Streptozotocin-induced insulin deficiency leads to development of behavioral deficits in rats

The Aqueous Extract of Sclerocarya birrea, Nauclea latifolia, and Piper longum Mixture Protects Striatal Neurons and Movement-Associated Functionalities in a Rat Model of Diabetes-Induced Locomotion Dysfunction

Among the many complications of type 2 diabetes (T2D), locomotor disorders have been poorly studied and understood. Therefore, no disease-modifying treatment is usually considered. The study aimed to investigate the effect of the aqueous extract of Sclerocarya birrea, Nauclea latifolia, and Piper longum (SNP) mixture on locomotor activity in fructose/streptozotocin-induced diabetic rats. T2D was induced by 10% fructose orally (6 weeks) and streptozotocin (STZ, 35 mg/kg, i.v.) in 25 male rats. Diabetic animals received distilled water, metformin (200 mg/kg), or the aqueous extract of the SNP mixture (75, 150, or 300 mg/kg). A 10-minute open field test was performed in diabetic rats (glycemia: 126 and 350 mg/dL) to assess locomotor activity before and after treatment. A group of 5 normal rats (NC) served as controls throughout the study. Rats were sacrificed, and the striatum was removed for biochemical and histological studies. In untreated diabetic rats, fructose/STZ administration resulted in hyperglycemia that altered locomotor function as characterized by increased freezing time, decreased mobility time, number of lines crossed, and total travel time compared to NC. MDA, TNF-α, INF-γ, and nitrite levels were elevated in the striatum of diabetic rats, while catalase activity and GSH levels were decreased, indicating oxidative stress and neuroinflammatory changes. In untreated diabetic rats, the microstructure of the HE-stained striatum revealed lipid vacuolation (hydropic degeneration) of the parenchyma, indicating a loss of neuronal integrity. The locomotor dysfunction was significantly improved by the aqueous extract of the SNP mixture, both biochemically and histologically. As a result, our findings support the mixture's ability to correct diabetes-related locomotion disorders as a glucose-lowering product and antioxidant, anti-inflammatory, and neuroprotective agent. These results justify the use of the aqueous extract of a combination of these three plants to manage diabetes and neuroinflammatory complications in Northern Cameroon.

Investigating the effects of Citrullus colocynthis on cognitive performance and anxiety-like behaviors in STZ-induced diabetic rats

Background: Diabetes can impair cognitive performance and lead to dementia. Patients with type 1 diabetes mellitus (T1DM) are reported with different levels of cognitive dysfunctions in various cognitive domains ranging from general intellectual testing to specific deficits with visuospatial abilities, motor speed, writing, attention, reading, and psychomotor efficiency. The present study aimed to investigate the effect of Citrullus colocynthis on cognitive functions.Methods: A total of 42 male Wistar rats (3-4  months old and weighing 200-250  g) were tested in the current study. Rats were randomly allocated into 3 groups of control, Diabetes, and Diabetes + Drug. The diabetic rats received Citrullus colocynthis extraction orally. The behavioral tests included the open field, elevated plus maze (EPM), novel object recognition (NOR), passive avoidance tests, and Morris Water Maze (MWM) tests. Data were analyzed using student and paired t-tests via SPSS software version 16.Results: Our results showed the protective effects of Citrullus colocynthis administration against cognitive impairments. This is followed by STZ-induced diabetes in the MWM, novel object recognition, and passive avoidance tasks. Also, it was found that Citrullus colocynthis improved anxiety in diabetic rats.Conclusion According to the findings of this study, the administration of 200  mg/kg C. colocynthis once per day for 40  days can lead to ameliorated cognitive impairments and antidiabetic effects such as increasing body weight and decreasing FBS.

Parkin-mediated mitophagy is negatively regulated by FOXO3A, which inhibits Plk3-mediated mitochondrial ROS generation in STZ diabetic stress-treated pancreatic β cells

Diabetes mellitus (DM) is one of the most researched metabolic diseases worldwide. It leads to extensive complications such as cardiovascular disease, nephropathy, retinopathy, and peripheral and central nervous system through an inability to produce or respond to insulin. Although oxidative stress-mediated mitophagy has been reported to play an important role in the pathogenesis of DM, specific studies are still lacking as well as remain highly controversial. Here, we found that Parkin-mediated mitophagy in pancreatic β cells under streptozotocin (STZ)-diabetic stress was induced by Polo-like kinase 3 (Plk3) and inhibited by the transcription factor Forkhead Box O3A (FOXO3A). STZ stress induces mitochondrial recruitment of Parkin through Plk3-mediated mitochondrial reactive oxygen species (ROS) generation, which causes pancreatic cell damage. Conversely, FOXO3A acts as negative feedback to prevent diabetic stress by inhibiting Plk3. Meanwhile, antioxidants including N-acetylcysteine (NAC) and natural COA water scientifically block these mitochondrial ROS and mitochondrial recruitment of Parkin by inhibiting Plk3. Through a 3D organoid ex vivo model, we confirmed that not only ROS inhibitors but also mitophagy inhibitory factors such as 3-MA or Parkin deletion can compensate for pancreatic cell growth and insulin secretion under STZ diabetic stress. These findings suggest that the Plk3-mtROS-PINK1-Parkin axis is a novel mitophagy process that inhibits pancreatic β-cell growth and insulin secretion and FOXO3A and antioxidants may provide new alternatives for effective diabetes treatment strategies in the future.

