The sequence of the human genome

A 2.91-billion base pair (bp) consensus sequence of the euchromatic portion of the human genome was generated by the whole-genome shotgun sequencing method. The 14.8-billion bp DNA sequence was generated over 9 months from 27,271,853 high-quality sequence reads (5.11-fold coverage of the genome) from both ends of plasmid clones made from the DNA of five individuals. Two assembly strategies-a whole-genome assembly and a regional chromosome assembly-were used, each combining sequence data from Celera and the publicly funded genome effort. The public data were shredded into 550-bp segments to create a 2.9-fold coverage of those genome regions that had been sequenced, without including biases inherent in the cloning and assembly procedure used by the publicly funded group. This brought the effective coverage in the assemblies to eightfold, reducing the number and size of gaps in the final assembly over what would be obtained with 5.11-fold coverage. The two assembly strategies yielded very similar results that largely agree with independent mapping data. The assemblies effectively cover the euchromatic regions of the human chromosomes. More than 90% of the genome is in scaffold assemblies of 100,000 bp or more, and 25% of the genome is in scaffolds of 10 million bp or larger. Analysis of the genome sequence revealed 26,588 protein-encoding transcripts for which there was strong corroborating evidence and an additional approximately 12,000 computationally derived genes with mouse matches or other weak supporting evidence. Although gene-dense clusters are obvious, almost half the genes are dispersed in low G+C sequence separated by large tracts of apparently noncoding sequence. Only 1.1% of the genome is spanned by exons, whereas 24% is in introns, with 75% of the genome being intergenic DNA. Duplications of segmental blocks, ranging in size up to chromosomal lengths, are abundant throughout the genome and reveal a complex evolutionary history. Comparative genomic analysis indicates vertebrate expansions of genes associated with neuronal function, with tissue-specific developmental regulation, and with the hemostasis and immune systems. DNA sequence comparisons between the consensus sequence and publicly funded genome data provided locations of 2.1 million single-nucleotide polymorphisms (SNPs). A random pair of human haploid genomes differed at a rate of 1 bp per 1250 on average, but there was marked heterogeneity in the level of polymorphism across the genome. Less than 1% of all SNPs resulted in variation in proteins, but the task of determining which SNPs have functional consequences remains an open challenge.

The genome sequence of Drosophila melanogaster

The fly Drosophila melanogaster is one of the most intensively studied organisms in biology and serves as a model system for the investigation of many developmental and cellular processes common to higher eukaryotes, including humans. We have determined the nucleotide sequence of nearly all of the approximately 120-megabase euchromatic portion of the Drosophila genome using a whole-genome shotgun sequencing strategy supported by extensive clone-based sequence and a high-quality bacterial artificial chromosome physical map. Efforts are under way to close the remaining gaps; however, the sequence is of sufficient accuracy and contiguity to be declared substantially complete and to support an initial analysis of genome structure and preliminary gene annotation and interpretation. The genome encodes approximately 13,600 genes, somewhat fewer than the smaller Caenorhabditis elegans genome, but with comparable functional diversity.

Structural analysis of substrate binding by the molecular chaperone DnaK

DnaK and other members of the 70-kilodalton heat-shock protein (hsp70) family promote protein folding, interaction, and translocation, both constitutively and in response to stress, by binding to unfolded polypeptide segments. These proteins have two functional units: a substrate-binding portion binds the polypeptide, and an adenosine triphosphatase portion facilitates substrate exchange. The crystal structure of a peptide complex with the substrate-binding unit of DnaK has now been determined at 2.0 angstroms resolution. The structure consists of a beta-sandwich subdomain followed by alpha-helical segments. The peptide is bound to DnaK in an extended conformation through a channel defined by loops from the beta sandwich. An alpha-helical domain stabilizes the complex, but does not contact the peptide directly. This domain is rotated in the molecules of a second crystal lattice, which suggests a model of conformation-dependent substrate binding that features a latch mechanism for maintaining long lifetime complexes.

