Hypertensive nephrosclerosis: wider kidney biopsy indications may be needed to improve diagnostics.

BACKGROUND: Hypertensive nephrosclerosis is the presumed underlying cause in many end-stage kidney disease (ESKD) patients, but the diagnosis is disputed and based on clinical criteria with low diagnostic accuracy. OBJECTIVE: To evaluate and improve the diagnostic process for nephrosclerosis patients. METHODS: We included adults from the population-based HUNT study (n = 50 552), Norwegian CKD patients referred for kidney biopsy 1988-2012 (n = 7261), and unselected nephrology clinic patients (n = 193) used for matching. Decision tree analysis and ROC curve-based methods of optimal cut-offs were used to improve clinical nephrosclerosis criteria. RESULTS: Nephrosclerosis prevalence was 2.7% in the general population, and eGFR decline and risk for kidney-related hospital admissions and ESKD were comparable to patients with diabetic kidney disease. In the biopsy cohort, current clinical criteria had very low sensitivity (0.13) but high specificity (0.94) for biopsy-verified arterionephrosclerosis. A new optimized diagnostic algorithm based on proteinuria (<0.75 g d-1 ), systolic blood pressure (>155 mm Hg) and age (>75 years) only marginally improved diagnostic accuracy (sensitivity 0.19, specificity 0.96). Likewise, there were still false-positive cases with treatable diagnoses like glomerulonephritis, interstitial nephritis and others (40% of all test positive). Decision curve analysis showed that the new criteria can lead to higher clinical utility, especially for patients considering the potential harms to be close to the potential benefits, while the more risk-tolerant ones (harm:benefit ratio < 1:4) should consider kidney biopsy. CONCLUSION: Further improvements of the current clinical criteria seem difficult, so risks and benefits of kidney biopsy could be more actively discussed with selected patients to reduce misclassification and direct treatment.

Thin Glomerular Basement Membrane in a Kidney Transplant of an Alport's Syndrome Patient: A Case Report.

Alport syndrome (AS) and thin basement membrane lesions are caused by various mutations in type IV collagen genes. Although AS is considered a rare disease, thin basement membrane is a frequent pattern, especially in families with a history of persistent hematuria. We report a patient with a diagnosis of AS who developed end-stage kidney disease (ESKD) and received a kidney transplant from a living unrelated donor. The graft biopsy specimen surprisingly showed a pattern of thin basement membranes.

Postinfectious glomerulonephritis: Is there a role for steroids?

The role of steroids in treatment of postinfectious glomerulonephritis (PIGN) has been controversial. The reason for such controversy is the risk of infection relapse associated with steroid therapy. Steroids may have a place in the treatment of resistant cases where renal function does not improve despite aggressive antibiotic therapy as well as in patients with crescentic form of PIGN. We report a case of a 39 year-old Caucasian man who was diagnosed with methicillin-resistant Staphylococcus aureus (MRSA) bacteremia resulting in acute IgA dominant PIGN that failed to respond to antibiotic treatment alone, but responded significantly to steroids in addition to antibiotics. This anecdotal experience suggests that steroids could be considered in conjunction with antibiotic therapy for the treatment of refractory cases of PIGN or crescentic form of PIGN. More studies with long-term follow-up of patients treated with steroids in addition to antimicrobial agents are required to quantify the risk of infection relapse with steroid therapy.

Banff 07 classification of renal allograft pathology: updates and future directions.

The 9th Banff Conference on Allograft Pathology was held in La Coruna, Spain on June 23-29, 2007. A total of 235 pathologists, clinicians and scientists met to address unsolved issues in transplantation and adapt the Banff schema for renal allograft rejection in response to emerging data and technologies. The outcome of the consensus discussions on renal pathology is provided in this article. Major updates from the 2007 Banff Conference were: inclusion of peritubular capillaritis grading, C4d scoring, interpretation of C4d deposition without morphological evidence of active rejection, application of the Banff criteria to zero-time and protocol biopsies and introduction of a new scoring for total interstitial inflammation (ti-score). In addition, emerging research data led to the establishment of collaborative working groups addressing issues like isolated 'v' lesion and incorporation of omics-technologies, paving the way for future combination of graft biopsy and molecular parameters within the Banff process.

