Kevin W. Huggins

Central insulin resistance and synaptic dysfunction in intracerebroventricular-streptozotocin injected rodents

To better understand the role of insulin signaling in the development of Alzheimers disease (AD), we utilized an animal model (intracerebroventricular injection of streptozotocin-ic-streptozotocin (STZ)) that displays insulin resistance only in the brain and exhibits AD pathology. In this model, deficits in hippocampal synaptic transmission and long-term potentiation (LTP) were observed. The decline in LTP correlated with decreased expression of NMDAR subunits NR2A and NR2B. The deficits in LTP were accompanied by changes in the expression and function of synaptic AMPARs. In ic-STZ animals, an alteration in integrin-linked kinase (ILK)-glycogen synthase kinase 3 beta (GSK-3-β) signaling was identified (p < 0.05). Similarly, there was decreased expression (p < 0.05) of brain derived neurotropic factor (BDNF) and stargazin, an AMPAR auxiliary subunit; both are required for driving AMPA receptors to the surface of the postsynaptic membrane. Our data illustrate that altered ILK-GSK-3β signaling due to impaired insulin signaling may decrease the trafficking and function of postsynaptic glutamate receptors; thereby, leading to synaptic deficits contributing to memory loss.

Resveratrol Protects the Brain of Obese Mice from Oxidative Damage

Resveratrol (3,5,4′-trihydroxy-trans-stilbene) is a polyphenolic phytoalexin that exerts cardioprotective, neuroprotective, and antioxidant effects. Recently it has been shown that obesity is associated with an increase in cerebral oxidative stress levels, which may enhance neurodegeneration. The present study evaluates the neuroprotective action of resveratrol in brain of obese (ob/ob) mice. Resveratrol was administered orally at the dose of 25 mg kg−1 body weight daily for three weeks to lean and obese mice. Resveratrol had no effect on body weight or blood glucose levels in obese mice. Lipid peroxides were significantly increased in brain of obese mice. The enzymatic antioxidants superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glucose-6-phosphate dehydrogenase and nonenzymatic antioxidants tocopherol, ascorbic acid, and glutathione were decreased in obese mice brain. Administration of resveratrol decreased lipid peroxide levels and upregulated the antioxidant activities in obese mice brain. Our findings indicate a neuroprotective effect of resveratrol by preventing oxidative damage in brain tissue of obese mice.

Consumption of a high glycemic index diet increases abdominal adiposity but does not influence adipose tissue pro-oxidant and antioxidant gene expression in C57BL/6 mice.

The hypothesis of this study is that consumption of a high glycemic index (GI) starch will increase adiposity, increase expression of the pro-oxidant enzyme (nicotinamide adenine dinucleotide phosphate [NADPH] oxidase), and decrease expression of the antioxidant enzymes (catalase, glutathione peroxidase [GPx], and superoxide dismutase [SOD]) in adipose tissue of mice. C57BL/6 mice (n = 5-8/group) were fed a diet containing either high-GI starch (100% amylopectin) or low-GI starch (60% amylose/40% amylopectin) under low-fat (LF) or high-fat (HF) conditions for 16 weeks. Meal tolerance tests (MTTs) indicated that the postprandial blood glucose response over 120 minutes for the high-GI mice under LF and HF conditions was significantly greater than for mice fed low-GI diets. This result was not due to increased food consumption by the high-GI mice during the MTT. Although there was no difference in body weight between mice fed high-GI or low-GI starch, LF high-GI mice had significantly greater adiposity compared to LF low-GI mice. High-fat mice had a significant increase in NADPH oxidase expression compared to LF mice, but there was no significant effect of starch on NADPH oxidase expression. High-fat diet significantly decreased the expression of GPx and catalase, but there was no significant effect of starch on GPx and catalase expression. There was no difference in SOD expression among any of the diet groups. In conclusion, high GI diets increase adiposity under LF conditions but do not influence pro-oxidant or antioxidant enzyme gene expression in adipose tissue of C57BL/6 mice.

