Dapagliflozin Ameliorates Cognitive Impairment in Aluminum-Chloride-Induced Alzheimer's Disease via Modulation of AMPK/mTOR, Oxidative Stress and Glucose Metabolism.

Alzheimer's disease (AD) is a progressive neurological illness characterized by memory loss and cognitive deterioration. Dapagliflozin was suggested to attenuate the memory impairment associated with AD; however, its mechanisms were not fully elucidated. This study aims to examine the possible mechanisms of the neuroprotective effects of dapagliflozin against aluminum chloride (AlCl3)-induced AD. Rats were distributed into four groups: group 1 received saline, group 2 received AlCl3 (70 mg/kg) daily for 9 weeks, and groups 3 and 4 were administered AlCl3 (70 mg/kg) daily for 5 weeks. Dapagliflozin (1 mg/kg) and dapagliflozin (5 mg/kg) were then given daily with AlCl3 for another 4 weeks. Two behavioral experiments were performed: the Morris Water Maze (MWM) and the Y-maze spontaneous alternation (Y-maze) task. Histopathological alterations in the brain, as well as changes in acetylcholinesterase (AChE) and amyloid ß (Aß) peptide activities and oxidative stress (OS) markers, were all evaluated. A western blot analysis was used for the detection of phosphorylated 5' AMP-activated protein kinase (p-AMPK), phosphorylated mammalian target of Rapamycin (p-mTOR) and heme oxygenase-1 (HO-1). Tissue samples were collected for the isolation of glucose transporters (GLUTs) and glycolytic enzymes using PCR analysis, and brain glucose levels were also measured. The current data demonstrate that dapagliflozin represents a possible approach to combat AlCl3-induced AD in rats through inhibiting oxidative stress, enhancing glucose metabolism and activating AMPK signaling.

Role of sodium glucose cotransporter type 2 inhibitors dapagliflozin on diabetic nephropathy in rats; Inflammation, angiogenesis and apoptosis.

AIMS: Diabetic nephropathy is a major cause of chronic kidney disease and end-stage renal failure worldwide. Dapagliflozin Sodium-glucose co-transporter 2 (SGLT2) inhibitor is a new class of diabetic medications prescribed for the treatment of type 2 diabetes. The current study investigates the possible impact of dapagliflozin (DAPA) on inflammations, apoptosis, angiogenesis and fibrosis in early-stage diabetic nephropathy using a rat model of type 2 diabetes. MAIN METHODS: Rats were divided into five groups, group1: normal vehicle group, group 2: diabetic group, group 3: diabetic+ DAPA (0.75 mg/kg), group 4: diabetic+DAPA (1.5 mg/kg), group 5: diabetic+DAPA (3 mg/kg). At the end of the study, Blood glucose level was measured. Serum insulin, BUN, and SCr were measured. Insulin resistance was determined using the homeostasis model assessment for insulin resistance (HOMA-IR) index. Renal tissue homogenization was done for assessment of inflammatory markers TNF-α, PEDF, and PTX-3, In addition to apoptosis markers BCL-2 and BAX. Histopathological examinations were done for tubular renal cells and immunohistochemical examination for fibrosis marker α-SMA and angiogenic factor VEGF. KEY FINDINGS: Treatments with dapagliflozin showed improvements in histopathological examinations, inflammatory and apoptotic markers compared to diabetic vehicles in a dose-dependent manner. SIGNIFICANCE: Thus, dapagliflozin may have renoprotective effects, which be promising in diabetic patients suffered from nephropathy.

The renoprotective effect of glycyrrhizic acid in insulin-resistant rats exposed to aluminum involves the inhibition of TLR4/NF-κB signaling pathway.

Aluminum is well recognized as a nephrotoxic agent. Its hazardous effects arise from the high risk of daily exposure. The consumption of fructose also represents a critical health issue that might negatively impact different organs, including the kidneys. To pursue our previous work, this study aimed to investigate the potential renoprotective effects of glycyrrhizic acid (GLYA) on aluminum-induced nephrotoxicity in insulin-resistant rats. Insulin resistance (IR) was induced by adding fructose (10%) in drinking water for 18 weeks. Male Wistar rats were divided into five groups: control (CTRL), aluminum chloride (ALM, 34 mg/kg/day), fructose (FRCT), aluminum plus fructose (AL/FR), and GLYA (rats received AL/FR and treated with 40 mg/kg GLYA daily). AL/FR resulted in abnormal renal function tests and renal tissue injury. This was associated with increased oxidative stress and inflammation in the renal tissue. Moreover, the expressions of the toll-like receptor 4 (TLR4) and its adaptor proteins were increased in AL/FR group. The administration of GLYA mollified AL/FR-induced renal injury, oxidative stress, activation of the TLR4 signaling pathway, and inflammation. In conclusion, we provide evidence for the promising renoprotective effect of GLYA against AL/FR-induced kidney damage in rats. The renoprotection is attributed to the suppression of oxidative stress and inhibition of the TLR4/NF-κB signaling pathway in the kidneys.

