Effect of High-Salt Diet on Age-Related High Blood Pressure and Hypothalamic Redox Signaling.

AIM: The aim of this study was to investigate the effect of a high salt (HS) diet on age-related changes in blood pressure (BP) and the possible role played by regulatory central mechanisms. METHODS: Young (5 months) and old (27 months) male Fischer 344 × Brown Norway (F344/BN) rats were fed standard chow or 8% HS diet for 12 days. BP and heart rate (HR) were measured by telemetry. RESULTS: Mean arterial BP (MAP) was significantly elevated in old rats during the day and night when compared with young animals. The HS diet further elevated MAP in both age groups, and the increase was more pronounced in the old animals, while HR was not altered by age or HS diet. In addition, cardiovascular responses to restraint stress were diminished in the old when compared with the young and were unchanged with HS diet in either age group. Both age and the HS diet elevated the adrenomedullary mRNA levels of tyrosine hydroxylase, an indicator for sympathoexcitation. HS diet enhanced intracerebroventricular angiotensin II (AngII)-induced BP and HR elevations in both age groups. AngII type 1 receptor mRNA increased significantly in the hypothalamus with age and HS diet. Furthermore, hypothalamic p22phox mRNA and gp91phox protein, subunits of NADPH oxidase, as well as NADPH oxidase activity increased with the HS diet in the old animals, whereas antioxidant enzymes that decreased with age yet remained unaltered with the HS diet. CONCLUSION: Our findings indicate that sensitivity of BP to HS diet increases with age, and that central AngII-induced pressor responses are diminished in old rats compared with the young both under control conditions and during HS diet treatment. These changes are paralleled by increases in the expression and NADPH oxidase activity in the hypothalamus, possibly leading to central oxidative stress-mediated sympathoexcitation and high BP.

Anorexic response to rapamycin does not appear to involve a central mechanism.

The authors have previously demonstrated that a low and intermittent peripheral dose of rapamycin (1 mg/kg three times/week) to rats inhibited mTORC1 signalling, but avoided the hyperlipidemia and diabetes-like syndrome associated with higher doses of rapamycin. The dosing regimen reduced food intake, body weight, adiposity, serum leptin and triglycerides. mTORC1 signalling was inhibited in both liver and hypothalamus, suggesting some of the actions, in particular the decrease in food intake, may be the results of a central mechanism. To test this hypothesis, rapamycin (30 µg/day for 4 weeks) was infused into 23-25-month-old F344xBN rats by intracerebroventricular (icv) mini pumps. Our results demonstrated that central infusion did not alter food intake or body weight, although there was a tendency for a decrease in body weight towards the end of the study. mTORC1 signalling, evidenced by decreased phosphorylation of S6 protein at end of 4 weeks, was not activated in liver, hypothalamus or hindbrain. Fat and lean mass, sum of white adipose tissues, brown adipose tissue, serum glucose, insulin and leptin levels remained unchanged. Thus, these data suggest that the anorexic and body weight responses evident with peripheral rapamycin are not the result of direct central action. The tendency for decreased body weight towards the end of study, suggests that there is either a slow transport of centrally administered rapamycin into the periphery, or that there is delayed action of rapamycin at sites in the brain.

The effects of enalapril and losartan on mechanical ventilation-induced sympathoadrenal activation and oxidative stress in rats.

BACKGROUND: Mechanical ventilation (MV) is a method of maintaining appropriate gas exchange in patients who are unable to sustain adequate alveolar ventilation. While lifesaving in the short-term, prolonged MV leads to altered cardiovascular responses and enhanced lung injury, but the exact mechanism is unknown. Therefore, we investigated the involvement of the sympathoadrenergic and renin-angiotensin system in MV-induced altered cardiovascular responses. METHODS: Sprague-Dawley rats were divided into six groups: (1) spontaneous breathing (SB); (2) SB + enalapril (100 µg/kg intravenous infusion); (3) SB + losartan (100 µg/kg infusion); (4) 12 h of MV; (5) MV + enalapril; and (6) MV + losartan. After the animals were sacrificed, blood and tissue samples were collected. Tyrosine hydroxylase, dopamine beta hydroxylase, and neuropeptide Y were measured in adrenal medulla and hypothalamus, whereas AT1 was measured in lung tissues by Western blot. Norepinephrine enzyme-linked immunosorbent assay and total antioxidant capacity were assayed in plasma. RESULTS: Our findings indicated that MV increases the sympathetic activation markers in adrenal medulla and hypothalamus. Moreover, oxidative stress was increased in lung and brain tissues. Treatment with enalapril or losartan reduced the lipid peroxidation in lung and brain tissues, while preserving the tissue glutathione content and plasma antioxidant capacity. CONCLUSIONS: These data demonstrate that the inhibition of the renin-angiotensin system by enalapril or losartan may reduce the MV-induced increase in sympathetic activity markers and oxidative stress, and thus, may have a beneficial effect as adjuvant therapy.

