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

Supernatants of intestinal luminal contents from mice fed high-fat diet impair intestinal motility by injuring enteric neurons and smooth muscle cells

BACKGROUND

Damage to enteric neurons and impaired gastrointestinal muscle contractions cause motility disorders in 70% of diabetic patients. It is thought that enteric neuropathy and dysmotility occur before overt diabetes, but triggers of these abnormalities are not fully known. We tested the hypothesis that intestinal contents of mice with and without high-fat diet- (HFD-) induced diabetic conditions contain molecules that impair gastrointestinal movements by damaging neurons and disrupting muscle contractions.

METHODS

Small and large intestinal segments were collected from healthy, standard chow diet (SCD) fed mice. Filtrates of ileocecal contents (ileocecal supernatants; ICS) from HFD or SCD mice were perfused through them. Cultured intact intestinal muscularis externa preparations were used to determine whether ICS and their fractions obtained by solid-phase extraction (SPE) and SPE subfractions collected by high-performance liquid chromatography (HPLC) disrupt muscle contractions by injuring neurons and smooth muscle cells.

KEY RESULTS

ICS from HFD mice reduced intestinal motility, but those from SCD mice had no effect. ICS, aqueous SPE fractions and two out of twenty HPLC subfractions of aqueous SPE fractions from HFD mice blocked muscle contractions, caused a loss of nitrergic myenteric neurons through inflammation, and reduced smooth muscle excitability. Lipopolysaccharide and palmitate caused a loss of nitrergic myenteric neurons but did not affect muscle contractions.

CONCLUSIONS & INFERENCES

Unknown molecules in intestinal contents of HFD mice trigger enteric neuropathy and dysmotility. Further studies are required to identify the toxic molecules and their mechanisms of action.

Cardiac Autonomic Neuropathy: A Progressive Consequence of Chronic Low-Grade Inflammation in Type 2 Diabetes and Related Metabolic Disorders

Cardiac autonomic neuropathy (CAN) is one of the earliest complications of type 2 diabetes (T2D), presenting a silent cause of cardiovascular morbidity and mortality. Recent research relates the pathogenesis of cardiovascular disease in T2D to an ensuing chronic, low-grade proinflammatory and pro-oxidative environment, being the hallmark of the metabolic syndrome. Metabolic inflammation emerges as adipose tissue inflammatory changes extending systemically, on the advent of hyperglycemia, to reach central regions of the brain. In light of changes in glucose and insulin homeostasis, dysbiosis or alteration of the gut microbiome (GM) emerges, further contributing to inflammatory processes through increased gut and blood-brain barrier permeability. Interestingly, studies reveal that the determinants of oxidative stress and inflammation progression exist at the crossroad of CAN manifestations, dictating their evolution along the natural course of T2D development. Indeed, sympathetic and parasympathetic deterioration was shown to correlate with markers of adipose, vascular, and systemic inflammation. Additionally, evidence points out that dysbiosis could promote a sympatho-excitatory state through differentially affecting the secretion of hormones and neuromodulators, such as norepinephrine, serotonin, and γ-aminobutyric acid, and acting along the renin-angiotensin-aldosterone axis. Emerging neuronal inflammation and concomitant autophagic defects in brainstem nuclei were described as possible underlying mechanisms of CAN in experimental models of metabolic syndrome and T2D. Drugs with anti-inflammatory characteristics provide potential avenues for targeting pathways involved in CAN initiation and progression. The aim of this review is to delineate the etiology of CAN in the context of a metabolic disorder characterized by elevated oxidative and inflammatory load.

Worsening baroreflex sensitivity on progression to type 2 diabetes: localized vs. systemic inflammation and role of antidiabetic therapy

Cardiac autonomic neuropathy (CAN) is an early cardiovascular manifestation of type 2 diabetes (T2D) that constitutes an independent risk factor for cardiovascular mortality and morbidity. Nevertheless, its underlying pathophysiology remains poorly understood. We recently showed that localized perivascular adipose tissue (PVAT) inflammation underlies the incidence of parasympathetic CAN in prediabetes. Here, we extend our investigation to provide a mechanistic framework for the evolution of autonomic impairment as the metabolic insult worsens. Early metabolic dysfunction was induced in rats fed a mild hypercaloric diet. Two low-dose streptozotocin injections were used to evoke a state of late decompensated T2D. Cardiac autonomic function was assessed by invasive measurement of baroreflex sensitivity using the vasoactive method. Progression into T2D was associated with aggravation of CAN to include both sympathetic and parasympathetic arms. Unlike prediabetic rats, T2D rats showed markers of brainstem neuronal injury and inflammation as well as increased serum levels of IL-1β. Experiments on PC12 cells differentiated into sympathetic-like neurons demonstrated that brainstem injury observed in T2D rats resulted from exposure to possible proinflammatory mediators in rat serum rather than a direct effect of the altered metabolic profile. CAN and the associated cardiovascular damage in T2D only responded to combined treatment with insulin to manage hyperglycemia in addition to a nonhypoglycemic dose of metformin or pioglitazone providing an anti-inflammatory effect, coincident with the effect of these combinations on serum IL-1β. Our present results indicate that CAN worsening upon progression to T2D involves brainstem inflammatory changes likely triggered by systemic inflammation.

Circulating human anti nucleolus antibody (ANCAb) and biochemical parameters in type 2 diabetic patients with and without complications

Introduction

There is no evidence on the role of Human Anti Nucleolus Antibody (ANCAb) in type 2 diabetes mellitus (T2DM). We compared prevalence and concentration of ANCAb between age and a gender-matched sample of T2DM with and without diabetes-related complications.

Methods

In this study, the reaction to ANCAb was compared quantitatively between 38 T2DM patients complicated with microvascular conditions and 43 T2DM without complications as controls.

Results

The patients in complicated and non-complicated groups were comparable in diabetes duration (9.0 vs. 5.0 years; P = 0.065), respectively. The study found that 27 cases (71.1%) of the complicated group reacted to ANCAb test compared to 25 (58.1%) in non-complicated patients (P = 0.226; 3.53 vs. 2.72 ng/mL; P = 0.413). The reaction response to ANCAb in patients with neuropathy and cardiovascular complications was 80.0%, 76.2% in patients with neuropathy compared to 58.1% in the control group (P = 0.398). The reaction response to ANCAb in patients with mono-complication was 72.7% compared 68.8% in patients with multi-complication (P = 0.466). Similarly, 76.2% of patients with T2DM and complicated with neuropathy (n = 21 patients) reacted to ANCAb compared to 58.1% in control patients with (P = 0.158).

Conclusions

Reaction to ANCAb was not statistically different between the T2DM patients with and without complications.

