Modification of purinergic signaling in the hippocampus of streptozotocin-induced diabetic rats

Density of Sphingosine-1-Phosphate Receptors Is Altered in Cortical Nerve-Terminals of Insulin-Resistant Goto-Kakizaki Rats and Diet-Induced Obese Mice

Sphingosine-1-phosphate (S1P) is a phosphosphingolipid with pleiotropic biological functions. S1P acts as an intracellular second messenger, as well as extracellular ligand to five G-protein coupled receptors (S1PR1-5). In the brain, S1P regulates neuronal proliferation, apoptosis, synaptic activity and neuroglia activation. Moreover, S1P metabolism alterations have been reported in neurodegenerative disorders. We have previously reported that S1PRs are present in nerve terminals, exhibiting distinct sub-synaptic localization and neuromodulation actions. Since type 2 diabetes (T2D) causes synaptic dysfunction, we hypothesized that S1P signaling is modified in nerve terminals. In this study, we determined the density of S1PRs in cortical synaptosomes from insulin-resistant Goto-Kakizaki (GK) rats and Wistar controls, and from mice fed a high-fat diet (HFD) and low-fat-fed controls. Relative to their controls, GK rats showed similar cortical S1P concentration despite higher S1P levels in plasma, yet lower density of S1PR1, S1PR2 and S1PR4 in nerve-terminal-enriched membranes. HFD-fed mice exhibited increased plasma and cortical concentrations of S1P, and decreased density of S1PR1 and S1PR4. These findings point towards altered S1P signaling in synapses of insulin resistance and diet-induced obesity models, suggesting a role of S1P signaling in T2D-associated synaptic dysfunction.

Affective and Cognitive Impairments in Rodent Models of Diabetes

Diabetes and related acute and long-term complications have a profound impact on cognitive, emotional, and social behavior, suggesting that the central nervous system (CNS) is a crucial substrate for diabetic complications. When anxiety, depression, and cognitive deficits occur in diabetic patients, the symptoms and complications related to the disease worsen, contributing to lower quality of life while increasing health care costs and mortality. Experimental models of diabetes in rodents are a fundamental and valuable tool for improving our understanding of the mechanisms underlying the close and reciprocal link between diabetes and CNS alterations, including the development of affective and cognitive disorders. Such models must reproduce the different components of this pathological condition in humans and, therefore, must be associated with affective and cognitive behavioral alterations. Beyond tight glycemic control, there are currently no specific therapies for neuropsychiatric comorbidities associated with diabetes; animal models are, therefore, essential for the development of adequate therapies. To our knowledge, there is currently no review article that summarizes changes in affective and cognitive behavior in the most common models of diabetes in rodents. Therefore, in this review, we have reported the main evidence on the alterations of affective and cognitive behavior in the different models of diabetes in rodents, the main mechanisms underlying these comorbidities, and the applicable therapeutic strategy.

Neuromodulatory effect of the combination of metformin and vitamin D3 triggered by purinergic signaling in type 1 diabetes induced-rats

Several studies have indicated the vitamin D deficiency in the development of macro- and microvascular complications of diabetes mellitus (DM) including DM-related cognitive dysfunction. The purinergic system plays an important role in the modulation of a variety of mechanisms, including neuroinflammation, plasticity, and cell-cell communication. In addition, purines, their receptors, and enzymes can regulate the purinergic axis at different levels in type 1 DM (T1DM). This study evaluated the effects of vitamin D₃ alone or in combination with metformin in the behavioral performance of streptozotocin-induced T1DM rats. The effects of this combination on the metabolism of ATP and ADP were also studied by NTPDase (CD39), AMP by 5'-nucleotidase (CD73), and adenosine by adenosine deaminase (E-ADA) in the brain and peripheral lymphocytes of type 1 diabetic STZ-induced rats. The results showed that anxiety and memory loss from the DM condition reverted after 30 days of vitamin D₃ treatment. Furthermore, the DM state affected systemic enzymes, with no effect on the central enzymes hydrolyzing extracellular nucleotides and nucleosides. Vitamin D₃ treatment positively regulated ectonucleotidase (NTPDase and 5'-nucleotidase) activity, E-ADA, and the purinergic receptors as a mechanism to prevent oxidative damage in the cerebral cortex of T1DM rats. A neuroprotector effect of vitamin D₃ through adenosine signaling was also observed, by regulating A1 and A_2A receptors proteins levels. The present findings suggest that purinergic signaling through vitamin D₃ modulation may be a novel alternative strategy for T1DM treatment, and may compensate for the negative changes in the central nervous system.

Hypothyroidism and Diabetes-Related Dementia: Focused on Neuronal Dysfunction, Insulin Resistance, and Dyslipidemia

The incidence of dementia is steadily increasing worldwide. The risk factors for dementia are diverse, and include genetic background, environmental factors, sex differences, and vascular abnormalities. Among the subtypes of dementia, diabetes-related dementia is emerging as a complex type of dementia related to metabolic imbalance, due to the increase in the number of patients with metabolic syndrome and dementia worldwide. Thyroid hormones are considered metabolic regulatory hormones and affect various diseases, such as liver failure, obesity, and dementia. Thyroid dysregulation affects various cellular mechanisms and is linked to multiple disease pathologies. In particular, hypothyroidism is considered a critical cause for various neurological problems-such as metabolic disease, depressive symptoms, and dementia-in the central nervous system. Recent studies have demonstrated the relationship between hypothyroidism and brain insulin resistance and dyslipidemia, leading to diabetes-related dementia. Therefore, we reviewed the relationship between hypothyroidism and diabetes-related dementia, with a focus on major features of diabetes-related dementia such as insulin resistance, neuronal dysfunction, and dyslipidemia.

Purinergic signaling as a new mechanism underlying physical exercise benefits: a narrative review

In the last years, it has become evident that both acute and chronic physical exercise trigger responses/adaptations in the purinergic signaling and these adaptations can be considered one important mechanism related to the exercise benefits for health improvement. Purinergic system is composed of enzymes (ectonucleotidases), receptors (P1 and P2 families), and molecules (ATP, ADP, adenosine) that are able to activate these receptors. These components are widely distributed in almost all cell types, and they respond/act in a specific manner depending on the exercise types and/or intensities as well as the cell type (organ/tissue analyzed). For example, while acute intense exercise can be associated with tissue damage, inflammation, and platelet aggregation, chronic exercise exerts anti-inflammatory and anti-aggregant effects, promoting health and/or treating diseases. All of these effects are dependent on the purinergic signaling. Thus, this review was designed to cover the aspects related to the relationship between physical exercise and purinergic signaling, with emphasis on the modulation of ectonucleotidases and receptors. Here, we discuss the impact of different exercise protocols as well as the differences between acute and chronic effects of exercise on the extracellular signaling exerted by purinergic system components. We also reinforce the concept that purinergic signaling must be understood/considered as a mechanism by which exercise exerts its effects.

