Synergistic action of advanced glycation end products and endogenous nitric oxide leads to neuronal apoptosis in vitro: a new insight into selective nitrergic neuropathy in diabetes

A. officinarum Hance - P. cablin (Blanco) Benth drug pair improves oxidative stress, intracellular Ca2+ concentrations and apoptosis by inhibiting the AGE/RAGE axis to ameliorate diabetic gastroparesis: In vitro and in vivo studies

ETHNOPHARMACOLOGICAL RELEVANCE

Alpinia officinarum Hance is a perennial natural medicine herbivorous plant, has been used in the management of treat stomach pain and diabetes, it is abundantly cultivated in Qiongzhong, Baisha and other places. P. cablin (Blanco) Benth, one of the most important traditional Chinese plants, which plays functions in antioxidant and gastrointestinal regulation, has been extensively planted in Hainan, Guangdong and other regions.

AIM OF THE STUDY

In this study, we investigated the role and underlying molecular mechanism of AP on diabetic gastroparesis (DGP) in vitro and in vivo.

MATERIALS AND METHODS

In this study, using ultra-high performance liquid chromatography-mass spectrometry/mass spectrometry (UPLC-MS/MS) to identify active compounds in A. officinarum Hance-P. cablin (Blanco) Benth drug pair (AP). Molecular docking were utilized to explore the potential mechanism of AP treatment of DGP. In in vitro assays, gastric smooth muscle cells (GSMCs) were treated with 35 mM glucose to promote apoptosis and construct the DGP model, which was treated with different concentrations of AP. Furthermore, transfection technology was used to overexpress RAGE in GSMCs and elucidate the underlying mechanisms of alleviation of DGP by AP.

RESULTS

Using UPLC-MS/MS analysis, nine components of AP were identified. We found that AP effectively blocked the increase in apoptosis, oxidative stress, and intracellular Ca2+ concentrations. For in vivo experiments, mice were fed with a high-fat irregular diet to construct DGP model, and AP was co-administered via oral gavage daily to prevent the development of DGP. Compared with DGP mice, AP significantly decreased fasting blood glucose levels and increased gastric emptying levels. Consistent with in vitro experiments, AP also considerably decreased the increase in oxidative stress in DGP mice. Mechanistically, AP alleviates apoptosis and DGP by decreasing oxidative stress and intracellular Ca2+ concentrations via the inhibition of the AGE/RAGE axis.

CONCLUSIONS

Collectively, this study has established that AP can improve DGP, and the mechanism may be related to the inhibition the AGE/RAGE axis to mitigate apoptosis and DGP. To summarize, this study provides a novel supplementary strategy for DGP treatment.

Constipation in DM are associated with both poor glycemic control and diabetic complications: Current status and future directions

Constipation is a major complications of diabetes mellitus. With the accelerating prevalence of diabetes worldwide and an aging population, there is considerable research interest regarding the altered function and structure of the gastrointestinal tract in diabetic patients. Despite current advances in hyperglycemic treatment strategies, the specific pathogenesis of diabetic constipation remains unknown. Patients with constipation, may be reluctant to eat regularly, which may worsen glycemic control and thus worsen symptoms associated with underlying diabetic bowel disease. This paper presents a review of the complex relationship between diabetes and constipation, exploring the morphological alterations and biomechanical remodeling associated with intestinal motility dysfunction, as well as alterations in intestinal neurons, cellular signaling pathways, and oxidative stress. Further studies focusing on new targets that may play a role in the pathogenesis of diabetic constipation may, provide new ideas for the development of novel therapies to treat or even prevent diabetic constipation.

Neural control of pancreatic peptide hormone secretion

Pancreatic peptide hormone secretion is inextricably linked to maintenance of normal levels of blood glucose. In animals and man, pancreatic peptide hormone secretion is controlled, at least in part, by input from parasympathetic (vagal) premotor neurons that are found principally in the dorsal motor nucleus of the vagus (DMV). Iatrogenic (insulin-induced) hypoglycaemia evokes a homeostatic response commonly referred to as the glucose counter-regulatory response. This homeostatic response is of particular importance in Type 1 diabetes in which episodes of hypoglycaemia are common, debilitating and lead to suboptimal control of blood glucose. Glucagon is the principal counterregulatory hormone but for reasons unknown, its secretion during insulin-induced hypoglycaemia is impaired. Pancreatic parasympathetic neurons are distinguishable electrophysiologically from those that control other (e.g. gastric) functions and are controlled by supramedullary inputs from hypothalamic structures such as the perifornical region. During hypoglycaemia, glucose-sensitive, GABAergic neurons in the ventromedial hypothalamus are inhibited leading to disinhibition of perifornical orexin neurons with projections to the DMV which, in turn, leads to increased secretion of glucagon.

6-C-(E-Phenylethenyl)-naringenin, a Styryl Flavonoid, Inhibits Advanced Glycation End Product-Induced Inflammation by Upregulation of Nrf2

Styryl flavonoids can be formed during the thermal processing of meats and flavonoid-enriched foods, showing high potentials in the prevention of different diseases. In this study, the protective effects of several styryl flavonoids against advanced glycation end product (AGE)-induced inflammation were evaluated, with 6-C-(E-phenylethenyl)-naringenin (6-PN) showing the strongest activity among them. The results indicated that 6-PN significantly ameliorated AGE-induced damages in human umbilical vein endothelial cells, including inhibition of pro-inflammatory cytokines and reactive oxygen species (ROS) production through downregulating the protein levels of the receptor for AGEs (RAGE) and NADPH oxidase. Notably, 6-PN possessed a much higher bioavailability than its parental compound, naringenin. Furthermore, 6-PN also promoted the activation of the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway that was suppressed by AGEs, and the anti-inflammatory effects of 6-PN disappeared when the cells were treated with ML385, a Nrf2 inhibitor. Hence, 6-PN might inhibit AGE-induced inflammation by the RAGE/ROS/Nrf2 signaling pathway.

Nitrergic perivascular innervation in health and diseases: Focus on vascular tone regulation

For a long time, the vascular tone was considered to be regulated exclusively by tonic innervation of vasoconstrictor adrenergic nerves. However, accumulating experimental evidence has revealed the existence of nerves mediating vasodilatation, including perivascular nitrergic nerves (PNN), in a wide variety of mammalian species. Functioning of nitrergic vasodilator nerves is evidenced in several territories, including cerebral, mesenteric, pulmonary, renal, penile, uterine and cutaneous arteries. Nitric oxide (NO) is the main neurogenic vasodilator in cerebral arteries and acts as a counter-regulatory mechanism for adrenergic vasoconstriction in other vascular territories. In the penis, NO relaxes the vascular and cavernous smooth muscles leading to penile erection. Furthermore, when interacting with other perivascular nerves, NO can act as a neuromodulator. PNN dysfunction is involved in the genesis and maintenance of vascular disorders associated with arterial and portal hypertension, diabetes, ageing, obesity, cirrhosis and hormonal changes. For example defective nitrergic function contributes to enhanced sympathetic neurotransmission, vasoconstriction and blood pressure in some animal models of hypertension. In diabetic animals and humans, dysfunctional nitrergic neurotransmission in the corpus cavernosum is associated with erectile dysfunction. However, in some vascular beds of hypertensive and diabetic animals, an increased PNN function has been described as a compensatory mechanism to the increased vascular resistance. The present review summarizes current understanding on the role of PNN in control of vascular tone, its alterations under different conditions and the associated mechanisms. The knowledge of these changes can serve to better understand the mechanisms involved in these disorders and help in planning new treatments.

