Background and objectives: Sickle cell anemia-associated nephropathy is a growing matter of concern because renal failure affects most aging sickle cell anemia patients. Glomerular damage is a common feature revealed by a microalbuminuria or a macroalbuminuria. Although glomerular hyperfiltration has been described for decades in this population, its prevalence in young adults is unknown.Design, setting, participants, & measurements: To address this issue, as well as the clinical and biologic correlates of hyperfiltration, a single-center, cross-sectional study of 280 homozygous SS disease patients was performed.Results: The prevalence of hyperfiltration assessed by Modification of Diet in Renal Disease estimated GFR was 51%. Among patients with hyperfiltration, 49% had hyperfiltration alone, whereas 36% and 15% had an associated microalbuminuria or macroalbuminuria, respectively. Estimated GFR sensitivity and specificity for hyperfiltration were 94% and 63%, respectively, in a selected subgroup of 48 patients (measured GFR was assessed by urinary 51 Cr EDTA clearance). In patients with no albuminuria, hyperfiltration status was significantly associated with a young age (years), the absence of alpha thalassemia, a lower hemoglobin level (g/dl), and a lower fetal hemoglobin. The role of chronic hemolysis was further strengthened by multivariate analysis showing a correlation between estimated GFR and a low plasma fetal hemoglobin level, a young age, and a high reticulocyte count (r 2 ‫؍‬ 0.54). Conclusions: Together, the data suggest that the pathophysiology of hyperfiltration would rather be attributable to the hemolysis-associated vasculopathy rather than a viscosity-vaso-occlusive process.

Abstract-In hypertension, angiotensin (Ang) II is a critical mediator of cardiovascular remodeling, whose prominent features include myocardial and vascular media hypertrophy, perivascular inflammation, and fibrosis. The signaling pathways responsible for these alterations are not completely understood. Here, we investigated the importance of calpains, calcium-dependent cysteine proteases. We generated transgenic mice constitutively expressing high levels of calpastatin, a calpain-specific inhibitor. Chronic infusion of Ang II led to similar increases in systolic blood pressure in wild-type and transgenic mice. In contrast, compared with wild-type mice, transgenic mice displayed a marked blunting of Ang II-induced hypertrophy of left ventricle. Ang II-dependent vascular remodeling, ie, media hypertrophy and perivascular inflammation and fibrosis, was also limited in both large arteries (aorta) and small kidney arteries from transgenic mice as compared with wild type. In vitro experiments using vascular smooth muscle cells showed that calpastatin transgene expression blunted calpain activation by Ang II through epidermal growth factor receptor transactivation. In vivo and in vitro models of inflammation showed that impaired recruitment of mononuclear cells in transgenic mice was attributable to a decrease in both the release of and the chemotactic response to monocyte chemoattractant protein-1. Finally, results from collagen synthesis assay and zymography suggested that limited fibrogenesis was attributable to a decrease in collagen deposition rather than an increase in collagen degradation.

Stimulation of macrophages with endotoxin and/or cytokines is responsible for the expression of the inducible isoform of nitric oxide synthase (iNOS). Because macrophages are exposed to low pH within the microenvironment of inflammatory lesions, the potential role of acidic pH as an additional regulator of iNOS was investigated. Substitution of the culture medium of rat peritoneal macrophages at pH 7.4 with medium at pH 7.0 up-regulated iNOS activity, as reflected by a 2.5-fold increase in nitrite accumulation. The increase in iNOS activity was associated with a similar increase in iNOS mRNA expression that reflected an increase in iNOS mRNA synthesis rather than stability. Low environmental pH-induced iNOS gene transcription involved the activation of nuclear factor-B (NF-B) transcription factor since exposure of macrophages to low environmental pH both increased NF-B binding activity in the nucleus and enhanced NF-B-driven reporter gene expression. In addition, treatment of macrophages with pyrrolidine dithiocarbamate or n-acetyl-leucinyl-leucinyl-norleucinal, two drugs preventing NF-B translocation to the nucleus, canceled low pH-induced nitrite accumulation. The overall mechanism required the synthesis of tumor necrosis factor ␣ (TNF␣). Indeed, 1) elevated TNF␣ bioactivity was observed in the medium of macrophages exposed to pH 7.0, and 2) incubation of macrophages with a neutralizing anti-TNF␣ antibody impaired both NF-B activation and nitrite accumulation in response to acid challenge. In summary, exposure of macrophages to acidic microenvironment in inflammatory lesions leads to the up-regulation of iNOS activity through the activation of NF-B.Acidosis is a hallmark of both ischemia and inflammation processes. The decrease of pH in tissue ischemia is secondary to the release of H ϩ during ATP hydrolysis and to the accumulation of CO 2 (1). The acidic environment in inflammatory lesions and abscesses (2) is due to increased metabolic acid generation during cell activation. This originates primarily from the hexose monophosphate shunt, by the dissociation of hydrated CO 2 (3).In most cases, acidosis occurs along with nitric oxide (NO) 1 generation. In ischemia, NO generation is due in one part to the acidification and reduction of the large pool of nitrite present within the tissue (4). In inflammatory processes, macrophage exposure to bacterial lipopolysaccharide (LPS) or cytokines such as tumor necrosis factor ␣ (TNF␣) and interferon-␥ (IFN-␥) causes the expression of the inducible isoform of NO synthase (NOS II or iNOS) that is responsible for high output production of NO (5). The expression of iNOS is regulated mainly at the transcriptional level. Analyses of the murine iNOS promoter have shown the presence of numerous consensus sequences for the binding of transcription factors (6, 7), of which nuclear factor-B (NF-B) (8), interferon regulatory factor-1 (IRF-1) (9), and signal transducer and activator of transcription (STAT) 1␣ (10) are functionally important for iNOS induction. NF-B is composed of a p...