Modulation of angiotensin II and norepinephrine-induced plasminogen activator inhibitor-1 expression by AT1a receptor deficiency.

Angiotensin (Ang) II stimulates plasminogen activator inhibitor-1 (PAI-1) expression in many cell types by mechanisms that are cell-type specific. We measured effects of Ang II or norepinephrine on PAI-1 expression in wild type (WT) and Ang type-1a receptor knockout mice (AT(1a)-/-) in the presence or absence of the non-specific AT(1) antagonist losartan. Ang II and norepinephrine increased systolic blood pressure equally, whereas losartan decreased the pressor response of the former but not the latter in WT mice. In AT(1a)-/- mice, baseline systolic blood pressure was lower with no effect of Ang II, norepinephrine, or losartan. Ang II stimulated PAI-1 expression in the heart, aorta, and kidney and markedly in the liver of WT mice. In AT(1a)-/- mice, Ang II-stimulated PAI-1 was significantly attenuated compared with the WT in the heart and aorta but significantly enhanced in the kidney. Losartan decreased the induction in the aorta and liver of WT, and in the kidney and liver of AT(1a)-/- mice. Norepinephrine increased PAI-1 expression in WT heart and aorta, and in AT(1a)-/- heart, kidney, and liver with no effect of losartan. Renal PAI-1 expression correlated with AT(1b) receptor mRNA. We conclude that Ang II stimulates PAI-1 expression in part through the AT(1b) receptor in the kidney and liver. Further, norepinephrine induces PAI-1 expression in vivo with AT(1a) receptor deficiency modulating the effect.

PPAR-gamma agonist protects podocytes from injury.

Podocyte injury and loss contribute to progressive glomerulosclerosis. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a nuclear hormone receptor, which we have found to be increased in podocytes in a variety of kidney diseases. It is not known if PPAR-gamma contributes to renal injury or if it serves as a countermeasure to limit renal injury during disease progression. We tested these possibilities utilizing the puromycin aminonucleoside (PAN) model of renal injury in immortalized mouse podocytes. The cultured podocytes expressed PPAR-gamma mRNA at baseline but this was decreased by PAN. Pioglitazone, a pharmacologic agonist of PPAR-gamma, increased both PPAR-gamma mRNA and activity in injured podocytes, as assessed by a reporter plasmid assay. Further, pioglitazone significantly decreased PAN-induced podocyte apoptosis and necrosis while restoring podocyte differentiation. The PPAR-gamma agonist significantly restored expression of the cyclin-dependent kinase inhibitor p27 and the antiapoptotic molecule Bcl-xL while significantly decreasing proapoptotic caspase-3 activity. Pioglitazone tended to decrease PAN-induced transforming growth factor-beta (TGF-beta) mRNA expression. Our study shows that PPAR-gamma is normally expressed by podocytes and its activation is protective against PAN-induced apoptosis and necrosis. We postulate that this protective effect may be mediated in part by effects on p27 and TGF-beta expression.

Chronic myeloid leukemia-associated membranoproliferative glomerulonephritis that responded to imatinib mesylate therapy.

There is no known clinical association between chronic myelogenous leukemia (CML) and membranoproliferative glomerulonephritis (MPGN). We present a patient who was followed in the renal clinic for proteinuria of unknown etiology (3.2 g/24 h) and normal renal function who was diagnosed with CML as well as MPGN and acute renal failure at the same time. The patient's renal function and proteinuria improved when his CML was treated with imatinib mesylate, suggesting that CML either caused or exacerbated existing MGPN. To the best of our knowledge, this is the first reported case of MPGN associated with CML that improved with imatinib mesylate therapy.

The clot thickens.

Vascular sclerosis has been linked to many risk factors, including smoking, family history, low birth weight, and hypertension. In interesting studies, Goforth et al. show an increased rate of mutations in thrombophilic molecules in patients with vascular sclerosis in renal biopsies, suggesting yet another mechanism.