Sodium-glucose co-transporter (SGLT) inhibitor restores lost axonal varicosities of the myenteric plexus in a mouse model of high-fat diet-induced obesity

Diabetes impairs enteric nervous system functions; however, ultrastructural changes underlying the pathophysiology of the myenteric plexus and the effects of sodium-glucose co-transporter (SGLT) inhibitors are poorly understood. This study aimed to investigate three-dimensional ultrastructural changes in axonal varicosities in the myenteric plexus and the effect thereon of the SGLT inhibitor phlorizin in mice fed a high-fat diet (HFD). Three-dimensional ultrastructural analysis using serial block-face imaging revealed that non-treated HFD-fed mice had fewer axonal varicosities and synaptic vesicles in the myenteric plexus than did normal diet-fed control mice. Furthermore, mitochondrial volume was increased and lysosome number decreased in the axons of non-treated HFD-fed mice when compared to those of control mice. Phlorizin treatment restored the axonal varicosities and organelles in HFD-fed mice. Although HFD did not affect the immunolocalisation of PGP9.5, it reduced synaptophysin immunostaining in the myenteric plexus, which was restored by phlorizin treatment. These results suggest that impairment of the axonal varicosities and their synaptic vesicles underlies the damage to the enteric neurons caused by HFD feeding. SGLT inhibitor treatment could restore axonal varicosities and organelles, which may lead to improved gastrointestinal functions in HFD-induced obesity as well as diabetes.

Bergenin Reduces Experimental Painful Diabetic Neuropathy by Restoring Redox and Immune Homeostasis in the Nervous System

Diabetic neuropathy is a frequent complication of diabetes. Symptoms include neuropathic pain and sensory alterations—no effective treatments are currently available. This work characterized the therapeutic effect of bergenin in a mouse (C57/BL6) model of streptozotocin-induced painful diabetic neuropathy. Nociceptive thresholds were assessed by the von Frey test. Cytokines, antioxidant genes, and oxidative stress markers were measured in nervous tissues by ELISA, RT-qPCR, and biochemical analyses. Single (3.125–25 mg/kg) or multiple (25 mg/kg; twice a day for 14 days) treatments with bergenin reduced the behavioral signs of diabetic neuropathy in mice. Bergenin reduced both nitric oxide (NO) production in vitro and malondialdehyde (MDA)/nitrite amounts in vivo. These antioxidant properties can be attributed to the modulation of gene expression by the downregulation of inducible nitric oxide synthase (iNOS) and upregulation of glutathione peroxidase and Nrf2 in the nervous system. Bergenin also modulated the pro- and anti-inflammatory cytokines production in neuropathic mice. The long-lasting antinociceptive effect induced by bergenin in neuropathic mice, was associated with a shift of the cytokine balance toward anti-inflammatory predominance and upregulation of antioxidant pathways, favoring the reestablishment of redox and immune homeostasis in the nervous system. These results point to the therapeutic potential of bergenin in the treatment of painful diabetic neuropathy.

Apigenin and its methylglyoxal-adduct inhibit advanced glycation end products-induced oxidative stress and inflammation in endothelial cells

Protein glycation in the body can lead to malfunction of intracellular and extracellular proteins. Reactive carbonyl species (RCS) have been identified to be key intermediates in the reactions. The reaction products, generally termed as advanced glycation end products (AGEs), have been implicated in the development of diabetic complications. In this study, the activity of apigenin (API), a natural flavone in scavenging RCS and the molecular mechanism involved in its protective effect against AGEs-induced oxidative stress and inflammation were examined in vitro. Results showed that API could directly trap methylglyoxal (MGO) to form API-MGO adducts, thus inhibiting AGEs formation. API and di-apigenin adduct (DMA) were found to inhibit AGEs-induced oxidative stress and inflammation in human umbilical vein endothelial cells (HUVECs) by significantly suppressing reactive oxygen species (ROS) production (30% relative to control) and decreasing the protein expression of pro-inflammatory cytokines and adhesion molecules by 30-70%. Further mechanistic investigation revealed that the protective effect was likely mediated via suppression of the extracellular-signal-regulated kinase 1/2 (ERK)/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway initiated by AGEs-RAGE (receptor for AGEs) interaction and induction of ERK/nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway with subsequent up-regulation of antioxidant defense molecules. In summary, our results suggest that API possesses great potential to protect against AGEs-associated health disorders by modulating cellular inflammatory and antioxidant defense signaling pathways.

Anti-Inflammatory Effect of an Apigenin-Maillard Reaction Product in Macrophages and Macrophage-Endothelial Cocultures

Chronic inflammation is involved in the progression of various diseases, while dietary flavonoids are reported to possess antioxidative and anti-inflammatory properties against age-related diseases. Previously, an apigenin-Maillard reaction product, dimethylglyoxal apigenin (DMA), was identified by us and demonstrated to be antioxidative. In this study, we investigated the inhibitory effect of DMA on advanced glycation end product- (AGE-) induced inflammation in macrophages and macrophage-endothelial cocultures. Results showed that DMA remarkably inhibited the mRNA and protein expression of receptor for AGEs (RAGE), thereby inhibiting the production of ROS and proinflammatory cytokines, including tumor necrosis factor- (TNF-) α, interleukin (IL) 1, IL 6, and monocyte chemoattractant protein- (MCP-) 1 in RAW 264.7 cells. In the coculture system which was performed in the Boyden chamber, macrophage infiltration and adhesion to endothelial cells were significantly suppressed by DMA. Further study indicated that DMA decreased AGE-evoked IL 6 and MCP-1 secretion, which might be achieved through RAGE and its downstream-regulated transforming growth factor- (TGF-) β1 and intercellular adhesion molecule (ICAM) 1 expression in the coculture system. In conclusion, our study demonstrates that DMA, a thermally induced compound, has anti-inflammatory activity in both macrophages and macrophage-endothelial cocultures, offering a promising approach for slowing down the development of chronic diseases.

Undiagnosed prediabetes status is associated with a reduced effectiveness of phosphodiesterase type 5 inhibitors in men with erectile dysfunction

The efficacy of phosphodiesterase type 5 inhibitors (PDE5i) in patients with erectile dysfunction (ED) and undiagnosed prediabetes (PreDM) has been scantly analysed. We aimed to assess rates of and predictors of response to oral treatment in a cohort of ED men naïve for PDE5i with either normo-glycaemia or PreDM or diabetes mellitus (DM). Complete data from 466 men were analysed. Comorbidities were scored with the Charlson Comorbidity Index (CCI). Patients completed the International Index of Erectile Function (IIEF) at baseline and after 3 months of PDE5i treatment. Treatment response was evaluated using the minimal clinically important difference (MCID) (mild: +2; moderate: +5; severe: +7 from baseline IIEF-EF). PreDM status was defined as for the American Diabetes Association (2015) criteria. Descriptive statistics and logistic regression models tested the association between clinical predictors and MCID response. Overall, 253 (56.7%), 105 (23.5%) and 88 (19.7%) patients had normo-glycaemia (=controls), PreDM and DM, respectively. Diabetic and PreDM men were older, had higher BMI, higher CCI scores and lower total testosterone (tT) (all p < 0.01) compared to controls. Median baseline IIEF-EF was lower both in PreDM (14.0 vs. 18.0; p < 0.05) and DM patients (10.0 vs. 18.0; p < 0.001) than in controls. IIEF-EF improved in all groups after treatment (all p < 0.001), but scores were higher in controls compared to both PreDM and DM men at 3-mos assessment (26.0 vs. 20.0 vs. 17.5, respectively; all p < 0.001). Controls more frequently achieved significant MCID than both PreDM and DM patients (65.3 vs. 22.9 vs. 11.8%, respectively; p < 0.01). Age (p < 0.001), baseline IIEF-EF (p < 0.001), and DM status (p = 0.02) were independently associated with MCID. In conclusion, patients with undiagnosed PreDM depicted lower rates of response to PDE5i than normoglycemic men. These findings suggest that even milder forms of glucose impairment are associated with a poorer PDE5i effectiveness in men with ED.