Mutations in SCN9A, encoding a sodium channel alpha subunit, in patients with primary erythermalgia

Primary erythermalgia is a rare autosomal dominant disease characterised by intermittent burning pain with redness and heat in the extremities. A previous study established the linkage of primary erythermalgia to a 7.94 cM interval on chromosome 2q, but the causative gene was not identified. We performed linkage analysis in a Chinese family with primary erythermalgia, and screened the mutations in the two candidate genes, SCN9A and GCA, in the family and a sporadic patient. Linkage analysis yielded a maximum lod score of 2.11 for both markers D2S2370 and D2S2330. Based on critical recombination events in two patients in the family, we further limited the genetic region to 5.98 cM between D2S2370 and D2S2345. We then identified two missense mutations in SCN9A in the family (T2573A) and the sporadic patient (T2543C). Our data suggest that mutations in SCN9A cause primary erythermalgia. SCN9A, encoding a voltage-gated sodium channel alpha subunit predominantly expressed in sensory and sympathetic neurones, may play an important role in nociception and vasomotor regulation.

trp, a novel mammalian gene family essential for agonist-activated capacitative Ca2+ entry

SUMMARY

Capacitative calcium entry (CCE) describes CA2+ influx into cells that replenishes CA2+ stores emptied through the action of IP3 and other agents. It is an essential component of cellular responses to many hormones and growth factors. The molecular basis of this form of Ca2+ entry is complex and may involve more than one type of channel. Studies on visual signal transduction in Drosophila led to the hypothesis that a protein encoded in trp may be a component of CCE channels. We reported the existence of six trp-related genes in the mouse genome. Expression in L cells of small portions of these genes in antisense orientation suppressed CCE. Expression in COS cells of two full-length cDNAs encoding human trp homologs, Htrp1 and Htrp3, increased CCE. This identifies mammalian gene products that participate in CCE. We propose that trp homologs are subunits of CCE channels, not unlike those of classical voltage-gated ion channels.

CAFs secreted exosomes promote metastasis and chemotherapy resistance by enhancing cell stemness and epithelial-mesenchymal transition in colorectal cancer

BACKGROUND

Cancer associated fibroblasts (CAFs) are key stroma cells that play dominant roles in tumor progression. However, the CAFs-derived molecular determinants that regulate colorectal cancer (CRC) metastasis and chemoresistance have not been fully characterized.

METHODS

CAFs and NFs were obtained from fresh CRC and adjacent normal tissues. Exosomes were isolated from conditioned medium and serum of CRC patients using ultracentrifugation method and ExoQuick Exosome Precipitation Solution kit, and characterized by transmission electronic microscopy, nanosight and western blot. MicroRNA microarray was employed to identify differentially expressed miRNAs in exosomes secreted by CAFs or NFs. The internalization of exosomes, transfer of miR-92a-3p was observed by immunofluorescence. Boyden chamber migration and invasion, cell counting kit-8, flow cytometry, plate colony formation, sphere formation assays, tail vein injection and primary colon cancer liver metastasis assays were employed to explore the effect of NFs, CAFs and exosomes secreted by them on epithelial-mesenchymal transition, stemness, metastasis and chemotherapy resistance of CRC. Luciferase report assay, real-time qPCR, western blot, immunofluorescence, and immunohistochemistry staining were employed to explore the regulation of CRC metastasis and chemotherapy resistance by miR-92a-3p, FBXW7 and MOAP1.

RESULTS

CAFs promote the stemness, epithelial-mesenchymal transition (EMT), metastasis and chemotherapy resistance of CRC cells. Importantly, CAFs exert their roles by directly transferring exosomes to CRC cells, leading to a significant increase of miR-92a-3p level in CRC cells. Mechanically, increased expression of miR-92a-3p activates Wnt/β-catenin pathway and inhibits mitochondrial apoptosis by directly inhibiting FBXW7 and MOAP1, contributing to cell stemness, EMT, metastasis and 5-FU/L-OHP resistance in CRC. Clinically, miR-92a-3p expression is significantly increased in CRC tissues and negatively correlated with the levels of FBXW7 and MOAP1 in CRC specimens, and high expression of exosomal miR-92a-3p in serum was highly linked with metastasis and chemotherapy resistance in CRC patients.

