The spectrum of bone disease in end-stage renal failure--an evolving disorder

We have assessed the bone histology in 259 chronic dialysis patients, all of whom were in the same dialysis program. All patients had bone biopsies with quantitative histomorphometry, intact parathyroid hormone (PTH) measurements, basal and deferoxamine stimulated serum aluminum levels. Results demonstrate the increased incidence of the recently described aplastic bone lesion, particularly in patients treated with peritoneal dialysis (PD). Aluminum-related bone disease is much less common than previously described, perhaps in relation to the declining use of aluminum as a phosphate binder. A different pattern of bone lesions is seen in PD as compared with hemodialysis (HD), with low turnover disorders comprising 66% of the lesions seen in PD and high turnover lesions accounting for 62% of the bone histologic findings in HD. The difference in these patterns may relate to alterations in PTH levels, as mean PTH levels in HD patients were 2-1/2 times the levels found in PD patients (P < 0.0005), while older age, higher prevalence of diabetes and a shorter duration of dialysis may also have contributed to the findings in the PD patients. We suggest that PD, perhaps by maintaining calcium at higher levels, may more effectively suppress the parathyroid gland.

A Molecular-Based Magnet with a Fully Interlocked Three-Dimensional Structure

A compound has been synthesized with the formula (rad)(2)Mn(2)[Cu(opba)](3)(DMSO)(2).2H(2)O, where rad(+) is 2-(4-N-methylpyridinium)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, opba is orthophenylenebis(oxamato), and DMSO is dimethyl sulfoxide. It consists of two nearly perpendicular graphite-like networks with edge-sharing Mn(II)(6)Cu(II)(6) hexagons. The two networks are fully interlocked with the same topological relationship as that between adjacent rings of a necklace. The compound has three kinds of spin carriers: Mn(II) and Cu(II) ions, antiferromagnetically coupled through oxamato bridges, and rad(+) radical cations, bridging the Cu(II) ions through the nitronyl nitroxide groups and forming Cu-rad chains. The temperature dependence of the magnetization reveals that below 22.5 K, the compound behaves as a magnet.

PEGylated PLGA nanoparticles as protein carriers: synthesis, preparation and biodistribution in rats

The aim of the present work was to assess the merits of PEGylated poly(lactic-co-glycolic acid) (PEG-PLGA) nanoparticles as protein and peptide drugs (PPD) carriers. PEG-PLGA copolymer, which could be used to prepare the stealth nanoparticles or long-circulating nanoparticles, was synthesized with methoxypolyethyleneglycol (MePEG) and PLGA. The structure of PEG-PLGA was confirmed with (1)H NMR and Fourier transform infrared (FTIR) spectrum, and molecular weight was determined by gel permeation chromatography (GPC). Bovine serum albumin (BSA), chosen as model protein, was encapsulated within the stealth nanoparticles with the double emulsion method. The particles were characterized in terms of size, zeta potential and in vitro release of the protein. The biological fate of the BSA-loaded nanoparticles following intravenous administration was determined over 24 h in rats. The experimental results showed that PEG-PLGA could be obtained by ring-opening polymerization of lactide and glycolide in the presence of MePEG. (1)H NMR and FTIR spectrum were consistent with the structure of PEG-PLGA copolymer. Molecular weight determined by GPC was 50800. The stealth nanoparticles loading BSA could be prepared by the double emulsion technique. The entrapment efficiency was 48.6%, particle size about 200 nm and zeta potential -16.1 mV. BSA release from the stealth nanoparticles showed an initial burst release and then sustained release. PEG-PLGA nanoparticles could extend half-life of BSA from 13.6 min of loaded in PLGA nanoparticles to 4.5 h and obviously change the protein biodistribution in rats compared with that of PLGA nanoparticles. Thus, PEG-PLGA nanoparticles could be an effective carrier for PPD delivery.

