Mycophenolate mofetil prevents salt-sensitive hypertension resulting from nitric oxide synthesis inhibition

Angiotensin II, interstitial inflammation, and the pathogenesis of salt-sensitive hypertension

Transient administration of ANG II causes persistent salt-sensitive hypertension associated with arteriolopathy, interstitial inflammation, and cortical vasoconstriction; blocking the vascular and inflammatory changes with mycophenolate mofetil (MMF) prevents vasoconstriction. While infiltrating leukocytes during the salt-sensitive hypertension phase express ANG II, the functional role of ANG II during this phase is not known. We examined the acute effect of candesartan on renal hemodynamics during the established salt-sensitive hypertensive phase and related these findings to direct measurement of intrarenal ANG II and inflammatory cells in rats previously exposed to ANG II with or without MMF treatment. Sham controls were also examined. The administration of ANG II, followed by exposure to high-salt diet, resulted in hypertension, cortical vasoconstriction, an increase in interstitial inflammatory cells (44.8 +/- 1.3 lymphocytes/mm2, and 30.8 +/- 1.2 macrophages/mm2 ANG II vs. 19.6 +/- 2 lymphocytes/mm2, and 22 +/- 0.7 macrophages/mm2 Sham), and increase in renal ANG II levels (1,358 +/- 74.6 pg/ml ANG II vs. 194 +/- 9.28 pg/ml Sham). Treatment with MMF during the administration of exogenous ANG II resulted in reduction in renal interstitial inflammation (19.7 +/- 0.9 lymphocytes/mm2 and 15.9 +/- 0.8 machophages/mm2), ANG II levels (436.9 +/- 52.29 pg/ml), cortical vasoconstriction, and stable blood pressure levels during the subsequent challenge with a high-salt diet. Acute administration of candesartan similarly reduced renal vasoconstriction and blood pressure. We conclude that the cortical vasoconstriction occurring with salt-sensitive hypertension following exposure to ANG II is mediated by intrarenal ANG II, related, at least in part, to the interstitial inflammation.

Immune Suppression Attenuates Hypertension and Renal Disease in the Dahl Salt-Sensitive Rat

Experiments were performed to determine the importance of activation or infiltration of immune cells in the kidney during the development of hypertension and renal disease in Dahl salt-sensitive rats (SS/Mcw) fed a 4.0% NaCl diet. Compared with vehicle-treated rats, chronic administration of mycophenolate mofetil ([MMF] 30 mg/kg per day, IP), an immunosuppressive agent that has cytostatic effects on T and B cells, decreased cell-specific markers of T and B cells by 50% to 60% in the kidneys of SS/Mcw rats (n=5 per group). Further studies were performed on Dahl SS/Mcw rats, which were instrumented with chronic indwelling catheters and studied after 3 weeks on the 4.0% NaCl diet. Rats were administered MMF or 5% dextrose vehicle daily during the 3-week period of high NaCl intake. Mean arterial blood pressure in the rats administered MMF (122±2 mm Hg; n=11) was significantly decreased compared with vehicle-treated rats (139±4 mm Hg; n=9). Furthermore, the rate of protein (112±13 mg per day) and albumin excretion (15±3 mg per day) in the MMF-treated rats was significantly lower than the protein and albumin excretion rate in vehicle-treated rats (167±25 and 31±7 mg per day, respectively). Creatinine clearance and body weight were not different between the groups, averaging 0.52±0.08 mL/min per gram kidney weight and 322±10 g, respectively, in the MMF-treated group. These experiments indicate that the activation of the immune system or renal infiltration of immune cells plays an important role in the development of hypertension and renal disease in Dahl SS/Mcw rats consuming an elevated NaCl diet.

Inflammation as a Mediator of the Link between Mild to Moderate Renal Insufficiency and Endothelial Dysfunction in Essential Hypertension

The relationship among inflammation (plasma high-sensitivity C-reactive protein [CRP]), endothelial function (hemodynamic response to acetylcholine [ACh] in the forearm), and renal function (serum creatinine and GFR [Modification of Diet in Renal Disease formula]) was investigated in 264 never-treated individuals with uncomplicated essential hypertension and serum creatinine within the normal range. Multiple regression models of renal function (creatinine) were constructed in sequence including Framingham risk factors as well the hemodynamic response to ACh and plasma CRP. The inclusion of endothelial function into a model based on Framingham risk factors added highly significant (P < 0.001) power to this model (+5%). Of note, in an alternative model that included CRP (instead of endothelial function), the creatinine variance explained by this factor was two times higher (+10%) than that associated with endothelial function in the first model. In the full model that included both endothelial function and CRP, CRP maintained a much stronger independent link with the outcome measure than endothelial function. In individuals with untreated, uncomplicated essential hypertension, multivariate modeling indicated that inflammation is a crucial mechanism mediating the endothelial-renal function link. The proatherogenic potential of inflammation associated with subtle impairment in renal function may contribute to the cardiovascular risk of essential hypertension.

Early treatment with cGMP phosphodiesterase inhibitor ameliorates progression of renal damage

BACKGROUND

Chronic renal disease is associated with oxidative stress and reduced nitric oxide availability which, in turn, promotes hypertension and further progression of renal damage. Most actions of nitric oxide are mediated by cyclic 3',5' guanosine monophosphate (cGMP) which is rapidly degraded by phosphodiesterases (PDE). Therefore, we investigated if inhibition of PDE-5 would retard the progression of chronic renal failure.

METHODS

We studied rats with 5/6 nephrectomy treated with sildenafil (2.5 mg/kg(-1)/day(-1)) in two experimental protocols. In the first protocol, we started sildenafil therapy immediately after renal ablation and continued treatment for 8 weeks. Control groups consisted of rats with renal ablation treated with drug-free vehicle and sham-operated rats with and without sildenafil treatment.

RESULTS

In these studies, sildenafil treatment prevented hypertension and deterioration of renal function, reduced histologic damage, inflammation and apoptosis, delayed the onset of proteinuria, and preserved renal capillary integrity. In the second protocol we compared sildenafil with losartan (7.5 mg/kg(-1)/day(-1)) and the combination of both drugs in established renal disease, starting these drugs 4 weeks after 5/6 nephrectomy. Delayed sildenafil treatment failed to improve proteinuria and glomerulosclerosis but ameliorated hypertension and azotemia.

