Dietary salt intake modulates progression of antithymocyte serum nephritis through alteration of glomerular angiotensin II receptor expression

Angiotensin II Type 1 Receptor Antibodies Are Higher in Lupus Nephritis and Vasculitis than Other Glomerulonephritis Patients

Angiotensin II type 1 receptor (AT1R) antibodies are considered non-HLA (human leukocyte antigen) antibodies connected with humoral rejection after kidney transplantation. The role of AT1R antibodies in the pathogenesis of glomerular diseases and systemic vasculitis is unknown. We assessed the level of AT1R antibodies in 136 patients with different types of glomerulonephritis and systemic vasculitis and we observed kidney function and proteinuria, serum albumin and total protein levels for 2 years. The mean levels of AT1R antibodies were the following: 6.00 ± 1.31 U/ml in patients with membranous nephropathy (n = 18), 5.67 ± 1.31 U/ml with focal and segmental glomerulosclerosis (n = 25), 6.26 ± 2.25 U/ml with lupus nephropathy (n = 17), 10.60 ± 6.72 U/ml with IgA nephropathy (n = 14), 6.69 ± 2.52 U/ml with mesangial proliferative (non IgA) glomerulonephritis (n = 6), 6.63 ± 1.38 U/ml with systemic vasculitis (n = 56), including c-ANCA (anti-neutrophil cytoplasmic antibodies) vasculitis: 11.22 ± 10.78 U/ml (n = 40) and p-ANCA vasculitis: 12.65 ± 14.59 U/ml (n = 16). The mean AT1R antibodies level was higher in patients with lupus nephropathy and systemic vasculitis compared to glomerulonephritis groups. An inverse statistically significant correlation between AT1R antibodies and serum albumin (r =  − 0.51) in membranous nephropathy group was also found. Prospective analysis of creatinine levels indicated an increase of creatinine levels during time among patients with higher AT1R antibodies levels in p-ANCA vasculitis. Lupus nephropathy and systemic vasculitis patients may have high levels of AT1R antibodies. AT1R antibodies may be associated with the severity of membranous nephropathy and the course of p-ANCA vasculitis, although influence of concomitant factors is difficult to exclude.

Protective Effect of Gamma Aminobutyric Acid against Aggravation of Renal Injury Caused by High Salt Intake in Cisplatin-Induced Nephrotoxicity

Gamma-aminobutyric acid (GABA) is one of the inhibitory neurotransmitters. Several studies have suggested that GABA supplements can reduce blood pressure and modulate the renal immune system in vitro and in vivo. In the present study, we investigated the effect of GABA-enriched salt as an alternative to traditional salt on aggravated renal injury by high salt intake in cisplatin-induced nephrotoxicity mice. High salt intake accelerated the increase of biomarkers, such as blood urea nitrogen and serum creatinine levels for renal injury in cisplatin-induced nephrotoxicity mice. However, oral administration of GABA-contained salt notably suppressed serum BUN and creatinine levels. The efficacy of GABA salt was superior to lacto GABA salt and postbiotics GABA salt. Furthermore, GABA-enriched salt markedly restored histological symptoms of nephrotoxicity including renal hypertrophy, tubular dilation, hemorrhage, and collagen deposition aggravated by salt over-loading in cisplatin-exposed mice. Among them, GABA salt showed a higher protective effect against cisplatin-induced renal histological changes than lacto GABA salt and postbiotics GABA salt. In addition, administration of high salt significantly enhanced expression levels of apoptosis and inflammatory mediators in cisplatin-induced nephrotoxicity mice, while GABA-enriched salt greatly down-regulated the expression of these mediators. Taken together, these results demonstrate the protective effect of GABA against damage caused by high salt intake in cisplatin-induced renal toxicity. Its mechanism may be due to the suppression of hematological and biochemical toxicity, apoptosis, and inflammation. In conclusion, although the protective efficacy of GABA salt on renal injury is different depending on the sterilization and filtration process after fermentation with L. brevis BJ20 and L. plantarum BJ21, our findings suggest that GABA-enriched salt has a beneficial effect against immoderate high salt intake-mediated kidney injury in patients with cisplatin-induced nephrotoxicity.

