Neuropathology of diabetic neuropathy and its correlations with neurophysiology.

Although the detailed pathogenesis of diabetic polyneuropathy is not known, several mechanisms appear to be involved and may occur sequentially. Hence, the early and much researched activation of the polyol-pathway appears to secondarily affect nonenzymatic glycation, perturbation of vasoactive substances, the immune system and neurotrophism. These metabolic abnormalities may be differentially expressed in the neuropathy occurring in insulin dependent diabetes mellitus (IDDM) and non-insulin dependent diabetes mellitus (NIDDM) diabetes. This notion is supported by differences in the structural abnormalities of the neuropathies in the two types of diabetes. Distinct and characteristic nodal changes occur in IDDM but not in NIDDM neuropathy, which also shows a milder axonal atrophy. On the other hand, nerve fiber loss which characterizes diabetic neuropathy tends to be focal in the older NIDDM patients, suggesting a more prominent vascular genesis. A further characteristic feature of diabetic neuropathy is blunted fiber regeneration, which probably is consequent to impairments of the necessary immune response and local synthesis of neurotrophic factors. Nerve biopsies from diabetic patients, although not necessary for diagnosis, provide valuable tissue for biochemical and molecular analysis of underlying mechanisms, the detailed elucidation of which will facilitate the design of targeted therapies.

Glucose transporters in rat peripheral nerve: paranodal expression of GLUT1 and GLUT3.

Peripheral nerve depends on glucose oxidation to energize the repolarization of excitable axonal membranes following impulse conduction, hence requiring high-energy demands by the axon at the node of Ranvier. To enter the axon at this site, glucose must be transported from the endoneurial space across Schwann cell plasma membranes and the axolemma. Such transport is likely to be mediated by facilitative glucose transporters. Although immunohistochemical studies of peripheral nerves have detected high levels of the transporter GLUT1 in endoneurial capillaries and perineurium, localization of glucose transporters to Schwann cells or peripheral axons in vivo has not been documented. In this study, we demonstrate that the GLUT1 transporter is expressed in the plasma membrane and cytoplasm of myelinating Schwann cells around the nodes of Ranvier and in the Schmidt-Lanterman incisures, making them potential sites of transcellular glucose transport. No GLUT1 was detected in axonal membranes. GLUT3 mRNA was expressed only at low levels, but GLUT3 polypeptide was barely detected by immunocytochemistry or immunoblotting in peripheral nerve from young adult rats. However, in 13-month-old rats, GLUT3 polypeptide was present in myelinated fibers, endoneurial capillaries, and perineurium. In myelinated fibers, GLUT3 appeared to be preferentially expressed in the paranodal regions of Schwann cells and nodal axons, but was also present in the internodal aspects of these structures. The results of the present study suggest that both Schwann cell GLUT1 and axonal and Schwann cell GLUT3 are involved in the transport of glucose into the metabolically active regions of peripheral axons.

Nodal Na(+)-channel displacement is associated with nerve-conduction slowing in the chronically diabetic BB/W rat: prevention by aldose reductase inhibition.

Chronic nerve conduction showing in experimental diabetic neuropathy has been associated with decreased nodal Na+ permeability and an ultrastructurally identifiable loss of axo-glial junctions, which comprise the paranodal voltage channel barrier separating nodal Na+ channels from paranodal K+ channels. In human and experimental diabetic neuropathy these structural changes of the paranodal apparatus correlate closely with the nerve conduction defect. The present immunocytochemical study of the alpha-subunit of the Na+ channel examined whether the breach of the voltage channel barrier may account for a shift in the distribution of Na+ channels explaining decreased nodal Na+ permeability. Biobreeding Wistar (BB/W) rats diabetic for 4-8 months showed a progressive redistribution of nodal Na+ channels across the paranodal barrier into the paranodal and internodal domains which was associated with chronic nerve conduction slowing. The present data suggest that structural damage to the paranodal barrier system in diabetic nerve facilitates the lateral displacement of Na+ channels from the nodal axolemma thereby diminishing their nodal density and the nodal Na+ permeability associated with the chronic nerve conduction defect in experimental diabetes. These abnormalities were prevented by the treatment with an aldose reductase inhibitor, belonging to a class of drugs that, in neuropathic patients, improves nerve-conduction velocity and repairs axo-glial dysjunction of the paranodal apparatus.

