CD36 and lipid metabolism in the evolution of atherosclerosis.

Background: CD36 is a multi-functional class B scavenger receptor, which acts as an important modulator of lipid homeostasis and immune responses. Sources of data: This review uses academic articles. Areas of agreement: CD36 is closely related to the development and progression of atherosclerosis. Areas of controversy: Both persistent up-regulation of CD36 and deficiency of CD36 increase the risk for atherosclerosis. Abnormally up-regulated CD36 promotes inflammation, foam cell formation, endothelial apoptosis, macrophage trapping and thrombosis. However, CD36 deficiency also causes dyslipidemia, subclinical inflammation and metabolic disorders, which are established risk factors for atherosclerosis. Growing points: There may be an 'optimal protective window' of CD36 expression. Areas timely for developing research: In addition to traditionally modulating protein functions using gene overexpression or deficiency, the modulation of CD36 function at post-translational levels has recently been suggested to be a potential therapeutic strategy.

Functional anatomy of the lymphocyte in immunological reactions in vitro.

The motile lymphocyte in vitro has a prominent "tail" that becomes a means of "attachment" to other cells and debris during interaction. The term "uropod" is proposed to designate this specialized cytoplasmic projection which appears totally different, anatomically and functionally, from the pseudopods. Observations of lymphoblasts during mitosis indicate that the uropod is formed immediately following mitosis at the point of final cytoplasmic connection between daughter cells, a fact that may prove significant as lymphocyte function is better understood. In the mixed leukocyte reaction the lymphocyte interacts with macrophages, cell debris, and lymphoblasts via the uropod, suggesting that stimulatory material may be acquired through this specialized appendage. Lymphoblast-lymphocyte interaction is noteworthy and implies that immunologically committed cells may be mustered through horizontal as well as vertical processes: horizontally by lymphoblast-lymphocyte interaction and vertically by mitosis of transformed lymphoblasts. The possible relevance of these in vitro observations to lymphocyte functions in vivo is discussed.

Glomerular structures and lipids in progressive renal disease.

In the last few years, remarkable advances have been made in the understanding of lipoprotein metabolism in the pathogenesis of renal disease in animal models and in vitro cell culture. Central to this work is the problem of the progression of renal disease in humans. This review recapitulates the theory (Lancet 1982; II: 1309-1312) that the progression of disease depends in part on the damage inflicted on the glomerulus by lipoproteins. The glomerular environment of high or low pressure, basement membrane damage, and destruction or damage of the mesangial and epithelial cells permits the filtration of protein, the consequence of which is hyperlipidemia. Whatever the therapeutic measures employed, if proteinuria persists, hyperlipidemia will follow. This suggest that lipoprotein toxicity may contribute to the final common path of renal damage in progressive renal disease. "Lipoprotein toxicity" in arteries is called atherosclerosis, but this term ignores the complexity of the glomerulus and the possible tubular damage that might be caused by filtered lipoprotein. It is clear there is insufficient knowledge of the metabolism of the damaged kidney to confidently attribute the pathology of progression of disease to any single process.

In vitro cyclosporine toxicity. The effect of verapamil.