CONCLUSIONS

CAFs secreted exosomes promote metastasis and chemotherapy resistance of CRC. Inhibiting exosomal miR-92a-3p provides an alternative modality for the prediction and treatment of metastasis and chemotherapy resistance in CRC.

Targeted integration of adeno-associated virus (AAV) into human chromosome 19

A key feature in adeno-associated virus (AAV) replication is efficient integration of the viral genome into host cell DNA to establish latency when helper virus is absent. The steps involved in this process remain largely uncharacterized, even though AAV integration was first documented 20 years ago. Using a protein--DNA binding method we isolated AAV--cellular junction DNA sequences. The cellular component hybridized to a single restriction fragment in the virus-free parental cell line, and also co-migrated with AAV-specific sequences in numerous latently infected cell lines. Analysis of somatic cell hybrids indicated that this cellular sequence maps to the distal portion of the q arm of human chromosome 19. In situ hybridization of AAV DNA to chromosomes from latently infected cells confirms the physical location of AAV integrations to be q13.4-ter of chromosome 19. Sequence analysis of several independent integration sites shows breakpoints occurring within a 100 bp cellular region. This non-pathogenic parvovirus thus appears to establish viral latency by integrating its DNA specifically into one chromosomal region. Such specific integration is so far unique among the eukaryotic DNA viruses. The incorporation of site-specific integration into AAV vector schemes should make this vector system attractive for human gene therapy approaches.

Functional interaction between InsP3 receptors and store-operated Htrp3 channels

Calcium ions are released from intracellular stores in response to agonist-stimulated production of inositol 1,4,5-trisphosphate (InsP3), a second messenger generated at the cell membrane. Depletion of Ca2+ from internal stores triggers a capacitative influx of extracellular Ca2+ across the plasma membrane. The influx of Ca2+ can be recorded as store-operated channels (SOC) in the plasma membrane or as a current known as the Ca2+-release-activated current (I(crac)). A critical question in cell signalling is how SOC and I(crac) sense and respond to Ca2+-store depletion: in one model, a messenger molecule is generated that activates Ca2+ entry in response to store depletion; in an alternative model, InsP3 receptors in the stores are coupled to SOC and I(crac). The mammalian Htrp3 protein forms a well defined store-operated channel and so provides a suitable system for studying the effect of Ca2+-store depletion on SOC and I(crac). We show here that Htrp3 channels stably expressed in HEK293 cells are in a tight functional interaction with the InsP3 receptors. Htrp3 channels present in the same plasma membrane patch can be activated by Ca2+ mobilization in intact cells and by InsP3 in excised patches. This activation of Htrp3 by InsP3 is lost on extensive washing of excised patches but is restored by addition of native or recombinant InsP3-bound InsP3 receptors. Our results provide evidence for the coupling hypothesis, in which InsP3 receptors activated by InsP3 interact with SOC and regulate I(crac).

Mutation of BCL-6 gene in normal B cells by the process of somatic hypermutation of Ig genes

Immunoglobulin (Ig) genes are hypermutated in B lymphocytes that are the precursors to memory B cells. The mutations are linked to transcription initiation, but non-Ig promoters are permissible for the mutation process; thus, other genes expressed in mutating B cells may also be subject to somatic hypermutation. Significant mutations were not observed in c-MYC, S14, or alpha-fetoprotein (AFP) genes, but BCL-6 was highly mutated in a large proportion of memory B cells of normal individuals. The mutation pattern was similar to that of Ig genes.

