Regulation of heme oxygenase expression by cyclopentenone prostaglandins

The chemistry, biology and pharmacology of the cyclopentenone prostaglandins

The cyclopentenone prostaglandins (CyPGs) are a small group compounds that are a subset of the eicosanoid superfamily, which are metabolites of arachidonic acid as well as other polyunsaturated fatty acids. The CyPGs are defined by a structural feature, namely, a five-membered carbocyclic ring containing an alfa-beta unsaturated keto group. The two most studied members are PGA₂ and 15d-PGJ₂ (15-deoxy-Δ12,14-prostaglandin J₂); other less studied members are PGA₁, Δ¹²-PGJ₂, and PGJ₂. They are involved in a number of biological activities including the ability to resolve chronic inflammation and the growth and survival of cells, particularly those of cancerous or neurological origin. Also, they can activate the prostaglandin DP2 receptor as well as the ligand-dependent transcription factor PPAR-gamma. Their ability to promote the resolution of chronic inflammation makes it of particular interest to have a good understanding of their actions. Since their discovery, the literature on the CyPGs has greatly expanded both in size and in scope; these reports are covered in the current review.

Buyang Huanwu Decoction fraction protects against cerebral ischemia/reperfusion injury by attenuating the inflammatory response and cellular apoptosis

Buyang Huanwu Decoction fraction extracted from Buyang Huanwu Decoction contains saponins of Astragalus, total paeony glycoside and safflower flavones. The aim of this study was to demonstrate the neuroprotective effect and mechanism of Buyang Huanwu Decoction fraction on ischemic injury both in vivo and in vitro. In vivo experiments showed that 50-200 mg/kg Buyang Huanwu Decoction fraction reduced infarct volume and pathological injury in ischemia/reperfusion rats, markedly inhibited expression of nuclear factor-κB and tumor necrosis factor-α and promoted nestin protein expression in brain tissue. Buyang Huanwu Decoction fraction (200 mg/kg) exhibited significant effects, which were similar to those of 100 mg/kg Ginkgo biloba extract. In vitro experimental results demonstrated that 10-100 mg/L Buyang Huanwu Decoction fraction significantly improved cell viability, decreased the release of lactate dehydrogenase and malondialdehyde levels, and inhibited the rate of apoptosis in HT22 cells following oxygen-glucose deprivation. Buyang Huanwu Decoction fraction (100 mg/L) exhibited significant effects, which were similar to those of 100 mg/L Ginkgo biloba extract. These findings suggest that Buyang Huanwu Decoction fraction may represent a novel, protective strategy against cerebral ischemia/reperfusion injury in rats and oxygen-glucose deprivation-induced damage in HT22 cells in vitro by attenuating the inflammatory response and cellular apoptosis.

The evolving landscape of neurotoxicity by unconjugated bilirubin: role of glial cells and inflammation

Unconjugated hyperbilirubinemia is a common condition in the first week of postnatal life. Although generally harmless, some neonates may develop very high levels of unconjugated bilirubin (UCB), which may surpass the protective mechanisms of the brain in preventing UCB accumulation. In this case, both short-term and long-term neurodevelopmental disabilities, such as acute and chronic UCB encephalopathy, known as kernicterus, or more subtle alterations defined as bilirubin-induced neurological dysfunction (BIND) may be produced. There is a tremendous variability in babies' vulnerability toward UCB for reasons not yet explained, but preterm birth, sepsis, hypoxia, and hemolytic disease are comprised as risk factors. Therefore, UCB levels and neurological abnormalities are not strictly correlated. Even nowadays, the mechanisms of UCB neurotoxicity are still unclear, as are specific biomarkers, and little is known about lasting sequelae attributable to hyperbilirubinemia. On autopsy, UCB was shown to be within neurons, neuronal processes, and microglia, and to produce loss of neurons, demyelination, and gliosis. In isolated cell cultures, UCB was shown to impair neuronal arborization and to induce the release of pro-inflammatory cytokines from microglia and astrocytes. However, cell dependent sensitivity to UCB toxicity and the role of each nerve cell type remains not fully understood. This review provides a comprehensive insight into cell susceptibilities and molecular targets of UCB in neurons, astrocytes, and oligodendrocytes, and on phenotypic and functional responses of microglia to UCB. Interplay among glia elements and cross-talk with neurons, with a special emphasis in the UCB-induced immunostimulation, and the role of sepsis in BIND pathogenesis are highlighted. New and interesting data on the anti-inflammatory and antioxidant activities of different pharmacological agents are also presented, as novel and promising additional therapeutic approaches to BIND.

