Heat shock protein hsp70 overexpression confers resistance against nitric oxide

Heat stress is known to render rat islet cells resistant against the toxic effects of nitric oxide, reactive oxygen intermediates and the islet cell toxin streptozotocin. We report here for the first time that protection against nitric oxide is mediated by the major heat shock protein, hsp70, even in the absence of heat stress. The human hsp70 gene was stably transfected into the rat insulinoma cell line RINm5F. Constitutive expression of hsp70 caused protection from NO-induced cell lysis which was of the same extent as seen after heat stressing cells. Our results identify hsp70 as a defence molecule against nitric oxide.

Hyperpolarizing, small-field, amacrine cells in cone pathways of cat retina

Intracellular recording and horseradish peroxidase (HRP) staining of amacrine cells in the isolated arterially perfused cat retina have revealed examples of small-field cells that hyperpolarize to light. Two were examined in detailed electron microscopic reconstructions to determine patterns of synaptic relationships within the inner plexiform layer (IPL). The cells were morphologically similar to A8 and A13 types as described in Golgi-impregnated material (Kolb et al. [1981] Vision Res. 21:1081-1114). Both types received ribbon synaptic input from rod and cone bipolar cells. The latter input was numerically predominant, occurred in both a and b sublaminae of the IPL, and arose from at least three cone bipolar types. Reciprocal synapses were evident between A13 cells and cone bipolar cells. Amacrine input occurred throughout the dendritic tree of both A8 and A13 types, and numerically exceeded bipolar cell input for A13. Gap junctions between stained, and similar-appearing unstained dendritic profiles were observed for both amacrine types. In addition, A8 engaged in gap junctions with cone bipolar profiles in sublamina b which also provided ribbon input. Synaptic output for both amacrine types occurred primarily upon amacrine and ganglion cells in sublamina a. Both cells were presynaptic upon single OFF-center beta ganglion cells running through the middle of their dendritic trees. Mixtures of rod and cone signals were found in the centrally evoked hyperpolarizations of each type. Center mechanism space constants of such types ranged from 100 to 400 microns, with antagonistic surround in 1 of 5 cases. Dopamine (250 microM) reduced receptive field space constants by one-third in one case. The synaptic organization and potential circuitry implications of these cone system-dominated amacrine types are compared and contrasted to the better-known AII and A17 types previously described for the rod system.

Interleukin-12 gene-expression of macrophages is regulated by nitric oxide

Interleukin-12 is a heterodimeric cytokine, mainly produced by macrophages. In our present study we demonstrate that interleukin-12 expression is regulated by nitric oxide. Incubation of the macrophage cell line IC 21 with interferon-gamma gave rise to both interleukin-12 p40 mRNA and nitric oxide production. The concurrent addition of the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine inhibited nitrite production and in parallel completely suppressed interleukin-12 p40 mRNA formation. This indicated that endogenous nitric oxide synthase activity was required for IL-12 p40 gene expression. Exposure of the cells towards the nitric oxide generating compounds nitroprusside or S-nitroso-N-acetyl-penicillamine induced interleukin-12 p40 mRNA. Maximal mRNA levels were induced with nitric oxide donors at 1 microM concentration. We conclude that nitric oxide may exert an autoregulatory and paracrine control of interleukin-12 gene expression.

HLA-associated inverse correlation between T cell and antibody responsiveness to islet autoantigen in recent-onset insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) is a T cell-dependent immune-mediated disease. Recently, a novel islet cell antigen (ICA69) recognized by autoantibodies was described. We tested T cell responsiveness to ICA69 in peripheral blood of patients with recent onset IDDM (n = 46), patients with long-standing IDDM (n = 44), non-diabetic age-matched, islet cell autoantibody- and glutamic acid decarboxylase (GAD)65 antibody-negative first-degree relatives of IDDM patients (n = 15) and rheumatoid arthritis patients (n = 22). T cell responsiveness was significantly higher in recent onset IDDM patients, compared to IDDM patients post-disease onset, non-diabetic first degree relatives and rheumatoid arthritis patients (p < 0.001). In responding IDDM patients a significant inverse correlation between T cell and autoantibody responsiveness to ICA69 was observed (p < 0.0005). Immunogenetic evaluation revealed an association of HLA-DR3 with T cell responsiveness to ICA69 (p < 0.02) and absence of ICA69-reactive autoantibodies (p < 0.04). The increased T cell reactivity to ICA69 in the absence of antibody reactivity at onset of IDMM is associated with an HLA class II immune response gene, and therefore suggestive of a genetically controlled selective activation of T helper subsets to a specific autoantigen in humans.

