Mesangial cell immune injury. Synthesis, origin, and role of eicosanoids.

The synthesis, cell origin, and physiologic role of eicosanoids were investigated in a model of mesangial cell immune injury induced by a monoclonal antibody against the rat thymocyte antigen Thy 1.1 also expressed in rat mesangial cells. A single intravenous injection of the antibody resulted in enhanced glomerular synthesis of thromboxane (Tx)B2, leukotriene (LT)B4, and 12-hydroxyeicosatetraenoic acid (HETE), whereas that of PGE2 and PGF2 alpha was either unaltered or impaired. The enhanced eicosanoid synthesis was associated with decrements in glomerular filtration rate (GFR) and renal blood flow (RBF). Complement activation mediated both the increments in TxB2, LTB4, and 12-HETE and the decrements in GFR and RBF. The decrements in GFR were abolished by the TxA2 receptor antagonist SQ-29,548. Although both neutrophiles and Ia (+) leukocytes infiltrated glomeruli, glomerular LTB4 originated mainly from the latter. Platelets entirely accounted for the enhanced 12-HETE synthesis in isolated glomeruli and to a lesser extent for that of LTB4 and TxB2. Glomerular PGE2 and PGF2 alpha originated from mesangial cells as their impaired synthesis coincided with extensive mesangial cell lysis. The observations indicate that in mesangial cell immune injury vasoactive and proinflammatory eicosanoids originate from recruited or activated Ia (+) leukocytes and platelets and may exert paracrine effects on mesangial cells.

Mesangial cell immune injury. Hemodynamic role of leukocyte- and platelet-derived eicosanoids.

The role of leukocytes and platelets and of leukocyte- and platelet-derived eicosanoids in mediating acute changes in renal and glomerular hemodynamics was assessed in a model of antibody-induced mesangial cell injury in the rat. After a single intravenous injection (6 mg/kg) of the monoclonal antibody (ER4) against the mesangial cell membrane antigen Thy 1, significant decrements in glomerular filtration rate (GFR) and renal blood flow (RBF) were observed at 1 h, and were associated with increments in glomerular LC (+) leukocyte counts and in the synthesis of thromboxane (Tx)B2, leukotriene (LT)B4, and 12-hydroxyeicosatetraenoic acid (HETE). In rats with immune leukopenia, the rise in glomerular LC (+) leukocytes and in eicosanoid synthesis were abolished and the fall in GFR and RBF after administration of ER4 were completely ameliorated. Likewise, pretreatment of rats with both a thromboxane synthase and a 5-lipoxygenase inhibitor also blocked the fall in GFR and RBF and the rise in glomerular synthesis of TxB2 and LTB4 produced by ER4 without changing glomerular LC (+) leukocyte counts. Selective inhibition of thromboxane or 5-lipoxygenase alone only partially ameliorated the decrements in GFR and RBF produced by ER4. In animals with immune thrombocytopenia, the elevated glomerular synthesis of 12-HETE and fall in RBF but not GFR was ameliorated after administration of ER4. The ER4 antibody-induced fall in GFR was mainly caused by a marked decrement in the ultrafiltration coefficient, Kf, which was dependent on TxA2 and 5-lipoxygenase products, since pretreatment of animals with a thromboxane receptor antagonist or with a 5-lipoxygenase inhibitor partially ameliorated this decrement. Structural changes such as infiltration of glomerular capillaries by leukocytes and endothelial cell damage may also have accounted for the fall in Kf. These observations indicate that in antibody-mediated mesangial cell injury, infiltrating leukocytes and platelets mediate the changes in renal hemodynamics via synthesis of thromboxane and arachidonate 5-lipoxygenation products.

Risk factors for renal allograft survival from pediatric cadaver donors: an analysis of united network for organ sharing data.