PGD2 and PGE2 regulate gene expression of Prx 6 in primary macrophages via Nrf2

Peroxiredoxin 6 (Prx 6) is a bifunctional enzyme with both glutathione peroxidase and acidic Ca(2+)-independent phospholipase A(2) activities. We have recently shown that exposure of murine bone marrow-derived macrophages to LPS and IFN-γ leads to induction of COX-2 expression and secretion of PGE(2), up-regulating Prx 6 mRNA levels. This study was designed to investigate various prostaglandins (PGs) for their ability to induce gene expression of Prxs, in particular Prx 6, and to determine the underlying regulatory mechanisms. We provide evidence that both conventional and cyclopentenone PGs enhance Prx 6 mRNA expression. Treatment with either activators or inhibitors of adenylate cyclase as well as cAMP analogs indicated that Prx 6 gene expression is regulated by adenylate cyclase in response to PGD(2) or PGE(2). Furthermore, our study revealed that JAK2, PI3K, PKC, and p38 MAPK contribute to the PGD(2)- or PGE(2)-dependent Prx 6 induction. Using stimulated macrophages from Nrf2-deficient mice or activators of Nrf2 and PPARγ, we found that Nrf2, but not PPARγ, is involved in the PG-dependent increase in Prx 6 mRNA expression. In summary, our data suggest multiple signaling pathways of Prx 6 regulation by PGs and identified Nrf2 as a critical player mediating transcriptional induction.

Possible role of heme oxygenase-1 and prostaglandins in the pathogenesis of cerebral malaria: heme oxygenase-1 induction by prostaglandin D(2) and metabolite by a human astrocyte cell line

Astrocytes are the most abundant cells in the central nervous system that play roles in maintaining the blood-brain-barrier and in neural injury, including cerebral malaria, a severe complication of Plasmodium falciparum infection. Prostaglandin (PG) D(2) is abundantly produced in the brain and regulates the sleep response. Moreover, PGD(2) is a potential factor derived from P. falciparum within erythrocytes. Heme oxygenase-1 (HO-1) is catalyzing enzyme in heme breakdown process to release iron, carbon monoxide, and biliverdin/bilirubin, and may influence iron supply to the P. falciparum parasites. Here, we showed that treatment of a human astrocyte cell line, CCF-STTG1, with PGD(2) significantly increased the expression levels of HO-1 mRNA by RT-PCR. Western blot analysis showed that PGD(2) treatment increased the level of HO-1 protein, in a dose- and time-dependent manner. Thus, PGD(2) may be involved in the pathogenesis of cerebral malaria by inducing HO-1 expression in malaria patients.

C-Terminal membrane spanning region of human heme oxygenase-1 mediates a time-dependent complex formation with cytochrome P450 reductase