Cutaneous manifestations of diabetic peripheral neuropathy

There is a rise in number of people diagnosed with Diabetes Mellitus. The incidence is rising in modern Indian society because of Industrial development and drastically changing lifestyles. Diabetic neuropathies are microvascular disorders that are usually associated with the duration of Diabetes. Among the various forms, the most common is Diabetic Peripheral Neuropathy. The disease if neglected leads to chronic ulcer formation leading to amputations frequently. Hence the aim of this study is to document the early cutaneous changes and create an early awareness in the importance of controlling Diabetes. The study consisted of 205 patients with Type 2 DM. Participant's neuropathy status was determined based on Neuropathy Disability Score and Diabetic Neuropathy Symptom Score. Among the Skin changes documented, the common changes seen were: Peripheral hair loss in 185 (90.2%), Xerosis in 168 (82%), Anhydrosis in 162 (79%), Plantar Fissures in 136 (66.3%), Plantar Ulcer in 80 (39%), common nail changes documented were Onychomycosis in 165 (80.5%) and Onychauxis in 53 (25.8%) patients in relation to the occupation and duration of Diabetes mellitus. In conclusion, it is important to control glycemic levels in the all stages of Diabetes and institute foot care measures to prevent the complications of neuropathy.

Functional convergence of Akt protein with VEGFR-1 in human endothelial progenitor cells exposed to sera from patient with type 2 diabetes mellitus

Diabetes mellitus type 2 predisposes patients to various microvascular complications. In the current experiment, the potent role of diabetes mellitus was investigated on the content of VEGFR-1, -2, Tie-1 and -2, and Akt in human endothelial progenitor cells. The gene expression profile of mTOR and Hedgehog signaling pathways were measured by PCR array. The possible crosstalk between RTKs, mTOR and Hedgehog signaling was also studied by bioinformatic analysis. Endothelial progenitor cells were incubated with serum from normal and diabetic for 7days. Compared to non-treated cells, diabetic serum-induced cell apoptosis (~2-fold) and prohibited cell migration toward bFGF (p<0.001). ELISA analysis showed that diabetes exposed cells had increased abundance of Tie-1, -2 and VEGFR-2 and reduced amount of VEGFR-1 (p<0.0001) in diabetic cells. Western blotting showed a marked reduction in the protein level of Akt after cells exposure to serum from diabetic subjects (p<0.0001). PCR array revealed a significant stimulation of both mTOR and Hedgehog signaling pathways in diabetic cells (p<0.05). According to data from bioinformatic datasets, we showed VEGFR-1, -2 and Tie-2, but not Tie-1, are master regulators of angiogenesis. There is a crosstalk between RTKs and mTOR signaling by involving P62, GABARAPL1, and HTT genes. It seems that physical interaction and co-expression of Akt decreased the level of VEGFR-1 in diabetic cells. Regarding data from the present experiment, diabetic serum contributed to uncontrolled induction of both mTOR and Hedgehog signaling in endothelial progenitor cells. Diabetes mellitus induces mTOR pathway by involving receptor tyrosine kinases while Hedgehog stimulation is independent of these receptors.

Can Diabetic Neuropathy Be Modeled In Vitro?

Diabetic neuropathy is a common secondary complication of diabetes that impacts on patient's health and well-being. Distal axon degeneration is a key feature of diabetic neuropathy, but the pathological changes which underlie axonal die-back are incompletely understood; despite decades of research a treatment has not yet been identified. Basic research must focus on understanding the complex mechanisms underlying changes that occur in the nervous system during diabetes. To this end, tissue culture techniques are invaluable as they enable researchers to examine the intricate mechanistic responses of cells to high glucose or other factors in order to better understand the pathogenesis of nerve dysfunction. This chapter describes the use of in vitro models to study a wide range of specific cellular effects pertaining to diabetic neuropathy including apoptosis, neurite outgrowth, neurodegeneration, activity, and bioenergetics. We consider problems associated with in vitro modeling and future refinement such as use of induced pluripotent stem cells and microfluidic technology.

Salivary proteins associated with hyperglycemia in diabetes: a proteomic analysis

Effective monitoring of glucose levels is necessary for patients to achieve greater control over their diabetes. However, only about a quarter of subjects with diabetes who requires close serum glucose monitoring, regularly check their serum glucose daily. One of the potential barriers to patient compliance is the blood sampling requirement. Saliva and its protein contents can be altered in subjects with diabetes, possibly due to changes in glycemic control. We propose here that salivary proteomes of subjects with diabetes may be different based on their glycemic control as reflected in A1C levels. A total of 153 subjects with type 1 or 2 diabetes were recruited. Subjects in each type of diabetes were divided into 5 groups based on their A1C levels; <7, 7-8, 8-9, 9-10, >10. To examine the global proteomic changes associated with A1C, the proteomic profiling of pooled saliva samples from each group was created using label-free quantitative proteomics. Similar proteomic analysis for individual subjects (N=4, for each group) were then applied to examine proteins that may be less abundant in pooled samples. Principle component analysis (PCA) and cluster analysis (p<0.01 and p<0.001) were used to define the proteomic differences. We, therefore, defined the salivary proteomic changes associated with A1C changes. This study demonstrates that differences exist between salivary proteomic profiles in subjects with diabetes based on the A1C levels.

Proanthocyanidins protect against early diabetic peripheral neuropathy by modulating endoplasmic reticulum stress

Diabetic peripheral neuropathy (DPN) is the most common and troublesome complication of type 2 diabetes mellitus (T2DM). Recent findings reveal an important role of endoplasmic reticulum (ER) stress in the development of DPN and identify a potential new therapeutic target. Schwann cells (SC), the myelinating cells in peripheral nervous system, are highly susceptible to ER homeostasis. Grape seed proanthocyanidins (GSPs) have been reported to improve DPN of type 1 diabetic rats and relieve ER stress in skeletal muscles and pancreas of T2DM. We investigated the potential role of ER stress in SC in regulating DPN of T2DM and assessed whether early intervention of GSPs would prevent DPN by modulating ER stress. The present study was performed in Sprague-Dawley rats made T2DM with low-dose streptozotocin and a high-carbohydrate/high-fat diet and in rat SC cultured in serum from type 2 diabetic rats. Diabetic rats showed a typical characteristic of T2DM and slowing of nerve conduction velocity (NCV) in sciatic/tibial nerves. The lesions of SC, Ca(2+) overload and ER stress were present in sciatic nerves of diabetic rats, as well as in cell culture models. GSPs administration significantly decreased the low-density lipoprotein level and increased NCV in diabetic rats. GSPs or their metabolites also partially prevented cell injury, Ca(2+) overload and ER stress in animal and cell culture models. Therefore, ER stress is implicated in peripheral neuropathy in animal and cell culture models of T2DM. Prophylactic GSPs treatment might have auxiliary preventive potential for DPN partially by alleviating ER stress.

