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Biomedical subjects

J S Cameron

Publications and source records attributed to J S Cameron.

At least 73 records · Page 4Linked to original sources
PubMed1993

Gout, uric acid and purine metabolism in paediatric nephrology.

Although gout and hyperuricaemia are usually thought of as conditions of indulgent male middle age, in addition to the well-known uricosuria of the newborn, there is much of importance for the paediatric nephrologist in this field. Children and infants may present chronically with stones or acutely with renal failure from crystal nephropathy, as a result of inherited deficiencies of the purine salvage enzymes hypoxanthine-guanine phosphoribosyltransferase (HPRT) and adenine phosphoribosyltransferase (APRT) or of the catabolic enzyme xanthine dehydrogenase (XDH). Genetic purine overproduction in phosphoribosylpyrophosphate synthetase superactivity, or secondary to glycogen storage disease, can also present in infancy with renal complications. Children with APRT deficiency may be difficult to distinguish from those with HPRT deficiency because the insoluble product excreted, 2,8-dihydroxyadenine (2,8-DHA), is chemically very similar to uric acid. Moreover, because of the high uric acid clearance prior to puberty, hyperuricosuria rather than hyperuricaemia may provide the only clue to purine overproduction in childhood. Hyperuricaemic renal failure may be seen also in treated childhood leukaemia and lymphoma, and iatrogenic xanthine nephropathy is a potential complication of allopurinol therapy in these conditions. The latter is also an under-recognised complication of treatment in the Lesch-Nyhan syndrome or partial HPRT deficiency. The possibility of renal complications in these three situations is enhanced by infection, the use of uricosuric antibiotics and dehydration consequent upon fever, vomiting or diarrhoea. Disorders of urate transport in the renal tubule may also present in childhood. A kindred with X-linked hereditary nephrolithiasis, renal urate wasting and renal failure has been identified, but in general, the various rare types of net tubular wasting of urate into the urine are recessive and relatively benign, being found incidentally or presenting as colic from crystalluria. However, the opposite condition of a dominantly inherited increase in net urate reabsorption is far from benign, presenting as familial renal failure, with hyperuricaemia either preceding renal dysfunction or disproportionate to it. Paediatricians need to be aware of the lower plasma urate concentrations in children compared with adults when assessing plasma urate concentrations in childhood and infancy, so that early hyperuricosuria is not missed. This is of importance because most of the conditions mentioned above can be treated successfully using carefully controlled doses of allopurinol or means to render urate more soluble in the urine. Xanthine and 2,8-DHA are extremely insoluble at any pH. Whilst 2,8-DHA formation can also be controlled by allopurinol, alkali is contraindicated. A high fluid, low purine intake is the only possible therapy for XDH deficiency.

Adolescent↗
PubMed1993

Clinical significance of anti-endothelial cell antibodies in systemic vasculitis: a longitudinal study comparing anti-endothelial cell antibodies and anti-neutrophil cytoplasm antibodies.

Ten patients with systemic vasculitis, all positive for anti-neutrophil cytoplasm antibody (ANCA), were followed for a mean of 36 weeks to determine the prevalence of anti-endothelial cell antibodies (AECAs) and the relationship between AECAs, ANCAs, and disease activity. Anti-endothelial cell antibodies were detected in eight (80%) patients at some time during the study. The levels of both AECAs and ANCAs changed with time, and these autoantibodies were present in 48% and 63% of the total 100 serum samples, respectively. Eighteen clinical remissions were observed; in 16 (88.9%) cases the level of ANCAs dropped. Fifteen (83.3%) of the 18 remissions were among the AECA-positive patients and the level of AECAs decreased in 13 (86.7%) instances (P = not significant). There were 11 episodes of disease relapse; all were associated with an increase in the level of ANCAs. Nine (81.8%) of the 11 relapses were among AECA-positive patients, and the level of AECAs increased in eight (88.9%) cases (P = not significant). Serum levels of AECAs appeared less suppressible by cyclophosphamide therapy compared with ANCAs, and patients who were persistently positive for AECAs despite being ANCA-negative during remissions were at risk of subsequent relapse. Disease recrudescense was not observed in patients persistently tested negative for both AECAs and ANCAs. Intravenous immunoglobulin therapy was used in four patients and resulted in clinical improvement in all cases, but with variable changes in the levels of AECAs and ANCAs. We conclude that AECAs are commonly detected in patients with systemic vasculitis and their levels show a relationship to disease activity similar to that for ANCAs.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Identification of DNA-binding proteins on human umbilical vein endothelial cell plasma membrane.