Assessment of sexual behavior and neuromodulation of Cyperus esculentus L. and Tetracarpidium conophorum Müll. Arg dietary supplementation regulating the purinergic system in the cerebral cortex of L-NAME-challenged rats

This study examined the behavioral responses, purinergic receptor densities, ectonucleotidases (E-NTPDase), adenosine deaminase (ADA) activity, and nitric oxide (NO) levels along with the parameters of oxidative stress-related to erectile function in the cerebral cortex (CC) of L-NAME-challenged rats pretreated with tigernut (TN) and walnut (WN) dietary supplementation. Wistar rats (male) of 70 total animals (250-300 g) were used in this research and hence separated into seven groups (n = 10): Group I: normal control-fed basal diet; Group II: positive control-fed basal diet/L-NAME/Sildenafil citrate (5 mg kg-1  day-1 ); Group III: ED-induced (placed on a basal diet/L-NAME); Group IV: diet supplemented with processed TN (20%)/L-NAME; Group V: diet supplemented with raw TN (20%)/L-NAME; Group VI: diet supplemented with processed WN (20%)/L-NAME; and Group VII placed on a diet supplemented with raw WN (20%)/L-NAME. The rats were pretreated for 2 weeks before the L-NAME (40 mg kg-1  day-1 ) challenge on their respective diet. L-NAME brought about a decrease in the sexual behaviors evaluated while the effect was significantly reversed by supplemented diets containing TN and WN. L-NAME increased the levels of reactive oxygen species and malondialdehyde, E-NTPDase as well as ADA activities, and caused the level of NO in the CC as well as the purinoreceptor densities to be downregulated. Treatments with enriched diets, however, greatly reverse these effects. The behavioral responses and neuromodulatory capacity of the nuts displayed on the CC can, therefore, further support their aphrodisiac property. PRACTICAL APPLICATIONS: The results revealed the ability of tigernut (TN; Cyperus esculentus L.) and walnut (WN; Tetracarpidium conophorum Müll. Arg.) to enhance behavioral responses; modulate purinergic receptor densities, E-NTPDase, and ADA activities; increase NO levels; and prevent oxidative stress related to erectile function in the CC of L-NAME-challenged Wistar rats. The results show that these nuts are useful feeds for both animal and human nutrition.

Reduction of prefrontal purinergic signaling is necessary for the analgesic effect of morphine

Morphine is commonly used to relieve moderate to severe pain, but repeated doses cause opioid tolerance. Here, we used ATP sensor and fiber photometry to detect prefrontal ATP level. It showed that prefrontal ATP level decreased after morphine injection and the event amplitude tended to decrease with continuous morphine exposure. Morphine had little effect on prefrontal ATP due to its tolerance. Therefore, we hypothesized that the analgesic effect of morphine might be related to ATP in the medial prefrontal cortex (mPFC). Moreover, local infusion of ATP partially antagonized morphine analgesia. Then we found that inhibiting P2X7R in the mPFC mimicked morphine analgesia. In morphine-tolerant mice, pretreatment with P2X4R or P2X7R antagonists in the mPFC enhanced analgesic effect. Our findings suggest that reduction of prefrontal purinergic signaling is necessary for the morphine analgesia, which help elucidate the mechanism of morphine analgesia and may lead to the development of new clinical treatments for neuropathic pain.

Diabetes and hypertension: Pivotal involvement of purinergic signaling

Diabetes mellitus (DM) and hypertension are highly prevalent worldwide health problems and frequently associated with severe clinical complications, such as diabetic cardiomyopathy, nephropathy, retinopathy, neuropathy, stroke, and cardiac arrhythmia, among others. Despite all existing research results and reasonable speculations, knowledge about the role of purinergic system in individuals with DM and hypertension remains restricted. Purinergic signaling accounts for a complex network of receptors and extracellular enzymes responsible for the recognition and degradation of extracellular nucleotides and adenosine. The main components of this system that will be presented in this review are: P1 and P2 receptors and the enzymatic cascade composed by CD39 (NTPDase; with ATP and ADP as a substrate), CD73 (5′-nucleotidase; with AMP as a substrate), and adenosine deaminase (ADA; with adenosine as a substrate). The purinergic system has recently emerged as a central player in several physiopathological conditions, particularly those linked to inflammatory responses such as diabetes and hypertension. Therefore, the present review focuses on changes in both purinergic P1 and P2 receptor expression as well as the activities of CD39, CD73, and ADA in diabetes and hypertension conditions. It can be postulated that the manipulation of the purinergic axis at different levels can prevent or exacerbate the insurgency and evolution of diabetes and hypertension working as a compensatory mechanism.

Region-specific metabolic characterization of the type 1 diabetic brain in mice with and without cognitive impairment

Type 1 diabetes (T1D) has been reported to cause cognitive decline, but brain metabolic changes during this process are still far from being fully understood. Here, we found that streptozotocin (STZ)-induced T1D mice exhibited impaired learning and memory at 11 weeks after STZ treatment but not at 3 weeks. Therefore, we studied metabolic alterations in six different brain regions of T1D mice with and without cognitive decline, and attempted to identify key metabolic pathways related to diabetic cognitive dysfunction. The results demonstrate that lactate had already increased in all brain regions of T1D mice prior to cognitive decline, but a decreased TCA cycle was only observed in hippocampus, cortex and striatum of T1D mice with cognitive impairment. Reduced N-acetylaspartate and choline were found in all brain regions of T1D mice, irrespective of cognitive decline. In addition, disrupted neurotransmitter metabolism was noted to occur in T1D mice before cognitive deficit. Of note, we found that the level of uridine was significantly reduced in cerebellum, cortex, hypothalamus and midbrain of T1D mice when cognitive decline was presented. Therefore, brain region-specific metabolic alterations may comprise possible biomarkers for the early-diagnosis and monitoring of diabetic cognitive decline. Moreover, down-regulated TCA cycle and pyrimidine metabolism could be closely related to T1D-associated cognitive impairment.

‬The expression of purinergic P2X4 and P2X7 receptors in selected mesolimbic structures during morphine withdrawal in rats

Morphine is one of the most potent analgesics used in medicine and it's long-term use is associated with the risk of the state of dependence. The cessation of chronic morphine administration leads to withdrawal signs which are associated with neurotransmitter dysregulations within mesolimbic system. Adenosine 5'-triphosphate (ATP) and purinergic system play an important role in the activity of central nervous system (CNS). Purinergic receptors are widely distributed in neurons and glial cells throughout the CNS taking part in integration of functional activity between neurons, glial and vascular cells. In the present study the mRNA and protein expression of purinergic P2X4 and P2X7 receptors in selected mesolimbic structures (striatum, hippocampus and prefrontal cortex) during morphine withdrawal in rats was investigated by RT-PCR and Western Blot analysis. Two experimental models of morphine withdrawal were studied: single and repeated morphine withdrawal. We demonstrated that expression of P2X4 and P2X7 receptors was altered during morphine withdrawal period in rats. These alterations were varied in particular mesolimbic areas depending on the scheme of morphine administration. Our results extend the current knowledge on morphine withdrawal and for the first time high-light interactions between purinergic system and morphine withdrawal. It seems, the purinergic system may be a new, valuable tool in searching for a new strategy of management of opioid dependence.

