Kidney Mass Reduction Leads to l-Arginine Metabolism-Dependent Blood Pressure Increase in Mice

Potassium-Alkali-Enriched Diet, Hypertension, and Proteinuria following Uninephrectomy

Key Points

Background

Losing or donating a kidney is associated with risks of developing hypertension and albuminuria. Few studies address mechanisms or interventions. We investigate the potential benefits of a K+- alkali–enriched diet and the mechanisms underlying proteinuria.

Methods

Male Sprague Dawley rats were fed either a 2% NaCl+0.95% KCl diet (HNa-LK) or a 0.74% NaCl+3% K+-alkali diet (HK-alk) for 3 weeks before uninephrectomy and then maintained on respective diets for 12 weeks. BP (by tail-cuff), urine, blood, and kidney proteins were analyzed before and after uninephrectomy.

Results

Before uninephrectomy, HK-alk–fed versus HNa-LK–fed rats exhibited similar BPs and plasma [K+], [Na+], but lower proximal (NHE3, sodium bicarbonate cotransporter 1, NaPi2) and higher distal (NCC, ENaC, and pendrin) transporter abundance, a pattern facilitating K+ and HCO3 − secretion. After uninephrectomy, single-nephron GFR increased 50% and Li+ clearance doubled with both diets; in HK-alk versus HNa-LK, the increase in BP was less and ammoniagenesis was lower, abundance of proximal tubule transporters remained lower, ENaC-α fell, and NCCp increased, consistent with K+ conservation. After uninephrectomy, independent of diet, albuminuria increased eight-fold and abundance of endocytic receptors was reduced (megalin by 44%, disabled homolog 2 by 25%–35%) and kidney injury molecule-1 was increased.

Conclusions

The K-alkali–enriched diet blunted post-uninephrectomy hypertension and facilitated acid clearance by suppressing proximal Na+ transporters and increasing K+-alkali secretion. Furthermore, uninephrectomy-associated proteinuria could be attributed, at least in part, to elevated single-nephron GFR coupled with downregulation of megalin, which reduced fractional protein endocytosis and Vmax.

Chemo- and optogenetic activation of hypothalamic Foxb1-expressing neurons and their terminal endings in the rostral-dorsolateral PAG leads to tachypnea, bradycardia, and immobility

Foxb1 -expressing neurons occur in the dorsal premammillary nucleus (PMd) and further rostrally in the parvafox nucleus, a longitudinal cluster of neurons in the lateral hypothalamus of rodents. The descending projection of these Foxb1+ neurons end in the dorsolateral part of the periaqueductal gray (dlPAG). The functional role of the Foxb1+ neuronal subpopulation in the PMd and the parvafox nucleus remains elusive. In this study, the activity of the Foxb1+ neurons and of their terminal endings in the dlPAG in mice was selectively altered by employing chemo- and optogenetic tools. Our results show that in whole-body barometric plethysmography, hM3Dq-mediated, global Foxb1+ neuron excitation activates respiration. Time-resolved optogenetic gain-of-function manipulation of the terminal endings of Foxb1+ neurons in the rostral third of the dlPAG leads to abrupt immobility and bradycardia. Chemogenetic activation of Foxb1+ cell bodies and ChR2-mediated excitation of their axonal endings in the dlPAG led to a phenotypical presentation congruent with a 'freezing-like' situation during innate defensive behavior.

Spermidine from arginine metabolism activates Nrf2 and inhibits kidney fibrosis

Kidney metabolism may be greatly altered in chronic kidney disease. Here we report that arginine metabolism is the most altered in unilateral ureteral obstruction (UUO)-induced fibrosis of the kidneys in metabolomic analysis. Spermidine is the most increased metabolite of arginine. In human glomerulonephritis, the amount of spermidine shown by immunostaining is associated with the amount of fibrosis. In human proximal tubule cells, spermidine induces nuclear factor erythroid 2-related factor 2 (Nrf2). Subsequently, fibrotic signals, such as transforming growth factor β1 secretion, collagen 1 mRNA, and oxidative stress, represented by a decrease in the mitochondrial membrane potential is suppressed by spermidine. UUO kidneys of Arg2 knockout mice show less spermidine and significantly exacerbated fibrosis compared with wild-type mice. Nrf2 activation is reduced in Arg2 knockout UUO kidneys. Spermidine treatment prevents significant fibrotic progression in Arg2 knockout mice. Spermidine is increased in kidney fibrosis, but further increases in spermidine may reduce fibrosis.