Late pulmonary impairment following allogeneic bone marrow transplantation

The pulmonary function of 88 consecutive leukemic patients who had undergone allogeneic bone marrow transplantation (BMT) was studied beforehand, at 3 months, at 6 months, and annually thereafter until 5 years after grafting. The parameters for function which are indicative for obstructive and restrictive lung disease deteriorated in all patient groups during the first 3 to 6 months after BMT but partially recovered within one year. Long-term decline in lung function was similar in all patient groups, and neither the onset nor the magnitude of pulmonary dysfunction was related to the occurrence of pulmonary impairment within 6 months after grafting. Multivariate analysis was then employed to assess predictors for long-term pulmonary disease. Despite the obvious effect of chronic graft versus host disease on the course of lung function, it was in itself not a significant predictor of long-term pulmonary outcome. Rather, the conditioning regimen turned out to be indicative; compared with busulfan, fractionated total body irradiation was demonstrated to be clearly superior with a lower incidence of both restrictive and obstructive long-term lung impairment. Our data indicate a previously unknown long-term side effect of busulfan conditioning.

Generation and characterization of inducible nitric oxide synthase deficient macrophage cell lines

Stable inducible nitric oxide synthase deficient mouse macrophage cell lines were generated by the antisense technology. A 666 bp fragment of a mouse inducible nitric oxide synthase cDNA was cloned in antisense orientation into a mammalian expression vector behind the CMV promoter. This construct was transfected into J774.1A cells, a mouse macrophage cell line. The inducible nitric oxide synthase antisense lines showed up to 84% reduction of nitric oxide production in response to lipopolysaccharide stimulation and 66% reduction of nitric oxide production in response to interferon-gamma and a combination of interferon-gamma and lipopolysaccharide stimulation. The deficiency in inducible nitric oxide synthase expression had no impact on lipopolysaccharide induced tumor necrosis factor alpha and interleukin-1 secretion. The stable and specific inhibition of inducible nitric oxide synthase expression by antisense DNA vectors allows a direct analysis of contribution of inducible nitric oxide synthase activity to macrophage regulatory and immune defence functions.

Histochemical demonstration of glycogen in neurons of the cat retina

PURPOSE

To demonstrate histochemically the cellular distribution of particulate glycogen in the cat retina and to correlate it with glucose sensitivity of neuronal electrical activities.

METHODS

Free-floating, ultrathin sections of cat eyes (without glucose challenges) were stained by the periodic acid-thiocarbohydrazide-silver proteinate procedure and examined by electron microscopy.

RESULTS

Muller cells were filled uniformly with fine-grain glycogen throughout all retinal layers. Particle density was higher in Muller cells of the peripheral retina than in those of central retina. Astrocytes contained little, if any, particulate glycogen. Alpha and beta ganglion cells had a heavy content of clumped glycogen granules. Rod bipolar and A17 amacrine cells of the rod pathway were stained intensely with particulate glycogen. No glycogen was seen in photoreceptor cells, cone bipolar cells, and the majority of amacrine cells, including AII cells of the rod pathway. However, one type of cone bipolar-driven amacrine cell was intensely glycogen positive. Its ultrastructural morphology, stratification pattern, and synaptology suggest that is a wide-field, axon-bearing type called A22.

CONCLUSIONS

Except for the cone bipolar-driven ON-OFF A22 amacrine cell, it appears that glycogen staining preferentially labels neurons of the rod pathway. These observations are compatible with the reported sensitivity of the rod-driven electroretinogram and optic nerve response to glucose in the cat retina.

