Gaurav Chugh

Moderate treadmill exercise prevents oxidative stress-induced anxiety-like behavior in rats.

Recent work has suggested correlation of oxidative stress with anxiety-like behavior. There also is evidence for anxiolytic effects of physical exercise. However, a direct role of oxidative stress in anxiety is not clear and a protective role of physical exercise in oxidative stress-mediated anxiety has never been addressed. In this study, we have utilized rats to test direct involvement of oxidative stress with anxiety-like behavior and have identified oxidative stress mechanisms likely involved in anxiolytic effects of physical exercise. Intraperitoneal injections at non-toxic dose of l-buthionine-(S,R)-sulfoximine (BSO), an agent that increases oxidative stress markers, increased anxiety-like behavior of rats compared to vehicle-treated control rats. Prior 2 weeks treatment with the antioxidant, tempol attenuated BSO-induced anxiety-like behavior of rats suggesting a role of oxidative stress in this phenomenon. Moreover, moderate treadmill exercise prevented BSO-induced anxiety-like behavior of rats and also prevented BSO-mediated increase in oxidative stress markers in serum, urine and brain tissue homogenates from hippocampus, amygdala and locus coeruleus. Thus increasing oxidative stress increases anxiety-like behavior of rats. Moreover, antioxidant or treadmill exercise training both reduce oxidative stress in the rat brain regions implicated in anxiety response and prevent anxiety-like behavior of rats.

Oxidative Stress: A Potential Recipe For Anxiety, Hypertension and Insulin Resistance

We recently reported involvement of oxidative stress in anxiety-like behavior of rats. Others in separate studies have demonstrated a link between oxidative stress and hypertension as well as with type 2 diabetes/insulin resistance. In the present study, we have tested a putative role of oxidative stress in anxiety-like behavior, hypertension and insulin resistance using a rat model of oxidative stress. Oxidative stress in rats was produced by xanthine (0.1%; drinking water) and xanthine oxidase (5 U/kg; i.p.). X+XO-treated rats had increased plasma and urinary 8-isoprostane levels (a marker of oxidative stress) and increased malondialdehyde (MDA) levels in the hippocampus and amygdala as compared to control rats. Serum corticosterone (a systemic marker of stress and anxiety) levels also increased with X+XO treatment. Moreover, anxiety-like behavior measured via open-field and light-dark exploration behavior tests significantly increased in X+XO-treated rats. Mean arterial blood pressure measured in anesthetized rats increased in X+XO-treated compared to control rats. Furthermore, plasma insulin but not glucose levels together with homeostasis model assessment (HOMA), an index of insulin resistance, were higher in X+XO-treated rats. Our studies suggest that oxidative stress is a common factor that link anxiety-like behavior, hypertension and insulin resistance in rats.

Potential Contribution of Oxidative Stress and Inflammation to Anxiety and Hypertension

Previously, we have published that pharmacological induction of oxidative stress causes anxiety-like behavior in rats and also is associated with hypertension in these animals. Here, we report that sub-chronic induction of oxidative stress via pharmacological induction leads to i) reduction in glyoxalase (GLO)-1 and glutathione reductase (GSR)-1 expression; ii) calpain mediated reduction of brain derived neurotrophic factor (BDNF) levels; iii) NFκB mediated upregulation of proinflammatory factors interleukin (IL)-6 and tumor necrosis factor (TNF)-α and elevated angiotensin (AT)-1 receptor levels in hippocampus, amygdala and locus coeruleus regions of the brain. Acute oxidative stress has opposite effects. We speculate that regulation of GLO1, GSR1, BDNF, NFκB and AT-1 receptor may contribute to anxiety-like behavior and hypertension in rats.