BACKGROUND: The shortage of cadaveric donors for kidney transplantation has prompted many centers to use cadaver kidneys from pediatric donors. Use of kidneys from pediatric donors has been shown to have a lower graft survival. METHODS: Recipients receiving cadaver kidneys from pediatric and adult donors between 1988 and 1995 were analyzed. The data were obtained from United Network of Organ Sharing database. The actuarial kidney transplant graft survival was estimated by the Kaplan-Meier method. A logistic regression analysis was used to identify various risk factors for 1-year graft failure. Odds ratios (OR) were estimated for various risk factors. RESULTS: Kidney transplant survival rates for donor age <18 years (n=12,838) at 1, 2, 3, 4, and 5 years were 81.5%, 76.3%, 71.3%, 66.4%, and 61.7%, respectively. The corresponding results for adult donors from age 18 to 50 years (n=35, 442) were 83.5%, 78.4%, 73.1%, 67.9%, and 62.4%, respectively, Log-rank test P<0.01. Pediatric donors were further divided into three groups according to donor age: group I (0-5 years), group II (6-11 years), and group III (12-17 years). The actuarial survival rates for 1, 3, and 5 years for group I (n=2198) were 73.6%, 63.3%, and 55.6%, respectively. The corresponding values for group II (n=2873) were 78.0%, 67.5%, and 57.8% and for group III (n=7767) were 85%, 75.0%, and 64.8%, respectively, P<0.01. Although the recipients of group I had lower graft survival, en bloc grafts (n=751) had much better 1-, 3-, and 5-year graft survival rates (76.3%, 67.7%, and 60.7%, respectively) compared with single grafts (n=1447; 72.2%, 61.1%, and 53.2%, P=0.02) from donors 0 to 5 years. Graft thrombosis as a cause of graft failure was seen in 10% of group I compared with 6% in group II and 5% in group III. In group I, lower OR were seen when an en bloc transplant was performed (0.688, P<0.01) and when donor body weight was>15 kg (0.547, P<0.01). However, OR were elevated in recipients of previous transplants (1.556, P<0.01), with prolonged cold ischemic time (1.097, P=0.03), for black recipients (1.288, P=0.03), and for recipients with body mass index> or =25 (1.286, P=0.02). Progressive increase in the donor age was associated with lower OR in group II (0.894, P<0.01). CONCLUSIONS: (1) Overall, poorer graft survival was seen in pediatric donor transplants, (2) transplant kidney survival with en bloc kidneys was better than a single kidney from donors 0-5 years, (3) progressive increase in donor age was associated with improved graft survival when the donors were 6-11 years, whereas progressive increase in donor weight was associated with improved graft survival when the donors were 0-5 years.

Polyoma virus infection after renal transplantation. Use of immunostaining as a guide to diagnosis.

BACKGROUND: Polyoma virus infection is characterized by lymphocytic interstitial infiltrate in the kidney, and it mimics acute rejection. The purpose of this study is to estimate renal allograft outcome with this infection and characterize the lymphocytic infiltrates in polyoma virus-infected renal allografts. METHODS: Patients who had polyoma virus inclusions in renal allograft biopsies were identified. Other viral inclusions were excluded by immunohistochemistry. The lymphocytic infiltrates of six cases of polyoma virus infection were compared with six cases of definite acute rejection by immunostaining for T and B cells. RESULTS: There were 10 cases of polyoma virus infections in renal transplant recipients. Immunosuppressants consisted of mycophenolate mofetil with tacrolimus in eight cases and mycophenolate mofetil with cyclosporine in two. The median time of diagnosis of polyoma virus infection after transplantation was 9.5 months, and the time to graft failure after the diagnosis was 4 months. Reduced allograft survival was seen in patients who had polyoma virus infection. Immunostaining for T and B cells revealed marked increase in the B cells (CD20) in renal allografts with polyoma virus infection of 21% (range, 5-40%) compared with 6% (range, 0-10%) in those with acute rejection (P=0.039). Reduced cytotoxic T cells (TIA-1: median, 7%; range, 2-15%) were seen in polyoma virus-infected allografts compared with 24% (range, 15-30%) in those patients who had acute rejection (P=0.0159). CONCLUSION: Irreversible graft failure is more prevalent with polyoma virus infection. Enhanced immunosuppressants with mycophenolate mofetil with tacrolimus may play a role in the development of this infection. An increase in CD20 and a decrease in cytotoxic T cells in allografts is characteristic of polyoma virus infection.

Cytokine inhibition preserves renal hemodynamic function following mesangial cell immune injury.