Heme oxygenase-1 (HO-1) catalyzes the oxidative degradation of heme to biliverdin, carbon monoxide, and free iron in a reaction requiring the interaction of HO-1 with NADPH-cytochrome P450 reductase (CPR). HO-1 is bound to the endoplasmic reticulum by 23 C-terminal amino acids; however, a soluble HO-1 (sHO-1) lacking this membrane spanning region has been extensively studied. The goal of this project was to characterize the effect of the C-terminal hydrophobic domain on formation of the HO-1/CPR complex. Full-length HO-1 was shown to exhibit higher reaction rates than sHO-1, particularly at subsaturating CPR, indicating that the C-terminal region influences HO-1 binding to CPR. The increased activity of HO-1 was attributable to a time-dependent formation of a low K(m) HO-1/CPR complex that was not seen with sHO1. Gel filtration analysis confirmed the formation of multiple high molecular weight complexes in the presence and absence of the synthetic lipid dilauroylphosphatidylcholine (DLPC). However, the largest complex appeared following a 2 h incubation of HO-1 and CPR in DLPC, suggesting that the C-terminal region was required for the high-affinity HO-1/CPR complex formation and membrane incorporation. These data demonstrate that the C-terminal region of HO-1 influenced complex formation and ultimately its affinity for CPR.

Microsomal prostaglandin E synthase-1 inhibition in cardiovascular inflammatory disease

Prostaglandins (PGs), particularly PGE2 and prostacyclin (PGI2), are potent mediators of pain and inflammation. Both atherosclerosis and aortic aneurysm exhibit the hallmarks of inflammation. However, randomized trials of inhibitors of PG synthesis--nonsteroidal anti-inflammatory drugs--reveal that they predispose to cardiovascular risk. This appears to be consequent to inhibition of PGI2 and PGE2 formed by cyclooxygenase-2 (COX-2). Inhibitors of microsomal PGE synthase-1 (mPGES-1) are being developed for relief of pain and interest has focused on their potential impact on the cardiovascular system. Deletion of mPGES-1 retards atherogenesis and limits aortic aneurysm formation in hyperlipidaemic mice. However, it does not predispose to thrombogenesis and has a limited impact on blood pressure compared to inhibition of COX-2. This occurs despite the potential of the suppressed PGE2 in affording cardioprotection via its EP2 and EP4 receptors. However, deletion of mPGES-1 permits rediversion of the PGH2 substrate to other PG synthases and augmented formation of PGI2 and PGD2 mitigates this effect. However, increased PGI2 may also attenuate relief of pain. Pain relief seems likely to be a nuanced indication for mPGES-1 inhibitors, but they have therapeutic potential in syndromes of cardiovascular inflammation, cancer and perhaps in neurodegenerative disease. However, as the products of substrate rediversion vary according to cell type, these drugs may have contrasting impact amongst individuals at varied stages of disease evolution.

ABCB1 (P-glycoprotein) but not ABCC1 (MRP1) is downregulated in peripheral blood mononuclear cells of spontaneously hypertensive rats

Although the kidney is a major target in hypertension, several studies have correlated important immune alterations with the development of hypertension in spontaneously hypertensive rats (SHR), like increased secretion of pro-inflammatory cytokines, inflammatory infiltration in kidneys and thymic atrophy. Because adenosine-triphosphate-binding cassette sub-family B member 1 (ABCB1; P-glycoprotein) and adenosine-triphosphate-binding cassette sub-family C member 1 (ABCC1; multidrug resistance protein 1), two proteins first described in multidrug resistant tumors, physiologically transport several immune mediators and are required for the adequate functioning of the immune system, we aimed to measure the expression and activity of these proteins in peripheral blood mononuclear cells (PBMC), thymocytes, and also kidneys of normotensive Wistar Kyoto rats and SHR. Our results showed that ABCB1, but not ABCC1, activity was diminished (nearly 50%) in PBMC. Moreover, Abcb1b gene was downregulated in PBMC and kidney of SHR and this was not counterbalanced by an upregulation of its homolog Abcb1a, suggesting that the diminished activity is due to downregulation of the gene. No alteration was detected in ABCB1 activity in SHR thymocytes, indicating that this downregulation occurs after lymphocytes leave the primary lymphoid organs. Even though it is not known at present which parameter(s) is(are) responsible for this downregulation, it may contribute for the altered immune response observed in hypertension and to possible altered drug disposition in hypertensive individuals, resulting in greater drug interaction and increased drug toxicity.