Understanding the Two Faces of Low-Salt Intake

Fierce debate has developed whether low-sodium intake, like high-sodium intake, could be associated with adverse outcome. The debate originates in earlier epidemiological studies associating high-sodium intake with high blood pressure and more recent studies demonstrating a higher cardiovascular event rate with both low- and high-sodium intake. This brings into question whether we entirely understand the consequences of high- and (very) low-sodium intake for the systemic hemodynamics, the kidney function, the vascular wall, the immune system, and the brain. Evolutionarily, sodium retention mechanisms in the context of low dietary sodium provided a survival advantage and are highly conserved, exemplified by the renin-angiotensin system. What is the potential for this sodium-retaining mechanism to cause harm? In this paper, we will consider current views on how a sodium load is handled, visiting aspects including the effect of sodium on the vessel wall, the sympathetic nervous system, the brain renin-angiotensin system, the skin as "third compartment" coupling to vascular endothelial growth factor C, and the kidneys. From these perspectives, several mechanisms can be envisioned whereby a low-sodium diet could potentially cause harm, including the renin-angiotensin system and the sympathetic nervous system. Altogether, the uncertainties preclude a unifying model or practical clinical guidance regarding the effects of a low-sodium diet for an individual. There is a very strong need for fundamental and translational studies to enhance the understanding of the potential adverse consequences of low-salt intake as an initial step to facilitate better clinical guidance.

A Salt-Induced Reno-Cerebral Reflex Activates Renin-Angiotensin Systems and Promotes CKD Progression

Salt intake promotes progression of CKD by uncertain mechanisms. We hypothesized that a salt-induced reno-cerebral reflex activates a renin-angiotensin axis to promote CKD. Sham-operated and 5/6-nephrectomized rats received a normal-salt (0.4%), low-salt (0.02%), or high-salt (4%) diet for 2 weeks. High salt in 5/6-nephrectomized rats increased renal NADPH oxidase, inflammation, BP, and albuminuria. Furthermore, high salt activated the intrarenal and cerebral, but not the systemic, renin-angiotensin axes and increased the activity of renal sympathetic nerves and neurons in the forebrain of these rats. Renal fibrosis was increased 2.2-fold by high versus low salt, but intracerebroventricular tempol, losartan, or clonidine reduced this fibrosis by 65%, 69%, or 59%, respectively, and renal denervation or deafferentation reduced this fibrosis by 43% or 38%, respectively (all P<0.05). Salt-induced fibrosis persisted after normalization of BP with hydralazine. These data suggest that the renal and cerebral renin-angiotensin axes are interlinked by a reno-cerebral reflex that is activated by salt and promotes oxidative stress, fibrosis, and progression of CKD independent of BP.

Enhanced intrarenal receptor-mediated prorenin activation in chronic progressive anti-thymocyte serum nephritis rats on high salt intake

Despite suppression of the circulating renin-angiotensin system (RAS), high salt intake (HSI) aggravates kidney injury in chronic kidney disease. To elucidate the effect of HSI on intrarenal RAS, we investigated the levels of intrarenal prorenin, renin, (pro)renin receptor (PRR), receptor-mediated prorenin activation, and ANG II in chronic anti-thymocyte serum (ATS) nephritic rats on HSI. Kidney fibrosis grew more severe in the nephritic rats on HSI than normal salt intake. Despite suppression of plasma renin and ANG II, marked increases in tubular prorenin and renin proteins without concomitant rises in renin mRNA, non-proteolytically activated prorenin, and ANG II were noted in the nephritic rats on HSI. Redistribution of PRR from the cytoplasm to the apical membrane, along with elevated non-proteolytically activated prorenin and ANG II, was observed in the collecting ducts and connecting tubules in the nephritic rats on HSI. Olmesartan decreased cortical prorenin, non-proteolytically activated prorenin and ANG II, and apical membranous PRR in the collecting ducts and connecting tubules, and attenuated the renal lesions. Cell surface trafficking of PRR was enhanced by ANG II and was suppressed by olmesartan in Madin-Darby canine kidney cells. These data suggest the involvement of the ANG II-dependent increase in apical membrane PRR in the augmentation of intrarenal binding of prorenin and renin, followed by nonproteolytic activation of prorenin, enhancement of renin catalytic activity, ANG II generation, and progression of kidney fibrosis in the nephritic rat kidneys on HSI. The origin of the increased tubular prorenin and renin remains to be clarified. Further studies measuring the urinary prorenin and renin are needed.

Comparison of ROCK and EGFR activation pathways in the progression of glomerular injuries in AngII-infused rats

AIM

The roles of rho-kinase (ROCK) and epidermal growth factor receptor (EGFR) were studied using an angiotensin II (AngII)-dependent hypertension rat model.