The concurrent exposure to aluminium and fructose induces liver injury in rats: Protection by monoammonium glycyrrhizinate.

Aluminium is a ubiquitous element that occurs naturally in the soil making human exposure to it unavoidable. It is implicated in the aetiology of different neurodegenerative diseases and can induce liver injury. In addition, insulin resistance (IR) plays an essential role in the pathogenesis and the progression of liver disorders. The increased consumption of fructose contained in soft drinks and western pattern diet results in IR that along with the wide distribution of aluminium make the concurrent exposure conceivable and increase the risk of liver injury. Therefore, the present study explores the hepatotoxic effects of aluminium and fructose administered concurrently and evaluates the possible protection by monoammonium glycyrrhizinate (MAG). Liver injury was induced by the administration of aluminium chloride (34 mg/kg/d) plus 10% (w/v) fructose in drinking water. Male rats were treated with either MAG (40 mg/kg/d) or silymarin (SIL, 100 mg/kg/d). The concurrent administration of aluminium and fructose (FRUAL) induced liver injury manifested as a significant elevation of serum liver enzymes activities, bilirubin level, and prothrombin time, as well as reduction of albumin level. On the other hand, the administration of MAG improved the FRUAL-induced aberrations of liver function tests and hepatic cytoarchitecture. We assume that the MAG-induced suppression of oxidative stress, toll-like receptor 4 pathway activation, inflammation, and apoptosis might play a crucial role in the hepatoprotective effect of MAG in this model. Intriguingly, the hepatoprotective effect MAG against FRUAL-induced liver injury surpasses that of the gold standard SIL, suggesting MAG as a better alternative to SIL.

Effect of imidazoline-1 receptor agonists on renal dysfunction in rats associated with chronic, sequential fructose and ethanol administration.

Insulin resistance and chronic alcoholism are risk factors for renal dysfunction. This study investigated the therapeutic effects of two imidazoline-1 receptor (I1R) agonists on renal dysfunction in rats after chronic, sequential fructose and ethanol administration. Daily drinking water was supplemented with fructose (10%, w/v) for 12 weeks and then with ethanol (20%, v/v) for another 8 weeks. Rats were treated with rilmenidine and clonidine in the last two weeks of the study. Blood glucose and serum insulin (sIns) levels, lipid profiles, kidney function and renal histopathology were evaluated at the end of the experiment. Additionally, renal gene expression of nischarin, phosphatidylcholine-specific phospholipase C (PC-PLC) and prostaglandin E2 (PGE2) were measured. Renal levels of superoxide dismutase (SOD), malondialdehyde (MDA), myeloperoxidase (MPO), inducible nitric oxide synthase (iNOS) and total NO (tNO) were detected, and we determined the relative renal gene expression levels of alpha smooth muscle actin (α-SMA), hydroxyproline, interleukin 10 (IL-10), tumour necrosis factor alpha (TNF-α) and caspase-3. The results showed significant deterioration of blood glucose, sIns, lipid profiles, kidney function and renal histopathology in fructose/ethanol-fed rats. Additionally, markers of inflammation, fibrosis, apoptosis and oxidative stress were upregulated. The administration of rilmenidine or clonidine significantly improved blood glucose and sIns levels and reduced renal dysfunction. Our work showed that chronic, sequential fructose and ethanol administration induced fasting hyperglycaemia and renal impairment, and these effects were ameliorated by I1R agonists.

Effects of diosmin and crocin on metabolic syndrome-associated cardio-vascular complications in rats.