Effect of age on high-fat diet-induced hypertension.

Aging and obesity both have a significant impact on central blood pressure (BP) regulation, and previous studies indicated that changes in central redox signaling with age may affect high-fat (HF) diet-induced cardiovascular responses. Therefore, we investigated the effects of 60% HF feeding on BP regulation in young adult (5 mo) and old (26 mo) Fischer-344 × Brown-Norway rats. Radiotelemetric transmitters were implanted to measure BP, heart rate (HR), locomotor activity, and spontaneous baroreflex sensitivity. Expression and activity of NADPH oxidase and ANG II type 1 receptor were assessed in the hypothalamus and in the nucleus tractus solitarii. Old animals gained more weight on HF diet compared with young, whereas central NADPH oxidase expression and activity elevated similarly in the two age groups. After an initial hypotensive and tachycardic response during the first week of HF feeding, BP in young animals increased and became significantly elevated after 6 wk of HF feeding. In contrast, BP in old animals remained depressed. Nighttime HR and locomotor activity decreased in both young and old rats fed with HF diet, but these changes were more significant in young rats. As a result, amplitudes of circadian variation of BP, HR, and activity that were originally higher in young rats declined significantly and became similar in the two age groups. In conclusion, our experiments led to the surprising finding that HF diet has a more serious impact on cardiovascular regulation in young animals compared with old.

Lifelong caloric restriction prevents age-induced oxidative stress in the sympathoadrenal system of Fischer 344 x Brown Norway rats.

Aging is associated with oxidative damage and an imbalance in redox signaling in a variety of tissues, yet little is known about the extent of age-induced oxidative stress in the sympathoadrenal system. Lifelong caloric restriction has been shown to lower levels of oxidative stress and slow the aging process. Therefore, the aims of this study were twofold: (1) to investigate the effect of aging on oxidative stress in the adrenal medulla and hypothalamus and (2) determine if lifelong 40% caloric restriction (CR) reverses the adverse effects of age-induced oxidative stress in the sympathetic adrenomedullary system. Adult (18months) and very old (38months) male Fischer 344 x Brown Norway rats were divided into ad libitum or 40% CR groups and parameters of oxidative stress were analyzed in the adrenal medulla and the hypothalamus. A significant age-dependent increase in lipid peroxidation (+20%, P<0.05) and tyrosine nitration (+111%, P<0.001) were observed in the adrenal medulla while age resulted in a reduction in the protein expression of key antioxidant enzymes, CuZnSOD (-27%, P<0.01) and catalase (-27%, P<0.05) in the hypothalamus. Lifelong CR completely prevented the age-induced increase in lipid peroxidation in the adrenal medulla and restored the age-related decline in antioxidant enzymes in the hypothalamus. These data indicate that aging results in a significant increase in oxidative stress in the sympathoadrenal system. Importantly, lifelong CR restored the age-related changes in oxidative stress in the adrenal medulla and hypothalamus. Caloric restriction could be a potential non-pharmacological intervention to prevent increased oxidative stress in the sympathetic adrenomedullary system with age.

Overpressure blast injury-induced oxidative stress and neuroinflammation response in rat frontal cortex and cerebellum.