Microglia activation and inflammation in hippocampus attenuates memory and mood functions during experimentally induced diabetes in rat

Incidence of cognitive and emotional alterations are reportedly two times more in diabetic patients than in non-diabetic population with hitherto unexplained causation and mechanism. Purview of the hippocampus functional diversity sanctions the accessibility and the necessity to investigate the regional neuro-immunological aspects of neurodegeneration and related functional alterations following diabetes. We examined the possible involvement of microglia activation, macrophage response, oxidative stress and inflammatory stature in both ventral and dorsal hippocampus of rats rendered diabetic by a single injection of streptozotocin (STZ; 45 mg/ kg body weight; intraperitoneal). Cognitive and behavioural alterations were studied using open field test (locomotor activity), elevated plus maze (anxiety), Barnes maze (spatial cognition) and T maze (working memory) at 2nd, 4th, 6th, 8th, 10th and 12th week post diabetic confirmation. Oxidative stress was investigated via measuring the level of lipid peroxidation biochemically. Scenario of microglia activation, macrophage response and inflammation was gauged using qualitative and quantitative analysis. Pronounced macrophage expression and activation directed microglia phenotypic switching was prominent in both ventral and dorsal hippocampus indicating the impact of oxidative stress following diabetes in hippocampus. The resultant inflammatory response was also progressive and persistent in both ventral and dorsal hippocampus parallel to the altered cognitive, locomotor ability and anxiety behaviour in diabetic rats. Conclusively, present data not only comprehends the microglia, macrophage physiology and related immune response in functionally different hippocampal regions associated cognitive and behavioural deficits, but also offers a suggestive region-specific cellular mechanism pathway for developing an imminent therapeutic approach during particular diabetes deficits.

Control of Obesity, Blood Glucose, and Blood Lipid with Olax imbricata Roxb. Root Extract in High-Fat Diet-Induced Obese Mice

Mice were used in in vivo experiments to evaluate the effects of doses of n-hexane extract (from 100 to 1,300 mg/kg body weight/day) on the ability to control obesity, blood glucose, and blood lipid. In this study, body weight gain, caloric intake, glucose tolerance, blood lipid, histopathological study, and locomotion activity were examined. Furthermore, this study evaluated the lethality of the extract in extremely high doses in the tested mice. After 3 months of use with an extremely high dose of 5,000 mg/kg body weight/day (equivalent to 350 g/day for a 70 kg person), no animals with abnormal conditions or death were observed. This initially demonstrated the safety of the extract. In addition, after 6 weeks of testing on high-fat diet-induced obese mice, n-hexane extract at a dose of 500 mg/kg body weight/day (equivalent to 35 g/day for a 70 kg person) demonstrated a positive effect on the ability to control obesity, blood glucose, and blood lipid through the results of body weight, blood lipids, glucose tolerance, and histopathology (white fat, liver, and kidney tissues). In this study, n-hexane extract from the roots of Duong-dau tree has proven to be strongly biologically active in preventing and supporting the treatment of diseases related to overweight and obesity, helping to control blood glucose levels thereby reducing the risk of type 2 diabetes.

Nutritional importance of tryptophan for improving treatment in depression and diabetes

The importance of nutrients in our diet is becoming increasingly recognized. From the viewpoint of protein synthesis and other physiologic and metabolic functions, all amino acids are important, but some of these amino acids are not synthesized endogenously. This subset, called essential amino acids, comprise dietarily indispensable nutrients. Tryptophan, an essential amino acid, is the sole precursor of neuronal as well as peripheral serotonin (5-hydroxytryptamine). Its systemic or oral administration increases serotonin synthesis because tryptophan hydroxylase, the rate-limiting enzyme of 5-hydroxytryptamine biosynthesis, is physiologically unsaturated with its substrate. Central serotonin is implicated in a number of psychiatric illnesses, including depression, and in responses to stress. Acting peripherally, serotonin affects vasoconstriction, intestinal motility, control of T cell–mediated immunity, and liver and pancreatic functions. Depression and diabetes are 2 highly prevalent diseases that often coexist. There is evidence that occurrence of depression is 2–3 times higher in people with diabetes mellitus. A comorbid condition of diabetes and depression worsens the treatment and increases risk for death. Stress, known for its causal role in depression, can also enhance risk for diabetes. Stress-induced decreases in the circulating levels of tryptophan can impair brain and pancreatic serotonin-dependent functions to precipitate these diseases. The importance of tryptophan supplementation for improving therapeutic intervention in depression and diabetes is the focus of this article. A deficiency of this essential amino acid may enhance risk for depression as well as diabetes, and can also weaken treatment efficacy of medicinal compounds for treating these diseases. Guidelines for optimal levels of circulating tryptophan can help if supplements of this amino acid can improve treatment efficacy.