Impact of Caffeine Consumption on Type 2 Diabetes-Induced Spatial Memory Impairment and Neurochemical Alterations in the Hippocampus

Diabetes affects the morphology and plasticity of the hippocampus, and leads to learning and memory deficits. Caffeine has been proposed to prevent memory impairment upon multiple chronic disorders with neurological involvement. We tested whether long-term caffeine consumption prevents type 2 diabetes (T2D)-induced spatial memory impairment and hippocampal alterations, including synaptic degeneration, astrogliosis, and metabolic modifications. Control Wistar rats and Goto-Kakizaki (GK) rats that develop T2D were treated with caffeine (1 g/L in drinking water) for 4 months. Spatial memory was evaluated in a Y-maze. Hippocampal metabolic profile and glucose homeostasis were investigated by ¹H magnetic resonance spectroscopy. The density of neuronal, synaptic, and glial-specific markers was evaluated by Western blot analysis. GK rats displayed reduced Y-maze spontaneous alternation and a lower amplitude of hippocampal long-term potentiation when compared to controls, suggesting impaired hippocampal-dependent spatial memory. Diabetes did not impact the relation of hippocampal to plasma glucose concentrations, but altered the neurochemical profile of the hippocampus, such as increased in levels of the osmolites taurine (P < 0.001) and myo-inositol (P < 0.05). The diabetic hippocampus showed decreased density of the presynaptic proteins synaptophysin (P < 0.05) and SNAP25 (P < 0.05), suggesting synaptic degeneration, and increased GFAP (P < 0.001) and vimentin (P < 0.05) immunoreactivities that are indicative of astrogliosis. The effects of caffeine intake on hippocampal metabolism added to those of T2D, namely reducing myo-inositol levels (P < 0.001) and further increasing taurine levels (P < 0.05). Caffeine prevented T2D-induced alterations of GFAP, vimentin and SNAP25, and improved memory deficits. We conclude that caffeine consumption has beneficial effects counteracting alterations in the hippocampus of GK rats, leading to the improvement of T2D-associated memory impairment.

Characteristic Metabolic Alterations Identified in Primary Neurons Under High Glucose Exposure

Cognitive dysfunction is a central nervous system (CNS) complication of diabetes mellitus (DM) that is characterized by impaired memory and cognitive ability. An in-depth understanding of metabolic alterations in the brain associated with DM will facilitate our understanding of the pathogenesis of cognitive dysfunction. The present study used an in vitro culture of primary neurons in a high-glucose (HG) environment to investigate characteristic alterations in neuron metabolism using nuclear magnetic resonance (NMR)-based metabonomics. High performance liquid chromatography (HPLC) was also used to measure changes in the adenosine phosphate levels in the hippocampal regions of streptozotocin (STZ)-induced diabetic rats. Our results revealed significant elevations in phosphocholine and ATP production in neurons and decreased formate, nicotinamide adenine dinucleotide (NAD⁺), tyrosine, methionine, acetate and phenylalanine levels after HG treatment. However, the significant changes in lactate, glutamate, taurine and myo-inositol levels in astrocytes we defined previously in astrocytes, were not found in neurons, suggested cell-specific metabolic alterations. We also confirmed an astrocyte-neuron lactate shuttle between different compartments in the brain under HG conditions, which was accompanied by abnormal acetate transport. These alterations reveal specific information on the metabolite levels and transport processes related to neurons under diabetic conditions. Our findings contribute to the understanding of the metabolic alterations and underlying pathogenesis of cognitive decline in diabetic patients.

Lingonberry Extract Provides Neuroprotection by Regulating the Purinergic System and Reducing Oxidative Stress in Diabetic Rats

SCOPE

Beneficial effects produced by polyphenolic compounds are used in the treatment of various diseases, including diabetes. Thus it is relevant to investigate the protective effect of lingonberry extract (LB) on the activities of nucleoside triphosphate diphosphohydrolase (NTPDase), 5'-nucleotidase (5'-NT), and adenosine deaminase (ADA); the density of A1, A2A, and P2×7 receptors; production of reactive species (RS); and the levels of thiobarbituric acid reactive substances (TBARS) in the cerebral cortex of streptozotocin-induced diabetic rats.

METHODS AND RESULTS

Animals were divided into five groups (n = 10): control/saline; control/LB 50 mg kg^-1 ; diabetic/saline; diabetic/LB 25 mg kg^-1 ; and diabetic/LB 50 mg kg^-1 ; and treated for 30 days. Our results demonstrate that the treatment with LB increased NTPDase activity in the diabetic/LB 50 group compared to diabetic/saline group. Western blot analysis showed that LB restored the density of purinergic receptors to the approximate values of the control/saline group. An increase in the levels of RS and TBARS was observed in the diabetic/saline group compared with the control/saline group, and treatment with LB can prevent this increase.

CONCLUSION

This study showed that LB could reverse the modifications found in the diabetic state, suggesting that lingonberry may be a coadjuvant in the treatment of diabetes.

The diabetic brain and cognition

The prevalence of both Alzheimer's disease (AD) and vascular dementia (VaD) is increasing with the aging of the population. Studies from the last several years have shown that people with diabetes have an increased risk for dementia and cognitive impairment. Therefore, the authors of this consensus review tried to elaborate on the role of diabetes, especially diabetes type 2 (T2DM) in both AD and VaD. Based on the clinical and experimental work of scientists from 18 countries participating in the International Congress on Vascular Disorders and on literature search using PUBMED, it can be concluded that T2DM is a risk factor for both, AD and VaD, based on a pathology of glucose utilization. This pathology is the consequence of a disturbance of insulin-related mechanisms leading to brain insulin resistance. Although the underlying pathological mechanisms for AD and VaD are different in many aspects, the contribution of T2DM and insulin resistant brain state (IRBS) to cerebrovascular disturbances in both disorders cannot be neglected. Therefore, early diagnosis of metabolic parameters including those relevant for T2DM is required. Moreover, it is possible that therapeutic options utilized today for diabetes treatment may also have an effect on the risk for dementia. T2DM/IRBS contribute to pathological processes in AD and VaD.

