Lipid nephrotoxicity in chronic progressive glomerular and tubulo-interstitial disease

It is hypothesised that chronic progressive kidney disease may be mediated by abnormalities of lipid metabolism. A series of self-perpetuating secondary events follows an initial glomerular injury. Increased glomerular basement membrane permeability leads to loss of lipoprotein lipase activators, resulting in hyperlipidaemia. Circulating low-density lipoprotein binds with glycosaminoglycans in the glomerular basement membrane and increases its permeability. Filtered lipoprotein accumulates in mesangial cells and stimulates them to proliferate and produce excess basement membrane material. The proximal tubular cells metabolise some of the filtered lipoprotein and the remainder are altered on passage down the nephron. Luminal apoprotein precipitates, initiating or aggravating tubulo-interstitial disease, if the intraluminal pH is close to the isoelectric point of the apoprotein. The hypothesis offers new approaches to the study of chronic progressive kidney disease by proposing a major pathogenetic role for lipid abnormalities.

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.

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.

Cyclosporine A enhances platelet aggregation

In view of the reported increase in thromboembolic episodes following cyclosporine A (CyA) therapy, the effect of this drug on platelet aggregation and thromboxane A2 release was investigated. The addition of CyA, at therapeutic concentrations to platelet rich plasma from normal subjects in vitro was found to increase aggregation in response to adrenaline, collagen and ADP. Ingestion of CyA by healthy volunteers was also associated with enhanced platelet aggregation. The CyA-mediated enhancement of aggregation was further enhanced by the addition in vitro of therapeutic concentrations of heparin. Platelets from renal allograft recipients treated with CyA also showed hyperaggregability and increased thromboxane A2 release, which were most marked at "peak" plasma CyA concentration and less so at "trough" concentrations. Platelet hyperaggregability in renal allograft patients on long-term CyA therapy tended to revert towards normal following the replacement of CyA with azathioprine. Hypertensive patients with renal allografts on nifedipine therapy had normal platelet function and thromboxane release in spite of CyA therapy. These observations suggest that CyA-mediated platelet activation may contribute to the pathogenesis of the thromboembolic phenomena associated with the use of this drug. The increased release of thromboxane A2 (a vasoconstrictor) may also play a role in mediating CyA-related nephrotoxicity.

Dysregulation of LDL receptor under the influence of inflammatory cytokines: a new pathway for foam cell formation

BACKGROUND

Lipid-mediated renal injury is an important component of glomerulosclerosis and its similarity to atherosclerosis is well described. This study focused on the relationship between lipid-mediated injury and inflammation by examining the role of inflammatory cytokines in the regulation of human mesangial cell low-density lipoprotein (LDL) receptors.

METHODS

A human mesangial cell line (HMCL) was used to study the effects of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) on the regulation of LDL receptor mRNA and protein in the presence of a high concentration of native LDL (250 microg/mL).

RESULTS

Native LDL caused foam cell formation in HMCL in the presence of antioxidants, TNF-alpha and IL-1beta. Both cytokines overrode LDL receptor suppression induced by a high concentration of LDL and increased LDL uptake by enhancing receptor expression. These cytokines also caused increased expression of SCAP [sterol responsive element binding protein (SREBP) cleavage activation protein], and an increase in the nuclear translocation of SREBP, which induces LDL receptor expression.

CONCLUSION

These observations demonstrate that inflammatory cytokines can modify cholesterol-mediated LDL receptor regulation in mesangial cells, permitting unregulated intracellular accumulation of unmodified LDL and causing foam cell formation. These findings suggest that inflammatory cytokines contribute to lipid-mediated renal damage, and also may have wider implications for the study of inflammation in the atherosclerotic process.

