Identification of the synaptic pedicles belonging to the different spectral types of photoreceptor in the turtle retina

In this paper we describe the morphology of the different spectral types of photoreceptor pedicles in the outer plexiform layer (OPL) of the Pseudemys turtle as studied by light (LM) and electron microscopy (EM). Tangential serial thick sections were cut from the oil droplet region to the level where the axons emerge from cell bodies and then serial thin sections through the axons and the entire pedicles were collected and examined. Thus photoreceptor pedicles could be identified by tracing cells from their oil droplets to their synapses in the OPL. Double cone pedicles consisted of closely applied pairs with the principal member's pedicle wrapping around the accessory member's pedicle. Each pedicle was approx. 104 microns 2 in area and contained 12 and 8 synaptic ribbons respectively. Rods comprised 8% of the pedicles in the field, were small (84 microns 2), contained closely packed synaptic vesicles, and on average, 9 long ribbons. Single red and green cone pedicles could not be told apart without following them from their oil droplets, however, both were about the same size (106-127 microns 2) and contained 10-12 ribbons. Blue cone pedicles were small and round (80 microns 2) and arose from short oblique axons giving off from large, greenish, clear oil droplet-containing cell bodies (13% of the cone population). The least common pedicle types (5% of the cone population) were identified tentatively as UV cones because they originated from small, clear oil droplet-containing cell bodies. UV cones had spherical pedicles, elongated in the vertical axis, that arose from extremely long, angled axons. Their very small pedicles (64 microns 2) exhibited characteristic "horns" that projected from the top sides of the pedicle. Both putative UV and blue cone pedicles ended more vitread in the OPL than other pedicles and contained only 5-6 and 8-10 ribbons respectively. Understanding the ultrastructural features that distinguish the different types of photoreceptor pedicle will allow us to begin a study of spectral connections to second order neutrons in the turtle OPL in the future.

Fusidic acid suppresses nitric oxide toxicity in pancreatic islet cells

Earlier preclinical and clinical trials indicate that fusidic acid, a triterpenoid compound originally described as an antimicrobial drug may protect islet beta cells from destruction in type I (insulin-dependent) diabetes mellitus. Since nitric oxide appears to be an important mediator of inflammatory islet cell death we analyzed whether fusidic acid interferes with nitric oxide production or action. We report here that fusidic acid dose-dependently inhibits lysis of isolated islet cells by activated macrophages, a process mediated by nitric oxide. In the presence of 100 microM fusidic acid macrophage-mediated islet cell lysis was reduced from 52.5 to 1.7% (P < 0.001). Fusidic acid only slightly affected macrophage function and did not inhibit the release of nitric oxide. We therefore tested whether fusidic acid suppresses nitric oxide toxicity in target cells. Isolated islet cells were exposed to the nitric oxide donor nitroprusside which led to DNA strand breaks and plasma membrane lysis. DNA strand breaks were reduced from 54.6 to 34.9% (P < 0.001) in the presence of 100 microM fusidic acid and cell lysis was reduced from 60.1 to 27.5% with 100 microM (P < 0.001). In the presence of 500 microM fusidic acid DNA strand breaks and cell lysis were reduced further to 27.1 and 10.7%, respectively (P < 0.001). No protection by fusidic acid was observed when cells were exposed to oxygen radicals or the alkylating beta cell toxin streptozotocin. The suppression of nitric oxide toxicity by fusidic acid was not due to its known inhibitory action on protein biosynthesis and thus represents a hitherto unknown activity of this drug.