Diabetic neuropathy: cellular mechanisms as therapeutic targets

In patients with diabetes, nerve injury is a common complication that leads to chronic pain, numbness and substantial loss of quality of life. Good glycemic control can decrease the incidence of diabetic neuropathy, but more than half of all patients with diabetes still develop this complication. There is no approved treatment to prevent or halt diabetic neuropathy, and only symptomatic pain therapies, with variable efficacy, are available. New insights into the mechanisms leading to the development of diabetic neuropathy continue to point to systemic and cellular imbalances in metabolites of glucose and lipids. In the PNS, sensory neurons, Schwann cells and the microvascular endothelium are vulnerable to oxidative and inflammatory stress in the presence of these altered metabolic substrates. This Review discusses the emerging cellular mechanisms that are activated in the diabetic milieu of hyperglycemia, dyslipidemia and impaired insulin signaling. We highlight the pathways to cellular injury, thereby identifying promising therapeutic targets, including mitochondrial function and inflammation.

Anti-endothelial and anti-neuronal effects from auto-antibodies in subsets of adult diabetes having a cluster of microvascular complications

AIMS

To test autoantibodies from subsets of diabetes with painful neuropathy, maculopathy and nephropathy for effects in neurons.

METHODS

Protein-A eluates from plasma of 27 diabetic and 19 age-matched controls were tested for effects on endothelial cell survival, and neurite outgrowth in rat pheochromocytoma PC12 cells. Painful diabetic neuropathy or control autoantibodies were compared for binding to PC12-derived heparan sulfate proteoglycans. The mechanism of the effects from pathologic autoantibodies was investigated by changes in intracellular calcium in endothelial cells, whole cell current in neurons, or using the Rho kinase inhibitor Y27632.

RESULTS

Autoantibodies from diabetic patients with maculopathy, nephropathy, and painful neuropathy (n=5) caused significantly greater mean inhibition of neurite outgrowth (p<0.005) than diabetic or control patients with fewer or no complications (n=30). Painful diabetic autoantibodies (3 μg/mL) bound neuronal heparan sulfate proteoglycan (HSPG) more than autoantibodies from diabetic or control subjects without painful neuropathy (p<.0001). Inhibition of PC12 neurite outgrowth by the painful neuropathy antibodies was completely prevented by 1 μM concentrations of Y27632.

CONCLUSION

These results suggest anti-endothelial and anti-neuronal effects from auto-antibodies in a subset of diabetic patients with a cluster of microvascular complications.

cAMP antagonizes ERK-dependent antiapoptotic action of insulin

Insulin has antiapoptotic activity in various cell types. However, the signaling pathways underlying the antiapoptotic activity of insulin is not yet known. This study was conducted to determine if cAMP affects the antiapoptotic activity of insulin and the activity of PI3K and ERK in CHO cells expressing human insulin receptors (CHO-IR). Insulin-stimulated ERK activity was completely suppressed by cAMP-elevating agents like as pertussis toxin (Ptx) and cholera toxin (Ctx) after 4 h treatment. Insulin-stimulated PKB/Akt activity was not affected at all. Ptx treatment together with insulin increased the number of apoptotic cells and the degree of DNA fragmentation. Ctx or 8-brcAMP treatment also increased the number of apoptotic cells and stimulated the cleavage of caspase-3 and the hydrolysis of PARP. Taken together, cAMP antagonizes the antiapoptotic activity of insulin and the main target molecule of cAMP in this process is likely ERK, not PI3K-dependent PKB/Akt.

The serum of dysautonomia patients enhances proliferation and signaling in Schwann cells

Disorders of the autonomic nervous system, or dysautonomias, affect a large segment of the population, especially women, and represent a diagnostic challenge. Identification of biomarkers for autonomic disorders, and the subsequent development of screening methods, would benefit diagnosis and symptom management. We studied the effect of sera from fifteen well-characterized dysautonomia patients (mean age 49+/-16 years, 10 females, 5 males) and ten control subjects (mean age 31+/-14 years, 5 females, 5 males) on the proliferation of cultured Schwann cells and activity of mitogen-activated protein kinases (MAPKs) in these cells. We correlated characteristics of patients with the effects on cell proliferation and signaling. Overall, we observed a significant increase in proliferation when Schwann cells were incubated with sera from female dysautonomia patients when compared to control subjects and male patients. Interestingly, removal of IgGs significantly reduced the proliferative effect of patient sera. We also observed significant activation of p38 MAPK following incubation with both male and female patient sera. These results suggest that patient sera contain factors that contribute to aberrant Schwann cell proliferation and signaling and may ultimately lead to autonomic nerve dysfunction. Our observations represent a promising first step in the identification of dysautonomia biomarkers.

Dorsal Root Ganglia Sensory Neuronal Cultures: a tool for drug discovery for peripheral neuropathies

BACKGROUND: Peripheral neuropathies affect many people worldwide and are caused by or associated with a wide range of conditions, both genetic and acquired. Current therapies are directed at symptomatic control because no effective regenerative treatment exists. Primary challenge is that mechanisms that lead to distal axonal degeneration, a common feature of all peripheral neuropathies, are largely unknown. OBJECTIVE/METHODS: To address the role and specific characteristics of dorsal root ganglia (DRG) derived sensory neuron culture system as a useful model in evaluating the pathogenic mechanisms of peripheral neuropathies and examination and validation of potential therapeutic compounds. A thorough review of the recent literature was completed and select examples of the use of DRG neurons in different peripheral neuropathy models were chosen to highlight the utility of these cultures. CONCLUSION: Many useful models of different peripheral neuropathies have been developed using DRG neuronal culture and potential therapeutic targets have been examined, but so far none of the potential therapeutic compounds have succeeded in clinical trials. In recent years, focus has changed to evaluation of axon degeneration as the primary outcome measure advocating a drug development strategy starting with phenotypic drug screening, followed by validation in primary complex co-cultures and animal models.

