The apoptotic death of neuroblastoma cells caused by serum from patients with insulin-dependent diabetes and neuropathy may be Fas-mediated

Plasma Levels of Cell-Free Apoptotic DNA Ladders and Gamma-Glutamyltranspeptidase (GGT) in Diabetic Children

The plasma levels of apoptotic DNA ladders (i.e., apoptosemia) and γ-glutamyltranspeptidase (GGT) in diabetic outpatients and rats were investigated. Apoptotic DNA ladders were detected in plasma from 26.8% of type 1 (T1) and 18.5% of type 2 (T2) diabetic children 1–20 years of age, 25.7% of hospitalized children and 35.7% of adult RA outpatients, but in only 3.5% of adult pre-op patients. Plasma from 7.7% of young streptozotocin-induced diabetic but not control rats contained apoptotic DNA ladders. Apoptosemia was detected more often in male T1 (31%) and T2 (30.8%) diabetic outpatients than in female T1 (20.8%) and T2 (15.4%) diabetic outpatients. GGT in apoptosemic plasma was significantly higher than in nonapoptosemic plasma from T1 ( P = 0.001) but not T2 diabetic children. The highest amounts of apoptotic DNA were detected most often in diabetic children ≥14 years of age. In vitro study results suggest that cell-free apoptotic DNA ladders appear prior to an increase in GGT activity in serum from human blood incubated at 37°C. The results suggest that 24.7% of plasma samples from diabetic children contained apoptotic DNA ladders, the incidence and amounts of apoptotic DNA ladders were higher in the older diabetic children, and GGT was elevated in apoptosemic T1 diabetic children ( P = 0.01). The results indicate that “silent” apoptosemia occurs in T1 and T2 diabetic children and suggest elevated GGT in diabetic children could be due to release from apoptotic cells.

Protection of neuronal cell death against diabetes-induced apoptosis by Fas blocker ZB4

Objective

To determine the role of apoptosis inhibition in the prevention of diabetic neuropathy using the antiFas cell surface death receptor (Fas) antagonistic monoclonal antibody ZB4.

Methods

This prospective study enrolled patients with type 2 diabetes with and without neuropathy and a group of healthy controls. The serum concentrations of Fas and Fas ligand (FasL) were measured in all study participants using an enzyme-linked immunosorbent assay. The ability of serum from study participants to induce apoptosis was evaluated in a human neuronal cell line using flow cytometry.

Results

A total of 28 healthy subjects and 57 patients with diabetes were enrolled in the study. Serum Fas concentrations were significantly increased in diabetes patients with and without neuropathy compared with the controls. Cells treated with the serum from diabetes patients with neuropathy had significantly higher rates of early apoptosis compared with cells treated with control serum. Monoclonal antibody ZB4 was able to block serum-induced apoptosis.

Conclusions

Serum-induced apoptosis of a human neuronal cell line appeared to be mediated via Fas, which suggests that targeting and inhibiting Fas might offer a therapeutic target for diabetic neuropathy.

The conductor of the autonomic orchestra

Bad bedfellows - autonomic dysfunction, inflammation, and diabetes! Are they related? How? Evidence suggests the activation of inflammatory cytokines like IL-6 and TNFα in newly diagnosed type 2 diabetes and that the inflammatory change correlates with abnormalities in sympathovagal balance. Dysfunction of the autonomic system predicts cardiovascular risk and sudden death in patients with type 2 diabetes. It occurs in prediabetes, providing opportunities for early intervention. The importance of recognizing autonomic dysfunction as a predictor of morbidity and mortality with intensification of treatment suggests that all patients with type 2 diabetes at onset, and those with type 1 diabetes after 5 years should be screened for autonomic imbalance. These tests can be performed at the bedside with real time output of information - within the scope of the practicing physician - facilitates diagnosis and allows the application of sound strategies for management. The window of opportunity for aggressive control of all the traditional risk factors for cardiovascular events or sudden death with intensification of therapy is with short duration diabetes, the absence of cardiovascular disease, and a history of severe hypoglycemic events. To this list we can now add autonomic dysfunction and neuropathy, which have become the most powerful predictors of risk for mortality. It seems prudent that practitioners should be encouraged to become familiar with this information and apply risk stratification in clinical practice. After all, how difficult is it to ask patients "do you have numb feet?" and to determine their heart rate variability - it could be lifesaving. Ultimately methods to reset the hypothalamus and the inflammatory cascade are needed if we are to impact the care of patients with this compendium of conditions.

