Biomedical subjects
Publications and source records attributed to P J Horton.
A 39-year-old male developed painful ulceration of the glans penis following simultaneous pancreas and kidney transplantation for end-stage renal failure complicating insulin-dependent diabetes mellitus. Infection was excluded. Diversion of the pancreatic secretions away from the urinary bladder into the bowel resulted in healing.
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The structure of the (-)-(7S,8R,9S,10R)-N6-[10-(7,8,910-tetrahydrobenzo [a]pyrenyl)]-2'-deoxyadenosyl adduct at X6 of 5'-d(CGGACXAGAAG)-3'-5'-d(CTTCTTGTCCG)-3', derived from trans addition of the exocyclic N6-amino group of dA to (-)-(7S,8R,9R,10S)-7, 8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(-)-DE2], was determined using molecular dynamics simulations restrained by 369 NOEs from 1H NMR. This was named the SRSR(61,2) adduct, derived from the N-ras protooncogene at and adjacent to the nucleotides encoding amino acid 61 (underlined) of the p21 gene product. NOEs between C5, S.R.S.R A6, and A7 were disrupted, as were those between T17 and G18. NOEs between benzo[a]pyrene and DNA protons were localized on the two faces of the pyrenyl ring. The benzo[a]pyrene H3-H6 protons showed NOEs to T17 CH3, while H1, H2, and H3 showed NOEs to T17 deoxyribose; the latter protons and H4 showed NOEs to T17 H2', H2" and to T17 H6. Noes were observed between H11 and H12 and C5 H]',H2', H2". G18 N1H showed NOEs to both faces of benzo[a]pyrene. Upfield shifts of 2.6 ppm for T17 N3H and 1.8 ppm for G18 N1H. 1 ppm for T17 H6 and CH3, and 0.75 ppm for C5 H5, with a smaller shift for C5 H6, and a 1.5 ppm dispersion of the pyrenyl protons suggested that benzo[a]pyrene intercalated above the 5'-face of S.R.S.R A6. The precision of the refined structures was monitored by pairwise root mean square deviations. which were < 1.5 A; accuracy was measured by complete relaxation matrix calculations, which yielded a sixth root R factor of 8.1 x 10(-2). Interstrand stacking between the pyrenyl ring and the T17 pyrimidine and G18 purine rings was enhanced by the bay ring. Changes of +30 degrees and -25 degrees in buckle for C5.G18 and S.R.S.R A6.T17, respectively, were calculated, as was a -40 degrees change in propeller twist for C5.G18. The rise between C5.G18 and S.R.S.R A6.T17 was calculated to be 7 A. The work extended the pattern for adenine N6 benzo[a]pyrene adducts, in which the R stereochemistry at C10 predicted 5'-intercalation of the pyrenyl moiety.
The United States currently relies on a voluntary, altruistic system for supplying organs for transplantation. It is now generally recognized that this system, as currently operated, produces a seriously inadequate supply of organs. A number of scholars have argued that some type of (generally unspecified) market system is necessary. Two articles appearing in the Journal of Health Politics, Policy and Law have proposed relatively specific market systems for increasing the supply of organs. In this paper we argue that market systems are at best premature. In particular, there is little to suggest that any type of market system for organs will be permitted in the United States in the foreseeable future. We present data that strongly suggest that the current voluntary, altruistic system has not been developed to its full potential and offer a number of specific suggestions for improving the system.
This article presents two models of the decision to become a potential organ donor. In the first model the act of carrying or requesting an organ donor card is related to values and factual knowledge regarding organ donation, through intervening attitude and willingness constructs. A sample of 286 students is used to test this model via the LISREL computer program for modeling latent variables. All hypothesized relationships had the predicted sign and were significant. This model is extended by adding the variables attitude towards death, prior blood donation, and age of subject to the model. A second sample of 365 adults from the local community is used to test the second model via LISREL. With two exceptions in the adult sample, all hypothesized relationships had the predicted sign and were significant. Where the two models overlap the results are generally similar. Implications of the models for marketing the act of becoming a potential organ donor are discussed.
Four-hundred and fifty-five undergraduate students, 26 MBA students, and 465 people from the surrounding community responded to 21 true/false questions regarding factual knowledge about organ donation. The mean number of correct answers was 74.6%. The correct response rate, however, varied widely over questions. Four questions with very large error rates suggest possible 'barriers to donation'. Specifically, these questions concerned religious support for organ donation, the concept of brain death, the normally rigid separation of physician teams who are primarily responsible for the welfare of the donor and donee, and a mistaken belief that to be valid an organ donor card must be filed with the U.S. Department of Health and Human Services. Knowledge of organ donation facts was found to be related to whether subjects carried or requested an organ donor card, their attitude towards organ donation and their willingness to donate their own organs or the organs of a deceased loved one. These findings suggest strategies for raising public support for organ donation.