The binding of anti-DNA antibodies to the endothelial cell is mediated through DNA, which forms a bridge between the immunoglobulin and the plasma membrane. We have shown that 32P-labelled DNA bound to the plasma membrane of human umbilical vein endothelial cells (HUVEC) by a saturable process, which could be competitively inhibited by non-radiolabelled DNA. In addition, DNA-binding was enhanced in HUVEC that had been treated with IL-1 alpha or tumour necrosis factor-alpha (TNF-alpha). DNA-binding proteins of mol. wt 46,000, 92,000, and 84,000 were identified by the binding of 32P-labelled DNA to plasma membrane proteins separated on SDS-PAGE. DNA-binding proteins of mol. wt 46,000 and 84,000 were also present in the cytosol and nucleus. Murine anti-DNA MoAb410 bound to a single band, at mol. wt 46,000, of plasma membrane protein, in the presence of DNA. Our results showed that DNA-binding proteins are present in different cellular fractions of endothelial cells. DNA-binding proteins on the cell membrane could participate in the in situ formation of immune deposits; and their presence in the cell nucleus suggests a potential role in the modulation of cell function.

Antibodies, Monoclonal↗
PubMed1993

Fast and slow methylators: do racial differences influence risk of allograft rejection?

A catabolic route for azathioprine involving methylation by thiopurine methyltransferase has been directly implicated in the drug's immunosuppressive efficacy. Since ethnic differences in thiopurine methyltransferase activity have been reported in a study of Lapps, this study compared the distribution of thiopurine methyltransferase activity in erythrocyte lysates from 134 healthy, randomly selected subjects living in Brazil, comprising 39 blacks (i.e. Afro-Brazilians), 33 white subjects, 30 mixed-race subjects, and 32 Brazilian-residing Japanese subjects. The results demonstrated bimodality of thiopurine methyltransferase activity compatible with genetic polymorphism in the white, black and mixed-race groups, but not in the Japanese, who were homogeneously 'fast methylators' (high thiopurine methyltransferase activity). Thiopurine methyltransferase activity was generally higher in Brazilian males than females, and some individuals in the black and mixed-race groups had very high activity. Azathioprine-immunosuppressed transplant patients with thiopurine methyltransferase activity above 35 pmol/h/mgHb have previously been shown to have significantly poorer outcomes. Using this thiopurine methyltransferase value as the cut-off point between 'poor responders' and 'good responders' to azathioprine, 65% of the Japanese, 59% of the black subjects, and 63% of the mixed-race subjects fell into the 'poor responder' category, compared with only 42% of the white group. Interestingly, this approximately 20% difference in azathioprine response corresponds to the racial differences seen in allograft survival.

Adult↗
PubMed1993

Recurrent disease in renal allografts.

Recurrent or de novo diseases account for only 5% of graft failure in children, but have much to teach us about mechanisms. In children, almost the only metabolic disease with recurrence is type I hyperoxaluria, in which the poor long-term results of isolated renal transplantation makes combined liver and renal transplantation, or even prophylactic liver transplantation before renal failure the preferable alternative. While many forms of nephritis may show histological recurrence in allografts, it is notable that in many patients this is accompanied no clinical manifestations or only mild disease; this is particularly so in MCGN type II, IgA-associated nephropathy and Schönlein-Henoch purpura. However, FSGS and MCGN type I recur with frequency and severity. Hemolytic-uremic syndromes may recur, even repeatedly, but this is unusual. As many as 10% of pediatric grafts may show de novo membranous nephropathy, but in the majority this is mild or not clinically evident. In contrast, the rare anti-GBM nephritis affecting some patients with Alport's syndrome usually results in graft failure, but occurs in only a minority of Alport recipients. For all types of disease in allografts, risk factors for recurrence are poorly worked out, and attempts at treatment generally ineffective.