Nitrergic Enteric Neurons in Health and Disease-Focus on Animal Models

Nitrergic enteric neurons are key players of the descending inhibitory reflex of intestinal peristalsis, therefore loss or damage of these neurons can contribute to developing gastrointestinal motility disturbances suffered by patients worldwide. There is accumulating evidence that the vulnerability of nitrergic enteric neurons to neuropathy is strictly region-specific and that the two main enteric plexuses display different nitrergic neuronal damage. Alterations both in the proportion of the nitrergic subpopulation and in the total number of enteric neurons suggest that modification of the neurochemical character or neuronal death occurs in the investigated gut segments. This review aims to summarize the gastrointestinal region and/or plexus-dependent pathological changes in the number of nitric oxide synthase (NOS)-containing neurons, the NO release and the cellular and subcellular expression of different NOS isoforms. Additionally, some of the underlying mechanisms associated with the nitrergic pathway in the background of different diseases, e.g., type 1 diabetes, chronic alcoholism, intestinal inflammation or ischaemia, will be discussed.

Penile alterations at early stage of type 1 diabetes in rats

Objective

Diabetes affects the erectile function significantly. However, the penile alterations in the early stage of diabetes in experimental animal models have not been well studied. We examined the changes of the penis and its main erectile components in diabetic rats.

Materials and methods

Male Sprague-Dawley rats were divided into 2 groups: streptozotocin (STZ)-induced diabetics and age-matched controls. Three or nine weeks after diabetes induction, the penis was removed for immunohistochemical staining of smooth muscle and neuronal nitric oxide synthase (nNOS) in midshaft penile tissues. The cross-sectional areas of the whole midshaft penis and the corpora cavernosa were quantified. The smooth muscle in the corpora cavernosa and nNOS in the dorsal nerves were quantified.

Results

The weight, but not the length, of the penis was lower in diabetics. The cross-sectional areas of the total midshaft penis and the corpora cavernosa were lower in diabetic rats compared with controls 9 weeks, but not 3 weeks after diabetes induction. The cross-sectional area of smooth muscle in the corpora cavernosa as percentage of the overall area of the corpora cavernosa was lower in diabetic rats than in controls 9 weeks, but not 3 weeks after diabetes induction. Percentage change of nNOS in dorsal nerves was similar at 3 weeks, and has a decreased trend at 9 weeks in diabetic rats compared with controls.

Conclusions

Diabetes causes temporal alterations in the penis, and the significant changes in STZ rat model begin 3-9 weeks after induction. Further studies on the reversibility of the observed changes are warranted.

Longitudinal Patterns of Occurrence and Remission of Erectile Dysfunction in Men With Type 1 Diabetes

BACKGROUND

Men with diabetes are at greater risk of erectile dysfunction (ED).

AIM

To describe the natural history of ED in men with type 1 diabetes.

METHODS

We examined up to 30 years of prospectively collected annual ED status and demographic and clinical variables from 600 male participants in the Diabetes Control and Complications Trial (DCCT; 1983-1993) and its follow-up study, the Epidemiology of Diabetes Interventions and Complications (1994-present; data in this study are through 2012).

OUTCOMES

Yes vs no response to whether the participant had experienced impotence in the past year and whether he had used ED medication.

RESULTS

Sixty-one percent of men reported ED at least once during the study. For some men, the initial report of ED was permanent. For others, potency returned and was lost multiple times. Visual display of the data showed four longitudinal ED phenotypes: never (38.7%), isolated (6.7%), intermittent (41.8%), and persistent (12.8%). Men who never reported ED or in only 1 isolated year were younger, had lower body mass index, and better glycemic control than men in the intermittent and persistent groups at DCCT baseline. In a multivariable logistic model comparing men at their first year reporting ED, men who were older had lower odds of remission and men who were in the conventional DCCT treatment group had higher odds of remission.

CLINICAL TRANSLATION

If validated in other cohorts, such findings could be used to guide individualized interventions for patients with ED.

STRENGTHS AND LIMITATIONS

This is the first examination of ED with repeated measures at an annual resolution, with up to 30 years of responses for each participant. However, the yes vs no response is a limitation because the real phenotype is not binary and the question can be interpreted differently depending on the participant.

CONCLUSIONS

Age, glycemic control, and BMI were important longitudinal predictors of ED. We have described a more complex ED phenotype, with variation in remission patterns, which could offer insight into different mechanisms or opportunities for intervention. If validated in other cohorts, such findings could be used to establish more accurate prognostication of outcomes for patients with ED to guide individualized interventions. Palmer MR, Holt SK, Sarma AV, et al. Longitudinal Patterns of Occurrence and Remission of Erectile Dysfunction in Men With Type 1 Diabetes. J Sex Med 2017;14:1187-1194.

eNOS Function and Dysfunction in the Penis

Endothelial nitric oxide (NO) synthase (eNOS) has an indispensable role in the erectile response. In the penis, eNOS activity and endothelial NO bioavailability are regulated by multiple post-translatlonal molecular mechanisms, such as eNOS phosphorylation, eNOS interaction with regulatory proteins and contractile pathways, and actions of reactive oxygen species (ROS). These mechanisms regulate eNOS-mediated responses under physiologic circumstances and provide various mechanisms whereby endothelial NO availability may be altered in states of vasculogenlc erectile dysfunction (ED), in view of the recent advances in the field of eNOS function in the penis and its role in penile erection, the emphasis in this review is placed on the mechanisms regulating eNOS activity and its interaction with the RhoA/Rho-kinase pathway in the physiology of penile erection and the pathophysiology of ED.

Quantification of nitrergic neurons in the myenteric plexus of gastric antrum and ileum of healthy and diabetic dogs

Diabetes mellitus (DM) determines a wide array of severe clinical complications including gastrointestinal motility disorders. The present study investigates the effects of spontaneous DM on the intramural innervation and in particular on nitrergic neurons of the myenteric plexus (MP) of the canine gastric antrum and ileum. Specimens of antrum and ileum from eight control-dogs and five insulin-dependent DM-dogs were collected. MP neurons were immunohistochemically identified with the anti-HuC/HuD antibody, while nitrergic neurons were identified with the antibody anti-neuronal nitric oxide synthase (nNOS). The density of HuC/HuD-immunoreactive (IR) neurons was determined and the nitrergic neurons were quantified as a relative percentage, in consideration of the total number of HuC/HuD-IR neurons. Furthermore, the density of nitrergic fibers in the muscular layers was calculated. Data were expressed as mean±standard deviation. Compared to control-dogs, no significant differences resulted in the density of HuC/HuD-IR neurons in the antrum and ileum of DM-dogs; however, HuC/HuD-immunolabeling showed nuclear localization and fragmentation in DM-dogs. In the stomachs of control- and DM-dogs, the percentages of nitrergic neurons were 30±6% and 25±2%, respectively (P=0.112). In the ileum of the control-dogs, the percentage of nitrergic neurons was 29±5%, while in the DM-dogs, it was significantly reduced 19±5% (P=0.006). The density of nNOS-IR nervous fibers was meaningful reduced in either the tracts considered. Notably, the ganglia of DM-dogs showed also a thickening of the periganglionic connective tissue. These findings indicate that DM in dogs induce modification of the myenteric neurons and, in particular, of the nitrergic neuronal subpopulation.

Damaging effects of hyperglycemia on cardiovascular function: spotlight on glucose metabolic pathways

The incidence of cardiovascular complications associated with hyperglycemia is a growing global health problem. This review discusses the link between hyperglycemia and cardiovascular diseases onset, focusing on the role of recently emerging downstream mediators, namely, oxidative stress and glucose metabolic pathway perturbations. The role of hyperglycemia-mediated activation of nonoxidative glucose pathways (NOGPs) [i.e., the polyol pathway, hexosamine biosynthetic pathway, advanced glycation end products (AGEs), and protein kinase C] in this process is extensively reviewed. The proposal is made that there is a unique interplay between NOGPs and a downstream convergence of detrimental effects that especially affect cardiac endothelial cells, thereby contributing to contractile dysfunction. In this process the AGE pathway emerges as a crucial mediator of hyperglycemia-mediated detrimental effects. In addition, a vicious metabolic cycle is established whereby hyperglycemia-induced NOGPs further fuel their own activation by generating even more oxidative stress, thereby exacerbating damaging effects on cardiac function. Thus NOGP inhibition, and particularly that of the AGE pathway, emerges as a novel therapeutic intervention for the treatment of cardiovascular complications such as acute myocardial infarction in the presence hyperglycemia.