Aplastic osteodystrophy without aluminum: the role of "suppressed" parathyroid function

We evaluated 259 dialysis patients using serum parathyroid hormone (PTH, IRMA; normal range 1 to 5.5 pM or 10 to 55 pg/ml), the deferoxamine infusion test and iliac crest bone biopsy to determine the various forms of renal osteodystrophy and their risk factors. Although half of the biopsied patients had low turnover osteodystrophy, evidence of aluminum toxicity was present in only 1/3 of them. Additional risk factors for this bone lesion included treatment with peritoneal dialysis, ingestion of calcium carbonate, diabetes mellitus and advanced age. The PTH levels in patients with the aplastic lesion were significantly lower than in patients with normal or high bone turnover lesions [7.7 +/- 6.1 vs. 36.9 +/- 3.2 pM (77 +/- 61 vs. 369 +/- 32 pg/ml), P < 0.0001]. Aside from hypercalcemia, these patients were relatively asymptomatic. In a second study, 10 patients on peritoneal dialysis with the aplastic lesion had their dialysate calcium lowered from 1.62 to 1.0 mM. This resulted in a significant increase in PTH levels, from [3.7 +/- 0.8 to 10.6 +/- 1.9 pM (37 +/- 8 to 106 +/- 19 pg/ml), P < 0.001] which persisted over the nine-month observation period. In conclusion, the aplastic lesion is the most common form of renal osteodystrophy, with aluminum intoxication implicated in only 1/3 of the cases. In the remainder, factors identified include therapy with peritoneal dialysis using supraphysiological dialysate calcium, oral CaCO3 intake and diabetes mellitus.(ABSTRACT TRUNCATED AT 250 WORDS)

Validation of a predictive model of idiopathic membranous nephropathy: its clinical and research implications

Although a number of factors have consistently correlated with progression to chronic renal insufficiency (CRI) in idiopathic membranous glomerulonephropathy (IMGN), they appear late, are not quantitative in nature and have not been validated. We have determined that the highest sustained six-month period of proteinuria is an important predictor of progression. Using multiple logistic modelling, the only additional prognostic variables of importance in 184 Canadian patients were the initial creatinine clearance and the rate of change in function over this six-month interval. Independent data from Italy (101 patients) and Finland (78 patients) were obtained for comparison. Sensitivity, specificity, negative and positive predictive values and overall accuracy, as well as Pearson's goodness-of-fit and Harrell's "C" statistic were used to assess the fits of the model. Accuracy of prediction was > or = 85% in all three countries. Pearson's Chi-square goodness-of-fit showed good agreement across the spectrum and Harrell's "C" statistic was > or = 90%. Therefore, a predictive, semiquantitative algorithm in IMGN has been validated. Its relevance in patient management and in clinical trials is illustrated.

Relationship between intact 1-84 parathyroid hormone and bone histomorphometric parameters in dialysis patients without aluminum toxicity

With the markedly reduced usage of aluminum salts in renal failure, parathyroid hormone (PTH) has become the major determinant of currently seen bone disease. Clinicians now must consider what PTH level should be sought. Too low a level may lead to the aplastic bone lesion (low turnover bone), and too high a level may cause osteitis fibrosa. Furthermore, conventional normal PTH levels may not be a suitable target because of the well-known resistance to PTH in uremic patients. In this report, we derive the PTH levels that best distinguish patients with low and high bone formation states from those with normal bone formation in a group of 175 dialysis patients without aluminum toxicity. Using bone histological parameters, we propose that ideally PTH levels should be maintained between 10 pmol/L (100 pg/mL) and 20 to 30 pmol/L (200 to 300 pg/mL) in chronic dialysis patients, levels two to four times the upper limit of values found in normal subjects.

Identification and localization of polycystin, the PKD1 gene product

Polycystin, the product of autosomal dominant polycystic kidney disease (ADPKD) 1 gene (PKD1) is the cardinal member of a novel class of proteins. As a first step towards elucidating the function of polycystin and the pathogenesis of ADPKD, three types of information were collected in the current study: the subcellular localization of polycystin, the spatial and temporal distribution of the protein within normal tissues and the effects of ADPKD mutations on the pattern of expression in affected tissues. Antisera directed against a synthetic peptide and two recombinant proteins of different domains of polycystin revealed the presence of an approximately 400-kD protein (polycystin) in the membrane fractions of normal fetal, adult, and ADPKD kidneys. Immunohistological studies localized polycystin to renal tubular epithelia, hepatic bile ductules, and pancreatic ducts, all sites of cystic changes in ADPKD, as well as in tissues such as skin that are not known to be affected in ADPKD. By electron microscopy, polycystin was predominantly associated with plasma membranes. Polycystin was significantly less abundant in adult than in fetal epithelia. In contrast, polycystin was overexpressed in most, but not all, cysts in ADPKD kidneys.