CONCLUSION

These observations suggest that currently available PDE-5 inhibitors have potential clinical value in the treatment of chronic renal disease.

Mycophenolate mofetil ameliorates nephropathy in the obese Zucker rat

BACKGROUND

The obese Zucker rat has metabolic condition resembling type II diabetes, including hyperlipidemia, obesity, insulin resistance, and hyperglycemia. With advancing age, the obese Zucker rat develops glomerulosclerosis, proteinuria, and renal failure. Since immune cells play a central role in the development of chronic renal injury, we evaluated the potential benefit of mycophenolate mofetil (MMF), alone and in combination with angiotensin receptor type 1 blockade (ARB) in the obese Zucker rat.

METHODS

Thirteen-week-old male obese Zucker rats (fa/fa) were randomly assigned to four experimental groups (five rats each) that received the following treatments for 3 months: (1) losartan (100 mg/L in the drinking water), (2) MMF (20 mg/kg/day), (3) MMF and losartan, and (4) placebo. Lean Zucker rats (N = 5) were included as normal controls. Renal function, biochemical parameters, renal histology, and immunohistology were evaluated.

RESULTS

The placebo-treated obese Zucker rats exhibited proteinuria and significant glomerular and tubulointerstitial injury in association with renal immune cell infiltration. Proteinuria, histologic damage, and renal immune cell infiltration were all reduced by MMF treatment alone or in combination with ARB. The improvement of proteinuria and structural damage was more pronounced in the group that received the combination of MMF and losartan.

CONCLUSION

MMF treatment alone, and especially in combination with ARB, improves nephropathy in the obese Zucker rat.

Macrophages and progressive tubulointerstitial disease

Macrophages and progressive tubulointerstitial disease. In chronic renal disease, tubulointerstitial inflammation and injury is associated with infiltrating macrophages. As a consequence of primary injury, proteinuria, chronic hypoxia, and glomerular-derived cytokines may all differentially modulate the expression of factors that promote macrophage recruitment. In addition to adhesion molecules and chemokines, products of complement system and renin-angiotensin system activation may direct this process. Once present at interstitial sites, macrophages interact with resident cells and extracellular matrix to generate a proinflammatory microenvironment that amplifies tissues injury and promotes scarring. There is now increasing evidence for the efficacy of interventions directed against factors that recruit, activate, or are produced by macrophages. A detailed understanding of the biology of this area may lead to the further development of therapies that will improve the outcome of renal disease.

Short-term nitric oxide inhibition induces progressive nephropathy after regression of initial renal injury

Chronic nitric oxide (NO) inhibition and salt overload (HS) promote severe hypertension and renal injury, which regress quickly, although not completely, on treatment withdrawal. We investigated whether renal function and structure remain stable 6 mo after cessation of these treatments. Adult male Munich-Wistar rats were distributed among three groups: HS, receiving 3.1% Na diet; HS+N, receiving HS and the NO inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME; 30 mg.kg(-1).day(-1) orally); and HS+N+L, receiving HS+N and the ANG II blocker losartan (L; 50 mg.kg(-1).day(-1) orally). In studies performed after 20 days of treatment (protocol 1), HS+N rats exhibited severe glomerular and systemic hypertension, massive albuminuria, glomerular and interstitial injury, and infiltration by macrophages and cells expressing ANG II. These abnormalities were largely prevented in the HS+N+L group. A second cohort (protocol 2) received HS+N for 20 days, followed by a conventional (0.5% Na) diet and no l-NAME treatment during the subsequent 30 days. At this time, systemic and glomerular pressure, along with parameters of renal injury and inflammation, were still higher than in HS or HS+N+L rats, although differences were much smaller than in protocol 1. Six months after 20-day l-NAME/salt overload treatment was ceased (protocol 3), severe albuminuria, hypertension, and renal injury developed in HS+N rats. Again, losartan prevented most of these changes. We conclude 1) short-term HS+N treatment triggers the autonomous development of progressive glomerulosclerosis; 2) this process may involve activation of the AT(1) receptor; and 3) temporary HS+N treatment may represent a new model of slowly progressive chronic nephropathy.

Hypertension in Page (cellophane-wrapped) kidney is due to interstitial nephritis

BACKGROUND

Cellophane wrapping of the kidneys (Page kidney) induces perinephrits and hypertension, assumed to be due to renal ischemia resulting from parenchymal compression by the fibrous hull surrounding the kidneys. We investigated if interstitial nephritis, rather than plasma angiotensin activity, played a role in the development of hypertension in the Page kidney model.

METHODS

We followed for 7 weeks rats with bilateral cellophane wrapping of the kidneys that received 20 mg/kg/day of the immunosuppressive antiproliferative drug mycophenolate mofetil (MMF) (two-kidney wrap/MMF) (N = 10) or vehicle (two-kidney wrap) (N = 10), and sham-operated rats (N = 10).

RESULTS

The two-kidney wrap group had progressive increment in blood pressure, inflammatory damage occupying 25% to 50% of the renal tubulointerstitial region and increased number of angiotensin II-positive cells, angiotensin II content, and oxidative stress in the kidney. MMF treatment prevented the development of hypertension and renal inflammation without modifying the perinephritic hull or the increment it induced in the intrarenal pressure. The plasma levels of angiotensin II were similar in the two-kidney wrap group, the two-kidney wrap/MMF group and the sham-operated animals and unchanged from baseline, despite the blood pressure increase in the two-kidney wrap group.

CONCLUSION

Our results indicate that renal wrap hypertension is unrelated to plasma angiotensin II levels and related to the inflammatory damage caused by the external compression of the kidney.