Quercetin Isolated from Toona sinensis Leaves Attenuates Hyperglycemia and Protects Hepatocytes in High-Carbohydrate/High-Fat Diet and Alloxan Induced Experimental Diabetic Mice

The development of diabetes mellitus is related to oxidant stress induced by a high carbohydrate/high-fat diet (HFD). Quercetin, as a major bioactive component in Toona sinensis leaves (QTL), is a natural antioxidant. However, the exact mechanism by which QTL ameliorate diabetes mellitus is still unknown. In this study, we investigated the hypoglycemic effects and hepatocytes protection of QTL on HFD and alloxan induced diabetic mice. Intragastric administration of QTL significantly reduced body weight gain, serum glucose, insulin, total cholesterol, triglyceride, low density lipoprotein-cholesterol, alanine aminotransferase, and aspartate aminotransferase serum levels compared to those of diabetic mice. Furthermore, it significantly attenuated oxidative stress, as determined by lipid peroxidation, nitric oxide content, and inducible nitric oxide synthase activity and as a result attenuated liver injury. QTL also significantly suppressed the diabetes-induced activation of the p65/NF-κB and ERK1/2/MAPK pathways, as well as caspase-9 and caspase-3 levels in liver tissues of diabetic mice. Finally, micrograph analysis of liver samples showed decreased cellular organelle injury in hepatocytes of QTL treated mice. Taken together, QTL can be viewed as a promising dietary agent that can be used to reduce the risk of diabetes mellitus and its secondary complications by ameliorating oxidative stress in the liver.

Differences Between Tg2576 and Wild Type Mice in the NMDA Receptor-Nitric Oxide Pathway After Prolonged Application of a Diet High in Advanced Glycation End Products

It has been suggested that advanced glycation end (AGE) products, via cognate receptor activation, are implicated in several diseases, including Alzheimer's disease. The NMDA receptor-nitric oxide pathway appears to be influenced by AGE products and involved in the pathogenesis of this type of dementia. In this study, C57BL/6J (WT) and transgenic (Tg2576) mice expressing human mutant amyloid precursor protein were kept on prolonged (8 months) diets containing regular or high amounts of AGE products. After the decapitation of 11-months old mice, brain tissue analyses were performed [expressions of the NR1, NR2A and NR2B subunits of NMDA receptors, activities of neuronal, endothelial and inducible nitric oxide synthase (nNOS, eNOS and iNOS)]. Moreover, levels of malondialdehyde and of human amyloid β 1-42 were estimated. We found increased activity of nNOS in WT mice maintained on a high compared to regular AGE diet; however, no similar differences were found in Tg2576 mice. In addition, we observed an increase in NR1 expression in Tg2576 compared to WT mice, both kept on a diet high in AGE products. Correlation analyses performed on mice kept on the regular AGE diet supported close links between particular subunits (NR2A-NR2B, in WT as well as in Tg2576 mice), between subunits and synthase (NR2A/NR2B-nNOS, only in WT mice) or between particular synthases (nNOS-iNOS, only in WT). Correlation analysis also revealed differences between WT mice kept on both diets (changed correlations between NR2A/NR2B-nNOS, between nNOS-eNOS and between eNOS-iNOS). Malondialdehyde levels were increased in both Tg2576 groups when compared to the corresponding WT mice, but no effects of the diets were observed. Analogously, no significant effects of diets were found in the levels of soluble or insoluble amyloid β 1-42 in Tg2576 mice. Our results demonstrate that prolonged ingestion of AGE products can influence the NMDA receptor-nitric oxide pathway in the brain and that only WT mice, not Tg2576 mice, are able to maintain homeostasis among subunits and synthases or among particular synthases. The prolonged application of AGE products enhanced differences between 11-months old Tg2576 and WT mice regarding this pathway. Observed differences in the pathway between WT mice kept on regular or high AGE diets suggest that the prolonged application of a diet low in AGE products could have beneficial effects in older or diabetic people and perhaps also in people with Alzheimer's disease.

Advanced glycation end-product expression is upregulated in the gastrointestinal tract of type 2 diabetic rats

AIM: To investigate changes in advanced glycation end products (AGEs) and their receptor (RAGE) expression in the gastrointestinal (GI) tract in type 2 diabetic rats.

METHODS: Eight inherited type 2 diabetic rats Goto-Kakizak (GK) and ten age-matched normal rats were used in the study. From 18 wk of age, the body weight and blood glucose were measured every week and 2 wk respectively. When the rats reached 32 wk, two-centimeter segments of esophagus, duodenum, jejunum, ileum, and colon were excised and the wet weight was measured. The segments were fixed in 10% formalin, embedded in paraffin and five micron sections were cut. The layer thickness was measured in Hematoxylin and Eosin-stained slides. AGE [N epsilon-(carboxymethyl) lysine and N epsilon-(carboxyethyl)lysine] and RAGE were detected by immunohistochemistry staining and image analysis was done using Sigmascan Pro 4.0 image analysis software.

RESULTS: The blood glucose concentration (mmol/L) at 18 wk age was highest in the GK group (8.88 ± 1.87 vs 6.90 ± 0.43, P < 0.001), a difference that continued to exist until the end of the experiment. The wet weight per unit length (mg/cm) increased in esophagus, jejunum and colon from the normal to the GK group (60.64 ± 9.96 vs 68.56 ± 11.69, P < 0.05 for esophagus; 87.01 ± 9.35 vs 105.29 ± 15.45, P < 0.01 for jejunum; 91.37 ± 7.25 vs 97.28 ± 10.90, P < 0.05 for colon). Histologically, the layer thickness of the GI tract was higher for esophagus, jejunum and colon in the GK group [full thickness (μm): 575.37 ± 69.22 vs 753.20 ± 150.41, P < 0.01 for esophagus; 813.51 ± 44.44 vs 884.81 ± 45.31, P < 0.05 for jejunum; 467.12 ± 65.92 vs 572.26 ± 93.60, P < 0.05 for colon]. In esophagus, the AGE and RAGE mainly distributed in striated muscle cells and squamous epithelial cells. The AGE distribution was much stronger in the GK group compared to the normal group both in the striated muscle layer and mucosa layer (immuno-positive area/ total measuring area %: 4.52 ± 0.89 vs 10.96 ± 1.34, P < 0.01 for muscle; 8.90 ± 2.62 vs 22.45 ± 1.26, P < 0.01 for mucosa). No visible difference was found for RAGE distribution between the two groups. In the intestine AGE and RAGE distributed in epithelial cells of villi and crypt. RAGE was also found in neurons in the myenteric and submucosal plexus. The intensity of AGE staining in mucosa of all segments and RAGE staining in neurons in all segments were strongest in the diabetes group. Significant difference for AGE was found in the epithelial cells of villi and crypt in duodenum (immuno-positive area/total measuring area %: 13.37 ± 3.51 vs 37.48 ± 8.43, P < 0.05 for villi; 0.38 ± 0.12 vs 1.87 ± 0.53, P < 0.05 for crypt) and for RAGE in neurons of all segments (e.g., for jejunum: no staining neurons% 0 vs 0, mild 36.0 ± 5.2 vs 28.7 ± 3.5, moderate 53.2 ± 4.8 vs 55.8 ± 5.4, strong 10.7 ± 1.1 vs 15.4 ± 2.0, P < 0.05). In the colon, RAGE was primarily found in neurons in the myenteric and submucosal plexus. It was stronger in the diabetes group than in the normal group (no staining neurons% 6.2 ± 0.2 vs 0.3 ± 0.04, mild 14.9 ± 2.1 vs 17.6 ± 1.5, moderate 53.1 ± 4.6 vs 44.7 ± 4.4, strong 25.6 ± 18 vs 43.6 ± 4.0, P < 0.05). In the rectum, RAGE was primarily found in the mucosa epithelial cells.