ON-OFF amacrine cells in cat retina

We studied the morphology, photic responses, and synaptic connections of ON-OFF amacrine cells in the cat retina by penetrating them with intracellular electrodes, staining them with horseradish peroxidase, and examining them with the electron microscope. In a sample of seven cells, we found two different morphological types: the A19, which ramifies narrowly in stratum 2 (sublamina a) of the inner plexiform layer, and the A22, which ramifies mostly in stratum 4 (sublamina b) but extends some dendrites to sublamina a. Both of these cell types have axon-like processes that extend > 800 microns from the conventional dendritic arbor. ON-OFF amacrine cells in our sample had receptive fields (1.7 +/- 0.3 mm diameter) that were broader than their dendritic arbors (425 +/- 35 microns diameter) and that extended over the region of axon-like processes. In addition, we found many features in common with ON-OFF amacrine cells in poikilotherm vertebrates: a broad receptive field without surround antagonism, two sizes of spike-like events, narrow dynamic range (1 log unit intensity), and excitatory postsynaptic potentials at light on and light off. Two A19 amacrine cells were examined in the electron microscope: most synaptic inputs (93 and 76%, respectively) to either cell were from amacrine cells, with minor inputs from cone bipolar cells. Synaptic outputs were to bipolar, amacrine, and ganglion cells, including the OFF-alpha cell.

Interleukin-12 gene expression is associated with rapid development of diabetes mellitus in non-obese diabetic mice

A single dose of cyclophosphamide (250 mg/kg) is known to synchronize and accelerate development of diabetes in non-obese diabetic mice. We have reported previously that cyclophosphamide treatment of 10-week-old female non-obese diabetic mice induces a shift from T-helper type 2 to T-helper type 1 activity in islet lesions. We now show that this shift in regulatory T-cell function is preceded by the expression of interleukin-12 in the islets as well as in the spleen. In the spleen macrophages were identified as the interleukin-12 expressing cell type. At the same time there was little induction of tumour necrosis factor alpha gene expression by macrophages. Since interleukin-12 is well known to drive T-helper cell type 1 responses we assume that interleukin-12 released by macrophages mediates the accelerating effect of cyclophosphamide on islet inflammation in non-obese diabetic mice. mRNA expression of the p40 chain of interleukin-12 in response to cyclophosphamide was not seen in macrophages of Balb/c mice and thus represents an immune abnormality of non-obese diabetic mice favouring T-helper type 1 reactions.

Skeletal growth of transgenic mice with elevated levels of circulating insulin-like growth factor-II

Insulin-like growth factor-II (IGF-II) is a major factor produced by skeletal tissues. To evaluate endocrine effects of IGF-II on bone growth, we measured skeletal dimensions of 12-week-old transgenic mice harbouring fusion genes where a human IGF-II cDNA is transcriptionally controlled by rat phospheonolpyruvate carboxykinase (PEPCK) promoter sequences. Transgene expression in liver, kidney and intestine resulted in circulating IGF-II levels in transgenic mice which were 2-3-fold higher than in controls. Serum IGF-I concentrations of transgenic mice were lower than in controls. Body weight was not influenced by the expression of the IGF-II transgene. Only 1 out of 5 measurements taken from the radius was significantly affected by the presence of the transgene, while in 60 measurements taken from eight other bones there was no difference between transgenic mice and controls. Furthermore, serum levels of calcium and phosphate as well as alkaline phosphatase activity were not significantly altered in PEPCK-IGF-II transgenic mice. Our findings demonstrate that moderately increased levels of circulating IGF-II do not cause major changes in skeletal growth and turnover in mice. This may be due to a lack of activity of circulating IGF-II on bone growth or to physiological consequences of elevated IGF-II, like a reduction of circulating IGF-I or an increase in IGF binding proteins.