Chronic exposure to low doses of lead results in renal infiltration of immune cells, NF-kappaB activation, and overexpression of tubulointerstitial angiotensin II

Chronic exposure to low doses of lead results in generation of reactive oxygen species, reduced nitric oxide availability, and arterial hypertension. The present studies were done to define if other conditions associated with oxidative stress, such as renal interstitial inflammation, nuclear factor-kappaB (NF-kappaB) activation, and cells expressing angiotensin II, are, in fact, features of low-dose lead exposure. Male Sprague-Dawley rats were randomly assigned to the lead group (n = 8) or the control group (n = 9). The lead group received 100 ppm lead acetate in the drinking water for 14 weeks. At the end of this period of time, rats were killed under general anesthesia, and the kidneys were harvested for studies. The lead-exposed group presented focal tubulointerstitial damage and highly significant increments in nitrotyrosine immune staining, lymphocyte and macrophage infiltration, angiotensin II-positive cells, and intranuclear positive staining for the p65 DNA-binding subunit of NF-kappaB in tubulointerstitial cells. Tubulointerstitial inflammation, cells expressing angiotensin II, and NF-kappaB activation are consequences of a 3-month low-dose exposure to lead and likely play a role in the development of hypertension and chronic lead nephropathy.

An extremely high dose of losartan affords superior renoprotection in the remnant model

BACKGROUND

Rats subjected to 5/6 renal ablation (NX) exhibit large renal amounts of angiotensin II (Ang II) and of its main receptor, AT-1R. At previously used doses, AT-1R blockers (ARB) offer only partial renal protection. A possible explanation for this limited effect is that these doses are insufficient to block most of the abnormally expressed AT-1R. We investigated whether extremely high doses of the ARB, losartan (L), offer better protection than conventional doses in the NX model.

METHODS

Thirty days after NX, tail-cuff pressure (TCP), albuminuria (U(alb)V, mg/day), glomerulosclerosis index (GSI), fractional interstitial area (%INT), and macrophage infiltration (MO) were evaluated in a separate group (NX(pre)). The remaining rats were then subdivided among 4 groups: NX+V, receiving vehicle; NX+L50, treated with L, at the "conventional" dose of 50 mg/kg/day; NX+L500, receiving L, 500 mg/kg/day; and NX+HH, receiving hydrochlorothiazide and hydralazine to lower blood pressure to a similar extent as in group L500.

RESULTS

After a month of treatment, blood pressure and renal vascular resistance were lowest in group L500. Glomerular pressure was lowered by a similar extent by L50 and L500, while GFR was similar among groups. U(alb)V, TCP, and renal injury were only partially reduced by L50 120 days after renal ablation. By contrast, L500 arrested renal inflammation and glomerular/interstitial injury at pretreatment levels, and promoted regression of hypertension and U(alb)V, causing no apparent untoward effects.

CONCLUSION

The renal protection afforded by ARB in NX is dose dependent. Maximal protection may require doses several fold higher than those currently employed.

Mild hyperuricemia induces vasoconstriction and maintains glomerular hypertension in normal and remnant kidney rats

BACKGROUND

Hyperuricemia has been associated with renal disease. Because glomerular hemodynamic alterations critically contribute to initiation and progression of renal disease, we evaluated the effect of mild hyperuricemia in glomerular microcirculatory changes in rats under normal conditions and with renal injury induced by subtotal renal ablation (RK).

METHODS

Hyperuricemia was induced in normal and remnant kidney (RK) rats on a normal sodium diet by administration of oxonic acid (OA). To prevent hyperuricemia, allopurinol (AP) was administered concomitantly. Glomerular hemodynamics were evaluated by micropuncture techniques. Systolic blood pressure (SBP), proteinuria, arterial morphology, and serum uric acid were measured. In RK rats, glomerulosclerosis, fibrosis, and inflammatory cell infiltration (CD5+) were also assessed.

RESULTS

In normal rats, hyperuricemia resulted in afferent arteriole thickening associated with renal cortical vasoconstriction [single nephron glomerular filtration rate (SNGFR) -35%, P < 0.05) and glomerular hypertension (P < 0.05). Allopurinol treatment prevented structural and functional alterations. In RK rats, hyperuricemia produced more renal vascular damage than control animals coupled with severe cortical vasoconstriction (SNGFR -40%, P < 0.05) and persistent glomerular hypertension. Allopurinol partially prevented cortical vasoconstriction, and fully prevented arteriolopathy and glomerular hypertension associated with significantly less infiltration of CD5+ cells.

CONCLUSION

Hyperuricemia induces arteriolopathy of preglomerular vessels, which impairs the autoregulatory response of afferent arterioles, resulting in glomerular hypertension. Lumen obliteration induced by vascular wall thickening produces severe renal hypoperfusion. The resulting ischemia is a potent stimulus that induces tubulointerstitial inflammation and fibrosis, as well as arterial hypertension. These studies provide a potential mechanism by which hyperuricemia can mediate hypertension and renal disease.

Hypothesis: Uric acid, nephron number, and the pathogenesis of essential hypertension

BACKGROUND

Essential hypertension affects more than 25% of the world's population. Genetic, physiologic, and epidemiologic studies provide clues to its origins, but a clear understanding has been elusive. Recent experimental and clinical studies have implicated uric acid in the onset of essential hypertension.

METHODS

In a retrospective chart review, we identified 95 children with confirmed, new onset hypertension, and evaluated the cause of hypertension and parental history of hypertension, birth weight, and serum uric acid. In an open-label, cross-over trial we treated 5 children with confirmed essential hypertension with allopurinol as single treatment agent, and screened for change in blood pressure by casual and ambulatory methods. In tissue culture experiments, we evaluated the effect of uric acid on glomerular endothelial cell function.

RESULTS

Elevation of serum uric acid is related to the onset of essential hypertension in children, reduced birth weight, and endothelial dysfunction. Normalization of uric acid appears to ameliorate new onset essential hypertension.

CONCLUSION

These findings, combined with animal model data, support the hypothesis that uric acid has a key role in the pathogenesis of early onset essential hypertension, and may unify some of the disparate theories of the origins of essential hypertension.

