel is highly expressed in the renal sensory nerves and the dorsal root ganglias (DRGs) projected by PRAT. However, it is currently unclear whether Trpv1 in DRGs projected from PRAT can regulate renal hypertension.

METHODS

We used resintoxin (RTX) to block the afferent sensory nerves of rat PRAT. We also constructed Trpv1 -/- mice and Trpv1 +/- mice or used the injection of AAV2-retro-shTrpv1 to detect the effects of Trpv1 knockout or knockdown of PRAT-projected DRGs on deoxycorticosterone acetate (DOCA)-Salt-induced hypertension and kidney injury.

RESULTS

Blocking the afferent sensory nerves of PRAT with RTX can alleviate DOCA-Salt-induced hypertension and renal injury in rats. And this blockade reduces the expression of Trpv1 in the DRGs projected by PRAT. Injecting AAV2-retro-shTrpv1 into the PRAT of DOCA-Salt mice also achieved the same therapeutic effect. However, DOCA-Salt-induced hypertension and renal injury can be treated in Trpv1 +/- mice but not alleviated or even worsened in Trpv1 -/- mice, possibly because of compensatory increase of Trpv5 in DRG of Trpv1 -/- mice.

CONCLUSION

Reducing, rather than eliminating, Trpv1 in DRG from PRAT-projection can reduce blood pressure and kidney damage in DOCA-Salt in rats or mice. Trpv1 in PRAT-DRGs may serve as a therapeutic target for salt-sensitive hypertension and its renal complications.

Kidney failure, arterial hypertension and left ventricular hypertrophy in rats with loss of function mutation of SOD3

Chronic kidney disease (CKD) poses a considerable medical and public health challenge, and the Dahl/Salt Sensitive (Dahl/SS) strain is often used for CKD study. Extracellular superoxide dismutase (SOD3) is important for removing extracellular superoxide anions and is highly expressed in renal tissue. Using a novel rat strain with loss-of-function mutation of SOD3 created by replacing glutamate 124 of SOD3 with aspartic acid (SOD3^E124D rat strain), we determined the effect of SOD3 on renal function and blood pressure in Dahl/SS rats. We find that SOD3^E124D rats are phenotypically indistinguishable from wild type rats through 8 weeks of age, but develop profound CKD characterized by focal necrosis and fibrosis, glomerulosclerosis, massive proteinaceous cast accumulation with tubular dilatation, interstitial fibrosis with hypertension and renal failure by 21 weeks. The SOD3^E124D strain represents a unique rat model that spontaneously develops CKD in an age-dependent fashion. The finding that loss of SOD3 causes CKD indicates that extracellular oxidative stress contributes to CKD and renal failure.

Pharmacological inhibition of the NLRP3 inflammasome reduces blood pressure, renal damage, and dysfunction in salt-sensitive hypertension

Aims

Renal inflammation, leading to fibrosis and impaired function is a major contributor to the development of hypertension. The NLRP3 inflammasome mediates inflammation in several chronic diseases by processing the cytokines pro-interleukin (IL)-1β and pro-IL-18. In this study, we investigated whether MCC950, a recently-identified inhibitor of NLRP3 activity, reduces blood pressure (BP), renal inflammation, fibrosis and dysfunction in mice with established hypertension.

Methods and results

C57BL6/J mice were made hypertensive by uninephrectomy and treatment with deoxycorticosterone acetate (2.4 mg/day, s.c.) and 0.9% NaCl in the drinking water (1K/DOCA/salt). Normotensive controls were uninephrectomized and received normal drinking water. Ten days later, mice were treated with MCC950 (10 mg/kg/day, s.c.) or vehicle (saline, s.c.) for up to 25 days. BP was monitored by tail-cuff or radiotelemetry; renal function by biochemical analysis of 24-h urine collections; and kidney inflammation/pathology was assessed by real-time PCR for inflammatory gene expression, flow cytometry for leucocyte influx, and Picrosirius red histology for collagen. Over the 10 days post-surgery, 1K/DOCA/salt-treated mice became hypertensive, developed impaired renal function, and displayed elevated renal levels of inflammatory markers, collagen and immune cells. MCC950 treatment from day 10 attenuated 1K/DOCA/salt-induced increases in renal expression of inflammasome subunits (NLRP3, ASC, pro-caspase-1) and inflammatory/injury markers (pro-IL-18, pro-IL-1β, IL-17A, TNF-α, osteopontin, ICAM-1, VCAM-1, CCL2, vimentin), each by 25–40%. MCC950 reduced interstitial collagen and accumulation of certain leucocyte subsets in kidneys of 1K/DOCA/salt-treated mice, including CD206⁺ (M2-like) macrophages and interferon-gamma-producing T cells. Finally, MCC950 partially reversed 1K/DOCA/salt-induced elevations in BP, urine output, osmolality, [Na⁺], and albuminuria (each by 20–25%). None of the above parameters were altered by MCC950 in normotensive mice.