METHOD

Male Wistar rats were infused with AngII at a rate of 400 ng/kg body weight (BW)/min for 14 days. Effects of ROCK inhibitor, fasudil (20 mg/kg BW), and EGFR inhibitor, gefitinib (3 mg/kg BW), were studied.

RESULTS

AngII infusion increased blood pressure (BP; 220 ± 19 mmHg) as well as the number of proliferating cells in glomeruli judged by Ki67 and proliferating cell nuclear antigen immunostaining and urinary protein excretion (118 ± 19 mg/day). AngII also decreased p27 expression and increased cyclin D1 expression in glomeruli, as well as induced dissociation of the nephrin- and podocin-immunostaining patterns in podocytes. Treatment with fasudil or gefitinib completely inhibited glomerular cell proliferation without changing the BP. Although the decreased p27 expression was reversed by both treatments, cyclin D1 induction was abolished only by gefitinib. Fasudil significantly reduced proteinuria (57.2 ± 17.5 mg/day), but not gefitinib (133.3 ± 30.9 mg/day). The dissociation of podocin and nephrin was ameliorated by fasudil, but not by gefitinib.

CONCLUSION

ROCK and EGFR have distinct roles in proteinuria and glomerular cell proliferation in this model.

Barriers to blood pressure control as reported by African American patients

PURPOSE

To understand African American patients' opinions as to barriers to hypertension treatment.

METHODS

Focus groups (n=3) were led by a trained African American moderator of African American patients with hypertension (n=26) who receive their care from a large primary care network. Discussions were transcribed verbatim. Information was displayed in a data matrix and analyzed for emerging themes. Descriptive statistics were used to enhance the content validity of lifestyle modification efforts planned as part of this ongoing research.

RESULTS

Most participants were female (n=20), and the mean age was 49 years. All participants were at least high school graduates. Four major levels of influence emerged from data analysis: (1) the health care system, (2) the community, (3) the family, and (4) the individual. The most prevalent concerns about hypertension centered on sodium, diet, neighborhoods, mistrust, and denial. Of great concern was lack of provider trust and a fatalistic, hopeless mindset. To improve trust, our participants suggested developing a hypertension education program and providing patients with culturally specific materials.

CONCLUSIONS

Culturally sensitive materials need to be designed and tested to improve blood pressure control. Community input regarding cultural issues is essential for designing effective and successful programs for reducing health disparities.

High salt loading alters the expression and localization of glial aquaporins in rat retina

In the neural retina, glial cells control the ionic concentrations in part by mediation of transmembrane water fluxes through aquaporin (AQP) water channels. The expression and immunolocalization of two water channels, AQP1 and AQP4, in the rat retina during experimental high salt loading were investigated in this study. Six-week-old Wistar rats were allowed free access to rat chow with 8% NaCl concentration. Of these rats, 6 were killed after 2, 6, 10 and 20 weeks. Twelve-week-old and 26-week-old Wistar rats with a normal diet (0.5% NaCl concentration) were used as controls. Retinal tissues were collected. Ultrathin sections stained with uranyl acetate and lead citrate were photographed using a transmission electron microscope (TEM). Retinal whole mounts and cryosections were immunostained with AQP1 and AQP4 antibodies to detect the immunolocalization changes by confocal microscopy. The AQP1 and AQP4 contents were evaluated by western blot analysis. In control tissues, no intracellular edema and mitochondria swelling were observed by TEM. The immunoreactive AQP4 was expressed by glial cells (Müller cells and astrocytes) predominantly in the inner retina, and AQP1 was expressed in the outer retina. In the retinas of high salt loading animals, obvious intracellular edema was observed by TEM in retinal ganglion cell (RGC) and mitochondria swelling was observed in glial cells. Strong expression of AQP1 was found in glial cells located in the innermost retinal layers, mainly in astrocytes. The superficial retinal vessels were surrounded by AQP4 in control retinas, but by both AQP4 and AQP1 in retina of high salt loading animals. A similar alteration in the localization of AQP1 has been described in the rat retina after transient ischemia and diabetes. Western blot results supported the conclusion that the AQP1 expression increased during high salt diet. Our findings indicate that high salt loading may induce neural retina edema, and that altered glial cell-mediated water transport via AQP channels in the retina may be one of the reasons for intracellular edema in the neural retina.

Salt restriction in kidney disease--a missed therapeutic opportunity?