Evaluation of Bcl-2 family gene expression and Caspase-3 activity in hippocampus STZ-induced diabetic rats

We assessed the expression of Bcl-2 family members at both mRNA and protein levels as well as the Caspase-3 activity, in order to investigate the occurrence of apoptosis in hippocampus of STZ-induced diabetic rats. We selected twenty-four Wistar rats; half of them were made diabetic by intraperitoneal injection of a single 60 mg/kg dose of streptozotocin (STZ, IP), while the others received normal saline and served as controls. The expressions of Bcl-2, Bcl-x(L), and Bax mRNA and proteins were measured using RT-PCR and western blotting, respectively. Caspases-3 activity was determined by using the Caspase-3/CPP32 Fluorometric Assay Kit. The result showed that mRNA and protein levels of Bcl-2 and Bcl-x(L) were lower in hippocampus of diabetic group than that of the control group, whereas expressions of Bax in hippocampus of diabetic rats were higher than that of controls at both mRNA and protein levels (P < .01). Hyperglycemia was found to raise 6.9-fold hippocampal caspase-3 activity in diabetic group compared with control group (P < .001). Therefore, the induction of diabetes is associated with increased ratios of Bax/Bcl-2, Bax/Bcl-x(L), and increased caspase-3 activity in hippocampus which shows that apoptosis is favored in hippocampal region.

Neurogenic chronic intestinal pseudo-obstruction: antineuronal antibody-mediated activation of autophagy via Fas

BACKGROUND & AIMS

Activation of autoimmune pathways has been implicated as a contributing mechanism to the pathophysiology in some patients with chronic intestinal pseudoobstruction (CIP). In this study we tested the hypothesis that sera from a subpopulation of patients with CIP contain autoantibodies that activate autophagy via a Fas-dependent pathway in cultured human neuroblastoma SH-Sy5Y cells.

METHODS

Twenty-five patients with established neurogenic CIP (20 women, 5 men; age range, 21-57 y) were investigated and circulating antineuronal antibodies to enteric neurons were found in 6 (24%) patients. The ability of antineuronal antibodies to induce autophagy was assessed using immunohistochemical, Western immunoblot, and molecular techniques. The presence of autophagosomes was monitored using a specific immunohistochemical marker, anti-microtubule-associated light chain immunoreactivity, and colocalization with mitochondrial- and Fas-activated death domain immunofluorescence using appropriate antibodies in cells exposed to sera from matched healthy controls and patients with neurogenic CIP.

RESULTS

Exposure of SH-Sy5Y cells to sera from patients with CIP containing antineuronal antibodies revealed increased binding of autoimmune immunoglobulin (IgG class) to the surface of SH-Sy5Y cells and increased formation of autophagosomes showing colocalization with mitochondria and Fas-activated death domain compared with control sera. Pretreatment of sera with either protein L agarose beads or a soluble Fas receptor (extracellular domain) chimera prevented the stimulation of autophagy.

CONCLUSIONS

We provide novel evidence that antineuronal antibodies may contribute to neuronal dysfunction observed in a subset of patients with neurogenic CIP via autoantibody-mediated activation of autophagy involving the Fas receptor complex.

Enteric autoantibodies and gut motility disorders

Increasing evidence suggests that a subset of gastrointestinal motility disorders is associated with the presence of circulating antibodies. These antibodies are directed against various molecular targets, the best known being anti-neuronal nuclear antibody (ANNA-1 or anti-Hu) associated with paraneoplastic motility disorders. There is also evidence that the presence of distinct autoantibody profiles is associated with non-paraneoplastic motility disorders. This review focuses on the types of antibodies associated with gastrointestinal motility disorders and the significance of these antibodies. Algorithms are suggested for the work-up and treatment of patients with circulating antibodies associated with gastrointestinal motility disorders.

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.

Importance of pericytes and mechanisms of pericyte loss during diabetes retinopathy

Pericytes are distinctive regulators of angiogenesis and are adumbrated to provide vessel stability and control of endothelial proliferation. The present article spotlights the persona of pericytes in physiological angiogenesis, recruitment of pericytes and different mechanisms of pericyte depletion. Developing retina appears particularly dependent on pericytes, and pericyte loss is considered as hallmark of early diabetic retinopathies. Several factors are contemplated to be engaged in pericyte conscription including angiopoietin-1 and its receptor tyrosine kinase Tie-2, vascular endothelial growth factor-A and its receptor flk-1 and the platelet-derived growth factor PDGF-B/PDGF-beta system. At present, the mechanisms by which diabetes persuade apoptosis in the retinal microvasculature remain indecisive, albeit oxidative stress, formation of advanced glycation end products , upregulation of protein kinase C, increased polyol pathway flux and focal leukostasis may be important. In this context, accelerated microvascular cell death may become a constructive surrogate end-point in pharmacological studies of experimental diabetic.

Diabetes and the enteric nervous system

Diabetes is associated with several changes in gastrointestinal (GI) motility and associated symptoms such as nausea, bloating, abdominal pain, diarrhoea and constipation. The pathogenesis of altered GI functions in diabetes is multifactorial and the role of the enteric nervous system (ENS) in this respect has gained significant importance. In this review, we summarize the research carried out on diabetes-related changes in the ENS. Changes in the inhibitory and excitatory enteric neurons are described highlighting the role of loss of inhibitory neurons in early diabetic enteric neuropathy. The functional consequences of these neuronal changes result in altered gastric emptying, diarrhoea or constipation. Diabetes can also affect GI motility through changes in intestinal smooth muscle or alterations in extrinsic neuronal control. Hyperglycaemia and oxidative stress play an important role in the pathophysiology of these ENS changes. Antioxidants to prevent or treat diabetic GI motility problems have therapeutic potential. Recent research on the nerve-immune interactions demonstrates inflammation-associated neurodegeneration which can lead to motility related problems in diabetes.

Autophagy: highlighting a novel player in the autoimmunity scenario

Autophagy is a physiological cellular mechanism that degrades and recycles proteins and other molecules to maintain an adequate amino acid level during nutritional starvation of the cell. Autophagy is involved in cellular homeostasis and differentiation, as well as in tissue remodeling, aging, cancer, and other diseases. Under particular environmental conditions, autophagy can also be a contributor to programmed cell death, or can act as a defense mechanism for the elimination of intracellular bacteria and viruses. According to recent experimental data, autophagy may be implicated in autoimmunity by promotion of major histocompatibility complex (MHC) class II presentation of cytosolic antigens and control of T lymphocyte homeostasis, and its induction by Th1 cytokines and perhaps by specific serum autoantibodies. We review herein the role of autophagy in immune function and its possible contribution to breakdown of tolerance and development of autoimmunity.

Mechanisms of disease: the pathological basis of gastroparesis--a review of experimental and clinical studies

The pathogenesis of gastroparesis is complicated and poorly understood. This lack of understanding remains a major impediment to the development of effective therapies for this condition. Most of the scientific information available on the pathogenesis of gastroparesis has been derived from experimental studies of diabetes in animals. These studies suggest that the disease process can affect nerves (particularly those producing nitric oxide, but also the vagus nerve), interstitial cells of Cajal and smooth muscle. By contrast, human data are sparse, outdated and generally inadequate for the validation of data obtained from experimental models. The available data do, however, suggest that multiple cellular targets are involved. In practice, though, symptoms seldom correlate with objective measures of gastric function and there is still a lot to learn about the pathophysiology of gastroparesis. Future studies should focus on understanding the molecular pathways that lead to gastric dysfunction, in animal models and in humans, and pave the way for the development of rational therapies.