BACKGROUND & AIM: Overpressure blast-wave induced brain injury (OBI) and its long-term neurological outcome pose significant concerns for military personnel. Our aim is to investigate the mechanism of injury due to OBI. METHODS: Rats were divided into 3 groups: (1) Control, (2) OBI (exposed 30psi peak pressure, 2-2.5ms), (3) Repeated OBI (r-OBI) (three exposures over one-week period). Lung and brain (cortex and cerebellum) tissues were collected at 24h post injury. RESULTS: The neurological examination score was worse in OBI and r-OBI (4.2±0.6 and 3.7±0.5, respectively) versus controls (0.7±0.2). A significant positive correlation between lung and brain edema was found. Malondialdehyde (index for lipid peroxidation), significantly increased in OBI and r-OBI groups in cortex (p<0.05) and cerebellum (p<0.01-0.001). The glutathione (endogenous antioxidant) level decreased in cortex (p<0.01) and cerebellum (p<0.05) of r-OBI group when compared with the controls. Myeloperoxidase activity indicating neutrophil infiltration, was significantly (p<0.01-0.05) elevated in r-OBI. Additionally, tissue thromboplastin activity, a coagulation marker, was elevated, indicating a tendency to bleed. NGF and NF-κB proteins along with Iba-1 and GFAP immunoreactivity significantly augmented in the frontal cortex demonstrating microglial activation. Serum biomarkers of injury, NSE, TNF-alpha and leptin, were also elevated. CONCLUSION: OBI triggers both inflammation and oxidative injury in the brain. This data in conjunction with our previous observations suggests that OBI triggers a cascade of events beginning with impaired cerebral vascular function leading to ischemia and chronic neurological consequences.

ACE2 activator diminazene aceturate reduces adiposity but preserves lean mass in young and old rats.

The obesity epidemic is multi-generational and is particularly debilitating in the aging population, necessitating the use of pharmaceutical interventions. Recent evidence suggests that increasing the activity of the angiotensin converting enzyme-2 [ACE2]/angiotensin-(1-7)[Ang-(1-7)]/Mas receptor (MasR) axis in obese animal models leads to significant reductions in body weight. It was hypothesized that activation of ACE2 via diminazene aceturate (DIZE) will significantly reduce body weight of rats fed a high fat diet. Young and old (4 and 23 months, respectively) male Fisher 344 × Brown Norway rats were fed 60% high fat diet for one week, and subsequently given either 15 mg/kg/day DIZE s.c. or vehicle for three weeks. DIZE treatment resulted in a significant reduction of food intake and body weight in both young and old animals. However, that decrease was so dramatic in the older animals that they all nearly stopped eating. Interestingly, the TD-NMR assessments revealed that the weight-loss was primarily a result of decreased body fat percentage, with a relative preservation of lean mass. Tissue weights confirm the significant loss of white adipose tissue (WAT), with no change in muscle weights. Gene expression and serum ACE2 activity analyses implied that increased activation of the ACE2/Ang-(1-7)/MasR axis plays a role in reducing fat mass. Collectively, our results suggest that DIZE may be a useful tool in the study of obesity; however, caution is recommended when using this compound in older animals due to severe anorectic effects, although there is a mechanism by which muscle is preserved.

Intracerebroventricular tempol administration in older rats reduces oxidative stress in the hypothalamus but does not change STAT3 signalling or SIRT1/AMPK pathway.

Hypothalamic inflammation and increased oxidative stress are believed to be mechanisms that contribute to obesity. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (tempol), a free radical scavenger, has been shown to reduce inflammation and oxidative stress. We hypothesized that brain infusion of tempol would reduce oxidative stress, and thus would reduce food intake and body weight and improve body composition in rats with age-related obesity and known elevated oxidative stress. Furthermore, we predicted an associated increase in markers of leptin signalling, including the silent mating type information regulator 2 homolog 1 (SIRT1)/5'AMP-activated protein kinase (AMPK) pathway and the signal transducer and activator of transcription 3 (STAT3) pathway. For this purpose, osmotic minipumps were placed in the intracerebroventricular region of young (3 months) and aged (23 months) male Fischer 344 x Brown Norway rats for the continuous infusion of tempol or vehicle for 2 weeks. Tempol significantly decreased (p < 0.01) nicotinamide adenine dinucleotide phosphate oxidase activity in the hypothalamus but failed to reduce food intake or weight gain and did not alter body composition. SIRT1 activity and Acetyl p53 were decreased and phosphorylation of AMPK was increased with age, but they were unchanged with tempol. Basal phosphorylation of STAT3 was unchanged with age or tempol. These results indicate that tempol decreases oxidative stress but fails to alter feeding behaviour, body weight, or body composition. Moreover, tempol does not modulate the SIRT1/AMPK/p53 pathway and does not change leptin signalling. Thus, a reduction in hypothalamic oxidative stress is not sufficient to reverse age-related obesity.