BACKGROUND: We assessed the effect of a cytokine inhibitor, compound SKF 86002 (a bicyclic imidazole), on changes in renal hemodynamics (renal blood flow and glomerular filtration rate) that occur acutely following immune injury of glomerular mesangial cells. METHODS: Injury was induced in Munich-Wistar rats by the administration of a monoclonal antibody against the mesangial cell membrane antigen Thy 1.1. An acute drop in renal blood flow (RBF) and glomerular filtration rate (GFR) occurred within one hour of injury. RESULTS: Pretreatment of animals with the cytokine inhibitor SKF 86002 prevented this drop. SKF 86002 had no effect on glomerular synthesis of vasoconstrictor eicosanoids. CONCLUSIONS: The observations indicate that in mesangial cell immune injury, cytokines mediate renal hemodynamic impairment.

Effect of thromboxane A2 inhibition and antagonism on prostaglandin and leukotriene synthesis in glomerular immune injury.

In glomerulonephritis there is co-activation of the arachidonic acid cyclooxygenase pathway toward synthesis of prostaglandins (PG) and thromboxane (Tx) and of lipoxypenase pathways toward synthesis of hydroxyeicosatetraenoic acids (HETEs) and leukotrienes (LTs). Cyclooxygenase inhibition with non-steroidal anti-inflammatory drugs results in enhanced glomerular LT synthesis with potentially adverse effects on the severity of the inflammation. The effect of Tx inhibition or antagonism on LT synthesis is unknown. Because TxA2 is the most abundant eicosanoid synthesized in nephritic glomeruli, and because TxA2 synthase inhibitors and receptor antagonists are now available for the treatment of glomerulonephritis, it becomes important to address this question. In this study we assessed the effect of a TxA2 synthase inhibitor, Dazmegrel, and a TxA2 receptor antagonist, SQ-29 548, on glomerular PGE2, LTB4, and 12-HETE synthesis in a model of mesangial nephritis induced in the rat by the administration of a monoclonal antibody against the Thy 1.1 antigen of rat mesangial cells. Dazmegrel, in doses sufficient to effectively block glomerular TxA2 synthesis, significantly increased 12-HETE and PGE2 synthesis without an effect on the synthesis of LTB4. SQ-29 548 had no effect on glomerular PGE2, LTB4, or 12-HETE production. Because PGE2 preserves kidney function in glomerulonephritis, and because 12-HETE inhibits 5-lipoxygenase, the enhanced PGE2 and 12-HETE production within nephritic glomeruli after TxA2 synthase inhibition may be a superior anti-inflammatory strategy when compared with TxA2 receptor antagonism.

Hemodynamic role of arachidonate 12- and 5-lipoxygenases in nephrotoxic serum nephritis.

The role of arachidonate 12- and 5-lipoxygenation eicosanoids in mediating acute changes in renal hemodynamics was assessed in nephrotoxic serum nephritis (NSN) in the rat. Following a single intravenous injection of nephrotoxic serum (NTS), significant decrements in glomerular filtration rate (GFR) and renal blood flow (RBF) occurred at one hour, and were associated with increments in glomerular polymorphonuclear leukocyte (PMN) counts and in the synthesis of thromboxane (Tx) B2, leukotriene (LT) B4 and 12-hydroxyeicosatetraenoic acid (12-HETE). Pretreatment of rats with the arachidonate 12-lipoxygenase inhibitor, baicalein, partially but significantly ameliorated the decrements in GFR and RBF, and blocked the enhanced glomerular synthesis of 12-HETE following administration of NTS. Likewise, pretreatment of rats with the arachidonate 5-lipoxygenase inhibitor, U-66858, partially ameliorated the decrements in GFR and RBF induced by NTS. Combined pretreatment of rats with baicalein and U-66858 ameliorated the decrements in GFR and RBF to an extent no different to that of U-66858 alone. In rats pretreated with the LTB4 receptor antagonist, U-75302, GFR and RBF remained depressed to levels no different than in animals which received NTS alone. These observations indicate that in NSN, the acute decrements in GFR and RBF are partially mediated by 12-HETE and arachidonate 5-lipoxygenation products. Leukotrienes other than LTB4, such as LTD4 and LTC4, are the likely candidates.