Coordinate expression of the autosomal dominant polycystic kidney disease proteins, polycystin-2 and polycystin-1, in normal and cystic tissue

A second gene for autosomal dominant polycystic kidney disease (ADPKD), PKD2, has been recently identified. Using antisera raised to the human PKD2 protein, polycystin-2, we describe for the first time its distribution in human fetal tissues, as well as its expression in adult kidney and polycystic PKD2 tissues. Its expression pattern is correlated with that of the PKD1 protein, polycystin-1. In normal kidney, expression of polycystin-2 strikingly parallels that of polycystin-1, with prominent expression by maturing proximal and distal tubules during development, but with a more pronounced distal pattern in adult life. In nonrenal tissues expression of both polycystin molecules is identical and especially notable in the developing epithelial structures of the pancreas, liver, lung, bowel, brain, reproductive organs, placenta, and thymus. Of interest, nonepithelial cell types such as vascular smooth muscle, skeletal muscle, myocardial cells, and neurons also express both proteins. In PKD2 cystic kidney and liver, we find polycystin-2 expression in the majority of cysts, although a significant minority are negative, a pattern mirrored by the PKD1 protein. The continued expression of polycystin-2 in PKD2 cysts is similar to that seen by polycystin-1 in PKD1 cysts, but contrasts with the reported absence of polycystin-2 expression in the renal cysts of Pkd2+/- mice. These results suggest that if a two-hit mechanism is required for cyst formation in PKD2 there is a high rate of somatic missense mutation. The coordinate presence or loss of both polycystin molecules in the same cysts supports previous experimental evidence that heterotypic interactions may stabilize these proteins.

Bilineal disease and trans-heterozygotes in autosomal dominant polycystic kidney disease

In searching for a putative third gene for autosomal dominant polycystic kidney disease (ADPKD), we studied the genetic inheritance of a large family (NFL10) previously excluded from linkage to both the PKD1 locus and the PKD2 locus. We screened 48 members of the NFL10 pedigree, by ultrasonography, and genotyped them, with informative markers, at both the PKD1 locus and the PKD2 locus. Twenty-eight of 48 individuals assessed were affected with ADPKD. Inspection of the haplotypes of these individuals suggested the possibility of bilineal disease from independently segregating PKD1 and PKD2 mutations. Using single-stranded conformational analysis, we screened for and found a PKD2 mutation (i.e., 2152delA; L736X) in 12 affected pedigree members. Additionally, when the disease status of these individuals was coded as "unknown" in linkage analysis, we also found, with markers at the PKD1 locus, significant LOD scores (i.e., >3.0). These findings strongly support the presence of a PKD1 mutation in 15 other affected pedigree members, who lack the PKD2 mutation. Two additional affected individuals had trans-heterozygous mutations involving both genes, and they had renal disease that was more severe than that in affected individuals who had either mutation alone. This is the first documentation of bilineal disease in ADPKD. In humans, trans-heterozygous mutations involving both PKD1 and PKD2 are not necessarily embryonically lethal. However, the disease associated with the presence of both mutations appears to be more severe than the disease associated with either mutation alone. The presence of bilineal disease as a confounder needs to be considered seriously in the search for the elusive PKD3 locus.