Lysosomal dysfunction produces distinct alterations in synaptic α-amino -3 -hydroxy -5 -methylisoxazolepropionic acid and N-Methyl-D-Aspartate receptor currents in hippocampus

The early processes that lead to synaptic dysfunction during aging are not clearly understood. Dysregulation of &agr;-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors may cause age-related cognitive decline. Using hippocampal slice cultures exhibiting lysosomal dysfunction, an early marker of brain aging that is linked to pr otein accumulation, we identified alterations to AMPA and NMDA receptor-mediated synaptic currents. The miniature and spontaneous excitatory postsynaptic currents that were examined after 3, 6, and 9 days of lysosomal disruption showed progressive changes in amplitude, frequency, and rise and decay kinetics. To investigate whether modifications in specific channel properties of single synaptic receptors contributed to changes in the amplitude and time course of synaptic currents, we examined the single channel properties of synaptic AMPA and NMDA receptors. The channel open probability and the mean open times showed decreases in both receptor populations, whereas the closed times were increased without any change in the channel conductance. The Western blot analysis revealed a progressive decline in synaptic markers including glutamate receptor subunits. These results indicate that lysosomal dysfunction leads to progressive functional perturbation of AMPA and NMDA receptors in this slice model of protein accumulation, suggesting that age-related cognitive decline could result from altered glutamate receptor function before reductions in synaptic density.

The pancreas-brain axis: insight into disrupted mechanisms associating type 2 diabetes and Alzheimer's disease.

Epidemiological and observational studies indicate a positive correlation between type 2 diabetes (T2DM) and dementia, with an increased risk of dementia and Alzheimers disease (AD) associated with insulin-treated diabetes patients. The purpose of this review is to reveal the molecular mechanisms that connect physiological and pathological processes commonly observed in T2DM and AD. Conformational modifications in peptide residues, such as amyloid-β peptide in AD and amylin in T2DM have been shown to instigate formation of insoluble protein aggregates that get deposited in extracellular spaces of brain and pancreatic tissue thus disrupting their normal function. Impaired insulin signaling plays a critical role in AD pathogenesis by reducing IRS-associated PI3 kinase activity and increasing GSK-3β activity. GSK-3β has been suggested to be a component of the γ-secretase complex and is involved in amyloid-β protein precursor processing. GSK-3β along with CDK5 is responsible for hyperphosphorylation of tau leading to the formation of neurofibrillary tangles. In summary, there is evidence to believe that a molecular link connects AD and T2DM and has potential for further investigation toward development of an effective therapeutic target.

Design, development and evaluation of novel dual PPARδ/PPARγ agonists.

Type 2 diabetes is at epidemic proportions and thus development of novel pharmaceutical therapies for improving insulin sensitivity has become of paramount importance. The objectives of the current study were to develop novel dual PPARγ/δ agonists without the deleterious side effects associated with full PPARγ agonists. Docking simulations of 23 novel compounds within the ligand binding domain of PPARγ/δ were performed using AutoDock Vina which consistently reproduced experimental binding poses from known PPAR agonists. Comparisons were made and described with other docking programs AutoDock and Surflex-Dock (from SYBYL-X). Biological evaluation of compounds was accomplished by transcriptional promoter activity assays, quantitative PCR gene analysis for known PPARγ/δ targets as well as in vitro assays for lipid accumulation and mitochondrial biogenesis verses known PPAR agonists. We found one (compound 9) out of the 23 compounds evaluated, to be the most potent and selective dual PPARγ/δ agonist which did not display the deleterious side effects associated with full PPARγ agonists.

Guanethidine treatment does not block the ability of central leptin administration to decrease blood glucose concentrations in streptozotocin-induced diabetic rats

Leptin, administered either into the ventricles of the brain or systemically, has been shown to normalize blood glucose concentrations in streptozotocin (STZ)-induced diabetic rats. We hypothesized that an intact sympathetic nervous system is necessary for centrally administered leptin to normalize or attenuate high blood glucose concentrations in STZ-induced diabetic rats. Young male Wistar rats (approximately 50 g) were treated every other day with either s.c. guanethidine (100 mg/kg) or vehicle for 2 weeks. Rats were then implanted with an intracerebroventricular cannula directed to the lateral ventricle and made diabetic with an i.v. injection of STZ (50 mg/kg). Half of the animals in each group were given daily injections of leptin (10 microl), while the remaining animals received vehicle injections. Blood glucose concentrations were measured daily and tissue norepinephrine content was determined by high performance liquid chromatography at the end of the study. Guanethidine pretreatment did not block the ability of centrally administered leptin to decrease blood glucose concentrations in diabetic rats. This suggests that the sympathetic nervous system does not mediate the leptin-induced attenuation of high blood glucose concentrations observed in diabetic rats.