The epithelial cell line LLC-PK1, which expresses many proximal tubular characteristics, was used to investigate the relationship between calcium, the calcium channel blocker verapamil, and cyclosporine toxicity. The LLC-PK1 cells took up cyclosporine when this was added in a concentration of 2 micrograms/ml, and this uptake was maximal at 30 min (112 +/- 3 ng cyclosporine/mg cell protein). At 12 micrograms/ml it inhibited the sodium glucose cotransporter, as assessed by phlorizin-inhibitable 14C-alpha-methyl glucopyranoside (alpha-MG) uptake (control 37.2 +/- 6.3, 12 micrograms/ml 21.2 +/- 1.1 mumol/hr/mg protein). Cyclosporine at 2 micrograms/ml did not affect cell growth after 5 days (control 945 +/- 60 micrograms cell protein per 25 cm2 flask, 2 micrograms/ml cyclosporine/ml 1046 +/- 32 micrograms protein/flask), even in the presence of 7.6 mM ionized calcium (862 +/- 37 micrograms protein/flask). Cyclosporine at 12 micrograms/ml inhibited cell growth (286 +/- 27 micrograms protein/flask), and raising the ambient ionized calcium concentration to 7.6 mM reduced cell growth further (91 +/- 6 micrograms protein/flask). Cyclosporine at concentrations of 2 and 12 micrograms/ml produced increasing cell vacuolation, as seen in vivo. Short-term uptake of 2 micrograms/ml cyclosporine could be inhibited by 1.0 mM and 0.5 mM verapamil (49 +/- 9.5 and 71 +/- 6.4 ng cyclosporine/mg cell protein, respectively, at 30 min). However, in the presence of 2 micrograms/ml cyclosporine 0.1 mM verapamil was toxic to the cells grown over five days (44 +/- 5 micrograms protein/flask). At 0.01 mM verapamil was not toxic to cell growth (921 +/- 29 micrograms protein/flask), but raising the medium calcium to 7.6 mM reduced cell growth (652 +/- 96 micrograms/ml). Inhibition of cyclosporine uptake did not occur with 0.01 mm verapamil (control 145.6 +/- 12.3 vs. 0.01 mM verapamil 150.4 +/- 3.8 ng cyclosporine/mg cell protein). The LLC-PK1 cell line represents a good in vitro model for cyclosporine renal tubular toxicity, as the in vivo observation of glycosuria and proximal tubular cell vacuolation in cyclosporine nephrotoxicity can be reproduced. In vitro this is shown to be associated with inhibition of sodium-dependent glucose cotransport. Verapamil inhibited cyclosporine uptake, but only at concentrations that were toxic to the cells. Verapamil potentiated rather than reduced the increased cyclosporine toxicity produced by increasing the medium calcium concentration. The suggested protective effect of verapamil against cyclosporine nephrotoxicity is therefore unlikely to be due to inhibition of cyclosporine uptake or of calcium entry into proximal tubular cells.

The enhancing and sensitizing effects of donor blood components, including dendritic cells, in a rat renal allograft model.

In the DA-to-Lewis renal allograft model, donor whole blood enhanced renal allograft survival (14.5 +/- 7.6 days versus 6.9 +/- 0.6 days in controls [P less than 0.01]). The effect of individual cell components given in numbers equivalent to those present in the enhancing volumes of donor whole blood was studied. Immunization with donor red cells alone produced greater enhancement than that produced by whole blood (36.14 +/- 19.5 days [P less than 0.01]). B lymphocytes also enhanced allograft survival (16.0 +/- 3.9 days [P less than 0.01]). Although slight enhancement was observed with platelets (8.5 +/- 0.6 days) and 10(5) dendritic cells (8.4 +/- 0.5 days), in terms of allograft function dendritic cell immunization produced evidence of dose-dependent accelerated rejection. A similar finding was obtained with donor T cell immunization. Donor plasma had no effect. We conclude that, although donor blood has an overall enhancing effect on renal allograft survival in this model, the sensitizing and enhancing effects can be ascribed to individual types of cells.

Lipiduria in renal disease.

This article reviews the published data on lipiduria in both health and disease. Small amounts of lipid appear in the urine under normal circumstances but, in the nephrotic syndrome in humans, there is also a considerable amount of high-density lipoprotein in the urine as well as smaller amounts of other lipoproteins. Potential tubular re-uptake mechanisms for lipoproteins have been demonstrated in both animal and cell-culture models. In humans, there is no direct evidence for these specific re-uptake mechanisms--it is only through specific staining of renal biopsies for apolipoproteins that the presence of such mechanisms in intracellular vesicular structures is suggested. It is possible that lipoprotein filtration and re-uptake by the tubule are important mechanisms in tubular injury.

Glycosylated haemoglobin in chronic renal failure and after renal transplantation.