Peroxisome proliferator-activated receptor-gamma agonist is protective in podocyte injury-associated sclerosis.

We have previously observed increased expression of peroxisome proliferator-activated receptor gamma (PPARgamma) in podocytes in both rat and human sclerotic conditions. The aim of the present study was to investigate whether activation of PPARgamma can attenuate podocyte injury-associated glomerulosclerosis in vivo. Puromycin aminonucleoside nephropathy was induced in Sprague-Dawley rats. The animals then either received no further treatment (control group (CONT)); or the PPARgamma agonist, pioglitazone (Pio) starting at week 0 (P0); or Pio starting at week 6 (P6), with sacrifice at week 12. At week 12, urinary protein excretion and systolic blood pressure were similar in the three groups. Glomerular filtration rate and glomerulosclerosis were decreased in CONT and P0 at week 12, but preserved in P6 rats. PPARgamma expression in CONT at 12 weeks was increased in podocytes and in mesangial WT-1 cells in segmentally sclerotic glomeruli, with less Wilms' tumor 1 (WT-1) staining. In P6 rats, mesangial WT-1 staining was lessened, but podocyte staining was strongly accentuated. Delayed treatment with Pio partially restored podocyte staining and tended to decrease the ratio of proliferating cell nuclear antigen-positive to apoptotic cells in glomeruli. Both treatment groups showed significantly reduced infiltrating glomerular macrophages and plasminogen activator inhibitor-1 mRNA expression in cortex, with no change in transforming growth factor-beta1 and tissue inhibitor of metalloproteinase-1 mRNA. Pio also decreased renal cortical angiopoietin-like protein 4 expression to almost 20% of CONT group, associated with increased vascular endothelial-derived growth factor expression in glomeruli. We conclude that treatment with PPARgamma agonist has protective effects on progression of glomerulosclerosis.

Plasminogen activator inhibitor-1 deficiency protects against aldosterone-induced glomerular injury.

This study tests the hypothesis that plasminogen activator inhibitor-1 (PAI-1) contributes to aldosterone-induced renal and cardiac injury. The effects of 12-week aldosterone (2.8 microg/day)/salt (1% drinking water) versus vehicle/salt on renal and cardiac histology and mRNA expression were determined in wild-type (WT) and PAI-1 deficient (PAI-1(-/-)) mice. Systolic blood pressure was similar in aldosterone-infused WT and PAI-1(-/-) mice until 12 weeks, when it was significantly higher in the WT mice. At 12 weeks, urine volume, sodium excretion, and sodium/potassium ratio were similarly increased in the two aldosterone-infused groups. In contrast, urine albumin excretion was greater in aldosterone-infused WT mice (mean+/-s.d.: 699.0+/-873.0 microg/24 h) compared to vehicle-infused WT (23.6+/-9.0 microg/24 h, P=0.003) or aldosterone-infused PAI-1(-/-) mice (131.6+/-110.6 microg/24 h, P=0.007). Aldosterone increased glomerular area to a greater extent in WT (4651+/-577 versus 3278+/-488 microm2/glomerulus in vehicle-infused WT, P<0.001) than in PAI-1(-/-) mice (3713+/-705 microm2/glomerulus, P=0.001 versus aldosterone-infused WT), with corresponding mesangial expansion. Renal collagen content was also increased in aldosterone-infused WT versus PAI-1(-/-) mice. In WT mice, aldosterone increased renal mRNA expression of PAI-1, collagen I, collagen III, osteopontin, fibronectin, monocyte chemoattractant protein-1 (MCP-1), and F4/80 (all P<0.05), but not transforming growth factor beta (TGF-beta). In PAI-1(-/-) mice, aldosterone increased renal expression of collagen I, osteopontin, fibronectin, and MCP-1, and tended to increase collagen III. Renal osteopontin expression was diminished in aldosterone-treated PAI-1(-/-) compared to aldosterone-treated WT mice (P=0.05). Aldosterone induced cardiac hypertrophy but not fibrosis in WT and PAI-1(-/-) mice. PAI-1 contributes to aldosterone-induced glomerular injury.

Role of angiotensin II in glomerular injury.

