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R J Johnson

Publications and source records attributed to R J Johnson.

At least 127 records · Page 7Linked to original sources
PubMed1997

Age-related glomerulosclerosis and interstitial fibrosis in Milan normotensive rats: a podocyte disease.

In Milan normotensive (MNS) rats glomerulosclerosis and interstitial fibrosis develop spontaneously in the absence of hypertension. Renal changes were sequentially assessed in these rats between 2 and 10 months of age. At 10 months, rats were characterized by heavy proteinuria, increased serum creatinine, focal or global glomerulosclerosis in 51 +/- 12% of the glomeruli as well as tubulointerstitial injury involving > 25% of the section area. Cell injury in podocytes (evidenced as increased expression of desmin and by electron microscopy) and interstitial fibroblasts (increased expression of alpha-smooth muscle actin) and mild glomerular hypertrophy were witnessed as early as three to four months of age and preceded glomerulosclerosis and interstitial fibrosis. Only minor evidence of mesangial cell activation (as assessed by glomerular (de novo alpha-smooth muscle actin or type I collagen expression or increased cell proliferation) was noted throughout the observation period. Later stages of the disease were characterized by glomerular and/or tubulointerstitial macrophage influx and osteopontin expression (a chemoattractant), mild accumulation of lymphocytes, platelets, fibrinogen, as well as by a progressive accumulation of various matrix proteins. Progressive renal disease in MNS rats is thus noteworthy for the relative lack of mesangial cell activation. Rather, early podocyte damage, induced by yet unknown mechanisms, may underlie the development of glomerulosclerosis and subsequent interstitial fibrosis.

Actins↗
PubMed1997

A new model of renal microvascular endothelial injury.

Although the importance of injury with consequent activation of endothelium is well-recognized in diseases affecting the glomerular endothelial cell (GEN), research on GEN injury in vivo has been hampered by the lack of adequate animal models. Here we report the establishment and characterization of a new GEN injury model in rats. This model was induced by selective renal artery perfusion with anti-GEN IgG and resulted in the severe acute renal failure with marked platelet deposition and development of a thrombotic microangiopathy involving glomeruli. Peritubular capillary endothelial cells were also damaged that was associated with severe tubular necrosis. Although the glomerular changes were severe, half of the glomeruli recovered by day 10, while interstitial changes remained throughout our observation time course. Proliferation of GEN was observed during the recovery phase. An increased expression of endothelial nitric oxide synthase in GEN was also observed, and may be an adaptive mechanism to counteract the thrombosis and ischemia. This model should be useful to investigate the pathophysiology of renal microvascular diseases and the mechanisms of GEN injury, activation and recovery in vivo.

Acute Kidney Injury↗
PubMed1997

Cyclin kinase inhibitors are increased during experimental membranous nephropathy: potential role in limiting glomerular epithelial cell proliferation in vivo.

The inadequate proliferative response of the visceral glomerular epithelial cell (GEC) following injury in vivo may contribute to the development of progressive glomerulosclerosis in many forms of glomerular disease. Cell proliferation is ultimately controlled by cell-cycle regulatory proteins, including cyclins that bind to cyclin dependent kinases (CDK), and the active complex formed is necessary for progression through the cell-cycle. By inhibiting cyclin-CDK complexes, cyclin kinase inhibitors arrest the cell-cycle and prevent proliferation. To determine the mechanisms that may be responsible for the lack of GEC proliferation in vivo, we examined GEC expression of specific cell-cycle proteins in normal rats and in the passive Heymann nephritis (PHN) model of membranous nephropathy, where the GEC are the target of complement-mediated injury. Following antibody deposition and complement activation there was a marked up-regulation in the cyclin kinase inhibitors p21 and p27 in rats with PHN. By associating with cyclin A-CDK2 complexes, p21 and p27 limited the kinase activity of CDK2. Giving bFGF to rats with PHN was associated with an increase in GEC mitosis and ploidy and a decrease in expression of p21, but not CDK2 or p27. Furthermore, apoptosis was not present in PHN, but was increased in rats given bFGF. In conclusion, this study shows that the low proliferative capacity of the GEC in vivo in response to immune injury may be due to an increase in the expression of specific cyclin kinase inhibitors. The increase in mitosis in PHN rats given bFGF may be due to a decrease in p21. Thus, changes in cell cycle regulatory proteins may regulate the response of GEC to injury and underlie the development of progressive glomerulosclerosis in diseases of the GEC.