Oxidative stress in hypertension and chronic kidney disease: role of angiotensin II

Angiotensin II, via the type 1 (AT1) receptor, stimulates oxidative stress. The vasculature, interstitium, juxtaglomerular apparatus, and the distal nephron in the kidney express nicotinamide adenine dinucleotide phosphate (NADPH) oxidase that generates superoxide anion, which is an important component of angiotensin II-induced oxidative stress. The angiotensinogen gene is stimulated by NF-kappaB activation, which is sensitive to the redox ratio, providing a positive feedback loop that can upregulate angiotensin II production. Oxidative stress can accompany hypertension in many models, including the spontaneously hypertensive rat (SHR), angiotensin II-infused rats, renovascular hypertension, and the deoxycorticosterone acetate (DOCA) salt model of hypertension. AT1 receptor antagonists can abrogate the effects of angiotensin II on oxidative stress, thus providing an important mechanistic insight onto the renal protective effects of these agents in conditions associated with angiotensin II excess.

AT-1 receptor blockade prevents proteinuria, renal failure, hyperlipidemia, and glomerulosclerosis in the Imai rat

BACKGROUND

The Imai rat is a model of spontaneous focal glomerulosclerosis which leads to nephrotic syndrome, hyperlipidemia, hypertension, and progressive renal failure. We evaluated the effects of angiotensin II receptor type 1 (AT-1)blockade, and compared the results with the effects of the administration of hypolipidemic treatment with a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor. All treatments were started at 10 weeks of age when the rats were already proteinuric and continued for 6 months when rats were sacrificed.

METHODS

The following groups (N= 6 each) were studied: (1) control Sprague-Dawley rats, 34 weeks old; (2) Imai group that received vehicle; (3) Imai + angiotensin II receptor blockade (ARB) group that received olmesartan (10 mg/kg/day by gastric gavage); (4) Imai + prava group, that received pravastatin (20 mg/kg/day by gastric gavage); and (5) Imai + ARB + prava group that received both ARB and pravastatin. Lipid profile, renal function, and structure were assessed at 6 months.

RESULTS

As expected, the untreated Imai rats exhibited heavy proteinuria, hypoalbuminemia, hypertension, renal insufficiency, marked glomerulosclerosis, tubulointerstitial inflammation, and profound hyperlipidemia. Pravastatin treatment alone led to a significant, but partial improvement of hyperlipidemia and renal disease. The ARB treatment alone or in combination with pravastatin resulted in normalization of the blood pressure, urinary protein excretion, plasma cholesterol, triglycerides, low-density lipoproteins (LDLs), very low-density lipoproteins (VLDLs), and albumin concentrations and renal function. Significant glomerulosclerosis was prevented and tubulointerstitial injury and immune cell infiltration were reduced by long-term AT-1 blockade.

CONCLUSION

The study revealed that long-term AT-1 blockade corrects proteinuria, hyperlipidemia, and nephropathy in this model of spontaneous glomerulosclerosis.

Endothelial Dysfunction and Mild Renal Insufficiency in Essential Hypertension

Background— Mild to moderate renal insufficiency in individuals with essential hypertension is currently considered the expression of a renal microvasculopathy characterized by preglomerular arteriolar involvement and tubulo-interstitial changes. Whether endothelial dysfunction plays a role in this alteration is still undefined.

Methods and Results— We investigated the relationship between endothelial function (hemodynamic response to acetylcholine [ACh] in the forearm) and renal function in 500 patients with uncomplicated, never-treated, essential hypertension and serum creatinine within the normal range (ie, ≤1.5 mg/dL). Serum creatinine, creatinine clearance, and estimated glomerular filtration rate (GFR, by the Modification of Diet in Renal Disease formula) were related to the forearm blood flow response to ACh (all P ≤0.003), and these relationships held true in multiple regression analyses that included age, gender, systolic pressure, serum cholesterol and glucose, smoking, and body mass index. Accordingly, on multiple logistic regression analysis, the risk of moderate renal dysfunction (ie, an estimated GFR <60 mL · min −1 · 1.73 m −2 ) was 64% lower (OR 0.36, 95% CI 0.18 to 0.70) in patients in the third ACh tertile (ie, those showing the higher vasodilatory response) than in those in the first tertile (ie, showing the lower response). C-reactive protein was related directly to serum creatinine and inversely to GFR and vasodilatory response to ACh, which suggests that endothelial dysfunction is a possible mechanism linking inflammation and impaired renal function in essential hypertension.

Conclusions— An impaired vasodilatory response to ACh appears to be associated with renal function loss in patients with essential hypertension. This association suggests that systemic endothelial dysfunction is involved in mild to moderate renal insufficiency in patients with uncomplicated essential hypertension.

Oxidative stress, renal infiltration of immune cells, and salt-sensitive hypertension: all for one and one for all

Recent evidence indicates that interstitial infiltration of T cells and macrophages plays a role in the pathogenesis of salt-sensitive hypertension. The present review examines this evidence and summarizes the investigations linking the renal accumulation of immune cells and oxidative stress in the development of hypertension. The mechanisms involved in the hypertensive effects of oxidant stress and tubulointerstitial inflammation, in particular intrarenal ANG II activity, are discussed, focusing on their potential for sodium retention. The possibility of autoimmune reactivity in hypertension is raised in the light of the proinflammatory and immunogenic pathways stimulated by the interrelationship between oxidant stress and inflammatory response. Finally, we present some clinical considerations derived from the recognition of this interrelationship.

Up-regulation of kidney NAD(P)H oxidase and calcineurin in SHR: Reversal by lifelong antioxidant supplementation

BACKGROUND

Spontaneously hypertensive rats (SHR) are born normotensive and develop hypertension (HTN) later in life (age 4 to 5 weeks). HTN in SHR is associated with and caused in part, by oxidative stress and renal interstitial inflammation. This study tested the hypothesis that lifelong antioxidant supplementation beginning at prenatal period may delay the onset and reduce the severity of HTN in SHR. The study further sought to explore the effect of diet modification on renal tissue NAD(P)H oxidase and calcineurin abundance.

METHODS

Pregnant SHR and their offspring were fed either an antioxidant-fortified diet (a chow containing alpha-tocopherol 5000 IU/kg, ascorbic acid 500 ppm, selenium 2.76 ppm, and zinc 350 ppm) or regular diet (alpha-tocopherol 40 IU/kg, selenium 0.2 ppm, and zinc 70 ppm). Animals were observed for 24 weeks. Wistar-Kyoto rats fed either a regular or antioxidant diet served as control.