The components of the renin-angiotensin system (RAS) in progressive renal disease have been extensively investigated, indicating multiple actions beyond hemodynamic and salt/water homeostasis. Studies in various human diseases and in animal models have shown that angiotensin (Ang) I-converting enzyme inhibitors (ACEI) are superior to other antihypertensive agents in protecting the kidney against progressive deterioration, even in conditions without systemic hypertension. These findings suggest that Ang II has nonhemodynamic effects in progressive renal disease. Interactions of the RAS with aldosterone and bradykinin may have impact on both blood pressure and tissue injury. The RAS is now recognized to be linked to induction of plasminogen activator inhibitor-1 (PAI-1) likely via both the type 1 (AT1) and type 4 (AT4) receptors, thus, promoting both thrombosis and fibrosis. A role of angiotensin in the regulation of immune injury and inflammation has also been identified. Polymorphisms of genes relevant to the RAS appear to affect the risk and course of cardiovascular and renal diseases and response to treatment. The beneficial effect on renal fibrosis of inhibiting the RAS likely reflects the central role that angiotensin has in regulating renal function and structure by its multifaceted actions. This article will focus on the role of the RAS in glomerular injury.

Renal fibrosis and the renin-angiotensin system.

These data demonstrate that regression of biopsy-proven glomerulosclerosis can be achieved in various experimental settings. The potential importance of the RAS in renal fibrosis is underscored by the effectiveness of therapies that aim to inhibit its manifold actions, including induction of PAI-1. An understanding of the interactions of the RAS with the immune response, aldosterone, and PAI-1, as well as the dynamic control of cell proliferation, apoptosis, and regeneration, is now evolving. Ongoing studies will establish which of these recent provocative findings from animal models are relevant to human diseases, and may lead to optimal therapies to fore-stall progression and perhaps even induce regression of sclerosis.

Plasminogen activator inhibitor-1 deficiency prevents hypertension and vascular fibrosis in response to long-term nitric oxide synthase inhibition.

BACKGROUND: Long-term inhibition of nitric oxide synthase (NOS) is known to induce hypertension and perivascular fibrosis. Recent evidence also suggests that long-term NOS inhibition induces expression of plasminogen activator inhibitor-1 (PAI-1) in vascular tissues and that PAI-1 may contribute to the development of fibrosis after chemical or ionizing injury. On the basis of these observations, we hypothesized that PAI-1 may influence the vascular response to long-term NOS inhibition by N(omega)-nitro-L-arginine methyl ester (L-NAME). METHODS AND RESULTS: We compared the temporal changes in systolic blood pressure and coronary perivascular fibrosis in PAI-1-deficient (PAI-1(-/-)) and wild-type (WT) male mice (N=6 per group). At baseline, there were no significant differences in blood pressure between groups. After initiation of L-NAME, systolic blood pressure increased in both groups at 2 weeks. Over an 8-week study period, systolic blood pressure increased to 141+/-3 mm Hg in WT animals versus 112+/-4 mm Hg in PAI-1(-/-) mice (P<0.0001). The extent of coronary perivascular fibrosis increased significantly in L-NAME-treated WT mice (P<0.01 versus PAI-1(-/-) mice). Cardiac type I collagen mRNA expression was greater in control (P<0.01) and L-NAME-treated PAI-1(-/-) (P<0.05) groups than in control WT mice, indicating that PAI-1 deficiency prevents the increase of collagen deposition by promoting matrix degradation. CONCLUSIONS: These findings suggest that PAI-1 deficiency alone is sufficient to protect against the structural vascular changes that accompany hypertension in the setting of long-term NOS inhibition. Direct inhibition of vascular PAI-1 activity may provide a new therapeutic strategy for the prevention of arteriosclerotic cardiovascular disease.

Peroxisome proliferator-activated receptor-gamma agonist troglitazone protects against nondiabetic glomerulosclerosis in rats.

