Jerrold S. Levine

Albumin is a major serum survival factor for renal tubular cells and macrophages through scavenging of ROS

We have previously shown that lysophosphatidic acid (LPA), an abundant serum lipid that binds with high affinity to albumin, is a potent survival factor for mouse proximal tubular cells and peritoneal macrophages. We show here that BSA also has potent survival activity independent of bound lipids. Delipidated BSA (dBSA) protected cells from apoptosis induced by FCS withdrawal at concentrations as low as 1% of that in FCS. dBSA did not activate phosphatidylinositol 3-kinase, implying that its survival activity occurs via a mechanism distinct from that for most cytokines. On the basis of the following evidence, we propose that dBSA inhibits apoptosis by scavenging reactive oxygen species (ROS): 1) FCS withdrawal leads to ROS accumulation that is inhibitable by dBSA; 2) during protection from apoptosis, sulfhydryl and hydroxyl groups of dBSA are oxidized; and 3) chemical blockage of free sulfhydryl groups or preoxidation of dBSA with H(2)O(2) removes its survival activity. Moreover, dBSA confers almost complete protection from cell death in a well-established model of oxidative injury (xanthine/xanthine oxidase). These results implicate albumin as a major serum survival factor. Inhibition of apoptosis by albumin occurs through at least two distinct mechanisms: carriage of LPA and scavenging of ROS.We have previously shown that lysophosphatidic acid (LPA), an abundant serum lipid that binds with high affinity to albumin, is a potent survival factor for mouse proximal tubular cells and peritoneal macrophages. We show here that BSA also has potent survival activity independent of bound lipids. Delipidated BSA (dBSA) protected cells from apoptosis induced by FCS withdrawal at concentrations as low as 1% of that in FCS. dBSA did not activate phosphatidylinositol 3-kinase, implying that its survival activity occurs via a mechanism distinct from that for most cytokines. On the basis of the following evidence, we propose that dBSA inhibits apoptosis by scavenging reactive oxygen species (ROS): 1) FCS withdrawal leads to ROS accumulation that is inhibitable by dBSA; 2) during protection from apoptosis, sulfhydryl and hydroxyl groups of dBSA are oxidized; and 3) chemical blockage of free sulfhydryl groups or preoxidation of dBSA with H2O2removes its survival activity. Moreover, dBSA confers almost complete protection from cell death in a well-established model of oxidative injury (xanthine/xanthine oxidase). These results implicate albumin as a major serum survival factor. Inhibition of apoptosis by albumin occurs through at least two distinct mechanisms: carriage of LPA and scavenging of ROS.

Phagocytosis of Apoptotic Cells by Macrophages Induces Novel Signaling Events Leading to Cytokine-Independent Survival and Inhibition of Proliferation: Activation of Akt and Inhibition of Extracellular Signal-Regulated Kinases 1 and 2

Recent evidence indicates that phagocytic clearance of apoptotic cells, initially thought to be a silent event, can modulate macrophage (Mφ) function. We show in this work that phagocytic uptake of apoptotic cells or bodies, in the absence of serum or soluble survival factors, inhibits apoptosis and maintains viability of primary cultures of murine peritoneal and bone marrow Mφ with a potency approaching that of serum-supplemented medium. Apoptotic uptake also profoundly inhibits the proliferation of bone marrow Mφ stimulated to proliferate by M-CSF. While inhibition of proliferation is an unusual property for survival factors, the combination of increased survival and decreased proliferation may aid the Mφ in its role as a scavenger during resolution of inflammation. The ability of apoptotic cells to promote survival and inhibit proliferation appears to be the result of simultaneous activation of Akt and inhibition of the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK)1 and ERK2 (ERK1/2). While several activators of the innate immune system, or danger signals, also inhibit apoptosis and proliferation, danger signals and necrotic cells differ from apoptotic cells in that they activate, rather than inhibit, ERK1/2. These signaling differences may underlie the opposing tendencies of apoptotic cells and danger signals in promoting tolerance vs immunity.

Cytokine Dysregulation Induced by Apoptotic Cells Is a Shared Characteristic of Murine Lupus

Of the multiple murine models of autoimmunity, the three most closely resembling human systemic lupus erythematosus (SLE) are the MRL/lpr, New Zealand Black/White F1, and male BXSB. Although these strains share many disease characteristics, no common cellular defect has previously been found in prediseased mice from all these strains. We show in this study that macrophages from prediseased mice of all three SLE-prone strains, as well as macrophages from mice whose genomes contribute to the development of SLE (MRL/+, New Zealand White, New Zealand Black, female BXSB, and LG/J), have an identical and profound defect in cytokine expression that is triggered by apoptotic cells. Strikingly, none of 13 nonautoimmune strains tested exhibited this defect. Given that apoptotic Ags have been increasingly recognized as the target of autoantibodies, a defect in cytokine expression that is triggered by apoptotic cells has broad potential to upset the balance between tolerance and immunity.