RESULTS

Onset of HTN was delayed and severity of HTN was reduced in antioxidant-treated compared with untreated SHR. Markers of oxidative stress (i.e., plasma hydrogen peroxide, renal tissue malondialdehyde, and nitrotyrosine abundance) were elevated in untreated but not in antioxidant-treated SHR. gp91phox and p22phox subunits of NAD(P)H oxidase were markedly elevated in the renal cortex of untreated SHR and partially restored in the treated SHR. Similarly, renal calcineurin Aalpha and B subunits were elevated in untreated SHR and were partially restored in the treated SHR. Antioxidant therapy had no effect on the measured parameters in the WKY control.

CONCLUSION

Lifelong consumption of antioxidant-rich diet ameliorates HTN and oxidative stress in SHR. This is associated with the reduction of superoxide-generating enzyme, NAD(P)H oxidase, and immunoregulatory factor calcineurin. Antioxidant-rich diet appears to attenuate oxidative stress, not only by fortifying antioxidant defense capacity but also by lowering NAD(P)H oxidase, which is a major source of reactive oxygen species.

Renal kallikrein-kinin system damage and salt sensitivity: insights from experimental models

The importance of tubulointerstitial injury in the pathophysiology of human essential hypertension, and particularly salt sensitivity, is increasingly recognized. Since the renal kallikrein-kinin system (KKS) is located in the tubulointerstitial region of the kidney it is reasonable to expect that injury to this area, whatever the cause, may impair KKS production and compromise its role in blood pressure regulation. In this review we discuss evidence of injury in the renal kallikrein-producing structures in three different experimental models characterized by prominent tubulointerstitial lesions: subtotal nephrectomy; inhibition of nitric oxide synthase; and overload proteinuria. These three experimental models have in common the development of important tubulointerstitial damage and salt-sensitive hypertension expressed after the initial injury has ceased. In these three models, reduced KKS activity may contribute to the establishment of a pathophysiologic state characterized by unopposed hyperactivity of the renin-angiotensin system, resulting in salt retention.

Apoptosis and NFkappaB activation are simultaneously induced in renal tubulointerstitium in experimental hypertension

BACKGROUND

Oxidative stress is known to induce apoptosis and activation of pro-inflammatory transcription factor nuclear factor kappa B (NFkappaB), which are biologic effects that may play a role in the renal damage associated with arterial hypertension. We investigated if increased apoptosis and NFkappaB activation were present in experimental models of hypertension.

METHODS

Sprague-Dawley rats fed with regular rodent chow and free access to water were studied. The Ang II group (N = 6) received 435 ng/kg/min of angiotensin II during 2 weeks by subcutaneous minipumps. The l-NAME group (N = 5) received Nomega-nitro-l-arginine-methyl-ester (l-NAME) in the drinking water (70 mg/100 mL) for 3 weeks. The control group consisted of 6 rats. Systolic blood pressure (tail cuff plethysmography), serum creatinine, and proteinuria were determined weekly. Kidneys were examined for superoxide-positive cells (histochemistry) and for apoptosis [terminal deoxynucleotidyl transferase-mediated uridine triphosphate nick-end labeling (TUNEL)-positive cells], proliferation [proliferating cell nuclear antigen (PCNA)-positive cells), and activation of NFkappaB (p65 subunit) with the appropriate antibodies.

RESULTS

As expected, hypertension developed in experimental groups. Tubulointerstitial superoxide-positive cells were increased 7 times (P < 0.001), TUNEL-positive cells were increased 3 to 4 times (P < 0.001), PCNA-positive cells were increased 20 to 30 times (P < 0.001), and NFkappaB activation was increased 4 to 5 times (P < 0.001) in the experimental groups. NFkappaB expression correlated with the number of interstitial lymphocytes (r = 0.667, P < 0.01) and macrophages (r = 0.835, P < 0.001).

CONCLUSION

Angiotensin II infusion and l-NAME administration induce oxidative stress and increased apoptosis and activation of the transcription factor NFkappaB. These effects may participate in the development of progressive renal injury resulting from uncontrolled hypertension

Vimentin and heat shock protein expression are induced in the kidney by angiotensin and by nitric oxide inhibition

BACKGROUND

Angiotensin II (Ang II) infusion and nitric oxide synthesis (NOS) inhibition with Nomega-nitro-l-arginine-methyl-ester (l-NAME) are experimental models of hypertension associated with renal inflammation and oxidative stress. To gain insight into the nature of the tubulointerstitial injury induced in these models, we studied lectin-binding specificities, vimentin expression, and heat shock protein (HSP) 60 and 70 in these experimental models.

METHODS

Sprague-Dawley rats received Ang II infusion (435 ng/kg/min) for 2 weeks by subcutaneous minipumps (Ang II group, N = 5) or l-NAME in the drinking water (70 mg/100 mL) for 3 weeks (l-NAME group N = 7). The control group consisted of 10 rats. Systolic blood pressure (tail-cuff plethysmography), serum creatinine, and proteinuria were determined weekly. At the end of the treatment period, rats were sacrificed and kidneys studied. Binding specificities of fluorescein-labeled lectins were examined in frozen sections, and cellular infiltrates were identified by immunohistology and expression of vimentin and HSP 60 and 70 with immunohistochemistry and computer image analysis.

RESULTS

Tubulointerstitial accumulation of macrophages, lymphocytes, and Ang II-positive cells were present in the Ang II group and l-NAME group. Vimentin, HSP 60, and HSP 70 were increased 8 to 20 times in the cortex of the rats of the Ang II group and the l-NAME groups. Neoexpression of vimentin and HSPs was found primarily in proximal tubular cells.

CONCLUSION

Ang II infusion and NOS inhibition induce tubular injury with epithelial cell transdifferentiation and expression of stress proteins. The role of these changes in the accumulation and activation of the interstitial inflammatory infiltrate merits further investigation.