Neuroprotective effects of quercetin on memory and anxiogenic-like behavior in diabetic rats: Role of ectonucleotidases and acetylcholinesterase activities

The present study investigated the protective effect of quercetin (Querc) on memory, anxiety-like behavior and impairment of ectonucleotidases and acetylcholinesterase (AChE) activities in brain of streptozotocin-induced diabetic rats (STZ-diabetes). The type 1 diabetes mellitus was induced by an intraperitoneal injection of 70mg/kg of streptozotocin (STZ), diluted in 0.1M sodium-citrate buffer (pH 4.5). Querc was dissolved in 25% ethanol and administered by gavage at the doses of 5, 25 and 50mg/kg once a day during 40days. The animals were distributed in eight groups of ten animals as follows: vehicle, Querc 5mg/kg, Querc 25mg/kg, Querc 50mg/kg, diabetes, diabetes plus Querc 5mg/kg, diabetes plus Querc 25mg/kg and diabetes plus Querc 50mg/kg. Querc was able to prevent the impairment of memory and the anxiogenic-like behavior induced by STZ-diabetes. In addition, Querc prevents the decrease in the NTPDase and increase in the adenosine deaminase (ADA) activities in SN from cerebral cortex of STZ-diabetes. STZ-diabetes increased the AChE activity in SN from cerebral cortex and hippocampus. Querc 50mg/kg was more effective to prevent the increase in AChE activity in the brain of STZ-diabetes. Querc also prevented an increase in the malondialdehyde levels in all the brain structures. In conclusion, the present findings showed that Querc could prevent the impairment of the enzymes that regulate the purinergic and cholinergic extracellular signaling and improve the memory and anxiety-like behavior induced by STZ-diabetes.

Inside the Diabetic Brain: Role of Different Players Involved in Cognitive Decline

Diabetes mellitus is the most common metabolic disease, and its prevalence is increasing. A growing body of evidence, both in animal models and epidemiological studies, has demonstrated that metabolic diseases like obesity, insulin resistance, and diabetes are associated with alterations in the central nervous system (CNS), being linked with development of cognitive and memory impairments and presenting a higher risk for dementia and Alzheimer's disease. The rising prevalence of diabetes together with its increasing earlier onset suggests that diabetes-related cognitive dysfunction will increase in the near future, causing substantial socioeconomic impact. Decreased insulin secretion or action, dysregulation of glucose homeostasis, impairment in the hypothalamic-pituitary-adrenal axis, obesity, hyperleptinemia, and inflammation may act independently or synergistically to disrupt neuronal homeostasis and cause diabetes-associated cognitive decline. However, the crosstalk between those factors and the mechanisms underlying the diabetes-related CNS complications is still elusive. During the past few years, different strategies (neuroprotective and antioxidant drugs) have emerged as promising therapies for this complication, which still remains to be preventable or treatable. This Review summarizes fundamental past and ongoing research on diabetes-associated cognitive decline, highlighting potential contributors, mechanistic mediators, and new pharmacological approaches to prevent and/or delay this complication.

Hyperglycemia alters E-NTPDases, ecto-5'-nucleotidase, and ectosolic and cytosolic adenosine deaminase activities and expression from encephala of adult zebrafish (Danio rerio)

Hyperglycemia is the main feature for the diagnosis of diabetes mellitus (DM). Some studies have demonstrated the relationship between DM and dysfunction on neurotransmission systems, such as the purinergic system. In this study, we evaluated the extracellular nucleotide hydrolysis and adenosine deamination activities from encephalic membranes of hyperglycemic zebrafish. A significant decrease in ATP, ADP, and AMP hydrolyses was observed at 111-mM glucose-treated group, which returned to normal levels after 7 days of glucose withdrawal. A significant increase in ecto-adenosine deaminase activity was observed in 111-mM glucose group, which remain elevated after 7 days of glucose withdrawal. The soluble-adenosine deaminase activity was significantly increased just after 7 days of glucose withdrawal. We also evaluated the gene expressions of ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases), ecto-5'-nucleotidase, ADA, and adenosine receptors from encephala of adult zebrafish. The entpd 2a.1, entpd 2a.2, entpd 3, and entpd 8 mRNA levels from encephala of adult zebrafish were decreased in 111-mM glucose-treated and glucose withdrawal groups. The gene expressions of adenosine receptors (adora 1 , adora 2aa , adora 2ab , and adora 2b ) were decreased in 111-mM glucose-treated and glucose withdrawal groups. The gene expression of ADA (ada 2a.1) was decreased in glucose withdrawal group. Maltodextrin, used as a control, did not affect the expression of adenosine receptors, ADA and E-NTPDases 2, 3, and 8, while the expression of ecto-5'-nucleotidase was slightly increased and the E-NTPDases 1 decreased. These findings demonstrated that hyperglycemia might affect the ecto-nucleotidase and adenosine deaminase activities and gene expression in zebrafish, probably through a mechanism involving the osmotic effect, suggesting that the modifications caused on purinergic system may also contribute to the diabetes-induced progressive cognitive impairment.

Metabolic Alterations Associated to Brain Dysfunction in Diabetes

From epidemiological studies it is known that diabetes patients display increased risk of developing dementia. Moreover, cognitive impairment and Alzheimer's disease (AD) are also accompanied by impaired glucose homeostasis and insulin signalling. Although there is plenty of evidence for a connection between insulin-resistant diabetes and AD, definitive linking mechanisms remain elusive. Cerebrovascular complications of diabetes, alterations in glucose homeostasis and insulin signalling, as well as recurrent hypoglycaemia are the factors that most likely affect brain function and structure. While difficult to study in patients, the mechanisms by which diabetes leads to brain dysfunction have been investigated in experimental models that display phenotypes of the disease. The present article reviews the impact of diabetes and AD on brain structure and function, and discusses recent findings from translational studies in animal models that link insulin resistance to metabolic alterations that underlie brain dysfunction. Such modifications of brain metabolism are likely to occur at early stages of neurodegeneration and impact regional neurochemical profiles and constitute non-invasive biomarkers detectable by magnetic resonance spectroscopy (MRS).

Introduction and perspective, historical note

P2 nucleotide receptors were proposed to consist of two subfamilies based on pharmacology in 1985, named P2X and P2Y receptors. Later, this was confirmed following cloning of the receptors for nucleotides and studies of transduction mechanisms in the early 1990s. P2X receptors are ion channels and seven subtypes are recognized that form trimeric homomultimers or heteromultimers. P2X receptors are involved in neuromuscular and synaptic neurotransmission and neuromodulation. They are also expressed on many types of non-neuronal cells to mediate smooth muscle contraction, secretion, and immune modulation. The emphasis in this review will be on the pathophysiology of P2X receptors and therapeutic potential of P2X receptor agonists and antagonists for neurodegenerative and inflammatory disorders, visceral and neuropathic pain, irritable bowel syndrome, diabetes, kidney failure, bladder incontinence and cancer, as well as disorders if the special senses, airways, skin, cardiovascular, and musculoskeletal systems.

Purinergic signalling and diabetes

The pancreas is an organ with a central role in nutrient breakdown, nutrient sensing and release of hormones regulating whole body nutrient homeostasis. In diabetes mellitus, the balance is broken-cells can be starving in the midst of plenty. There are indications that the incidence of diabetes type 1 and 2, and possibly pancreatogenic diabetes, is rising globally. Events leading to insulin secretion and action are complex, but there is emerging evidence that intracellular nucleotides and nucleotides are not only important as intracellular energy molecules but also as extracellular signalling molecules in purinergic signalling cascades. This signalling takes place at the level of the pancreas, where the close apposition of various cells-endocrine, exocrine, stromal and immune cells-contributes to the integrated function. Following an introduction to diabetes, the pancreas and purinergic signalling, we will focus on the role of purinergic signalling and its changes associated with diabetes in the pancreas and selected tissues/organ systems affected by hyperglycaemia and other stress molecules of diabetes. Since this is the first review of this kind, a comprehensive historical angle is taken, and common and divergent roles of receptors for nucleotides and nucleosides in different organ systems will be given. This integrated picture will aid our understanding of the challenges of the potential and currently used drugs targeted to specific organ/cells or disorders associated with diabetes.