BACKGROUND: Peroxisome proliferator-activated receptor-gamma (PPAR gamma) is a member of the nuclear receptor superfamily of ligand-dependent transcriptional factors with beneficial effects in diabetes mediated by improved insulin sensitivity and lipid metabolism, but potential adverse effects in atherosclerosis by promoting in vitro foam cell formation. We explored whether a PPAR gamma agonist, troglitazone (TGL), affects sclerosis by mechanisms unrelated to insulin and lipid effects in a model of nondiabetic glomerulosclerosis. METHODS: Adult male Sprague Dawley rats underwent 5/6 nephrectomy and were treated for 12 weeks as follows: control (CONT), no further treatment; triple antihypertensive therapy (TRX); and TGL or TGL + TRX. Functional, morphological, and molecular analyses were performed. RESULTS: Systolic blood pressure (SBP) was increased in CONT and TGL groups (161 +/- 1 and 160 +/- 3 mm Hg), but not in TGL + TRX and TRX (120 +/- 3 vs. 126 +/- 1 mm Hg, P < 0.0001 vs. non-TRX). Serum triglyceride and cholesterol levels in all groups remained normal except for slightly higher serum cholesterol levels in TRX group. TGL groups had reduced proteinuria, serum creatinine, and glomerulosclerosis versus CONT, in contrast to no significant effect with TRX alone (sclerosis index, 0 to 4+ scale: CONT 1.99 +/- 0.42, TGL 0.85 +/- 0.12, TGL + TRX 0.56 +/- 0.14, TRX 1.30 +/- 0.21; TGL, P < 0.05; TGL + TRX, P = 0.01 vs. CONT). Glomerular cell proliferation, assessed by proliferating cell nuclear antigen (PCNA), was decreased after treatment with TGL or TGL + TRX, in parallel with decreases in glomerular p21 mRNA and p27 protein compared with CONT and TRX (PCNA + cells/glomerulus: CONT 2.04 +/- 0.64, TGL 0.84 +/- 0.21, TGL + TRX 0.30 +/- 0.07, TRX 1.38 +/- 0.37; TGL, P < 0.05, TGL + TRX, P < 0.01 vs. CONT). Glomerular plasminogen activator inhibitor-1 (PAI-1) immunostaining was decreased in TGL or TGL + TRX groups (0 to 4+ scale, CONT 2.42 +/- 0.32, TGL 1.40 +/- 0.24, TGL + TRX 1.24 +/- 0.17, TRX 2.53 +/- 0.24; TGL or TGL + TRX vs. CONT, P < 0.05), with a parallel decrease in PAI-1 mRNA by in situ hybridization. Glomerular and tubular transforming growth factor-beta (TGF-beta) mRNA expression was decreased with TGL treatment. Glomerular macrophages, present in CONT and TRX rats, did not express PPAR gamma, in contrast to PPAR gamma + macrophages in control carotid artery plaque. PPAR gamma was expressed in resident cells. CONCLUSIONS: Our results demonstrate in vivo that the PPAR gamma ligand TGL ameliorates the progression of glomerulosclerosis in a nondiabetic model. Macrophages show phenotypic diversity in glomerular versus vascular sclerosis, with macrophage PPAR gamma expression in only the latter. PPAR gamma beneficial effects are independent of insulin/glucose effects and are associated with regulation of glomerular cell proliferation, hypertrophy, and decreased PAI-1 and TGF-beta expression.

Mechanisms in nephrosclerosis and hypertension-beyond hemodynamics.

These studies support that global glomerulosclerosis is a key lesion in human hypertensive nephrosclerosis, and cannot be simply explained by worse vascular sclerosis caused by higher blood pressure. Possible pathogenetic mechanisms include genetic susceptibility, accelerated aging and a primary microvascular disease. The potential importance of the renin angiotensin system in glomerular sclerosis is underscored by the effectiveness of therapies that aim to inhibit its manifold actions, including induction of plasminogen activator inhibitor-1 (PAI-1). Further, regression of existing glomerulosclerosis, including age-related renal and vascular sclerosis, can be achieved in various experimental settings by high dose angiotensin inhibiton, and is linked to inhibition of PAI-1. Ongoing studies will establish which of these provocative findings from animal models are relevant to human diseases, and may lead to optimal therapies to forestall progression and perhaps even induce regression of sclerosis.