Hyperuricemia in childhood primary hypertension

Experimental animal models suggest that uric acid might have a pathogenic role in the early development of primary hypertension. We hypothesized that serum uric acid is correlated with blood pressure in children with new-onset, untreated, primary hypertension. We evaluated 125 consecutive children referred to the Baylor Pediatric Renal Program for evaluation of hypertension. None of the subjects had previously been evaluated or treated for hypertension. The children ranged in age from 6 to 18 years (mean, 13.4+/-3.3) and had normal renal function (creatinine clearance >80 mL x min(-1) x 1.73 m(-2)). Sixty-three children had primary hypertension, 40 had secondary hypertension, and 22 had white-coat hypertension. Forty controls with normal blood pressure were recruited from the renal clinic. Uric acid levels were directly correlated with systolic (r=0.80, P=0.0002) and diastolic (r=0.66, P=0.0006) blood pressure in controls and in subjects with primary hypertension and were independent of renal function. Serum uric acid concentrations >5.5 mg/dL were found in 89% of subjects with primary hypertension, in 30% with secondary hypertension, in 0% with white-coat hypertension, and in 0% of controls. We conclude that serum uric acid is directly correlated with blood pressure in untreated children and that a serum uric acid value >5.5 mg/dL in an adolescent being evaluated for hypertension strongly suggests primary hypertension as opposed to white-coat or secondary hypertension. These results are consistent with the hypothesis that uric acid might have a role in the early pathogenesis of primary hypertension.

Microvascular and tubulointerstitial injury associated with chronic hypoxia-induced hypertension

BACKGROUND

Rats submitted to chronic hypoxia develop hypertension that persists despite cessation of the hypoxia or correction of the hematocrit. We examined whether chronic hypoxia might induce subtle renal injury since studies in other animal models of hypertension suggest this may cause persistent hypertension.

METHODS

Chronic hypoxia was induced in rats by placement in a hypobaric chamber for up to 24 days. Blood pressure and kidney biopsies were performed at baseline, 6 hours, 24 hours, and 24 days of hypoxia.

RESULTS

Chronic hypoxia induced hypertension and erythrocytosis at 24 days. Acute hypoxia was associated with endothelial cell swelling in arterioles (6 and 24 hours), followed by thickening of the arterioles at 24 days. Subtle tubulointerstitial injury and inflammation occurred and was progressive. The influx of macrophages increased steadily over the 24 days and was associated with a progressive increase in interstitial collagen III deposition. Hypoxia was associated with increased tubular expression of osteopontin as early as 6 hours, the same period when an increase of proximal tubular cell proliferation occurred. Interstitial cell proliferation peaked twice, at 6 hours and at 24 days. Glomerular hypertrophy was manifest at 24 days.

CONCLUSION

Both afferent arteriolar disease and subtle tubulointerstitial inflammation and injury occur early in hypoxic rats. These changes may predispose these animals to persistent hypertension.

Tubulointerstitial disease: role of ischemia and microvascular disease

PURPOSE OF REVIEW

Tubulointerstitial injury is characteristic of aging-associated renal injury and progressive renal disease. Salt-sensitive hypertension is also associated with tubulointerstitial inflammation, especially when accompanied by microvascular disease. Here we summarize recent studies on the pathogenesis and consequences of tubulointerstitial disease, emphasizing the role of ischemia and the microvasculature.

RECENT FINDINGS

Tubulointerstitial injury occurs via several mechanisms of which one of the most important is chronic ischemia. Recent studies suggest that chronic vasoconstriction may contribute to the renal injury associated with angiotensin II, catecholamines, nitric oxide inhibition, hypokalemia, hyperuricemia, and cyclosporine nephropathy. Salt-sensitivity may result as a consequence of the tubulointerstitial inflammatory response to these conditions, and this appears to be perpetuated by the development of preglomerular vascular disease. With progression of tubulointerstitial disease there is also a loss of peritubular capillaries, and stimulating microvascular growth with angiogenic factors can stabilize renal function in these models.

SUMMARY

Ischemia secondary to vasoconstriction or to structural changes of the renal vasculature may have important consequences both in terms of mediating salt-sensitive hypertension and renal progression. Angiogenic factors may have potential benefit in preventing or treating these conditions.

Melatonin reduces renal interstitial inflammation and improves hypertension in spontaneously hypertensive rats

Several studies have demonstrated that treatment with antioxidants improves hypertension in spontaneously hypertensive rats (SHR). Because our laboratory has shown that renal infiltration of immune cells plays a role in the development of hypertension (Rodriguez-Iturbe B, Quiroz Y, Nava M, Bonet L, Chavez M, Herrera-Acosta J, Johnson RJ, and Pons HA. Am J Physiol Renal Physiol 282: F191-F201, 2002), we did the present studies to define whether the antihypertensive effect of antioxidants was associated with an improvement in renal inflammation. Melatonin was administered as an antioxidant. For 6 wk, melatonin was added to the drinking water (10 mg/100 ml) given to a group of SHR (SHR-Mel; n = 10), and we compared them with groups of untreated SHR (n = 10) and Wistar-Kyoto (WKY) control rats (n = 10). Hypertension became increasingly severe in the SHR group [195 +/- 14.3 (SD) mmHg at the end of the experiment] and improved in the SHR-Mel group (149 +/- 20.4 mmHg, P < 0.001) in association with a 40-60% reduction in the renal infiltration of lymphocytes, macrophages, and angiotensin II-positive cells. Intracellular superoxide and renal malondialdehyde content were reduced by melatonin treatment as was the immunohistological expression of the 65-kDA DNA-binding subunit of NF-kappaB. We conclude that melatonin treatment ameliorates hypertension in SHR in association with a reduction in interstitial renal inflammation. Decreased activation of NF-kappaB, likely resulting from a reduction in local oxidative stress, may play a role in the suppression of renal immune infiltration and, thereby, in the antihypertensive effects of melatonin.

Synergistic effects of mycophenolate mofetil and losartan in a model of chronic cyclosporine nephropathy

BACKGROUND

Combined treatments of mycophenolate mofetil (MMF) and losartan (LSRT) have synergistic effects on various renal diseases through their hemodynamic and anti-inflammatory effects. This study investigated whether MMF treatment is effective in inhibiting inflammatory processes in chronic cyclosporine A (CsA) nephrotoxicity, and whether combined treatment using MMF and LSRT affords superior protection compared with the respective monotherapies.

