Phytoestrogen consumption and endometrial cancer risk: a population-based case–control study in New Jersey

Phytoestrogens have been shown to exert anti-estrogenic and estrogenic effects in some tissues, including the breast. However, only a few studies have evaluated their role in endometrial cancer risk. We evaluated this association in a population-based case–control study in New Jersey. A total of 424 cases and 398 controls completed an interview, including a food frequency questionnaire with supplemental questions for phytoestrogen foods. Risk estimates were derived using an unconditional logistic regression, adjusting for major risk factors for endometrial cancer. There was some suggestion of a decreased risk with quercetin intake (OR: 0.65; 95% CI: 0.41–1.01 for the highest compared to the lowest quartile; p for trend: 0.02). We found a limited evidence of an association with any of the lignans evaluated, total lignans, coumestrol, individual isoflavones, total isoflavones, or total phytoestrogens. However, there was some suggestion of an inverse association with total isoflavone intake limited to lean women (BMI <25; OR for the highest tertile: 0.50; 95% CI: 0.25–0.98) and those with a waist-to-hip ratio ≤0.85 (OR: 0.59; 95% CI: 0.33–1.05). There was no evidence of effect modification by HRT use. This study suggests a reduction in endometrial cancer risk with quercetin intake and with isoflavone intake in lean women.     

Deletion of a previously uncharacterized lipoprotein lirL confers resistance to an inhibitor of type II signal peptidase in Acinetobacter baumannii

Acinetobacter baumannii is a clinically important, predominantly health care–associated gram-negative bacterium with high rates of emerging resistance worldwide. Given the urgent need for novel antibacterial therapies against A. baumannii, we focused on inhibiting lipoprotein biosynthesis, a pathway that is essential for envelope biogenesis in gram-negative bacteria. The natural product globomycin, which inhibits the essential type II signal peptidase prolipoprotein signal peptidase (LspA), is ineffective against wild-type A. baumannii clinical isolates due to its poor penetration through the outer membrane. Here, we describe a globomycin analog, G5132, that is more potent against wild-type and clinical A. baumannii isolates. Mutations leading to G5132 resistance in A. baumannii map to the signal peptide of a single hypothetical gene, which we confirm encodes an alanine-rich lipoprotein and have renamed lirL (prolipoprotein signal peptidase inhibitor resistance lipoprotein). LirL is a highly abundant lipoprotein primarily localized to the inner membrane. Deletion of lirL leads to G5132 resistance, inefficient cell division, increased sensitivity to serum, and attenuated virulence. Signal peptide mutations that confer resistance to G5132 lead to the accumulation of diacylglyceryl-modified LirL prolipoprotein in untreated cells without significant loss in cell viability, suggesting that these mutations overcome a block in lipoprotein biosynthetic flux by decreasing LirL prolipoprotein substrate sensitivity to processing by LspA. This study characterizes a lipoprotein that plays a critical role in resistance to LspA inhibitors and validates lipoprotein biosynthesis as a antibacterial target in A. baumannii.