Haemoglobin A1 (HbA1) was determined by ion-exchange chromatography in 37 normoglycaemic patients with chronic renal failure (CRF) and 26 with successful renal transplants. Blood glucose concentrations in patients with CRF were similar to those in controls, and there was a significant correlation between fasting blood glucose concentration and HbA1 in these groups. HbA1 in patients with CRF was, however, significantly lower than that in control subjects. Concentrations of HbA1 in patients on haemodialysis, peritoneal dialysis, and those with steady state CRF prior to dialysis were not significantly different from each other. Whereas patients with successful renal transplants of greater than 3 months' duration had HbA1 concentrations indistinguishable from controls, HbA1 in patients with transplants of shorter duration were significantly lower. These observations are suggestive of a shortened erythrocyte survival in CRF per se. Furthermore, these results indicate: (a) the inadequacy of HbA1 in monitoring the quality of diabetic control in patients with CRF, and (b) the absence of a specific effect of dialysis on HbA1, and the restoration to normal HbA1 after successful renal transplantation.

Gastric function and histology in chronic renal failure.

Gastric function and histology were investigated in 24 patients with untreated chronic renal failure. At endoscopy nine patients had oesophagitis, 12 patients were considered to have gastritis, and the duodenum appeared inflamed in 20 patients. Endoscopic biopsies were taken at standard sites in the stomach and duodenum; gastritis was found in all patients, and 17 patients had duodenitis. Stimulated acid secretion was impaired in seven out of 20 patients and acid hypersecretion was found in a further two patients. Pepsin output correlated well with acid output in these patients. Fasting serum gastrin levels were elevated in 12 of the 19 patients tested. Patients with atrophic gastritis had low acid outputs and hypergastrinaemia, and when extensive gastritis was present, the patients tended to have more severe renal failure and hyposecretion of acid. Three patients were studied again after regular haemodialysis or renal transplantation and were found to show marked endoscopic and histological improvement.

Heterogeneity of HLA-DR+ cells in normal human kidney. Immunohistological and cytochemical characterisation of discrete cell populations.

Biopsies of normal kidneys taken at time of transplantation were studied using a variety of immunofluorescent and cytochemical techniques. A heterogeneous population of HLA-DR+ cells was found, mainly confined to the intertubular interstitium. The majority of these cells (80%) were positive when stained with a rabbit anti-factor VIII antiserum suggesting that they were endothelial cells. A minority however (20%) were factor VIII- but were positively stained with FMC17, a monoclonal antibody (McAb) directed against human monocyte/macrophage antigens. Positive staining of this subpopulation was also noted with RFD1, a McAb which reacts with an antigen on human interdigitating cells (ID cells). Cytochemical reactions revealed that these cells contain adenosine triphosphatase (ATPase) and acid phosphatase (ACP) and thus do not conform to the phenotype of tissue histiocytes. The phenotype of this latter population is identical with that of the ID cells found in tonsil, thymus and spleen and it is suggested that they play a major role in initiating the process of renal allograft rejection.

Plasma histamine in patients with chronic renal failure and nephrotic syndrome.

Plasma histamine concentrations were measured using a commercially available monoclonal antibody radioimmunoassay in 38 patients with nephrotic syndrome, end stage renal failure, those receiving haemodialysis, and those receiving continuous ambulatory peritoneal dialysis to determine whether histamine may mediate damage to glomerular capillaries and arterial endothelium. Plasma histamine concentrations were significantly increased in all four patient groups when compared with those of controls and were the highest in two patients with pruritus. Raised plasma histamine concentrations in such patients are consistent with the hypothesis that histamine may contribute to the damage to glomerular capillaries and to arterial endothelium. These effects may be relevant to the pathogenesis of glomerular disease and atherosclerosis. Histamine may also contribute to the pathogenesis of pruritus in patients with chronic renal failure.

Lipids and progressive kidney disease.