Pathogenic roles of post-heparin lipases in lipid abnormalities in hemodialysis patients

The relative roles of hepatic lipase and lipoprotein lipase in the pathogenesis of uremic lipid abnormalities were studied in 92 hemodialysis patients. Fasting serum cholesterol, triglyceride, and HDL-cholesterol concentrations were measured. Plasma lipoprotein electrophoretic patterns were determined in all patients. Hepatic lipase and lipoprotein lipase activities were selectively measured in post-heparin plasma in 59 patients. Hemodialysis patients had higher serum triglyceride and lower HDL-cholesterol concentrations than did their age and sex-matched control subjects. Both hepatic and lipoprotein lipase activities were reduced in hemodialysis patients. An inverse relation between lipoprotein lipase activities and serum triglyceride concentrations emerged. Lipoprotein lipase activities correlated with in vivo post-heparin fractional clearance rates of Intralipid. A positive correlation between lipoprotein lipase activities and HDL-cholesterol concentrations probably reflected impaired catabolism of triglyceride-rich lipoproteins being responsible for the low HDL-cholesterol concentrations. Hemodialysis patients (41.3%) had an abnormal lipoprotein (the 'mid-band'). While hepatic lipase activities did not correlate with any parameters of lipid metabolism, patients with 'low' hepatic lipase activities had a significantly higher prevalence of 'mid-bands' than did those with 'normal' activities. No evidence was developed to prove that the 'mid-band' lipoproteins were remnant particles.

Selective effect of low protein diets in chronic renal diseases

It has recently been established that the rate of progression of chronic renal failure in man can be slowed by restricting dietary protein. Consequently, the short term and long term effects of a low protein diet on the course of different chronic nephropathies were studied in an attempt to delineate the factors that determine the response to such a diet. When a low protein diet was given for six months renal function improved significantly in nine patients with chronic tubulointerstitial nephritis (p less than 0.025); the diet had a marginally beneficial effect in 12 patients with chronic glomerulonephritis (p less than 0.05) and no effect in nine with hypertensive nephrosclerosis. The heterogeneous functional response in the patients with chronic glomerulonephritis correlated closely with the effect of the diet on these patients' proteinuria (r = 0.76, p less than 0.01). In a short term study (four weeks) of 12 patients with chronic renal failure changes in renal plasma flow were proportional to dietary protein intake. Renal vascular resistance fell during a high protein diet and increased when dietary protein was restricted. The changes in renal plasma flow during the low protein diet correlated well with the patients' long term functional response to the diet (r = 0.76, p less than 0.01). It is concluded that the response to a low protein diet in chronic renal failure is determined, firstly, by the nature of the underlying nephropathy, with maximal benefit being observed in non-glomerular disorders; secondly, by the effect of the diet on the proteinuria in chronic glomerulonephritis; and, thirdly, by the haemodynamic response to the diet, with patients with a reactive renal vascular bed improving with a low protein diet.

Influence of HLA matching and blood-transfusion on outcome of 502 London Transplant Group renal-graft recipients

The outcome of 502 cadaver kidney transplants has been followed for up to six years; these grafts were arranged through the Tissue Immunology Unit of the London Hospital Medical College, the coordinating centre of the London Transplant Group. An analysis of HLA (A and B) recepient-donor matching revealed, as in previous analyses, clear differences (now highly significant) between the best as compared with the lesser matched recipients. A quarter of the patients (group 4 and 3a) had a superior outcome 20-30% greater than poorly matched (2 or less group) which constituted 53% of individuals. The results in the 3b group (28% of patients) were intermediate 10-15% better than the "2 or less antigens in common" group. A small number of recipients mostly 4 or 3 matched who were retrospectively HLA-D matched showed an even better graft survival. The effect of blood-transfusion before transplantation was studied and found to improve the outlook especially in the best-matched groups. No difference was apparent between those receiving less or more than ten units except in a group of patients with cytotoxic antibodies and/or retransplants. This "immunocompetent-presensitised" group had the best outcome provided these recipients had few transfusions and were subsequently well matched. These findings emphasise the continued need for successful collaborative associations, so that improved matching can be achieved which if universally applied would ensure better graft survival for a large number of patients in renal failure.