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.

Serum from achalasia patients alters neurochemical coding in the myenteric plexus and nitric oxide mediated motor response in normal human fundus

BACKGROUND AND AIMS

Achalasia is a disease of unknown aetiology. An immune mechanism has been suggested on the basis of previous morphological observations. The objective of this study was to test whether the serum of achalasia patients could reproduce the phenotype and functional changes that occur with disease progression in an ex vivo human model.

METHODS

Specimens of normal human fundus were maintained in culture in the presence of serum from patients with achalasia, gastro-oesophageal reflux disease (GORD), or healthy subjects (controls). Immunohistochemical detection of choline acetyltransferase (ChAT), neurone specific enolase (NSE), vasoactive intestinal polypeptide (VIP), nitric oxide synthase (NOS), and substance P was carried out in whole mounts of gastric fundus myenteric plexus. In addition, the effects of achalasia serum on electrical field stimulation (EFS) induced contractions were measured in circular muscle preparations.

RESULTS

Serum from achalasia patients did not affect the number of myenteric neurones. Tissues incubated with serum from achalasia patients showed a decrease in the proportion of NOS (-26% of NSE positive neurones; p=0.016) and VIP (-54%; p=0.09) neurones, and a concomitant increase in ChAT neurones (+16%; p<0.001) compared with controls. In contrast, GORD serum did not modify the phenotype of myenteric neurones. Area under the curve of EFS induced relaxations (abolished by N-nitro-L-arginine methyl ester) was significantly decreased following incubation with serum from achalasia patients compared with controls (-7.6 (2.6) v -14.5 (5.0); p=0.036).

CONCLUSIONS

Serum from achalasia patients can induce phenotypic and functional changes which reproduce the characteristics of the disease. Further identification of putative seric factors and mechanisms involved could lead to the development of novel diagnostic and/or therapeutic strategies in achalasia.

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.

Different types of chronic inflammatory demyelinating polyneuropathy have a different clinical course and response to treatment

Chronic inflammatory demyelinating polyneuropathy (CIDP) can occur in association with other systemic diseases such as diabetes mellitus (DM) and IgG or IgA monoclonal gammopathy of undetermined significance (MGUS). Whether CIDP that is idiopathic (I-CIDP) or associated with diabetes (CIDP-DM) or MGUS (CIDP-MGUS) differ in clinical presentation, laboratory features, response to treatment, and long-term outcome is unclear, as is the relationship between these coexisting diseases and CIDP. In order to clarify this issue, we began a prospective follow-up study. Thirty-one consecutive patients with untreated CIDP, fulfilling the most restrictive diagnostic criteria, were enrolled over 18 months. Among the patients, 16 were diabetic, 7 had a MGUS, and 8 had an idiopathic CIDP. All patients were treated with IVIg, and the responders were treated again if they relapsed. In all three groups, improvement occurred after treatment. At the end of the follow-up, there was no difference in clinical conditions between groups, but a significant difference existed in the number of relapses and of IVIg administrations. CIDP-DM is a more severe disease, but with a significantly better response to IVIg and fewer relapses, than the other types that we studied.

Serum from Sydenham's chorea patients modifies intracellular calcium levels in PC12 cells by a complement-independent mechanism

The proposed pathogenesis of Sydenham's chorea (SC) is an autoantibody-mediated basal ganglia dysfunction. Our study has shown that incubation of PC12 cells with complement-inactivated serum from SC patients was associated with a significant increase in Ca2+ levels evoked by KCl stimulus (mean +/- SEM, 341.0 +/- 8.7% of fluorescence intensity, arbitrary units) when compared with incubation with control serum (313.8 +/- 8.7% of fluorescence intensity, arbitrary units; P = 0.01). The increase in Ca2+ levels determined by SC patients sera correlated directly with the enzyme-linked immunosorbent assay optical density values for anti-basal ganglia antibodies. Our study supports the hypothesis that antibodies against basal ganglia in SC may cause their dysfunction.

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.

Can diabetic neuropathy be prevented?

The incidence of diabetes and its complication have rapidly increased. Decreased quality of life and increased mortality are the major problems of people with diabetes. These problems are mainly caused by chronic complications. The incidence of diabetic neuropathy, which is one of these chronic complications, approaches 50% in most diabetic patients. The intensive metabolic management alone cannot completely prevent the development and progression of diabetic complications. Therefore, blocking and management of pathogenic mechanism of complication are required. Pathogenesis of diabetic neuropathy has multifactorial causes. Diabetic neuropathy is thought to occur both from direct hyperglycemia-induced damage to the nerve parenchyma and from neuronal ischemia brought about indirectly by hyperglycemia-induced decreases in neurovascular flow. The effects of hyperglycemia get converted to neuronal dysfunction via at least three secondary biochemical pathways: the polyol pathway, non-enzymatic glycation of proteins, oxidative stress and protein kinase C, and the interactions between them. Because of these interactions, interference with one of these biochemical pathways could either worsen or attenuate the effects of the others. So, the use of therapeutic intervention of these pathways is inevitable and valid to prevent the progression of diabetic neuropathy. As yet, a satisfactory and fundamental, preventive, and therapeutic method is not available with us to prevent progression. So, we will introduce the earlier diagnostic methods of diabetic neuropathy and will discuss the advantages and limitations of each method.

Role of small GTP binding proteins in the growth-promoting and antiapoptotic actions of gastrin

G17 has growth promoting and antiapoptotic effects on the AR4-2J pancreatic acinar cell line. We previously reported that whereas MAPK regulates G17-stimulation of AR4-2J cell proliferation, Akt mediates the antiapoptotic action of G17. We examined the signal-transduction pathways mediating G17 stimulation of AR4-2J cell growth and survival. G17 activated the small GTP binding proteins Ras, Rac, Rho, and Cdc42. Transduction of the cells with adenoviral vectors expressing dominant negative Akt, Ras, Rho, and Cdc42 but not dominant negative Rac inhibited AR4-2J cell proliferation and survival. Both exoenzyme C3 from Clostridium botulinum (C3), a toxin known to inactivate Rho, and PD98059, a MAPK inhibitor, reversed G17 inhibition of AR4-2J cell apoptosis. G17 induction of Akt activation was reduced by >60% by both dominant negative Ras and Rho and by 30% by dominant negative Cdc42. In contrast, G17-stimulated MAPK activation was blocked by >80% by dominant negative Ras but not by dominant negative Rho and Cdc42. Similar results were observed in the presence of C3. Dominant negative Rac failed to affect G17 induction of both Akt and MAPK, whereas it inhibited sorbitol by almost 50% but not G17-stimulated activation of p38 kinase. Thus G17 promotes AR4-2J cell growth and survival through the activation of multiple GTP binding proteins, which, in turn, regulate different protein kinase cascades. Whereas Ras activates Akt and MAPK, Rho and Cdc42 appear to regulate Akt and possibly other as yet unidentified kinases mediating the growth-stimulatory actions of G17.

