Vitamin D3 mitigates type 2 diabetes induced by a high carbohydrate-high fat diet in rats: Role of the purinergic system

This study evaluated the effect of vitamin D3 (VIT D3) supplementation on the enzymatic activities and density of ectonucleoside triphosphate diphosphohydrolase (E-NTPDase), ecto-5-nucleotidase (E-5'-NT), adenosine deaminase (ADA), as well as the density of P2 × 7R, P2Y12R, A1R, A2AR receptors, IL-1β, and oxidative parameters in type 2 diabetic rats. Forty male Wistar rats were fed a high carbohydrate-high fat diet (HCHFD) and received an intraperitoneal injection containing a single dose of streptozotocin (STZ, 35 mg/kg). Animals were divided into four groups: 1) control; 2) control/VIT D3 12 µg/kg; 3) diabetic; and 4) diabetic/VIT D3 12 µg/kg. Results show that VIT D3 reduced blood glucose, ATP hydrolysis, ADA activity, P2Y12R density (platelets), as well as ATP, ADP, and AMP hydrolysis and ADA activity (synaptosomes). Moreover, VIT D3 increased insulin levels and AMP hydrolysis (platelets) and improved antioxidant defense. Therefore, we suggest that VIT D3 treatment modulates hyperglycemia-induced changes via purinergic enzymes and receptor expression, consequently attenuating insulin homeostasis dysregulation in the diabetic state.

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.

Long-term treatment with roflumilast improves learning of fear extinction memory and anxiety-like response in a type-1 diabetes mellitus animal model

Diabetic encephalopathy is related to serious damage to the Central Nervous System leading to several disturbances in memory processing and emotions. It is known that the cyclic adenosine 3',5'-monophosphate (cAMP) responsive element-binding protein (CREB) pathway participates in neuronal plasticity and prevention of neuroinflammation, as well as the mediation of learning/memory processes and emotions in brain areas such as the hippocampus (HIP) and prefrontal cortex (PFC). We aimed to investigate the effect of acute (one injection) and long-term treatment (21 days) with roflumilast (ROF; i.p.; 0, 0.01, 0.03, 0.1 mg/kg), a drug able to inhibit the enzyme phosphodiesterase-4 (PDE-4) responsible for cAMP hydrolysis, on parameters related to the acquisition of fear extinction memory and anxiety-like responses in animals with type-1 diabetes mellitus (T1DM) induced through one injection of streptozotocin (60 mg/kg; ip; STZ animals). When we performed acute treatment, no difference was observed between all the groups when resubmitted to the same context paired with an aversive stimulus (footshock) or to a neutral context. In contrast, long-term treatment was able to improve learning of extinction fear memory and discriminating between a conditioned and neutral context. Moreover, this treatment decreased the pronounced anxiety-like response of STZ animals. In addition, there was an increase in the product of the CREB signaling pathway, the pro brain-derived neurotrophic factor, in the HIP and PFC of these animals. The treatment did not impair glycemic control, whereas it decreased the animal's blood glucose levels. To conclude, these findings suggest that ROF treatment repositioning has potential for future translational investigations involving diabetic patients considering its beneficial effects on emotional processes related to fear memory and anxiety, in addition to improvement of glycemic control.

Protective effects of vitamin D on neurophysiologic alterations in brain aging: role of brain-derived neurotrophic factor (BDNF)

Background/aim: Vitamin D has been hypothesized to be main regulator of the aging rate, alongside evidences support its role in neuroprotection. However, data about the protective role of vitamin D against neurophysiologic alterations associated with brain aging is limited. This study investigated the possible protective effects that vitamin D has on brain-derived neurotrophic factor (BDNF), cholinergic function, oxidative stress and apoptosis in aging rat brain.Methods: Male Wister albino rats aged 5 months (young), 12 months (middle aged) and 24 months (old) (n = 20 each) were used. Each age group subdivided to either vitamin D3 supplementation (500 IU/kg/day orally for 5 weeks) or no supplementation (control) group (n = 10 each). Serum 25-hydroxyvitamin D [25(OH)D], brain BDNF and malondialdehyde levels and activities of acetylcholinesterase (AChE), antioxidant enzymes (glutathione reductase, glutathione peroxidase and superoxide dismutase) and caspase-3 were quantified.Results: Vitamin D supplementation significantly mitigated the observed aging-related reduction in brain BDNF level and activities of AChE and antioxidant enzymes and elevation in malondialdehyde level and caspase-3 activity compared to control groups. Brain BDNF level correlated positively with serum 25(OH) D level and brain AChE activity and negatively with brain malondialdehyde level and caspase-3 activity in supplemented groups.Conclusion: Restoring vitamin D levels may, therefore, represent a useful strategy for healthy brain aging. Augmenting brain BDNF seems to be a key mechanism through which vitamin D counteracts age-related brain dysfunction.

Associations of Triglycerides/High-Density Lipoprotein Cholesterol Ratio With Insulin Resistance, Impaired Glucose Tolerance, and Diabetes in American Adults at Different Vitamin D3 Levels

BACKGROUND

Previous studies have shown that vitamin D3 (VD3) may be a protective factor for diabetes mellitus (DM), while triglycerides/high-density lipoprotein (TG/HDL) may be a risk factor for diabetes. However, no existing study has elucidated the interaction between TG/HDL and VD3. Therefore, this work aimed to investigate the relationships of TG/HDL with insulin resistance (IR), impaired glucose tolerance (IGT), and DM at different VD3 levels.