Acinetobacter baumannii is a glucose-nonfermentative, nonmotile, aerobic gram-negative coccobacillus and one of the major causes of health care–associated infections, due in part to its antimicrobial resistance capabilities and tolerance to desiccation (1, 2). A. baumannii uses multiple mechanisms of resistance to evade antibiotics, including enzymatic degradation of antibiotics, modifications of the antibiotic target, and regulation of multidrug efflux pump expression (2–4). Hospital outbreaks of multidrug-resistant A. baumannii infection are increasingly prevalent worldwide (5–7) and according to the World Health Organization, are among the most serious priority 1 threats posed by ESKAPE organisms, which also include Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Enterobacter species. For these reasons, there is an urgent need to identify antibacterials against A. baumannii with novel mechanisms of action.Similar to other gram-negative bacteria, the A. baumannii cell envelope consists of a phospholipid inner membrane (IM) and an asymmetrical outer membrane (OM) separated by the periplasm, which contains a peptidoglycan (PGN) cell wall (8). Apart from this overall similarity, there are many differences in the cell wall structure between A. baumannii and other gram-negative bacteria, such as Escherichia coli. The A. baumannii OM contains two types of glycolipids, lipopolysaccharide (LPS) and lipooligosaccharide (LOS) (9), and can uniquely grow in the absence of Lipid A. More recent studies have found increased levels of a number of OM lipoproteins in LOS-deficient A. baumannii (10), suggesting that A. baumannii can compensate for the lack of LPS by increasing transport of OM lipoproteins. E. coli encodes >90 lipoproteins (11, 12), which play essential roles in adhesion, antibiotic resistance, virulence, invasion, and immune evasion (13). Although inhibitors of Lgt and prolipoprotein signal peptidase (LspA) are bactericidal against E. coli, these inhibitors lack sufficient potency against nonfermenting bacteria, such as A. baumannii. Therefore, we hypothesized that enhancing the antibacterial activity against wild-type E. coli may identify analogs with greater antibacterial activity against wild-type A. baumannii.Bacterial lipoprotein biosynthesis is a multistep pathway starting from the translation of a preprolipoprotein, which contains a signal peptide followed by a conserved four–amino acid sequence, [LVI][ASTVI][GAS]C, also known as the lipobox (14). After translation, the preprolipoprotein is secreted through the IM via the Sec or Tat pathways, followed by modification by three enzymes (Lgt, LspA, and N-acyl transferase [Lnt]) to generate the mature triacylated lipoproteins. First, Lgt recognizes the lipobox and catalyzes the transfer of diacylglyceryl (DG) from phosphatidylglycerol to the thiol group of the conserved cysteine residue in the lipobox sequence. The second enzyme, LspA, is an aspartyl endopeptidase, which cleaves off the signal peptide N terminal of the conserved diacylated +1 cysteine (15), and is the molecular target of the natural product antibiotics globomycin and myxovirescin (16–19). In gram-negative and high-GC gram-positive bacteria, a third enzyme, Lnt, catalyzes the addition of a third acyl chain to the amino group of the N-terminal cysteine via an amide linkage. Unlike lgt and lspA, lnt is dispensable for A. baumannii growth in vitro (20). In A. baumannii, mature triacylated lipoproteins destined for the OM are recognized by the localization of lipoprotein (Lol) pathway DF complex (LolDF) (21), analogous to the LolCDE adenosine triphosphate (ATP)–binding cassette transporter expressed in Enterobacteriaceae and Pseudomonas species.In E. coli, resistance to inhibitors of LspA has been well studied and is mediated by deletion or decreased expression of the major OM lipoprotein, lpp. Lpp (also known as Murein lipoprotein or Braun’s lipoprotein) is a small ∼8-kDa lipoprotein that is the most abundant OM protein in E. coli (∼500,000 molecules per cell) and that forms covalent interactions between the PGN layer and the OM. A third of all Lpp is covalently linked to PGN through a covalent interaction between the C-terminal lysine and the meso-diaminopimelic acid residue of the PGN layer (11, 22–26). E. coli mutants deficient in lpp exhibit increased OM permeability, leakage of periplasmic components, increased outer membrane vesicle (OMV) release, and increased sensitivity to complement-mediated lysis (27). Inhibitors of LspA (19, 28) and LolCDE (29, 30) lead to the mislocalization and accumulation of PGN-linked DG-modified Lpp in the IM, resulting in E. coli cell death. Consequently, lpp deletion and decreased expression are major mechanisms of E. coli resistance to inhibitors of LspA and LolCDE (19, 28–32). Given that inhibitors of lipoprotein biosynthesis have minimal activity against A. baumannii strains, which do not express Lpp homologs, the resistance mechanisms to LspA inhibitors in A. baumannii remain unknown.In this study, we describe a potent globomycin analog, G5132, with increased antibacterial activity against multiple laboratory and clinical antibiotic-resistant A. baumannii isolates. Resistance to G1532 in A. baumannii maps to a single hypothetical gene encoding a putative lipoprotein. We confirm that this gene encodes an abundant alanine-rich lipoprotein, which we have renamed LirL (prolipoprotein signal peptidase inhibitor resistance lipoprotein), and describe the initial characterization of this lipoprotein and its role in A. baumannii growth and virulence.     

INFECTIOUS MOTOR PARALYSIS IN YOUNG RABBITS

1. The attempt to infect young rabbits and guinea pigs with material containing in all probability the virus of human infantile paralysis failed. 2. Failure to infect the primary animals almost of necessity brought failure with the secondary flea-bitten animals. It is, however barely conceivable that a non-infectious form of an organism might circulate in the blood of the primary animal and that this form, through development in an intermediate host, the flea, might become virulent for the secondary flea-bitten animal. 3. Incidentally, and presumably accidentally, a paralytic disease was observed in young rabbits associated with the presence of an organism showing certain definite characters. So far as we know this paralysis and the associated organism have not been previously described. 4. This organism is found widely distributed in the organs of the affected animals and can be demonstrated in the urine. The active destruction by the organism of the nerve cells of the spinal cord is particularly striking, and gives complete explanation for the paralysis observed clinically. 5. With the organism present in the urine the spread of the disease by contact can be easily understood. 6. The transfer of the infection from animal to animal by fleabites is possible but not probable. 7. The nature of the observed organisms is in doubt. They represent probably an intermediate stage in the life history of some protozoan parasite.