Disruption of intestinal motility by a calcium channel-stimulating autoantibody in type 1 diabetes

BACKGROUND & AIMS

Autonomic neuropathy, including gastrointestinal dysfunction, is a common complication of type 1 diabetes; however, its cause is uncertain. This study aimed to test whether functional autoantibodies cause the gastrointestinal dysfunction.

METHODS

We used isolated mouse colon undergoing colonic migrating motor complex (MMC) activity to test for autoantibodies that disrupt colonic motility. Purified immunoglobulin G (IgG) from patients with type 1 diabetes or from controls was tested either in vitro or after passive transfer. Pharmacological studies of the interaction between the IgG and L-type calcium channel activator (Bay K8644) and inhibitors (nicardipine and verapamil) were performed. The effect of IgG on nerve-evoked contraction of the vas deferens longitudinal smooth muscle was also assessed.

RESULTS

MMC activity was disrupted by IgG (0.2 mg/mL) from 8 of 16 patients with type 1 diabetes but not by control IgG. Passive transfer of diabetic IgG to mice also disrupted MMCs, showing access to the antigen in vivo. The acute effect of the autoantibody was mimicked by the dihydropyridine agonist, Bay K8644 (2-10 nmol/L), and both Bay K8644 and the autoantibody competitively inhibited the effect on MMC contraction of the dihydropyridine antagonist, nicardipine. Diabetic IgG, but not control IgG, altered the nerve-evoked contractile activity of vas deferens smooth muscle effects mimicked by Bay K8644.

CONCLUSIONS

A novel functional autoantibody that activates smooth muscle L-type calcium channels at the dihydropyridine binding site is produced specifically by patients with type 1 diabetes and may mediate gastrointestinal and autonomic dysfunction in these patients.

Nitrosative Injury and Antioxidant Therapy in the Management of Diabetic Neuropathy

Strong evidence implicates oxidative stress as a mediator of diabetes-induced microvascular complications, including distal symmetric polyneuropathy. Dorsal root ganglia neurons are particularly susceptible to glucose-mediated oxidative stress and die by apoptotic mechanisms in animal and cell culture models of diabetes. Key mediators of glucose-induced oxidative injury are superoxide anions and nitric oxide (NO). Superoxides are believed to underlie many of the oxidative changes in hyperglycemic conditions, including increases in aldose reductase and protein kinase C activity. Superoxides can also react with NO, forming peroxynitrite (ONOO-), which rapidly causes protein nitration or nitrosylation, lipid peroxidation, deoxyribonucleic acid (DNA) damage, and cell death. ONOO- formation is dependent on both superoxide and NO concentrations; therefore, cells that constitutively express NO synthase, such as endothelial cells and neurons, may be more vulnerable to ONOO–induced cell death in conditions favoring the production of superoxides. Although NO and ONOO- can cause endothelial and neuronal cell death in vitro, in animal models of diabetes, reductions in endothelial NO production can inhibit vasodilatation and cause nerve ischemia. Therefore, ideal therapeutic approaches should limit the formation of superoxides and ONOO while preventing reductions in vascular NO. Despite strong evidence that oxidative stress is associated with complications of diabetes, including neuropathy, the results of clinical trials of antioxidants have shown some promise but not established therapeutic efficacy. Clinical studies of several antioxidants, including α-lipoic acid, vitamins C and E, aldose reductase inhibitors, and growth factors, in diabetic neuropathy are discussed.

Systemic and local regulation of the growth plate

The growth plate is the final target organ for longitudinal growth and results from chondrocyte proliferation and differentiation. During the first year of life, longitudinal growth rates are high, followed by a decade of modest longitudinal growth. The age at onset of puberty and the growth rate during the pubertal growth spurt (which occurs under the influence of estrogens and GH) contribute to sex difference in final height between boys and girls. At the end of puberty, growth plates fuse, thereby ceasing longitudinal growth. It has been recognized that receptors for many hormones such as estrogen, GH, and glucocorticoids are present in or on growth plate chondrocytes, suggesting that these hormones may influence processes in the growth plate directly. Moreover, many growth factors, i.e., IGF-I, Indian hedgehog, PTHrP, fibroblast growth factors, bone morphogenetic proteins, and vascular endothelial growth factor, are now considered as crucial regulators of chondrocyte proliferation and differentiation. In this review, we present an update on the present perception of growth plate function and the regulation of chondrocyte proliferation and differentiation by systemic and local regulators of which most are now related to human growth disorders.

Anti-HuD-induced neuronal apoptosis underlying paraneoplastic gut dysmotility

BACKGROUND & AIMS

The role of autoimmunity underlying paraneoplastic gut dysmotility remains unsettled. Because anti-Hu antibodies may impair enteric neuronal function, we tested whether anti-HuD-positive sera from patients with paraneoplastic gut dysmotility or commercial anti-HuD antibodies activated the apoptotic cascade in a neuroblastoma cell line and cultured myenteric neurons.

METHODS

Anti-HuD antibodies from patients with severe paraneoplastic gut dysmotility were characterized by immunofluorescence and immunoblot. SH-Sy5Y neuroblasts and cultured myenteric neurons were exposed to sera containing anti-HuD antibodies or 2 commercial anti-HuD antibodies. Cells were processed for terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) technique to evaluate apoptosis. Immunofluorescence was used to identify activated caspase-3 and apaf-1, along with microtubule-associated protein 2.

RESULTS

In SH-Sy5Y cells, the percentage of TUNEL-positive nuclei observed after exposure to anti-HuD-positive sera (32% +/- 7%) or anti-HuD antibodies (23% +/- 2%) was significantly greater than that of control sera or fetal calf serum (P < 0.001). The time-course analysis showed a significantly greater number of apoptotic neuroblastoma cells evoked by the 2 commercial anti-HuD antibodies at 24, 48, and 72 hours versus controls. The number of TUNEL-positive myenteric neurons exposed to anti-HuD antibodies (60% +/- 14%) was significantly greater than that of fetal calf serum (7% +/- 2%; P < 0.001). Apaf-1 and caspase-3 immunolabeling showed intense cytoplasmic staining in a significantly greater proportion of cells exposed to anti-HuD-positive sera or to commercial anti-HuD antibodies compared with controls.