Levels of the terminal complement complex, C3a-desArg and C1-inhibitor in adult patients with capillary leak syndrome following bone marrow transplantation

Capillary leak syndrome (CLS) is a severe complication after bone marrow transplantation (BMT). To investigate whether there is a pathogenetic role of the complement system, we monitored the levels of the terminal complement complex C5b-9 (TCC) and C3a-desArg as indicators of an activation of the complement system and the inhibitor of the classical pathway of the complement cascade, C1 inhibitor (C1-INH), in 48 bone marrow transplant recipients from 1 week before to 5 weeks after transplantation. Capillary leak syndrome developed in 7 out of 48 patients between days 1 and 12 after BMT. Complement activation as indicated by TCC levels was more pronounced in patients with CLS (n = 7) from day -8 to +28 (p < 0.05; day -1) and the elevation of TCC levels lasted longer in CLS patients (peak day 21) than in patients without this complication (peak day 7). Mean C3a-desArg levels were highest in patients with CLS reaching a peak at day 7. During the early posttransplant period a significant elevation of C1-INH levels (p < 0.01 and p < 0.05 respectively) compared with baseline levels (day -8) was found in patients with and without CLS, which was more pronounced in those patients with CLS (p < 0.05). Although we could not observe an absolute C1-INH deficiency as compared to healthy individuals our data support the presence of a relative deficiency of the inhibitor which might explain the reported beneficial effects of C1-INH substitution in BMT related CLS.

Insulitis and islet-cell antibody formation in rats with experimentally reduced beta-cell mass

We studied the effect of severe reduction of beta-cell mass by 90% pancreatectomy on the immune tolerance to the endocrine pancreas. Four months after subtotal pancreatectomy all LEW.Han rats had developed mononuclear infiltration of islets and 9 of 14 rats were positive for islet-cell antibodies. Electron microscopy revealed lymphocytic invasion of endocrine tissue, lysis of beta cells and phagocytotic macrophages. None of these changes were seen 2 weeks after 90% pancreatectomy or 4 months after 10% pancreatectomy. Weekly substitution of islet antigens in the form of a homogenate of 100 islets into 90% pancreatectomized LEW.Han rats almost completely prevented the development of insulitis and autoantibodies. The dependence of insulitis on T cells was shown when 90% pancreatectomy in LEW.rnu rats (i.e., the congenic athymic nude strain), did not result in islet infiltration. The exocrine tissue remained normal in all experimental groups. During the observation period insulitis was not associated with overt diabetes but was accompanied by substantial enlargement of islets and of beta-cell mass, as shown by morphometry. Suppression of islet inflammation by injection of islet antigens abolished beta-cell regeneration, despite continuing metabolic stress in rats with 90% pancreatectomy. The findings indicate induction of islet autoimmunity in response to 90% but not to 10% pancreatectomy. We conclude that severe reduction of the islet-antigen mass allows the development of T-cell-dependent islet autoimmunity which indicates a loss of immune tolerance. In addition, the data suggest the existence of islet-antigen autoreactive immune cells in rats not genetically predisposed to autoimmune diabetes. Finally, we conclude that selective beta-cell regeneration occurs in association with insulitis.

Three-dimensional reconstruction and surface rendering of the five different spectral types of cone pedicle in the turtle retina

Pseudo-3-dimensional models and surface renderings of a small group of neighboring cone pedicles in the turtle retina, in which the 5 different spectral types are represented, have been made from scanned serial electron micrographs using a Macintosh personal computer, Autocad and Studio Pro software. The resultant computer generated images clarify the morphological differences between the spectral types and show how they are related to each other via telodendrial connections and different levels of ending in the neuropil of the outer plexiform layer (OPL). The double cone pedicles end highest in the neuropil and the single red and green pedicles lie slightly lower into the OPL with the single blue and ultraviolent (UV)-sensitive cone pedicles coming in from obliquely angled axons to assume positions between the others much more vitread in the OPL. Telodendria interconnect the double and single red and green cones but not the blue and UV-sensitive cones.

Substance P: a neurotransmitter of amacrine and ganglion cells in the vertebrate retina