This study aims to scrutinize the potential protective effect of diosmin and crocin against cardio-vascular complications attributed to metabolic syndrome (MS). For 16 weeks, the rats were given 10% fructose in water and 3% salt in diet to induce MS over a 16-week period. At week 7 and for 10 weeks, diosmin (50 mg/kg, PO) or crocin (50 mg/kg, PO) was administered daily. Non-invasive blood pressure (BP) was recorded in conscious animals. Thoracic aorta (macro vessels) and kidney (micro vessels) concentration-response curves for phenylephrine (PE) and acetylcholine (ACh) were analyzed. Electrocardiogram (ECG) parameters were recorded. Blood glucose level, serum insulin level, troponin T, advanced glycation end products (AGEs), malondialdehyde (MDA), and tumor necrosis factor-α (TNF-α) were measured. In addition, histological examination of aorta and heart tissues was performed. Diosmin and crocin alleviated cardio-vascular complications associated with MS. This is manifested in improvement of systolic and diastolic BP and ECG parameters. They ameliorated MS-induced exaggerated contractility to PE and improved the impaired dilatation to Ach in macro and micro vasculature. Diosmin and crocin reduced the elevated serum levels of insulin, AGEs, TNF-α, and MDA and reversed MS-induced structural changes of aorta and cardiac tissues. Diosmin and crocin offset the cardiac changes and vascular impairment associated with MS via attenuation of oxidative stress and suppression of inflammation.

Glycyrrhizic acid and silymarin alleviate the neurotoxic effects of aluminum in rats challenged with fructose-induced insulin resistance: possible role of toll-like receptor 4 pathway.

Aluminum is implicated in the etiology of different neurodegenerative diseases, diabetes and cancer. The current study was conducted to evaluate the protective effects of glycyrrhizic acid (GAM) and silymarin (SLY) on AlCl3-induced neurotoxicity in insulin resistant rats. Insulin resistance (IR) was induced by fructose (10%) in drinking water for 18 weeks. Rats received AlCl3 (34 mg/kg/day) with or without fructose, GAM (40 mg/kg/day), or SLY (100 mg/kg/day). The administration of GAM or SLY suppressed AlCl3-induced memory deficit, oxidative stress, and neuroinflammation in brain tissue of IR rats. Both agents inhibited AlCl3-induced activation of TLR4 signaling pathway including the downstream activation of NF-κB. The results show that IR can partly exacerbate AlCl3-induced neurotoxicity, particularly memory deficit and neuroinflammation. In addition, GAM and SLY showed promising neuroprotective effect against AlCl3-induced brain damage in IR rats. The neuroprotection induced by these natural products might be mediated through their antioxidant and anti-inflammatory effects. The latter effect seems to be mediated via inhibition of TLR4 signaling pathway providing new insights on the mechanisms implicated in AlCl3-induced neurotoxicity and the neuroprotection afforded by GAM and SLY.

Beta-caryophyllene protects against diet-induced dyslipidemia and vascular inflammation in rats: Involvement of CB2 and PPAR-γ receptors.

Beta-caryophyllene (BCP) is a phytocannabinoid possessing selective agonistic activity to cannabinoid type-2 receptors (CB2R) and peroxisome proliferator-activated receptors-α (PPAR-α). However, few studies reported the contribution of PPAR-γ receptors in BCP effects. The aim of this study was to investigate the BCP effects on diet-induced dyslipidemia and vascular inflammation as well as the involvement of CB2R and PPAR-γ receptors. Wistar rats were fed a high-fat diet and administered 10% fructose for 12 weeks. Treatment with pioglitazone, BCP, BCP + CB2R antagonist, AM630, or BCP + PPAR-γ antagonist, BADGE was started from the 9th week and continued till the 12th week. BCP significantly ameliorated all diet-induced alterations in a CB2R-dependant manner as it improved glycemic parameters, dyslipidemia, and vascular oxidative stress and inflammation. It also downregulated proatherogenic adhesion molecule (VCAM-1) and restored vascular eNOS/iNOS expression balance. PPAR-γ was involved in BCP-evoked suppression of vascular inflammation, VCAM-1 and restoration of normal vascular eNOS/iNOS balance thus normal NO level. Furthermore, part of BCP hypolipidemic effects (lowering total cholesterol, LDL, VLDL) involved both CB2R and PPAR-γ receptors. BCP treatment was superior to pioglitazone in anti-inflammatory and anti-atherosclerotic measures. BCP may represent a more potent alternate to pioglitazone avoiding its side effects in the treatment of insulin resistance and vascular inflammation.

Beta-caryophyllene alleviates diet-induced neurobehavioral changes in rats: The role of CB2 and PPAR-γ receptors.