Animals↗
PubMed1997

Hypothesis: the role of acquired tubulointerstitial disease in the pathogenesis of salt-dependent hypertension.

We present a new hypothesis to explain the development of salt-dependent hypertension in humans. We propose that hypertension has two phases: an early phase in which elevations in blood pressure (BP) are mainly episodic and are mediated by a hyperactive sympathetic nervous or renin-angiotensin system, and a second phase in which BP is persistently elevated and that is primarily mediated by an impaired ability of the kidney to excrete salt (NaCl). We propose that the transition from the first phase to the second occurs as a consequence of catecholamine-induced elevations in BP that preferentially damage regions of the kidney (juxtamedullary and medullary regions) that do not autoregulate well to changes in renal perfusion pressure. The catecholamine response is associated with both an increase in peritubular capillary pressure and a reduction in peritubular capillary plasma flow, resulting in injury to the peritubular capillaries with ischemia to the tubules and interstitium. The local injury triggers the release or activation (angiotensin II, adenosine, renal sympathetic nerves) or inhibition (nitric oxide, prostaglandins, dopamine) of vasoactive mediators that further augment ischemia and result in abnormal tubuloglomerular feedback and enhanced NaCl reabsorption. The peritubular capillary injury with rarefaction simultaneously blunts the pressure natriuresis mechanism. The combined effect of enhanced tubuloglomerular feedback and impaired pressure natriuresis results in a defect in NaCl excretion which, on the exposure to salt, results in the development of persistent hypertension. Evidence is provided to suggest that this may be the major mechanism for the development of salt-dependent hypertension, and particularly for the hypertension associated with blacks, aging and obesity. Thus, essential hypertension may be a type of acquired tubulointerstitial renal disease.

Animals↗
PubMed1997

Renal microvascular injury induced by antibody to glomerular endothelial cells is mediated by C5b-9.

We have recently developed a model of thrombotic microangiopathy with injury to the glomerular endothelial cell (GEN) induced by heterologous antibody to rat GEN. In addition to GEN injury rats developed glomerular platelet aggregation and fibrin deposition, acute renal failure, and acute tubular necrosis with interstitial inflammation. To study the role of complement in mediating this lesion, we induced the disease in normal complement PVG rats and measured the effects of generalized complement depletion with cobra venom factor (CVF) and of selective C6 deficiency using genetically C6 deficient PVG animals. Complement sufficient rats developed severe endothelial injury accompanied by platelet aggregation, fibrin deposition, decrease in endothelial cells assessed by antibody staining in the glomerulus, and macrophage infiltration. These changes were associated with marked reduction in renal function. These features were either absent or markedly diminished in complement depleted or C6 deficient rats. This demonstrates that C5b-9, the terminal product of activation of the complement cascade, plays an important role in the pathogenesis of this immune renal microvascular endothelial injury model. Thus, the complement system may play a pathogenic role in renal microvascular diseases such as thrombotic microangiopathy.

Acute Kidney Injury↗
PubMed1997

Circulating plasma cells in multiple myeloma: characterization and correlation with disease stage.