Low-Frequency Oscillations of In Vivo Ambient Extracellular Brain Serotonin

Serotonin is an important neurotransmitter that plays a major role in many aspects of neuroscience. Fast-scan cyclic voltammetry measures fast in vivo serotonin dynamics using carbon fiber microelectrodes. More recently, fast-scan controlled-adsorption voltammetry (FSCAV) has been developed to measure slower, minute-to-minute changes in ambient extracellular serotonin. We have previously demonstrated that FSCAV measurements of basal serotonin levels give critical information regarding brain physiology and disease. In this work, we revealed the presence of low-periodicity fluctuations in serotonin levels in mouse hippocampi, measured in vivo with FSCAV. Using correlation analyses, we found robust evidence of oscillations in the basal serotonin levels, which had a period of 10 min and were not present in vitro. Under control conditions, the oscillations did not differ between male and female mice, nor do they differ between mice that underwent a chronic stress paradigm and those in the control group. After the acute administration of a selective serotonin reuptake inhibitor, we observed a shift in the frequency of the oscillations, leading us to hypothesize that the newly observed fluctuations were transporter regulated. Finally, we optimized the experimental parameters of the FSCAV to measure at a higher temporal resolution and found more pronounced shifts in the oscillation frequency, along with a decreased oscillation amplitude. We postulate that this work may serve as a potential bridge for studying serotonin/endocrine interactions that occur on the same time scale.

Putative Anti-Immobility Action of Acute Insulin Is Attributable to an Increase in Locomotor Activity in Healthy Wistar Rats

BACKGROUND/AIMS

Anti-immobility actions of insulin in diabetic rats that are subjected to the forced swim test (FST) have been reported. In this test, low doses of antidepressants exert actions after long-term treatment, without affecting locomotor activity in healthy rats. Few studies have compared acute and chronic actions of insulin with antidepressants in healthy rats.

METHODS

We hypothesized that if insulin exerts a true anti-immobility action, then its effects must be comparable to fluoxetine in both a 1-day treatment regimen and a 21-day treatment regimen in healthy, gonadally intact female Wistar rats.

RESULTS

The results showed that low levels of glycemia were produced by all treatments, including fluoxetine, and glycemia was lower in proestrus-estrus than in diestrus-metestrus. None of the treatments or regimens produced actions on indicators of anxiety in the elevated plus maze. Insulin in the 1-day regimen increased the number of crossings and rearings in the open field test and caused a low cumulative immobility time in the FST. These actions disappeared in the 21-day regimen. Compared with the other treatments, fluoxetine treatment alone or combined with insulin produced a longer latency to the first period of immobility and a shorter immobility time in the chronic regimen in the FST, without affecting locomotor activity, and more pronounced actions were observed in proestrus-estrus (i.e., a true anti-immobility effect).

CONCLUSION

These results indicate that insulin does not produce a true antidepressant action in healthy rats. The purported antidepressant effects that were observed were instead attributable to an increase in locomotor activity only in the 1-day regimen.

Myrsinoic acid B from Myrsine coriacea reverses depressive-like behavior and brain oxidative stress in streptozotocin-diabetic rats

AIMS

Major depressive disorder (MDD) affects approximately 322 million people worldwide and is a common comorbidity in patients with diabetes mellitus (DM). A possible pathophysiological mechanism correlating both diseases is the increased oxidative stress in brain regions due to hyperglycemia. Myrsine coriacea (Primulaceae) is popularly known as "capororoca" and studies have been shown that this plant exhibits several pharmacological properties attributed to myrsinoic acid A (MAA) and B (MAB). Indeed, previous results have been shown its effects on the central nervous system, leading us to explore possible psychotropic effects.

MAIN METHODS

The effects of treatment with hydroalcoholic extract of the barks from Myrsine coriacea (HEBMC, 150 mg/kg, o.g.), MAA (5 mg/kg, o.g.), and MAB (3 mg/kg, o.g.) were evaluated in streptozotocin (75 mg/kg, i.p.)-induced diabetic female rats. After 28 days of treatments, rats were submitted to the forced swim test (FST) and open field test (OFT). Also, superoxide dismutase (SOD) and catalase (CAT) activities, reduced glutathione (GSH) and lipid hydroperoxides (LOOH) levels were evaluated in the hippocampus (HIP) and prefrontal cortex (PFC) of these rats.

KEY FINDINGS

The treatment with MAA or MAB increased the latency of first immobility in diabetic rats, and the HEBMC administration decreased the immobility time, and increase the climbing in FST. However, only MAB treatment reduces the immobility time, increases the climbing, and swimming in FST, and increases the crossing of diabetic animals in the OFT. Besides, this behavioral improvement promoted by MAB administration was accompanied by reducing in oxidative stress in the HIP and PFC, but not reducing hyperglycemia in diabetic rats.

SIGNIFICANCE

The results suggest that MAB's antioxidant effect in the HIP of diabetic animals may be essential to its antidepressant-like effect.

Altered theta rhythm and hippocampal-cortical interactions underlie working memory deficits in a hyperglycemia risk factor model of Alzheimer's disease

Diabetes mellitus is a metabolic disease associated with dysregulated glucose and insulin levels and an increased risk of developing Alzheimer’s disease (AD) later in life. It is thought that chronic hyperglycemia leads to neuroinflammation and tau hyperphosphorylation in the hippocampus leading to cognitive decline, but effects on hippocampal network activity are unknown. A sustained hyperglycemic state was induced in otherwise healthy animals and subjects were then tested on a spatial delayed alternation task while recording from the hippocampus and anterior cingulate cortex (ACC). Hyperglycemic animals performed worse on long delay trials and had multiple electrophysiological differences throughout the task. We found increased delta power and decreased theta power in the hippocampus, which led to altered theta/delta ratios at the end of the delay period. Cross frequency coupling was significantly higher in multiple bands and delay period hippocampus-ACC theta coherence was elevated, revealing hypersynchrony. The highest coherence values appeared long delays on error trials for STZ animals, the opposite of what was observed in controls, where lower delay period coherence was associated with errors. Consistent with previous investigations, we found increases in phosphorylated tau in STZ animals’ hippocampus and cortex, which might account for the observed oscillatory and cognitive changes.