BACKGROUND AND PURPOSE: Insulin resistance (IR) and obesity predispose diseases such as diabetes, cardiovascular and neurodegenerative disorders. Beta-caryophyllene (BCP), a natural sesquiterpene, exerts neuroprotective, anxiolytic and antidepressant effects via its selective agonism to cannabinoid receptor 2 (CB2R). BCP was shown to have an anti-diabetic effect, however, the implication of CB2R is yet to be elucidated. A link between CB2R agonism and PPAR-γ activation has been discussed, but the exact mechanism is not well-defined. This study was designed to examine the role of BCP in improving diet-induced metabolic (insulin resistance), neurobehavioral (anxiety, depression and memory deficit), and neurochemical (oxidative, inflammatory and neurotrophic factor) alterations in the prefrontal cortex of obese rats' brain. The involvement of CB2R and/or PPAR-γ dependent activity was also investigated. EXPERIMENTAL APPROACH: Male Wistar rats were fed a high fat/fructose diet (HFFD) for 12 weeks to induce IR and obesity. Rats were treated with BCP for the last 4 weeks. Either CB2R antagonist AM630 or PPAR-γ antagonist BADGE was administered before BCP treatment to study the mechanism of BCP actions. KEY RESULTS: Beta-caryophyllene alleviated HFFD-induced IR, oxidative-stress, neuroinflammation and behavioral changes. The anxiolytic, anti-oxidant and anti-inflammatory effects of BCP were mediated by both PPAR-γ and CB2R. The effects of BCP on glycemic parameters seem to be CB2R-dependent with the non-significant role of PPAR-γ. Furthermore, BCP-evoked antidepressant and memory improvement are likely mediated only via CB2R, mainly by upregulation of PGC-1α and BDNF. CONCLUSION: This study suggests the potential effect of BCP in treating HFFD-induced metabolic and neurobehavioral alterations. BCP seems to activate PPAR-γ in a ligand-independent manner, via upregulation and activation of PGC-1α. The BCP activation of PPAR--γ seems to be CB2R-dependent.

Diosmin and crocin alleviate nephropathy in metabolic syndrome rat model: Effect on oxidative stress and low grade inflammation.

Nephropathy is a serious complication of metabolic syndrome (MS), a global epidemic disorder. This study was undertaken to investigate the actions of diosmin and crocin, two natural ingredients, on diabetic nephropathy in a rat model of MS and the underlying mechanism(s). Metabolic syndrome was induced by the addition of 10% fructose to drinking water and placing the rats on high-salt diet for 16 weeks. Diosmin and Crocin were orally administrated daily for 10 weeks starting at week 6. At the end of study, arterial blood pressure was non-invasively recorded. Urine, serum and kidneys were collected for renal function, oxidative stress, glycemic parameters, inflammatory markers and histological analysis. Both Diosmin and Crocin improved insulin resistance, decreased blood pressure, uric acid, lipoproteins and blocked diabetic nephropathy as indicated by reduction of albumin excretion rate and albumin/creatinine ratio. They alleviated the impaired filtration in MS as indicated by increased creatinine clearance. They also ameliorated oxidative stress and the low-grade 1inflammation as indicated by reduction of serum TNF-α and inflammatory cells. These observations suggest that both Diosmin and Crocin alleviate metabolic syndrome and the associated nephropathy in rats, possibly, through inhibiting oxidative stress and inflammation.

Ameliorative effects of clonidine on ethanol induced kidney injury in rats: Potential role for imidazoline-1 receptor.

Chronic alcoholism is a risk factor for kidney injury. Clonidine is an α2-adrenergic receptor/imidazoline-1 receptor agonist that can reduce blood pressure and maintain renal functions. This study aims to investigate the possible ameliorative effects of clonidine on ethanol induced kidney injury and its mechanism of action. Kidney injury was induced in rats by adding ethanol to drinking water for eight weeks. Clonidine effects on kidney functions and histopathology were measured. Moreover, phentolamine (α-adrenergic receptor antagonist), efaroxan (imidazoline-1 receptor antagonist) and rilmenidine (imidazoline-1 receptor agonist) were used to clarify the role of imidazoline-1 receptor in mediating renal ameliorative effects. Also, the effect of clonidine on liver functions and metabolic changes, in addition to renal oxidative stress, inflammatory and apoptotic pathways were measured. Results showed that, clonidine improved renal functions and reduced ethanol induced renal inflammation and fibrosis. On the other hand, efaroxan, only, blocked clonidine effects on kidney functions. Rilmenidine decreased kidney injury like clonidine. Both clonidine and rilmenidine increased renal nischarin gene expression. Furthermore, clonidine improved liver functions, increased serum insulin and decreased serum advanced glycation end products (metabolic markers). Also, clonidine reduced renal oxidative stress as reflected by decreased myeloperoxidase, malondialdehyde, inducible nitric oxide synthase and total nitric oxide levels and increased superoxide dismutase level. Moreover, clonidine reduced renal tumor necrosis factor-α (inflammatory marker) and caspase-3 (apoptotic marker) levels, while increased renal prostaglandine E2 and interleukin-10 levels (anti-inflammatory markers). In conclusion, clonidine can reduce ethanol induced kidney injury, at least in part, by stimulating imidazoline-1 receptor signaling.