Altered potassium ATP channel signaling in mesenteric arteries of old high salt-fed rats.

PURPOSE: Both aging and the consumption of a high salt diet are associated with clear changes in the vascular system that can lead to the development of cardiovascular disease; however the mechanisms are not clearly understood. Therefore, we examined whether aging and the consumption of excess salt alters the function of potassium ATP-dependent channel signaling in mesenteric arteries. METHODS: Young (7 months) and old (29 months) Fischer 344 x Brown Norway rats were fed a control or a high salt diet (8% NaCl) for 12 days and mesenteric arteries were utilized for vascular reactivity measurements. RESULTS: Acetylcholine-induced endothelium relaxation was significantly reduced in old arteries (81 ± 4%) when compared with young arteries (92 ± 2%). Pretreatment with the potassium-ATP channel blocker glibenclamide reduced relaxation to acetylcholine in young arteries but did not alter dilation in old arteries. On a high salt diet, endothelium dilation to acetylcholine was significantly reduced in old salt arteries (60 ± 3%) when compared with old control arteries (81 ± 4%). Glibenclamide reduced acetylcholine-induced dilation in young salt arteries but had no effect on old salt arteries. Dilation to cromakalim, a potassium-ATP channel opener, was reduced in old salt arteries when compared with old control arteries. CONCLUSION: These findings demonstrate that aging impairs endothelium-dependent relaxation in mesenteric arteries. Furthermore, a high salt diet alters the function of potassium-ATP-dependent channel signaling in old isolated mesenteric arteries and affects the mediation of relaxation stimuli.

Age Impaired endothelium-dependent vasodilation is improved by resveratrol in rat mesenteric arteries.

PURPOSE: To determine whether resveratrol improves the adverse effects age on vascular function in mesenteric arteries (MAs), and diminishes the hyperactivity in adrenal gland with age. METHODS: Male F344 x Brown Norway rats were assigned to 6-month control (YC), 6-month resveratrol (YR), 24-month control (OC) and 24-month resveratrol (OR). Resveratrol (15 mg/kg) was provided to resveratrol groups in drinking water for 14 days. RESULTS: Concentration response curves to phenylephrine (PE, 10(-9)-10(-5)M), acetylcholine (Ach, 10(-9)-10(-5)M) and resveratrol (10(-8)-10(-4)M) were evaluated in pressurized isolated MAs. The Ach concentration-response curve was right shifted with maximal response diminished in OC compared with YC rats. These effects were reversed by resveratrol treatment. The resveratrol-mediated relaxant responses were unchanged with age or resveratrol suggesting an endothelium-independent mechanism. Resveratrol tended to increase endothelial nitric oxide synthase; caused no effect on copper-zinc superoxide dismutase; and normalized the age-related elevatation in DßH and NPY levels in adrenal medulla, two indicators of sympathetic activity. CONCLUSION: These data indicate that resveratrol reverses age-related dysfunction in endothelium-dependent vasodilation in MAs and partially reverses hyperactivity of adrenomedullary function with age. This treatment may have a therapeuticpotential in the treatment of cardiovascular diseases or hypertension in the elderly.

Rapamycin Normalizes Serum Leptin by Alleviating Obesity and Reducing Leptin Synthesis in Aged Rats.