Nerve fiber regeneration following axotomy in the diabetic biobreeding Worcester rat: the effect of ARI treatment.

Diabetic neuropathy is characterized by progressive nerve fiber degeneration resulting in nerve fiber loss. In order to examine what role impaired nerve fiber regeneration may play in the progressive net nerve fiber loss, spontaneously diabetic biobreeding Worcester (BB/W) rats were subjected to sciatic nerve axotomy at 6 weeks of diabetes. Myelinated nerve fiber regeneration was examined morphologically and morphometrically at various time points following axotomy. The data were compared with those of axotomized control rats and diabetic rats treated with an aldose reductase inhibitor (ARI) from 1 week after onset of diabetes. Diabetic rats showed a significant attenuation of nerve fiber regeneration during the first 6 weeks following axotomy, which was normalized at 4 months postaxotomy. ARI treatment resulted in an initial burst of supranormal regeneration, which was normalized at 4 months postaxotomy. Impaired nerve fiber regeneration in diabetic rats was associated with a marked delay in preceding Wallerian degeneration and decreased phagocytic activity by macrophages, changes not demonstrated in ARI-treated diabetic rats. We propose that the impaired nerve fiber regeneration in the diabetic BB/W rat may, in part, be the result of impaired recruitment and/or function of macrophages necessary for the initiation of normal nerve fiber regeneration. The corrective effects of ARI treatment on the regenerative ability of diabetic peripheral nerve suggest that an activated polyol pathway may impact on both intrinsic and extrinsic mechanisms governing nerve fiber regeneration.

Galactosemia produces ARI-preventable nodal changes similar to those of diabetic neuropathy.

The present study was designed to examine the development of structural changes, characteristic of diabetic neuropathy, in chronic galactosemia and their responsiveness to inhibition of the polyol-pathway. Sprague-Dawley rats weighing 70-90 g were given a 50% galactose diet continued for 4 or 8 months. Half of these animals were simultaneously given the aldose reductase inhibitor (ARI) WAY 121-509. ARI-treatment normalized galactitol and myoinositol levels in the sciatic nerve. At 4 months, sciatic nerve conduction velocity (NCV) in galactosemic rats was reduced by 30% which was prevented in ARI-treated rats. At 8 months galactosemia reduced NCV to 58% of control values, while ARI-treatment for 8 months improved NCV to 71% of control values. ARI-treatment prevented in galactosemic rats nodal structural changes characteristic of diabetic neuropathy, whereas axonal atrophy was not affected by ARI-treatment, which may in part account for the only partial prevention of the NCV slowing at 8 months. Nerve fiber regeneration was increased 4-fold in ARI-treated rats compared with untreated galactosemic rats. These data suggest that chronic galactosemia produces a neuropathy structurally similar to diabetic neuropathy. The lack of an ARI-treatment effect on axonal atrophy suggests that this defect is not polyol related in galactosemia.

Urinary bladder dysfunction in the BB/W diabetic rat: effect of ganglioside treatment on functional and structural alterations.

Urinary bladder dysfunction in the diabetic BB/W rat is characterized by infrequent irregular contractions of high amplitude. Initially these occur in the absence of detectable neuroanatomical lesions of sensory afferent and parasympathetic fibers of the pelvic nerve, which constitute the micturition reflex arc. Structural lesions consisting of progressive axonal atrophy of myelinated and unmyelinated fibers become detectable only after 4 months of diabetes. In the current study we evaluated the effect of ganglioside treatment (10 mg./kg. body weight) for one month. This drug regimen was initiated at 4 months of diabetes, when functional bladder abnormalities were well established, whereas structural lesions were yet to appear. Animals examined 1 or 3 months after termination of the one-month treatment protocol showed sustained normalization of the characteristic functional abnormalities, accompanied by prevention of the neuroanatomical lesions of sensory afferent and parasympathetic efferent myelinated fibers in the pelvic nerve. These data suggest that ganglioside treatment may be beneficial in delaying the progression of diabetic autonomic neuropathy in this experimental animal model.