Identification of PKDL, a novel polycystic kidney disease 2-like gene whose murine homologue is deleted in mice with kidney and retinal defects

Polycystin-1 and polycystin-2 are the products of PKD1 and PKD2, genes that are mutated in most cases of autosomal dominant polycystic kidney disease. Polycystin-2 shares approximately 46% homology with pore-forming domains of a number of cation channels. It has been suggested that polycystin-2 may function as a subunit of an ion channel whose activity is regulated by polycystin-1. Here we report the identification of a human gene, PKDL, which encodes a new member of the polycystin protein family designated polycystin-L. Polycystin-L has 50% amino acid sequence identity and 71% homology to polycystin-2 and has striking sequence and structural resemblance to the pore-forming alpha1 subunits of Ca2+ channels, suggesting that polycystin-L may function as a subunit of an ion channel. The full-length transcript of PKDL is expressed at high levels in fetal tissues, including kidney and liver, and down-regulated in adult tissues. PKDL was assigned to 10q24 by fluorescence in situ hybridization and is linked to D10S603 by radiation hybrid mapping. There is no evidence of linkage to PKDL in six ADPKD families that are unlinked to PKD1 or PKD2. The mouse homologue of PKDL is deleted in Krd mice, a deletion mutant with defects in the kidney and eye. We propose that PKDL is an excellent candidate for as yet unmapped cystic diseases in man and animals.

Somatic PKD2 mutations in individual kidney and liver cysts support a "two-hit" model of cystogenesis in type 2 autosomal dominant polycystic kidney disease

An intriguing feature of autosomal dominant polycystic kidney disease (ADPKD) is the focal and sporadic formation of renal and extrarenal cysts. Recent documentation of somatic PKD1 mutations in cystic epithelia of patients with germ-line PKD1 mutations suggests a "two-hit" model for cystogenesis in type 1 ADPKD. This study tests whether the same mechanism for cystogenesis might also occur in type 2 ADPKD. Genomic DNA was obtained from 54 kidney and liver cysts from three patients with known germ-line PKD2 mutations, using procedures that minimize contamination of cells from noncystic tissue. Using intragenic and microsatellite markers, these cyst samples were screened for loss of heterozygosity. The same samples were also screened for somatic mutations in five of the 15 exons in PKD2 by single-stranded conformational polymorphism analysis. Loss of heterozygosity was found in five cysts, and unique intragenic mutations were found in seven other cysts. In 11 of these 12 cysts, it was also determined that the somatic mutation occurred nonrandomly in the copy of PKD2 inherited from the unaffected parent. These findings support the "two-hit" model as a unified mechanism for cystogenesis in ADPKD. In this model, the requirement of a somatic mutation as the rate-limiting step for individual cyst formation has potential therapeutic implications.

Predicting chronic renal insufficiency in idiopathic membranous glomerulonephritis

We developed an approach in quantifying the risk of developing chronic renal insufficiency (CRI) based on a cohort of 184 patients with idiopathic membranous glomerulonephritis (IMGN), prospectively followed by the Toronto Glomerulonephritis Registry between 1974 and 1988. After a mean follow-up period of 5.8 years, 26% of patients developed CRI (defined as persistent reduction of creatinine clearance (CCr) less than or equal to 60 ml/min/1.73 m2 for greater than or equal to 12 months). We found that when compared to the baseline probability of the unselected patients, the severity of proteinuria at kidney biopsy added only marginally to the prediction of CRI. We introduced a special test condition: persistent proteinuria (PP) (that is, duration of proteinuria, g/day, above different cut-off levels). We examined the positive predictive value (PPV) and sensitivity (SEN) of 15 arbitrarily chosen levels of PP (that is, proteinuria greater than or equal to 4, 6 or 8 g/day persisting for greater than or equal to 6, 9, 12, 18 or 24 months) to select levels with optimal predictive characteristics. We found that PP greater than or equal to 8 g/day for greater than or equal to six months was a simple and useful predictor of CRI with a PPV and SEN of 66%. To further improve our prediction, we tested the following parameters: age, sex, initial SCr and CCr, proteinuria, serum albumin, hypertension, rate of change of CCr over time, and therapy (steroids +/- immunosuppressive drugs) in a multivariate analysis. Proteinuria, initial CCr, and rate of change of CCr were most important in predicting CRI.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence suggesting under-treatment in adults with idiopathic focal segmental glomerulosclerosis. Regional Glomerulonephritis Registry Study