This investigation examines whether a low intermittent dose of rapamycin will avoid the hyperlipidemia and diabetes-like syndrome associated with rapamycin while still decreasing body weight and adiposity in aged obese rats. Furthermore, we examined if the rapamycin-mediated decrease in serum leptin was a reflection of decreased adiposity, diminished leptin synthesis, or both. To these ends, rapamycin (1mg/kg) was administered three times a week to 3 and 24-month old rats. Body weight, food intake, body composition, mTORC1 signaling, markers of metabolism, as well as serum leptin levels and leptin synthesis in adipose tissue were examined and compared to that following a central infusion of rapamycin. Our data suggest that the dosing schedule of rapamycin acts on peripheral targets to inhibit mTORC1 signaling, preferentially reducing adiposity and sparing lean mass in an aged model of obesity resulting in favorable outcomes on blood triglycerides, increasing lean/fat ratio, and normalizing elevated serum leptin with age. The initial mechanism underlying the rapamycin responses appears to have a peripheral action and not central. The peripheral rapamycin responses may communicate an excessive nutrients signal to the hypothalamus that triggers an anorexic response to reduce food consumption. This coupled with potential peripheral mechanism serves to decrease adiposity and synthesis of leptin.

Rapamycin Versus Intermittent Feeding: Dissociable Effects on Physiological and Behavioral Outcomes When Initiated Early and Late in Life.

Rapamycin, an inhibitor of the mammalian target of rapamycin pathway, has been shown to increase mammalian life span; less is known concerning its effect on healthspan. The primary aim of this study was to examine rapamycin's role in the alteration of several physiological and behavioral outcomes compared with the healthspan-inducing effects of intermittent feeding (IF), another life-span-enhancing intervention. Male Fisher 344 × Brown Norway rats (6 and 25 months of age) were treated with rapamycin or IF for 5 weeks. IF and rapamycin reduced food consumption and body weight. Rapamycin increased relative lean mass and decreased fat mass. IF failed to alter fat mass but lowered relative lean mass. Behaviorally, rapamycin resulted in high activity levels in old animals, IF increased levels of "anxiety" for both ages, and grip strength was not significantly altered by either treatment. Rapamycin, not IF, decreased circulating leptin in older animals to the level of young animals. Glucose levels were unchanged with age or treatment. Hypothalamic AMPK and pAMPK levels decreased in both older treated groups. This pattern of results suggests that rapamycin has more selective and healthspan-inducing effects when initiated late in life.

Onset of leptin resistance shows temporal differences related to dose or pulsed treatment.

Leptin administration results in leptin resistance presenting a significant barrier to therapeutic use of leptin. Consequently, we examined two hypotheses. The first examined the relationship between leptin dose and development of physiological and biochemical signs of leptin resistance. We hypothesized lower doses of leptin would produce proportional reductions in body weight without the adverse leptin-induced leptin resistance. The second compared pulsed central leptin infusion to continuous leptin infusion. We hypothesized that pulsed infusion at specific times of the day would evoke favorable body weight reductions while tempering the development of leptin-induced leptin resistance. The first experiment examined leptin responsiveness, including food intake, body weight and hypothalamic STAT3 phosphorylation to increasing doses of viral gene delivery of leptin. Varying the dose proved inconsequential with respect to long-term therapy and demonstrated proportional development of leptin resistance. The second experiment examined leptin responsiveness to pulsed central leptin infusion, comparing pulsed versus constant infusion of 3µg/day leptin or a 2h morning versus a 2h evening pulsed leptin infusion. Pulsed delivery of the supramaximal dose of 3µg/day was not different than constant delivery. Morning pulsed infusion of the submaximal dose of 0.25µg reduces food intake only over subsequent immediate meal period and was associated with body weight reductions, but results in cellular leptin resistance. Evening pulsed infusion did not decrease food intake but reduces body weight and maintains full leptin signaling. The positive benefit for pulsed delivery remains speculative, yet potentially may provide an alternative mode of leptin therapy.

Overpressure blast-wave induced brain injury elevates oxidative stress in the hypothalamus and catecholamine biosynthesis in the rat adrenal medulla.

