Founder effects of the homogentisate 1,2-dioxygenase (HGD) gene in a gypsy population and mutation spectrum in the gene among alkaptonuria patients from India

Clinical Rheumatology - Alkaptonuria (AKU) is a rare metabolic disease. The global incidence is 1:100,000 to 1:250,000. However, identification of a founder mutation in a gypsy population from...     

Attempted Salvage Resection for Recurrent Gastric or Gastroesophageal Cancer

The purpose of this study was to determine the outcome of surgery for patients with recurrent gastric or gastroesophageal cancer. We queried records from 7,459 patients who presented with gastric or gastroesophageal cancer to our institution from 1973 through 2005 to identify those for whom resection of recurrent disease had been attempted. We assessed the associations between various clinicopathologic factors and resectability with logistic regression analysis and between clinicopathologic factors and overall survival (OS) with the Cox proportional hazards model. Sixty patients underwent attempted resection for recurrent cancer. In 31 cases (52%), recurrent disease proved unresectable at laparotomy. Factors associated with the ability to undergo re-resection included neoadjuvant treatment prior to initial resection [odds ratio (OR) 12.2, 95% confidence interval (CI) 1.9–75.6] and having an isolated local recurrence (OR 5.1, 95% CI 1.3–20.5). Of the 29 patients who underwent re-resection, 14 required adjacent organ resection, and 6 required interposition grafting. Three- and 5-year OS rates for all 60 patients were 21% and 12%, respectively; median follow-up time was 23 months. Median OS for patients undergoing resection was 25.8 months (95% CI 17.1–49.8) versus 6.0 months (95% CI 4.0–10.5) for unresectable patients (P < 0.001). Initial tumor location at the gastroesophageal junction was associated with diminished OS [hazard ratio (HR) 2.8, 95% CI 1.2–6.5] and ability to undergo resection of recurrence was associated with improved OS (HR 0.2, 95% CI 0.1–0.6). We conclude that surgical resection of select patients with recurrent gastric or gastroesophageal cancer can result in improved OS but often requires adjacent organ resection or interposition graft placement.     

Remodeling of intermediate metabolism in the diatom Phaeodactylum tricornutum under nitrogen stress

Diatoms are unicellular algae that accumulate significant amounts of triacylglycerols as storage lipids when their growth is limited by nutrients. Using biochemical, physiological, bioinformatics, and reverse genetic approaches, we analyzed how the flux of carbon into lipids is influenced by nitrogen stress in a model diatom, Phaeodactylum tricornutum. Our results reveal that the accumulation of lipids is a consequence of remodeling of intermediate metabolism, especially reactions in the tricarboxylic acid and the urea cycles. Specifically, approximately one-half of the cellular proteins are cannibalized; whereas the nitrogen is scavenged by the urea and glutamine synthetase/glutamine 2-oxoglutarate aminotransferase pathways and redirected to the de novo synthesis of nitrogen assimilation machinery, simultaneously, the photobiological flux of carbon and reductants is used to synthesize lipids. To further examine how nitrogen stress triggers the remodeling process, we knocked down the gene encoding for nitrate reductase, a key enzyme required for the assimilation of nitrate. The strain exhibits 40–50% of the mRNA copy numbers, protein content, and enzymatic activity of the wild type, concomitant with a 43% increase in cellular lipid content. We suggest a negative feedback sensor that couples photosynthetic carbon fixation to lipid biosynthesis and is regulated by the nitrogen assimilation pathway. This metabolic feedback enables diatoms to rapidly respond to fluctuations in environmental nitrogen availability.In plants, carbon and nitrogen are directed to specific tissues or structures in accordance with developmental programs. In contrast, unicellular algae flexibly direct carbon and nitrogen to various macromolecules associated with specific intracellular compartments to optimize growth under varying environmental conditions. The signals responsible for this optimization strategy are poorly understood. They clearly are not driven by a developmental program but rather, responses to environmental cues. For example, under optimal growth conditions, ∼40% of the photosynthetically fixed carbon in typical eukaryotic microalga is directed toward the synthesis of amino acids that ultimately are incorporated into proteins (1–3). Over 50 y ago, however, it was recognized that, when nitrogen limits growth, intermediate metabolism is altered, and many microalgae can accumulate storage lipids, mainly in the form of triacylglycerols (TAGs) (4–6). This phenomenon is especially pronounced in diatoms.Diatoms, a highly successful class of eukaryotic algae that rose to ecological prominence during the past 30 My (7), often form massive blooms under turbulent conditions when nutrient supplies are highly variable (8). The ability of these organisms to optimize their growth under such conditions requires coordination of intermediate metabolism of carbon and nitrogen (9, 10). To optimize their growth, the first priority of the cells is to assimilate nitrogen into proteins, which also requires reducing equivalents and carbon skeletons that are primarily supplied by the tricarboxylic acid (TCA) cycle. However, when nitrogen availability decreases, the sink for TCA cycle metabolites declines, and acetyl-CoA, the source of carbon for the cycle, can be shunted toward fatty acid (FA) biosynthesis. Therefore, under nitrogen stress, cellular protein content decreases, whereas storage lipids increase (11, 12). This phenomenon has led to the hypothesis that overexpression of genes involved in lipid biosynthesis may increase the flux of carbon toward lipids (13, 14). Although this phenomenon is well-known, the signals that trigger the process remain unresolved. Genetic manipulations of lipid production in the model diatom, Phaeodactylum tricornutum, are ambiguous. Although there is one report showing that an overexpression of a type II diacylglycerol acyltransferase (DGAT; ProtID 49462) involved in TAG biosynthesis increases the accumulation of natural lipids in P. tricornutum (15), there are several reports indicating that manipulating FA biosynthesis does not significantly affect rates of lipid production (13, 14, 16).Using biochemical, physiological, bioinformatic, and reverse genetic approaches, we examine here how a diatom remodels intermediate metabolism to rapidly respond to nitrogen stress and its resupply. Our results reveal how carbon is redirected toward lipid biosynthesis under nitrogen stress in P. tricornutum.     

Thermo‐responsive Poly(methyl methacrylate)‐block‐poly(N‐isopropylacrylamide) Block Copolymers Synthesized by RAFT Polymerization: Micellization and Gelation

Summary: RAFT polymerization was used to prepare PMMA‐b‐PNIPAM copolymers. Two different chain transfer agents, tBDB and MCPDB, were used to mediate the sequential polymerizations. Micellar solutions and gels were prepared from the resulting copolymers in aqueous solution. When heated above T_c of PNIPAM (about 31 °C), DLS revealed that PNIPAM coronas collapsed, resulting in aggregation of the original micelles. The micellar gels underwent syneresis above T_c as water was expelled from the ordered gel structure, the lattice periodicity of which was determined by SANS. A large decrease in lattice spacing was observed above T_c. The gel became more viscoelastic at high temperature, as revealed by shear rheometry which showed a large increase in G″.