Grape Powder Supplementation Prevents Oxidative Stress–Induced Anxiety-Like Behavior, Memory Impairment, and High Blood Pressure in Rats

We examined whether or not grape powder treatment ameliorates oxidative stress-induced anxiety-like behavior, memory impairment, and hypertension in rats. Oxidative stress in Sprague-Dawley rats was produced by using L-buthionine-(S,R)-sulfoximine (BSO). Four groups of rats were used: 1) control (C; injected with vehicle and provided with tap water), 2) grape powder-treated (GP; injected with vehicle and provided for 3 wk with 15 g/L grape powder dissolved in tap water), 3) BSO-treated [injected with BSO (300 mg/kg body weight), i.p. for 7 d and provided with tap water], and 4) BSO plus grape powder-treated (GP+BSO; injected with BSO and provided with grape powder-treated tap water). Anxiety-like behavior was significantly greater in BSO rats compared with C or GP rats (P < 0.05). Grape powder attenuated BSO-induced anxiety-like behavior in GP+BSO rats. BSO rats made significantly more errors in both short- and long-term memory tests compared with C or GP rats (P < 0.05), which was prevented in GP+BSO rats. Systolic and diastolic blood pressure was significantly greater in BSO rats compared with C or GP rats (P < 0.05), whereas grape powder prevented high blood pressure in GP+BSO rats. Furthermore, brain extracellular signal-regulated kinase-1/2 (ERK-1/2) was activated (P < 0.05), whereas levels of glyoxalase-1 (GLO-1), glutathione reductase-1 (GSR-1), calcium/calmodulin-dependent protein kinase type IV (CAMK-IV), cAMP response element-binding protein (CREB), and brain-derived neurotrophic factor (BDNF) were significantly less (P < 0.05) in BSO but not in GP+BSO rats compared with C or GP rats. We suggest that by regulating brain ERK-1/2, GLO-1, GSR-1, CAMK-IV, CREB, and BDNF levels, grape powder prevents oxidative stress-induced anxiety, memory impairment, and hypertension in rats.

Grape Powder Intake Prevents Ovariectomy-Induced Anxiety-Like Behavior, Memory Impairment and High Blood Pressure in Female Wistar Rats

Diminished estrogen influence at menopause is reported to be associated with cognitive decline, heightened anxiety and hypertension. While estrogen therapy is often prescribed to overcome these behavioral and physiological deficits, antioxidants which have been shown beneficial are gaining nutritional intervention and popularity. Therefore, in the present study, utilizing the antioxidant properties of grapes, we have examined effect of 3 weeks of grape powder (GP; 15 g/L dissolved in tap water) treatment on anxiety-like behavior, learning-memory impairment and high blood pressure in ovariectomized (OVX) rats. Four groups of female Wistar rats were used; sham control, sham-GP treated, OVX and OVX+GP treated. We observed a significant increase in systolic and diastolic blood pressure in OVX rats as compared to sham-controls. Furthermore, ovariectomy increased anxiety-like behavior and caused learning and memory impairment in rats as compared to sham-controls. Interestingly, providing grape powder treated water to OVX rats restored both systolic and diastolic blood pressure, decreased anxiety-like behavior and improved memory function. Moreover, OVX rats exhibited an impaired long term potentiation which was restored with grape powder treatment. Furthermore, ovariectomy increased oxidative stress in the brain, serum and urine, selectively decreasing antioxidant enzyme, glyoxalase-1 protein expression in the hippocampus but not in the cortex and amygdala of OVX rats, while grape powder treatment reversed these effects. Other antioxidant enzyme levels, including manganese superoxide dismutase (SOD) and Cu/Zn SOD remained unchanged. We suggest that grape powder by regulating oxidative stress mechanisms exerts its protective effect on blood pressure, learning-memory and anxiety-like behavior. Our study is the first to examine behavioral, biochemical, physiological and electrophysiological outcome of estrogen depletion in rats and to test protective role of grape powder, all in the same study.