During the past 11 years, the Metro Toronto Glomerulonephritis Registry has prospectively followed all cases of glomerulonephritis starting from the time of biopsy. Focal segmental glomerulosclerosis was diagnosed by strict histologic criteria in 103 patients. Exclusion of patients with follow-up of less than 12 months reduced the number to 93 (55 adults and 38 children). Mean length of follow-up from the time of biopsy was 61 months. Ninety percent of children, but only 33 percent of adults received treatment with steroids, with or without cytotoxic drugs (p less than 0.001). Complete remission, defined as daily proteinuria of less than 250 mg, was not different in adults (39 percent) from that in children (44 percent), with a mean remission duration for all patients of 38 months. Chronic renal insufficiency, defined as a creatinine clearance of less than 0.8 ml/second/1.73 m2 for more than 12 months, was similar in adults (40 percent) and children (34 percent). Five-year renal actuarial survival, defined as the absence of chronic renal insufficiency, was 96 percent for patients with a history of complete remission, and 55 percent for those without (p less than 0.0002). Logistic regression analysis showed treatment to be the only significant factor for complete remission (p less than 0.001). Complete remission, in turn, was important for renal preservation, defined as the absence of chronic renal insufficiency (p less than 0.001). Age did not affect the treatment response or long-term renal outcome in focal segmental glomerulosclerosis. yet, the percent of adults treated was much lower than that of children, despite the fact that the majority of the untreated adults had the same clinical parameters as the treated adults and children. Thus, a judicious course of treatment is as much indicated in adults as in children with this disorder.

Association of angiotensinogen gene T235 variant with progression of immunoglobin A nephropathy in Caucasian patients

Genetic variability in the renin-angiotensin system may modify renal responses to injury and disease progression. We examined whether the M235T polymorphism of the angiotensinogen (AGT) gene, the insertion/deletion polymorphism of the angiotensin-converting enzyme (ACE) gene, and the A1166--> C polymorphism of the angiotensin II type 1 receptor gene may be associated with disease progression in 168 Caucasian patients with IgA nephropathy. All patients had serial measurements of their creatinine clearance, proteinuria, and blood pressure (mean+/-SD) with a follow-up of 6.1+/-4.7 yr. The genotype frequencies for each gene were consistent with Hardy-Weinberg equilibrium, and were similar to those of 100 Caucasian control subjects. We examined two primary outcomes: (a) the rate of deterioration of Ccr, and (b) the maximal level of proteinuria. We found that patients with the AGT MT (n = 79) and TT (n = 29) genotypes had a faster rate of deterioration of Ccr than those with the MM (n = 60) genotype (i.e., median values, -6.6 and -6.2 vs. -3. 0 ml/min/yr, respectively; P = 0.01 by Kruskal-Wallis test). Similarly, patients with AGT MT and TT genotypes had higher maximal values of proteinuria than those with the MM genotype (i.e., median values, 2.5 and 3.5 vs. 2.0 g/d, respectively; P < 0.02 by Kruskal-Wallis test). Neither the ACE insertion/deletion nor angiotensin II type I A1166--> C gene polymorphism was associated with disease progression or proteinuria in univariate analysis. Multivariant analysis, however, detected an interaction between the AGT and ACE gene polymorphisms with the presence of ACE/DD polymorphism adversely affecting disease progression only in patients with the AGT/MM genotype (P = 0.008). Neither of these gene polymorphisms was associated with systemic hypertension. Our results suggest that polymorphisms at the AGT and ACE gene loci are important markers for predicting progression to chronic renal failure in Caucasian patients with IgA nephropathy.

Mutations of PKD1 in ADPKD2 cysts suggest a pathogenic effect of trans-heterozygous mutations

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in PKD1 and PKD2. The products of these genes associate to form heteromeric complexes. Several models have been proposed to explain the mechanism of cyst formation. Here we find somatic mutations of PKD2 in 71% of ADPKD2 cysts analysed. Clonal somatic mutations of PKD1 were identified in a subset of cysts that lacked PKD2 mutations.

Patients treated by cardiologists have a lower in-hospital mortality for acute myocardial infarction

OBJECTIVES

We sought to determine the effect of specialty care on in-hospital mortality in patients with acute myocardial infarction.

BACKGROUND

There has been increasing pressure to limit access to specialists as a method to reduce the cost of health care. There is little known about the effect on outcome of this shift in the care of acutely ill patients.