Neuroprotective effect of paeonol on cognition deficits of diabetic encephalopathy in streptozotocin-induced diabetic rat

Diabetic encephalopathy (DE) has been characterized by the impaired cognition and the abnormalities of neurochemistry and neurostructure. The study was conducted to evaluate the neuroprotective effect of paeonol on STZ-induced DE rats. Paeonol of 25, 50, 100mg/kg (p.o.) could decrease the latency time and path length, and enhance significantly the spent time in the target quadrant and platform crossings in Morris water maze test. The treatment with paeonol could also increase significantly Na(+)-K(+)-ATP enzyme and ChAT activities, as well as decreasing significantly AchE activity in hippocampal tissue. Immunohistochemistry and TUNEL staining showed that paeonol could attenuate apoptosis of neurons and caspase 3 expression, improve two neurotrophic factors BDNF and IGF expressions, and also ameliorate Aβ deposition in the hippocampus and cerebral cortex. In conclusion, the present study demonstrated diabetic rats treated with paeonol could ameliorate the cognition deficits. These findings indicated paeonol might act as a beneficial agent for the prevention and treatment of DE.

Adenosine kinase: exploitation for therapeutic gain

Adenosine kinase (ADK; EC 2.7.1.20) is an evolutionarily conserved phosphotransferase that converts the purine ribonucleoside adenosine into 5'-adenosine-monophosphate. This enzymatic reaction plays a fundamental role in determining the tone of adenosine, which fulfills essential functions as a homeostatic and metabolic regulator in all living systems. Adenosine not only activates specific signaling pathways by activation of four types of adenosine receptors but it is also a primordial metabolite and regulator of biochemical enzyme reactions that couple to bioenergetic and epigenetic functions. By regulating adenosine, ADK can thus be identified as an upstream regulator of complex homeostatic and metabolic networks. Not surprisingly, ADK dysfunction is involved in several pathologies, including diabetes, epilepsy, and cancer. Consequently, ADK emerges as a rational therapeutic target, and adenosine-regulating drugs have been tested extensively. In recent attempts to improve specificity of treatment, localized therapies have been developed to augment adenosine signaling at sites of injury or pathology; those approaches include transplantation of stem cells with deletions of ADK or the use of gene therapy vectors to downregulate ADK expression. More recently, the first human mutations in ADK have been described, and novel findings suggest an unexpected role of ADK in a wider range of pathologies. ADK-regulating strategies thus represent innovative therapeutic opportunities to reconstruct network homeostasis in a multitude of conditions. This review will provide a comprehensive overview of the genetics, biochemistry, and pharmacology of ADK and will then focus on pathologies and therapeutic interventions. Challenges to translate ADK-based therapies into clinical use will be discussed critically.

Physical training normalizes nucleotide hydrolysis and biochemical parameters in blood serum from streptozotocin-diabetic rats

Ectonucleotidases and the nucleotide metabolism have been implicated as important regulators in diabetes disease. We evaluated the ectonucleotidase activities and biochemical parameters in blood serum of streptozotocin (STZ)-induced diabetic rats submitted a physical training protocol. We observed a raise in ATP, ADP, AMP and p-Nph-5'-TMP hydrolysis rate and in the levels of cholesterol and triglycerides in rat blood serum, after 30 days of diabetes induction. However, in serum of rats submitted a physical training protocol by forced swimming, both the nucleotide hydrolysis rate and the lipids levels returned to the control values. Considering that diabetes leads to multiple pathophysiological alterations, the modulations observed in ectonucleotidase activities may be part of the events involved in these alterations. Then the physical training is a very important way to control the vascular alterations developed in diabetes.

Alteration of purinergic neurotransmission in isolated atria of streptozotocin-induced diabetic rats

Cardiac dysfunctions are described in diabetes. However, the role of purinergic neurotransmission in diabetes-related cardiovascular diseases is unknown. The purpose of this study was to evaluate the purinergic neurotransmission in isolated atria from streptozotocin-induced diabetic rats. The animals were grouped as control and diabetic with 30 days (D30) and 60 days (D60) after streptozotocin-induced diabetes. The isolated left and right atria were used in functional experiments. The effects of adenosine triphosphate, uridine diphosphate, and adenosine were evaluated on atrial inotropism and chronotropism. The antagonists 8-cyclopentyl-1,3-dipropylxanthine and pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate were also used, as blockers of P1 and P2 receptors, respectively. A negative inotropic effect followed by a positive inotropic effect was induced by adenosine triphosphate in isolated atria. This negative inotropic effect was decreased by 25% in left atria of D30. Additionally, the apparent affinity for adenosine was diminished in left atria of D30, suggesting changes in P1 receptor function. No changes were found in the right atria of D30 stimulated by adenosine. The left atria and right atria stimulated by uridine diphosphate showed an increased inotropic effect of 92% and 17%, respectively. No changes were observed in left and right atria of D30 stimulated by uridine diphosphate. Our data showed the involvement of purinergic neurotransmission in diabetes-related cardiovascular changes.

1H-NMR-based metabonomic analysis of metabolic profiling in diabetic nephropathy rats induced by streptozotocin

Elucidation of the metabolic profiling in diabetic nephropathy (DN) rats is of great assistance for understanding the pathogenesis of DN. In this study, 1H-nuclear magnetic resonance (NMR)-based metabonomics combined with HPLC measurements was used to quantitatively analyze the metabolic changes in urine and kidney extracts from diabetic 2-wk and 8-wk rats induced by streptozotocin (STZ). Pattern recognition analysis of either urine or kidney extracts indicated that the two diabetic groups were separated obviously from the control group, suggesting that the metabolic profiles of the diabetic groups were markedly different from the control. The diabetic 8-wk rats showed lower levels of creatine, dimethylamine, and higher levels of ascorbate, succinate, lactate, citrate, allantoin, 2-ketoglutarate, and 3-hydrobutyrate (3-HB) in the urine samples. Moreover, the diabetic 8-wk rats displayed lower levels of succinate, creatine, myo-inositol, alanine, lactate, and ATP, and higher levels of 3-HB and glucose in the kidney extracts. The observed metabolic changes imply the enhanced pathways of either lipid or ketone body synthesis and decreased pathways of either tricarboxylic acid cycle or glycolysis in DN rats compared with the control. Our results suggest that the energy metabolic changes are associated with the pathogenic process of DN.