Altered Functioning of Both Renal Dopamine D1 and Angiotensin II Type 1 Receptors Causes Hypertension in Old Rats

Activation of renal dopamine D1 (D1R) and angiotensin II type 1 receptors (AT1Rs) influences the activity of proximal tubular sodium transporter Na,K-ATPase and maintains sodium homeostasis and blood pressure. We reported recently that diminished D1R and exaggerated AT1R functions are associated with hypertension in old Fischer 344 × Brown Norway F1 (FBN) rats, and oxidative stress plays a central role in this phenomenon. Here we studied the mechanisms of age-associated increase in oxidative stress on diminished D1R and exaggerated AT1R functions in the renal proximal tubules of control and antioxidant Tempol-treated adult and old FBN rats. Although D1R numbers and D1R agonist SKF38393-mediated stimulation of [35S]-GTP&ggr;S binding (index of D1R activation) were lower, G protein–coupled receptor kinase 4 (kinase that uncouples D1R) levels were higher in old FBN rats. Tempol treatment restored D1R numbers and G protein coupling and reduced G protein–coupled receptor kinase 4 levels in old FBN rats. Angiotensin II–mediated stimulation of [35S]-GTP&ggr;S binding and Na,K-ATPase activity were higher in old FBN rats, which were also restored with Tempol treatment. We also measured renal AT1R function in adult and old Fischer 344 (F344) rats, which, despite exhibiting an age-related increase in oxidative stress and diminished renal D1R function, are normotensive. We found that diuretic and natriuretic responses to candesartan (indices of AT1R function) were similar in F344 rats, a likely explanation for the absence of age-associated hypertension in these rats. Perhaps, alterations in both D1R (diminished) and AT1R (exaggerated) functions are necessary for the development of age-associated hypertension, as seen in old FBN rats.

Oxidative stress alters renal D1 and AT1 receptor functions and increases blood pressure in old rats

Aging is associated with an increase in oxidative stress and blood pressure (BP). Renal dopamine D1 (D1R) and angiotensin II AT1 (AT1R) receptors maintain sodium homeostasis and BP. We hypothesized that age-associated increase in oxidative stress causes altered D1R and AT1R functions and high BP in aging. To test this, adult (3 mo) and old (21 mo) Fischer 344 × Brown Norway F1 rats were supplemented without/with antioxidant tempol followed by determining oxidative stress markers (urinary antioxidant capacity, proximal tubular NADPH-gp91phox, and plasma 8-isoprostane), D1R and AT1R functions, and BP. The D1R and AT1R functions were determined by measuring diuretic and natriuretic responses to D1R agonist (SKF-38393; 1 μg·kg(-1)·min(-1) iv) and AT1R antagonist (candesartan; 10 μg/kg iv), respectively. We found that the total urinary antioxidant capacity was lower in old rats, which increased with tempol treatment. In addition, tempol decreased the elevated NADPH-gp91phox and 8-isoprostane levels in old rats. Systolic, diastolic, and mean arterial BPs were higher in old rats and were reduced by tempol. Although SKF-38393 produced diuresis in both adult and old rats, urinary sodium excretion (UNaV) increased only in adult rats. While candesartan increased diuresis and UNaV in adult and old rats, the magnitude of response was greater in old rats. Tempol treatment in old rats reduced candesartan-induced increase in diuresis and UNaV. Our results demonstrate that diminished renal D1R and exaggerated AT1R functions are associated with high BP in old rats. Furthermore, oxidative stress may cause altered renal D1R and AT1R functions and high BP in old rats.