The aim of this study was to develop a flow cytometric test to quantitate low levels of circulating myeloma plasma cells, and to determine the relationship of these cells with disease stage. Cells were characterized using five-parameter flow cytometric analysis with a panel of antibodies, and results were evaluated by comparison with fluorescent consensus-primer IgH-PCR. Bone marrow myeloma plasma cells, defined by high CD38 and Syndecan-1 expression, did not express CD10, 23, 30, 34 or 45RO, and demonstrated weak expression of CD37 and CD45. 65% of patients had CD19- 56+ plasma cells, 30% CD19- 56(low), and 5% CD19+ 56+, and these two antigens discriminated myeloma from normal plasma cells, which were all CD19+ 56(low). Peripheral blood myeloma plasma cells had the same composite phenotype, but expressed significantly lower levels of CD56 and Syndecan-1, and were detected in 75% (38/51) of patients at presentation, 92% (11/12) of patients in relapse, and 40% (4/10) of stem cell harvests. Circulating plasma cells were not detectable in patients in CR (n = 9) or normals (n = 10), at a sensitivity of up to 1 in 10,000 cells. There was good correlation between the flow cytometric test and IgH-PCR results: myeloma plasma cells were detectable by flow cytometry in all PCR positive samples, and samples with no detectable myeloma plasma cells were PCR negative. Absolute numbers decreased in patients responding to treatment, remained elevated in patients with refractory disease, and increased in patients undergoing relapse. We conclude that flow cytometry can provide an effective aternative to IgH-PCR that will allow quantitative assessment of low levels of residual disease.

Adult↗
PubMed1997

Impact of super sidecut skis on the epidemiology of skiing injuries.

Concerns about whether a new type of ski--the super sidecut or carving ski--has the potential to significantly alter the incidence and type of skiing injuries have arisen in the past two years. These skis have become extremely popular during the past ski season. A case control study of skiing injuries done in a serial fashion at a Northern Vermont ski area since 1972 offers the potential to monitor changes in skiing injuries as these skis increase in popularity. Only during the last ski season have a significant number of skiers in our study (approximately 18% of all) utilized these skis. Our data reveals that skiing injuries associated with super sidecut skis occurred at a higher rate than expected in comparison to conventional skis. We also have observed that expert skiers using super sidecut skis apparently have higher than the expected incidence of ski injuries. It is hoped that in another season or two of continued study that stronger statements can be made and that the preliminary trends we have observed can be confirmed or refuted.

Athletic Injuries↗
PubMed1997

The structure of health status among Hispanic, African American, and white older adults.

Activities of daily living (ADLs), instrumental ADLs, and disability markers have traditionally been the most common indicators of functional status. The study on Asset and Health Dynamics Among the Oldest Old (AHEAD) is used to replicate a five-dimensional measurement model composed of these observable indicators among the older adult self-respondents. The items available to measure upper body disability were found wanting, but the lower body disability, and the basic, household, and advanced ADL constructs were confirmed. Analyses of the measurement model separately among subgroups of women, men, Hispanics, Mexican Americans, African Americans, and Whites found no meaningful differences. Two structural models linking the lower body disability, and the basic, household, and advanced ADL constructs to perceived health and depression were also replicated among the older adult self-respondents, as well as separately among African Americans and among Whites. These models reaffirmed the dominant role of lower body disability on the everyday activities of older adults, and on their perceived health and depression.

Activities of Daily Living↗
PubMed1997

Involvement of complement components in renal disease.

The complement system is a critical element of innate immunity whose role in renal physiology and disease is illustrated by the following observations: (1) a deficiency or inhibition of a complement regulatory protein results in renal tissue damage; (2) inhibition of complement activation (with cobra venom factor or sCR1), or in C6-deficient rats, attenuates complement-mediated tissue destruction; and (3) ongoing glomerular disease has been associated with the deposition/expression of complement proteins in glomerular or tubular structures and the excretion of C5b-9 and CD59 proteins. Complement activation by cellulosic membranes results in the production of C5a, which has now been shown to provoke most of the same inflammatory responses observed during hemodialysis. Controlling the dose of C5a given during dialysis, by controlling blood flow rates or membrane types, may have an impact on patient health. Finally, lessons learned in the xenotransplant setting suggest that complement activation can be effectively controlled to limit inflammation (with sCR1 or anti-C5 monoclonal antibodies). Recent developments in this area may lead to new therapeutic approaches to deal with the complex etiology of renal disease.