Reactive oxygen species (ROS) are formed by incomplete reduction of molecular oxygen. They include superoxide anion (O2-.), hydrogen peroxide (H2O2), hydroxyl radical (OH.), and singlet oxygen (1O2). ROS may induce different types of cell injury, particularly lipid peroxidation and membrane damage. ROS have been shown to play an essential role in the mechanisms of experimental models of several renal diseases: ischemic acute renal failure, renal graft rejection, acute glomerulonephritis, and toxic renal diseases. They are produced by the renal cells and also by the inflammatory bone marrow-derived cells invading the renal tissue. ROS, regardless of their origin, may degrade the glomerular basement membrane and alter the glomerular and tubular cell functions. Particularly, they produce an increase in cyclic AMP synthesis and prostaglandin production in the glomeruli. Recent studies have shown that the glomerular mesangial cells themselves generated ROS on stimulation by phagocytosis of foreign particles or exposure to the complement membrane attack complex or platelet-activating factor. Production of ROS is in narrow relationship with the metabolism of arachidonic acid. Conversion of this fatty acid via the lipoxygenase pathway is associated with an increase of ROS, whereas its transformation into prostaglandins via the cyclooxygenase pathway results in the opposite effect. Production of ROS in activated mesangial cells can be inhibited by glucocorticoids via a receptor-mediated mechanism. The fact that some of these characteristics are different in leukocytes suggests the possibility in the future of the more specific pharmacological control of the inflammatory process in the glomerular mesangium.

Calpains are cytosolic calcium-activated cysteine proteases. Recently, they have been proposed to influence signal transduction processes leading to myocardial remodelling and heart failure. In this review, we will first describe some of these molecular mechanisms. Calpains may contribute to myocardial hypertrophy and inflammation, mainly through the activation of transcription factors such as NF-κB. They play an important role in the fibrosis process partly by activating transforming growth factor β. They are also implicated in cell death as they cause the breakdown of sarcolemma and sarcomeres. Nevertheless, a key to understanding the molecular basis of calpain-mediated myocardial remodelling likely lies in the identification of mechanisms involved in calpain secretion, since cytosolic and extracellular proteases would have different functions. Finally, we will provide an overview of the available evidence that calpains are indeed actively involved in the common causes of heart failure, including hypertension, diabetes, atherosclerosis, ischaemia-reperfusion, atrial fibrillation, congestive failure, and mechanical unloading.

There is considerable evidence suggesting that reactive oxygen species (ROS) are implicated in the pathogenesis of ischemic, toxic, and immunologically-mediated renal injury. In experimental renal ischemia, ROS sources include the electron transport chain, oxidant enzymes (xanthine oxidase), phagocytes, and auto-oxidation of epinephrine. ROS cause lipid peroxidation of cell and organelle membranes and, hence, disruption of the structural integrity and capacity for cell transport and energy production, especially in the proximal tubule segment. In experimental immune glomerulonephritis, ROS are generated by both infiltrating blood-borne cells (polymorphonuclear leukocytes and monocytes) and resident glomerular cells, mainly mesangial cells. Their formation results in morphologic lesions and in modifications of glomerular permeability to proteins through activation of proteases and reduction of proteoglycan synthesis. Additionally, they promote a reduction in glomerular blood flow and glomerular filtration rate through liberation of vasoconstrictory bioactive lipids (prostaglandins, thromboxane, and platelet activating factor) and, possibly, inactivation of relaxing nitric oxide. Further studies are needed to address the role of ROS in human glomerular diseases.

