Hypertension in chronic kidney disease: What lies behind the scene

Hypertension is a frequent condition encountered during kidney disease development and a leading cause in its progression. Hallmark factors contributing to hypertension constitute a complexity of events that progress chronic kidney disease (CKD) into end-stage renal disease (ESRD). Multiple crosstalk mechanisms are involved in sustaining the inevitable high blood pressure (BP) state in CKD, and these play an important role in the pathogenesis of increased cardiovascular (CV) events associated with CKD. The present review discusses relevant contributory mechanisms underpinning the promotion of hypertension and their consequent eventuation to renal damage and CV disease. In particular, salt and volume expansion, sympathetic nervous system (SNS) hyperactivity, upregulated renin–angiotensin–aldosterone system (RAAS), oxidative stress, vascular remodeling, endothelial dysfunction, and a range of mediators and signaling molecules which are thought to play a role in this concert of events are emphasized. As the control of high BP via therapeutic interventions can represent the key strategy to not only reduce BP but also the CV burden in kidney disease, evidence for major strategic pathways that can alleviate the progression of hypertensive kidney disease are highlighted. This review provides a particular focus on the impact of RAAS antagonists, renal nerve denervation, baroreflex stimulation, and other modalities affecting BP in the context of CKD, to provide interesting perspectives on the management of hypertensive nephropathy and associated CV comorbidities.

Matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases in kidney disease

Matrix metalloproteinases (MMPs) are a group of zinc and calcium endopeptidases which cleave extracellular matrix (ECM) proteins. They are also involved in the degradation of cell surface components and regulate multiple cellular processes, cell to cell interactions, cell proliferation, and cell signaling pathways. MMPs function in close interaction with the endogenous tissue inhibitors of matrix metalloproteinases (TIMPs), both of which regulate cell turnover, modulate various growth factors, and participate in the progression of tissue fibrosis and apoptosis. The multiple roles of MMPs and TIMPs are continuously elucidated in kidney development and repair, as well as in a number of kidney diseases. This chapter focuses on the current findings of the significance of MMPs and TIMPs in a wide range of kidney diseases, whether they result from kidney tissue changes, hemodynamic alterations, tubular epithelial cell apoptosis, inflammation, or fibrosis. In addition, the potential use of these endopeptidases as biomarkers of renal dysfunction and as targets for therapeutic interventions to attenuate kidney disease are also explored in this review.

Renal denervation does not affect hypertension or the renin-angiotensin system in a rodent model of juvenile-onset polycystic kidney disease: clinical implications

We examined the effect of total and afferent renal denervation (RDN) on hypertension and the renin-angiotensin system (RAS) in a rodent model of juvenile-onset polycystic kidney disease (PKD). Lewis Polycystic Kidney (LPK) and control rats received total, afferent or sham RDN by periaxonal application of phenol, capsaicin or normal saline, respectively, and were monitored for 4-weeks. Afferent RDN did not affect systolic blood pressure (SBP) determined by radiotelemetry in either strain (n = 19) while total RDN significantly reduced SBP in Lewis rats 4-weeks post-denervation (total vs. sham, 122 ± 1 vs. 130 ± 2 mmHg, P = 0.002, n = 25). Plasma and kidney renin content determined by radioimmunoassay were significantly lower in LPK vs. Lewis (plasma: 278.2 ± 6.7 vs. 376.5 ± 11.9 ng Ang I/ml/h; kidney: 260.1 ± 6.3 vs. 753.2 ± 37.9 ng Ang I/mg/h, P < 0.001, n = 26). These parameters were not affected by RDN. Intrarenal mRNA expression levels of renin, angiotensinogen, angiotensin-converting enzyme (ACE)2, and angiotensin II receptor type 1a were significantly lower, whereas ACE1 expression was significantly higher in the LPK vs. Lewis (all P < 0.05, n = 26). This pattern of intrarenal RAS expression was not changed by RDN. In conclusion, RDN does not affect hypertension or the RAS in the LPK model and indicates RDN might not be a suitable antihypertensive strategy for individuals with juvenile-onset PKD.

The subfornical organ drives hypertension in polycystic kidney disease via the hypothalamic paraventricular nucleus

AIMS

Hypertension is a prevalent yet poorly understood feature of polycystic kidney disease. Previously we demonstrated that increased glutamatergic neurotransmission within the hypothalamic paraventricular nucleus produces hypertension in the Lewis Polycystic Kidney rat model of polycystic kidney disease. Here we tested the hypothesis that augmented glutamatergic drive to the paraventricular nucleus in Lewis Polycystic Kidney rats originates from the forebrain lamina terminalis, a sensory structure that relays blood-borne information throughout the brain.