The preventive effect of aldose reductase inhibition on diabetic optic neuropathy in the BB/W-rat.

A polyol-pathway-related mechanism has been invoked in the pathogenesis of murine and human diabetic peripheral neuropathy in which progressive axonal atrophy and axo-glial dysjunction constitute the cardinal structural abnormalities. We have previously reported similar neuroanatomical changes in the optic nerve of 6-month diabetic BB/W-rats. In the present study we demonstrate progression of axonal atrophy and axo-glial dysjunction in the optic nerve in 12-month diabetic BB/W-rats. These structural lesions showed highly significant correlations with the associated prolongation of the latencies of the visual evoked potentials, suggesting that axo-glial dysjunction and axonal atrophy are major determinants for impaired optic nerve function. As in peripheral nerve, the polyol-pathway is present in the optic nerve and is activated by hyperglycaemia and galactosaemia. In this study we further examined the treatment effect of the aldose reductase inhibitor ponalrestat, given from 3 weeks of diabetes and continued throughout the study protocol. This regimen resulted in complete prevention of axo-glial dysjunction, and had a significant ameliorating effect on visual evoked potential latencies, but had no effect on optic nerve axonal atrophy. This latter finding differs from the effect of aldose reductase inhibition on diabetic peripheral nerve and suggests that axonal atrophy of central nerve tracts in diabetes may be the consequence of other metabolic abnormalities or alternatively the present regimen was insufficient to protect central axons from the effects of an increased activity of the polyol pathway.

The effect of acarbose on diabetes- and age-related basement membrane thickening in retinal capillaries of the BB/W-rat.

The effect of the alpha-glucosidase inhibitor acarbose on retinal capillary basement membrane thickening was examined in the spontaneously diabetic BB/W-rat. Four months of diabetes resulted in significant thickening of the basement membranes of both the superficial and deep capillary nets of the retina. This characteristic change of the retinal microvasculature in diabetes was completely prevented by acarbose treatment that substantially reduced postprandial hyperglycemia. A similar but less pronounced effect was seen on the age-related increase in basement membrane thickening in acarbose-treated non-diabetic control rats who demonstrated decreased glycated hemoglobin levels compared to non-treated control rats. Significant positive correlations between basement membrane thickness and glycated hemoglobin area suggest that diabetic retinal microangiopathy may be prevented by lowering the cumulative glucose exposure to the microvasculature, and that age-related basement membrane thickening is mediated by long-term exposure to normal glucose levels.

Impaired visual evoked potential and primary axonopathy of the optic nerve in the diabetic BB/W-rat.

The spontaneously diabetic BB/W-rat has emerged as an important model system for somatic and autonomic diabetic polyneuropathy. In this study we examined visual evoked potentials and the presence of morphometric and structural changes in the optic nerve and the retinal ganglion cells and their afferent axons contained in the retinal nerve fibre layer. A six-month duration of diabetes mellitus was associated with significant increases in the latencies of the visual evoked potentials. The latency of the first positive potential showed a 44% increase, and that of the first negative potential was prolonged by 41%. No significant changes were demonstrated at any of the amplitudes. In the optic nerve mean myelinated fibre size was significantly reduced to 82% of control values, which was accounted for by a significant reduction in axonal size. Axo-glial dysjunction, a prominent structural defect of diabetic somato-sensory neuropathy in both man and diabetic rodents, was non-significantly increased in the optic nerve. In diabetic animals retinal ganglion cells displayed dystrophic changes. No such changes were observed in age- and sex-matched control animals. Proximal axons of the retinal nerve fibre layer showed an increase in dystrophic axons in diabetic BB/W-rats. Morphometric analysis of optic nerve capillaries revealed no abnormalities except for basement membrane thickening. The present data suggest that the diabetic BB/W-rat develops a central sensory neuropathy, characterized functionally by prolonged latencies of the visual evoked potentials and structurally by an axonopathy of optic nerve fibres.

Intraluminal fibrosis induced unilaterally by lobar instillation of CdCl2 into the rat lung.