A short history and summary of the occurrence of substance P in the vertebrate body is presented. Substance P is now generally accepted to be a neurotransmitter and can be visualized by immunocytochemistry to occur in various nerve cells in the CNS. In the retina, substance P-immunoreactivity (SP-IR) occurs in amacrine cell populations in all the species so far studied. In some vertebrates retinas SP is also apparent in one or more ganglion cell types. Anatomical investigations have revealed the morphology and connectivity of SP-IR amacrine cells: they branch in several strata of the inner plexiform layer receiving input from bipolar and amacrine cells and making synapses upon bipolar and ganglion cells. Most commonly SP-IR amacrines emit axon-like process that pass to both the outer plexiform layer and the ganglion cell and nerve fiber layers. These processes often end upon the retinal vasculature. SP-IR ganglion cells have been described in turtle, rabbit and human retinas. In turtle, intracellular dye injection has revealed the morphology of one type of SP-IR ganglion cell as being a large-field monostratified cell with a branches in the outer stratum of the inner plexiform layer. It may correspond to a "Dogiel cell" type. Intracellular investigation of SP-IR amacrine cells in turtle reveal their physiological responses to be ON-OFF in nature with some color-coding characteristics. In general SP acts as an excitatory neurotransmitter raising the spontaneous activity level of ganglion cell responses. The SP-IR ganglion cell is an OFF-center unit in the turtle retina and may be driven in the center of its receptive field by luminosity bipolar cells and in its surround by amacrine cells with color-opponent properties.

The organization of the turtle inner retina. I. ON- and OFF-center pathways

Intracellular recordings and dye injections of Lucifer yellow, horseradish peroxidase, or Neurobiotin were made in bipolar, amacrine, and ganglion cells of the Pseudemys turtle retina. By using a standard light-stimulation protocol in a sample of 375 labeled neurons, we were able to identify morphological and physiological characteristics of 11 types of bipolar cell, 37 types of amacrine cell, and 24 types of ganglion cell. To make sense of these data, we have chosen to group the 72 essentially different neuron types into traditional, functionally significant pathways. In this paper we look at the neuronal types in the inner plexiform layer (IPL) in terms of their contribution to generalized luminosity responses such as sustained ON- or OFF-center and transient ON-OFF ganglion cells; in the companion paper (J. Ammermüller, J.F. Muller, and H. Kolb, 1995, J. Comp. Neurol. 358:35-62) we look at them in terms of their involvement in color opponency and directional selectivity. A functional organization of the turtle IPL into OFF sublaminae (strata 1 and 2) and ON sublaminae (strata 3, 4, and 5), as has been described for other vertebrate retinas, was quite clear for two varieties of OFF-center bipolar cells (B4 and B5) and for all four types of sustained ON-center bipolar cell (B1, B2, B6, and B7). Thus, we found no sustained ON-center bipolar cell terminating in strata 1 and 2. We did, however, see three varieties of sustained OFF-center bipolar cells (B3, B9, and B10) having axon terminals in strata 3-5 (the ON sublamina) in addition to their terminations in stratum 1 or 2 (the OFF sublamina). Monostratified sustained ON- and OFF-center amacrine and ganglion cells rigidly obeyed the border of ON and OFF sublaminae. However, multistratified and diffuse sustained amacrine and ganglion cells could be either ON-center or OFF-center, and they did not strictly obey the border: such ON-center cells always had processes in one of the ON sublaminae (strata 3-5), and the equivalent OFF-center cells always had processes in one of the OFF sublaminae (strata 1 and 2). Monostratified transient amacrine and ganglion cells were concentrated in the middle of the IPL (around stratum 3), whereas bi-, tri-, or multistratified transient amacrine or ganglion cells always had processes in both the ON and the OFF sublaminae.(ABSTRACT TRUNCATED AT 400 WORDS)

The organization of the turtle inner retina. II. Analysis of color-coded and directionally selective cells