Diabetes induces early transient changes in the content of vesicular transporters and no major effects in neurotransmitter release in hippocampus and retina

Diabetes induces changes in neurotransmitter release in central nervous system, which depend on the type of neurotransmitter and region studied. In this study, we evaluated the effect of diabetes (two and eight weeks duration) on basal and evoked release of [(14)C]glutamate and [(3)H]GABA in hippocampal and retinal synaptosomes. We also analyzed the effect of diabetes on the protein content of vesicular glutamate and GABA transporters, VGluT-1, VGluT-2 and VGAT, and on the α(1A) subunit of P/Q type calcium channels, which are abundant in nerve terminals. The protein content of vesicular glutamate and GABA transporters, and of the α(1A) subunit, was differently affected by diabetes in hippocampal and retinal synaptosomes. The changes were more pronounced in the retina than in hippocampus. VGluT-1 and VGluT-2 content was not affected in hippocampus. Moreover, changes occurred early, at two weeks of diabetes, but after eight weeks almost no changes were detected, with the exception of VGAT in the retina. Regarding neurotransmitter release, no major changes were detected. After two weeks of diabetes, neurotransmitter release was similar to controls. After eight weeks of diabetes, the basal release of glutamate slightly increased in hippocampus and the evoked GABA release decreased in retina. In conclusion, diabetes induces early transient changes in the content of glutamate and/or GABA vesicular transporters, and on calcium channels subunit, in retinal or hippocampal synaptosomes, but only minor changes in the release of glutamate or GABA. These results point to the importance of diabetes-induced changes in neural tissues at the presynaptic level, which may underlie alterations in synaptic transmission, particularly if they become permanent during the later stages of the disease.

P2X receptors in health and disease

Seven P2X receptor subunits have been cloned which form functional homo- and heterotrimers. These are cation-selective channels, equally permeable to Na(+) and K(+) and with significant Ca(2+) permeability. The three-dimensional structure of the P2X receptor is described. The channel pore is formed by the α-helical transmembrane spanning region 2 of each subunit. When ATP binds to a P2X receptor, the pore opens within milliseconds, allowing the cations to flow. P2X receptors are expressed on both central and peripheral neurons, where they are involved in neuromuscular and synaptic neurotransmission and neuromodulation. They are also expressed in most types of nonneuronal cells and mediate a wide range of actions, such as contraction of smooth muscle, secretion, and immunomodulation. Changes in the expression of P2X receptors have been characterized in many pathological conditions of the cardiovascular, gastrointestinal, respiratory, and urinogenital systems and in the brain and special senses. The therapeutic potential of P2X receptor agonists and antagonists is currently being investigated in a range of disorders, including chronic neuropathic and inflammatory pain, depression, cystic fibrosis, dry eye, irritable bowel syndrome, interstitial cystitis, dysfunctional urinary bladder, and cancer.

Purinergic modulation of glucose uptake into cultured rat podocytes: effect of diabetic milieu

Extracellular purines act via P1 and P2 receptors on podocytes and may influence on their function. This action may be modified under various (patho)physiological conditions leading to development of podocytopathy. Aim of study was to investigate effects of diabetic milieu, represented by high glucose concentration (HG, 30 mM glucose) on purinergic-induced changes of 2-deoxy-D-glucose (2-DG) uptake and on extracellular purines metabolism in cultured rat podocytes. Basal 2-DG uptake was 2.7-fold enhanced in HG compared to normal glucose concentration, NG (1271 ± 86 vs. 477 ± 37 nmol/h/mg protein, P<0.001). ATP stimulated 2-DG uptake by 44 ± 4% and 29 ± 5% in NG and HG, respectively. ATP analogues, β, γ-methylene ATP and 2-methylthio ATP stimulated 2-DG uptake in range of 18-34% in NG and 16-17% in HG. Benzoylbenzoyl ATP increased 2-DG uptake about 24 ± 2% in NG however, its effect in HG reached 50 ± 1%. The antagonists of P2 receptors (suramin, reactive blue 2, PPADS) decreased basal 2-DG uptake in NG and HG; suramin and reactive blue 2 at average of 15 ± 4% in NG but in HG the effect was in following order: suramin 28 ± 3%; PPADS 20 ± 3% and RB-2 9 ± 0.9%. Extracellular adenosine concentration was higher in HG than in NG (0.48 ± 0.01 vs. 5.05 ± 0.39 μM, P < 0.05), however intracellular ATP content and extracellular ATP concentration were not affected. Neither ecto-ATPase nor ecto-5'-nucleotidase activities were affected in HG. In conclusion, diabetic milieu affects purinergic modulation of glucose transport into podocytes which may play a role in development of diabetic podocytopathy.

Choline-deprivation alters crucial brain enzyme activities in a rat model of diabetic encephalopathy

Diabetic encephalopathy describes the moderate cognitive deficits, neurophysiological and structural central nervous system changes associated with untreated diabetes. It involves neurotoxic effects such as the generation of oxidative stress, the enhanced formation of advanced glycation end-products, as well as the disturbance of calcium homeostasis. Due to the direct connection of choline (Ch) with acetylcholine availability and signal transduction, a background of Ch-deficiency might be unfavorable for the pathology and subsequently for the treatment of several metabolic brain diseases, including that of diabetic encephalopathy. The aim of this study was to shed more light on the effects of adult-onset streptozotocin (STZ)-induced diabetes and/or Ch-deprivation on the activities of acetylcholinesterase (AChE) and two important adenosine triphosphatases, namely Na(+),K(+)-ATPase and Mg(2+)-ATPase. Male adult Wistar rats were divided into four main groups, as follows: control (C), diabetic (D), Ch-deprived (CD), and Ch-deprived diabetic (D+CD). Deprivation of Ch was provoked through the administration of Ch-deficient diet. Both the induction of diabetes and the beginning of dietary-mediated provoking of Ch-deprivation occurred at the same day, and rats were killed by decapitation after 30 days (1 month; groups C1, D1, CD1 and D1+CD1) and 60 days (2 months; groups C2, D2, CD2 and D2+CD2, respectively). The adult rat brain AChE activity was found to be significantly increased by both diabetes (+10%, p < 0.001 and +11%, p < 0.01) and Ch-deprivation (+19%, p < 0.001 and +14%, p < 0.001) when compared to the control group by the end of the first (C1) and the second month (C2), respectively. However, the Ch-deprived diabetic rats' brain AChE activity was significantly altered only after a 60-day period of exposure, resulting in a +27% increase (D2+CD2 vs. C2, p < 0.001). Although the only significant change recorded in the brain Na(+),K(+)-ATPase activity after the end of the first month is attributed to Ch-deprivation (+21%, p < 0.05, CD1 vs. C1), all groups of the second month exhibited a statistically significant decrease in brain Na(+),K(+)-ATPase activity (-24%, p < 0.01, D2 vs. C2; -21%, p < 0.01, CD2 vs. C2; -22%, p < 0.01, D2+CD2 vs. C2). As concerns Mg(2+)-ATPase, the enzyme's activity demonstrates no significant changes, with the sole exception of the D2+CD2 group (+21%, p < 0.05, D2+CD2 vs. C2). In addition, statistically significant time-dependent changes concerning the brain Mg(2+)-ATPase activity were recorded within the diabetic (p < 0.05, D2 vs. D1) and the Ch-deprived (p < 0.05, CD2 vs. CD1) rat groups. Our data indicate that Ch-deprivation seems to be an undesirable background for the above-mentioned enzymatic activities under untreated diabetes, in a time-evolving way. Further studies on the issue should focus on a region-specific reevaluation of these crucial enzymes' activities as well as on the possible oxidative mechanisms involved.