Animals↗
PubMed1997

Role of endothelin in hypertension of experimental chronic renal failure.

Surgical ablation of renal mass leads to a reduction in kidney function and commonly to the development of hypertension and chronic renal failure (CRF) in rats. The objective of this study was to determine whether endothelin (ET)-1 is involved in the maintenance of the hypertension that accompanies loss of renal mass. First, we demonstrated the antihypertensive efficacy of PD 155080, a selective, orally active ET(A) receptor antagonist, in a group of rats made hypertensive by continuous intravenous infusion of ET-1 (2.5 pmol x kg(-1) x min[-1]) for 7 days. ET-1 produced a sustained hypertension and PD 155080 (56.4 micromol/kg [25mg/kg] BID PO) normalized blood pressure (BP) during the 5 days of drug administration. In a second experiment, Sprague-Dawley rats underwent a 5/6 reduction in renal mass (RRM); 4 weeks later, PD 155080 administered for 7 days resulted in a sustained reduction in BP. Sham-operated rats also showed a slight hypotensive response to PD 155080 administration. Plasma urea nitrogen, plasma creatinine, urinary protein excretion, and creatinine clearance were not altered by PD 155080 administration in RRM or sham rats. In a third experiment, we investigated the contribution of the renin-angiotensin system to BP control in RRM rats given PD 155080. In these rats, PD 155080 reduced BP during 5 treatment days, and this antihypertensive effect was not altered by coadministration of the angiotensin-converting enzyme inhibitor enalapril in the drinking water (508 micromol/L [250 mg/L]). These results demonstrate that (1) ET-1 plays a role in established RRM hypertension through activation of the ET(A) receptor subtype, (2) lowering blood pressure with PD 155080 in RRM rats does not adversely affect renal function, and 3) the antihypertensive effect of ET(A) receptor antagonism is not opposed by the renin-angiotensin system.

Animals↗
PubMed1997

A role for P-selectin in neutrophil and platelet infiltration in immune complex glomerulonephritis.

P-selectin is one of the key early mediators of leukocyte adhesion in inflammatory conditions. This report examines the role of P-selectin in a neutrophil- and platelet-mediated model of glomerulonephritis (the concanavalin A [con A] model). The administration of neutralizing anti-P-selectin antibody (PB 1.3) reduced the platelet influx at 10 min (P < 0.05) and was associated with a 60% reduction in the neutrophil infiltrate and a 50% reduction in the number of oxidant-producing cells at 3 h within glomeruli. No effect on glomerular monocyte-macrophage accumulation was observed, and proteinuria was reduced by 20% but did not reach significance. It is concluded that P-selectin plays an important role in mediating the neutrophil and platelet accumulation in this model and likely has a role in mediating the glomerular injury.

Animals↗
PubMed1997

Overexpression of Crry protects mesangial cells from complement-mediated injury.

Crry is a membrane-associated complement regulatory protein expressed on glomerular mesangial, endothelial, and epithelial cells, which reduces C3/C5 convertase activity. This study utilized an overexpression strategy to determine the functional significance of Crry in cultured rat mesangial cells. A Crry expression vector was constructed and was tagged with a c-myc epitope that allowed transfected Crry to be distinguished from the constitutively expressed protein. In stable clones, overexpressed Crry was clearly detected immunocytochemically both by anti-c-myc and anti-Crry antibody in a membrane localization. The overexpression of Crry was also confirmed by Western blotting and immunoprecipitation. To determine if overexpression of Crry by mesangial cells confers a protective effect from complement attack, complement-mediated cell lysis assays were performed. Crry-transfected mesangial cells demonstrated complete resistance to complement-mediated cell lysis, which was reversed by neutralization of Crry with both monoclonal antibody and F(ab')2 fragments of the antibody. This study also investigated the role of Crry in protecting cells from the effects of sublytic complement attack. Overexpressed Crry suppressed antibody/complement induced production of superoxide, one of the inflammatory mediators induced by sublytic complement attack. Immunocytochemical staining confirmed a reduction in C3 and C5b-9 deposition in Crry-transfected cells. These results demonstrate directly that transfected Crry functions as a potent protector of mesangial cells against complement-mediated injury. Crry may play an important role in modulating the glomerular response to immune injury in vivo.