SPERM APOPTOSIS IN NONPREGNANT LUTEALPHASE SERA AFTER IN VITRO FERTILIZATION AS ASSESSED BY COMPARATIVE GENOMIC HYBRIDIZATION

Toxicity in serum has been reported in cases of recurrent spontaneous abortions and endometriosis. The null hypothesis was that serum toxicity was not involved in failed pregnancies after in vitro fertilization procedures. The objective was to expose donor sperm to pregnant versus nonpregnant patient sera and analyze for sperm DNA damaging effects using a novel comparative genomic hybridization method. Luteal phase sera (N = 21 cases) were drawn one week after embryo transfer. Colloid-washed donor sperm were incubated (48 h, 37 degrees C, 5% CO2 in air) in 0% or 50% sera. Single-stranded DNA (ssDNA) of control sperm were stained in Hoechst 33342 and hybridized to Sybr Gold-stained ssDNA of sera-treated sperm. Image analyses were performed and fluorescent intensities analyzed. Nonpregnant patient sera (57% of cases) were associated with DNA fragmentation (64.4 +/- 8.8 pixels; mean +/- S.E.M.) when compared with pregnant patient sera (106.3 +/- 8.4 pixels). There were no differences in the sera of biochemical (108.2 +/- 15.3) versus clinical pregnancy cases (105.3 +/- 11.4). The results suggest that nonpregnant patient sera contained factor(s) that cause DNA fragmentation leading to pregnancy losses.

A 70-year-old male with peripheral neuropathy, ataxia and antigliadin antibodies shows improvement in neuropathy, but not ataxia, after intravenous immunoglobulin and gluten-free diet

This is a case of a 70-year-old man with severe peripheral neuropathy, type 2 diabetes and progressively worsening cerebellar ataxia. He was found to have circulating antigliadin and antireticulin antibodies compatible with celiac disease in the absence of intestinal pathology. The peripheral neuropathy improved with a gluten-free diet, antioxidants and intravenous immunoglobulin, whereas the ataxia did not. This case illustrates the need to test for celiac disease in patients with idiopathic ataxia and peripheral neuropathy and the need for alternative therapies for ataxia.

Type 2 diabetes with neuropathy: autoantibody stimulation of autophagy via Fas

We reported previously that sera from patients with type 2 diabetes and neuropathy induce autophagy in human neuroblastoma (SH-SY5Y) cells. Here we report that enriched immunoglobulin fractions from a subpopulation of these patients induce autophagy and colocalization with Fas-activated death domain (FADD), a component of the Fas-activated death domain receptor signaling pathway. These effects were replicated by treatment of SY5Y cells with Fas ligand, tumor necrosis factor alpha and an agonist anti-Fas antibody. Preincubation of these sera with a soluble Fas receptor chimera (extracellular domain) markedly decreased the stimulation of autophagy. The results suggest that sera from subset of individuals with type 2 diabetes and neuropathy contain autoantibodies that activate the Fas cascade.

Sera of patients with celiac disease and neurologic disorders evoke a mitochondrial-dependent apoptosis in vitro

BACKGROUND & AIMS

The mechanisms underlying neurologic impairment in celiac disease remain unknown. We tested whether antineuronal antibody-positive sera of patients with celiac disease evoke neurodegeneration via apoptosis in vitro.

METHODS

SH-Sy5Y cells were exposed to crude sera, isolated immunoglobulin (Ig) G and IgG-depleted sera of patients with and without celiac disease with and without neurologic disorders, and antineuronal antibodies. Adsorption studies with gliadin and tissue transglutaminase (tTG) were performed in celiac disease sera. Apoptosis activated caspase-3, apaf-1, Bax, cytochrome c, cleaved caspase-8 and caspase-9 and mitochondrial respiratory chain complexes were evaluated with different methods.

RESULTS

SH-Sy5Y cells exposed to antineuronal antibody-positive sera and isolated IgG from the same sera exhibited a greater percentage of TUNEL-positive nuclei than that of antineuronal antibody-negative sera. Neuroblasts exposed to antineuronal antibody-negative celiac disease sera also showed greater TUNEL positivity and apaf-1 immunolabeled cells than controls. Antigliadin- and anti-tTG-depleted celiac disease sera had an apoptotic effect similar to controls. Anti-caspase-3 immunostained cells were greater than controls when exposed to positive sera. The mitochondrial respiratory chain complex was reduced by positive sera. Western blot demonstrated only caspase-9 cleavage in positive sera. Cytochrome c and Bax showed reciprocal translocation (from mitochondria to cytoplasm and vice versa) after treatment with positive sera.