Humans↗
PubMed1993

Antiendothelial cell antibodies in lupus: correlations with renal injury and circulating markers of endothelial damage.

Systemic lupus erythematosus is characterized by the production of a broad spectrum of autoantibodies. Autoantibodies directed against endothelial cells (AECA) have been particularly well documented. We investigated associations between such antibodies, double-stranded DNA (dsDNAb), phospholipid (cardiolipin, ACA), and indices of activity and chronicity scored on renal biopsy specimens from 22 patients with acute lupus. AECA were present in 73% of these patients, and both the percentage of patients with AECA and the mean antibody titre fell significantly as patients entered remission. When patients already on immunosuppressive therapy were excluded from analysis (n = 7), only levels of AECA and DNAb (p = 0.02) correlated with histological evidence of active lesions and the presence of glomerular epithelial cell crescents; no correlation was found with chronic changes in the renal biopsies. Serum von Willebrand factor (vWf) and serum total protein S levels, two parameters reflecting endothelial cell function, were also measured during acute disease and remission. vWf concentrations were elevated during acute disease (m = 1.9 IU/ml, p = 0.02), but the values did not correlate with AECA titres. In contrast, total protein S levels were reduced (0.81 IU/ml vs. 0.97 IU/ml, p = 0.01) during active disease, but remained within the normal range (0.56-1.16 IU/ml). Furthermore, protein S levels were inversely related to levels of AECA (r = -0.4, p = 0.01). AECA were therefore present in most patients with acute lupus nephritis and were associated with histological evidence of active renal injury and serological evidence of endothelial cell dysfunction. These data provide indirect support for a pathogenic role for AECA in lupus nephritis.

Antibodies, Anticardiolipin↗
PubMed1993

Adherence of Staphylococcus aureus to cultures of human peritoneal mesothelial cells.

Strains of Staphylococcus aureus, isolated from the effluent of patients with peritonitis on CAPD (continuous ambulatory peritoneal dialysis), adhered well to both cultured human mesothelial cells and to fibronectin, but not to laminin or gelatin. Mesothelial cells grown in medium M199 exhibited more surface fibronectin compared to cells grown in MEM-Dval and demonstrated higher levels of S. aureus adherence. Soluble fibronectin concentrations up to 10 micrograms/ml increased the adherence of S. aureus to cultured mesothelial cells. The dose-response curve was consistent with the binding of fibronectin to a saturable receptor of apparent dissociation constant (KD) = 1.7 x 10(-10) M. This corresponds closely to the KD (2 x 10(-10) M) of the staphylococcal fibronectin-binding protein. S. aureus adherence was increased following the preincubation of mesothelial cell monolayers with interleukin-1 and was maximal after 6 h preincubation. Treating mesothelial cells with interferon-gamma for 48-72 h reduced the adherence of S. aureus.

Bacterial Adhesion↗
PubMed1992

Tubular and interstitial factors in the progression of glomerulonephritis.

All recent studies of the outcome of different forms of progressive glomerulonephritis concur that a major factor, apparently determining outcome, is the presence and severity of tubulointerstitial changes, and not the degree of glomerular alteration. Moreover, at the time of biopsy, tubulointerstitial changes correlate much better with the glomerular filtration rate. These at first surprising findings are not only useful clinically, but should make us think about our models of how progression takes place in so-called glomerular nephritides. In fact, a major tubulointerstitial infiltrate of immune-competent cells is present in all forms of progressive glomerulonephritis, and again correlates with outcome. In addition, it is now clear the tubular epithelium is capable of synthesising and secreting a number of factors important in fibrogenesis, and of displaying major histocompatibility complex class II antigens and leucocyte-adhesion molecules. Tubular cells could thus present peptides to T helper cells and amplify, or maybe even initiate, immune reactions. Finally, fibrogenesis within the kidney is at last being studied, long after studies have been performed on liver and lung. In the past, too much attention has been paid to reversible inflammation and not enough to irreversible cirrhosis of the kidney.