Animals↗
PubMed1997

Osteopontin in chronic puromycin aminonucleoside nephrosis.

Increased expression of osteopontin (OPN) associated with interstitial monocyte infiltration has been demonstrated in the early phase of a variety of experimental renal diseases. Whether these changes occur in the chronic phase of progressive glomerular disease is unknown. Chronic puromycin aminonucleoside nephrosis (PAN) was induced in 16 rats by the injection of a single bolus of PA into the internal jugular vein, which results in a triphasic disease characterized by minimal glomerular change and marked proteinuria, peaking at about 10 to 14 d and subsiding by 28 d, followed by a quiescent 4-wk period of no or minimal proteinuria and then the development of progressive focal glomerulosclerosis (FGS) and increasing proteinuria. Fifteen rats injected similarly with normal saline served as controls. At 11 d after injection, PA rats demonstrated significantly greater urinary protein excretion (P = 0.0107), cortical tubular OPN expression (P = 0.0086), and intraglomerular (P = 0.0009) and interstitial (P = 0.0212) monocyte infiltration than did the controls. At 42 d, no significant differences between the two groups with respect to the above parameters were detected. At 98 d, PA rats had FGS and showed a definite trend to increased proteinuria, cortical tubular OPN, and intraglomerular monocyte infiltration. Although the cortical interstitial monocyte count was not elevated in PA rats compared with controls, there were significantly more monocytes around OPN-positive cortical tubules than around OPN-negative ones (P = 0.0011). Cortical tubular OPN expression correlated well with urinary protein excretion (r = 0.932, P < 0.0001), cortical tubular proliferating cell nuclear antigen (r = 0.796, P < 0.0001), and intraglomerular monocyte count (r = 0.552, P = 0.0013). The results are consistent with a monocyte chemoattractant role for OPN and suggest that OPN is upregulated in the chronic phase of PAN and that this increase in expression is a result of glomerular events.

Animals↗
PubMed1997

Mobilisation and reinfusion of Philadelphia negative peripheral blood mononuclear cells in chronic myeloid leukaemia with hydroxyurea and G-CSF.

Unmanipulated autologous transplantation of marrow of peripheral blood stem cells has been performed in small numbers of patients with CML for many years. More recently there has been interest in attempting to 'purge' the autograft of clonal cells as defined by the presence of the Philadelphia chromosome or BCR-ABL rearrangement. One method by which this might be achieved in vivo has been developed in Genoa and involves the administration of high dose chemotherapy and G-CSF followed by peripheral blood stem cell collection. These collections are frequently devoid of Philadelphia positive cells and the hope is that this will enhance the effects of subsequent autograft. We have investigated the use of a less toxic regimen for this procedure using oral hydroxyurea and G-CSF. In this review we describe the background to autografting in CML and the development of strategies to mobilise Philadelphia negative cells into the peripheral blood. We go on to present an update of our data using hydroxyurea and discuss some of the practical and theoretical issues behind the procedure.

Adult↗
PubMed1997

Neutrophil fate in experimental glomerular capillary injury in the rat. Emigration exceeds in situ clearance by apoptosis.

Neutrophils (PMNs) and their toxic contents can injure glomeruli, but to date their fate in glomerulonephritis has been unknown. We studied glomerulonephritis induced in rats by formation of concanavalin A (Con A)/anti-Con A immune complexes on glomerular endothelial cells. PMN infiltration, which was almost exclusively confined to the lumen of glomerular capillaries, was transient, peaking at 4 hours, with only 9.0 +/- 4.1% (mean +/- SEM) of the maximum remaining at 24 hours. There was clear evidence of PMN apoptosis leading to phagocytosis in situ by intraluminal macrophages. However, the kinetics of leukocyte infiltration and PMN apoptosis, the preferential location at 24 hours of apoptotic PMNs within occluded capillary loops, and tracking of radiolabeled PMNs all indicated that in situ phagocytic clearance after apoptosis was the fate of a minority of PMNs, amounting to no more than one-fifth of the peak infiltrating load. Instead, the majority of infiltrating PMNs (72.9 +/- 3.1%) had emigrated from inflamed glomeruli by 24 hours, apparently returning to the circulation. We conclude that PMN emigration from inflamed glomeruli is a hitherto unrecognized mechanism for regulation of PMN-mediated glomerular injury.