CONCLUSIONS

Antineuronal antibodies and, to a lower extent, combined antigliadin and anti-tTG antibodies in celiac disease sera contribute to neurologic impairment via apoptosis. Apaf-1 activation with Bax and cytochrome c translocation suggest a mitochondrial-dependent apoptosis.

The role of voltage-gated calcium channels in pancreatic beta-cell physiology and pathophysiology

Voltage-gated calcium (CaV) channels are ubiquitously expressed in various cell types throughout the body. In principle, the molecular identity, biophysical profile, and pharmacological property of CaV channels are independent of the cell type where they reside, whereas these channels execute unique functions in different cell types, such as muscle contraction, neurotransmitter release, and hormone secretion. At least six CaValpha1 subunits, including CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1, have been identified in pancreatic beta-cells. These pore-forming subunits complex with certain auxiliary subunits to conduct L-, P/Q-, N-, R-, and T-type CaV currents, respectively. beta-Cell CaV channels take center stage in insulin secretion and play an important role in beta-cell physiology and pathophysiology. CaV3 channels become expressed in diabetes-prone mouse beta-cells. Point mutation in the human CaV1.2 gene results in excessive insulin secretion. Trinucleotide expansion in the human CaV1.3 and CaV2.1 gene is revealed in a subgroup of patients with type 2 diabetes. beta-Cell CaV channels are regulated by a wide range of mechanisms, either shared by other cell types or specific to beta-cells, to always guarantee a satisfactory concentration of Ca2+. Inappropriate regulation of beta-cell CaV channels causes beta-cell dysfunction and even death manifested in both type 1 and type 2 diabetes. This review summarizes current knowledge of CaV channels in beta-cell physiology and pathophysiology.

Distinct effector mechanisms in the development of autoimmune neuropathy versus diabetes in nonobese diabetic mice

NOD mice deficient for the costimulatory molecule B7-2 (NOD-B7-2KO mice) are protected from autoimmune diabetes but develop a spontaneous autoimmune peripheral neuropathy that resembles human diseases Guillain-Barre syndrome and chronic inflammatory demyelinating polyradiculoneuropathy. Similar observations have now been made in conventional NOD mice. We have shown previously that this disease was mediated by autoreactive T cells inducing demyelination in the peripheral nervous system. In this study, we analyzed the molecular pathways involved in the disease. Our data showed that neuropathy developed in the absence of perforin or fas, suggesting that classic cytotoxicity pathways were dispensable for nerve damage in NOD-B7-2KO mice. In contrast, IFN-gamma played an obligatory role in the development of neuropathy as demonstrated by the complete protection from disease and infiltration in the nerves in NOD-B7-2KO mice deficient for IFN-gamma. This result was consistent with the inflammatory phenotype of T cells infiltrating the peripheral nerves. Importantly, the relative role of perforin, fas, and IFN-gamma appears completely different in autoimmune diabetes vs neuropathy. Thus, there are sharp contrasts in the pathogenesis of autoimmune diseases targeting different tissues in the same NOD background.

Taurine replacement attenuates hyperalgesia and abnormal calcium signaling in sensory neurons of STZ-D rats

The etiology of painful diabetic neuropathy is poorly understood, but may result from neuronal hyperexcitability secondary to alterations of Ca2+ signaling in sensory neurons. The naturally occurring amino acid taurine functions as an osmolyte, antioxidant, Ca2+ modulator, inhibitory neurotransmitter, and analgesic such that its depletion in diabetes may predispose one to neuronal hyperexcitability and pain. This study reports the effects of taurine replacement on hyperalgesia and sensory neuron Ca2+ homeostasis in streptozotocin-diabetic (STZ-D) rats. Nondiabetic and STZ-D rats were treated with a 2% taurine-supplemented diet for 6-12 wk. Thermal hyperalgesia and mechanical allodynia were determined by measuring hindpaw withdrawal latency to radiant heat and the withdrawal threshold to the von Frey anesthesiometer. Intracellular Ca2+ signaling was explored in neurons from L4-L6 dorsal root ganglia (DRG), using fura 2 fluorescence. Taurine replacement of diabetic rats attenuated deficits of nerve conduction and prevented reductions of mechanical and thermal withdrawal threshold and latency, respectively. In small DRG sensory neurons from diabetic rats, recovery of intracellular Ca2+ concentration ([Ca2+]i) in response to KCl was slowed and 73% corrected by taurine. The amplitudes of caffeine and ATP-induced [Ca2+]i transients were decreased by 47 and 27% (P < 0.05), respectively, in diabetic rat DRG sensory neurons and corrected by 74 and 93% (P < 0.05), respectively, by taurine replacement. These data indicate that taurine is important in the regulation of neuronal Ca2+ signaling and that taurine deficiency may predispose one to nerve hyperexcitability and pain, complicating diabetes.

