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Biomedical subjects

R A Hoffman

Publications and source records attributed to R A Hoffman.

At least 19 recordsLinked to original sources
PubMed1992

Stimulation of the nitric oxide synthase pathway in human hepatocytes by cytokines and endotoxin.

Nitric oxide (NO) is a short-lived biologic mediator that is shown to be induced in various cell types and to cause many metabolic changes in target cells. Inhibition of tumor cell growth and antimicrobial activity has been attributed to the stimulation of the inducible type of the NO synthase (NOS). However, there is limited evidence for the existence of such inducible NOS in a human cell type. We show here the induction of NO biosynthesis in freshly isolated human hepatocytes (HC) after stimulation with interleukin 1, tumor necrosis factor (TNF), IFN-gamma, and endotoxin. Increased levels of nitrite (NO2-) and nitrate (NO3-) in culture supernatants were associated with NADPH-dependent NOS activity in the cell lysates. The production of NO2- and NO3- was inhibited by NG-monomethyl L-arginine and was associated with an increase in cyclic guanylate monophosphate release. The data presented here provide evidence for the existence of typical inducible NO biosynthesis in a human cell type.

Amino Acid Oxidoreductases↗
PubMed1992

EPR detection of heme and nonheme iron-containing protein nitrosylation by nitric oxide during rejection of rat heart allograft.

The paramagnetic molecule nitric oxide (NO), produced from L-arginine by a specific enzyme (NO synthase), has been shown to be involved in a surprising variety of mammalian cellular responses, including the regulation of T cell immunity to alloantigens in vitro. In cytotoxic activated macrophages, NO production results in a characteristic pattern of alteration of iron-containing enzyme function that is mimicked by exposure to NO. Electron paramagnetic resonance (EPR) studies have shown the formation of iron-nitrosyl species during macrophage activation and also during sepsis, indicating that alteration of iron-containing protein function may be the result of the well-documented tendency of NO to bind to metal ions. We have recently shown that the NO synthesis induced during alloantigenic activation of rat splenocytes inhibits lymphocyte proliferation and cytotoxic T-lymphocyte generation. This report demonstrates that iron-nitrosyl EPR signals similar to those observed in macrophages and during sepsis are present in the blood and in the grafted tissue of rats during the rejection of allogeneic (but not syngeneic) heart grafts. These signals are found in the blood and at the site of allograft rejection, but are not found in other tissues (such as spleen and lung), and are obliterated by administration of the immunosuppressant FK506. These results directly demonstrate the formation of iron-nitrosyl complexes during vascularized allograft rejection and suggest that consequent destruction of iron-containing protein function plays an important role in the rejection response.

Animals↗
PubMed1992

Structural features of a water-soluble arabinoxylan from the endosperm of wheat.

A cold-water-soluble wheat-endosperm arabinoxylan consisting of a backbone of (1----4)-linked beta-D-xylopyranosyl residues that are variously unsubstituted, and 3- or 2,3-substituted with single alpha-L-arabinofuranosyl groups, was subjected to 1H-n.m.r. spectroscopy. The results of 2D homonuclear Hartmann-Hahn and 1D 1H-n.m.r. spectroscopy allowed the identification of 3- and 2,3-substituted xylose residues, each with adjacent unsubstituted xylose residues, and also substituted xylose residues with a substituted xylose residue as a neighbour. The 1H-n.m.r. data were correlated with 13C-n.m.r. data by means of a 13C-1H 2D proton-detected heteronuclear multiple-quantum correlation experiment, which showed that only different types of branching (i.e., 3- and 2,3-) can be identified by the 13C-n.m.r. data.

Carbohydrate Sequence↗
PubMed1992

FK-506 inhibits proliferation and IL-4 messenger RNA production by a T-helper 2 cell line.