Sequences responsible for intracellular localization of beta-actin messenger RNA also affect cell phenotype

We have characterized the structure and function of RNA sequences that direct beta-cytoplasmic actin mRNA to the cell periphery were mapped to two segments of 3'-untranslated region by expression of LacZ/beta-actin chimeric mRNAs in chicken embryo fibroblasts (CEFs). A 54-nt segment, the "RNA zipcode," and a homologous but less active 43-nt segment each localized beta-galactosidase activity to the leading lamellae. This zipcode contains the full activity, and mutations or deletions within it reduce, but do not eliminate, its activity, indicating that several motifs contribute to the activity. Two of these motifs, when multimerized, can regenerate almost full activity. These sequences are highly conserved in evolution, since the human beta-actin zipcode, positioned identically in the 3'UTR localizes equally well in chicken cells. Complementary phosphorothioate oligonucleotides against the zipcode delocalized endogenous beta-actin mRNA, whereas those complementary to the region just outside the zipcode, or sense oligonucleotides, did not. Actin mRNA or protein levels were unaffected by the antisense treatments, but a dramatic change in lamellipodia structure, and actin stress fiber organization was observed using the same antizipcode oligonucleotides which delocalized the mRNA. Hence, discrete 3'UTR sequences direct beta-actin isoform synthesis to the leading lamellae and affect cell morphology, presumably through the actin cytoskeleton.

Biased distribution of msp1 and msp2 allelic variants in Plasmodium falciparum populations in Thailand

Plasmodium falciparum isolates were obtained from Thai patients attending a malaria clinic on the Thai-Kampuchean border over 4 cross-sectional surveys carried out at 3-monthly intervals. The genetic structure of the parasite populations was determined by nested polymerase chain reaction (PCR) amplification of polymorphic regions of 3 P. falciparum antigen genes: msp1, msp2 and glurp. Although a high degree of diversity characterized these isolates, the overall population structure of the parasites associated with patent malaria infections was observed to remain relatively stable over time. The highest degree of polymorphism was observed with msp2, and the mean number of lines per infection (multiplicity of infection) calculated with this marker was higher than that obtained using msp1 or glurp alone, or combined. Infections with > or = 2 parasite lines were seen in 76% of the samples, and were proportionally more numerous at the start and end of the rainy season. Two interesting exceptions to the random distribution were observed and involved 2 allelic variants which in one case were found dissociated (msp1 MAD20-family) and in the other were associated (msp2 FC27-family). The epidemiological significance of these types of data is discussed.

Adhesion-dependent cell cycle progression linked to the expression of cyclin D1, activation of cyclin E-cdk2, and phosphorylation of the retinoblastoma protein

Growth factors and cell anchorage jointly regulate transit through G1 in almost all cell types, but the cell cycle basis for this combined requirement remains largely uncharacterized. We show here that cell adhesion and growth factors jointly regulate the cyclin D1- and E-dependent kinases. Adhesion to substratum regulates both the induction and translation of cyclin D1 mRNA. Nonadherent cells fail to phosphorylate the retinoblastoma protein (Rb), and enforced expression of cyclin D1 rescues Rb phosphorylation and entry into S phase when G1 cells are cultured in the absence of substratum. Nonadherent cells also fail to activate the cyclin E-associated kinase, and this effect can be linked to an increased association of the cdk inhibitors, p21 and p27. These data describe a striking convergence in the cell cycle controls used by the two major signal transduction systems responsible for normal and abnormal cell growth. Taken together with our previous studies showing adhesion-dependent expression of cyclin A, they also establish the cell cycle basis for explaining the combined requirement for growth factors and the extracellular matrix in transit through the Rb checkpoint, entry into S phase, and anchorage-dependent growth.

Pten regulates neuronal soma size: a mouse model of Lhermitte-Duclos disease

Somatic inactivation of PTEN occurs in different human tumors including glioblastoma, endometrial carcinoma and prostate carcinoma. Germline mutations in PTEN result in a range of phenotypic abnormalities that occur with variable penetrance, including neurological features such as macrocephaly, seizures, ataxia and Lhermitte-Duclos disease (also described as dysplastic gangliocytoma of the cerebellum). Homozygous deletion of Pten causes embryonic lethality in mice. To investigate function in the brain, we used Cre-loxP technology to selectively inactivate Pten in specific mouse neuronal populations. Loss of Pten resulted in progressive macrocephaly and seizures. Neurons lacking Pten expressed high levels of phosphorylated Akt and showed a progressive increase in soma size without evidence of abnormal proliferation. Cerebellar abnormalities closely resembled the histopathology of human Lhermitte-Duclos disease. These results indicate that Pten regulates neuronal size in vivo in a cell-autonomous manner and provide new insights into the etiology of Lhermitte-Duclos disease.