METHODS

We analyzed the data from 30,715 direct hospital admissions for the treatment of acute myocardial infarction in Pennsylvania in 1993. A risk-adjusted in-hospital mortality model was developed in which 12 of 20 clinical variables were significant independent predictors of in-hospital mortality. To determine whether there were factors other than patient risk that significantly influenced in-hospital mortality, multiple logistic regression analysis was performed on physician, hospital and payer variables.

RESULTS

After adjustment for patient characteristics, a multiple logistic regression analysis identified treatment by a cardiologist (odds ratio=0.83 [confidence interval ¿CI¿=0.74 to 0.94] p < 0.003) and physicians treating a high volume of acute myocardial infarction patients (odds ratio=0.89 [CI=0.80 to 0.99] p < 0.03) as independent predictors of lower in-hospital mortality. Treatment by a cardiologist as compared to primary care physicians was also associated with a significantly lower length of stay for both medically treated patients (p < 0.01) and those undergoing revascularization (p < 0.01).

CONCLUSIONS

Treatment by a cardiologist is associated with approximately a 17% reduction in hospital mortality in acute myocardial infarction patients. In addition, patients of physicians treating a high volume of patients have approximately an 11% reduction in mortality. This has important implications for the optimal treatment of acute myocardial infarction in the current transformation of the health care delivery system.

Renal osteodystrophy in diabetic patients

To assess the effects of diabetes mellitus on renal osteodystrophy, we examined the database of 256 patients (45% on hemodialysis and 55% on peritoneal dialysis) who were prospectively studied in three Toronto dialysis centers between October of 1987 and 1989. All patients had serial documentation of their clinical, laboratory and risk parameters of bone disease, and completed a series of investigations that included the deferoxamine test, measurement of intact 1-84 PTH levels, and an iliac crest bone biopsy. Twenty-five percent of these patients were diabetic. When compared to non-diabetic patients, they were on dialysis for a shorter duration (2.4 +/- 0.3 vs. 4.7 +/- 0.3 years; P < 0.0002), used calcium carbonate as the only phosphate binder more frequently (40 vs. 25%; P < 0.007), and had lower parathyroid hormone levels (12 +/- 1.4 vs. 24 +/- 2.3 pmol/liter; P < 0.002). High-turnover bone disorders (that is, osteitis fibrosa and mixed disorder) were distinctly uncommon (8 vs. 33%; P < 0.01 by Fisher's exact test), while the mild (19 vs. 9%; P = NS) and the aplastic disorders (with mean stainable bone surface aluminum of 6.5 +/- 0.7%) (46 vs. 31%; P = NS) tended to be more common in diabetic patients. The prevalence of aluminum bone disease was the same in both groups (27%). Diabetic patients ingested a smaller cumulative dose of aluminum gels (3.7 +/- 0.6 vs. 9.3 +/- 1.1 kg; P < 0.005), yet had a higher rate of aluminium accumulation on bone surfaces than non-diabetic patients (1.5 +/- 0.19 vs. 0.96 +/- 0.10% per month on dialysis; P < 0.015).(ABSTRACT TRUNCATED AT 250 WORDS)

LINE-1 elements at the sites of molecular rearrangements in Alport syndrome-diffuse leiomyomatosis

Deletions encompassing the 5' termini of the paired type IV collagen genes COL4A5 and COL4A6 on chromosome Xq22 give rise to Alport syndrome (AS) and associated diffuse leiomyomatosis (DL), a syndrome of disseminated smooth-muscle tumors involving the esophagus, large airways, and female reproductive tract. In this study, we report isolation and characterization of two deletion junctions. The first, in a patient described elsewhere, arose by a nonhomologous recombination event fusing a LINE-1 (L1) repetitive element in intron 1 of COL4A5 to intron 2 of COL4A6, resulting in a 13.4-kb deletion. The second, in a previously undescribed family, arose by unequal homologous recombination between the same L1 and a colinear L1 element in intron 2 of COL4A6, resulting in a>40-kb deletion. L1 elements have contributed to the emergence of this locus as a site of frequent recombinations by diverse mechanisms. These give rise to AS-DL by disruption of type IV collagen and perhaps other as yet unidentified genes, evidenced by deletions as small as 13.4 kb.