FK-506 is a potent immunosuppressant which is known to decrease the generation of allospecific cytotoxic T cells, possibly through its effect on cytokine production. FK-506 has been reported to have a suppressive effect on cytokine synthesis and secretion by pooled lymphocytes; its action on more selective subsets of lymphocytes is unknown. We currently report the effect of FK-506 on proliferation and IL-4 messenger RNA production by the differentiated mouse T-helper 2 cell line Ly1+2-/9. Ly1+2-/9 cells were grown in culture and treated with (1) media alone, (2) Con A, (3) FK-506, and (4) Con A + FK-506. Proliferation to Con A was determined by treating cells with 10 micrograms/ml Con A +/- FK-506 and measuring [3H]TdR uptake. Reverse transcriptase-polymerase chain reaction amplification was used to quantitate the level of IL-4 mRNA expression. FK-506 markedly inhibits Con A-induced proliferation and IL-4 mRNA production by the T-helper 2 cell line Ly1+2-/9. The ability of FK-506 to block the proliferation and IL-4 production by this helper cell subset suggests that this effect may contribute to its observed marked immunosuppressive properties in vitro and in vivo.

Cell Division↗
PubMed1992

Tumor necrosis factor alpha inhibits hepatocyte mitochondrial respiration.

Although direct cytotoxicity is a well-established phenomenon of tumor necrosis factor alpha (TNF alpha)-induced tissue damage, the intracellular events leading to cell death are still poorly understood. To study the cytotoxic effects of TNF alpha on normal parenchymal cells, rat hepatocytes were purified and incubated with various concentrations of TNF alpha. Mitochondrial respiration, total protein synthesis, and enzyme release were measured to assess metabolic performance and cell integrity. Treatment with TNF alpha suppressed mitochondrial respiration in a concentration-dependent fashion, resulting in a reduction of the activity of complex I of the respiratory chain to 67.0 +/- 3.5% of that of untreated hepatocytes by 2000 U/mL TNF alpha. Under these conditions protein synthesis and the release of intracellular enzymes were significantly increased. Both hepatocellular enzyme release and inhibition of mitochondrial respiration appear to be associated with the generation of reactive oxygen intermediates by the hepatocyte itself, because oxygen radical scavengers prevented these adverse effects of TNF alpha. Inhibition of protein synthesis by cycloheximide as well as addition of cyclic adenosine monophosphate synergistically enhanced the suppression of mitochondrial respiration by TNF alpha, resulting in complex I activity of 6.9 +/- 1.6% and 24.9 +/- 2.9% of that of untreated cells. These data indicate that inhibition of mitochondrial respiration is one of the mechanisms by which TNF alpha induces tissue injury.

Alanine Transaminase↗
PubMed1992

Evidence that nitric oxide production by in vivo allosensitized cells inhibits the development of allospecific CTL.

The oxidative metabolism of L-arginine to its bioactive product, nitric oxide (.N = O) has been shown to inhibit rat splenocyte mixed lymphocyte reactions. To determine if alloantigen-induced .N = O production might be operative in vivo, cells that had infiltrated a rat sponge matrix allograft were tested for de novo .N = O production as well as .N = O production upon restimulation with the sensitizing alloantigen. When graft-infiltrating cells were placed in culture, a peak in de novo .N = O production was observed by day 6 graft-infiltrating cells, the time when donor-specific CTL activity by the graft-infiltrating cells was first observed. Upon restimulation with alloantigen, allograft-infiltrating cells produced greatly increased levels of .N = O, and this production was associated with inhibition of lymphocyte cytolytic function. The addition of NG-monomethyl-L-arginine (NMA), the competitive inhibitor of oxidative L-arginine metabolism, inhibited .N = O production and promoted allospecific CTL development. Both observed effects of NMA were reversed by addition of excess L-arginine. Cytokine(s) able to induce proliferation of the IL-2-dependent T cell line CTLL-2 could be detected in alloantigen-stimulated cultures in both the presence and absence of NMA. However, proliferation of the graft-infiltrating cells in response to these cytokines was observed only in the presence of NMA. The immunosuppressive macrolide FK506 was a potent inhibitor of .N = O production in these cultures, presumably acting by inhibiting the production of those cytokines that induce the oxidative L-arginine pathway.

