Vascular remodelling in the internal mammary artery graft and association with elevated endothelin-1 expression

Introduction: The vasoconstricting peptide Endothelin-1 (ET-1) has been associated with atherosclerotic cardiovascular disease, AAA, hypertension and hypercholesterolemia. It is known to stimulate quiescent vascular smooth muscle cells (VSMC) into the growth cycle and has been linked to intimal thickening following endothelial injury and is associated with vessel wall remodelling in salt-sensitive hypertension models. Enhanced ET-1 expression has been reported in the internal mammary artery (IMA) and was markedly higher in patients undergoing cardiac bypass surgery who were diabetic and /or hypercholesterolemic. Aims: To firstly review the histopathology of the IMA and secondly, determine the relationship between ET-1 expression in this vessel and mitogenic activity in the medial VSMC. Methods: Vessel tissue collected at the time of CABG surgery was formalin-fixed and paraffin-embedded for histological investigation. Cross sections of the left distal IMAwere stained with Alcian Blue/Verhoeff’s van Gieson to assess medial degeneration and identify the elastic lamellae and picrosirius red to determine the collagen content (specifically type I and type III). Immunohistochemistry staining was used to assess VSMC growth (PCNA label), tissue ET-1 expression, VSMC (SMCa-actin) area and macrophage/monocyte (anti-CD68) infiltration. Quantitative analysis was performed to measure the VSMC area in relation to ET-1 staining. Results: Fifty-five IMA specimens from the CABG patients (10F; 45M; mean age 65 years) were collected for this study. Fourteen donor IMAspecimens were used as controls (7F; 7M; mean age 45 years). Significant medial hypertrophy, VSMC disorganisation and elastic lamellae destruction was detected in the CABG IMA. The amount of Alcian blue staining in the CABG IMA was almost double that of the control (31.85+/14.52% Vs 17.10+/9.96%, P= .0006). Total collagen and type I collagen content was significantly increased compared with controls (65.8+/18.3% Vs 33.7 + / 13.7%, P= .07), (14.2 + /10.0% Vs 4.8 + /2.8%, P= .01), respectively. Tissue ET-1 and PCNA labelling were also significantly elevated the CABG IMA specimens relative to the controls (69.99 + /18.74%Vs 23.33 + /20.53%, P= .0001, and 37.29 + /12.88% Vs 11.06 + /8.18, P= .0001), respectively. There was mild presence of macrophages and monocytes in both CABG and control tissue. Conclusions: The IMA from CABG patients has elevated levels of type I collagen in the extracellular matrix indicative of fibrosis and was coupled with deleterious structural remodelling. Abnormally high levels of ET-1 were measured in the medial SMC layer and was associated with VSMC growth but not related to any chronic inflammatory response within the vessel wall.

Free volume and water uptake in a copolymer hydrogel series

A copolymer of X-hydroxyethyl methacrylate (HEMA) with 2-ethoxy ethyl methacrylate (EEMA) was synthesized and the molecular mobility, free volume, and density properties examined as a function of composition. These properties were correlated with the equilibrium water uptake in order to determine which of the properties were most influential in causing high water sorption, as these materials are suitable candidates for hydrogel systems. It was found that the polar HEMA repeat unit results in a rigid, glassy sample at room temperature due to the high degree of hydrogen bonding between chains whereas high EEMA content leads to rubbery samples with subambient glass transition temperatures. The free volume properties on the molecular scale measured by positron annihilation Lifetime spectroscopy (PALS) showed that higher HEMA content led to smaller, fewer holes and a lower free volume fraction than EEMA. Therefore the high water uptake of HEEMA-containing copolymers is largely related to the high polarity of the HEMA unit compared to EEMA, despite the low content of free volume into which the water can initially diffuse. Trends in density with copolymer composition, as measured on a macroscopic level, differs to that seen by PALS and indicates that the two techniques are measuring different scales of packing. (C) 1998 John Wiley & Sons, Inc.

Effect of temperature and a crosslinking promoter on the gamma-radiolysis of a perfluoroelastomer

Methods of promoting the radiation-induced cross linking of poly(tetrafluoro-ethylene-co-perfluoromethyl vinyl ether) (TFE/PMVE) have been investigated. Greater control of the crosslinking and chain-scission reactions was achieved by varying the radiolysis temperature. This was attributed to temperature affecting the mobilities of reactive species such as polymeric free radicals. These reactive species are precursors to radiation-induced cross links and chain-ends. Analysis of the sol/gel behaviour, tensile properties and FTIR indicated that the optimum temperature for the radiation crosslinking of TFE/PMVE, at a dose of 150 kGy, was 263 K. This temperature was 10 K below the glass transition temperature. Incorporation of 1 wt% triallyl isocyanurate (TAIC) greatly amplified the radiation crosslinking of TFE/PMVE, The dose for gelation was decreased by 70%, and the additive imparted superior mechanical properties compared to the neat irradiated TFE/PMVE. Electron spin resonance (ESR) measurements showed higher radical yields at 77 K with the 1 wt% TAIC, indicating that the crosslinking promoter was acting as a radical trap. (C) 1999 Society of Chemical Industry.