To investigate the effects of chronic hyperglycemia on hippocampal network activity Wirt et al induced sustained hyperglycemia in rats and tested them in a spatial delayed alternation task while recording from the hippocampus and anterior cingulate cortex. They demonstrated that hyperglycemia impaired task performance and altered theta rhythm as well as increasing tau phosphorylation, which suggest there is potentially a direct link between chronic hyperglycemia and Alzheimer’s disease.

Catalpol Weakens Depressive-like Behavior in Mice with Streptozotocin-induced Hyperglycemia via PI3K/AKT/Nrf2/HO-1 Signaling Pathway

Depression has huge social risks of high incidence, disability, and suicide. Its prevalence and harm in people with hyperglycemia are 2-3 times higher than in normal people. However, antidepressants with precise curative effects and clear mechanisms for patients with hyperglycemia are currently lacking. Prescriptions containing Rehmannia glutinosa, a traditional medicinal herb with a wide range of nutritional and medicinal values, are often used as antidepressants in Chinese clinical medicine. Catalpol is one of the main effective compounds of R. glutinosa, with multiple biological activities such as hypoglycemia. Here, the antidepressant effect of catalpol on the pathological state of streptozotocin (STZ)-induced hyperglycemia and the underlying molecular mechanisms were analyzed. Results showed that administering catalpol orally to hyperglycemic mice for 21 consecutive days significantly reversed the abnormalities in tail suspension, forced swimming, and open field tests. Catalpol also reversed the abnormal phosphorylation of phosphoinositide 3-kinase (PI3K) and protein kinase B (AKT) and the abnormal levels of nuclear factor erythroid 2-related factor 2 (Nrf2) protein, heme oxygenase-1 (HO-1), and antioxidants, including superoxide dismutase, glutathione peroxidase, glutathione-s transferase, reduced glutathione, and malondialdehyde in the hippocampus and frontal cortex of STZ-induced hyperglycemic mice. Thus, catalpol attenuates depressive-like behavior in pathological hyperglycemic state, and the antidepressant mechanism could at least be partly attributed to the upregulation of the PI3K/AKT/Nrf2/HO-1 signaling pathway in both brain regions, thus restoring the balance between oxidative and antioxidant damage. These data expanded the scientific understanding of catalpol and provided preclinical experimental evidence for its application.

Bixin attenuates mechanical allodynia, anxious and depressive-like behaviors associated with experimental diabetes counteracting oxidative stress and glycated hemoglobin

Neuropathic pain, depression, and anxiety are common comorbidities in diabetic patients, whose pathophysiology involves hyperglycemia-induced increased oxidative stress. Bixin (BIX), an apocarotenoid extracted from the seeds of Bixa orellana, has been used in traditional medicine to treat diabetes and has been recognized by its antioxidant profile. We aimed to investigate the effect of the BIX over the mechanical allodynia, depressive, and anxious-like behaviors associated with experimental diabetes, along with its involved mechanisms. Streptozotocin-induced diabetic rats were treated for 17 days (starting 14 days after diabetes induction) with the corresponding vehicle, BIX (10, 30 or 90 mg/kg; p.o), or INS (6 IU; s.c.). Mechanical allodynia, depressive, and anxious-like behavior were assessed by electronic Von Frey, forced swimming, and elevated plus-maze tests, respectively. Locomotor activity was assessed by the open field test. Blood glycated hemoglobin (HbA1) and the levels of lipid peroxidation (LPO) and reduced glutathione (GSH) were evaluated on the hippocampus, pre-frontal cortex, lumbar spinal cord, and sciatic nerve. Diabetic animals developed mechanical allodynia, depressive and anxious-like behavior, increased plasma HbA1, increased LPO, and decreased GSH levels in tissues analyzed. Repeated BIX-treatment (at all tested doses) significantly attenuated mechanical allodynia, the depressive (30 and 90 mg/kg) and, anxious-like behaviors (all doses) in diabetic rats, without changing the locomotor performance. BIX (at all tested doses) restored the oxidative parameters in tissues analyzed and reduced the plasma HbA1. Thereby, bixin may represent an alternative for the treatment of comorbidities associated with diabetes, counteracting oxidative stress and plasma HbA1.

Hyperglycemia induces RAGE-dependent hippocampal spatial memory impairments

Diabetes is a prevalent metabolic disorder that has long been associated with changes in different regions of the brain, including the hippocampus. Changes in hippocampal synaptic plasticity and subsequent impairment in cognitive functions such as learning and memory, are well documented in animal models of type 1 and type 2 diabetes. It is known that RAGE contributes to peripheral micro- and macro-vascular complications of diabetes. However, it is still unknown if RAGE plays a similar role in the development of CNS complications of diabetes. Therefore, we hypothesize that RAGE contributes to cognitive dysfunction, such as learning and memory impairments, in a mouse model of STZ-induced hyperglycemia. Control and STZ-induced hyperglycemic mice from WT and RAGE-KO groups were used for the behavioral experiments. While STZ-induced hyperglycemia decreased locomotor activity in the open field (OF) test, it did not affect the recognition memory in the novel object recognition (NOR) test in either genotype. Spatial memory, however, was impaired in STZ-induced hyperglycemic mice in WT but not in RAGE-KO group in both the Barnes maze (BM) and the Morris water maze (MWM) tests. Consistently, the RAGE antagonist FPS-ZM1 protected WT STZ-induced hyperglycemic mice from spatial memory impairment in the BM test. Our findings indicate that the parameters associated with locomotor activity and recognition memory were independent of RAGE in STZ-induced hyperglycemic mice. In contrast, the parameters associated with hippocampal-dependent spatial memory were dependent on RAGE expression.