Integrin-dependent activation of MAP kinase: a link to shape-dependent cell proliferation

Adhesion to extracellular matrix mediates cell cycle progression in mid-late G1; this effect involves an integrin-dependent organization of the cytoskeleton and a consequent change in cell shape. In an effort to identify potential signal-transducing agents that are associated with integrin-dependent shape changes, we looked for kinase activities that were stimulated by long-term adhesion of G0-synchronized NIH-3T3 cells to fibronectin-coated dishes. Several kinase activities were stimulated by this procedure, two of which migrated at 42 and 44 kDa and phosphorylated myelin basic protein in vitro. Blotting with anti-phosphotyrosine and anti-mitogen-activated protein (MAP) kinase antibodies identified these enzymes as ERK 1 and ERK 2. In contrast to the rapid and transient activation of these MAP kinases by platelet-derived growth factor, stimulation of MAP kinase activity by fibronectin was gradual, persistent, and associated with cell spreading rather than cell attachment itself. Cytochalasin D blocked the activation of MAP kinase activity that was induced by the binding of cells to fibronectin. Moreover, MAP kinase was also activated by adhesion of cells to vitronectin and type IV collagen; these effects were also associated with cell spreading. These results distinguish the regulation of G1 phase MAP kinase activity by soluble mitogens and extracellular matrix. They also implicate MAP kinase in shape-dependent cell cycle progression.

Bidirectional FcRn-dependent IgG transport in a polarized human intestinal epithelial cell line

The MHC class I-related Fc receptor, FcRn, mediates the intestinal absorption of maternal IgG in neonatal rodents and the transplacental transport of maternal IgG in humans by receptor-mediated transcytosis. In mice and rats, expression of FcRn in intestinal epithelial cells is limited to the suckling period. We have recently observed, however, clear expression of FcRn in the adult human intestine, suggesting a function for FcRn in intestinal IgG transport beyond neonatal life in humans. We tested this hypothesis using the polarized human intestinal T84 cell line as a model epithelium. Immunocytochemical data show that FcRn is present in T84 cells in a punctate apical pattern similar to that found in human small intestinal enterocytes. Solute flux studies show that FcRn transports IgG across T84 monolayers by receptor-mediated transcytosis. Transport is bidirectional, specific for FcRn, and dependent upon endosomal acidification. These data define a novel bidirectional mechanism of IgG transport across epithelial barriers that predicts an important effect of FcRn on IgG function in immune surveillance and host defense at mucosal surfaces.

Activation and redistribution of c-jun N-terminal kinase/stress activated protein kinase in degenerating neurons in Alzheimer's disease

Cellular responses to increased oxidative stress appear to be a mechanism that contributes to the varied cytopathology of Alzheimer's disease (AD). In this regard, we suspect that c-Jun N-terminal kinase/Stress activated protein kinase (JNK/SAPK), a major cellular stress response protein induced by oxidative stress, plays an important role in Alzheimer disease in susceptible neurons facing the dilemma of proliferation or death. We found that JNK2/SAPK-alpha and JNK3/SAPK-beta were related to neurofibrillary pathology and JNK1/SAP-Kgamma related to Hirano bodies in cases of AD but were only weakly diffuse in the cytoplasm in all neurons in control cases and in non-involved neurons in diseased brain. In this regard, in hippocampal and cortical regions of individuals with severe AD, the activated phospho-JNK/SAPK was localized exclusively in association with neurofibrillar alterations including neurofibrillary tangles, senile plaque neurites, neuropil threads and granulovacuolar degeneration structures (GVD), completely overlapping with tau-positive neurofibrillary pathology, but was virtually absent in these brain regions in younger and age-matched controls without pathology. However, in control patients with some pathology, as well as in mild AD cases, there was nuclear phospho-JNK/SAPK and translocation of phospho-JNK/SAPK from nuclei to cytoplasm, respectively, indicating that the activation and re-distribution of JNK/SAPK correlates with the progress of the disease. By immunoblot analysis, phospho-JNK/SAPK is significantly increased in AD over control cases. Together, these findings suggest that JNK/SAPK dysregulation, probably resulting from oxidative stress, plays an important role in the increased phosphorylation of cytoskeletal proteins found in AD.