Site-specific mutants of human Cu,Zn superoxide dismutase (Cu,ZnSOD) have been prepared in which the active-site arginine at position 143 (i.e., SODR143) has been replaced by either lysine (SODK143) or isoleucine (SODI143). As reported previously (W.F. Beyer, Jr., et al. (1987) J. Biol. Chem. 262, 11182-11187), SODK143 and SODI143 have 43 and 11%, respectively, of the catalytic activity of SODR143. H2O2, at low concentrations, acts as an affinity reagent for the inactivation of SODR143. At pH 9.0 and 25 degrees C, the process is characterized by a half-saturation constant for H2O2, K50, of 5.1 mM and a maximum pseudo-first-order rate constant for inactivation, Kmax, of 0.53 min-1. At pH 11.5, the corresponding values are 0.63 mM and 1.23 min-1. The active species in the inactivation is likely HO2-, as previously found with yeast and bovine Cu,ZnSODs (see C.L. Borders, Jr., and I. Fridovich (1985) Arch. Biochem. Biophys. 241, 472-476). SODK143 is also inactivated by HO2- by an affinity mechanism, i.e., one where reversible binding of H2O2 (HO2-) is a prerequisite for inactivation. At pH values of 9.0 and 11.5, the kmax values are 0.92 and 1.08 min-1, respectively; however, the corresponding K50 values increase to 42.5 and 15.8 mM, respectively. SODI143 is also inactivated by H2O2, but no evidence for an affinity mechanism was found; instead, a second-order kinetic mechanism was observed. Inactivation of each of the three enzymes is accompanied by the loss of one histidine per subunit. At elevated concentrations of H2O2, a second nonaffinity mechanism of inactivation of both SODR143 and SODK143 was found, in which a second equivalent of H2O2 reacts with the Cu,ZnSOD.HO2- complex to give a competing second-order inactivation. It appears that the positive charge of arginine-143 plays a role in the binding of HO2- at the active site of human Cu,ZnSOD, and that replacement of the arginine by lysine gives an enzyme with a similar affinity mechanism of inactivation, but with a greatly reduced affinity for HO2-. However, replacement with isoleucine causes an entirely different mechanism of inactivation; this raises the possibility that the mechanism of enzyme catalysis of superoxide dismutation by SODI143 is also different.
The manganese-containing (MnSOD) and iron-containing (FeSOD) superoxide dismutases from Escherichia coli are extensively (greater than 95%) inactivated by treatment with phenylglyoxal. The relatively high concentrations of phenylglyoxal and high pH required for optimal inactivation suggest that inactivation may be due to modification of an arginine with a "normal" elevated pKa, i.e., one not in an active site cavity where the pKa is likely to be lowered because of lower solvent accessibility and decreased polarity of the local environment. Treatment of either enzyme with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, 2-hydroxy-5-nitrobenzyl bromide, m-chloroperoxybenzoate, or tetranitromethane causes no inactivation, while 2,4,6-trinitrobenzenesulfonate, N-acetylimidazole, or diethyl pyrocarbonate cause 55-75% inactivation of each enzyme. Failure of hydroxylamine to reverse inactivation by the latter two suggests that in each instance loss of activity is due to lysine modification. The previously reported inactivation of FeSOD by H2O2 was further investigated, and no evidence was found for an affinity mechanism, i.e., a reversible binding of peroxide that precedes inactivation.
Using commercially available monoclonal antibodies that bind to human lymphocyte subsets, we examined lymph nodes from the rhesus monkey and the dog for their binding ability to these monoclonal antibodies. The avidin biotin-peroxidase immunostaining procedure was used, and the following antibodies were reactive in the rhesus monkey: Leu 4, Leu 3a, OKT4, Leu 2a, OKT8, T8, Leu 5b, T11, Leu 14, B1, and Leu 12. No immunoreactivity was observed in the dog lymph node except for moderate reactivity of OKT8. The following antibodies failed to react in both the rhesus monkey and the dog: OKT3, T1, T2, T1B, T4, T8A, Pan B, and T29/33. Kappa and lambda immunoglobulin light chains were positive in both the dog and monkey.
For islet allotransplantation to become a therapy widely applicable to patients with insulin-dependent diabetes, it will be important to avoid conventional immunosuppression and yet maintain long-term rejection-free islet survival. This possibility was tested in a large-animal model using mixed allogeneic chimeras established using total lymphoid irradiation (TLI) and donor-specific bone marrow transplantation (BMTX). Four recipient sex-mismatched and DLA class II-matched English springer spaniels became chimeric after TLI and donor-specific BMTX. Subsequent donor-specific renal allografts survived for more than a year. Acceptance of a donor-specific skin graft and rejection of a third-party graft demonstrated tolerance with maintenance of immunocompetence. Pancreatic microfragments containing islets were refluxed into the splenic vein of the recipient. Purified islets were placed under the capsule of spleen and liver. After 75 days, recipients underwent total native pancreatectomy. All four chimeric pancreatectomized dogs had functioning islet grafts 75 days after transplantation, evidenced by a prompt rise in serum insulin levels following an IVGTT and histological demonstration of islet tissue at the site of transplantation. After removal of the transplanted islet tissue, no insulin was released after IVGTT. In summary, intrasplenic allogeneic canine islets transplanted into chimeric dogs rendered tolerant to donor MHC survive and function for greater than 75 days in the absence of immunosuppression. This study represents proof of the concept that allogeneic islet transplants have the potential to reverse diabetes without the use of conventional immunosuppression.
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