Effect of Glycemic Control on Electrophysiologic Changes of Diabetic Neuropathy in Type 2 Diabetic Patients

Diabetic neuropathy is a common complication of diabetes mellitus. Effective blood glucose control retards changes in nerve conduction velocity in type 1 diabetes. This study examined the relationship between glycemic control and electrophysiologic changes in diabetic neuropathy in 57 type 2 diabetic patients. Nerve conduction in the peroneal motor nerve, tibial motor nerve, and sural nerve were measured at study entry and at follow-up 24+/-3.12 months later. Changes in individual nerves are expressed as a percentage change (PC) and overall electrophysiologic changes are expressed as the sum of individual PCs. The PCs for peroneal motor nerve velocity, tibial motor nerve velocity, and sural nerve velocity were all lower in patients with a mean HbA1c of 8.5% or less compared with those in patients with a mean HbA1c of more than 8.5%, and SPCV (sum of PC in velocity) was significantly inversely correlated with mean HbA1c. However, there was no significant difference in SPCV in subjects with or without hypertension, hypertriglyceridemia, or low high-density lipoprotein cholesterol concentration. In conclusion, hyperglycemia is the most important etiology for electrophysiologic progression in type 2 diabetic patients. Furthermore, a mean HbA1c of more than 8.5% will result in significant deterioration in electrophysiology.

Beta-cell CaV channel regulation in physiology and pathophysiology

The beta-cell is equipped with at least six voltage-gated Ca2+ (CaV) channel alpha1-subunits designated CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1. These principal subunits, together with certain auxiliary subunits, assemble into different types of CaV channels conducting L-, P/Q-, N-, R-, and T-type Ca2+ currents, respectively. The beta-cell shares customary mechanisms of CaV channel regulation with other excitable cells, such as protein phosphorylation, Ca2+-dependent inactivation, and G protein modulation. However, the beta-cell displays some characteristic features to bring these mechanisms into play. In islet beta-cells, CaV channels can be highly phosphorylated under basal conditions and thus marginally respond to further phosphorylation. In beta-cell lines, CaV channels can be surrounded by tonically activated protein phosphatases dominating over protein kinases; thus their activity is dramatically enhanced by inhibition of protein phosphatases. During the last 10 years, we have revealed some novel mechanisms of beta-cell CaV channel regulation under physiological and pathophysiological conditions, including the involvement of exocytotic proteins, inositol hexakisphosphate, and type 1 diabetic serum. This minireview highlights characteristic features of customary mechanisms of CaV channel regulation in beta-cells and also reviews our studies on newly identified mechanisms of beta-cell CaV channel regulation.

Asp299Gly and Thr399Ile genotypes of the TLR4 gene are associated with a reduced prevalence of diabetic neuropathy in patients with type 2 diabetes

OBJECTIVE

To establish whether single nucleotide polymorphisms (Asp299Gly and Thr399Ile) of the toll-like receptor 4 have an association with late diabetic complications.

RESEARCH DESIGN AND METHODS

The study was conducted in 246 type 1 and 530 type 2 diabetic patients. The alleles of both polymorphisms were detected using PCR and subsequent cleavage by NcoI and HinfI restriction endonucleases.

