Novel polymer biomaterials and interfaces inspired from cell membrane functions

Background

Materials with excellent biocompatibility on interfaces between artificial system and biological system are needed to develop any equipments and devices in bioscience, bioengineering and medicinal science. Suppression of unfavorable biological response on the interface is most important for understanding real functions of biomolecules on the surface. So, we should design and prepare such biomaterials.

Scoop of review

One of the best ways to design the biomaterials is generated from mimicking a cell membrane structure. It is composed of a phospholipid bilayered membrane and embedded proteins and polysaccharides. The surface of the cell membrane-like structure is constructed artificially by molecular integration of phospholipid polymer as platform and conjugated biomolecules. Here, it is introduced as the effectiveness of biointerface with highly biological functions observed on artificial cell membrane structure.

Major conclusions

Reduction of nonspecific protein adsorption is essential for suppression of unfavorable bioresponse and achievement of versatile biomedical applications. Simultaneously, bioconjugation of biomolecules on the phospholipid polymer platform is crucial for a high-performance interface.

General significance

The biointerfaces with both biocompatibility and biofunctionality based on biomolecules must be installed on advanced devices, which are applied in the fields of nanobioscience and nanomedicine.This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.     

An association of 27- and 40-kDa molecules with glycolipids that bind A-B bacterial enterotoxins to cultured cells

It is well recognized that the Shiga-like toxins (Stxs) preferentially bind to Gb3 glycolipids and the cholera toxin (CT) and heat-labile enterotoxin (LTp) bind to GM1 gangliosides. After binding to the cell surface, A-B bacterial enterotoxins have to be internalized by endocytosis. The transport of the toxin-glycolipid complex has been documented in several manners but the actual mechanisms are yet to be clarified. We applied a heterobifunctional cross-linker, sulfosuccinimidyl-2-(p-azidosalicylamido)-1,3'-dithiopropionate (SASD), to detect the membrane proteins involved in the binding and the transport of A-B bacterial enterotoxins in cultured cells. Both Stx1 and Stx2 bound to the detergent-insoluble microdomain (DIM) of Vero cells and Caco-2 cells, which were susceptible to the toxin, but neither was bound to insusceptible CHO-K1 cells. Both CT and LTp bound to the DIM of Vero cells, Caco-2 cells, and CHO-K1 cells. In a cross-linking experiment, Stx1 cross-linked only with a 27-kDa molecule, while Stx2, which was more potently toxic than Stx1, cross-linked with 27- and 40-kDa molecules of Vero cells as well as of Caco-2 cells; moreover, no molecules were cross-linked with the insusceptible CHO-K1 cells. LTp was cross-linked only to the 27-kDa molecule of these three cell types but the CT, which was more toxic than LTp, was also cross-linked with 27- and 40-kDa molecules of Vero cells, Caco-2 cells, and CHO-K1 cells. The 27- and the 40-kDa molecules might play a role in the endocytosis and retrograde transport of A-B bacterial enterotoxins.     

Active site of Zn(2+)-dependent sn-glycerol-1-phosphate dehydrogenase from Aeropyrum pernix K1

The enzyme sn-glycerol-1-phosphate dehydrogenase (Gro1PDH, EC 1.1.1.261) is key to the formation of the enantiomeric configuration of the glycerophosphate backbone (sn-glycerol-1-phosphate) of archaeal ether lipids. This enzyme catalyzes the reversible conversion between dihydroxyacetone phosphate and glycerol-1-phosphate. To date, no information about the active site and catalytic mechanism of this enzyme has been reported. Using the sequence and structural information for glycerol dehydrogenase, we constructed six mutants (D144N, D144A, D191N, H271A, H287A and D191N/H271A) of Gro1PDH from Aeropyrum pernix K1 and examined their characteristics to clarify the active site of this enzyme. The enzyme was found to be a zinc-dependent metalloenzyme, containing one zinc ion for every monomer protein that was essential for activity. Site-directed mutagenesis of D144 increased the activity of the enzyme. Mutants D144N and D144A exhibited low affinity for the substrates and higher activity than the wild type, but their affinity for the zinc ion was the same as that of the wild type. Mutants D191N, H271A and H287A had a low affinity for the zinc ion and a low activity compared with the wild type. The double mutation, D191N/H271A, had no enzyme activity and bound no zinc. From these results, it was clarified that residues D191, H271 and H287 participate in the catalytic activity of the enzyme by binding the zinc ion, and that D144 has an effect on substrate binding. The structure of the active site of Gro1PDH from A. pernix K1 seems to be similar to that of glycerol dehydrogenase, despite the differences in substrate specificity and biological role.     