CONCLUSIONS

Anti-HuD antibodies evoked neuronal apoptosis that may contribute to enteric nervous system impairment underlying paraneoplastic gut dysmotility. Apaf-1 activation suggests participation of a mitochondria-dependent apoptotic pathway.

The role of polyol pathway in glucose-induced apoptosis of cultured retinal pericytes

The pathogenesis of pericyte loss, an initial deficit in the early stage of diabetic retinopathy, remains unclear. Recent studies have suggested that polyol pathway hyperactivity and apoptosis may be involved in pericyte loss. The mechanisms of the glucose-induced apoptosis in retinal pericytes were investigated to evaluate the pathogenesis of diabetic retinopathy. Under the 20 mM glucose condition, intracellular calcium concentrations and caspase-3 activities were significantly increased, and reduced glutathione (GSH) contents were significantly decreased compared with those under the 5.5 mM glucose condition. These abnormalities were all significantly prevented by an aldose reductase inhibitor, SNK-860. Glucose-induced apoptosis was partially but significantly prevented by SNK-860, an inhibitor of calcium-dependent cysteine protease, calpain, or GSH supplementation, and completely normalized by a caspase-3 inhibitor. These observations suggest that glucose-induced apoptosis in retinal pericytes, as one of the pathogenic factors of diabetic retinopathy, would be mediated through an aldose reductase-sensitive pathway including calcium-calpain cascade and increased oxidative stress, and that caspase-3 would be located furthest downstream of these apoptotic signals.

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.

Annexin-mediated Ca2+ influx regulates growth plate chondrocyte maturation and apoptosis

Maturation of epiphyseal growth plate chondrocytes plays an important role in endochondral bone formation. Previously, we demonstrated that retinoic acid (RA) treatment stimulated annexin-mediated Ca(2+) influx into growth plate chondrocytes leading to a significant increase in cytosolic Ca(2+), whereas K-201, a specific annexin Ca(2+) channel blocker, inhibited this increase markedly. The present study addressed the hypothesis that annexin-mediated Ca(2+) influx into growth plate chondrocytes is a major regulator of terminal differentiation, mineralization, and apoptosis of these cells. We found that K-201 significantly reduced up-regulation of expression of terminal differentiation marker genes, such as cbfa1, alkaline phosphatase (APase), osteocalcin, and type I collagen in RA-treated cultures. Furthermore, K-201 inhibited up-regulation of annexin II, V, and VI gene expression in these cells. RA-treated chondrocytes released mineralization-competent matrix vesicles, which contained significantly higher amounts of annexins II, V, and VI as well as APase activity than vesicles isolated from untreated or RA/K-201-treated cultures. Consistently, only RA-treated cultures showed significant mineralization. RA treatment stimulated the whole sequence of terminal differentiation events, including apoptosis as the final event. After a 6-day treatment gene expression of bcl-2, an anti-apoptotic protein, was down-regulated, whereas caspase-3 activity and the percentage of TUNEL-positive cells were significantly increased in RA-treated cultures compared with untreated cultures. Interestingly, the cytosolic calcium chelator BAPTA-AM and K-201 protected RA-treated chondrocytes from undergoing apoptotic changes, as indicated by higher bcl-2 gene expression, reduced caspase-3 activity, and the percentage of TUNEL-positive cells. In conclusion, annexin-mediated Ca(2+) influx into growth plate chondrocytes is a positive regulator of terminal differentiation, mineralization, and apoptosis events in growth plate chondrocytes.

Aldose reductase mediates cytotoxic signals of hyperglycemia and TNF-alpha in human lens epithelial cells

Chronic hyperglycemia and cytokines such as tumor necrosis factor alpha (TNF-alpha) cause oxidative stress leading to dysregulated cell growth or apoptosis that contributes to the development of inflammation and secondary complications of diabetes. However, the mechanisms regulating hyperglycemic or cytokine injury are not well understood. Herein we report that inhibition of the polyol pathway enzyme aldose reductase (AR) by two structurally unrelated inhibitors--sorbinil and tolrestat--prevents, in the human lens epithelial cell line B-3, the apoptosis and activation of caspase-3 caused by exposure to high glucose levels or TNF-alpha. Inhibition of AR attenuated TNF-alpha and hyperglycemia-induced activation of protein kinase C (PKC), phosphorylation of the inhibitory subunit of nuclear factor-kappaB (NF-kappaB), and stimulation of NF-kappaB, but it did not prevent the activation of NF-kappaB and PKC by phorbol ester. Inhibition of AR also attenuated the increase in p38 mitogen-activated protein kinase and c-Jun N-terminal kinase phosphorylation. These signaling pathways were also inhibited in cells in which the expression of AR was reduced by antisense ablation. Collectively, these results identify a new participant in apoptotic signaling and suggest that AR is an obligatory mediator of the apoptotic events upstream of PKC. These observations could provide new insights into the pathophysiology of diabetes and the role of aberrant glucose metabolism in apoptotic cell death.

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.

Elevation of von Willebrand factor in plasma in diabetic patients with neuropathic foot ulceration

AIMS

The present study examines the relationship between markers of endothelial dysfunction and diabetic neuropathy or consequent neuropathic foot ulceration in patients with Type 2 diabetes mellitus.

METHODS

We studied 65 Type 2 diabetic patients including 25 diabetic patients without neuropathy, 27 with neuropathy but no history of foot ulceration, and 13 with neuropathic ulceration. Plasma concentrations of von Willebrand factor (vWF) and soluble thrombomodulin (TM), measures of endothelial dysfunction, were determined by enzyme immunoassays. We performed various tests quantifying aspects of diabetic neuropathy including vibration perception threshold (VPT; for sensory neuropathy), coefficient of variation of R-R intervals (CVR-R; for cardiac autonomic neuropathy), and cold-induced vasodilation in the great toe for peripheral sympathetic neuropathy.

RESULTS

CVR-R and cold-induced vasodilation were significantly diminished in patients with neuropathic foot ulceration compared with patients with neuropathy but no history of foot ulceration. Plasma vWF concentrations were positively correlated with VPT and cold-induced vasodilation test, and were inversely correlated with CVR-R. Multivariate analysis disclosed that VPT and percentage vasodilation were independent factors for plasma vWF. Plasma vWF was significantly elevated in patients with foot ulceration compared with patients without neuropathy or those with neuropathy but not foot ulceration. However, plasma TM concentrations did not differ between the three groups.