Animals↗
PubMed1997

Aprotinin, an antifibrinolytic drug, attenuates bradykinin-induced permeability in conscious rats via platelets and neutrophils.

Two antifibrinolytic drugs, tranexamic acid (TXA) and aprotinin (APR), are used to improve the recovery of patients following cardiac surgery while reducing blood loss. Their mechanisms of action have yet to be fully understood. To investigate their possible mechanisms of action during cardiopulmonary bypass, we examined (i) the effects of TXA and APR on bradykinin (BK) induced vascular permeability (VP) in conscious rats, (ii) the roles of platelets and neutrophils in this reaction, and (iii) the effects of TXA or APR on BK responses in platelet- or neutrophil-depleted rats. Evans blue dye (EB) was used as the marker of extravasation. The animals were treated with antiplatelet serum for platelet depletion or with methotrexate for neutrophil depletion. In normal rats, BK increased VP in most tissues. Thrombocytopenia and neutropenia also increased basal VP. TXA had no significant effect whereas APR decreased basal VP. In the second series of experiments, APR significantly attenuated BK-induced increases in VP, whereas TXA was completely ineffective. Platelet depletion did not affect BK-induced increases of VP, except for a massive plasma exudation in the lung parenchyma. Neutrophil depletion also had no effect on BK-induced increases of VP, except for an attenuation in the duodenum. In the third and last series of experiments, TXA potentiated the effect of BK in the upper and lower bronchi of platelet-depleted rats, compared with the effects of TXA on BK in normal animals, except in the lung parenchyma, where TXA blocked the increase of VP induced by BK. APR also potentiated the effect of BK in the lower bronchi of platelet-depleted rats. Overall, the inhibitory effect of APR on the VP induced by BK in normal rats was attenuated in platelet-depleted rats. Like TXA, APR blocked the increase of VP induced by BK in the lung parenchyma of platelet-depleted rats. In neutrophil-depleted rats, TXA did not affect the permeabilizing response to BK. In those rats, the inhibitory effect of APR against BK increases of VP was attenuated. These results show that the beneficial effect of APR, but not TXA, following cardiac surgery may be attributed to the inhibition of plasma exudation mediated, in part, by BK. In addition, platelets and neutrophils do not appear to be involved in BK-mediated plasma exudation. However, both cell types are essential for the regulation of basal VP. Finally, the mechanism underlying the protective inhibitory effect of APR on BK-induced increases of VP involves, at least in part, platelets and neutrophils, since the inhibitory effect of APR is attenuated in thrombocytopenic and neutropenic rats. Both cell types are not involved in the action of TXA on VP. Therefore, maintaining platelet and neutrophil counts following cardiopulmonary bypass could enhance the protective effect of APR.

Animals↗
PubMed1997

Cytokines, growth factors and renal injury: where do we go now?

The renal response to injury is mediated by a wide variety of cytokines and growth factors. This review provides a simplified schema in which the mediators are grouped into four categories: proinflammatory cytokines, vasoactive mediators, growth factor/matrix modulating molecules, and protease/matrix proteins that modulate cell behavior. Included are examples of how each group of mediators affect renal injury. Also discussed are the problems of modulating the cytokine response, including the problems of compensation or redundancy, modulating cytokines that have multiple actions, the consequences of partial versus complete blockade of a cytokine, and modifying renal disease when the renal injury in heterogenous. Despite these concerns, the recent progress in cytokines in disease pathogenesis is very likely to lead to new treatments of kidney disease.

Animals↗