METHODS

With the use of the data from five National Health and Nutrition Examination Survey (NHANES) cycles, a total of 2,929 males and 3,031 females were divided into 4 groups according to their VD3 levels. Logistic regression was performed to observe the associations of TG/HDL ratio with IR, IGT, and DM in different groups.

RESULTS

The relationships of TG/HDL with IR, IGT, and DM showed a threshold effect, with the cutoff values of 1.094, 1.51, and 1.11, respectively. On both sides of the cutoff values, the correlation was first weakened and then enhanced with the increase in VD3 levels.

CONCLUSION

TG/HDL is a risk factor for IR, IGT, and DM. Both too low and too high levels of VD3 can strengthen this association, whereas keeping VD3 at a reasonable level helps to reduce the associations of TG/HDL with IR, IGT, and DM.

TLR2 knockout protects against diabetes-mediated changes in cerebral perfusion and cognitive deficits

The risk of cognitive decline in diabetes (Type 1 and Type 2) is significantly greater compared with normoglycemic patients, and the risk of developing dementia in diabetic patients is doubled. The etiology for this is likely multifactorial, but one mechanism that has gained increasing attention is decreased cerebral perfusion as a result of cerebrovascular dysfunction. The innate immune system has been shown to play a role in diabetic vascular complications, notably through the Toll-like receptor (TLR)-stimulated release of proinflammatory cytokines and chemokines that lead to vascular damage. TLR2 has been implicated in playing a crucial role in the development of diabetic microvascular complications, such as nephropathy, and thus, we hypothesized that TLR2-mediated cerebrovascular dysfunction leads to decreased cerebral blood flow (CBF) and cognitive impairment in diabetes. Knockout of TLR2 conferred protection from impaired CBF in early-stage diabetes and from hyperperfusion in long-term diabetes, prevented the development of endothelium-dependent vascular dysfunction in diabetes, created a hyperactive and anxiolytic phenotype, and protected against diabetes-induced impairment of long-term hippocampal and prefrontal cortex-mediated fear learning. In conclusion, these findings support the involvement of TLR2 in the pathogenesis of diabetic vascular disease and cognitive impairment.

An evaluation of aversive memory and hippocampal oxidative status in streptozotocin-induced diabetic rats treated with resveratrol

The present study evaluated the effects of streptozotocin (STZ)-induced diabetes on aversive memory, free radical content and enzymatic antioxidant activity in the hippocampus of adult Wistar rats submitted to oral treatment with resveratrol. Animals were divided into eight groups: non-diabetic rats treated with saline (ND SAL), non-diabetic rats treated with resveratrol at a dose 5mg/kg (ND RSV 5), non-diabetic rats treated with resveratrol at a dose 10mg/kg (ND RSV 10), non-diabetic rats treated with resveratrol at a dose 20mg/kg (ND RSV 20), diabetic rats treated with saline (D SAL), diabetic rats treated with resveratrol at a dose 5mg/kg (D RSV 5), diabetic rats treated with resveratrol at a dose 10mg/kg (D RSV 10) and diabetic rats treated with resveratrol at a dose 20mg/kg (D RSV 20). The animals received oral gavage for 35days. The contextual fear conditioning task was performed to evaluate aversive-based learning and memory. The oxidative status was evaluated in the hippocampus, by measuring the free radical content - using a 2',7'-dichlorofluorescein diacetate probe - and enzymatic antioxidant activities, such as superoxide dismutase and glutathione peroxidase. Our main behavioral results demonstrated that rats from the D RSV 10 and D RSV 20 groups showed an increase in freezing behavior when compared, respectively, to the ND RSV 10 (p<0.01) and ND RSV 20 (p<0.05). Oxidative stress parameters remained unchanged in the hippocampus of all the experimental groups. In contrast to previous experimental findings, our study was unable to detect either cognitive impairments or oxidative stress in the hippocampus of the diabetic rats. We suggest additional long-term investigations be conducted into the temporal pattern of STZ-induced diabetic disruption in memory and hippocampal oxidative status, as well as the effects of resveratrol on these parameters, in a time and dose-dependent manner.

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.

Falls, physical limitations, confusion and memory problems in people with type II diabetes, undiagnosed diabetes and prediabetes, and the influence of vitamins A, D and E

AIMS

To examine the association between type II diabetes, prediabetes and undiagnosed diabetes with falls, physical limitations, confusion and memory problems, and to evaluate the effects of vitamins A, D and E levels on the associations.

METHODS

Data from 37,973 participants of the National Health and Nutrition Examination Survey was analyzed.

RESULTS

The participants' mean age was 46±17years, 20% had diabetes of which 17% were unaware of their condition (undiagnosed diabetes), and 21% had prediabetes. Diabetes was significantly associated with falls, difficulties in stooping, crouching, kneeling, completing house chores, getting in and out bed, standing and sitting for long periods, reaching over head, grasping, holding objects, and attending social events. The association between diabetes and confusion or memory problems was stronger for those diagnosed before age 40. Memory problems were reported only by people with diabetes with lower vitamin D levels. Vitamin A and E levels did not modify the association between diabetes and falls or any of the physical functions, confusion or memory problems. Prediabetes was only associated with difficulty standing for long periods.

CONCLUSIONS

Diabetes was associated with falls, difficulties in physical functioning and attending social events. Vitamin D levels modified the effects on confusion and memory problems.