Simvastatin therapy for hypercholesterolemic patients with nephrotic syndrome or significant proteinuria

Experimental evidence suggests that lipid lowering therapy could slow the progression of renal disease in humans. We have conducted a double-blind, placebo controlled trial of the HMG CoA reductase inhibitor simvastatin in patients with the nephrotic syndrome or significant proteinuria (> 1 g/day) and hypercholesterolemia (> or = 6.5 mmol/liter). Patients were placed on a lipid lowering diet for at least 10 weeks before randomization. After a four-week placebo run-in, 30 adults were randomized to simvastatin or placebo therapy (10 mg/day, increasing to 20 to 40 mg/day as required) for 24 weeks. There were seven dropouts, none of whom were "definitely" related to drug therapy. Total and LDL cholesterol levels fell by a mean of 33 and 31%, respectively, in simvastatin treated patients, compared with only 5 and 1% in patients on placebo (P < 0.001, P = 0.002, respectively). Apolipoprotein B100 levels fell by a mean of 31% in the simvastatin group but rose 0.3% in the placebo group (P = 0.014). There were no significant changes in HDL levels. There were no significant differences between the groups in their urine protein levels, their rise in plasma creatinine, or decline in plasma inulin clearance. Simvastatin is a safe, effective therapy for hypercholesterolemia in proteinuric states. A much larger trial is needed to show if potent lipid-lowering therapy slows progression of hypercholesterolemic proteinuric diseases.

Cancer in patients receiving dialysis

The incidence of cancer and related mortality was studied in 1651 patients from six dialysis centres in England over 10 years. The only type of cancer for which there was a significant excess was non-Hodgkin's lymphoma (four cases observed against an expected incidence of 0.15 (p < 0.001); three deaths against an expected 0.1 (p < 0.001)). This excess could not be attributed to either subsequent transplantation or treatment with immunosuppressive drugs. Since immunodepression is a feature of chronic renal failure, these observations together with those on patints treated with immunosuppressive drugs suggest that immunosuppression favours the development of non-Hodgkin's lymphoma. Studies in which it is concluded that patients receiving dialysis show an excess of other types of cancer have certain shortcomings; the unusual opportunities for detecting cancer in such patients may account for some of the reported excess.

Serum ferritin assay and iron status in chronic renal failure and haemodialysis

Forty-four patients with chronic renal failure on haemodialysis for four months to eight years were studied. All recieved intravenous iron dextran 100 mg on alternate weeks. Serum ferritin concentrations correlated well with body iron stores estimated by grading the bone marrow stainable iron. Altogether 34 patients showed increased bone marrow iron stores and serum ferritin concentrations greater than controls; four patients showed absence of iron in the marrow, and three of these had subnormal serum ferritin concentrations. Serum ferritin assay represents the best method of repeatedly monitoring the exact amount of iron therapy needed by patients with chronic renal failure, particularly those on regular haemodialysis.

Three years' experience of continuous ambulatory peritoneal dialysis

Patients on continuous ambulatory peritoneal dialysis (CAPD) were studied for three years. 29 of them who had been on CAPD for six months or more were compared with patients on intermittent peritoneal dialysis (IPD) and on haemodialysis (HD). CAPD patients had significantly higher levels of HDL-cholesterol than HD patients. Urea, potassium, phosphate, and urate levels were significantly lower, and haemoglobin levels significantly higher, than in the IPD and HD groups. 43 CAPD patients studied had a peritonitis rate of 2.22 episodes per patient-year. CAPD offers an alternative form of dialysis to those unsuitable for HD, but until peritonitis rates can be reduced CAPD cannot rival HD as a long-term treatment.

Evolution of bone disease over 10 years in 135 patients with terminal renal failure

An objective radiographic study of erosions, fractures, and periarticular and vascular calcification was made in a series of 135 patients over 10 years of maintenance haemodialysis therapy. The four lesions progressed at different rates, consistent with variation in the response of tissues to a changing biochemical milieu and deficiency in vitamin D metabolites. The half time for development of individual radiographic signs was 3.4 years for vascular calcification, 9 years for fractures, 16 years for periarticular calcification, and 22.9 years for erosions. Calcification of the dorsalis pedis artery seen as a developing ring or tube was an early and valuable sign of disturbed calcium metabolism. In these patients renal osteodystrophy is a chronic condition with a prolonged time course.