Telomere shortening in T cells correlates with Alzheimer's disease status

Telomeres, the repeated sequences that cap chromosome ends, undergo shortening with each cell division, and therefore serve as markers of a cell's replicative history. In vivo, clonal expansion of T cells during immune responses to both foreign and autoantigens is associated with telomere shortening. To investigate possible immune alterations in Alzheimer's disease (AD) that might impact current vaccine-based therapeutic strategies, we analyzed telomere lengths in immune cell populations from AD patients. Our data show a significant telomere shortening in PBMC from AD versus controls (P=0.04). Importantly, telomere length of T cells, but not of B cells or monocytes, correlated with AD disease status, measured by Mini Mental Status Exam (MMSE) scores (P=0.025). T cell telomere length also inversely correlated with serum levels of the proinflammatory cytokine TNFalpha (a clinical marker of disease status), with the proportion of CD8+ T cells lacking expression of the CD28 costimulatory molecule, and with apoptosis. These findings suggest an immune involvement in AD pathogenesis.

On the molecular basis and regulation of cellular capacitative calcium entry: roles for Trp proteins

During the last 2 years, our laboratory has worked on the elucidation of the molecular basis of capacitative calcium entry (CCE) into cells. Specifically, we tested the hypothesis that CCE channels are formed of subunits encoded in genes related to the Drosophila trp gene. The first step in this pursuit was to search for mammalian trp genes. We found not one but six mammalian genes and cloned several of their cDNAs, some in their full length. As assayed in mammalian cells, overexpression of some mammalian Trps increases CCE, while expression of partial trp cDNAs in antisense orientation can interfere with endogenous CCE. These findings provided a firm connection between CCE and mammalian Trps. This article reviews the known forms of CCE and highlights unanswered questions in our understanding of intracellular Ca2+ homeostasis and the physiological roles of CCE.

Three-dimensional structures of acidic and basic fibroblast growth factors

Members of the fibroblast growth factor (FGF) family of proteins stimulate the proliferation and differentiation of a variety of cell types through receptor-mediated pathways. The three-dimensional structures of two members of this family, bovine acidic FGF and human basic FGF, have been crystallographically determined. These structures contain 12 antiparallel beta strands organized into a folding pattern with approximate threefold internal symmetry. Topologically equivalent folds have been previously observed for soybean trypsin inhibitor and interleukins-1 beta and -1 alpha. The locations of sequences implicated in receptor and heparin binding by FGF are presented. These sites include beta-sheet strand 10, which is adjacent to the site of an extended sequence insertion in several oncogene proteins of the FGF family, and which shows sequence conservation among the FGF family and interleukin-1 beta.

Receptor-activated Ca2+ influx via human Trp3 stably expressed in human embryonic kidney (HEK)293 cells. Evidence for a non-capacitative Ca2+ entry