METHODS

Rats on a low-salt diet were given vehicle (VH group, olive oil, 1 mg/kg per day), CsA (15 mg/kg per day), CsA and LSRT (CsA+LSRT group, 100 mg/L per day), CsA and MMF (CsA+MMF group; 40 mg/kg per day), or CsA, LSRT and MMF (CsA+LSRT MMF group). Control groups received each drug without CsA treatment. Renal function, histologic parameters (arteriolopathy, tubulointerstitial fibrosis, and inflammatory cell infiltration), and mediators of CsA-induced nephrotoxicity (angiotensin-II, osteopontin, and transforming growth factor [TGF]-beta1) were studied.

RESULTS

The CsA-treated rats showed decreased renal function and increased histologic parameters compared with the VH-treated rats. The CsA+MMF treatment significantly improved renal function and histopathologic parameters compared with the CsA group, and combined treatment with MMF and LSRT further improved those parameters compared with the CsA+LSRT and CsA+MMF groups. At a molecular level, increased expression of angiotensin II protein, osteopontin, and TGF-beta1 mRNAs in the CsA group were significantly decreased with MMF, and further decrease was observed with the combined treatment using MMF and LSRT.

CONCLUSIONS

MMF treatment decreases CsA-induced nephrotoxicity, and combined treatment with LSRT has a synergistic effect in preventing chronic CsA nephrotoxicity.

Antioxidant-rich diet relieves hypertension and reduces renal immune infiltration in spontaneously hypertensive rats

Previous studies have demonstrated that oxidative stress contributes to hypertension and treatments with either antioxidant or immunosuppressive/anti-inflammatory agents improve hypertension in spontaneously hypertensive rats (SHR). The present study was performed to determine if the antihypertensive effects of an antioxidant-rich diet are associated with reduction in the renal immune infiltration. Rats were divided into experimental groups (n=5 each) that were followed 7 months after birth, during which they were fed either a regular or antioxidant-enriched (test) diet as follows: SHR-R group=regular diet; SHR-T group=test diet throughout the experiment; SHR-S group=test diet for 4 months switched to regular diet thereafter; WKY group=control rats given regular diet. The SHR-T rats showed a significant reduction in systolic blood pressure (mm Hg): SHR-T=179.6+/-12.9 versus SHR-R=207.5+/-9.6 (P<0.001) and plasma hydrogen peroxide concentration (SHR-T=15+/-4 micro mol/L versus 34+/-9 in SHR-R rats). This was accompanied by significant reductions of renal tissue nitrotyrosine abundance, tubulointerstitial infiltration (cells/mm(2)) of lymphocytes (SHR-T=18+/-3 versus SHR-R=30+/-4, P<0.001), macrophages (SHR-T= 17+/-3 versus SHR-R=22+/-3), and angiotensin II-positive cells (SHR-T= 17+/-2 versus SHR-R=25+/-5, P<0.01). Results in the SHR-S group were intermediate between the SHR-R and SHR-T groups. The intensity of the infiltration of lymphocytes, macrophages, and angiotensin II-positive cells significantly correlated with systolic blood pressure. Thus, the present study demonstrates that an antioxidant-enriched diet reduces the renal interstitial inflammation and improves hypertension in SHR. These findings point to interrelation between oxidative stress and inflammatory reactivity in the pathogenesis of hypertension.

Experimental and clinical rationale for use of MMF in nontransplant progressive nephropathies

The incidence of progressive nephropathies and, consequently, the population suffering from end-stage renal disease have increased steadily in recent years, posing an ever-growing cost, in both human and financial terms, to society. There is mounting evidence that, in both immune-mediated and nonimmune-mediated chronic nephropathies, renal inflammatory events are key to the propagation and perpetuation of renal injury. Mycophenolate mofetil (MMF) is an antilymphocyte agent recently introduced in clinical practice for the prevention of allograft rejection. The present review discusses clinical and experimental evidence that the anti-inflammatory action of MMF can be advantageously used to arrest immune- and nonimmune-mediated progressive injury of native kidneys as well.

Overload proteinuria is followed by salt-sensitive hypertension caused by renal infiltration of immune cells

Recent evidence suggests that salt-sensitive hypertension develops as a consequence of renal infiltration with immunocompetent cells. We investigated whether proteinuria, which is known to induce interstitial nephritis, causes salt-sensitive hypertension. Female Lewis rats received 2 g of BSA intraperitoneally daily for 2 wk. After protein overload (PO), 6 wk of a high-salt diet induced hypertension [systolic blood pressure (SBP) = 156 +/- 11.8 mmHg], whereas rats that remained on a normal-salt diet and control rats (without PO) on a high-salt diet were normotensive. Administration of mycophenolate mofetil (20 mg. kg(-1). day(-1)) during PO resulted in prevention of proteinuria-related interstitial nephritis, reduction of renal angiotensin II-positive cells and oxidative stress (superoxide-positive cells and renal malondialdehyde content), and resistance to the hypertensive effect of the high-salt diet (SBP = 129 +/- 12.2 mmHg). The present studies support the participation of renal inflammatory infiltrate in the pathogenesis of salt-sensitive hypertension and provide a direct link between two risk factors of progressive renal damage: proteinuria and hypertension.

Cyclosporine withdrawal and mycophenolate mofetil treatment effects on the progression of chronic cyclosporine nephrotoxicity

BACKGROUND

Recent clinical trials of mycophenolate mofetil (MMF) in chronic allograft nephropathy (CAN) demonstrated that the dose of cyclosporine A (CsA) is one of the critical factors in determining graft function in CAN, but the effect of MMF on chronic CsA nephropathy is undetermined. We undertook this study to evaluate the effect of MMF on CsA-induced nephrotoxicity in an animal model of chronic CsA nephropathy.

METHODS

In the first experiment, Sprague-Dawley rats on a low-salt diet were treated with CsA (7.5 mg/kg per day) for 10 weeks, or were treated with CsA for five weeks and then MMF (20 mg/kg per day) was administered five weeks later. In the second experiment, rats were treated with CsA for five weeks, and CsA was then withdrawn for five weeks with or without MMF treatment. Renal function, histologic parameters (tubulointerstitial fibrosis, arteriolopathy, ED-1-positive cells, renin-positive glomeruli, TUNEL-positive cells) and the expression of osteopontin and transforming growth factor (TGF)-beta1 mRNA expressions were compared for different treatment groups.