Water diffusion in hydroxyethyl methacrylate (HEMA)-based hydrogels formed by gamma-radiolysis

Polymer hydrogels based upon methacrylates are used extensively in the pharmaceutical industry, particularly as controlled release drug delivery systems. These materials are generally prepared by chemically initiated polymerization, but this can lead to the presence of unwanted initiator fragments in the polymer matrix. In the present work, initiation of polymerization by gamma-irradiation of hydroxyethyl methacrylate, with and without added crosslinkers, has been investigated, and the diffusion coefficients for water in the resulting polymers have been measured through mass uptake by the polymers. The diffusion of water in poly(hydroxyethyl methacrylate) at 310 K was found to be Fickian, with a diffusion coefficient of 1.96 +/- 0.1 x 10(11) m(2) s(-1) and an equilibrium water content of 58%, NMR imaging analyses confirmed the adherance to a Fickian model of the diffusion of water into polymer cylinders. The incorporation of small amounts (0.2-0.5 wt%) of added ethyleneglycol-dimethacrylate-based crosslinkers was found to have only a small effect on the diffusion coefficient and the equilibrium water content for the copolymers. (C) 1999 Society of Chemical Industry.

Copolymer hydrogels of 2-hydroxyethyl methacrylate with n-butyl methacrylate and cyclohexyl methacrylate: synthesis, characterization and uptake of water

The bulk free radical copolymerizations of 2-hydroxyethyl methacrylate (HEMA) with n-butyl methacrylate (BMA) or cyclohexyl methacrylate (CHMA) were studied over the composition mole fraction interval of 0-1 for HEMA in the monomer feed. The C-13 NMR (125 MHz) spectra of the copolymers were analysed to determine the copolymer composition and the stereochemical configuration of the copolymers. The terminal model reactivity ratios of HEMA and BMA were found to be r(HEMA) = 1.73 and r(BMA) = 0.65 and for HEMA and CHMA, r(HEMA) = 1.26 and r(CHMA) = 0.31. The BMA and CHMA homopolymers were found to be predominantly syndiotactic with isotacticity parameters of theta(BB) = 0.18 and theta(CC) = 0.19, respectively. The copolymers were also found to be predominantly syndiotactic, indicating a strong tendency for racemic additions of the monomers in the formation of the copolymers. The diffusion of water into cylinders of poly(HEMA-co-BMA) and poly(HEMA-co-CHMA) was studied over a range of copolymer compositions and was found to be Fickian. The diffusion coefficients of water at 37 degrees C were determined from swelling measurements and were found to vary from 1.72 x 10(-11) m(2) s(-1) for polyHEMA to 0.97 x 10(-11) m(2) s(-1) for poly(HEMA-co-BMA) having a mole fraction F-HEMA = 0.80 and to 0.91 x 10(-11) m(2) s(-1) for a poly(HEMA-co-CHMA) also having F-HEMA = 0.80. The mass of water absorbed at equilibrium relative to the mass of dry polymer varied from 58.8 for polyHEMA to 27.2% for poly(HEMA-co-BMA) having F-HEMA = 0.85 and to 21.3% for poly(HEMA-co-CHMA) having F-HEMA = 0.80. (C) 1999 Elsevier Science Ltd. All rights reserved.

Comparative analysis of dendritic cell density and total number in commonly transplanted organs: morphometric estimation in normal mice

Dendritic cells (DC) are considered to be the major cell type responsible for induction of primary immune responses. While they have been shown to play a critical role in eliciting allosensitization via the direct pathway, there is evidence that maturational and/or activational heterogeneity between DC in different donor organs may be crucial to allograft outcome. Despite such an important perceived role for DC, no accurate estimates of their number in commonly transplanted organs have been reported. Therefore, leukocytes and DC were visualized and enumerated in cryostat sections of normal mouse (C57BL/10, B10.BR, C3H) liver, heart, kidney and pancreas by immunohistochemistry (CD45 and MHC class II staining, respectively). Total immunopositive cell number and MHC class II+ cell density (C57BL/10 mice only) were estimated using established morphometric techniques - the fractionator and disector principles, respectively. Liver contained considerably more leukocytes (similar to 5-20 x 10(6)) and DC (similar to 1-3 x 10(6)) than the other organs examined (pancreas: similar to 0.6 x 10(6) and similar to 0.35 x 10(6): heart: similar to 0.8 x 10(6) and similar to 0.4 x 10(6); kidney similar to 1.2 x 10(6) and 0.65 x 10(6), respectively). In liver, DC comprised a lower proportion of all leukocytes (similar to 15-25%) than in the other parenchymal organs examined (similar to 40-60%). Comparatively, DC density in C57BL/10 mice was heart > kidney > pancreas much greater than liver (similar to 6.6 x 10(6), 5 x 10(6), 4.5 x 10(6) and 1.1 x 10(6) cells/cm(3), respectively). When compared to previously published data on allograft survival, the results indicate that the absolute number of MHC class II+ DC present in a donor organ is a poor predictor of graft outcome. Survival of solid organ allografts is more closely related to the density of the donor DC network within the graft. (C) 2000 Elsevier Science B.V. All rights reserved.

Free energy approximations in simple lattice proteins

This work addresses the question of whether it is possible to define simple pairwise interaction terms to approximate free energies of proteins or polymers. Rather than ask how reliable a potential of mean force is, one can ask how reliable it could possibly be. In a two-dimensional, infinite lattice model system one can calculate exact free energies by exhaustive enumeration. A series of approximations were fitted to exact results to assess the feasibility and utility of pairwise free energy terms. Approximating the true free energy with pairwise interactions gives a poor fit with little transferability between systems of different size. Adding extra artificial terms to the approximation yields better fits, but does not improve the ability to generalize from one system size to another. Furthermore, one cannot distinguish folding from nonfolding sequences via the approximated free energies. Most usefully, the methodology shows how one can assess the utility of various terms in lattice protein/polymer models. (C) 2001 American Institute of Physics.