Conclusion

MCC950 was effective at reducing BP and limiting renal inflammation, fibrosis and dysfunction in mice with established hypertension. This study provides proof-of-concept that pharmacological inhibition of the NLRP3 inflammasome is a viable anti-hypertensive strategy.

Effects of exercise on kidney function among non-diabetic patients with hypertension and renal disease: randomized controlled trial

Background

Chronic kidney disease is an important public health threat. Such patients present high morbidity and mortality due to cardiovascular disease, with low quality of life and survival, and also high expenditure resulting from the treatment. Arterial hypertension is both a cause and a complication of kidney disease; also, arterial hypertension is a risk factor for cardiovascular disease among patients with kidney diseases. There is some evidence that exercise interventions may be beneficial to chronic kidney disease patients, but previous studies included only end-stage patients, i.e. those undergoing dialysis. This study aims to evaluate the effect of exercise on kidney function, quality of life and other risk factors for cardiovascular disease among non-diabetic chronic hypertensive kidney disease patients who are not undergoing dialysis.

Methods

The participants will be located through screening hypertensive patients attended within the public healthcare network in Pelotas, a city in south of Brazil. Eligible individuals will be those with glomerular filtration rate between 15 and 59 ml/min x 1.73 m². The randomization will be done in fixed-size blocks of six individuals such that 75 participants will be allocated to each group. At baseline, information on demographic, socioeconomic, behavioral, anthropometric, blood pressure and quality-of-life variables will be collected, and laboratory tests will be performed. The intervention will consist of three weekly physical exercise sessions lasting 60–75 minutes each, with a total duration of 16 weeks. The outcomes will be the kidney function progression rate, quality of life, blood pressure, lipid profile, hemoglobin level, ultrasensitive C-reactive protein level, and ankle-arm index. The patients in both groups (intervention and control) will be reassessed and compared partway through the study (8^th week), at the end of the intervention (16^th week) and in the 8^th week after the end of the intervention.

Discussion

There is still a scarcity of data relating to the effect of physical exercise among the most numerous group of individuals with kidney disease, i.e. patients undergoing conservative treatment. In particular, there is a lack of randomized controlled studies. This study will help fill this gap.

How NaCl raises blood pressure: a new paradigm for the pathogenesis of salt-dependent hypertension

Excess dietary salt is a major cause of hypertension. Nevertheless, the specific mechanisms by which salt increases arterial constriction and peripheral vascular resistance, and thereby raises blood pressure (BP), are poorly understood. Here we summarize recent evidence that defines specific molecular links between Na(+) and the elevated vascular resistance that directly produces high BP. In this new paradigm, high dietary salt raises cerebrospinal fluid [Na(+)]. This leads, via the Na(+)-sensing circumventricular organs of the brain, to increased sympathetic nerve activity (SNA), a major trigger of vasoconstriction. Plasma levels of endogenous ouabain (EO), the Na(+) pump ligand, also become elevated. Remarkably, high cerebrospinal fluid [Na(+)]-evoked, locally secreted (hypothalamic) EO participates in a pathway that mediates the sustained increase in SNA. This hypothalamic signaling chain includes aldosterone, epithelial Na(+) channels, EO, ouabain-sensitive α(2) Na(+) pumps, and angiotensin II (ANG II). The EO increases (e.g.) hypothalamic ANG-II type-1 receptor and NADPH oxidase and decreases neuronal nitric oxide synthase protein expression. The aldosterone-epithelial Na(+) channel-EO-α(2) Na(+) pump-ANG-II pathway modulates the activity of brain cardiovascular control centers that regulate the BP set point and induce sustained changes in SNA. In the periphery, the EO secreted by the adrenal cortex directly enhances vasoconstriction via an EO-α(2) Na(+) pump-Na(+)/Ca(2+) exchanger-Ca(2+) signaling pathway. Circulating EO also activates an EO-α(2) Na(+) pump-Src kinase signaling cascade. This increases the expression of the Na(+)/Ca(2+) exchanger-transient receptor potential cation channel Ca(2+) signaling pathway in arterial smooth muscle but decreases the expression of endothelial vasodilator mechanisms. Additionally, EO is a growth factor and may directly participate in the arterial structural remodeling and lumen narrowing that is frequently observed in established hypertension. These several central and peripheral mechanisms are coordinated, in part by EO, to effect and maintain the salt-induced elevation of BP.

Intrathecal injection of TRPV1 shRNA leads to increases in blood pressure in rats

AIM

The transient receptor potential vanilloid type 1 (TRPV1) channels have been implicated to play a role in blood pressure regulation. However, contribution of tissue specific TRPV1 to blood pressure regulation is largely unknown. Here, we test the hypothesis that TRPV1 expressed in dorsal root ganglia (DRG) of lower thoracic and upper lumbar segments (T8-L3) of the spinal cord and their central and peripheral terminals constitutes a counter regulatory mechanism preventing the increases in blood pressure.