Ultrastructural and immunocytochemical analysis of the circuitry of two putative directionally selective ganglion cells in turtle retina

Two well-stained, horseradish peroxidase-filled varieties of putative ON-OFF directionally selective ganglion cells, G14a and G15, that project to the dorsolateral optic tectum (Guiloff and Kolb [1992a] Vis. Neurosci. 8:295-313) were studied qualitatively and quantitatively. Both were bistratified ganglion cells with one tier of dendrites in the OFF sublamina and the other in the ON sublamina of the inner plexiform layer (IPL). The cells were serially sectioned and examined for synaptic inputs by electron microscopy. Portions of the dendritic trees were also analyzed after postembedding immunocytochemistry for neurotransmitter candidates gamma aminobutyric acid (GABA), glycine, choline acetyltransferase (ChAT), and glutamate in presynaptic neurons. Both G14a and G15 are dominated by amacrine cell inputs and have only minor bipolar cell involvement. Probably at least two different types of bipolar cell are presynaptic. Both ganglion cells receive some GABA-positive (GABA+) amacrine inputs and G14a receives ChAT+ amacrine inputs. Glycine+ and glutamate+ inputs could not be detected in either cell. The GABA+ inputs appeared to be regionally arranged in the dendritic trees. The general distribution of amacrine and bipolar inputs to the two tiers of dendrites in both cell types appeared to be asymmetrical, both along the radial extent of the dendritic trees and within the depth of the IPL. Our data support some aspects of the current models for directional selectivity. We suggest candidate bipolar and amacrine cells that could have input to these ganglion cells. Since many of the putative presynaptic amacrine cells coincide with directionally selective types recorded and stained by other authors, we propose that in turtle retina directional selectivity arises in neurons presynaptic to the ganglion cells.

Complexity and scaling properties of amacrine, ganglion, horizontal, and bipolar cells in the turtle retina

In the present study we have evaluated the complexity and scaling properties of the morphology of retinal neurons using fractal dimension as a quantitative parameter. We examined a large number of cells from Pseudemys scripta and Mauremys caspica turtles that had been labeled using Golgi-impregnation techniques, intracellular injection of Lucifer Yellow followed by photooxidation, intracellular injection of rhodamine conjugated horseradish peroxidase, or intracellular injection of Lucifer Yellow or horseradish peroxidase alone. The fractal dimensions of two-dimensional projections of the cells were calculated using a box counting method. Discriminant analysis revealed fractal dimension to be a significant classification parameter among several other parameters typically used for placing turtle retinal neurons in different cell classes. The fractal dimension of amacrine cells was significantly correlated with dendritic field diameters, while the fractal dimensions of ganglion cells did not vary with dendritic field span. There were no significant differences between the same cell types in two different turtle species, or between the same types of neurons in the same species after labeling with different techniques. The application of fractal dimension, as a quantitative measure of complexity and scaling properties and as a classification criterion of neuronal types, appears to be useful and may have wide applicability to other parts of the central nervous system.

Analysis of oxygen radical toxicity in pancreatic islets at the single cell level

Despite extensive studies on streptozotocin, alloxan and nitric oxide toxicity in pancreatic islets the mechanism of oxygen radical induced islet cell death has not been determined. The present study shows at the level of single cells that following exposure to oxygen radicals generated from xanthine oxidase DNA strand breaks occur in cell nuclei within 5-60 min and precede cell death by several hours. Similar kinetics were seen when treating islet cells with the alkylating agent streptozotocin. Immunofluorescence studies demonstrated the endogenous formation of ADP-ribose polymers in nearly all islet cell nuclei within minutes of treatment with xanthine oxidase, indicating activation of the enzyme poly(ADP-ribose) polymerase (PARP). Concomitantly, cellular NAD+ depletion was noted. Nicotinamide largely prevented NAD+ depletion and in parallel resulted in islet cell survival. These findings identify islet cell nuclear DNA as a primary target of oxygen radical toxicity and suggest related pathways of oxygen radical, nitric oxide and streptozotocin toxicity.

Soluble forms of intercellular adhesion molecule-1 in insulin-dependent diabetes mellitus