The Role of Urea Kinetic Modeling, TACurea, and Kt/V in Achieving Optimal Dialysis: A Critical Reappraisal

The National Cooperative Dialysis Study (NCDS) established the importance of the time-averaged concentration of blood urea nitrogen (BUN) (TACurea) as a determinant of morbidity among patients maintained on hemodialysis. Although urea is not itself toxic, it serves as a surrogate for those low-molecular weight products of protein catabolism that do contribute to uremic toxicity. The NCDS also reported an association between low protein catabolic rates (a measure of dietary protein intake) and increased morbidity, but the validity of this result has been questioned. On the basis of a retrospective re-analysis of the data, Gotch and Sargent have proposed following the normalized whole-body urea clearance, Kt/V, as a more fundamental index of the level of dialytic therapy. In this review, a comparison is made between these two measures of adequate dialysis, namely, midweek predialysis urea concentration and Kt/V. At least for the cellulosic membranes used in the NCDS, they seem to be equivalent. Furthermore, each prescription defines adequate nutrition as a dietary protein intake (DPI) of 1.0 g/kg/d. At this DPI, a time-averaged concentration of BUN of 17.9 mmol/L (50 mg/dL) (corresponding roughly to a midweek predialysis BUN of 21.4 to 28.6 mmol/L (60 to 80 mg/dL), as recommended by the NCDS, is equivalent to a Kt/V of 1.0, as recommended by Gotch and Sargent. Based on ease and accuracy of measurement, TACurea would seem the more reliable marker for monitoring the adequacy of dialysis. Extrapolation of the utility of TACurea and/or Kt/V to noncellulosic membranes remains to be established. Urea kinetic modeling constitutes a powerful mathematical tool for implementing these recommendations. Urea kinetic modeling may also be used as a means of monitoring DPI and thereby ensuring adequate nutrition.

Cytokine Dysregulation Induced by Apoptotic Cells Is a Shared Characteristic of Macrophages from Nonobese Diabetic and Systemic Lupus Erythematosus-Prone Mice

Macrophages from nonobese diabetic (NOD) mice, which spontaneously develop type I diabetes, share a defect in elicited cytokine production with macrophages from multiple diverse strains of systemic lupus erythematosus (SLE)-prone mice. We have previously shown that, in SLE-prone mice, this defect is triggered by exposure to apoptotic cells. We report in this work that macrophages from prediseased NOD mice also respond abnormally to apoptotic cells, mimicking closely the apoptotic cell-dependent abnormality that we have observed in multiple SLE-prone strains. This defect is characterized by the underexpression of IL-1β and multiple other cytokines. In the presence of apoptotic cells or FBS, elicited expression of IL-1β by NOD macrophages is markedly reduced compared with that by macrophages from control mice, including three strains of mice that develop type II (nonautoimmune) diabetes. Given the increasing role of apoptotic cells in tolerance and autoimmunity, a macrophage defect triggered by apoptotic cells has broad potential to upset the balance between tolerance and immunity. The concordance of this defect among so many diverse autoimmune-prone strains suggests that the genetic basis for this abnormality may constitute a permissive background for autoimmunity.

Profound persistent eosinophilia in a patient with spontaneous renal atheroembolic disease

We describe an elderly women who died of renal failure secondary to spontaneous renal atheroembolic disease. The sole clinical clue to this diagnosis was a profound eosinophilia up to 19,100/mm3 and a relative eosinophil count of 80%. Renal atheroembolic disease should be a prominent consideration in any patient with both renal insufficiency and peripheral eosinophilia.

A Continuous Ambulatory Peritoneal Dialysis Patient With Fungal Peritonitis

A 42-year-old black man with end-stage renal disease (ESRD) was admitted to the hospital because of cloudy peritoneal dialysate, nausea, anorexia, and abdominal pain. Eight years previously he had had advanced chronic renal failure, malignant hypertension, and bilaterally small kidneys. Aggressive management of his hypertension led to no improvement of his renal function and he started on chronic hemodialysis. A cadaver donor kidney transplant performed in 1985 was lost to chronic rejection in 1987. He subsequently began chronic ambulatory peritoneal dialysis (CAPD), using four daily exchanges of 2 liters of dialysate. He did well until 6 weeks before the present admission when an episode of bacterial peritonitis was successfully treated with appropriate antibiotics. One week later he was admitted with right lower lobe pneumonia and received intravenous antibiotics for 10 days. The respiratory infection resolved, but no etiologic agent was demonstrated. Three weeks later, he returned because of cloudy peritoneal effluent, mild abdominal pain, nausea and vomiting, and low-grade fever. His temperature was 37.0C and he had diffuse abdominal tenderness with guarding. Laboratory abnormalities included blood urea nitrogen of 73 mg/dl, serum creatinine of 17.1 mg/dl, and a peripheral white blood cell (WBC) count of 1 l,200/mm3. The peritoneal fluid contained 110 red blood cells and 2,200 WBC/mm3, with 82% neutrophils and 18% mononuclear cells. A Grams stain demonstrated budding yeast forms and pseudohyphae, later identified as Candida albicans.