METHODS

The expression of TRPV1 was knocked down by intrathecal injection of TRPV1 short-hairpin RNA (shRNA) in rats. Systolic blood pressure and mean arterial pressure (MAP) were recorded. The level of TRPV1 and tyrosine hydroxylase (TH) was measured by Western blot.

RESULTS

Intrathecal injection of TRPV1 shRNA (6 μg kg(-1) day(-1) ) for 3 days increased systolic blood pressure and MAP when compared to rats that received control shRNA (control shRNA: 112 ± 2 vs. TRPV1 shRNA: 123 ± 2 mmHg). TRPV1 expression was suppressed in T8-L3 segments of dorsal horn and DRG as well as mesenteric arteries of rats given TRPV1 shRNA. Contents of TH, a marker of sympathetic nerves, were increased in mesenteric arteries of rats treated with TRPV1 shRNA. Pretreatment with the α1-adrenoceptor blocker, prazosin (1 mg kg(-1) day(-1) , p.o.), abolished the TRPV1 shRNA-induced pressor effects.

CONCLUSION

Our data show that selective knockdown of TRPV1 expressed in DRG of T8-L3 segments of the spinal cord and their central and peripheral terminals increases blood pressure, suggesting that neuronal TRPV1 in these segments possesses a tonic anti-hypertensive effect possibly via suppression of the sympathetic nerve activity.

Enhanced salt sensitivity following shRNA silencing of neuronal TRPV1 in rat spinal cord

AIM

To investigate the effects of selective knockdown of TRPV1 channels in the lower thoracic and upper lumbar segments of spinal cord, dorsal root ganglia (DRG) and mesenteric arteries on rat blood pressure responses to high salt intake.

METHODS

TRPV1 short-hairpin RNA (shRNA) was delivered using intrathecal injection (6 μg · kg(-1) · d(-1), for 3 d). Levels of TRPV1 and tyrosine hydroxylase expression were determined by Western blot analysis. Systolic blood pressure and mean arterial pressure (MAP) were examined using tail-cuff and direct arterial measurement, respectively.

RESULTS

In rats injected with control shRNA, high-salt diet (HS) caused higher systolic blood pressure compared with normal-salt diet (NS) (HS:149 ± 4 mmHg; NS:126 ± 2 mmHg, P<0.05). Intrathecal injection of TRPV1 shRNA significantly increased the systolic blood pressure in both HS rats and NS rats (HS:169 ± 3 mmHg; NS:139 ± 2 mmHg). The increases was greater in HS rats than in NS rats (HS: 13.9% ± 1.8%; NS: 9.8 ± 0.7, P<0.05). After TRPV1 shRNA treatment, TRPV1 expression in the dorsal horn and DRG of T8-L3 segments and in mesenteric arteries was knocked down to a greater extent in HS rats compared with NS rats. Blockade of α1-adrenoceptors abolished the TRPV1 shRNA-induced pressor effects. In rats injected with TRPV1 shRNA, level of tyrosine hydroxylase in mesenteric arteries was increased to a greater extent in HS rats compared with NS rats.

CONCLUSION

Selective knockdown of TRPV1 expression in the lower thoracic and upper lumbar segments of spinal cord, DRG, and mesenteric arteries enhanced the prohypertensive effects of high salt intake, suggesting that TRPV1 channels in these sites protect against increased salt sensitivity, possibly via suppression of sympatho-excitatory responses.

Device-guided slow-breathing effects on end-tidal CO(2) and heart-rate variability

Previous studies have reported that regular practice of a device-guided slow-breathing (DGB) exercise decreases resting blood pressure (BP) in hypertensive patients. The performance of DGB is associated with acute decreases in sympathetic vascular tone, and it has been suggested that the decreases in resting BP produced by regular practice of DGB over periods of weeks are due to chronic decreases in sympathetic nervous system activity. However, the kidneys respond to sympathetically mediated changes in BP by readjusting blood volume levels within a few days. Thus, the mechanism by which DGB could produce long-term BP changes remains to be clarified. Previous research with laboratory animals and human subjects has shown that slow, shallow breathing that increases pCO(2) potentiates BP sensitivity to high sodium intake. These findings raise the possibility that deeper breathing during DGB that decreases BP might involve opposite changes in pCO(2). The present study tested the hypothesis that performance of DGB acutely decreases a marker of pCO(2), end-tidal CO(2) (PetCO(2)). Breathing rate, tidal volume, and PetCO(2) were monitored before, during, and after a 15-min session of DGB by patients with elevated BP. BP, heart rate, and heart-rate variability (HRV) were also measured under these conditions. A control group was also studied before, during, and after a 15-min session of spontaneous breathing (SB). The DGB group, but not the SB group, showed progressive and substantial increases in tidal volume and low-frequency HRV and decreases in PetCO(2) and systolic BP. The PetCO(2) effects persisted into the posttask, rest period. The findings are consistent with the hypothesis that habitual changes in breathing patterns of the kind observed during DGB could potentiate an antihypertensive adaptation via effects on pCO(2) and its role in cardiovascular homeostasis.