A "two-hit" model of cystogenesis in autosomal dominant polycystic kidney disease?

An intriguing feature of autosomal dominant polycystic kidney disease (ADPKD) is the focal and sporadic nature of individual cyst formation. Typically, only a few renal cysts are detectable in an affected individual during the first two decades of life. By the fifth decade, however, hundreds to thousands of renal cysts can be found in most patients. Additionally, significant intra-familial variability of ADPKD has been well documented. Taken together, these findings suggest that factor(s) in addition to the germline mutation of a polycystic kidney disease gene might be required for individual cyst formation. Indeed, recent studies have provided compelling evidence in support of a "two-hit" model of cystogenesis in ADPKD. In this model, inactivation of both copies of a polycystic kidney disease gene by germline and somatic mutations within an epithelial cell provides growth advantages for it to proliferate clonally into a cyst. This article highlights key findings of these recent studies and discusses the controversies and implications of the "two-hit" model in ADPKD.

Risk factors for renal osteodystrophy: a multivariant analysis

To assess the risk factors associated with renal osteodystrophy, we examined the database of 256 patients who were prospectively studied in three Toronto dialysis centers between October of 1987 and 1989. The potential risk factors examined included age, sex, type and duration of dialysis, type and dose of phosphate binders, vitamin D treatment, and history of diabetes mellitus, renal allograft failure, parathyroidectomy, and bilateral nephrectomy. All patients had undergone a bone biopsy and were categorized into one of four disease groupings: (1) osteitis fibrosa and mixed bone disease, (2) aluminum bone disease, (3) mild bone disorder, and (4) aplastic bone disorder. The mean (+/- SD) age of the patients at bone biopsy was 57 +/- 15 years, and 62% were men. Forty-five percent of patients were treated by hemodialysis and 55% by peritoneal dialysis. The mean duration of dialysis was 4 +/- 4 years. Twenty-five percent were also diabetic. The most common disorder was the aplastic (or "adynamic") bone disorder, found in 34% of patients. Aluminum bone disease was found in 27%, osteitis fibrosa or mixed bone disease in 27%, and mild bone disorder in 12% of patients. Cumulative intake of aluminum gels was associated with aluminum bone disease, whereas peritoneal dialysis with supraphysiologic calcium concentrations, ingestion of calcium carbonate, and diabetes mellitus were associated with both mild bone disorder and aplastic bone disorder. These three latter risk factors may be important in predisposing patients to a low bone turnover state through modulation of parathyroid hormone secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporine nephrotoxicity in lung transplant recipients

End-stage lung disease has been treated successfully by lung transplantation (LTXP) at our institution since 1983. We report on the renal function of 30 LTXP recipients who were followed for at least 6 months (mean, 39 months; range, 6-60 months). All patients received quadruple immunosuppressive therapy including cyclosporine A, with a trough serum level (RIA) between 150 and 250 ng/ml for the first 6 months between 125 and 150 mg/ml after 6 months. The mean serum creatinine (SeCr) increased from a baseline value of 75 +/- 3.5 to 182 +/- 13.9 microM at the end of the follow-up. The greatest change in SeCr occurred within the first 6 months post LTXP. Fifteen of 30 patients who were initially normotensive required at least one antihypertensive medication post LTXP. By the end of the follow-up, 9 patients had SeCr > 200 microM. Two patients in this institution have progressed to end-stage renal disease requiring dialytic therapy. CsA nephrotoxicity has emerged as a major source of morbidity in the lung transplant population. Nephrotoxicity occurs early, and there does not appear to be any trend toward reversibility despite a lowering of the dose. Renal parenchymal injury may be progressive, despite an apparent plateau of the SeCr in some patients.