Human mesangial cells express inducible macrophage scavenger receptor

BACKGROUND

Type A scavenger receptors (Scr) mediate the uptake of modified low-density lipoproteins by macrophages. The accumulation of lipids via this process is thought to lead to foam cell formation in atherosclerotic plaques. Human mesangial cells (HMCs) have not been previously shown to express Scr in normal culture. We therefore investigated whether there is an inducible form of Scr in a human mesangial cell line (HMCL).

METHODS

Scr activity was analyzed by cellular uptake of fluorescently labeled acetylated low-density lipoprotein using a flow cytometer. Scr mRNA expression was examined using reverse transcription-polymerase chain reaction, followed by Southern blotting. To investigate the molecular mechanism of Scr expression, several reporter gene constructs were designed. The first contained a full Scr promoter, the second a part of the Scr promoter that has both AP-1 and ets transcription factor binding sites. Other constructs were identical to the second, except that they contained either AP-1 or ets motif mutations.

RESULTS

Phorbol 12-Myristate 13-acetate (PMA) and angiotensin II (Ang II) increased both the percentage of Scr-positive cells and the Scr mean fluorescence intensity. PMA and Ang II also increased Scr mRNA and promoter activity in a time- and dose-responsive manner. Protein kinase C and calmodulin transduction pathways were involved in Scr up-regulation induced by PMA and Ang II. Additionally, a serine/threonine kinase was involved in PMA stimulation. Functional analysis showed that both AP-1 and ets motifs were specific response elements to PMA stimulation in HMCLs.

CONCLUSIONS

This study suggests that HMCs may express an inducible Scr, by which cells can acquire lipids and convert to foam cells in developing glomerulosclerosis.

Hyperlipidaemia in untreated nephrotic syndrome, increased production or decreased removal?

The relative importance of increased lipoprotein synthesis and decreased lipoprotein catabolism is examined in 13 patients with untreated nephrotic syndrome by the use of intravenous fat tolerance tests analysed in relation to other parameters of lipid metabolism. Increased lipoprotein synthesis in nephrotic patients was indicated by the fact that at a given fractional clearance rate of Intralipid (K2), nephrotic patients had higher serum TG concentrations than did control subjects. A defect in lipoprotein catabolism was also suggested by the frequent finding of intermediate density lipoproteins on electrophoresis and the marginally low (p = 0.05) mean K2 in nephrotic patients. A highly significant (p less than 0.001) positive correlation between HDL-cholesterol concentrations and postheparin fractional clearance rates (K'2) of Intralipid led to the speculation that in the severe nephrotic state (albumin less than 20 g/l) the loss of high density lipoproteins may contribute to the hyperlipidaemia.

Vitamin A toxicity and hypercalcaemia in chronic renal failure

Serum vitamin A concentrations were measured in 38 patients undergoing haemodialysis, 24 of whom were taking multivitamin preparations containing vitamin A. Vitamin A concentrations were significantly higher in patients undergoing haemodialysis than in 28 normal controls (p less than 0.001). Patients taking vitamin A supplements had significantly higher vitamin A concentrations than those not taking them (p less than 0.05), and hypercalcaemic patients had higher concentrations than normocalcaemic patients (p less than 0.005). Withdrawal of vitamin A supplements in seven patients caused significant falls in serum vitamin A concentrations and plasma calcium concentrations (p less than 0.01 at two and three months in both cases) and in plasma alkaline phosphatase concentrations (p less than 0.01 at two months). Vitamin A toxicity can contribute to hypercalcaemia in patients undergoing haemodialysis, probably by an osteolytic effect. Multivitamin preparations containing vitamin A should therefore be prescribed with caution in these patients.