Color coding and directional selectivity (DS) of retinal neurons were studied in the Pseudemys turtle by using similar intracellular recording and staining techniques as in the preceding paper (J. Ammermüller and H. Kolb, 1995, J. Comp. Neuronal. 358:1-34). Color-coded responses were elicited by red (621 or 694 nm), green (525 or 514 nm), and blue (455 nm) light flashes. In addition to red/green and yellow/blue types of chromaticity horizontal cells, in our sample of 305 identified cells we found that 17% of bipolar cells, 6.5% of amacrine cells, and 18% of ganglion cells exhibit color-coded responses. DS responses were found in 37% of the tested ganglion cells and 41% of the tested amacrine cells. Two morphologically identified bipolar cell types, B10 and B11, were red-ON/blue-OFF and red-OFF/green, blue-ON, respectively. Of five identified amacrine cell types, three were red-OFF/blue-ON center (A1, A3, A23b), one was red-OFF/green-ON center (A32), and one (A33) was double color-opponent of red-ON/blue-OFF center:red-OFF/blue-ON surround. Five ganglion cell types had variously color-coded centers (G14 and G24) or surrounds (G3 and G18), including one type, G6, that was double color-opponent (red-OFF/green-ON center:red-ON/green-OFF surround). Responses to colors were found primarily in sustained responses of bipolar and ganglion cells. However, in amacrine cells, transient components of the response also showed color dependence. Red-OFF-center responses were found in ganglion cells that were in a position to make connections at the strata 2/3 border with the red-OFF bipolar cell (B11); red-ON-center responses occurred in ganglion cells with branches in stratum 4 of the IPL where the red-ON-center bipolar (B10) ended. Blue-ON-center signals appeared to be processed mainly in strata 1-2/3, and blue-OFF-center signals in strata 3-5 of the IPL, with contributions of amacrine cells and bipolar cells. Labeled DS amacrine cells could be identified as A9, A20, and A22, and ganglion cells as G19, G20, and G24. The latter type (G24) showed DS and color coding. All response types (ON-center, OFF-center, ON-OFF) were encountered. DS amacrine cells were monostratified near the middle of the IPL, whereas DS ganglion cells were mono-, bi-, and multistratified, although all DS ganglion cells had one feature in common: they had dendrites in stratum 1 of the IPL.(ABSTRACT TRUNCATED AT 400 WORDS)

Substance P-immunoreactive neurons in the human retina

Substance P (SP) is a neuropeptide that acts as a neurotransmitter or a neuromodulator in the retina. The aim of this study was to identify the type(s) and the distribution of the SP-immunoreactive (SP-IR) cells in the human retina. We have used an antiserum to SP to immunostain neurons in postmortem human retinae. Immunostained retinae were processed with the avidin-biotin complex (ABC) to visualize the cells either whole mounted in glycerol or embedded in plastic. Some retinae were also sectioned at 20 microns in order to obtain radial views of stained cells. SP-IR amacrine cells stain intensely and appear to be of a single type in the human retina. They are large-field cells with large cell bodies (16 microns diameter) lying in normal or displaced positions on either side of the inner plexiform layer (IPL). Their sturdy, spiny, and appendage-bearing dendrites stratify in stratum 3 (S3) of the IPL, where many overlapping, fine dendrites intermingle to form a plexus of stained processes. Either cell bodies or primary dendrites emit an "axon-like" process that, typically, divides into two long, fine processes, which run in opposite directions for hundreds of micrometers in S5 and S3 before disappearing as distinct entities in the stained plexus in S3. Long, fine dendrites also pass from the dendritic plexus to run in S5 and down to the nerve fiber layer to end as large varicosities at blood vessel walls. In addition, fine processes are emitted from the dendritic plexus that runs in S1, and some pass up to the outer plexiform layer (OPL) to run therein for short distances. The SP-IR amacrine cell has many similarities to the thorny, type 2 amacrine cells described from Golgi studies. In addition to the SP-IR amacrine cells, a presumed ganglion cell type is faintly immunoreactive. Its 20-22 microns cell body gives rise to a radiate, sparsely branched, wide-spreading dendritic tree running in S3. Its dendrites and cell body become enveloped by the more intensely SP-IR processes and boutons from the SP-IR amacrine cell type. The SP-IR ganglion cell type most resembles G21 from a Golgi study.