Yeast and viral RNA 5' triphosphatases comprise a new nucleoside triphosphatase family

Saccharomyces cerevisiae Cet1p catalyzes the first step of mRNA capping, the hydrolysis of the gamma phosphate of triphosphate-terminated RNA to form a 5' diphosphate end. The RNA triphosphatase activity of Cet1p is magnesium-dependent and has a turnover number of 1 s-1. Here we show that purified recombinant Cet1p possesses a robust ATPase activity (Km = 2.8 microM; Vmax = 25 s-1) in the presence of manganese. Cobalt is also an effective cofactor, but magnesium, calcium, copper, and zinc are not. Cet1p displays broad specificity in converting ribonucleoside triphosphates and deoxynucleoside triphosphates to their respective diphosphates. The manganese- and cobalt-dependent nucleoside triphosphatase of Cet1p resembles the nucleoside triphosphatase activities of the baculovirus LEF-4 and vaccinia virus D1 capping enzymes. Cet1p, LEF-4, and D1 share three collinear sequence motifs. Mutational analysis establishes that conserved glutamate and arginine side chains within these motifs are essential for the RNA triphosphatase and ATPase activities of Cet1p in vitro and for Cet1p function in vivo. These findings are in accord with the effects of single alanine mutations at analogous positions of vaccinia capping enzyme. We suggest that the metal-dependent RNA triphosphatases encoded by yeast and DNA viruses comprise a novel family of phosphohydrolase enzymes with a common active site.

Association between angiotensin-converting enzyme and Alzheimer disease

BACKGROUND

Angiotensin-converting enzyme has been reported to show altered activity in patients with neurologic diseases. An insertion-deletion polymorphism in ACE has recently been linked to heart disease, cerebrovascular disease, and AD.

OBJECTIVE

To determine whether the angiotensin-converting enzyme (ACE) is associated with risk of Alzheimer disease (AD).

METHODS

We investigated the ACE polymorphism as a potential risk factor for AD in 151 patients with AD and 206 ethnically matched controls from Russia and in 236 patients with AD and 169 controls from North America by means of allele association methods and logistic regression.

RESULTS

None of the ACE genotypes was associated with increased susceptibility to AD in the total sample or in subsets stratified by apolipoprotein E gene (APOE) epsilon4 status. However, the D allele was more frequent among AD cases between ages 66 and 70 years compared with controls in both the Russian (P = .02) and North American (P = .001) datasets. In this age group, the effect of D (odds ratio, 11.2; 95% confidence interval, 2.9-44.0) appeared to be independent of and equal or greater in magnitude to the effect of APOE epsilon4 (odds ratio, 7.8; 95% confidence interval, 3.5-7.4).

CONCLUSIONS

Our results suggest that APOE and ACE genotypes may be independent risk factors for late-onset AD, but the ACE association needs to be confirmed in independent samples in which the time and extent of vascular cofactors can be assessed.

Prevalence of hepatitis E virus antibodies in Canadian swine herds and identification of a novel variant of swine hepatitis E virus

Swine hepatitis E virus is a newly identified potentially zoonotic virus from pigs of particular concern for possible direct transmission to a human xenotransplant recipient by organ transplantation. In the present study, prevalence of serum antibodies to hepatitis E virus was examined in Canadian swine herds. A total of 998 serum samples collected from 6-month-old healthy slaughter hogs were examined by enzyme immunoassay and Western blot analysis for antibodies to the recombinant open reading frame 3 (ORF3) protein of hepatitis E virus expressed in Escherichia coli. These samples represented more than 80 different swine production units from five major swine-producing provinces across Canada. From this study, 594 samples (59.4%) were found to be positive for hepatitis E virus antibody. The seroprevalence was higher in Quebec (88.8%) and Ontario (80.1%) than in Alberta and Saskatchewan (38.3%). By PCR using a pair of oligonucleotide primers deduced from the ORF2 sequence of human hepatitis E virus, a specific hepatitis E virus sequence was recovered from feces of pigs. The nucleotide sequence identity between the U.S. swine hepatitis E virus and the Canadian isolate (SK3) was only 85.8%, suggesting that genotypic variations may exist in swine hepatitis E virus in North America. Among 165 serum samples collected from humans in Saskatchewan, 2.4% were found to be positive for antibodies to the hepatitis E virus ORF3 protein. Our data indicate that hepatitis E virus is highly prevalent in commercial swine populations in Canada and support the suggestion that the swine hepatitis E virus may be an important zoonotic agent for humans.