Soluble adhesion molecules are detectable at low levels in healthy people but are increased in various disorders. However, their physiological role is unknown. Circulating intercellular adhesion molecule-1 (cICAM-1) may modulate inflammation or arise as a consequence of inflammation. We have described elevated concentrations of cICAM-1 in subjects at risk of developing insulin-dependent diabetes mellitus (IDDM), compared with recent-onset IDDM patients and healthy controls. Here we tested the ability of a monomeric soluble recombinant form of ICAM-1 (rICAM-1), to prevent the proliferation of T cells to islet-cell and other antigens. We also tested the ability of two multivalent ICAM-1-immunoglobulin (ICAM-1-Ig) fusion proteins to stop proliferation of T cells in vitro. Autoreactive T-cell proliferation was suppressed by monoclonal antibodies directed against ICAM-1 or lymphocyte-function antigen-1 (LFA-1). Furthermore, 100 mumol rICAM-1 blocked T-cell proliferation in response to an islet-cell autoantigen, and multivalent ICAM-1-Ig fusion proteins were approximately 1,000-fold more effective. The usual interleukin-2-induced proliferation of T cells was unaffected by ICAM or ICAM-Ig. In addition, rICAM-1 blocked primary T-cell responses from peripheral blood mononuclear cells of newly diagnosed IDDM patients in concentrations similar to elevated cICAM-1 concentrations in individuals at risk for the disease. Thus, naturally circulating ICAM-1 may downregulate inflammation in subjects at risk of developing IDDM. Ig-ICAM-1 fusion proteins may thus provide novel means to intervene in the pathogenesis of autoimmune diseases.

Regulation of 92-kD gelatinase release in HL-60 leukemia cells: tumor necrosis factor-alpha as an autocrine stimulus for basal- and phorbol ester-induced secretion

Matrix metalloproteinase 9 (MMP-9), also known as 92-kD type IV collagenase/gelatinase, is believed to play a critical role in tumor invasion and metastasis. Here, we report that MMP-9 was constitutively released from the human promyelocytic cell line HL-60 as determined by zymographic analysis. Tumor necrosis factor-alpha (TNF-alpha) enhanced the enzyme release threefold to fourfold and the protein kinase C (PKC) activator and differentiation inducer 12-O-tetradecanoylphorbol-13-acetate (TPA) eightfold to ninefold. Gelatinase induction by TNF-alpha and TPA was inhibited by actinomycin D or cycloheximide, indicating that de novo protein synthesis was required. Neutralizing monoclonal antibodies to TNF-alpha (anti-TNF-alpha) decreased the basal MMP-9 release of these cells. In addition, these antibodies also significantly interfered with the TPA-induced enzyme release. Agents that inhibit TNF-alpha expression in HL-60 cells, such as pentoxifylline and dexamethasone, completely abrogated both the constitutive and TPA-evoked MMP-9 release. Diethyldithiocarbamate, which is known to stimulate TNF-alpha production in HL-60 cells, exerted a positive effect on MMP-9 release in untreated cells but was inhibitory in TPA-treated HL-60 cells. The PKC inhibitor staurosporine at low concentrations (100 ng/mL) caused a significant augmentation of MMP-9 release in untreated cultures that was blocked by the addition of anti-TNF-alpha. High concentrations (2 mumol/L) of staurosporine completely abolished the extracellular enzyme activity both in untreated and TPA-stimulated cells. These results suggest, that TNF-alpha is required for basal and PKC-mediated MMP-9 release in HL-60 leukemia cells. Thus, MMP-9 secretion may be regulated by TNF-alpha not only in a paracrine but also in an autocrine fashion. This may potentiate the matrix degradative capacity of immature leukemic cells in the processes of bone marrow egress and the evasion of these cells into peripheral tissue.

Human osteosarcoma (U-2 OS) cells express both insulin-like growth factor-I (IGF-I) receptors and insulin-like growth factor-II/mannose-6-phosphate (IGF-II/M6P) receptors and synthesize IGF-II: autocrine growth stimulation by IGF-II via the IGF-I receptor