RESULTS

No difference was found between type 1 and type 2 diabetic patients in the prevalence of alleles of the Asp299Gly and Thr399Ile polymorphisms. In most cases, the alleles Gly299 and Ile399 occurred in a co-segregatory manner. The prevalence of the Gly299/Ile399 haplotype was 10.6 and 12.1% in type 1 and type 2 diabetic patients, respectively (P = 0.63). No association with diabetic nephropathy or diabetic neuropathy was found in type 1 diabetic patients. In type 2 diabetic patients, however, heterozygote carriers of the Asp299Gly and Thr399Ile genotypes had a significantly reduced prevalence of diabetic neuropathy (odds ratio 0.35 [95% CI 0.19-0.61]; P = 0.0002); no association with diabetic nephropathy was found.

CONCLUSIONS

Our data indicate that Asp299Gly and Thr399Ile genotypes of the TLR4 gene are associated with reduced prevalence of diabetic neuropathy in type 2, but not in type 1, diabetes. Thus different mechanisms may be involved in the pathophysiology of diabetic neuropathy in type 1 and type 2 diabetes.

Diabetic neuropathy and nerve regeneration

Diabetic neuropathy is the most common peripheral neuropathy in western countries. Although every effort has been made to clarify the pathogenic mechanism of diabetic neuropathy, thereby devising its ideal therapeutic drugs, neither convinced hypotheses nor unequivocally effective drugs have been established. In view of the pathologic basis for the treatment of diabetic neuropathy, it is important to enhance nerve regeneration as well as prevent nerve degeneration. Nerve regeneration or sprouting in diabetes may occur not only in the nerve trunk but also in the dermis and around dorsal root ganglion neurons, thereby being implicated in the generation of pain sensation. Thus, inadequate nerve regeneration unequivocally contributes to the pathophysiologic mechanism of diabetic neuropathy. In this context, the research on nerve regeneration in diabetes should be more accelerated. Indeed, nerve regenerative capacity has been shown to be decreased in diabetic patients as well as in diabetic animals. Disturbed nerve regeneration in diabetes has been ascribed at least in part to all or some of decreased levels of neurotrophic factors, decreased expression of their receptors, altered cellular signal pathways and/or abnormal expression of cell adhesion molecules, although the mechanisms of their changes remain almost unclear. In addition to their steady-state changes in diabetes, nerve injury induces injury-specific changes in individual neurotrophic factors, their receptors and their intracellular signal pathways, which are closely linked with altered neuronal function, varying from neuronal survival and neurite extension/nerve regeneration to apoptosis. Although it is essential to clarify those changes for understanding the mechanism of disturbed nerve regeneration in diabetes, very few data are now available. Rationally accepted replacement therapy with neurotrophic factors has not provided any success in treating diabetic neuropathy. Aside from adverse effects of those factors, more rigorous consideration for their delivery system may be needed for any possible success. Although conventional therapeutic drugs like aldose reductase (AR) inhibitors and vasodilators have been shown to enhance nerve regeneration, their efficacy should be strictly evaluated with respect to nerve regenerative capacity. For this purpose, especially clinically, skin biopsy, by which cutaneous nerve pathology including nerve regeneration can be morphometrically evaluated, might be a safe and useful examination.

Neuropathology and pathogenesis of diabetic autonomic neuropathy

Autonomic neuropathy is a significant complication of diabetes resulting in increased patient morbidity and mortality. A number of studies, which have shown correspondence between neuropathologic findings in experimental animals and human subjects, have demonstrated that axonal and dendritic pathology in sympathetic ganglia in the absence of significant neuron loss represents a neuropathologic hallmark of diabetic autonomic neuropathy. A recurring theme in sympathetic ganglia, as well as in the pot-ganglionic autonomic innervation of various end organs, is the involvement of distal portions of axons and nerve terminals by degenerative or dystrophic changes. In both animals and humans, there is a surprising selectivity of the diabetic process for subpopulations of autonomic ganglia, nerve terminals within sympathetic ganglia and end organs, from end organ to end organ, and between vascular and other targets within individual end organs. Although the involvement or autonomic axons in somatic nerves may reflect an ischemic pathogenesis, the selectivity of the diabetic process confounds simple global explanations of diabetic autonomic neuropathy as the result of diminished blood flow with resultant tissue hypoxia. A single unifying pathogenetic hypothesis has not yet emerged from clinical and experimental animal studies, and it is likely that diabetic autonomic neuropathy will be shown to have multiple causative mechanisms, which will interact to result in the variety of presentations of autonomic injury in diabetes. Some of these mechanisms will be shared with aging changes in the autonomic nervous system. The role of various neurotrophic substances and the polyol pathway in the pathogenesis and treatment of diabetic neuropathy likely represents a two-edged sword with both salutary and exacerbating effects. The basic neurobiologic process underlying the diabetes-induced development of neuroaxonal dystrophy, synaptic dysplasia, defective axonal regeneration, and alterations in neurotrophic substance may be mechanistically related.