CONCLUSION: The AGE and RAGE expression was up-regulated in the GI tract of GK diabetic rats and may contribute to GI dysfunction in type 2 diabetic patients.

Prolonged high fat diet ingestion, obesity, and type 2 diabetes symptoms correlate with phenotypic plasticity in myenteric neurons and nerve damage in the mouse duodenum

Symptoms of diabetic gastrointestinal dysmotility indicate neuropathy of the enteric nervous system. Long-standing diabetic enteric neuropathy has not been fully characterized, however. We used prolonged high fat diet ingestion (20 weeks) in a mouse model to mimic human obese and type 2 diabetic conditions, and analyzed changes seen in neurons of the duodenal myenteric plexus. Ganglionic and neuronal size, number of neurons per ganglionic area, density indices of neuronal phenotypes (immunoreactive nerve cell bodies and varicosities per ganglion or tissue area) and nerve injury were measured. Findings were compared with results previously seen in mice fed the same diet for 8 weeks. Compared to mice fed standard chow, those on a prolonged high fat diet had smaller ganglionic and cell soma areas. Myenteric VIP- and ChAT-immunoreactive density indices were also reduced. Myenteric nerve fibers were markedly swollen and cytoskeletal protein networks were disrupted. The number of nNOS nerve cell bodies per ganglia was increased, contrary to the reduction previously seen after 8 weeks, but the density index of nNOS varicosities was reduced. Mice fed high fat and standard chow diets experienced an age-related reduction in total neurons, with bias towards neurons of sensory phenotype. Meanwhile, ageing was associated with an increase in excitatory neuronal markers. Collectively, these results support a notion that nerve damage underlies diabetic symptoms of dysmotility, and reveals adaptive ENS responses to the prolonged ingestion of a high fat diet. This highlights a need to mechanistically study long-term diet-induced nerve damage and age-related impacts on the ENS.

Is the present cut-point to define type 2 diabetes appropriate in Latin-Americans?

The diagnosis of diabetes mellitus type 2 (DM2) is based either on increased plasma glucose or Glycated hemoglobin levels. Since these measures are the only means for diagnosis of DM2, they must be well adapted to each population according to their metabolic characteristics, given that these may vary in each population. The World Health Organization (WHO) determined the cut-points of plasma glucose levels for the diagnosis of DM2 by associating hyperglycemia with the risk of a specific microvascular complication-retinopathy. Cardiovascular diseases are however the principal causes of mortality in patients with DM2 and we reported that in the Colombo-Ecuadorian population impaired fasting glucose and impaired glucose tolerance are both risk markers for myocardial infarction. We propose that the current cut-points accepted by the WHO need to be revaluated in populations such as Latin America and that there should be lower cut points for glycaemia in this population, to reduce the prevalence of cardiovascular complications associated with DM2.

Hydroxyl fasudil, an inhibitor of Rho signaling, improves erectile function in diabetic rats: a role for neuronal ROCK

INTRODUCTION

The pathogenesis of diabetic erectile dysfunction (ED) includes neuropathy, but the molecular basis for neurogenic ED is incompletely understood. The RhoA/ROCK pathway has been implicated in diabetic neuropathy and in ED, but its role in diabetic neurogenic ED is not known.

AIMS

The aim of this study was to determine whether hydroxyl fasudil, a ROCK inhibitor, affects diabetic neuropathy-related ED.

METHODS

Type 1 diabetes mellitus was induced in male rats by streptozotocin (75 mg/kg, intraperitoneally). After 8 weeks, diabetic rats were administered hydroxyl fasudil, a selective ROCK inhibitor (10 mg/kg/day, intraperitoneally) or vehicle, for 4 weeks. Age-matched control, nondiabetic, rats were treated intraperitoneally for 4 weeks with saline. At week 12, after a 2 day washout, neuro-stimulated erectile function was evaluated. Major pelvic ganglia (MPG) were collected for Western blot analysis of RhoA, ROCK-1, ROCK-2, phospho (P)-AKT (Ser(473) ), and P-phosphatase and tensin homolog (P-PTEN) (Ser(380) /Thr(382/383) ).

MAIN OUTCOME MEASURES

Effect of ROCK inhibitor hydroxyl fasudil on erectile function and ROCK/P-AKT/P-PTEN pathway in the MPG of diabetic rats.

RESULTS

Erectile response was significantly (P < 0.05) reduced in diabetic rats compared with nondiabetic rats and was preserved (P < 0.05) in diabetic rats treated with hydroxyl fasudil. In diabetic rats, RhoA and ROCK-2 protein expressions in MPG were increased (P < 0.05) and remained increased in hydroxyl fasudil-treated rats. P-AKT (Ser(473) ) expression was decreased (P < 0.05), whereas P-PTEN (Ser(380) /Thr(382/383) ) expression was increased (P < 0.05) in MPG of diabetic rats compared with nondiabetic rats, and both were reversed (P < 0.05) in diabetic rats treated with hydroxyl fasudil.

CONCLUSION

Improved erectile function and restored P-AKT and P-PTEN in the MPG with hydroxyl fasudil treatment suggest the role of Rho signaling via PTEN/AKT pathway in neurogenic diabetic ED.

A spontaneous animal model of intestinal dysmotility evoked by inflammatory nitrergic dysfunction

Background and Aims

Recent reports indicate the presence of low grade inflammation in functional gastrointestinal disorders (FGID), in these cases often called “post-inflammatory” FGIDs. However, suitable animal models to study these disorders are not available. The Biobreeding (BB) rat consists of a diabetes-resistant (BBDR) and a diabetes-prone (BBDP) strain. In the diabetes-prone strain, 40–60% of the animals develop diabetes and concomitant nitrergic dysfunction. Our aim was to investigate the occurrence of intestinal inflammation, nitrergic dysfunction and intestinal dysmotility in non-diabetic animals.

Methods

Jejunal inflammation (MPO assay, Hematoxylin&Eosin staining and inducible nitric oxide synthase (iNOS) mRNA expression), in vitro jejunal motility (video analysis) and myenteric neuronal numbers (immunohistochemistry) were assessed in control, normoglycaemic BBDP and diabetic BBDP rats. To study the impact of iNOS inhibition on these parameters, normoglycaemic BBDP rats were treated with aminoguanidine.

Results

Compared to control, significant polymorphonuclear (PMN) cell infiltration, enhanced MPO activity, increased iNOS mRNA expression and a decreased ratio of nNOS to Hu-C/D positive neurons were observed in both normoglycaemic and diabetic BBDP rats. Aminoguanidine treatment decreased PMN infiltration, iNOS mRNA expression and MPO activity. Moreover, it restored the ratio of nNOS to Hu-C/D positive nerves in the myenteric plexus and decreased the abnormal jejunal elongation and dilation observed in normoglycaemic BBDP rats.

Conclusions

Aminoguanidine treatment counteracts the inflammation-induced nitrergic dysfunction and prevents dysmotility, both of which are independent of hyperglycaemia in BB rats. Nitrergic dysfunction may contribute to the pathophysiology of “low-grade inflammatory” FGIDs. Normoglycaemic BBDP rats may be considered a suitable animal model to study the pathogenesis of FGIDs.