Role of peripheral 5-HT5A receptors in 5-HT-induced cardiac sympatho-inhibition in type 1 diabetic rats

5-HT inhibits cardiac sympathetic neurotransmission in normoglycaemic rats, via 5-HT1B, 5-HT1Dand 5-HT5Areceptor activation. Since type 1 diabetes impairs the cardiac sympathetic innervation leading to cardiopathies, this study aimed to investigate whether the serotonergic influence on cardiac noradrenergic control is altered in type 1 diabetic rats. Diabetes was induced in male Wistar rats by streptozotocin (50 mg/kg, i.p.). Four weeks later, the rats were anaesthetized, pithed and prepared for producing tachycardic responses by electrical preganglionic stimulation (C7-T1) of the cardioaccelerator sympathetic outflow or i.v. noradrenaline bolus injections. Immunohistochemistry was performed to study 5-HT1B, 5-HT1Dand 5-HT5Areceptor expression in the stellate ganglion from normoglycaemic and diabetic rats. In the diabetic group, i) i.v. continuous infusions of 5-HT induced a cardiac sympatho-inhibition that was mimicked by the 5-HT1/5Aagonist 5-carboxamidotryptamine (without modifying noradrenaline-induced tachycardia), but not by the agonists indorenate (5-HT1A), CP 93,129 (5-HT1B), PNU 142633 (5-HT1D), or LY344864 (5-HT1F); ii) SB 699551 (5-HT5Aantagonist; i.v.) completely reversed 5-CT-induced cardiac sympatho-inhibition; and iii) 5-HT5Areceptors were more expressed in the stellate ganglion compared to normoglycaemic rats. These results show the prominent role of the peripheral 5-HT5Areceptors prejunctionally inhibiting the cardiac sympathetic drive in type 1 diabetic rats.

Role of peripheral 5-HT5A receptors in 5-HT-induced cardiac sympatho-inhibition in type 1 diabetic rats

5-HT inhibits cardiac sympathetic neurotransmission in normoglycaemic rats, via 5-HT_1B, 5-HT_1D and 5-HT_5A receptor activation. Since type 1 diabetes impairs the cardiac sympathetic innervation leading to cardiopathies, this study aimed to investigate whether the serotonergic influence on cardiac noradrenergic control is altered in type 1 diabetic rats. Diabetes was induced in male Wistar rats by streptozotocin (50 mg/kg, i.p.). Four weeks later, the rats were anaesthetized, pithed and prepared for producing tachycardic responses by electrical preganglionic stimulation (C₇-T₁) of the cardioaccelerator sympathetic outflow or i.v. noradrenaline bolus injections. Immunohistochemistry was performed to study 5-HT_1B, 5-HT_1D and 5-HT_5A receptor expression in the stellate ganglion from normoglycaemic and diabetic rats. In the diabetic group, i) i.v. continuous infusions of 5-HT induced a cardiac sympatho-inhibition that was mimicked by the 5-HT_1/5A agonist 5-carboxamidotryptamine (without modifying noradrenaline-induced tachycardia), but not by the agonists indorenate (5-HT_1A), CP 93,129 (5-HT_1B), PNU 142633 (5-HT_1D), or LY344864 (5-HT_1F); ii) SB 699551 (5-HT_5A antagonist; i.v.) completely reversed 5-CT-induced cardiac sympatho-inhibition; and iii) 5-HT_5A receptors were more expressed in the stellate ganglion compared to normoglycaemic rats. These results show the prominent role of the peripheral 5-HT_5A receptors prejunctionally inhibiting the cardiac sympathetic drive in type 1 diabetic rats.

Metformin and ascorbic acid combination therapy ameliorates type 2 diabetes mellitus and comorbid depression in rats

Diabetes mellitus and depression are the common comorbid disorders affecting humans worldwide. There is an unmet need to develop therapeutic strategies to treat both diabetes mellitus and comorbid depression. The present study evaluated the effectiveness of metformin and ascorbic acid against type 2 diabetes mellitus and comorbid depression in rats. Four groups of diabetic rats were orally administered with vehicle (1mL/kg), metformin (25mg/kg), ascorbic acid (25mg/kg), or combination of metformin (25mg/kg) and ascorbic acid (25mg/kg) for 11 consecutive days. Diabetes was induced by single-dose administration of streptozotocin (65mg/kg, i.p.) with nicotinamide (120mg/kg, i.p.). Comorbid depression was induced by five inescapable foot-shocks (2mA, 2ms duration) at 10s intervals on days 1, 5, 7, and 10. One group of healthy rats received only vehicles to serve as nondiabetic control group. On day 11, animals were sacrificed, and blood and brain samples were collected from each rat following forced swim test. Plasma glucose, insulin, and corticosterone levels were estimated in plasma. The levels of monoamines, proinflammatory cytokines, and oxidative stress were measured in prefrontal cortex. The combination therapy significantly reduced immobility period, glucose, and corticosterone levels relative to diabetes with comorbid depression group. Furthermore, the combination therapy increased the levels of insulin and monoamines, and caused a significant reductions in oxidative stress and proinflammatory cytokines. In conclusion, the present study revealed that metformin and ascorbic acid combination therapy could be a potential strategy to treat type 2 diabetes mellitus and comorbid depression.