Inflammation compromises renal dopamine D1 receptor function in rats

We tested the effects of inflammation on renal dopamine D1 receptor signaling cascade, a key pathway that maintains sodium homeostasis and blood pressure during increased salt intake. Inflammation was produced by administering lipopolysaccharide (LPS; 4 mg/kg ip) to rats provided without (normal salt) and with 1% NaCl in drinking water for 2 wk (high salt). Control rats had saline injection and received tap water. We found that LPS increased the levels of inflammatory cytokines, interleukin-6, and tumor necrosis factor-alpha in the rats given either normal- or high-salt intake. Also, these rats had higher levels of oxidative stress markers, malondialdehyde and nitrotyrosine, and lower levels of antioxidant enzyme superoxide dismutase in the renal proximal tubules (RPTs). The nuclear levels of transcription factors NF-kappaB increased and Nrf2 decreased in the RPTs in response to LPS in rats given normal and high salt. Furthermore, D1 receptor numbers, D1 receptor proteins, and D1 receptor agonist (SKF38393)-mediated (35)S-GTPgammaS binding decreased in the RPTs in these rats. The basal activities of Na-K-ATPase in the RPTs were similar in control and LPS-treated rats given normal and high salt. SKF38393 caused inhibition of Na-K-ATPase activity in the primary cultures of RPTs treated with vehicle but not in the cultures treated with LPS. Furthermore, LPS caused an increase in blood pressure in the rats given high salt but not in the rats given normal salt. These results suggest that LPS differentially regulates NF-kappaB and Nrf2, produces inflammation, decreases antioxidant enzyme, increases oxidative stress, and causes D1 receptor dysfunction in the RPTs. The LPS-induced dysfunction of renal D1 receptors alters salt handling and causes hypertension in rats during salt overload.

A High-Salt Diet Further Impairs Age-Associated Declines in Cognitive, Behavioral, and Cardiovascular Functions in Male Fischer Brown Norway Rats

Aging-associated declines in cognitive, emotional, and cardiovascular function are well known. Environmental stress triggers critical changes in the brain, further compromising cardiovascular and behavioral health during aging. Excessive dietary salt intake is one such stressor. Here, we tested the effect of high salt (HS) on anxiety, learning-memory function, and blood pressure (BP) in male Fischer brown Norway (FBN) rats. Adult (A; 2 mo) and old (O; 20 mo) male rats were fed normal-salt (NS; 0.4% NaCl) or HS (8% NaCl) diets for 4 wk after being implanted with telemeter probes for conscious BP measurement. Thereafter, tests to assess anxiety-like behavior and learning-memory were conducted. The rats were then killed, and samples of plasma, urine, and brain tissue were collected. We found that systolic BP was higher in O-NS (117 ± 1.2 mm Hg) than in A-NS (105 ± 0.8 mm Hg) rats (P < 0.05). Furthermore, BP was higher in O-HS (124 ± 1.4 mm Hg) than in O-NS (117 ± 1.2 mm Hg) rats (P < 0.05). Moreover, anxiety-like behavior (light-dark and open-field tests) was not different between A-NS and O-NS rats but was greater in O-HS rats than in A-NS, O-NS, or A-HS rats (P < 0.05). Short-term memory (radial arm water maze test) was similar in A-NS and O-NS rats but was significantly impaired in O-HS rats compared with A-NS, O-NS, or A-HS rats (P < 0.05). Furthermore, oxidative stress variables (in plasma, urine, and brain) as well as corticosterone (plasma) were greater in O-HS rats when compared with A-NS, O-NS, or A-HS rats (P < 0.05). The antioxidant enzyme glyoxalase-1 expression was selectively reduced in the hippocampus and amygdala of O-HS rats compared with A-NS, O-NS, or A-HS rats (P < 0.05), whereas other antioxidant enzymes, glutathione reductase 1, manganese superoxide dismutase (SOD), and Cu/Zn SOD remained unchanged. We suggest that salt-sensitive hypertension and behavioral derangement are associated with a redox imbalance in the brain of aged FBN rats.

Renal dopamine and angiotensin II receptor signaling in age-related hypertension.

Kidneys play a vital role in long-term regulation of blood pressure. This is achieved by actions of many renal and nonrenal factors acting on the kidney that help maintain the bodys water and electrolyte balance and thus control blood pressure. Several endogenously formed or circulating hormones/peptides, by acting within the kidney, regulate fluid and water homeostasis and blood pressure. Dopamine and angiotensin II are the two key renal factors that, via acting on their receptors and counterregulating each others function, maintain water and sodium balance. In this review, we provide recent advances in the signaling cascades of these renal receptors, especially at the level of their cross talk, and discuss their roles in blood pressure regulation in the aging process.