Heat shock induces resistance in rat pancreatic islet cells against nitric oxide, oxygen radicals and streptozotocin toxicity in vitro

When cultures of pancreatic islet cells are exposed to the nitric oxide donor sodium nitroprusside, to enzymatically generated reactive oxygen intermediates or to streptozotocin cell lysis occurs after 4-12 h. We report here that a heat shock at 43 degrees C for 90 min reduces cell lysis from nitric oxide (0.45 mM sodium nitroprusside) by 70%, from reactive oxygen intermediates (12 mU xanthine oxidase and 0.05 mM hypoxanthine) by 80% and from streptozotocin (1.5 mM) by 90%. Heat shock induced resistance was observed immediately after termination of the 90 min culture at 43 degrees C and correlated with enhanced expression of hsp70. The occurrence of DNA strand breaks, a major early consequence of nitric oxide, reactive oxygen intermediates, or streptozotocin action, was not suppressed by heat shock treatment. However, the depletion of NAD+, the major cause of radical induced islet cell death, was suppressed after heat shock (P < 0.01). We conclude that pancreatic islet cells can rapidly activate defence mechanisms against nitric oxide, reactive oxygen intermediates and streptozotocin by culture at 43 degrees C. Islet cell survival is due to the prevention of lethal NAD+ depletion during DNA repair, probably by slowing down poly(ADP-ribose)polymerase activation.

Suppression of nitric oxide toxicity in islet cells by alpha-tocopherol

We show here that preincubation of pancreatic islet cells with alpha-tocopherol significantly improves their resistance to toxic doses of nitric oxide (NO). No protection was afforded by other antioxidants such as vitamin C or glutathione-monoethyl ester. The pathway of NO induced islet cell death involves DNA damage and excessive activation of poly(ADP-ribose)polymerase leading to irreversible depletion of intracellular NAD+. alpha-Tocopherol was found to interfere at early steps of this pathway, by preventing the occurrence of DNA strand breaks. This indicates that alpha-tocopherol directly interacts with NO or its reactive intermediates. We conclude that alpha-tocopherol is not only part of the cellular defence system against oxygen radicals but also protects eukaryotic cells from NO toxicity.

Inactivation of the poly(ADP-ribose) polymerase gene affects oxygen radical and nitric oxide toxicity in islet cells

Activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) is an early response of cells exposed to DNA-damaging compounds such as nitric oxide (NO) or reactive oxygen intermediates (ROI). Excessive poly-(ADP-ribose) formation by PARP has been assumed to deplete cellular NAD+ pools and to induce the death of several cell types, including the loss of insulin-producing islet cells in type I diabetes. In the present study we used cells from mice with a disrupted and thus inactivated PARP gene to provide direct evidence for a causal relationship between PARP activation, NAD+ depletion, and cell death. We found that mutant islet cells do not show NAD+ depletion after exposure to DNA-damaging radicals and are more resistant to the toxicity of both NO and ROI. These findings directly prove that PARP activation is responsible for most of the loss of NAD+ following such treatment. The ADP-ribosylation inhibitor 3-aminobenzamide partially protected islet cells with intact PARP gene but not mutant cells from lysis following either NO or ROI treatment. Hence the protective action of 3-aminobenzamide must be due to inhibition of PARP and does not result from its other pharmacological properties such as oxygen radical scavenging. Finally, the use of mutant cells an alternative pathway of cell death was discovered which does not require PARP activation and NAD+ depletion. In conclusion, the data prove the causal relationship of PARP activation and subsequent islet cell death and demonstrate the existence of an alternative pathway of cell death independent of PARP activation and NAD+ depletion.

Cyclophosphamide treatment of female non-obese diabetic mice causes enhanced expression of inducible nitric oxide synthase and interferon-gamma, but not of interleukin-4

In pancreatic lesions of non-obese diabetic (NOD) mice the expression of inducible nitric oxide synthase (iNOS) and of the cytokines interferon-gamma and interleukin-4 were studied. Strong iNOS expression as determined at the level of transcription, translation and of enzyme activity was associated with destructive insulitis as seen 8-10 days after cyclophosphamide treatment of 70- to 80-day-old female NOD mice. Immunohistochemistry showed iNOS associated with infiltrating macrophages but not in endocrine cells. The enhancement of iNOS after cyclophosphamide correlated with an increase of T-helper type 1 (Th1) associated interferon-gamma expression while T-helper type 2 (Th2) associated interleukin-4 was the dominant cytokine prior to cyclophosphamide and after diabetes onset. We conclude that insulitis in young NOD mice is carried by Th2 cells while cyclophosphamide enhanced insulitis is determined by Th1 cells. Macrophages show two different functional states in insulitis; strong iNOS expression in macrophages is associated with destructive insulitis.