Recently, insulin-like growth factor-I and -II (IGF-I and -II) have been implicated in the growth promotion of tumors in vivo and tumor cells in vitro. We have studied the human osteosarcoma cell line U-2 OS in order 1) to gain more insight into the growth promoting actions of the IGFs and 2) to establish an in vitro tissue culture model of IGF action in human tumor cells. Specific binding of 125I-IGF-I and 125I-IGF-II to IGF-I receptors and IGF-II/mannose-6-phosphate (M6P) receptors on U-2 OS cells was demonstrated in competitive binding experiments and in affinity crosslinking experiments. Western blotting of cell extracts confirmed the expression of the IGF-II/M6P receptor. In addition, in Northern blotting experiments using total RNA from U-2 OS cells IGF-I receptor RNA of 11 kb and IGF-II/M6P receptor RNA of approximately 9 kb were detected. Solution hybridization experiments confirmed the presence of IGF-I receptor and IGF-II/M6P receptor RNA. In a subset of experiments DNA synthesis was measured as 3H-thymidine uptake into cellular DNA of U-2 OS cells. Normal rat serum stimulated DNA synthesis maximally. IGF-I-deficient serum from hypophysectomized rats as well as IGF-I or IGF-II without serum were approximately twofold and tenfold, respectively, less potent than serum in stimulating 3H-thymidine uptake. The concentrations of IGF-I and IGF-II needed for half maximal stimulation of DNA synthesis corresponded well with the respective concentrations required for half maximal inhibition of 125I-IGF-I binding to U-2 OS cells. The anti-IGF-I receptor antibody alpha IR3 blocked the IGF-I and IGF-II stimulated increase of 3H-thymidine uptake. In addition, basal DNA synthesis was partially inhibited by the anti-IGF-I receptor antibody. These data suggest that U-2 OS cells synthesize and secrete IGF-like peptides. Northern blotting experiments confirmed that U-2 OS cells express an IGF-II RNA species of 5.3 kb but no IGF-I transcripts. In a series of RNase protection assays, protected RNA fragments were detected with an IGF-II riboprobe. Also, cell-conditioned medium from U-2 OS cells contained 1-2 ng/ml IGF-II immunoreactivity as measured in an IGF-binding protein blocked IGF-II radioimmunoassay.

IN CONCLUSION

1) U-2 OS cells express IGF-I and IGF-II/M6P receptors. 2) U-2 OS tumor cells respond to the addition of exogenous IGF-I and IGF-II with an increase of DNA synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Are there three types of horizontal cell in the human retina?

Golgi-impregnated horizontal cells (HCs) as viewed in whole mount human retinas have been studied by light microscopic (LM) techniques. Impregnated HCs have been drawn by camera lucida and by the Eutectics neuron tracing method to provide quantitative data on dendritic tree sizes, dendritic tree shapes, and dendritic terminals for statistical treatment and cluster analysis. In addition, fractal analyses of HC dendritic branching patterns have been performed. Three significantly different HCs can be classified on both subjective and objective morphological criteria in central and peripheral human retina. In the fovea all HCs are so small that it is difficult to achieve a clear separation of the subtypes, although they can be distinguished by the experienced observer. HI types are the classic HCs of Polyak (The Retina, Chicago: University of Chicago Press, 1941) with distinct dendritic terminal clusters going to cones and a fan-shaped axon terminal consisting of large numbers of rod-destined terminals. HII cells have profusely branched, overlapping dendrites, with poorly defined terminals going to cones and a short curled axon bearing small terminals also going to cones. The HIII types exhibit larger diameter, more asymmetrically shaped dendritic trees and 30% more dendritic terminal clusters than HI cells at any location on the retina. Many HIII cells appear to emit a process from the cell body in the inner nuclear layer (INL) that descends into the outer strata of the inner plexiform layer (IPL). The axon of the HIII cell may end in a loosely organized, sprawling arborization. Fractal dimensions of the horizontal cells also show significant differences between the three groups. HII cells exhibit the highest fractal dimension followed by HI and HIII cells with lower and lowest fractal dimensions, respectively. The fractal dimension of HII cells of rhesus monkey, as determined from drawings by other authors in other publications, are the same as HII cells of human retina.