Functional polymorphisms of HSPA5: possible association with bipolar disorder

Altered endoplasmic reticulum stress (ER) response signaling is suggested in bipolar disorder. Previously, we preliminarily reported the genetic association of HSPA5 (GRP78/BiP) with bipolar disorder. Here, we extended our analysis by increasing the number of Japanese case-control samples and NIMH Genetics Initiative bipolar trio samples (NIMH trios), and also analyzed schizophrenia samples. In Japanese, nominally significant association of one haplotype was observed in extended samples of bipolar disorder but not in schizophrenia. In NIMH trios, no association was found in total samples. However, an exploratory analysis suggested that the other haplotype was significantly over-transmitted to probands only from the paternal side. The associated haplotype in Japanese or NIMH pedigrees shared three common polymorphisms in the promotor, which was found to alter promotor activity. These findings suggested promotor polymorphisms of HSPA5 may affect the interindividual variability of ER stress response and may confer a genetic risk factor for bipolar disorder.     

Evaluation of mismatch-binding ligands as inhibitors for Rev-RRE interaction

Drugs targeting the stem-loop IIB of Rev responsible element (RRE) of HIV-1 mRNA are potential therapeutic agents for HIV-1 infection. The stem loop is characterized by an internal loop consist of consecutive G-G and G-A mismatches, which is the single binding site for Rev protein for nuclear export of viral mRNA. We report here that ligands binding to G-G and G-A mismatches in duplex DNA also bind to the internal loop in competition with Rev peptide and lead to the dissociation of pre-formed Rev-RRE complex in a model system.     

Endothelin-1, an ulcer inducer, promotes gastric ulcer healing via mobilizing gastric myofibroblasts and stimulates production of stroma-derived factors

Endothelin (ET)-1 is a potent inducer of peptic ulcers. The roles of ET-1 in ulcer healing, however, have remained unclear, and these were investigated in mice. Gastric ulcers were induced in mice by serosal application of acetic acid. Three days later, mice were given a neutralizing ET-1 antibody or nonimmunized serum. The ulcer size, amount of fibrosis and myofibroblasts, and localization of ET-1 and ET(A/B) receptors were analyzed. To elucidate the mechanisms underlying the effects of ET-1, we examined the proliferation, migration, and release of growth and angiogenic factors in gastric myofibroblasts with or without ET-1. The expression of prepro-ET-1 (an ET-1 precursor) and ET-converting enzyme-1 was examined in gastric myofibroblasts using RT-PCR. Immunoneutralization of ET-1 delayed gastric ulcer healing. The areas of fibrosis and myofibroblasts were smaller in the anti-ET-1 antibody group than in the control. ET-1 was expressed in the gastric epithelium, myofibroblasts, and other cell types. ET(A) receptors, but not ET(B) receptors, were present in myofibroblasts. ET-1 increased proliferation and migration of gastric myofibroblasts. ET-1 stimulated the release of hepatocyte growth factor, VEGF, PGE(2), and IL-6 from gastric myofibroblasts. mRNA for prepro-ET-1 and ET-converting enzyme-1 was also expressed. ET-1 promotes the accumulation of gastric myofibroblasts and collagen fibrils at gastric ulcers. ET-1 also stimulates migration and proliferation of gastric myofibroblasts and enhances the release of growth factors, angiogenic factors, and PGE(2). Thus ET-1 has important roles not only in ulcer formation but also in ulcer healing via mobilizing myofibroblasts and inducing production of stroma-derived factors.     

Urinary yttrium excretion and effects of yttrium chloride on renal function in rats

Evaluation of yttrium exposure in biological samples has not been fully examined. To evaluate yttrium nephrotoxicity, yttrium chloride was orally administered to male Wistar rats and the urine volume (UV) and N-acetyl-beta-D-glucosaminidase (NAG) and creatinine excretion (Crt) were measured in 24-h urine samples. The urinary yttrium concentration and excretion rate were determined by inductively coupled plasma-argon emission spectrometry (ICP-AES). Large significant decreases of UV (>30%) and Crt (>10%) were observed at yttrium doses of 58.3-116.7 mg per rat, but no significant NAG changes was observed. This response pattern shows that a high yttrium dosage alters glomerular function rather than the proximal convoluted tubules. A urinary yttrium excretion rate of 0.216% and good dose-dependent urinary excretion (r=0.77) were confirmed. These results suggest that urinary yttrium is a suitable indicator of occupational and environmental exposure to this element, an increasingly important health issue because recent technological advances present significant potential risks of exposure to rare earth elements. We propose that the ICP-AES analytical method and animal experimental model described in this study will be a valuable tool for future research on the toxicology of rare earth elements.