CONCLUSIONS

Diabetic patients with neuropathic foot ulceration had severe impairment of cardiac autonomic and peripheral sympathetic nerves. Elevation of vWF in plasma was associated with neuropathic foot ulceration, linking endothelial dysfunction to foot ulceration.

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.

Molecular mechanisms for the antiapoptotic action of gastrin

Gastrin (G17) has a CCK-B receptor-mediated growth-promoting effect on the AR42J rat acinar cell line. We examined whether G17 inhibits apoptosis induced by serum withdrawal of AR42J cells and CHO-K1 cells stably expressing CCK-B receptors (CHO-K1/CCK-B cells). Cellular apoptosis was measured by flow cytometry and the terminal deoxynucleotidyltransferase-mediated dUTP-FITC nick end-labeling method. Serum withdrawal induced AR42J and CHO-K1/CCK-B cell apoptosis. Addition of 10 nM G17 reversed these effects. We examined the action of G17 (10 nM) on phosphorylation and activation of protein kinase B/Akt, a kinase known to promote cell survival. Akt phosphorylation and activation were measured by kinase assays and Western blots with an anti-phospho-Akt antibody. G17 stimulated Akt phosphorylation and activation. G17 induction of Akt phosphorylation was inhibited by the phosphoinositide 3-kinase (PI 3-kinase) inhibitors LY-294002 (10 microM) and wortmannin (200 nM) but not by the mitogen-activated protein kinase kinase 1 inhibitor PD-98059 (50 microM). To study the role of p38 kinase in G17 signaling to Akt, we examined the effect of G17 on p38 kinase activation and phosphorylation using kinase assays and Western blots with an anti-phospho-p38 kinase antibody. G17 induced p38 kinase activity at doses and with kinetics similar to those observed for Akt induction. The p38 kinase inhibitor SB-203580 inhibited G17 induction of Akt phosphorylation and activation at a concentration (10 microM) 10-fold higher than necessary to block p38 kinase (1 microM), suggesting the possible involvement of kinase activities other than p38 kinase. Transduction of AR42J cells with the adenoviral vector Adeno-dn Akt, which overexpresses an inhibitor of Akt, reversed the antiapoptotic action of G17. In conclusion, G17 promotes AR42J cell survival through the induction of Akt via PI 3-kinase and SB-203580-sensitive kinase activities.

Treatment of aged rat sensory neurons in short-term, serum-free culture with nerve growth factor reverses the effect of aging on neurite outgrowth, calcium currents, and neuronal survival

Impaired NGF production and release has been documented in aged animals, suggesting that decreased NGF receptor stimulation may be one factor contributing to neuronal dysfunction with aging. Other studies have suggested that aging may be associated with impaired intracellular responses to NGF. Because aging-associated neuronal dysfunction contributes to morbidity and mortality in the geriatric population, it is important to determine whether the effects of aging on sensory neuron function and survival are reversible. In the present study, we observed significantly decreased neurite outgrowth and neuronal survival in short-term cultures (0-96 h) of dorsal root ganglion (DRG) neurons from aged (>22 months) Fisher 344 x Brown Norway F1 hybrid rats, compared to young (4-6 month) and middle-aged (14 month) animals. From 24 to 96 h in culture, diminished survival of aged neurons appeared to be due to an increased rate of apoptotic cell death. DRG neurons from aged animals also exhibited significantly decreased whole cell, high-threshold voltage-dependent calcium currents, with a larger proportion of L-type current, compared to youthful and middle-aged animals. Treatment of aged DRG neurons with NGF restored neurite outgrowth, neuronal survival and calcium current amplitude and subtype distribution to those observed in youthful DRG neurons.

Akt-dependent antiapoptotic action of insulin is sensitive to farnesyltransferase inhibitor

CHO cells expressing the human insulin receptors (IR) were used to evaluate the effect of the potent farnesyltransferase inhibitor, manumycin, on insulin antiapoptotic function. Cell treatment with manumycin blocked insulin's ability to suppress pro-apoptotic caspase-3 activity which led to time-dependent proteolytic cleavage of two nuclear target proteins. The Raf-1/MEK/ERK cascade and the serine/threonine protein kinase Akt are two survival pathways that may be activated in response to insulin. We tested the hypothesis that inhibition of farnesylated Ras was causally related to manumycin-induced apoptosis and showed that the response to manumycin was found to be independent of K-Ras function because membrane association and activation of endogenous K-Ras proteins in terms of GTP loading and ERK activation were unabated following treatment with manumycin. Moreover, blocking p21Ras/Raf-1/MEK/ERK cascade by the expression of a transdominant inhibitory mSOS1 mutant in CHO-IR cells kept cells sensitive to the antiapoptotic action of insulin. Insulin-dependent activation of Akt was blocked by 4 h treatment with manumycin (P < 0.01), a kinetic too rapid to be explained by Ras inhibition. This study suggests that the depletion of short-lived farnesylated proteins by manumycin suppresses the antiapoptotic action of insulin at least in part by disrupting Akt activation but not that of the K-Ras/Raf-1/ERK-dependent cascade.

Aldose reductase inhibition prevents glucose-induced apoptosis in cultured bovine retinal microvascular pericytes

The pathogenesis of pericyte loss, an initial deficit in the early stage of diabetic retinopathy, remains unclear. Polyol pathway hyperactivity has been implicated in the pathogenesis of diabetic retinopathy, and recent studies have suggested that apoptosis may be involved in pericyte loss. The present study was conducted to investigate whether high glucose induces apoptosis in cultured bovine retinal pericytes. The effect of an aldose reductase inhibitor, SNK-860, was also examined. After a 5 day incubation with various concentrations of glucose (5.5-40 m M) in the presence or absence of SNK-860, the cell viability and the percentages of dead cells were measured, and staining with the TUNEL method and Hoechst 33342, and DNA electrophoresis were performed. High glucose reduced the viability and increased the percentages of dead cells. TUNEL-positive cells were observed in pericytes under high glucose, but not in those under 5.5 m M glucose. In the staining of nuclei with Hoechst 33342, the percentage of apoptotic cells in total cells counted under high glucose was higher than that under 5.5 m M glucose. DNA electrophoresis of pericytes cultured with high glucose demonstrated a 'ladder pattern'. Hyperosmolarity also induced apoptosis in pericytes, but less than that by high glucose. SNK-860 inhibited the glucose-induced apoptosis in pericytes. These observations suggest that the pericyte loss in diabetic retinopathy involves an apoptotic process, and that the polyol pathway hyperactivity plays an important role in inducing apoptosis in pericytes by high glucose.