Lung injury induced by intratracheal instillation of cadmium chloride (CdCl2) into the rat lung may serve as a model of human interstitial lung disease. In this study, CdCl2 solutions were instilled through a lobar bronchus into the left lung of the rat. Two doses (400 micrograms or 50 micrograms of CdCl2, each in 400 microliters of neutral saline) were used and the morphologic changes occurring during the first 7 days after a single exposure were documented by light and electron microscopy. With the higher dose, inflammatory cells appeared in the alveolar interstitium 1 day after CdCl2 administration. Edema and thickening of the alveolar walls were evident, as were damaged type I epithelial cells and denuded basement membranes. Fibrin was found in the air spaces. Within 2 days, inflammatory cells were seen in large numbers and fibroblasts were observed passing through gaps in the alveolar basement membranes into the air spaces. By 4 and 7 days after CdCl2, various forms of intraluminal fibrosis, including intrabronchiolar budding, mural incorporation, and obliterative changes, were observed. The contralateral lungs had normal-appearing architecture for all the time points investigated. In the lower dose exposure, gradients of alveolar damage were observed in which normal lung, interstitial fibrosis, and/or intraluminal fibrosis were seen within treated lungs. In the mildly damaged regions, interstitial fibrosis predominated, while in the more severely damaged regions, mural incorporation of the convoluted basement membranes was observed. The pulmonary fibrosis that developed appeared to be similar to some human interstitial lung diseases and may offer a system in which to study the regulation of collagen deposition and fibrosis development in these pathologic conditions.

Monoclonal antibodies to Chlamydia psittaci guinea pig inclusion conjunctivitis (GPIC) strain.

Monoclonal antibodies to a strain of Chlamydia psittaci isolated from guinea pig inclusion conjunctivitis (GPIC) were developed. Only five of the 15 hybridomas isolated produced antibodies specific for the GPIC strain, while seven others produced antibodies which cross reacted with other strains and another species. Strain-specific and species-specific monoclonal antibodies were isotyped as IgG2a and IgG3, respectively. It appears that the GPIC strain has at least two epitopes, one of which is specific for the strain and the other common to the species. These monoclonal reagents may be used to immunotype GPIC agents, better than available methods and may be of potential use in the development of vaccines against chlamydial infections.

Light and electron microscopic studies on the synovial membrane in Reiter's syndrome. Immunocytochemical identification of chlamydial antigen in patients with early disease.

Studies by light microscopy on synovium obtained from 11 patients with Reiter's syndrome during the first month of an episode showed proliferation of synovial lining cells, polymorphonuclear neutrophils among the synovial lining cells, increased surface fibrin, and vascular congestion. Biopsy specimens taken later showed vascular congestion and still proliferated synovial lining cells, fewer polymorphonuclear neutrophils in some, and a tendency toward increased infiltration with lymphocytes and plasma cells. Electron microscopy of samples from 8 patients during the first month of disease activity showed occlusion of vessels by platelets in 4, and fibrin or dense granular material in the vessel walls in 4. Five of the patients with arthritis of less than 4 weeks duration had unidentified intracellular and extracellular particles; some of these were highly suggestive of Chlamydia. No such particles were noted in samples from patients with more chronic cases. Using an antibody to Chlamydia trachomatis and the peroxidase-antiperoxidase technique, immunocytochemistry showed reaction product in synovial macrophages in 2 patients with arthritis of less than 4 weeks duration, but not in the 1 patient studied who had more chronic disease. These studies provide support for dramatic synovial vascular injury consistent with that caused by endotoxin and the presence of chlamydial antigen in synovial macrophages, at least in the early phases of synovitis.

Products of polymorphonuclear cell injury inhibit IgG enhancement of monosodium urate-induced superoxide production.