Animals↗
PubMed1992

Evidence that indefinite survival of small bowel allografts achieved by a brief course of cyclosporine or FK506 is not due to systemic hyporesponsiveness.

The immunological status of Lewis (LEW) recipients of indefinitely surviving (greater than 400 days) orthotopic Brown-Norway (BN) small bowel allografts was investigated 1 to 1 1/2 years after cessation of immunosuppressive therapy with either cyclosporine or FK506 and compared with recipients of syngeneic grafts. A normal proliferative response (as measured by a mixed lymphocyte culture) of recipient peripheral lymph node lymphocytes in response to the donor-specific (BN) and the third-party (ACI) antigen, was observed in all experimental groups. Cytolytic T cell generation (as measured by a standard 51Cr-release cytotoxicity assay) in response to the donor-specific (BN) and the third-party (ACI) antigen was observed also in all groups. A FACS analysis of allograft-recipient splenocytes showed no evidence for systemic lymphoid chimerism. BN or ACI skin grafts transplanted onto recipients of allogeneic and syngeneic small bowel grafts were rejected completely in 12-17 days, while the intestinal grafts remained functional. Immunohistologic evaluation of the allografts, using anti-BN class I and anti-Lewis class II monoclonal antibodies showed anti-BN staining on the epithelial and endothelial structures, whereas the mononuclear cells in the lamina propria stained positively with the anti-LEW monoclonal antibody. However, lymphoid depletion and scarring of Peyer's patches and mesenteric lymph nodes as well as focal obliterative mesenteric arteriopathy, indicative of an indolent chronic rejection, were observed. These data demonstrate that recipients of indefinitely surviving small bowel allografts remain immune competent and do not retain the intestinal graft on the basis of specific hyporesponsiveness to the donor antigens.

Animals↗
PubMed1992

Nitric oxide production in host-versus-graft and graft-versus-host reactions in the rat.

The present study was designed to determine whether .N = O produced in vivo during the rejection of histoincompatible tissues might permit serum NO2-/NO3- levels to serve as markers of a rejection reaction. Rat syngeneic and allogeneic liver, heart, bone marrow/spleen cell, small bowel, skin, and sponge matrix grafts were performed and the stable end-products of .N = O, NO2-/NO3-, were serially assayed in the serum of the grafted animals. A significant rise of serum NO2-/NO3- levels in the allografted animals preceded the onset of clinical signs of rejection or graft-versus-host disease, with the exception of the skin and sponge matrix graft models, where elevated serum NO2-/NO3- levels were never observed. In all transplant models, normal serum NO2-/NO3- levels were observed at all times in animals that received syngeneic grafts. Furthermore, treatment of allograft recipients with the immunosuppressive agents FK 506 or cyclosporine A inhibited .N = O production. Determination of serum creatinine levels demonstrated that the elevated serum NO2-/NO3- levels were not caused by kidney dysfunction. Serum NO2-/NO3- levels might be useful early serum markers of the initiation of a rejection reaction or graft-versus-host disease when functional markers of graft dysfunction are not apparent.

Animals↗
PubMed1992

Hypophysectomy prevents the castration-induced increase in porphyrin concentrations in the harderian glands of the male golden hamster: a possible role for prolactin.