Impaired inhibitory G-protein function contributes to increased calcium currents in rats with diabetic neuropathy

There is a growing body of evidence that sensory neuropathy in diabetes is associated with abnormal calcium signaling in dorsal root ganglion (DRG) neurons. Enhanced influx of calcium via multiple high-threshold calcium currents is present in sensory neurons of several models of diabetes mellitus, including the spontaneously diabetic BioBred/Worchester (BB/W) rat and the chemical streptozotocin (STZ)-induced rat. We believe that abnormal calcium signaling in diabetes has pathologic significance as elevation of calcium influx and cytosolic calcium release has been implicated in other neurodegenerative conditions characterized by neuronal dysfunction and death. Using electrophysiologic and pharmacologic techniques, the present study provides evidence that significant impairment of G-protein-coupled modulation of calcium channel function may underlie the enhanced calcium entry in diabetes. N- and P-type voltage-activated, high-threshold calcium channels in DRGs are coupled to mu opiate receptors via inhibitory G(o)-type G proteins. The responsiveness of this receptor coupled model was tested in dorsal root ganglion (DRG) neurons from spontaneously-diabetic BB/W rats, and streptozotocin-induced (STZ) diabetic rats. Intracellular dialysis with GTPgammaS decreased calcium current amplitude in diabetic BB/W DRG neurons compared with those of age-matched, nondiabetic controls, suggesting that inhibitory G-protein activity was diminished in diabetes, resulting in larger calcium currents. Facilitation of calcium current density (I(DCa)) by large-amplitude depolarizing prepulses (proposed to transiently inactivate G proteins), was significantly less effective in neurons from BB/W and STZ-induced diabetic DRGs. Facilitation was enhanced by intracellular dialysis with GTPgammaS, decreased by pertussis toxin, and abolished by GDPbetaS within 5 min. Direct measurement of GTPase activity using opiate-mediated GTPgamma[(35)S] binding, confirmed that G-protein activity was significantly diminished in STZ-induced diabetic neurons compared with age-matched nondiabetic controls. Diabetes did not alter the level of expression of mu opiate receptors and G-protein alpha subunits. These studies indicate that impaired regulation of calcium channels by G proteins is an important mechanism contributing to enhanced calcium influx in diabetes.

Neurotrophic role of interleukin-6 and soluble interleukin-6 receptors in N1E-115 neuroblastoma cells

Interleukin 6 (IL-6) plays a role in physiological and pathophysiological processes in neuronal cells. We studied whether IL-6 plays a role in neuroblastoma cells in culture. These studies demonstrate that N1E-115 cells constitutively express IL-6 but not IL-6R. Exogenous IL-6 stimulated neuronal proliferation in a dose-dependent manner. Under serum-free conditions soluble IL-6 receptors (sIL-6R) alone or in combination with IL-6 exerted significant proliferative effects, while IL-6 alone failed to promote cell proliferation. Neutralizing anti-IL-6 antibody caused a 30-40% reduction in IL-6 mediated proliferation. Our results suggest the importance of IL-6/sIL-6R for proliferation and survival of N1E-115 adrenergic neuroblastoma cells.

Digitoxin is a potential anticancer agent for several types of cancer

The ability of digitalis to block cell proliferation has been well established for some time. Recently, digitalis in non-toxic concentrations has been showed to induce apoptosis in different malignant cell lines. In light of the pivotal role of apoptosis in cancer development and progression and this new experimental finding concerning digitalis, it seems probable that the apoptosis-inducing capability is explained by mechanisms other than just Na+/K+ ATPase inhibition. In this article, features of the cardiac glycosides which make them interesting to evaluate further as potential anticancer drugs are discussed. Some new data concerning inhibition and apoptosis in three human glioblastoma cell lines by digitoxin are also presented.