Explosive overpressure brain injury (OBI) impacts the lives of both military and civilian population. We hypothesize that a single exposure to OBI results in increased hypothalamic expression of oxidative stress and activation of the sympatho-adrenal medullary axis. Since a key component of blast-induced organ injury is the primary overpressure wave, we assessed selective biochemical markers of autonomic function and oxidative stress in male Sprague Dawley rats subjected to head-directed overpressure insult. Rats were subjected to single head-directed OBI with a 358kPa peak overpressure at the target. Control rats were exposed to just noise signal being placed at ~2m distance from the shock tube nozzle. Sympathetic nervous system activation of the adrenal medullae (AM) was evaluated at 6h following blast injury by assessing the expression of catecholamine biosynthesizing enzymes, tyrosine hydroxylase (TH), dopamine-ß hydroxylase (DßH), neuropeptide Y (NPY) along with plasma norepinephrine (NE). TH, DßH and NPY expression increased 20%, 25%, and 91% respectively, following OBI (P<0.05). Plasma NE was also significantly elevated by 23% (P<0.05) following OBI. OBI significantly elevated TH (49%, P<0.05) in the nucleus tractus solitarius (NTS) of the brain stem while AT1 receptor expression and NADPH oxidase activity, a marker of oxidative stress, was elevated in the hypothalamus following OBI. Collectively, the increased levels of TH, DßH and NPY expression in the rat AM, elevated TH in NTS along with increased plasma NE suggest that single OBI exposure results in increased sympathoexcitation. The mechanism may involve the elevated AT1 receptor expression and NADPH oxidase levels in the hypothalamus. Taken together, such effects may be important factors contributing to pathology of brain injury and autonomic dysfunction associated with the clinical profile of patients following OBI.

Assessing neuro-systemic & behavioral components in the pathophysiology of blast-related brain injury.

Among the U.S. military personnel, blast injury is among the leading causes of brain injury. During the past decade, it has become apparent that even blast injury as a form of mild traumatic brain injury (mTBI) may lead to multiple different adverse outcomes, such as neuropsychiatric symptoms and long-term cognitive disability. Blast injury is characterized by blast overpressure, blast duration, and blast impulse. While the blast injuries of a victim close to the explosion will be severe, majority of victims are usually at a distance leading to milder form described as mild blast TBI (mbTBI). A major feature of mbTBI is its complex manifestation occurring in concert at different organ levels involving systemic, cerebral, neuronal, and neuropsychiatric responses; some of which are shared with other forms of brain trauma such as acute brain injury and other neuropsychiatric disorders such as post-traumatic stress disorder. The pathophysiology of blast injury exposure involves complex cascades of chronic psychological stress, autonomic dysfunction, and neuro/systemic inflammation. These factors render blast injury as an arduous challenge in terms of diagnosis and treatment as well as identification of sensitive and specific biomarkers distinguishing mTBI from other non-TBI pathologies and from neuropsychiatric disorders with similar symptoms. This is due to the "distinct" but shared and partially identified biochemical pathways and neuro-histopathological changes that might be linked to behavioral deficits observed. Taken together, this article aims to provide an overview of the current status of the cellular and pathological mechanisms involved in blast overpressure injury and argues for the urgent need to identify potential biomarkers that can hint at the different mechanisms involved.

Microwave-assisted preparations of amidrazones and amidoximes.

In an operationally straightforward and efficient method, amidrazones and amidoximes are prepared in yields of 65-87% from imidoylbenzotriazoles by microwave heating for 5-20 min with the appropriate hydrazine or hydroxylamine.

Efficient synthesis of polysubstituted acylguanidines and guanylureas.

(Benzotriazol-1-yl)carboximidamides were applied for the preparation of polysubstituted acylguanidines and guanylureas. The reaction sequence utilized mild conditions and gave high yields for final compounds and intermediates. The protocol developed allows for variation of the substituents at all positions of the products.

Solid-phase preparation of amides using N-acylbenzotriazoles.

Wang resin linked amines were efficiently converted into amides using acylbenzotriazoles. Cleavage of resins gave the desired amides 7Aa-Gf in 30-99% yields with good to excellent purities.

Facile N-derivatization of alpha-amino esters and amides via benzotriazolylmethyl derivatives.

Alpha-(N-substituted amino)esters were prepared in a two-step procedure from available unsubstituted alpha-amino esters. alpha-Amino esters are first converted into the corresponding N-benzotriazolylmethyl derivatives; in the second step, the benzotriazole group is substituted by various nucleophiles with or without the presence of a Lewis acid to give substituted alpha-amino esters in high overall yield under mild conditions with no signs of racemization. Boc-protected amino acids were converted into alpha-amino amides; subsequent deprotection allowed the conversion into N-substituted derivatives analogously to the alpha-amino esters, without racemization in high yields under mild conditions.