Effect of cardamonin on hepatic ischemia reperfusion induced in rats: Role of nitric oxide.

Ischemia reperfusion (I/R) injury is a cellular damage in a hypoxic organ following the restoration of oxygen delivery. It may occur during organ transplantation, trauma and hepatectomies. Nitric oxide (NO) effects during hepatic I/R are complicated. The iNOS-derived NO has a deleterious effect, whereas eNOS-derived NO has a protective effect in liver I/R. Cardamonin (CDN) is an anti-inflammatory molecule and a novel iNOS inhibitor, and Nω-Nitro-L-arginine (L-NNA) is a NOS inhibitor. L-Arginine is a precursor of NOS. This study was designed to investigate the possible protective effects of CDN on hepatic I/R and the role of NO. Wistar rats were randomly divided into 5 groups (Sham, I/R, CDN, L-NNA and L-arginine). Liver ischemia was induced for 45min then reperfusion was allowed for 1h. L-Arginine and CDN ameliorated the deleterious effects of I/R through reducing the oxidative stress and hepatocyte degeneration. Both molecules decreased the elevated inflammatory cytokines and increased the antiapoptotic marker, Bcl2. Both agents increased NO and eNOS expression and decreased iNOS expression. In conclusion, increased NO/eNOS and suppression of iNOS expression have protective effects on I/R injury. While inhibition of eNOS and reduction of NO have deleterious effects on I/R injury. For the first time, we demonstrated that cardamonin improved functional and structural abnormalities of the liver following I/R by improving oxidative stress and inflammation and increasing the availability of NO produced by eNOS. Treatment with cardamonin could be a promising strategy in patients with hepatic I/R injury in different clinical situations.

Quercetin and tin protoporphyrin attenuate hepatic ischemia reperfusion injury: role of HO-1.

Ischemia reperfusion (IR) injury occurs in many clinical situations such as organ transplantation and hepatectomies resulting in oxidative stress and immune activation. Heme oxygenase-1(HO-1) is the rate-limiting step in the heme-degradation pathway and has a critical cytoprotective role. Induction of HO-1 improves liver I/R injury. Quercetin, a plant pigment (flavonoid), is an antioxidant and HO-1 inducer. Tin protoporphyrin (SnPP) is a HO-1 inhibitor. This study was designed to investigate the protective effect of quercetin in hepatic I/R injury and the role of HO-1. Wister rats were randomly divided into four groups (sham, I/R, quercetin, and SnPP). Liver ischemia was induced for 45 min then reperfusion was allowed for 1 h. Quercetin and surprisingly SnPP ameliorate the deleterious effect of I/R by reducing the oxidative stress and hepatocyte degeneration. Both agents decreased the elevated inflammatory cytokines and improved the inhibition of the antiapoptotic marker, Bcl2. They induced HO-1 content and expression. Quercetin has better cytoprotective effect than SnPP. These findings suggest that quercetin has a hepatoprotective effect against I/R injury via HO-1 induction and unexpectedly, SnPP showed the similar effect. Quercetin has more prominent protective effect than SnPP because of its superior ability to induce HO-1.

The effects of tramadol on hepatic ischemia/reperfusion injury in rats.