Diabetic neuropathy: pathogenesis and therapy

Diabetic neuropathies are complex, heterogeneous disorders that encompass a wide range of abnormalities affecting both peripheral and autonomic nervous systems, causing considerable morbidity and mortality. Treatment should be based upon the underlying etiology and not symptoms alone, although symptomatic therapy is needed. Neuropathies may be focal or diffuse, proximal or distal, and involve somatic and autonomic nerves. Focal syndromes are classified as (1) entrapment syndromes or (2) mononeuropathies. Entrapment syndromes are treated by means of relieving compression within confined spaces. Mononeuropathies are due to a vascular insult and resolve spontaneously. They are best treated by supportive therapy. Proximal neuropathies are usually due to an inflammatory, vasculitic, or autoimmune condition and are best treated with specific therapies for the underlying disorder based on biopsy findings. Therapies for distal polyneuropathies include metabolic treatments (e.g., aldose reductase inhibitors, aminoguanidine, gamma-linolenic acid), autoimmune therapies, and nerve growth factors. No definitive treatment is available for painful diabetic neuropathy. Several medications have been used, among them tricyclic antidepressants, antiepileptic drugs, phenothiazines, calcitonin, local anesthetics, nonsteroidal anti-inflammatory drugs, and dextromethorphan. Nonpharmacologic therapies include surgical sympathectomy, spinal cord blockade, electrical spinal cord stimulation, and prostaglandin.

Serum from patients with type 2 diabetes with neuropathy induces complement-independent, calcium-dependent apoptosis in cultured neuronal cells

We hypothesized that sera from type 2 diabetic patients with neuropathy contains an autoimmune immunoglobulin that promotes complement-independent, calcium-dependent apoptosis in neuronal cell lines. Neuronal cells were cultured in the presence of complement-inactivated sera obtained from patients with type 2 diabetes with and without neuropathy and healthy adult control patients. Serum from diabetic patients with neuropathy was associated with a significantly greater induction of apoptosis, compared to serum from diabetic patients without neuropathy and controls. In the presence of calcium channel antagonists, induction of apoptosis was reduced by approximately 50%. Pretreatment of neuronal cells with serum from diabetic patients with neuropathy was associated with a significant increase in elevated K+-evoked cytosolic calcium concentration. Serum-induced enhancement in cytosolic calcium and calcium current density was blocked by treatment with trypsin and filtration of the serum using a 100,000-kd molecular weight filter. Treatment with an anti-human IgG antibody was associated with intense fluorescence on the surface of neuronal cells exposed to sera from patients with type 2 diabetes mellitus with neuropathy. We conclude that sera from type 2 diabetic patients with neuropathy contains an autoimmune immunoglobulin that induces complement-independent, calcium-dependent apoptosis in neuronal cells.

Serum from diabetic BB/W rats enhances calcium currents in primary sensory neurons

We examined the hypothesis that exposure of nondiabetic rat dorsal root ganglion (DRG) neurons to sera from diabetic BB/W rats would produce an increase in calcium currents associated with impaired regulation of the inhibitory G protein-calcium channel complex. Acutely dissociated rat DRGs were incubated for 18-24 h in medium supplemented with sera (10% vol/vol) from either diabetic rats with neuropathy or age-matched, nondiabetic controls. Exposure of DRG neurons to sera from diabetic BB/W rats resulted in a surface membrane immunofluorescence pattern when treated with an anti-rat light-chain antibody that was not observed in neurons exposed to control sera. Calcium current density (IDCa) was assessed with the use of the whole cell variation of the patch-clamp technique. IDCa in neurons exposed to diabetic sera was significantly increased compared with neurons exposed to control sera. Guanine nucleotide-binding (G) protein regulation of calcium channel function was examined with the use of a two-pulse "facilitation" or IDCa enhancement protocol in the presence of activators [guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S)] or antagonists [guanosine 5'-O-(2-thiodiphosphate) (GDP beta S) and pertussis toxin (PTX)] of G protein function. Facilitation was significantly decreased in neurons exposed to diabetic sera. Intracellular diffusion of neurons with GDP beta s blocked facilitation, whereas dialysis with GTP gamma s increased facilitation to a similar magnitude in neurons exposed to either diabetic or control sera. Treatment with PTX resulted in a significant increase in IDCa and approximately 50% decrease in facilitation in neurons treated with control sera but no significant changes in neurons exposed to diabetic sera. We conclude that serum from diabetic BB/W rats with neuropathy contains an autoimmune immunoglobulin that impairs regulation of the inhibitory G protein-calcium channel complex, resulting in enhanced calcium influx. Regulation of the inhibitory G protein-calcium channel complex involves PTX-sensitive and -insensitive G proteins.