Mesangial cell immune injury: effects of thromboxane receptor antagonism.

We assessed the renal hemodynamic changes occurring acutely after glomerular mesangial cell immune injury and the effects of thromboxane receptor antagonism on these changes. A single intravenous proteinuric dose of a monoclonal antibody raised against the rat thymocyte antigen Thy 1.1 (ER4), which is also expressed in rat mesangial cells, induced acute decrements in glomerular filtration rate and in renal blood flow in male Munich-Wistar rats. One hour after administration of 4 to 6 mg/kg of ER4 antibody, glomerular filtration rate and renal blood flow decreased by 80 and 36%, respectively. These decrements were associated with significant increments in basal thromboxane B2 synthesis in isolated glomeruli and no changes in glomerular prostaglandin E2 synthesis. Pretreatment of animals with the thromboxane receptor antagonist SQ-29,548 (2 mg/kg) significantly ameliorated decrements in glomerular filtration rate and renal blood flow. Pretreatment with a structurally dissimilar thromboxane receptor antagonist, L-670,596 (3 mg/kg) had no effect. Both antagonists at the doses employed abolished the decrements in renal blood flow induced by systemic administration of the thromboxane mimetic U-46619. Whereas the SQ-29,548 antagonist had no effect on glomerular leukotriene B4 and 12-hydroxyeicosatetraenoic acid synthesis, the L-670,596 thromboxane receptor antagonist significantly inhibited glomerular synthesis of these eicosanoids in immunologically injured glomeruli. These observations indicate that in mesangial cell immune injury the protective effect of thromboxane A2 receptor antagonism on glomerular filtration rate and renal blood flow is not solely due to inhibition of the vasoconstrictor effects of thromboxane A2. An effect on the synthesis of arachidonate lipoxygenation products may also play a role.

Eicosanoid-induced growth and signaling events in rat glomerular mesangial cells.

Renal glomerular injury frequently results in proliferation of a specialized supporting cell of the glomerular capillary known as the mesangial cell. In various forms of renal injury there is enhanced glomerular synthesis of specific eicosanoids of the arachidonic cyclooxygenase and lipoxygenase pathways including prostaglandin (PG) F2 alpha, thromboxane (Tx) A2, the hydroxyeicosatetraenoic acids 12-HETE and 5-HETE, and the leukotrienes LTB4 and LTD4 and attempts have been made to link these eicosanoids with injury-induced mesangial cell growth. In this study, the growth promoting effect of these eicosanoids on glomerular mesangial cells was correlated with activation of two growth regulatory enzymes: phospholipase C (PLC) and protein kinase C (PKC). PGF2 alpha, and TxA2 endoperoxide analog U-46619, and LTD4 significantly enhanced DNA synthesis [(as assessed by [3H]thymidine (TdR) incorporation)] in relatively quiescent (0.5% serum) mesangial cells, activated PLC [as assessed by increased 1,4,5-inositol tris-phosphate (IP3) generation and diacylglycerol (DAG) synthesis], and activated PKC (as assessed by translocation of the enzyme activity from the cytosol to the membrane). The effect of PGF2 alpha on IP3 generation was not blocked by the TxA2 receptor antagonist, SQ-29,548. PGF2 alpha was the most effective eicosanoid in inducing all three events, and concentrations that enhanced TdR incorporation (1 microM) also activated PLC and PKC. In contrast, concentrations of U-46619 and LTD4 which enhanced TdR incorporation (1 microM), also activated PLC, but were insufficient to also activate PKC. Our observations indicate that the growth-promoting effect of PGF2 alpha, U-46619, and LTD4 can best be correlated with PLC activation. In addition, PGF2 alpha does not mediate PLC activation through binding to the TxA2 receptor.

Changes in glomerular thromboxane A2 receptor expression and ligand binding following immune injury.