METHODS AND RESULTS

Anatomical experiments revealed that 38% of paraventricular nucleus-projecting neurons in the subfornical organ of the lamina terminalis expressed Fos/Fra, an activation marker, in Lewis Polycystic Kidney rats while <1% of neurons were Fos/Fra+ in Lewis control rats (P = 0.01, n = 8). In anaesthetised rats, subfornical organ neuronal inhibition using isoguvacine produced a greater reduction in systolic blood pressure in the Lewis Polycystic Kidney versus Lewis rats (-21 ± 4 vs. -7 ± 2 mmHg, P < 0.01; n = 10), which could be prevented by prior blockade of paraventricular nucleus ionotropic glutamate receptors using kynurenic acid. Blockade of ionotropic glutamate receptors in the paraventricular nucleus produced an exaggerated depressor response in Lewis Polycystic Kidney relative to Lewis rats (-23 ± 4 vs. -2 ± 3 mmHg, P < 0.001; n = 13), which was corrected by prior inhibition of the subfornical organ with muscimol but unaffected by chronic systemic angiotensin II type I receptor antagonism or lowering of plasma hyperosmolality through high-water intake (P > 0.05); treatments that both nevertheless lowered blood pressure in Lewis Polycystic Kidney rats (P < 0.0001).

CONCLUSION

Our data reveal multiple independent mechanisms contribute to hypertension in polycystic kidney disease, and identify high plasma osmolality, angiotensin II type I receptor activation and, importantly, a hyperactive subfornical organ to paraventricular nucleus glutamatergic pathway as potential therapeutic targets.

TRANSLATIONAL PERSPECTIVE

Hypertension is a significant comorbidity for all forms of chronic kidney disease and for individuals with polycystic kidney disease, often an early presenting feature. Nevertheless, the cause(s) of hypertension in polycystic kidney disease are poorly defined. Here we define the contribution of a neural pathway that contributes to hypertension in polycystic kidney disease. Critically, targeting this pathway may provide an additional antihypertensive effect beyond that achieved with current conventional antihypertensive therapies. Future work identifying the drivers of this neural pathway will aid in the development of newer generation antihypertensive medication.

Regional functional and structural abnormalities within the aorta as a potential driver of vascular disease in metabolic syndrome

NEW FINDINGS

What is the central question of this study? Is aortic dysfunction, a significant contributor to cardiovascular disease in metabolic syndrome, expressed uniformly across both the thoracic and abdominal aorta? What is the main finding and its importance? Our study shows that, in the setting of metabolic syndrome, functional and structural deficits in the aorta are differentially expressed along its length, with the abdominal portion displaying more extensive vascular abnormalities. It is, therefore, likely that early interventional strategies targeting the abdominal aorta might alleviate cardiovascular pathologies driven by the metabolic syndrome.

ABSTRACT

The extent of vascular dysfunction associated with metabolic syndrome might vary along the length of the aorta. In this study, we investigated regional functional and structural changes in the thoracic and abdominal aorta of a rat model of metabolic syndrome, namely, high-fat diet (HFD) streptozotocin-induced diabetes mellitus (HFD-D). Four-week-old male Wistar albino rats were fed with either HFD or control diet (CD) for 10 weeks. At week 6, 40 mg/kg streptozotocin and its vehicle were injected i.p. into HFD and CD groups, respectively. At the end of the feeding period, rats were euthanised and aortic segments collected for assessment of vascular functional responses and histomorphometry. Tail-cuff systolic blood pressures (154 ± 6  vs. 110 ± 4 mmHg) and areas under the curve for oral glucose and i.p. insulin tolerance tests were greater in HFD-D versus CD rats. Abdominal aortic vasoconstriction in response to noradrenaline and KCl was greater in HFD-D compared with CD rats. Thoracic vasoconstrictor responses to noradrenaline, but not KCl, were greater in the HFD-D group. Abdominal, but not thoracic, endothelium-dependent vasorelaxation in response to acetylcholine was blunted in HFD-D relative to CD rats; however, nitric oxide-dependent vasorelaxation in HFD-D rats was impaired in both thoracic and abdominal segments. The abdominal aorta of HFD-D rats showed deranged interlamellar spacing and increased lipid plaque deposition. In conclusion, vascular dysfunction in metabolic syndrome is expressed differentially along the length of the aorta, with the abdominal aorta exhibiting increased susceptibility to vasoconstrictors and greater deficits in endothelium-dependent relaxation. These vascular functional abnormalities could potentially underlie the development of hypertensive cardiovascular disease associated with the metabolic syndrome.

Amlodipine Improves Vessel Function and Remodeling in the Lewis Polycystic Kidney Rat Mesenteric Artery

BACKGROUND

Hypertension is a common comorbidity associated with chronic kidney disease (CKD). Treatment in these patients often involves L-type Ca2+ channel (LTCC) blockers. The effect of chronic LTCC-blockade treatment on resistance vasculature was investigated in a genetic hypertensive rat model of CKD, the Lewis Polycystic Kidney (LPK) rat.