Ca2+ release from its internal stores as a result of activation of phospholipase C is accompanied by Ca2+ influx from the extracellular space. Ca2+ influx channels may be formed of proteins homologous to Drosophila Trp. At least six non-allelic Trp genes are present in the mouse genome. Full-length human, bovine, mouse, and rat cDNAs for Trp1, 3, 4, 6 have been cloned. Expression of these genes in various mammalian cells has provided evidence that Trp proteins form plasma membrane Ca2+-permeant channels that can be activated by an agonist that activates phospholipase C, by inositol 1,4, 5-trisphosphate, and/or store depletion. We have stably expressed human Trp3 (hTrp3) in human embryonic kidney (HEK)293 cells. Measurement of intracellular Ca2+ concentrations in Fura2-loaded cells showed that cell lines expressing hTrp3 have significantly higher basal and agonist-stimulated influxes of Ca2+, Mn2+, Ba2+, and Sr2+ than control cells. The increase in Ca2+ entry attributable to the expression of hTrp3 obtained upon store depletion by thapsigargin was much lower than that obtained by stimulation with agonists acting via a Gq-coupled receptor. Addition of agonists to thapsigargin-treated Trp3 cells resulted in a further increase in the entry of divalent cations. The increased cation entry in Trp3 cells was blocked by high concentrations of SKF 96365, verapamil, La3+, Ni2+, and Gd3+. The Trp3-mediated Ca2+ influx activated by agonists was inhibited by a phospholipase C inhibitor, U73122. We propose that expression of hTrp3 in these cells forms a non-selective cation channel that opens after the activation of phospholipase C but not after store depletion. In addition, a subpopulation of the expressed hTrp3 may form heteromultimeric channels with endogenous proteins that are sensitive to store depletion.

International Commission on Trichinellosis: recommendations on methods for the control of Trichinella in domestic and wild animals intended for human consumption

This document provides a uniform set of recommendations for the control of Trichinella at all levels (on the farm, at slaughter and in processed meats). These recommendations are based on the best scientific information available and represent the official position of the International Commission on Trichinellosis regarding acceptable control methods. These recommendations are subject to change as new scientific information becomes available.

Body weight-for-height relationships predict mortality in maintenance hemodialysis patients

BACKGROUND

Protein-energy malnutrition is a strong predictor of mortality in maintenance hemodialysis (MHD) patients. This association has generally been described for serum chemistry measures of protein-energy malnutrition. We hypothesized that body weight-for-height relationships also predict survival in MHD patients.

METHODS

During the last three months of 1993, data were obtained on 12,965 men and women concerning clinical characteristics (height, postdialysis weight, age, gender, race, and presence or absence of diabetes mellitus) and laboratory measurements (predialysis serum albumin, creatinine and cholesterol, and the urea reduction ratio). Patient survival during the next 12 months was evaluated retrospectively.

RESULTS

In comparison to values for normal Americans determined from the National Health and Nutrition Evaluation Survey II data, weight-for-height relationships tended to be slightly lower than normal in African American men and women and Caucasian men undergoing MHD and were normal or slightly greater in the taller Caucasian women. In both men and women, the mortality rate decreased progressively as the patients' weight-for-height increased. MHD patients who weighed more than normal had the lowest mortality rates. After adjustment for clinical characteristics and laboratory measurements, the inverse relationship between mortality rates and weight-for-height percentiles was still highly significant for patients within the lower 50th percentile of body weight-for-height. Serum albumin correlated directly with weight-for-height in patients in the lower 50th percentile of weight-for-height. Serum creatinine and cholesterol correlated directly with weight-for-height in the entire population of men and women. In contrast, the urea reduction ratio was inversely correlated with weight-for-height.

CONCLUSIONS

These data indicate that weight-for-height is a strong predictor of 12-month mortality in male and female MHD patients. Multivariate analyses indicate that body weight-for-height is an independent predictor of higher mortality in those patients who are in the lower 50th percentile for this measurement.

Redox-active iron mediates amyloid-beta toxicity

While amyloid-beta toxicity is mediated by oxidative stress and can be attenuated by antioxidants, the actual biochemical mechanism underlying neurotoxicity remains to be established. However, since aggregated amyloid-beta can interact with transition metals, such as iron, both in vitro and in vivo, we suspected that bound iron might be the mediator of toxicity such that holo- and apo-amyloid would have differential effects on cellular viability. Here we demonstrate that when amyloid-beta is pretreated with the iron chelator deferoxamine, neuronal toxicity is significantly attenuated while conversely, incubation of holo-amyloid-beta with excess free iron restores toxicity to original levels. These data, taken together with the known sequelae of amyloid-beta, suggest that the toxicity of amyloid-beta is mediated, at least in part, via redox-active iron that precipitates lipid peroxidation and cellular oxidative stress.