Diabetic gastrointestinal motility disorders and the role of enteric nervous system: current status and future directions

BACKGROUND

Gastrointestinal manifestations of diabetes are common and a source of significant discomfort and disability. Diabetes affects almost every part of gastrointestinal tract from the esophagus to the rectum and causes a variety of symptoms including heartburn, nausea, vomiting, abdominal pain, diarrhea and constipation. Understanding the underlying mechanisms of diabetic gastroenteropathy is important to guide development of therapies for this common problem. Over recent years, the data regarding the pathophysiology of diabetic gastroenteropathy is expanding. In addition to autonomic neuropathy causing gastrointestinal disturbances the role of enteric nervous system is becoming more evident.

PURPOSE

In this review, we summarize the reported alterations in enteric nervous system including enteric neurons, interstitial cells of Cajal and neurotransmission in diabetic animal models and patients. We also review the possible underlying mechanisms of these alterations, with focus on oxidative stress, growth factors and diabetes induced changes in gastrointestinal smooth muscle. Finally, we will discuss recent advances and potential areas for future research related to diabetes and the ENS such as gut microbiota, micro-RNAs and changes in the microvasculature and endothelial dysfunction.

MSTMP, a Stilbene Derivative, Protects SH-SY5Y Cells Against Oxidative Stress

OBJECTIVE

the protective effects of a novel stilbene derivative, (e)-2-(3,4,5- trimethoxystyryl)-3,5,6-trimethylpyrazine (MStMp), on hydrogen peroxide (h2o2)-induced human derived neuroblastoma cell (Sh-Sy5y) damage and its molecular mechanisms were investigated.

METHODS

Sh-Sy5y cells were exposed to 200 μmol.l-1 h2o2 for 12 h. the effect of MStMp on cell viability and apoptosis was assessed by 3-(4,5-dimethyl- thiazol-2-yl)-2,5-diphenyl tetrazolium bromide (Mtt) assay and flow cytometry method. the activities of lactate dehydrogenase (ldh), superoxide dismutase (Sod) and nitric oxide synthetase (noS) and the content of malondialdehyde (Mda), reduced glutathione (gSh) and nitric oxide (no) in cells were determined by commercial kits. the expressions of pro-apoptotic factor caspase-3, caspase-9 and inducible noS (inoS) were detected by Western blotting. intracellular formation of reactive oxygen species (roS) was assessed using 6-carboxy-2’,7’-dichlorofluorescin diacetate (dCfh-da) fluorescent probe.

RESULTS

MStMp increased the Sh-Sy5y cell viability by inhibition of cell apoptosis induced by h2o2. these effects were accompanied by an increase of Sod activity, gSh level, and a decrease of Mda content. Moreover, MStMp showed stronger effects on inhibition of ldh leakage, apoptotic cells, intracellular roS level and the expression of caspase-3 and caspase-9 than tMp. furthermore, MStMp induced a decrease of no level and the activity of inoS, tnoS in a time-dependent manner.

CONCLUSIONS

MStMp prevents h2o2-induced cell injury through anti-oxidation and anti-apoptosis via roS-no pathway.

Diabetic neuropathy: an evaluation of the use of quercetin in the cecum of rats

AIM

To investigate the effect of quercetin supplementation on the myenteric neurons and glia in the cecum of diabetic rats.

METHODS

Total preparations of the muscular tunic were prepared from the ceca of twenty-four rats divided into the following groups: control (C), control supplemented with quercetin (200 mg/kg quercetin body weight) (CQ), diabetic (D) and diabetic supplemented with quercetin (DQ). Immunohistochemical double staining technique was performed with HuC/D (general population)/nitric oxide synthase (nNOS), HuC-D/S-100 and VIP. Density analysis of the general neuronal population HuC/D-IR, the nNOS-IR (nitrergic subpopulation) and the enteric glial cells (S-100) was performed, and the morphometry and the reduction in varicosity population (VIP-IR) in these populations were analyzed.

RESULTS

Diabetes promoted a significant reduction (25%) in the neuronal density of the HuC/D-IR (general population) and the nNOS-IR (nitrergic subpopulation) compared with the C group. Diabetes also significantly increased the areas of neurons, glial cells and VIP-IR varicosities. Supplementation with quercetin in the DQ group prevented neuronal loss in the general population and increased its area (P < 0.001) and the area of nitrergic subpopulation (P < 0.001), when compared to C group. Quercetin induced a VIP-IR and glial cells areas (P < 0.001) in DQ group when compared to C, CQ and D groups.

CONCLUSION

In diabetes, quercetin exhibited a neuroprotective effect by maintaining the density of the general neuronal population but did not affect the density of the nNOS subpopulation.

The stem bark extracts of Cenostigma macrophyllum attenuates tactile allodynia in streptozotocin-induced diabetic rats

CONTEXT. Cenostigma macrophyllum Tul. var. acuminata Teles Freire (Leguminosae- Caesalpinioideae) is popularly known as "caneleiro". Previous studies showed antioxidant action and analgesic effects of the ethanol extract from the leaves of C. macrophyllum. The phytochemical evaluation of the stem bark revealed the presence of antinociceptive compounds.

OBJECTIVE

To investigate the antinociceptive actions of the ethanol extract and ethyl acetate fraction from C. macrophyllum stem bark in streptozotocin (STZ)-induced diabetic rats and the involvement of opioid and nitrergic mechanisms.

MATERIALS AND METHODS

STZ-rats received the ethanol extract (E.EtOH 200 and 300 mg/kg, p.o.) during 5 weeks. In acute experiments, untreated diabetic rats were treated with the ethyl acetate fraction (F.EtOAc 250 and 500 mg/kg, p.o.), on the 28th day of diabetes induction when the opioid and nitrergic mechanisms were investigated. The mechanical nociceptive threshold (MNT) was determined by application of von Frey filaments.

RESULTS

Data show that STZ-induced diabetic rats developed a significant tactile allodynia during 5 weeks. Diabetic rats that received E.EtOH (200 and 300 mg/kg) and F.EtOAc (250 and 500 mg/kg) had a pain threshold higher than those in the STZ-vehicle group. F.EtOAc effects were inhibited by pretreatment with naloxone and were not influenced by .-arginine.

DISCUSSION AND CONCLUSION

The results suggest that the ethanol extract and ethyl acetate fraction of C. macrophyllum presented antinociceptive activity. Thus, F.EtOAc may be exerting its effect by affecting the opioid system, but nitrergic mechanisms are not detectable. The observed activity may be due to its gallic acid, lupeol and bergenin content.

High-fat diet ingestion correlates with neuropathy in the duodenum myenteric plexus of obese mice with symptoms of type 2 diabetes

Obesity and type 2 diabetes are increasing in prevalence at an alarming rate in developed and developing nations and over 50% of patients with prolonged stages of disease experience forms of autonomic neuropathy. These patients have symptoms indicating disrupted enteric nervous system function including gastric discomfort, gastroparesis and intestinal dysmotility. Previous assessments have examined enteric neuronal injury within either type 1 diabetic or transgenic type 2 diabetic context. This study aims to assess damage to myenteric neurons within the duodenum of high-fat diet ingesting mice experiencing symptoms of type 2 diabetes, as this disease context is most parallel to the human condition and disrupted duodenal motility underlies negative gastrointestinal symptoms. Mice fed a high-fat diet developed symptoms of obesity and diabetes by 4 weeks. After 8 weeks, the total number of duodenal myenteric neurons and the synaptophysin density index were reduced and transmission electron microscopy showed axonal swelling and loss of neurofilaments and microtubules, suggesting compromised neuronal health. High-fat diet ingestion correlated with a loss of neurons expressing VIP and nNOS but did not affect the expression of ChAT, substance P, calbindin and CGRP. These results correlate high-fat diet ingestion, obesity and type 2 diabetes symptoms with a loss of duodenal neurons, biasing towards those with inhibitory nature. This pathology may underlie dysmotility and other negative GI symptoms experienced by human type 2 diabetic and obese patients.

Distribution of advanced glycation end products and their receptor in the gastrointestinal tract

AIM: To investigate the distribution of advanced glycation end products (AGEs) and their receptor (RAGE) in the gastrointestinal (GI) tract to provide a basis for further study of the association between AGE/RAGE and diabetic GI dysfunction.