Horizontal cells and cone photoreceptors in primate retina: a Golgi-light microscopic study of spectral connectivity

The relationship of primate horizontal cells (HC) to cone pedicles was assessed by superimposing the cone inner segment mosaic upon Golgi-impregnated HC dendritic terminal clusters in a light microscope (LM) study. The HI, HII, and HIII types of HC were identified, hand-drawn, photographed, and analyzed by computer graphics methods. Blue cone (B-cones) inner segments and their projected pedicles were distinguished from red (R-cones) and green (G-cones) cones on morphological criteria. Thus the inclusion or avoidance of B-cone pedicles by the various HC types' dendritic terminal clusters establishes whether there is any color specificity to their connections. In addition, we made counts of the number of dendritic terminals in the clusters going to cone pedicles in the various HCs' dendritic fields and plotted these against distances the cone pedicles lay from the cell body. In this way we could evaluate the weighting of spectral type of cone input. In general, the three HC types made the majority of their dendritic contacts with cones lying closest to their cell bodies at the center of their dendritic fields. However, HI and HIII cells, with their distinct terminal clusters, did not contact all the centrally located cones uniformly. They either avoided completely (HIII cells) or made only sparse dendritic connections (HI cells) with certain cones. The avoided or sparsely innervated cones were identified as B-cones. HII cells, on the other hand, with their more profuse and diffusely branched dendrites, appeared to contact all overlying cone pedicles and, in contrast to HI and HIII cells, directed a relatively larger number of dendrites to B-cone positions. Axon terminals of HII cells appeared to contact B-cones exclusively.

Horizontal cells and cone photoreceptors in human retina: a Golgi-electron microscopic study of spectral connectivity

Connections of the three human horizontal cell (HC) types with overlying cone pedicles have been studied via electron microscopy (EM). Because blue cones (B-cones) can be recognized on distinctive morphological criteria, we could determine their presence by light microscopy (LM) in the mosaic overlying HC dendritic trees. Then we could confirm the presence or absence of dendritic contacts to B-cone pedicles by examining EM serial sections and making reconstructions of examples of the three HC types. Three HI cells have been reconstructed. Their dendritic terminals ended as lateral elements of ribbon synapses in green and red cone pedicles (G- and R-cones) primarily. B-cone pedicles in HI cell dendritic fields received no more than one or two contacts. Six reconstructed HII cells were found to contact all the pedicles within their dendritic field. However, their dendrites reached especially for B-cone pedicles and innervated them with disproportionately large numbers of terminals compared with G- and R-cones. HII axons appeared to contact B-cones exclusively. The four reconstructed HIII cells were found to avoid completely B-cones in their dendritic fields. Data have been collected on synaptic ribbon lengths at HI and HII lateral elements in the B-cone as compared with G- and R-cone pedicles. HII dendritic terminals end almost exclusively at the smaller ribbons and HI dendrites at the larger ribbons. The number of dendritic terminals provided by the three HCs to G- and R-cone pedicles as compared B-cone pedicles has been more accurately quantitated than was possible in the LM analysis (accompanying paper). New findings on the morphology of B-cone pedicles in peripheral retina have revealed that 1) B-cone pedicles end further vitread in the outer plexiform layer (OPL) than other cone pedicles, thereby forming a sublayer of the OPL neuropil, here named OPLb, in comparison to OPLa, where the G- and R-cone pedicles end; 2) B-cone pedicles have very few telodendrial connections; and 3) in peripheral retina (probably beyond 8 mm from the fovea to the ora serrata), they are bi- or trilobed, with each lobe containing separate synaptic invaginations. The vitread position and unique morphology of B-cone pedicles appear to relate directly to the unique morphology and unusual connectivity patterns of both their B-cone-specific bipolar and B-cone-related horizontal cell, the HII cell.(ABSTRACT TRUNCATED AT 400 WORDS)

Inflammatory islet damage in patients bearing HLA-DR 3 and/or DR 4 haplotypes does not lead to islet autoimmunity

The hypothesis was tested that islet autoimmunity is induced by ongoing islet cell destruction in subjects with susceptibility genes HLA-DR 3 and/or DR 4. Sixty-one patients with confirmed chronic pancreatitis were analysed, 30 of whom expressed HLA-DR 3 and/or DR 4. Electron microscopy studies in 10 patients showed that the inflammatory process also affected islets, as recognisable from islet cell lysis, intrainsular fibrosis and immune cell infiltrates. None of the sera tested contained any of three markers of islet autoimmunity, ICA, IAA or GAD antibodies. A correlation was seen between the loss of exocrine function, as determined by the ALTAB-test, and of beta-cell function, as determined by the C-peptide response to i.v. glucagon. However, there was no preferential loss of beta-cell function in patients with HLA-DR 3 and/or DR 4. We conclude that islet cell destruction occurs during chronic pancreatitis, but does not trigger islet autoimmunity, even in the presence of HLA-DR 3 and/or DR 4.