Blocking 5-HT2 receptor restores cardiovascular disorders in type 1 experimental diabetes

This study aimed to determine whether the serotonergic modulation, through selective 5-HT₂ receptor blockade, restores cardiovascular disturbances in type 1 diabetic rats. Diabetes was induced by alloxan (150 mg/kg, s.c.) and maintained for 4 weeks. 5-HT₂ receptor was blocked by sarpogrelate (30 mg/kg.day; 14 days; p.o.). Systolic blood pressure (SBP), heart rate (HR), glycaemia and body weight (BW) were monitored periodically. Animals were sacrificed at the end of the study and the heart, right kidney and thoracic aorta were removed; plasma samples were also obtained. Left ventricular hypertrophy index (LVH) and renal hypertrophy index (RH) were determined. Vascular function was studied in aorta rings; additionally, superoxide anion (O₂•⁻) production (by lucigenin-enhanced chemiluminescence) and lipid peroxidation (by thiobarbituric acid reactive substances assay) were measured. Neither alloxan nor sarpogrelate treatments altered HR, LVH or endothelium-independent relaxation. SBP, glycaemia, BW, RH, O₂•⁻ production and lipid peroxidation were significantly altered in diabetic animals compared with controls. Sarpogrelate treatment considerably decreased SBP, RH, O₂•⁻ production and lipid peroxidation. Endothelium-dependent relaxation was severely reduced in diabetic animal aortas compared to controls; sarpogrelate treatment markedly improved it. Our outcomes show that selectively blocking 5-HT₂ receptors has beneficial effects on impaired cardiovascular parameters in diabetes.

Metabolic pathways in the periphery and brain: Contribution to mental disorders?

The association between mental disorders and diabetes has a long history. Recent large-scale, well-controlled epidemiological studies confirmed a link between diabetes and psychiatric illnesses. The scope of this review is to summarize our current understanding of this relationship from a molecular perspective. We first discuss the potential contribution of diabetes-associated metabolic impairments to the etiology of mental conditions. Then, we focus on possible shared molecular risk factors and mechanisms. Simple comorbidity, shared susceptibility loci, and common pathophysiological processes in diabetes and mental illnesses have changed our traditional way of thinking about mental illness. We conclude that schizophrenia and affective disorders are not limited to an imbalance in dopaminergic and serotoninergic neurotransmission in the brain. They are also systemic disorders that can be considered, to some extent, as metabolic disorders.

CHRONIC CAFFEINE'S EFFECTS ON BEHAVIOURAL CHANGES IN STREPTOZOTOCIN-INDUCED DIABETIC RATS

Context

Memory deficits, anxiety and depression are often associated with diabetes, worsening diabetic patients' prognosis. Caffeine, a worldwide used psychoactive substance, is a candidate for improving these conditions.

Objective

The aim of this study was to assess the behaviour in streptozotocin-induced diabetic Wistar rats and to evaluate the behavioural effects of caffeine administration.

Materials and methods

Diabetes was induced by a single intraperitoneal injection of 50 mg/kg BW streptozotocin (n=10), while control rats received the vehicle (n=9). After six weeks, behavioural tests for anxiety, memory and depression were performed: elevated plus maze (EPM) test, novel object recognition (NOR) test and forced swimming test (FST), respectively. The tests were repeated after further 2 weeks of continuous caffeine administration (20 mg/kg BW/day in drinking water).

Results

Diabetic rats manifested a high anxiety level, showed by a reduced exploratory activity compared to control rats (p<0.05) and long-term memory impairment, spending more time near the old object in NOR test. Caffeine administered for 2 weeks did not modify glycemic values in either group, and attenuated the behavioural changes observed in the EPM test. Also, in NOR test for long-term memory, caffeine administration induced an increased time spent with the novel object than with the old one in both groups.

Conclusions

Our data suggest that chronic caffeine administration has an anxiolytic effect in diabetic rats and improves long-term memory in both diabetic and control rats.

Insulin deficiency induces rat renal mesangial cell dysfunction via activation of IGF-1/IGF-1R pathway

AIM

Diabetic nephropathy is one of the major complications of diabetes and the major cause of end-stage renal disease. In this study we investigated the insulin deficiency (ID) induced changes in renal mesangial cells (MCs) and in the kidney of STZ-induced diabetic rats.

METHODS

Cultured rat renal MCs were incubated in ID media. Cell proliferation was analyzed using BrdU incorporation assay. The expression of insulin receptor (IR), insulin-like growth factor-1 receptor (IGF-1R), phosphorylated IGF-1R, fibronectin, and collagen IV was determined with Western blot analysis. STZ-induced diabetic rats were treated with an IGF-1R antagonist picropodophyllin (PPP, 20 mg·kg(-1)·d(-1), po) for 8 weeks. After the rats were euthanized, plasma and kidneys were collected. IGF-1 levels in renal cortex were measured with RT-PCR or ELISA. The morphological changes in the kidneys were also examined.