METHODS: The distribution of AGEs [N epsilon-(carboxymethyl) lysine and N epsilon-(carboxyethyl) lysine] and RAGE were detected in the esophageal, gastric, duodenal, jejunal, ileal, colonic and rectal tissues of normal adult Wistar rats using immunohistochemistry.

RESULTS: In the esophagus, AGEs and RAGE were mainly distributed in striated muscle cells and squamous epithelial cells. In the stomach, AGEs were mainly distributed in parietal cells, and RAGE was strongly expressed in chief cells, mast cells and neurons in ganglia, moderately in parietal cells, and mildly in surface mucous cells. In the intestine, colon and rectum, AGEs and RAGE were distributed in mucosal epithelial cells, and RAGE was also distributed in neurons in the myenteric and submucosal plexuses.

CONCLUSION: AGEs and RAGE are widely distributed in epithelial cells of the GI tract as well as striated muscle cells in the esophagus. AGEs are also distributed in parietal cells in the stomach. RAGE is also distributed in chief cells, mast cells, parietal cells and surface mucous cells in the stomach and neurons in the whole GI tract.

Pathophysiology of diabetic erectile dysfunction: potential contribution of vasa nervorum and advanced glycation endproducts

Erectile dysfunction (ED) due to diabetes mellitus remains difficult to treat medically despite advances in pharmacotherapeutic approaches in the field. This unmet need has resulted in a recent re-focus on the pathophysiology, in order to understand the cellular and molecular mechanisms leading to ED in diabetes. Diabetes-induced ED is often resistant to PDE5 inhibitor treatment, thus there is a need to discover targets that may lead to novel approaches for a successful treatment. The aim of this brief review is to update the reader in some of the latest development on that front, with a particular focus on the role of impaired neuronal blood flow and the formation of advanced glycation endproducts.

The antioxidant 3H-1,2-dithiole-3-thione potentiates advanced glycation end-product-induced oxidative stress in SH-SY5Y cells

Oxidative stress is implicated as a major factor in the development of diabetes complications and is caused in part by advanced glycation end products (AGEs). AGEs ligate to the receptor for AGEs (RAGE), promoting protein kinase C (PKC)-dependent activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and superoxide radical generation. While scavenging antioxidants are protective against AGEs, it is unknown if induction of endogenous antioxidant defenses has the same effect. In this study, we confirmed that the compound 3H-1,2-dithiole-3-thione (D3T) increases reduced-state glutathione (GSH) concentrations and NADPH:quinone oxidoreductase 1 (NQO1) activity in SH-SY5Y cells and provides protection against H₂O₂. Surprisingly, D3T potentiated oxidative damage caused by AGEs. In comparison to vehicle controls, D3T caused greater AGE-induced cytotoxicity and depletion of intracellular GSH levels while offering no protection against neurite degeneration or protein carbonylation. D3T potentiated AGE-induced reactive oxygen species (ROS) formation, an effect abrogated by inhibitors of PKC and NADPH oxidase. This study suggests that chemical induction of endogenous antioxidant defenses requires further examination in models of diabetes.

Diabetes-related alterations in the enteric nervous system and its microenvironment

Gastric intestinal symptoms common among diabetic patients are often caused by intestinal motility abnormalities related to enteric neuropathy. It has recently been demonstrated that the nitrergic subpopulation of myenteric neurons are especially susceptible to the development of diabetic neuropathy. Additionally, different susceptibility of nitrergic neurons located in different intestinal segments to diabetic damage and their different levels of responsiveness to insulin treatment have been revealed. These findings indicate the importance of the neuronal microenvironment in the pathogenesis of diabetic nitrergic neuropathy. The main focus of this review therefore was to summarize recent advances related to the diabetes-related selective nitrergic neuropathy and associated motility disturbances. Special attention was given to the findings on capillary endothelium and enteric glial cells. Growing evidence indicates that capillary endothelium adjacent to the myenteric ganglia and enteric glial cells surrounding them are determinative in establishing the ganglionic microenvironment. Additionally, recent advances in the development of new strategies to improve glycemic control in type 1 and type 2 diabetes mellitus are also considered in this review. Finally, looking to the future, the recent and promising results of metagenomics for the characterization of the gut microbiome in health and disease such as diabetes are highlighted.

Selective responses of myenteric neurons to oxidative stress and diabetic stimuli

BACKGROUND

Diabetes has a differential effect on different subpopulations of myenteric neurons. Our aim was to investigate an in vitro model to examine the pathways underlying the development of nerve changes in diabetes.

METHODS

The proportions of neuronal cell bodies containing vasoactive intestinal polypeptide (VIP), neuronal nitric oxide synthase (nNOS) and calbindin relative to the pan-neuronal marker HuC/D were quantified in wholemount preparations of the myenteric plexus of adult rat ileum using double labeling immunohistochemistry. Preparations were maintained in culture for 24 h in the presence and absence of stimuli mimicking the diabetic environment including oxidative stress, carbonyl stress, high glucose and advanced glycation end products (AGEs). Data were compared with the effect of streptozotocin-induced diabetes in vivo. KEY RESULTS Only oxidative stress in vitro produced the same pattern as observed in diabetes with an increase in VIP-, decrease in nNOS-, and no change in calbindin-positive neurons. Carbonyl stress and high glucose caused an increase in VIP-containing neurons without affecting nNOS expression. In contrast, exposure to AGEs only caused a decrease in nNOS-positive neurons. Calbindin expression was unaffected by any of the stimuli. The effects of the stimuli were prevented by the antioxidant, α-lipoic acid, or the carbonyl scavenger, aminoguanidine.

CONCLUSIONS & INFERENCES

The results provide evidence that oxidative stress is the common factor in the development of neuronal changes in diabetes; however, the mechanism by which oxidative stress occurs depends on the individual subpopulation of myenteric neurons examined. The presence of calbindin appears to protect myenteric neurons against harmful stimuli.

JSH-23 targets nuclear factor-kappa B and reverses various deficits in experimental diabetic neuropathy: effect on neuroinflammation and antioxidant defence

AIM

Nuclear factor-kappa B (NF-κB) being reported to play an important role in the pathogenesis of diabetic neuropathy is believed to be a central mechanism involved in the genesis and promulgation of inflammatory insult. Here we have targeted the nuclear translocation of NF-κB using JSH-23 to elucidate its role in diabetic neuropathy.

METHODS

JSH-23 (1 and 3 mg/kg) was administered for 2 weeks in diabetic rats, after 6 weeks of diabetes induction using streptozotocin (55 mg/kg) as diabetogenic agent. Functional (motor nerve conduction velocity and blood flow), behavioural (mechanical hyperalgesia), biochemical [malondialdehyde, glutathione, tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels] and NF-κB translocation studies (western blot technique) were then undertaken.

RESULTS

JSH-23 treatment significantly reversed the nerve conduction and nerve blood flow deficits seen in diabetic animals. Reduction in mechanical pain threshold was also partially corrected by the treatment. Protein expression studies showed that nuclear translocation of p65/p50 subunit was inhibited by JSH-23 treatment in the sciatic nerve. The treatment also lowered the elevated IL-6, TNF-α, cyclo-oxygenase (COX-2) and inducible nitric oxide synthase (iNOS) levels/expression, indicating reduction in the inflammatory damage of the sciatic nerve. Apart from these effects, JSH-23 also increased Nrf2 and hemeoxygenase-1 (HO-1) levels which could imply its potential in increasing the strength of antioxidant defence.

CONCLUSION

We observed that NF-κB inhibition partially reversed functional, behavioural and biochemical deficits with JSH-23 treatment. This study substantiates the role of NF-κB activation in the aetiology of diabetic neuropathy and protection afforded by inhibition of NF-κB by JSH-23, which can be attributed to its effect on neuroinflammation and oxidative stress.