The generation of polymorphonuclear cell (PMN) superoxide ion (O2-) by monosodium urate (MSU) crystals may be important in the pathogenesis of acute gout. Coating MSU crystals with IgG prior to exposure to PMN markedly augmented O2- generation. This augmentation was inhibited by supernates, termed cell lysate, derived from sonicated PMN or PMN exposed to MSU crystals for 5 hours at 37 degrees C. Lysate was effective in inhibiting O2- production when incubated with MSU crystals prior to, during, or after MSU crystals were exposed to IgG. No IgG could be eluted from crystals exposed to both lysate and IgG. Immunoelectron microscopy showed virtually no IgG on crystal surfaces after incubation of crystals with lysate and IgG. These data suggest that products of PMN injury can modulate further PMN responses to MSU crystals. This phenomenon provides a negative feedback loop and is one possible mechanism for the self-limitation of acute gouty attacks.

Immunochemical and ultrastructural characterization of serum proteins associated with monosodium urate crystals (MSU) in synovial fluid cells from patients with gout.

Immunoelectron microscopic (IEM) analysis of the surface coats of intracellular and extracellular monosodium urate (MSU) crystals in synovial fluid (SF) in gouty arthritis was performed using the ferritin-bridge method. Cells from patients with acute gout were fixed in 1% glutaraldehyde containing 0.05% saponin to permeabilize membranes for access of immunochemicals to intracellular antigens. Intracellular MSU crystals were observed in phagosomes of greater than 75% of both polymorphonuclear (PMNs) and mononuclear cells. Coating of crystals with IgG was more prominent than with IgM or IgA. Other proteins such as C3, and fibrinogen were also found to a lesser extent. Albumin was not detected in appreciable amounts on MSU crystals. Extracellular crystals also showed IgG to be bound more prominently than other proteins. The various proteins, shown here for the first time to be clearly associated with intracellular crystals by EM, and other materials associated with MSU crystals may influence the phlogistic properties of these crystals.

Palindromic rheumatism with rheumatoid nodules: a case report with ultrastructural studies.

Rheumatoid nodules developed on the finger tips of a patient with palindromic rheumatism. The patient had no bone cysts or erosions and had no rheumatoid factor. A light microscopic and ultrastructural study of a nodule showed a necrotic centre with fibrin, collagen, and granular material surrounded by large histiocytes, fibrocytes, lymphocytes, and vessels with adjacent mast cells as has been seen with nodules in classical rheumatoid arthritis (RA). We describe the first immunoperoxidase studies on a rheumatoid nodule and have identified reaction products for immunoglobulins and C3 in perivascular and endothelial cell vacuoles and in the necrotic centre.

Transmission electron microscopic studies on articular calcium crystals and associated protein coatings.

Calcium pyrophosphate (CPPD) and apatite crystals are associated with several types of arthritis. Using transmission electron microscopy both the tiny apatite-like crystals and larger CPPD can be seen to be associated with granular materials. With the ferritin bridge technique immunoglobulins and complement are seen in the material with the apatite but not the CPPD. Immunoprotein is seen both intracellularly and extracellularly. Further study of these coatings is needed to ascertain if they have consistent patterns on all crystals and how they affect the ability of the crystals to induce inflammation.

Immunoelectronmicroscopic characterization of intracellular inclusions in synovial fluid cells of patients with rheumatoid arthritis.

Qualitative immunoelectronmicroscopic (IEM) analysis of intracellular inclusions in synovial fluid (SF) cells in rheumatoid arthritis (RA) was performed using the peroxidase-antiperoxidase (PAP) method. Cells from patients with chronic RA were fixed in glutaraldehyde containing 0.05% saponin to permeabilize membranes before immunologic treatments. Intracellular inclusions of IgG, IgM, and C3 were observed in vacuoles of greater than 75% of both polymorphonuclear leukocytes (PMNs) and mononuclear phagocytic cells. IgA- and fibrinogen-containing inclusions were less frequent. Intracellular staining for albumin was minimal. Other membranous, vesicular, and granular unstained materials of potential importance were also often present in the same vacuoles. Stained inclusions were clearly distinct from lipid bodies, which were negative for immunostaining. Control samples had only occasional, scattered and weak stain that was easily recognizable as nonspecific and thus established the specificity of the reactions. A few lymphocytes in 2 patients showed positive staining for IgG in vacuoles. Extracellular staining of clumps of immunoglobulins, C3, and fibrinogen was also present. The various materials phagocytized by the different SF cells may be important in perpetuation of joint inflammation.