BACKGROUND: Thromboxane (Tx) A2 is a potent vasoconstrictor eicosanoid that attains high levels within nephritic glomeruli and mediates a drop in glomerular filtration rate (GFR). In the course of nephritis, however, GFR recovers despite high intraglomerular TxA2 levels. We hypothesized that this recovery indicates a reduced responsiveness of the glomerular vasculature to TxA2, and explored whether changes in TxA2 receptor protein expression and receptor-ligand binding are underlying mechanisms. METHODS: Glomerulonephritis was induced in male Sprague-Dawley rats using an antibody raised in rabbits against rat particulate glomerular basement membrane (GBM). Changes in Tx receptor levels were assessed in protein lysates of glomeruli on days 3 and 7 after a single intravenous injection of the anti-GBM antibody. Ligand-binding studies were performed at the same time points using isolated glomeruli and the TxA2 receptor ligand [3H]-SQ-29,548. GFR was measured as the clearance of endogenous creatinine. RESULTS: There was a marked increase in Tx receptor protein in the lysates of nephritic glomeruli on days 3 and 7. In contrast, binding sites (Bmax) of [3H]-SQ-29,548 decreased, indicating that the excess receptor became either inaccessible to its ligand (sequestered) or desensitized. Daily administration of the Tx synthase inhibitor Furegrelate starting prior to injection of anti-GBM antibody prevented the decrease in [3H]-SQ-29,548 binding. Furegrelate treatment starting in an established stage of nephritis had no effect. In these animals, GFR was lower than nephritic controls not treated with Furegrelate. CONCLUSIONS: These observations indicate that in the course of glomerulonephritis, there is a marked increase in glomerular Tx receptor expression. The enhanced intraglomerular TxA2 synthesis causes either a sequestration or desensitization of its receptor. As a result, access of unbound TxA2 to efferent arterioles may become facilitated, and constriction of these arterioles may preserve GFR.

Localization of authentic thromboxane A2/prostaglandin H2 receptor in the rat kidney.

Using a polyclonal antibody against authentic thromboxane A2/prostaglandin H2 (TxA2/PGH2) receptor protein, we assessed the distribution of this receptor in the normal rat kidney by routine methods of immunofluorescence microscopy. The receptor localized both in glomeruli and in tubules. In the former, the distribution of the receptor was most prominent along the lumen of glomerular capillary loops. Parietal epithelial cells of the Bowman's capsule, podocytes and mesangial cells also demonstrated immunostainable receptor. In the tubules, the receptor localized most prominently at the base of the brush border of proximal tubules and at the luminal surface of thick ascending limbs and distal convoluted tubules. These observations point to sites that are likely to be targeted by thromboxane A2 in forms of renal injury characterized by enhanced synthesis of this eicosanoid.

Improved graft survival after renal transplantation in the United States, 1988 to 1996.

BACKGROUND: The introduction of cyclosporine has resulted in improvement in the short-term outcome of renal transplantation, but its effect on the long-term survival of kidney transplants is not known. METHODS: We analyzed the influence of demographic characteristics (age, sex, and race), transplant-related variables (living or cadaveric donor, panel-reactive antibody titer, extent of HLA matching, and cold-ischemia time), and post-transplantation variables (presence or absence of acute rejection, delayed graft function, and therapy with mycophenolate mofetil and tacrolimus) on graft survival for all 93,934 renal transplantations performed in the United States between 1988 and 1996. A regression analysis adjusted for these variables was used to estimate the risk of graft failure within the first year and more than one year after transplantation. RESULTS: From 1988 to 1996, the one-year survival rate for grafts from living donors increased from 88.8 to 93.9 percent, and the rate for cadaveric grafts increased from 75.7 to 87.7 percent. The half-life for grafts from living donors increased steadily from 12.7 to 21.6 years, and that for cadaveric grafts increased from 7.9 to 13.8 years. After censoring of data for patients who died with functioning grafts, the half-life for grafts from living donors increased from 16.9 years to 35.9 years, and that for cadaveric grafts increased from 11.0 years to 19.5 years. The average yearly reduction in the relative hazard of graft failure after one year was 4.2 percent for all recipients (P<0.001), 0.4 percent for those who had acute rejection (P=0.57), and 6.3 percent for those who did not have acute rejection (P<0.001). CONCLUSIONS: Since 1988, there has been a substantial increase in short-term and long-term survival of kidney grafts from both living and cadaveric donors.