METHODS

Mixed-sex LPK and Lewis control rats (total n = 38) were allocated to treated (amlodipine 20 mg/kg/day p.o. from 4 to 18 weeks) and vehicle groups. Following systolic blood pressure and renal function assessment, animals were euthanized and mesenteric vasculature was collected for functional and structural assessment using pressure myography and histology.

RESULTS

Amlodipine treatment reduced LPK rat blood pressure (untreated vs. treated: 185 ± 5 vs. 165 ± 9 mm Hg; P = 0.019), reduced plasma creatinine (untreated vs. treated: 197 ± 17 vs. 140 ± 16 µmol/l; P = 0.002), and improved some vascular structural parameters (internal and external diameters and wall-lumen ratios); however wall thickness was still increased in LPK relative to Lewis despite treatment (Lewis vs. LPK: 31 ± 2 vs. 41 ± 2 µm, P = 0.047). Treatment improved LPK rats' endothelium dysfunction, and nitric oxide-dependent and endothelium-derived hyperpolarization vasorelaxation components, and downregulated prostanoid contributions. LTCC blockade had no effect on biomechanical properties of compliance and intrinsic stiffness, nor artery wall composition.

CONCLUSIONS

Our results indicate that blockade of LTCCs with amlodipine is effective in improving, to a certain extent, detrimental structural and functional vascular features of resistance arteries in CKD.

The protective effects of renin-angiotensin system componts on vascular calcification

Renin-angiotensin system (RAS) has important roles in cardiovascular disease. Angiotensin II (Ang II) and angiotensin-(1-7) (Ang-(1-7)) are major effector peptides of RAS. However, the roles of Ang II type 2 receptor (AT2R) need to be further explored and the roles of Ang-(1-7) are still not very clear on vascular calcification (VC). Therefore, we hypothesized they have effects on preventing VC in vivo and in vitro. VC model is established by inorganic phosphate (IP) cultured with vascular smooth muscle cells (VSMC) for in vitro study and by 5/6 nephrectomy in mice for in vivo study. Increased calcified nodules by Alizarin Red S staining and mRNA expressions of bone morphogenetic protein-2 (BMP-2) and osteocalcin (OCN) by reverse transcription polymerase chain reaction in calcified WT VSMC were significantly inhibited in calcified AT2R overexpression (SmAT2) VSMC or after Ang-(1-7) treatment. After 5/6 nephrectomy, the ratio of positive and total area by Alizarin Red S and von Kossa staining and mRNA expressions of BMP-2 and OCN were significantly increased in ApoE/AT2R knockout mice compared with apolipoprotein E knockout mice, and which were significantly inhibited with Ang-(1-7) administration. Both AT2R and Ang-(1-7) have the effects on preventing VC induced by IP, at least in part through inhibiting BMP-2, OCN expressions, and in which Ang-(1-7) had protective roles mainly through Mas receptor rather than AT2R.

AT1 Receptor Antagonism Improves Structural, Functional, and Biomechanical Properties in Resistance Arteries in a Rodent Chronic Kidney Disease Model

BACKGROUND

The renin-angiotensin system, in particular Angiotensin II (AngII), plays a significant role in the pathogenesis of hypertension in chronic kidney disease (CKD). Effects of chronic AT1 receptor antagonism were investigated in a genetic hypertensive rat model of CKD, the Lewis polycystic kidney (LPK) rat.

METHODS

Mixed-sex LPK and Lewis control rats (total n = 31) were split between treated (valsartan 60 mg/kg/day p.o. from 4 to 18 weeks) and vehicle groups. Animals were assessed for systolic blood pressure and urine biochemistry, and after euthanasia, blood collected for urea and creatinine analysis, confirming the hypertensive and renal phenotype. Mesenteric resistance vasculature was assessed using pressure myography and histology.

RESULTS

Valsartan treatment improved vascular structure in LPK rats, increasing internal and external diameter values and reducing wall thickness (untreated vs. treated LPK: 53.19 ± 3.29 vs. 33.93 ± 2.17 μm) and wall-lumen ratios (untreated vs. treated LPK: 0.52 ± 0.09 vs. 0.16 ± 0.01, all P < 0.0001). Endothelium dysfunction, as measured by maximal response to acetylcholine (Rmax), was normalized with treatment (untreated vs. treated LPK: 69.56 ± 4.34 vs. 103.05 ± 4.13, P < 0.05), increasing the relative contributions of nitric oxide and endothelium-derived hyperpolarization to vasorelaxation while downregulating the prostanoid contribution. Biomechanical properties also improved with treatment, as indicated by an increase in compliance, decrease in intrinsic stiffness and alterations in the artery wall composition, which included decreases in collagen density and collagen/elastin ratio.

CONCLUSIONS

Our results highlight the importance of AngII as a driver of resistance vessel structural, functional, and biomechanical dysfunction and provide insight as to how AT1 receptor blockade exerts therapeutic efficacy in CKD.