The nephrotic syndrome comprises proteinuria, oedema, albuminuria, hypoalbuminaemia, and hyperlipidaemia. Some of its manifestations are present throughout the course of progressive renal disease. Hyperlipidaemia is one of the most dramatic of the clinical manifestations of the syndrome, but has not been seen as relevant to the progression of renal disease. Recently, however, increasing interest has been shown in the lipid abnormalities of patients with persistent proteinuria, largely as a result of experimental data which have emphasised the connection between progressive disease and hyperlipidaemia in animal models. This review considers some aspects of the metabolic background against which the pathological changes in animal models of nephrotic syndrome take place. Attention is drawn to analogies between glomerular disease and atherosclerosis. Lack of information on the value of long-term lipid lowering therapy in patients with proteinuria, hyperlipidaemia, and progressive renal disease emphasises the need for long-term studies of lipid-lowering therapy in these individuals. A conceptual framework for understanding the role of lipids is discussed in relation to the underlying disease processes and possible therapeutic approaches in man.

Lipopheresis in the nephrotic syndrome.

BACKGROUND: Experimental models have established a role for lipoproteins in the pathogenesis of progressive renal failure. However, conventional treatment rarely normalizes the high serum cholesterol of the nephrotic syndrome. The removal of low-density lipoprotein by lipopheresis is discussed. METHODS: Lipopheresis may be beneficial in nephrotic patients with focal segmental glomerulosclerosis. The authors studied the long-term effects of low-density lipoprotein cholesterol (LDL-C) removal using the Kaneka Liposorber system, which binds LDL-C to dextran sulfate in a controlled trial in 20 nephrotic patients with different renal diseases. RESULTS: A 21-month clamp of plasma total cholesterol at 6.0 mmol/liter or below was significantly lower than controls (chi 2 = 84.3, P < 0.001), followed 12 aphereses over 6 to 12 weeks in all but three apheresed patients. 1/Cr slopes were unchanged when the 50-day average period of lipopheresis treatments was excluded from analysis. Proteinuria was not reduced, but serum albumin tended to rise (NS). Fibrinogen fell by 29.8%; high-density lipoprotein, apoA1, and Lp(a) were unchanged. Two apheresed patients had a prolonged remission with a reduction of proteinuria to less than 250 mg/24 hr. The reasons for prolonged reduction of total cholesterol include depletion of tissue cholesterol, an improved fractional catabolic rate of very low density lipoprotein (VLDL), increased hepatocyte LDL turnover, and the maintenance of statin therapy. CONCLUSION: Lipopheresis is a safe and effective method for the control of LDL in nephrotic syndrome. Early clamping of total cholesterol in the normal range resulted in a prolonged and significant reduction of LDL compared with controls.

Lysophosphatidylcholine induces platelet-derived growth factor gene expression in a human mesangial cell line.

BACKGROUND: Oxidized low-density lipoprotein (oxLDL) has been considered important in the pathogenesis of progressive renal injury. Lysophosphatidylcholine (lysoPC) is a major phospholipid component of oxLDL. On the other hand, platelet-derived growth factor (PDGF) has also been implicated in proliferative disease of the kidney. This study investigated the difference in the potential of PC and lysoPC to induce DNA synthesis and PDGF gene expression in a human glomerular mesangial cell line (HMCL). METHODS: DNA synthesis in HMCL was measured by [3H] thymidine incorporation. The mRNA expression levels of the PDGF A chain and B chain genes were measured using reverse transcription-polymerase chain reaction. RESULTS: LysoPC treatment up-regulated the [3H] thymidine incorporation level in a dose-dependent fashion. The [3H] thymidine incorporation level in HMCL coincubated with lysoPC started to increase after 4 hours of treatment, peaked at 24 hours, and decreased thereafter. The level in HMCL incubated with 100 microM of lysoPC (palmitoyl or stearoyl) increased to 7- or 10-fold of the control at peak time, respectively. However, PC treatment did not increase [3H] thymidine incorporation in HMCL. PC treatment did not induce mRNA expression of either PDGF A or B chain genes. LysoPC did not induce PDGF A chain mRNA expression either. The only B chain mRNA expression was induced by lysoPC. The mRNA expression level in HMCL treated with 50 microM lysoPC for two hours increased to 1.6-fold that of the control. CONCLUSION: LysoPC may induce DNA synthesis in a mesangial cell through the induction of PDGF BB as an autocrine and paracrine growth factor.