RESULTS

Incubation in ID media significantly increased cell proliferation, the synthesis of fibronectin and collagen IV, and the expression of IGF-1 and IGF-1R and phosphorylated IGF-1R in renal MCs. Pretreatment of the cells with PPP (50 nmol/L) blocked ID-induced increases in cell proliferation and the synthesis of fibronectin and collagen IV; knockdown of IGF-1R showed a similar effect as PPP did. In contrast, treatment of the cells with IGF-1 (50 ng/mL) exacerbated ID-induced increases in cell proliferation. In the kidneys of diabetic rats, the expression of IGF-1, IGF-1R and phosphorylated IGF-1R were significantly elevated. Treatment of diabetic rats with PPP did not lower the blood glucose levels, but significantly suppressed the expression of TGF-β, fibronectin and collagen IV in the kidneys, the plasma levels of urinary nitrogen and creatinine, and the urinary protein excretion.

CONCLUSION

Insulin deficiency increases the expression of IGF-1 and IGF-1R in renal MCs and the kidney of diabetic rats, which contributes to the development of diabetic nephropathy.

Resveratrol prevents akinesia and restores neuronal tyrosine hydroxylase immunoreactivity in the substantia nigra pars compacta of diabetic rats

This study evaluated the effects of resveratrol on locomotor behaviors, neuronal and glial densities, and tyrosine hydroxylase immunoreactivity in the substantia nigra pars compacta of rats with streptozotocin-induced diabetes. Animals were divided into four groups: non-diabetic rats treated with saline (SAL), non-diabetic rats treated with resveratrol (RSV), diabetic rats treated with saline (DM) and diabetic rats treated with resveratrol (DM+RSV). The animals received oral gavage with resveratrol (20 mg/kg) for 35 days. The open field test and the bar test were performed to evaluate bradykinesia and akinesia, respectively. The Nissl-stained neuronal and glial densities and the dopaminergic neuronal density were estimated using planar morphometry. Tyrosine hydroxylase immunoreactivity was evaluated using regional and cellular optical densitometry. In relation to the locomotor behaviors, it was observed that the DM group developed akinesia, which was attenuated by resveratrol in the DM+RSV group, while the DM and DM+RSV groups showed bradykinesia. Our main morpho-physiological results demonstrated: a decrease in the cellular tyrosine hydroxylase immunoreactivity in the DM group, which was attenuated by resveratrol in the DM+RSV group; a higher neuronal density in the RSV group, when compared to the DM and DM+RSV groups; an increase in the glial density in the DM group, which was also reversed by resveratrol in the DM+RSV group. Resveratrol treatment prevents akinesia development and restores neuronal tyrosine hydroxylase immunoreactivity and glial density in the substantia nigra pars compacta of diabetic rats, suggesting that this polyphenol could be a potential therapeutic option against diabetes-induced nigrostriatal dysfunctions.

Effects of exercise on brain functions in diabetic animal models

Human life span has dramatically increased over several decades, and the quality of life has been considered to be equally important. However, diabetes mellitus (DM) characterized by problems related to insulin secretion and recognition has become a serious health problem in recent years that threatens human health by causing decline in brain functions and finally leading to neurodegenerative diseases. Exercise is recognized as an effective therapy for DM without medication administration. Exercise studies using experimental animals are a suitable option to overcome this drawback, and animal studies have improved continuously according to the needs of the experimenters. Since brain health is the most significant factor in human life, it is very important to assess brain functions according to the different exercise conditions using experimental animal models. Generally, there are two types of DM; insulin-dependent type 1 DM and an insulin-independent type 2 DM (T2DM); however, the author will mostly discuss brain functions in T2DM animal models in this review. Additionally, many physiopathologic alterations are caused in the brain by DM such as increased adiposity, inflammation, hormonal dysregulation, uncontrolled hyperphagia, insulin and leptin resistance, and dysregulation of neurotransmitters and declined neurogenesis in the hippocampus and we describe how exercise corrects these alterations in animal models. The results of changes in the brain environment differ according to voluntary, involuntary running exercises and resistance exercise, and gender in the animal studies. These factors have been mentioned in this review, and this review will be a good reference for studying how exercise can be used with therapy for treating DM.

The effects of antidepressants "fluoxetine and imipramine" on vascular abnormalities and Toll like receptor-4 expression in diabetic and non-diabetic rats exposed to chronic stress

Several studies reveal that diabetes doubles the odds of comorbid depression with evidence of a pro-inflammatory state underlying its vascular complications. Indeed, little information is available about vascular effects of antidepressant drugs in diabetes.

METHOD

We investigated the effect of chronic administration of fluoxetine "FLU" and imipramine "IMIP" on behavioral, metabolic and vascular abnormalities in diabetic and non-diabetic rats exposed to chronic restraint stress (CRS).

RESULTS

Both diabetes and CRS induced depressive-like behavior which was more prominent in diabetic/depressed rats; this was reversed by chronic treatment with FLU and IMIP in a comparable manner. Diabetic and non-diabetic rats exposed to CRS exhibited abnormalities in glucose homeostasis, lipid profile and vascular function, manifested by decreased endothelium-dependent relaxation, increased systolic blood pressure and histopathological atherosclerotic changes. Vascular and metabolic dysfunctions were associated with significant increase in aortic expression of TLR-4, and pro-inflammatory cytokines (TNF-α and IL-1ß). FLU ameliorated these metabolic, vascular and inflammatory abnormalities, while IMIP induced either no change or even worsening of some parameters.