Associations among eating regulation and body mass index, weight, and body fat in college students: The moderating role of gender

This study investigated associations between eating regulation behaviors and body mass index (BMI), weight, and percent body fat in male and female students over the first two years of college. Subjects included 328 college students (215 females and 113 males). Height and weight (via standard techniques), body composition (via bioelectrical impedance analysis), and eating regulation behaviors (using the Regulation of Eating Behavior Scale) were conducted two to three times during both the freshman and sophomore years. Significant associations between eating regulation and BMI, weight, and/or percent body fat were shown mostly in females. In females, higher BMI, weight, and/or percent body fat at the end of the second year of college were found in those with low levels of autonomous, intrinsic motivation, and identified regulation, and high levels of amotivation, while lower BMI, weight, and/or percent body fat were associated with high levels of autonomous, intrinsic motivation, and identified regulation, and low levels of amotivation. The findings that specific eating behaviors in females during the first two years of college influence BMI, weight, and/or percent body fat may be useful for inclusion in university programs focused on college student health to help decrease the risk of obesity and disordered eating/eating disorders in female college students.

Suppression of adipocyte differentiation and lipid accumulation by stearidonic acid (SDA) in 3T3-L1 cells

BackgroundIncreased consumption of omega-3 (ω-3) fatty acids found in cold-water fish and fish oil has been reported to protect against obesity. A potential mechanism may be through reduction in adipocyte differentiation. Stearidonic acid (SDA), a plant-based ω-3 fatty acid, has been targeted as a potential surrogate for fish-based fatty acids; however, its role in adipocyte differentiation is unknown. This study was designed to evaluate the effects of SDA on adipocyte differentiation in 3T3-L1 cells.Methods3T3-L1 preadipocytes were differentiated in the presence of SDA or vehicle-control. Cell viability assay was conducted to determine potential toxicity of SDA. Lipid accumulation was measured by Oil Red O staining and triglyceride (TG) quantification in differentiated 3T3-L1 adipocytes. Adipocyte differentiation was evaluated by adipogenic transcription factors and lipid accumulation gene expression by quantitative real-time polymerase chain reaction (qRT-PCR). Fatty acid analysis was conducted by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS).Results3T3-L1 cells treated with SDA were viable at concentrations used for all studies. SDA treatment reduced lipid accumulation in 3T3-L1 adipocytes. This anti-adipogenic effect by SDA was a result of down-regulation of mRNA levels of the adipogenic transcription factors CCAAT/enhancer-binding proteins alpha and beta (C/EBPα, C/EBPβ), peroxisome proliferator-activated receptor gamma (PPARγ), and sterol-regulatory element binding protein-1c (SREBP-1c). SDA treatment resulted in decreased expression of the lipid accumulation genes adipocyte fatty-acid binding protein (AP2), fatty acid synthase (FAS), stearoyl-CoA desaturase (SCD-1), lipoprotein lipase (LPL), glucose transporter 4 (GLUT4) and phosphoenolpyruvate carboxykinase (PEPCK). The transcriptional activity of PPARγ was found to be decreased with SDA treatment. SDA treatment led to significant EPA enrichment in 3T3-L1 adipocytes compared to vehicle-control.ConclusionThese results demonstrated that SDA can suppress adipocyte differentiation and lipid accumulation in 3T3-L1 cells through down-regulation of adipogenic transcription factors and genes associated with lipid accumulation. This study suggests the use of SDA as a dietary treatment for obesity.

The impact of physical activity on body weight and fat gains during the first 3 years of college

Over two-thirds of students gain weight and body fat during college, especially during the freshman year. This study examined whether participation in physical activity during the first 3 years of college was associated with favorable changes in body weight and percent body fat. Participants included 535 college students (345 females, 190 males). Height and weight (assessed by standard techniques) and body fat (assessed by bioelectrical impedance analysis) were obtained at the beginning of fall semester and at the end of spring semester of each year; in addition during the first 2 years, assessments were also conducted at the end of fall semester for a total of eight assessments between 2007 and 2010. Physical activity participation was self-reported using a questionnaire that included a subset of questions from the National College Health Risk Behavior Survey. While both males and females exhibited significant increases in weight and percent body fat over the 3-year period; for the females, participation in strength training was associated with loss of weight and percent body fat. The results of this study emphasize the benefits of physical activity, especially strength training, for college females as a means to reduce or prevent body weight and fat gains during the first 3 years of college.