Deciphering the Q-markers of nourishing kidney-yin of Cortex Phellodendri amurense from ZhibaiDihuang pill based on Chinmedomics strategy

BACKGROUND

Cortex Phellodendri amurensis (CPA) has high medicinal value in the treatment of kidney-yin deficiency diseases. However, due to the lack of research on the therapeutic material basis of CPA, the current quality control standard for CPA is defective, and the effect of the nourishing kidney-yin of CPA was limited.

PURPOSE

Based on the principle of correspondence between the syndrome and prescriptions, we studied the CPA in ZhibaiDihuang pill (ZBDH) to identify quality markers (Q-markers) of CPA in ZBDH for treating kidney-yin deficiency and seek the potential Q-markers of CPA under nourishing kidney-yin effect combined with the analysis of single CPA.

METHODS

Taking Chinmedomics as the core strategy, metabonomics analysis and effective component identification were performed by UPLC-MS.

RESULTS

A total of 121 chemical components of ZBDH were identified, among which the contents of berberine, palmatine, jatrorrhizine and magnoflorine changed the most obviously with the addition of CPA. Forty-five components were identified in the blood in the markedly effective state, including berberine, palmatine, jatrorrhizine and magnoflorine. The therapeutic material basis of ZBDH in the treatment of kidney-yin deficiency was found, and 6 components were found to derive from CPA, including magnoflorine and jatrorrhizine. In addition, seventeen components were identified in the blood in the single CPA treatment, including berberine, palmatine, jatrorrhizine and magnoflorine.

CONCLUSIONS

Magnoflorine and jatrorrhizine were the Q-markers of CPA for treating kidney-yin deficiency in the formula of ZBDH and they were also potential Q-markers of the nourishing kidney-yin of CPA.

Fumarase Overexpression Abolishes Hypertension Attributable to endothelial NO synthase Haploinsufficiency in Dahl Salt-Sensitive Rats

Human blood pressure salt sensitivity is associated with changes in urinary metabolites related to fumarase (Fh) and nitric oxide (NO) metabolism, and fumarase promotes NO production through an arginine regeneration pathway. We examined the role of the fumarase-NO pathway in the development of hypertension using genetically engineered rat models. Dahl salt-sensitive (SS) rats with heterozygous mutation of eNOS (endothelial NO synthase or Nos3; SS-Nos3^+/-) were bred with SS rats with a hemizygous Fh transgene. SS-Nos3^+/- rats without the Fh transgene (SS-Nos3^+/-/Fh^0/0) developed substantial hypertension with a mean arterial pressure of 134.2±3.7 mm Hg on a 0.4% NaCl diet and 178.0±3.5 mm Hg after 14 days on a 4% NaCl diet. Mean arterial pressure decreased remarkably to 123.1±1.4 mm Hg on 0.4% NaCl, and 143.3±1.5 mm Hg on 4% NaCl in SS-Nos3^+/- rats with a Fh transgene (SS-Nos3^+/-/Fh^0/1), and proteinuria, renal fibrosis, and tubular casts were attenuated in SS-Nos3^+/-/Fh^0/1 rats compared with SS-Nos3^+/-/Fh^0/0 rats. eNOS protein abundance decreased in rats with the Nos3 heterozygous mutation, which was not influenced by Fh overexpression in rats on the 0.4% NaCl diet. However, the decrease in NO metabolite in the renal outer medulla of SS-Nos3^+/-/Fh^0/0 rats on the 0.4% NaCl diet was reversed in SS-Nos3^+/-/Fh^0/1 rats, and levels of L-arginine, but not the other 12 amino acids analyzed, were significantly higher in SS-Nos3^+/-/Fh^0/1 rats than in SS-Nos3^+/+/Fh^0/0 rats. In conclusion, fumarase has potent effects in restoring NO production and blunting the development of hypertension attributable to eNOS haploinsufficiency.

Effect of cocoa powder on hypertension and antioxidant status in uninephrectomized hypertensive rats

BACKGROUND AND AIM

High salt diet and uninephrectomy are associated with high blood pressure with attendant cardiovascular disease conditions such as hypertension, renal damage, myocardial infarction, and stroke. The aim of this study was to investigate the beneficial effects of consumption of cocoa and cocoa-containing products in the management of high blood pressure in uninephrectomized hypertensive rats.