CONCLUSION

FLU has favorable effect over IMIP on metabolic, vascular and inflammatory aberrations associated with DM and CRS in Wistar rats, clarifying the preference of FLU over IMIP in management of comorbid depression in diabetic subjects.

Insulin action in brain regulates systemic metabolism and brain function

Insulin receptors, as well as IGF-1 receptors and their postreceptor signaling partners, are distributed throughout the brain. Insulin acts on these receptors to modulate peripheral metabolism, including regulation of appetite, reproductive function, body temperature, white fat mass, hepatic glucose output, and response to hypoglycemia. Insulin signaling also modulates neurotransmitter channel activity, brain cholesterol synthesis, and mitochondrial function. Disruption of insulin action in the brain leads to impairment of neuronal function and synaptogenesis. In addition, insulin signaling modulates phosphorylation of tau protein, an early component in the development of Alzheimer disease. Thus, alterations in insulin action in the brain can contribute to metabolic syndrome, and the development of mood disorders and neurodegenerative diseases.

Antidepressant effects of insulin in streptozotocin induced diabetic mice: Modulation of brain serotonin system

Diabetes is a persistent metabolic disorder, which often leads to depression as a result of the impaired neurotransmitter function. Insulin is believed to have antidepressant effects in depression associated with diabetes; however, the mechanism underlying the postulated effect is poorly understood. In the present study, it is hypothesized that insulin mediates an antidepressant effect in streptozotocin (STZ) induced diabetes in mice through modulation of the serotonin system in the brain. Therefore, the current study investigated the antidepressant effect of insulin in STZ induced diabetes in mice and insulin mediated modulation in the brain serotonin system. In addition, the possible pathways that lead to altered serotonin levels as a result of insulin administration were examined. Experimentally, Swiss albino mice of either sex were rendered diabetic by a single intraperitoneal (i.p.) injection of STZ. After one week, diabetic mice received a single dose of either insulin or saline or escitalopram for 14days. Thereafter, behavioral studies were conducted to test the behavioral despair effects using forced swim test (FST) and tail suspension test (TST), followed by biochemical estimations of serotonin concentrations and monoamine oxidase (MAO) activity in the whole brain content. The results demonstrated that, STZ treated diabetic mice exhibited an increased duration of immobility in FST and TST as compared to non-diabetic mice, while insulin treatment significantly reversed the effect. Biochemical assays revealed that administration of insulin attenuated STZ treated diabetes induced neurochemical alterations as indicated by elevated serotonin levels and decreased MAO-A and MAO-B activities in the brain. Collectively, the data indicate that insulin exhibits antidepressant effects in depression associated with STZ induced diabetes in mice through the elevation of the brain serotonin levels.

Effect of tempol on the passive avoidance and novel object recognition task in diabetic rats

Diabetes mellitus (DM) has several effects, including cognitive impairment. Oxidative stress is associated with complications from diabetes. It seems that antioxidants can reduce some complications of the diabetes induced by oxidative stress. The objective of this study was to evaluate the effect of synthetic antioxidant, tempol on the passive avoidance (PA) memory and novel object recognition (NOR) tests in the diabetic rats. Forty male Wistar rats randomly divided into the control, diabetic, diabetic receiving tempol and healthy receiving tempol groups. Diabetes was induced by injection of streptozotocin (STZ) (60 mg/kg, i.p.). Then, the rats received saline or tempol (30 mg/kg) orally by gavages for 60 days. After that, they were assessed using the PA memory and NOR tests. The results of NOR test showed that the discrimination index (DI) in the healthy receiving tempol group and diabetic control group was significantly lower than control group. Also the amount of this index in diabetic receiving tempol group was significantly higher than diabetic group. The results of PA test indicated that the number of trials to acquisition in the diabetic rats is significantly more than control and diabetic tempol treated groups. Also, the time spent in the dark compartment (TDC) in the control and diabetic receiving tempol groups was less than diabetic group. TDC in the healthy receiving tempol group was more than control group. It can be concluded that although use of tempol is restricted as a cognitive enhancer in non-diabetic subjects but long-term administration of synthetic antioxidant, tempol, is able to dramatically improve diabetes-induced learning and memory deficit in both PA and NOR tests.

The functional state of hormone-sensitive adenylyl cyclase signaling system in diabetes mellitus

Diabetes mellitus (DM) induces a large number of diseases of the nervous, cardiovascular, and some other systems of the organism. One of the main causes of the diseases is the changes in the functional activity of hormonal signaling systems which lead to the alterations and abnormalities of the cellular processes and contribute to triggering and developing many DM complications. The key role in the control of physiological and biochemical processes belongs to the adenylyl cyclase (AC) signaling system, sensitive to biogenic amines and polypeptide hormones. The review is devoted to the changes in the GPCR-G protein-AC system in the brain, heart, skeletal muscles, liver, and the adipose tissue in experimental and human DM of the types 1 and 2 and also to the role of the changes in AC signaling in the pathogenesis and etiology of DM and its complications. It is shown that the changes of the functional state of hormone-sensitive AC system are dependent to a large extent on the type and duration of DM and in experimental DM on the model of the disease. The degree of alterations and abnormalities of AC signaling pathways correlates very well with the severity of DM and its complications.