The nucleotide hydrolysis is altered in blood serum of streptozotocin-induced diabetic rats

Ectonucleotidases and the nucleotide metabolism have been implicated as important regulators of various tissue functions in diabetes disease. Here we evaluated the ectonucleotidase activities and the profile of extracellular ATP metabolism in blood serum of streptozotocin (STZ)-induced diabetic rats. We observed a raise in ATP, ADP, AMP, and 5'-TMP hydrolysis in blood serum after 30 days of diabetes induction, when compared with the citrate group. However, in serum of rats treated 6 days with insulin, the hydrolysis returned to the control levels. Extracellular ATP metabolism estimated by HPLC analysis showed a rapid hydrolysis of extracellular ATP by diabetic animals, leading to the formation of high levels of adenosine when compared with citrate and insulin groups. Since in diabetes the vascular disease is frequently present, the alterations observed are important, because these enzymes control the nucleotides/nucleosides ratio in the circulation and thus the events related to haemostasis.

Treadmill exercise improves cognitive function and facilitates nerve growth factor signaling by activating mitogen-activated protein kinase/extracellular signal-regulated kinase1/2 in the streptozotocin-induced diabetic rat hippocampus

This study aimed to investigate the effects of regular treadmill exercise on nerve growth factor (NGF) expression, the improvement of cognitive function in the hippocampus of diabetic rats, and to understand the molecular mechanisms through which the relevant signaling factors act. We investigated the effects of regular treadmill exercise for 6 weeks on NGF, tyrosine kinase receptor A (TrkA), p75 receptor, phosphatidylinositol 3-kinase (PI3-K), mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase 1/2 (Erk1/2), cyclic AMP response element-binding protein (CREB), and caspase-3 protein levels; we also assessed cell survival and cognitive function. Forty male Sprague-Dawley rats were divided into four groups: (1) normal control group (NCG: n=10); (2) normal exercise group (NEG: n=10); (3) diabetes control group (DCG: n=10), and (4) diabetes exercise group (DEG: n=10). Diabetes was induced by injecting streptozotocin (STZ; 55 mg/kg dissolved in 0.05 M citrate buffer, pH 4.5, i.p.) into rats. Rats were subjected to treadmill exercise for 5 days a week over 6 weeks, and the speed of the treadmill was gradually increased. In a passive avoidance test, the retention latency in the DCG was significantly shorter than that in the DEG (P<0.05). Increased 5-bromo-2'-deoxyuridine-5'-mono-phosphate (BrdU)-labeled cells (P<0.001) and significant increases in NGF and TrkA protein levels were observed in the hippocampal dentate gyrus in the NEG and DEG (P<0.001 and P<0.01, respectively). The p75 receptor protein level significantly increased in the NEG but decreased in the DCG (P<0.001). The p-PI3-K and t-CREB protein levels significantly increased in the NEG (P<0.001 and P<0.05, respectively), whereas t-Erk1/2 significantly decreased in the DCG (P<0.01, P<0.01, respectively). p-Erk1/2 and p-CREB protein levels significantly increased in the NEG and DEG (P<0.001, P<0.001, and P<0.01, respectively). Caspase-3 protein levels significantly increased in the DCG (P<0.001). These results show that treadmill exercise improves cognitive function, increases the number of BrdU-labeled cells, and increases NGF levels, by the activation of the MAPK/Erk1/2 signaling pathway in the hippocampus of diabetic rats.

Ectonucleotidase and acetylcholinesterase activities in synaptosomes from the cerebral cortex of streptozotocin-induced diabetic rats and treated with resveratrol

The aim of the present study was to investigate the effects of resveratrol (RV), an important neuroprotective compound on NTPDase, 5'-nucleotidase and acetylcholinesterase (AChE) activities in cerebral cortex synaptosomes of streptozotocin (STZ)-induced diabetic rats. The animals were divided into six groups (n=8): control/saline; control/RV 10mg/kg; control/RV 20mg/kg; diabetic/saline; diabetic/RV 10mg/kg; diabetic/RV 20mg/kg. After 30 days of treatment with resveratrol the animals were sacrificed and the cerebral cortex was removed for synaptosomes preparation and enzymatic assays. The results demonstrated that NTPDase and 5'-nucleotidase activities were significantly increased in the diabetic/saline group (p<0.05) compared to control/saline group. Treatment with resveratrol significantly increased NTPDase, 5'-nucleotidase activities in the diabetic/RV10 and diabetic/RV20 groups (p<0.05) compared to diabetic/saline group. When resveratrol was administered per se there was also an increase in the activities of these enzymes in the control/RV10 and control/RV20 groups (p<0.05) compared to control/saline group. AChE activity was significantly increased in the diabetic/saline group (p<0.05) compared to control/saline group. The treatment with resveratrol prevented this increase in the diabetic/RV10 and diabetic/RV20 groups. In conclusion, this study demonstrated that the resveratrol interfere with the purinergic and cholinergic neurotransmission by altering NTPDase, 5'-nucleotidase and AChE activities in cerebral cortex synaptosomes of diabetic rats. In this context, we can suggest that resveratrol should be considered potential therapeutics and scientific tools to be investigated in brain disorders associated with the diabetes.

Effects of adult-onset streptozotocin-induced diabetes on the rat brain antioxidant status and the activities of acetylcholinesterase, (Na(+),K (+))- and Mg(2+)-ATPase: modulation by L-cysteine