MATERIALS AND METHODS

The effect of cocoa powder on blood pressure, markers of inflammation, oxidative stress, and histopathology were investigated in uninephrectomized animals fed with cocoa feed alone or in combination with a high salt diet. Male rats were randomly divided into five groups: Group A was the control group and fed with normal feed alone, Group B was fed with cocoa feed alone, Group C was fed with high salt diet (8% salt), GroupD was fed with cocoa-feed compounded with 8% salt for 4weeks after uninephrectomy, and GroupE was uninephrectomized rats on a normal diet. The left kidneys of animals in GroupsC, D, and E were removed by surgery. After 4weeks of treatment, the systolic, diastolic, and mean arterial blood pressure was measured. The serum markers of renal damage and oxidative stress were determined. Histological examination was also performed on renal and cardiac tissues.

RESULTS

Results showed significant increases in biomarkers of oxidative stress, inflammation, and renal damage with a concomitant decrease in antioxidant status in hypertensive uninephrectomized rats. Cocoa feed, however, significantly improved blood pressure and nitric oxide bioavailability, antioxidant status and reduced markers of inflammation and oxidative stress.

CONCLUSION

These findings show that cocoa powder could be used to maintain blood pressure levels in hypertensive rats through its antioxidant capacity.

Citrulline Generation Test: What Does It Measure?

BACKGROUND

The citrulline generation test (CGT) has been proposed as a tool to determine gut function. However, the increase in plasma citrulline concentration that follows a bolus dose of alanyl-glutamine may also result from a reduction in citrulline clearance due to competition with glutamine for transport.

MATERIALS AND METHODS

A swine model was developed, and stable isotope tracers were used to determine the mechanism behind the increase in plasma citrulline that follows a bolus dose of alanyl-glutamine. Plasma concentrations and enrichments were determined, and a non-steady-state model was used to calculate rates of appearance, disappearance, and conversion.

RESULTS

The pig model recapitulated the increase in plasma citrulline observed in humans after a dose of alanyl-glutamine. The dipeptide was rapidly hydrolyzed to its constitutive amino acids. Both citrulline plasma concentration and citrulline rate of appearance increased by ≈45% after the bolus dose of alanyl-glutamine. The conversion of citrulline to arginine and the rate of appearance of arginine also increased. Glutamine contributed up to 25% ± 2% of the rate of appearance of citrulline. No changes in the rate of disappearance of citrulline were observed.

CONCLUSION

Our results indicate that a single bolus dose of alanyl-glutamine increases plasma citrulline concentration by increasing citrulline production without any effect on citrulline disposal. Our findings strongly indicate that the CGT assesses the metabolic response of the gut and that CGT can become a useful tool to evaluate gut mass and function.

Arginase-II negatively regulates renal aquaporin-2 and water reabsorption

Type-II l-arginine:ureahydrolase, arginase-II (Arg-II), is abundantly expressed in the kidney. The physiologic role played by Arg-II in the kidney remains unknown. Herein, we report that in mice that are deficient in Arg-II (Arg-II^−/−), total and membrane-associated aquaporin-2 (AQP2) protein levels were significantly higher compared with wild-type (WT) controls. Water deprivation enhanced Arg-II expression, AQP2 levels, and membrane association in collecting ducts. Effects of water deprivation on AQP2 were stronger in Arg-II^−/− mice than in WT mice. Accordingly, a decrease in urine volume and an increase in urine osmolality under water deprivation were more pronounced in Arg-II^−/− mice than in WT mice, which correlated with a weaker increase in plasma osmolality in Arg-II^−/− mice. There was no difference in vasopressin release under water deprivation conditions between either genotype of mice. Although total AQP2 and phosphorylated AQP2-S256 levels (mediated by PKA) in kidneys under water deprivation conditions were significantly higher in Arg-II^−/− mice compared with WT animals, there is no difference in the ratio of AQP2-S256:AQP2. In cultured mouse collecting duct principal mCCD_cl1 cells, expression of both Arg-II and AQP2 were enhanced by the vasopressin type 2 receptor agonist, desamino-d-arginine vasopressin (dDAVP). Silencing Arg-II enhanced the expression and membrane association of AQP2 by dDAVP without influencing cAMP levels. In conclusion, in vivo and in vitro experiments demonstrate that Arg-II negatively regulates AQP2 and the urine-concentrating capability in kidneys via a mechanism that is not associated with the modulation of the cAMP pathway.—Huang, J., Montani, J.-P., Verrey, F., Feraille, E., Ming, X.-F., Yang, Z. Arginase-II negatively regulates renal aquaporin-2 and water reabsorption.