The Harderian glands of golden hamsters contain high concentrations of porphyrin pigments, with female hamsters having considerably higher porphyrin concentrations than males. Castration of male hamsters leads to a rapid increase in porphyrin concentrations; testosterone treatment of females has the opposite effect, suggesting a central role for androgens in inhibiting the realization of high porphyrin concentrations by this organ. Previous studies in our laboratories have shown, however, that administration of a dopamine agonist to castrated hamsters prevents the normal increase in Harderian porphyrins from occurring. This suggests that prolactin is necessary for low androgen levels to lead to maximal increases in Harderian porphyrin concentrations. The present study tested the hypothesis that prolactin is involved in the control of Harderian porphyrin levels in the golden hamster. Although hypophysectomy of male hamsters reduced serum testosterone to levels in castrated hamsters, the resultant increase in Harderian porphyrin concentrations was much less than that seen after a similar period of castration. Furthermore, combining the two procedures (castration and hypophysectomy) also led to a blunted increase in Harderian porphyrin, suggesting that a pituitary hormone is necessary for low testosterone levels to lead to increased porphyrins. Evidence that this pituitary hormone is prolactin comes from the observations that eliminating all pituitary hormones except prolactin, by severing the connection of the pituitary with the hypothalamus or transplanting the pituitary to a distant site (beneath the kidney capsule) led to greatly augmented Harderian porphyrin levels, in intact or castrated male hamsters.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Detection of nitric oxide by electron paramagnetic resonance spectroscopy during rejection and graft-versus-host disease after small-bowel transplantation in the rat.

BACKGROUND: Our previous observation that nitric oxide (NO) is synthesized during antigen-specific immune reactions in vitro led us to investigate whether NO is produced during the in vivo immune response to a vascularized organ allograft. METHODS: Orthotopic small-bowel transplantation in the rat was performed by standard microsurgical techniques in the LBNF1 to Lewis (rejection alone), Lewis to LBNF1 (graft-versus-host disease [GVHD] alone), and a syngeneic strain combination with and without immunosuppressive therapy with FK 506. The recipient serum NO2-/NO3- levels (stable end products of NO metabolism) were measured and erythrocytes were evaluated for the presence of nitrosylferrohemoglobin (specific for NO bound to hemoglobin). RESULTS: Animals that acutely rejected small-bowel allografts or suffered from acute GVHD showed significantly elevated serum NO2-/NO3- levels on days 6 and 9, and nitrosylferrohemoglobin electron paramagnetic resonance signals of different intensity were detected on days 3, 6, and 9. FK 506-treated allograft recipients and recipients of syngeneic grafts showed normal serum NO2-/NO3- levels and lacked nitrosylferrohemoglobin signals at all time points. CONCLUSIONS: This study indicates that NO is produced early during the course of small-bowel allograft rejection and GVHD and might therefore serve as a simple marker to detect such immune reactions.

Animals↗
PubMed1992

Cochlear implants in the management of bilateral acoustic neuromas.

Multichannel cochlear implants currently provide the only modality for successful auditory rehabilitation of patients with bilateral profound sensorineural hearing loss who derive no benefit from amplification. We have developed a protocol for patients with neurofibromatosis and bilateral acoustic neuromas in which every effort is made to preserve hearing in at least one ear. Failing that, the cochlear nerve is spared, potentially allowing for the insertion of a cochlear implant. We present our data on one such patient whose auditory function was restored with a Nucleus mini 22-channel cochlear implant following removal of his acoustic neuroma.

Adult↗
PubMed1992

Spontaneous temporal bone cerebrospinal fluid leak.

Eight patients with spontaneous cerebrospinal fluid leak of temporal bone origin are presented. Pertinent history and surgical findings are reviewed and contrasted with 33 previously reported patients. Unilateral ear fullness and mild hearing loss are the most common presenting symptoms. Profuse clear otorrhea following myringotomy is virtually pathognomonic. Diagnostic methods including high-resolution computed tomography, magnetic resonance imaging, and contrast cisternography are discussed. The indications for transmastoid and combined transmastoid/middle fossa surgical repairs are compared. Both surgical approaches were found to be equally effective. We favor the transmastoid as the initial approach because of simplicity, safety, and the ability to visualize both the middle fossa and posterior fossa plates as well as the middle ear.

Adult↗