Uncontrolled diabetes is known to affect the nervous system. The aim of this study was to investigate the effect of the antioxidant L: -cysteine (Cys) on the changes caused by adult-onset streptozotocin (STZ)-induced diabetes on the rat brain total antioxidant status (TAS) and the activities of acetylcholinesterase (AChE), (Na(+),K(+))-ATPase and Mg(2+)-ATPase. Thirty-eight male Wistar rats were divided into six groups: C(A) (8-week-control), C(B) (8-week-control + 1-week-saline-treated), C + Cys (8-week-control + 1-week-Cys-treated), D(A) (8-week-diabetic), D(B) (8-week-diabetic + 1-week-saline-treated) and D + Cys (8-week-diabetic + 1-week-Cys-treated). All diabetic rats were once treated with an intraperitoneal (i.p.) STZ injection (50 mg/kg body weight) at the beginning of the experiment, while all Cys-treated groups received i.p. injections of Cys 7 mg/kg body weight (daily, for 1-week, during the 9th-week). Whole rat brain parameters were measured spectrophotometrically. In vitro incubation with 0.83 mM of Cys or 10 mM of STZ for 3 h was performed on brain homogenate samples from groups C(B) and D(B), in order to study the enzymes' activities. Diabetic rats exhibited a statistically significant reduction in brain TAS (-28%, D(A) vs C(A);-30%, D(B) vs C(B)) that was reversed after 1-week-Cys-administration into basal levels. Diabetes caused a significant increase in AChE activity (+27%, D(A) vs C(A); +15%, D(B) vs C(B)), that was further enhanced by Cys-administration (+57%, D + Cys vs C(B)). The C + Cys group exhibited no significant difference compared to the C(B) group in TAS (+2%), but showed a significantly increased AChE activity (+66%, C + Cys vs C(B)). Diabetic rats exhibited a significant reduction in the activity of Na(+),K(+)-ATPase (-36%, D(A) vs C(A);-48%, D(B) vs C(B)) that was not reversed after 1-week Cys administration. However, in vitro incubation with Cys partially reversed the diabetes-induced Na(+),K(+)-ATPase inhibition. Mg(2+)-ATPase activity was not affected by STZ-induced diabetes, while Cys caused a significant inhibition of the enzyme, both in vivo (-14%, C + Cys vs C(B);-17%, D + Cys vs C(B)) and in vitro (-16%, D(B) + in vitro Cys vs C(B)). In vitro incubation with STZ had no effect on the studied enzymes. The present data revealed a protective role for Cys towards the oxidative effect of diabetes on the adult rat brain. Moreover, an increase in whole brain AChE activity due to diabetes was recorded (not repeatedly established in the literature, since contradictory findings exist), that was further increased by Cys. The inhibition of Na(+),K(+)-ATPase reflects a possible mechanism through which untreated diabetes could affect neuronal excitability, metabolic energy production and certain systems of neurotransmission. As concerns the use of Cys as a neuroprotective agent against diabetes, our in vitro findings could be indicative of a possible protective role of Cys under different in vivo experimental conditions.

High glucose changes extracellular adenosine triphosphate levels in rat retinal cultures

Diabetic retinopathy (DR) is the leading cause of blindness in adults. In diabetes, there is activation of microglial cells and a concomitant release of inflammatory mediators. However, it remains unclear how diabetes triggers an inflammatory response in the retina. Activation of P2 purinergic receptors by adenosine triphosphate (ATP) may contribute to the inflammatory response in the retina, insofar as it has been shown to be associated with microglial activation and cytokine release. In this work, we evaluated how high glucose, used as a model of hyperglycemia, considered the main factor in the development of DR, affects the extracellular levels of ATP in retinal cell cultures. We found that basal extracellular ATP levels were not affected by high glucose or mannitol, but the extracellular elevation of ATP, after a depolarizing stimulus, was significantly higher in retinal cells cultured in high glucose compared with control or mannitol-treated cells. The increase in the extracellular ATP was prevented by application of botulinum neurotoxin A or by removal of extracellular calcium. In addition, degradation of exogenously added ATP was significantly lower in high-glucose-treated cells. It was also observed that, in retinal cells cultured under high-glucose conditions, the changes in the intracellular calcium concentrations were greater than those in control or mannitol-treated cells. In conclusion, in this work we have shown that high glucose alters the purinergic signaling system in the retina, by increasing the exocytotic release of ATP and decreasing its extracellular degradation. The resulting high levels of extracellular ATP may lead to inflammation involved in the pathogenesis of DR.

Fetal and neonatal habituation in infants of diabetic mothers

OBJECTIVE

To evaluate whether maternal diabetes alters the habituation ability of fetuses and newborns.

STUDY DESIGN

Two nonrandomized clinical trials were performed. First, we studied prenatal fetuses of women with pregestational diabetes, and control subjects matched for gestational age, and then we studied infants of diabetic mothers (IDM) and control subjects matched for gestational age and mode of delivery. Fetus and newborns were stimulated with vibroacoustic stimulus.

RESULTS

In fetuses of diabetic mothers, the ability to habituate was lower, and the habituation rate was higher than in control subjects to all habituation tests. In the neonatal period, ability to habituate was lower (59% vs 100%; P< .001), and the habituation rate was higher (18 [14-21] vs 4 [1.2-6.8]; P< .001) in the IDM than in the control infants. We found a significant negative correlation between maternal glycosylated hemoglobin in each trimester of pregnancy and habituation ability in IDM.

CONCLUSIONS

Fetuses and infants of diabetic mothers have impaired habituation ability, which is related to the degree of maternal metabolic control.

Purinergic signalling and disorders of the central nervous system

Purines have key roles in neurotransmission and neuromodulation, with their effects being mediated by the purine and pyrimidine receptor subfamilies, P1, P2X and P2Y. Recently, purinergic mechanisms and specific receptor subtypes have been shown to be involved in various pathological conditions including brain trauma and ischaemia, neurodegenerative diseases involving neuroimmune and neuroinflammatory reactions, as well as in neuropsychiatric diseases, including depression and schizophrenia. This article reviews the role of purinergic signalling in CNS disorders, highlighting specific purinergic receptor subtypes, most notably A(2A), P2X(4) and P2X(7), that might be therapeutically targeted for the treatment of these conditions.

Increased amyloid beta-peptide (1-40) level in brain of streptozotocin-induced diabetic rats

The aims of the study were to investigate whether the level of amyloid beta-peptide (Abeta) (1-40) was increased in brain of diabetic rats and whether the increase was associated with dysfunction of P-glycoprotein at the blood-brain barrier. A diabetes-like condition was induced by single administration of 65 mg/kg streptozotocin via i.p. injection. Abeta (1-40) levels in brain of the diabetic rats were measured using an enzyme linked immunosorbent assay (ELISA) kit. The in vivo brain-to-blood efflux and blood-to-brain influx transport of [(125)I]-labeled human amyloid-beta-peptide (hAbeta) (1-40) were measured using the brain efflux index and brain permeability coefficient-surface area product, respectively. [(14)C]inulin served as a reference compound. The results showed that Abeta (1-40) levels significantly increased in temporal cortex and hippocampus of the diabetic rats. The brain remaining percentage of [(125)I]hAbeta (1-40) in diabetic rats significantly increased at 30 min after intracerebral microinjection, accompanied by decrease of the brain efflux index. Pretreatment of P-glycoprotein inhibitors verapamil or cyclosporin A significantly increased the brain remaining percentage of [(125)I]hAbeta (1-40). The brain permeability coefficient-surface area product of [(125)I]hAbeta (1-40) was increased in diabetic rats, accompanied by increased Abeta (1-40) levels in plasma. The present study demonstrated that a diabetic state could increase Abeta (1-40) levels in brain, which might be explained, at least in part, by the decline in brain-to-blood efflux of Abeta (1-40) due to deficient cerebral P-glycoprotein function in diabetic rats.