Tumor necrosis factor (TNF) is a cytokine which is produced by mononuclear phagocytes upon activation by bacterial lipopolysaccharide (LPS) and various other stimuli. In immune-mediated glomerulonephritis, infiltration of glomeruli by monocytes-macrophages is associated with production of TNF. The purpose of the present experiments was to determine whether mesangial cells could also contribute to glomerular TNF synthesis. TNF activity has been determined in the culture medium of rat mesangial cells using a L-929 fibroblast lytic assay. This activity was detectable only when the cells were exposed to LPS (0.1 to 10 micrograms/ml) and for periods longer than one hour. The cytotoxic factor was identified as TNF since: (1) the lytic activity was completely inhibited by an anti-mouse TNF polyclonal antibody and was associated with suppression of lipoprotein lipase activity in adipocytes; (2) its molecular weight (110,000 daltons) corresponded to that observed for murine TNF under non-denaturing conditions; and (3) mRNA encoding TNF was expressed by mesangial cells two hours after addition of LPS. To assess the mechanisms whereby TNF production was regulated, the role of prostaglandin E2 (PGE2) was determined. LPS caused a dose-dependent increase of PGE2 synthesis by mesangial cells. Treatment by indomethacin promoted a suppression of PGE2 production together with an increase of TNF synthesis, indicating that PGE2 acted in a negative feedback manner to regulate the production of TNF. Addition of PGE2 (0.1 to 300 nM) or 8-bromo cyclic AMP (0.1 to 100 microM) induced similar dose-dependent reductions of TNF synthesis. Thus the inhibitory effect of PGE2 probably required in part cyclic AMP accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Ischemic acute renal failure is characterized by damages to the proximal straight tubule in the outer medulla. Lesions include loss of polarity, shedding into the tubule lumen, and eventually necrotic or apoptotic death of epithelial cells. It was recently shown that peroxisome proliferator-activated receptor ␤/␦ (PPAR␤/␦) increases keratinocyte survival after an inflammatory reaction. Therefore, whether PPAR␤/␦ could contribute also to the control of tubular epithelium death after renal ischemia/ reperfusion was tested. It was found that PPAR␤/␦ ؉/؊ and PPAR␤/␦ ؊/؊ mutant mice exhibited much greater kidney dysfunction and injury than wild-type counterparts after a 30-min renal ischemia followed by a 36-h reperfusion. Conversely, wild-type mice that were given the specific PPAR␤/␦ ligand L-165041 before renal ischemia were completely protected against renal dysfunction, as indicated by the lack of rise in serum creatinine and fractional excretion of Na T he proximal straight tubule in the outer medulla of the kidney is particularly susceptible to ischemia/reperfusion injury, which remains the leading cause of acute renal failure (1,2). Damages to this segment are characterized initially by the disruption of tight junctions that control both paracellular permeability and cell polarity (3,4). The loss of cell polarity is responsible for the redistribution of integrin subunits from the basolateral to the apical membrane, contributing to the shedding of cells into the tubule lumen (4). Both increase in paracellular permeability and desquamation lead to back-leakage of glomerular filtrate (5). With more sustained ischemia/reperfusion, epithelial cells of the proximal tubule undergo necrotic or apoptotic cell death (6). Epithelial cells that do not die participate in the regeneration of tubular epithelium and the restoration of renal function (2,7). They use integrins to flatten, spread, and migrate into areas denuded by exfoliation, where they dedifferentiate, proliferate, and differentiate again (8).Peroxisome proliferator-activated receptor ␤/␦ (PPAR␤/␦; called PPAR␤ hereafter) is a ligand-activated transcription factor that belongs to the nuclear hormone receptor family (9). It plays a key role in cell survival (10 -14). For example, PPAR␤ activation leads to the expression of genes that increase the resistance of keratinocytes to apoptotic death (11,13). In these cells, PPAR␤ expression is also involved in the control of cell adhesion to the extracellular matrix and migration (10). All of these properties may account for the finding that PPAR␤ expression and activation participate in skin wound repair (10).By contrast with PPAR␣ and PPAR␥, PPAR␤ is ubiquitously expressed in all nephron segments within the kidney. In particular, it is the predominant PPAR isotype in the proximal straight tubule (15). Because of this high expression, we assessed whether PPAR␤ would contribute to the survival of proximal tubular cells in a model of ischemic acute renal failure. We found that PPAR␤-deficient mice were remarkably susc...