Generalized neuromuscular hypoplasia, reduced smooth muscle myosin and altered gut motility in the klotho model of premature aging

BACKGROUND

  Gastrointestinal symptoms, particularly constipation, increase with aging, but their underlying mechanisms are poorly understood due to lack of experimental models. Previously we established the progeric klotho mouse as a model of aging-associated anorexia and gastric dysmotility. We also detected reduced fecal output in these animals; therefore, the aim of this study was to investigate in vivo function and cellular make-up of the small intestinal and colonic neuromuscular apparatus.

METHODS

Klotho expression was studied by RT-PCR and immunohistochemistry. Motility was assessed by dye transit and bead expulsion. Smooth muscle and neuron-specific gene expression was studied by Western immunoblotting. Interstitial cells of Cajal (ICC) and precursors were analyzed by flow cytometry, confocal microscopy, and three-dimensional reconstruction. HuC/D(+) myenteric neurons were enumerated by fluorescent microscopy.

KEY RESULTS

Klotho protein was detected in neurons, smooth muscle cells, and some ICC classes. Small intestinal transit was slower but whole-gut transit of klotho mice was accelerated due to faster colonic transit and shorter intestinal lengths, apparent only after weaning. Fecal water content remained normal despite reduced output. Smooth muscle myosin expression was reduced. ICC, ICC precursors, as well as nitrergic and cholinergic neurons maintained their normal proportions in the shorter intestines.

CONCLUSIONS & INFERENCES

Progeric klotho mice express less contractile proteins and develop generalized intestinal neuromuscular hypoplasia mainly arising from stunted postweaning growth. As reduced fecal output in these mice occurs in the presence of accelerated colonic and whole-gut transit, it likely reflects reduced food intake rather than intestinal dysmotility.

Skin intrinsic fluorescence correlates with autonomic and distal symmetrical polyneuropathy in individuals with type 1 diabetes

OBJECTIVE

To determine whether skin intrinsic fluorescence (SIF) was associated with autonomic neuropathy and confirmed distal symmetrical polyneuropathy (CDSP) in 111 individuals with type 1 diabetes (mean age 49 years, mean diabetes duration 40 years).

RESEARCH DESIGN AND METHODS

SIF was measured using the SCOUT DM device. Autonomic neuropathy was defined as an electrocardiographic abnormal heart rate response to deep breathing (expiration-to-inspiration ratio <1.1). CDSP was defined using the Diabetes Control and Complications Trial clinical exam protocol (the presence of two or more of the following: symptoms, sensory and/or motor signs, and/or reduced/absent tendon reflexes consistent with DSP) confirmed by the presence of an abnormal age-specific vibratory threshold (using a Vibratron II tester).

RESULTS

The prevalence of autonomic neuropathy and CDSP were 61 and 66%, respectively. SIF was higher in those with autonomic neuropathy (P < 0.0001). In multivariable analyses controlling for age and updated mean (18-year average) HbA(1c), and allowing for other univariately and clinically significant correlates of autonomic neuropathy, each SD change in SIF was associated with a 2.6-greater likelihood of autonomic neuropathy (P = 0.006). Receiver operating characteristic (ROC) analyses revealed that SIF and updated mean HbA(1c) accounted for 80 and 57%, respectively, of the area under the curve (AUC) for autonomic neuropathy. SIF also was higher in those with CDSP (P < 0.0001) and remained so in multivariable analyses (odds ratio 2.70; P = 0.005). ROC analyses revealed that SIF and updated mean HbA(1c) accounted for 78 and 59%, respectively, of the AUC for CDSP.

CONCLUSIONS

SIF, a marker of dermal advanced glycation end products, appears to be more strongly associated with the presence of both CDSP and autonomic neuropathy than mean HbA(1c).

Morphological Changes and Immunohistochemical Expression of RAGE and its Ligands in the Sciatic Nerve of Hyperglycemic Pig (Sus Scrofa)

The aim of our project was to study the effect of streptozotocin (STZ)-induced hyperglycemia on sciatic nerve morphology, blood plasma markers and immunohistochemical expression of RAGE (the Receptor for Advanced Glycation End-products), and its ligands-S100B and Carboxymethyl Lysine (CML)-advanced glycation endproduct (AGE) in the laboratory pig. Six months after STZ-injections, blood plasma measurements, morphometric analysis of sciatic nerve fiber density, immunofluorescent distribution of potential molecular neuropathy contributors, ELISA measurement of plasma AGE level and HPLC analysis of sciatic nerve levels of one of the pre-AGE and the glycolysis intermediate products-methyl-glyoxal (MG) were performed. The results of our study revealed that STZ-injected animals displayed elevated levels of plasma glucose, gamma glutamyl transferase (GGT) and triglycerides. The sciatic nerve of STZ-injected pigs revealed significantly lower numbers of small-diameter myelinated fibers, higher immunoreactivity for RAGE and S100B and increased levels of MG as compared to control animals. Our results correspond to clinical findings in human patients with hyperglycemia/diabetes-evoked peripheral neuropathy and suggest that the domestic pig may be a suitable large animal model for the study of mechanisms underlying hyperglycemia-induced neurological complications in the peripheral nerve and may serve as a relevant model for the pre-clinical assessment of candidate drugs in neuropathy.

Statin treatment reduces oxidative stress-associated apoptosis of sciatic nerve in diabetes mellitus

Statins are lipid-lowering drugs that are widely used for treating hyperlipidemia, especially in diabetic patients. The aim of our study was to explore the effects of atorvastatin on oxidative stress and apoptosis in the sciatic nerve due to hyperglycemia. Diabetes was induced by streptozotocin. Atorvastatin was given orally for two weeks beginning from the sixth week. Microscopic examination of sciatic nerve revealed that normal tissue organization was disrupted in streptozotocin induced diabetic rats. Treatment with Atorvastatin reduced the histological damage and protected the morphological integrity of the sciatic nerve in streptozotocin induced diabetes. Increased expressions of transforming growth factor beta-1, endothelial nitric oxide synthase and TUNEL in sciatic nerve from streptozotocin induced diabetes were reduced by Atorvastatin. Atorvastatin could improve the effects of oxidative stress and apoptosis on the sciatic nerve due to diabetes.

Receptor for advanced glycation endproducts mediates pro-atherogenic responses to periodontal infection in vascular endothelial cells

OBJECTIVE

A link between periodontal infections and an increased risk for vascular disease has been demonstrated. Porphyromonas gingivalis, a major periodontal pathogen, localizes in human atherosclerotic plaques, accelerates atherosclerosis in animal models and modulates vascular cell function. The receptor for advanced glycation endproducts (RAGE) regulates vascular inflammation and atherogenesis. We hypothesized that RAGE is involved in P. gingivalis's contribution to pro-atherogenic responses in vascular endothelial cells.

METHODS AND RESULTS

Murine aortic endothelial cells (MAEC) were isolated from wild-type C57BL/6 or RAGE-/- mice and were infected with P. gingivalis strain 381. P. gingivalis 381 infection significantly enhanced expression of RAGE in wild-type MAEC. Levels of pro-atherogenic advanced glycation endproducts (AGEs) and monocyte chemoattractant protein 1 (MCP-1) were significantly increased in wild-type MAEC following P. gingivalis 381 infection, but were unaffected in MAEC from RAGE-/- mice or in MAEC infected with DPG3, a fimbriae-deficient mutant of P. gingivalis 381. Consistent with a role for oxidative stress and an AGE-dependent activation of RAGE in this setting, both antioxidant treatment and AGE blockade significantly suppressed RAGE gene expression and RAGE and MCP-1 protein levels in P. gingivalis 381-infected human aortic endothelial cells (HAEC).

CONCLUSION

The present findings implicate for the first time the AGE-RAGE axis in the amplification of pro-atherogenic responses triggered by P. gingivalis in vascular endothelial cells.