In situ nick-translation detects focal apoptosis in thymuses of glucocorticoid- and lipopolysaccharide-treated mice

In this study we used in situ nick-translation to analyze apoptotic events in the thymus and in cultured thymocytes at the level of individual cell nuclei. In vitro nuclear DNA strand breaks were observed 3 hr after exposure of thymocytes to dexamethasone (Dex) in 30% of cells and increased to 78% after 15 hr. In sections of 10-day-old mouse thymus, single cells with DNA strand breaks were dispersed throughout the cortex and to a lesser degree in the medulla. In contrast, a large number of clusters of apoptotic cells were seen in the thymic cortex 3-18 hr after injection of Dex or lipopolysaccharide (LPS). After 48 hr apoptotic cells were no longer detectable. Positive signals correlated with the detection of DNA ladders of multimers of about 180 BP size on agarose gels. Electron microscopy confirmed the presence of apoptotic cell clusters and showed that apoptotic foci were located around capillaries in LPS-injected animals. We conclude that in situ nick translation is a suitable method to detect apoptotic nuclei in cultured cells and on cryostat sections. With this method we could demonstrate that in vivo spontaneous apoptosis occurs in single dispersed thymocytes, also including the medulla, whereas experimentally induced apoptosis affects cell clusters, possibly due to high local concentrations of apoptosis inducers.

Human colon carcinoma cells (CaCo-2) synthesize IGF-II and express IGF-I receptors and IGF-II/M6P receptors

The IGFs have been implicated in the development of the intestinal tract. We have studied the human colon carcinoma cell line CaCo-2 to gain more insight into the function of the IGFs in the gut. [125I]IGF-I and -II bound specifically to CaCo-2 cells as measured in competitive binding experiments. The existence of IGF-I receptors was further demonstrated by affinity crosslinking studies using DSS as the crosslinking agent. Western blotting of CaCo-2 cell extracts using an anti IGF-II/M6P receptor antiserum provided additional evidence for the expression of the IGF-II/M6P receptor. In addition, Northern blotting experiments showed specific IGF-I receptor and IGF-II/M6P receptor gene expression in CaCo-2 cells. An 11 kb band was visualized with a 614 bp PstI IGF-I receptor probe on autoradiographs. Hybridization with a 663 bp IGF-II/M6P receptor probe yielded a 9 kb RNA species. Analysis of CaCo-2 cell RNA using solution hybridization/RNase protection assays yielded two protected fragments, approximately 379 bases in length, with a 394 base IGF-I receptor riboprobe and a 250 base protected fragment with a 260 base IGF-II/M6P receptor riboprobe. In a subset of experiments a PstI 700 base fragment of the IGF-I cDNA and a 554 base SalI fragment of the IGF-II cDNA were used for hybridization: no hybridization was detected with the IGF-I probe. However, using the [32P]IGF-II probe bands at 6.0 and 5.0 kb were labeled in Northern blotting experiments. Analysis of CaCo-2 cell RNA using solution hybridization/RNase protection assays yielded a 289 base protected fragment and a faint 534 base species with a 556 base human IGF-II riboprobe. In addition, IGF-II immunoreactivity was measured in CaCo-2 cell-conditioned medium using an IGF-binding protein blocked radioimmunoassay. CaCo-2 cell-conditioned medium contained 5-15 ng/ml IGF-II immunoreactivity. In conclusion, (1) CaCo-2 cells express both IGF-I receptor mRNA and IGF-II/M6P receptor mRNA and contain functional IGF-I receptor and IGF-II/M6P receptor protein. (2) CaCo-2 cells express IGF-II mRNA and secrete IGF-II immunoreactivity. We hypothesize that in human colon carcinoma cells IGF-II could act as an autocrine growth factor or alternatively could serve as a regulatory factor during differentiation.