The importance of salt restriction in the treatment of patients with renal disease has remained highly controversial. In the following we marshal the current evidence that salt plays a definite role in the genesis of hypertension and target organ damage, point to practical problems of salt restriction, and report on novel pathomechanisms of how salt affects blood pressure and causes target organ damage.

Salt: its role in chronic kidney disease

Few controversies in medicine have such a long history as that of whether salt is identifiably dangerous or not dangerous. The most common reported association between excess dietary salt intake and clinical outcome has been in the field of hypertension, but dietary sodium intake mediates effects that go far beyond, and are independent of, extracellular fluid expansion and elevation in blood pressure. For nephrologists, clinical trials that demonstrate no negative outcome of a high salt diet in the general population are thus not particularly assuasive, because patients with chronic kidney disease (CKD) represent an entity that is by no means comparable to the general population. This review takes a look at the challenges associated with salt balance in CKD patients (particularly at K/DOQI stage 5), followed by a summary of current concepts believed to play a part in salt-mediated pathophysiology, and the conclusion, based on the present state of scientific knowledge, that it appears advisable to advocate low dietary salt intake in this patient population.

Salt--a potential 'uremic toxin'?

It has been known for decades that salt (NaCl) determines extracellular volume as well as blood pressure and is one cause of hypertension. The difficulty to control the NaCl balance and thus treat sodium overload and hypertension in patients on dialysis has been recognized by Scribner in the early days of dialysis. In recent years, an impressive body of evidence has accumulated indicating that in essential hypertension, NaCl--blood pressure independently--causes target organ damage such as left ventricular hypertrophy, microalbuminuria, and increased aortic stiffness. It has further been recognized that NaCl increases oxidative stress and, again blood pressure independently, amplifies tissue injury induced by aldosterone. In renal damage models, progression is dramatically accelerated by high NaCl intake. Sodium as a potential culprit in progression to target organ damage in terminal renal failure has not been well investigated so far. However, it is possible, and indeed likely, that sodium plays an adverse role in the genesis of target organ damage in terminal renal failure.

Lifestyle modification and progressive renal failure

There is increasing evidence that lifestyle factors impact on the risk of developing chronic kidney disease (CKD) and the risk of progression of CKD. Equally important is the consideration that patients with CKD are more likely to die from cardiovascular disease than to reach the stage of end-stage renal failure. It is advantageous that manoeuvres that interfere with progression at the same time also reduce the risk of cardiovascular events. Lifestyle factors that aggravate progression include, among others, smoking, obesity and dietary salt intake. Alcohol consumption, according to some preliminary information, has a bimodal relationship to cardiovascular risk and progression, with moderate consumption being protective.

Tissue-specific expression of renin-angiotensin system components in IgA nephropathy

BACKGROUND

The renin-angiotensin II system (RAS) has been implicated in the development of glomerulonephritis. The aims of this study were to determine (1) the expression of RAS components, angiotensin (Ang II)-forming enzymes [angiotensin-I-converting enzyme (ACE) and chymase], and Ang II receptors, and (2) the correlation between RAS expression and severity of tissue injury in IgA nephropathy (IgAN).

METHODS

The expression levels of ACE, chymase, and Ang II type 1 and type 2 receptor (AT1R and AT2R) mRNAs were determined by in situ hybridization in renal specimens from 18 patients with IgAN, 5 patients with non-IgA mesangial proliferative glomerulonephritis (non-IgAN) and 10 patients with nonmesangial proliferative glomerulonephritis (minimal change nephrotic syndrome, n = 5, and membranous nephropathy, n = 5). Normal portions of surgically resected kidney served as control.

RESULTS

In normal kidney, a few mesangial cells and glomerular and tubular epithelial cells weakly expressed ACE, chymase and AT1R mRNAs. In IgAN and non-IgAN samples, ACE, chymase, AT1R and AT2R mRNAs were expressed in resident glomerular cells, including mesangial cells, glomerular epithelial cells and cells of Bowman's capsule. The glomerular expressions in IgAN were stronger than in minimal change nephrotic syndrome and membranous nephropathy. In IgAN, the expressions in glomeruli correlated with the degree of mesangial hypercellularity, whereas the expression levels were weaker at the area of mesangial expansion. IgAN with severe tubulointerstitial injury showed expression of ACE, chymase, AT1R and AT2R mRNAs in atrophic tubules and infiltrating cells and such expression correlated with the degree of tubulointerstitial damage.

CONCLUSION

Our results suggest that renal cells can produce RAS components and that locally synthesized Ang II may be involved in tissue injury in IgAN through Ang II receptors in the kidney.