RESULTS

CsA-treated rats showed decreased renal function and increased histologic parameters compared with the vehicle (VH)-treated rats. The addition of MMF did not improve these parameters compared with the CsA-treated rats. With CsA withdrawal, renal function and histologic parameters were significantly improved compared with the CsA-treated rats, and MMF treatment after CsA withdrawal further improved the histologic parameters. At the molecular level, the addition of MMF did not decrease the expression of osteopontin and transforming growth factor-beta1 (TGF-beta1) mRNAs, which were increased in the CsA-treated rat kidney. With CsA withdrawal, the expression of both mRNAs was significantly decreased compared with the CsA group, and a further decrease was observed with MMF treatment after CsA was withdrawn.

CONCLUSION

The combined treatment of CsA and MMF does not prevent the development of chronic CsA nephrotoxicity, but MMF treatment after CsA withdrawal does improve chronic CsA nephrotoxicity. This finding provides a rationale for MMF treatment in chronic CsA nephrotoxicity.

Dysregulation of angiotensin II synthesis is associated with salt sensitivity in the spontaneous hypertensive rat

(1) Salt sensitive hypertension, which occurs as a result of treatment with nitric oxide synthase inhibitors, is associated with a loss of the usual down-regulatory effect of dietary sodium on angiotensin II (Ang II) synthesis. In the spontaneous hypertensive rat (SHR), which suffers a relative NO deficiency, the hypertension is in part salt sensitive. We sought to determine therefore whether the salt sensitive component to the hypertension was associated with a loss of the regulatory effect of dietary sodium on Ang II synthesis. (2) Male SHR were placed on low, intermediate or high salt diets for 4 weeks and their blood pressure recorded. After 4 weeks, blood was collected for determination of renin, angiotensinogen, Ang I, Ang II and aldosterone concentrations, as well as ACE activity. (3) The increase in systolic blood pressure in rats on the high salt diet was significantly greater than in those on the low (P < 0.005) and intermediate salt diets (P < 0.0005). Plasma renin and aldosterone concentrations and ACE activity decreased with increasing dietary sodium. However, the concentrations of Ang II and angiotensinogen both increased in the rats on the high salt diet (Ang II: P < 0.05; angiotensinogen: P < 0.05). (4) We conclude that the hypertension in the SHR is in part salt sensitive and that this salt sensitive component is associated with a loss of the normal down-regulatory effect of dietary sodium on Ang II and angiotensinogen synthesis.

Reduction of renal immune cell infiltration results in blood pressure control in genetically hypertensive rats

Immunocompetent cells infiltrate the kidney in several models of experimental hypertension. We have previously shown that reduction of this infiltrate results in prevention of salt-sensitive hypertension induced by short-term angiotensin II infusion and nitric oxide inhibition (Quiroz Y, Pons H, Gordon KI, Rincón J, Chávez M, Parra G, Herrera-Acosta J, Gómez-Garre D, Largo R, Egido J, Johnson RJ, and Rodríguez-Iturbe B. Am J Physiol Renal Physiol 281: F38-F47, 2001; Rodríguez-Iturbe B, Pons H, Quiroz Y, Gordon K, Rincón J, Chávez M, Parra G, Herrera-Acosta J, Gómez-Garre D, Largo R, Egido J, and Johnson RJ. Kidney Int 59: 2222-2232, 2001). We therefore studied whether hypertension could be controlled in genetically hypertensive rats [spontaneously hypertensive rats (SHR)] by the administration of 20 mg x kg(-1) x day(-1) of the immunosuppressive drug mycophenolate mofetil (MMF group; n = 35). Other SHR received vehicle (n = 35), and Wistar-Kyoto rats (n = 20) were used as controls. MMF or vehicle was given in two separate 4-wk periods, separated by a 3-wk interval. Systemic hypertension was reduced to normal levels in both periods of MMF treatment in association with a reduction in lymphocyte, macrophage, and angiotensin II-positive cells infiltrating the kidney. Oxidative stress was also reduced by MMF, as indicated by a reduction in urinary malondialdehyde (MDA), renal MDA content, and superoxide-positive cells, and was highly correlated with blood pressure levels. We conclude that the renal immune infiltrate plays a major role in the hypertension in SHR.

Hypokalemia induces renal injury and alterations in vasoactive mediators that favor salt sensitivity

We investigated the hypothesis that hypokalemia might induce renal injury via a mechanism that involves subtle renal injury and alterations in local vasoactive mediators that would favor sodium retention. To test this hypothesis, we conducted studies in rats with diet-induced K+ deficiency. We also determined whether rats with hypokalemic nephropathy show salt sensitivity. Twelve weeks of hypokalemia resulted in a decrease in creatinine clearance, tubulointerstitial injury with macrophage infiltration, interstitial collagen type III deposition, and an increase in osteopontin expression (a tubular marker of injury). The renal injury was greatest in the outer medulla with radiation into the cortex, suggestive of an ischemic etiology. Consistent with this hypothesis, we found an increased uptake of a hypoxia marker, pimonidazole, in the cortex. The intrarenal injury was associated with increased cortical angiontensin-converting enzyme (ACE) expression and continued cortical angiotensin II generation despite systemic suppression of the renin-angiotensin system, an increase in renal endothelin-1, a decrease in renal kallikrein, and a decrease in urinary nitrite/nitrates and prostaglandin E(2) excretion. At 12 wk, hypokalemic rats were placed on a normal-K+ diet with either high (4%)- or low (0.01%)-NaCl content. Despite correction of hypokalemia and normalization of renal function, previously hypokalemic rats showed an elevated blood pressure in response to a high-salt diet compared with normokalemic controls. Hypokalemia is associated with alterations in vasoactive mediators that favor intrarenal vasoconstriction and an ischemic pattern of renal injury. These alterations may predispose the animals to salt-sensitive hypertension that manifests despite normalization of the serum K+.