Glomerulonephritis↗
PubMed1992

Peritoneal drainage: an important element in host defence against staphylococcal peritonitis in patients on CAPD.

The growth of Staphylococcus aureus and coagulase-negative staphylococci were studied in fresh and effluent peritoneal dialysate from patients on continuous ambulatory peritoneal dialysis (CAPD). Peritoneal drainage during CAPD removes bacterial contaminants from the peritoneal cavity with an efficiency that depends upon the volume of peritoneal fluid remaining after drainage (residual volume). Combination of our data on the growth of coagulase-negative staphylococci in dialysate with a mathematical model of peritoneal drainage during CAPD shows that a residual volume of less than 800 ml (normal = approximately 400 ml) will prevent survival in the peritoneal fluid. A residual volume of less than 200 ml is required to eliminate S. aureus because of its faster rate of growth in dialysate. Previous work has shown that numbers of macrophages are too few to influence bacterial growth in the peritoneal dialysate. Coagulase-negative staphylococci adhere poorly to mesothelial cells in culture. Survival within the peritoneal cavity during CAPD probably depends on colonization of the PD catheter. Coagulase-negative staphylococcal peritonitis is likely to be localized to areas of the peritoneal membrane in close contact with the PD catheter. S. aureus is able to multiply in the peritoneal dialysate during CAPD and thereby causes generalized peritonitis.

Drainage↗
PubMed1992

The importance of thiopurine methyltransferase activity for the use of azathioprine in transplant recipients.

The immunosuppressive efficacy of azathioprine is related to its rapid metabolism in vivo to 6-mercaptopurine (6MP), with subsequent conversion to thioguanine nucleotides by an anabolic route involving hypoxanthine-guanine phosphoribosyltransferase. Two alternative catabolic routes exist: oxidation to 6-thiouric acid via xanthine oxidase and methylation to 6-methylmercaptopurine via the enzyme thiopurine methyltransferase (TPMT). Catabolism via either route would restrict formation of the active metabolites. We analyzed TPMT activity in erythrocyte lysates of 25 controls, 25 uremic patients on dialysis, and 68 transplanted patients. Median activity was lower in controls (31.0 pmol/hr/mg Hb, range 16.2-43.0) and transplanted patients receiving only cyclosporine and prednisolone (31.7 pmol/hr/mg Hb, range 12.7-43.5) than in the azathioprine treated group, (36.1 pmol/hr/mg Hb, range 16.1-71.3), or the uremic group on dialysis, (35.5 pmol/hr/mg Hb, range 18.6-62.6) suggesting that both azathioprine and uremia induce the enzyme, but CsA does not. Only 3 patients demonstrated total intolerance to azathioprine, 2 of whom had very low TPMT activity (zero and 12.7 pmol/hr/mg Hb). The intolerance of the third patient, despite high TPMT activity, was attributed to concomitant cotrimoxazole therapy. Patients with intermediate activity (15-26 pmol/hr/mg Hb) could tolerate azathioprine well. Of 29 cadaver recipients given only azathioprine plus prednisolone, 24 with a better clinical outcome had a significantly lower activity (33.1 pmol/hr/mg Hb, range 16.1-46.1) than 5 with reduced allograft function (42.5 pmol/hr/mg Hb, range 33.8-51.5). TPMT activity in these 24 patients was also significantly lower than the general group of azathioprine-treated recipients. This inverse association between TPMT activity and allograft function was again found among 30 patients receiving triple therapy (azathioprine, CsA, prednisolone). Self-selection of the best recipients for azathioprine immunosuppression apparently occurred, based on low catabolism of the drug. We conclude that total intolerance to azathioprine is rare and usually appears in patients with very low TPMT activities. Our results also suggest that the wide range of TPMT activity may be an important factor in determining long-term graft survival in azathioprine-treated patients; those with high activity might benefit from doses near the upper limit generally recommended.

Adolescent↗