Nephrotoxicity of ionic and non-ionic contrast material in digital vascular imaging and selective renal arteriography

We assessed the nephrotoxicity of ionic and non-ionic radiocontrast material (CM) in two groups of patients in a prospective study. One group of 25 potential live kidney donors was studied following conventional renal angiography, carried out as part of the routine pre-operative assessment. The other group of 49 renal transplant patients with varying degrees of renal impairment was studied following digital vascular imaging carried out for investigation of hypertension. Plasma creatine, urinary N-acetyl-D-glucosaminidase (NAG), urinary microglobulin (B2M) and urinary protein excretion were measured before and after the imaging procedure. There were no significant changes in these parameters following digital vascular imaging, but there were increases in plasma creatinine (p less than 0.005) and urinary NAG creatinine ratio (p less than 0.002) in the conventional angiography group following the procedure. Substantial proteinuria developed in 35% of patients following conventional angiography. The differences in nephrotoxicity of radiocontrast agents during the two procedures could not be accounted for by the dose of material used, but probably reflect the effect of differences in the route of administration on the maximal concentration of the material reaching the kidney. Non-ionic radiocontrast material proved less toxic than ionic and may be preferable in conventional angiography.

Plasma immunoreactive melanotrophic hormones in patients on maintenance haemodialysis

Circulating levels of melanotrophic horomones and ACTH were determined in patients treated by maintenance dialysis for chronic renal failure. Plasma melanotrophic hormone levels were greatly increased in all patients studied (125-1100 ng/1 as compared with 12-36 ng/1 in normal adults) and were correlated with the duration of treatment. Skin pigmentation, especially in exposed areas, was notably increased, particularly in those patients with the highest plasma melanotrophic concentrations. Plasma ACTH levels were normal or only slightly raised and circulating corticosteroid concentrations, as determined by a fluorimetric method, all lay within the physiological range. The dissociation between ACTH and melanotrophic hormone levels in these patients may have been the result of a slower metabolic clearance of the latter.

Cytokine regulation of low-density lipoprotein receptor gene transcription in human mesangial cells

BACKGROUND

The intracellular transport of lipids through regulation of the LDL receptor (LDLr) may be important in the progression of renal dysfunction. The present study was undertaken to investigate whether cytokines have any major effects on LDLr regulation and lipid-mediated glomerular injury in human mesangial cells (HMC).

METHODS

We explored the effects of 50 ng/ml of tumour necrosis factor alpha (TNF alpha), 5 ng/ml of transforming growth factor beta (TGF beta), platelet-derived growth factor (PDGF), and interleukin-1beta (IL-1beta) on the regulation of LDLr gene transcription in a human mesangial cell line (HMCL) using cell proliferation, LDL binding, northern blot and LDLr promoter activity assays.

RESULTS

TNF alpha, TGF beta, PDGF or IL-1beta did not significantly stimulate HMCL proliferation at the concentrations given above, but maximally stimulated LDLr mRNA expression and increased LDLr promoter activity by 167.48+/-23.56%, 150.47+/-24.41%, 127.71+/-24.65% and 163.01+/-31.91% respectively, at 24 h. An increased LDL binding was observed in parallel with increased LDLr mRNA. The tyrosine kinase transduction pathway was involved in LDLr upregulation induced by all four cytokines. Additionally, TGF beta involved serine/threonine kinase and G-protein pathways, and IL-1beta involved calmodulin, serine/threonine kinase and PKC pathways in upregulating LDLr. A high concentration of LDL (250 microg/ml) inhibited promoter activity, but TNF alpha, TGF beta, PDGF and IL-1beta co-incubated with LDL could override transcriptional inhibition by LDL.

CONCLUSION

TNF alpha, TGF beta, PDGF and IL-1beta increased LDLr gene expression by increasing sterol-independent and mitogenesis-independent gene transcription. This process may contribute to lipid deposition and foam cell formation in HMC.