Nitric oxide toxicity in islet cells involves poly(ADP-ribose) polymerase activation and concomitant NAD+ depletion

Previous studies have shown that DNA strand breaks are an early consequence of nitric oxide toxicity in pancreatic islet cells. We show here that exposure of islet cells to chemical NO donors causes the formation of ADP-ribose polymers in cell nuclei, with concomitant depletion of intracellular NAD+. Islet cell lysis was largely prevented by the ADP-ribosylation inhibitors nicotinamide, 3-aminobenzamide, and 4-amino-1,8-naphthalimide, the latter being a potent new-generation compound with high selectivity for poly(ADP-ribosyl)-ation. These findings indicate a key role of poly(ADP-ribose) polymerase activation in NO toxicity in islet cells.

Abnormal TNF-alpha production in diabetes-prone BB rats: enhanced TNF-alpha expression and defective PGE2 feedback inhibition

Upon stimulation with lipopolysaccharide (LPS), peritoneal macrophages from diabetes-prone Bio-Breeding (BB) rats secrete more tumour necrosis factor-alpha (TNF-alpha) than macrophages from diabetes-resistant BB or normal Wistar rats. Enhanced transcription was demonstrated by Northern blot analysis and at the single cell level by mRNA: RNA hybridization. Cytofluorometry analysis showed 2-4 times more plasma membrane and total cell-associated TNF-alpha in macrophages of diabetes-prone BB rats. The analysis of fluorescence intensity showed a single peak, and TNF-alpha mRNA was found in > 90% of macrophages. These findings exclude TNF hypersecretion as being due to an abnormal subfraction of cells. TNF-alpha gene hyperexpression in diabetes-prone BB rats was not due to mutations in the regulatory regions of the promoter, which could be shown by cloning and sequencing of the TNF-alpha promoter in the three rat strains. When searching for other regulatory defects we found the production of prostaglandin E2 (PGE2) in response to LPS to be up to 10 times lower in macrophages from diabetes-prone BB rats than from Wistar rats. Furthermore, BB rats macrophages required significantly higher concentrations of PGE2 for suppression of TNF-alpha secretion. We conclude that abnormal TNF-alpha production in macrophages from diabetes-prone BB rats is due to enhanced gene transcription and translation and that this is associated with defective PGE2 feedback inhibition.

Linear loss of insulin secretory capacity during the last six months preceding IDDM. No effect of antiedematous therapy with ketotifen

OBJECTIVE

To investigate the effect of an antiedematous therapy with the histamine antagonist ketotifen on beta-cell function in late prediabetes.

RESEARCH DESIGN AND METHODS

In a randomized double-blind placebo-controlled study, ketotifen was administered for 3 months to 9 islet cell antibody positive (ICA+) prediabetic patients with a first-phase insulin response (FPIR) below the 2.5th percentile to preserve residual beta-cell function. Patients were followed by intravenous glucose tolerance tests (IVGTTs) every 4-6 weeks for determination of FPIR, HbA1, ICAs, and insulin autoantibodies. In 5 patients, the immune activation state was followed by determination of serum levels of tumor necrosis factor-alpha (TNF-alpha), beta 2-microglobulin, and C-reactive protein (CRP).

RESULTS

Seven of nine patients developed diabetes within one year of follow-up. Irrespective of treatment with ketotifen, a slow and linear decline (P < 0.05) of 1 + 3-min insulin values was observed in sequential IVGTTs in those 7 patients who developed insulin-dependent diabetes mellitus (IDDM) during follow-up. The 2 other patients showed wide fluctuations of the insulin response with a threefold increase of initial insulin levels. HbA1 did not correlate with FPIR. Fasting blood glucose increased significantly during the study (P < 0.05). Individual levels of serum TNF-alpha, CRP, and beta 2-microglobulin did not change during the study.

CONCLUSIONS

The study could not demonstrate preservation of beta-cell function by ketotifen in the late stage before manifestation of clinical diabetes. Manifestation is preceded in the last 6 months by a steady loss of the FPIR without rapid deterioration immediately before diagnosis and without signs of increased immune activity.