Human mesangial cells express inducible macrophage scavenger receptor: an Ap-1 and ets mediated response.

BACKGROUND: Type A scavenger (SR) mediate the uptake of modified low-density lipoproteins by macrophages. The accumulation of lipid via this process is thought to lead to foam cell formation in atherosclerotic plaques. Human mesangial cells (HMC), which can be converted to foam cells in vivo, have not previously been shown to express SR in normal culture. We investigated whether or not there was an inducible form of SR in a human mesangial cell line (HMCL). METHODS: SR activity was analyzed by cellular uptake of fluorescently labeled acetylated low-density lipoprotein using a flow cytometer. SR mRNA expression was examined using RT-PCR followed by Southern blotting. To investigate the molecular mechanism of SR expression, several reporter gene constructs were designed. The first contained a full SR promoter, the second a part of the SR promoter that has both activated protein-1 (AP-1) and ets transcriptional factor binding sites. Other constructs were identical to the second except they contained either AP-1 or ets motif mutations. RESULTS: Phorbol 12-myristate 13-acetate (PMA) increased both the percentage of SR positive cells and SR mean fluorescence intensity. PMA also increased SR mRNA and promoter activity in a time and dose responsive manner. Function analysis showed that both AP-1 and ets motifs were specific response elements to PMA stimulation in HMCL. CONCLUSIONS: The present study suggests that the combination of interaction between AP-1 and ets transcriptional factors may mediate the inducible expression of the SR gene in HMCL, which may contribute to foam cell formation.

Calcineurin inhibitors enhance low-density lipoprotein oxidation in transplant patients.

BACKGROUND: Our objective was to assess the pro-oxidant status of neoral and tacrolimus in renal transplant patients and monitor the protection provided by vitamin C and vitamin E in normalizing low density lipoprotein (LDL) oxidation lag time of tacrolimus-treated patients. METHODS: Plasma LDL was isolated by density gradient ultracentrifugation from renal transplant patients receiving neoral, tacrolimus and tacrolimus with vitamin C and vitamin E. Oxidation was initiated by the addition of CuCl2 at 37 degrees C and monitored at 234 nm over 480 minutes and oxidation lag time was computed. Total antioxidant capacity of serum was measured using the enhanced chemiluminescent method. RESULTS: LDL from tacrolimus-treated patients had significantly lower oxidation lag time and serum antioxidant activity in comparison with neoral-treated patients, and this was particularly significant during the first four months after transplantation. Vitamin C and E supplementation in tacrolimus treated patients provided protection against oxidation and normalized their oxidation lag time. CONCLUSION: Calcineurin-inhibiting drugs, CsA and tacrolimus, have pro-oxidant activity and they increase the susceptibility of LDL to oxidation. Neoral formulation is fortified with DL-alpha tocopherol and therefore provides protection against oxidation. The present study clearly demonstrates the benefit of giving vitamin C and E supplements to patients taking tacrolimus and this seems to be particularly important during the early period after transplantation.

Rejection encephalopathy. An acute neurological syndrome complicating renal transplantation.

Fifteen episodes of encephalopathy have been studied in 13 renal transplant recipients. All episodes of encephalopathy occurred during an acute rejection crisis. Clinical and biochemical features were recorded during rejection crises associated with encephalopathy and in an equal number of uncomplicated rejection episodes in the same patients. Encephalopathy was related to the severity of the rejection crisis and not to other features such as blood pressure, fever, steroid therapy or plasma electrolytes. The definition of the syndrome of rejection encephalopathy and its relation to the severity of the rejection has important therapeutic implications. Steroid therapy should not be withdrawn or reduced because of acute neurological features. Control of hypertension, fluid overload and electrolyte imbalance, in addition to treatment of the rejection episode, are necessary to reverse the encephalopathy. The prognosis of this syndrome is excellent with no long-term sequelae.