OBJECTIVES: Tramadol is a centrally acting synthetic analgesic. It has a cardioprotective effect against myocardial ischemia-reperfusion (I/R) injury in isolated rat heart. We hypothesized that tramadol may exert a similar protective effect on hepatic I/R injury. Hence, the current investigation was designed to study the possible protective effects of tramadol on experimentally-induced hepatic I/R injury in rats. MATERIALS AND METHODS: Tramadol was administered 30 min before ischemia following which the rats were subjected to 45 min of ischemia followed by 1 h of reperfusion. RESULTS: Tramadol attenuated hepatic injury induced by I/R as evidenced by the reduction of transaminases, structural changes, and apoptotic cell death. It decreased the level of inflammatory markers such as tumor necrosis factor-alpha (TNF-α), TNF-α/interleukin-10 (IL-10) ratio, and nuclear factor-κB gene expression. It also increased the anti-inflammatory cytokine, IL-10 levels in hepatic tissues. Furthermore, it reduced oxidative stress parameters except manganese superoxide dismutase activity. CONCLUSION: The results suggest that tramadol has hepatoprotective effects against hepatic I/R injury via anti-inflammatory, antiapoptotic, and antioxidant effects.

Limonin attenuates hepatocellular injury following liver ischemia and reperfusion in rats via toll-like receptor dependent pathway.

Limonin has been shown to exhibit anti-inflammatory and antioxidant properties in the settings of chemically induced hepatic injury. The current study aimed to investigate the protective effects of limonin on experimentally-induced hepatic ischemia reperfusion (I/R) injury in rats. Rats were injected IP with either DMSO or limonin (100 mg/kg BW), 30 min before submission to 45 min of ischemia, followed by 1 h of reperfusion. Limonin ameliorated the deleterious effects of I/R as indicated by improvement in liver function tests, reduction of lactate dehydrogenase, reduction of oxidative stress, decrease in hepatocyte degeneration, and pyknosis. Furthermore, pretreatment of I/R rats with limonin, induced a significant down regulation in the various elements of the toll like receptor (TLR)pathway including TLR-2 and TLR-4, myeloid differentiation factor 88 (MYD88) and toll/IR-1(TIR)-domain-containing adaptor protein inducing interferon-beta (TRIF) and the downstream effectors TNF-α, TNF-α/IL-10 ratio and nuclear factor-κB (NF-κB). It also increased the anti-inflammatory cytokine IL-10 and decreased the activity of the apoptotic marker, caspase-3. These data indicate that limonin exerts antioxidant and anti-inflammatory effects in ischemic liver, thus, protecting hepatocytes against I/R injury in rats. The mechanism of these hepatoprotective effects appears to be related to the antioxidant and anti-inflammatory potential of limonin mediated by the down regulation of TLR- signaling pathway.

Haem oxygenase-1 induction protects against tumour necrosis factor alpha impairment of endothelial-dependent relaxation in rat isolated pulmonary artery.

BACKGROUND AND PURPOSE: Disturbances in pulmonary vascular reactivity are important components of inflammatory lung disease. Haem oxygenase-1 (HO-1) is an important homeostatic enzyme upregulated in inflammation. Here we have investigated the potentially protective effect of HO-1 against cytokine-induced impairment in pulmonary artery relaxation. EXPERIMENTAL APPROACH: Haem oxygenase-1 protein levels were assessed by immunofluorescence. HO activity was assessed by conversion of haemin to bilirubin. Rings of rat isolated pulmonary artery in organ baths were used to measure relaxant responses to the endothelium-dependent agent ACh and the endothelium-independent agent sodium nitroprusside (SNP). Production of nitric oxide (NO) and reactive oxygen species (ROS) was assessed by confocal fluorescence microscopy and fluorescent probes. KEY RESULTS: Haem oxygenase-1 protein expression was strongly induced in pulmonary artery after 24-h incubation with either haemin (5 microM) or curcumin (2 microM), accompanied by a significant increase in HO activity. Incubation with tumour necrosis factor alpha (TNFalpha, 1 ng.mL(-1), 2 h) significantly decreased relaxation of arterial rings to ACh, without affecting responses to SNP. Induction of HO-1 by curcumin or haemin protected against TNFalpha-induced hyporesponsiveness to ACh. The competitive HO inhibitor, tin protoporphyrin (20 microM), abolished the protective effect of haemin. HO-1 induction prevented a TNFalpha-induced increase in NO generation without affecting the TNFalpha-induced increase in ROS generation. HO-1 induction prevented the TNFalpha-induced decrease in ACh-stimulated NO generation. CONCLUSIONS AND IMPLICATIONS: Induction of HO-1 protected against TNFalpha impairment of endothelium-dependent relaxation in pulmonary artery, by a mechanism involving a reduction in inducible NO synthase-derived NO production.