Plasma hydroxyproline fractions in patients with dialysis osteodystrophy.

Plasma hydroxyproline fractions were measured in 17 normal subjects and in 54 patients on maintenance haemodialysis therapy (MHT) with various degrees of dialysis osteodystrophy. On the basis of both radiological and histological findings these patients were divided into three groups: radiologically normal, histologically normal and those with osteitis fibrosa. The mean total plasma hydroxyproline concentrations were significantly elevated in all groups of MHT patients. However, these increases were mainly due to peptide-bound and free hydroxyproline fractions. The highest values for these two fractions were found in patients with osteitis fibrosa. The free to peptide-bound hydroxyproline ratio was not significantly altered in the majority of patients on dialysis; the mean ratio was significantly lower in patients with osteitis fibrosa when compared with patients with no histological evidence of bone disease. This finding would suggest that there is no inhibition of hydroxyproline catabolism in patients on haemodialysis and the measurements of both free and peptide-bound hydroxyproline were equally sensitive in identifying patients with osteitis fibrosa.

Differential ability of cells to promote oxidation of low density lipoproteins in vitro.

Atherosclerosis and focal segmental glomerulosclerosis share some common histological features and it is speculated that they result from similar pathobiological mechanisms. There is strong evidence that oxidation of low density lipoprotein (LDL) may be an initiating event in atherogenesis and that oxidised LDL may also be involved in the glomerulosclerotic process. In vitro studies have demonstrated that cells present in the arterial intima and kidney-derived cells promote LDL oxidation. The aim of this study was to compare LDL oxidation by kidney-derived human mesangial cells and proximal tubular cells, with human umbilical vein endothelial cells and the human monocyte cell line THP-1. We used the thiobarbituric acid assay and agarose gel electrophoresis to measure the extent of LDL oxidation. Our results demonstrate that all of the cell types used had the ability to oxidise LDL significantly more than cell-free controls and that endothelial cells induced the highest degree of oxidative modification of LDL under our experimental conditions.

The response to 1,25-dihydroxycholecalciferol and to dihydrotachysterol in adult-onset hypophosphataemic osteomalacia.

The biochemical changes observed in a patient with adult-onset hypophosphataemic osteomalacia after three weeks treatment with 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) followed by dihydrotachysterol (DHT) are reported. The treatment with 1,25-(OH)2D3 resulted in restoration of intestinal phosphate absorption to normal with a small rise in plasma phosphate concentration; there was no significant change in tubular reabsorption of phosphate. The tubular reabsorption of bicarbonate, which was initially low, returned almost into the normal range with normalisation of plasma bicarbonate concentration. Aminoaciduria decreased. There were no changes in plasma or urinary calcium but immunoreactive parathyroid hormone (i-PTH) which was initially elevated fell but still remained above the normal range. These changes were maintained after replacing the 1,25-(OH)2D3 treatment with dihydrotachysterol (DHT).

Fat clearance before and after heparin in chronic renal failure--haemodialysis reduces post-heparin fractional clearance rates of intralipid.

The effect of heparin on the kinetics of fat removal was studied in 15 subjects and it became apparent that the fat tolerance test could be performed after the administration of heparin. Therefore, fractional clearance rates of Intralipid were determined before and after heparin in three groups of patients: 18 in chronic renal failure, 11 on peritoneal dialysis and 17 on haemodialysis. Patients on peritoneal dialysis and on haemodialysis had similar serum triglyceride concentrations and comparable fractional clearance rates of Intralipid before heparin was given. However, the latter had significantly smaller increases in fractional rates of Intralipid clearance after the administration of heparin. Either gradual diminution of releasable releasable enzymes by regular heparinisation or activator concentrations becoming rate-limiting could be responsible for the low post-heparin fractional clearance rates observed in haemodialysis patients.