PGD(2) DP1 receptor protects brain from ischemia-reperfusion injury

Prostaglandin D(2) is the most abundant prostaglandin in the brain. It has long been described as a modulator of the neuroinflammatory process, but little is known regarding the role of its Galpha(s)-coupled receptor, DP1. Therefore, in this study, the effect of the DP1 receptor on the outcome of cerebral ischemia in wildtype (WT) and DP1 knockout (DP1(-/-)) C57Bl/6 mice was investigated. Ischemia-reperfusion injury was produced by a 90-min occlusion of the right middle cerebral artery followed by a 4-day reperfusion. Infarct size was 49.0 +/- 11.0% larger in DP1(-/-) mice (n = 11; P < 0.01) than in WT mice (n = 9 per group). However, no differences were detected in the relative cerebral blood flow (CBF) or any of the physiological parameters measured (n = 5 per group) or in the large blood vessel anatomy (n = 3 per group). To further address whether the DP1 protective role in the brain could be extended to neurons, mouse primary corticostriatal neuronal cultures were exposed to the DP1-selective agonist, BW245C, which provided dose-dependent protection against excitotoxicity induced by glutamate. Protection was significant at a dose as low as 0.05 microm. The results indicate that the DP1 receptor is neuroprotective in both in vivo and in vitro paradigms. Development of drugs to stimulate the DP1 receptor in brain could provide a new therapeutic strategy against cerebral ischemia and potentially other neurological conditions.

Stimulation of prostaglandin EP2 receptors prevents NMDA-induced excitotoxicity

Prostaglandin E(2) (PGE(2)) plays an important role in inflammation and neurologic disorders. The neuromodulatory effects of PGE(2) are mediated through regulation of four G-protein-coupled receptors known as EP1, EP2, EP3, and EP4. The goal of the current study was to determine whether EP2 receptor activation protects neurons from acute NMDA-mediated excitotoxicity. To examine the effects of EP2 activation, mice were given an injection of the EP2 receptor-selective agonist butaprost (K (i) = 110 nM for EP2 receptor; K (i) > 10,000 for other prostaglandin receptors) in the cerebral ventricle and then an injection of NMDA in the right striatum. After 48 h, a significant reduction in NMDA-induced lesion volume was observed in groups pretreated with butaprost (1-300 nmol/L), with maximal protection at 100 nmol/L (p < 0.001). To determine if EP2-activated protection was specific to neurons, mouse neuronal cultures were treated with butaprost, and cell viability was analyzed after 24 h of NMDA excitotoxicity. The results showed that butaprost significantly increased neuron survival in a dose-dependent fashion. Furthermore, treatment of primary neurons with butaprost significantly increased cAMP levels (p < 0.001). Together, these data reveal that EP2 receptor stimulation mediates neuroprotection against NMDA excitotoxicity both in vivo and in vitro and that butaprost can limit acute brain damage. Development and testing of specific PGE(2) receptor mimetics could lead to a decrease in side effects associated with anti-inflammatory drugs and could help to fight acute and/or chronic neurologic disorders.

Biochemistry of prostaglandins A

This review considers modern concepts on the structural-functional properties and antiproliferative, antitumor, and antiviral effects of cyclopentenone prostaglandins A and mechanisms underlying their actions. Possible directions of pharmacological application of these compounds and their analogs are discussed.

Heme oxygenase-1/carbon monoxide: from basic science to therapeutic applications

The heme oxygenases, which consist of constitutive and inducible isozymes (HO-1, HO-2), catalyze the rate-limiting step in the metabolic conversion of heme to the bile pigments (i.e., biliverdin and bilirubin) and thus constitute a major intracellular source of iron and carbon monoxide (CO). In recent years, endogenously produced CO has been shown to possess intriguing signaling properties affecting numerous critical cellular functions including but not limited to inflammation, cellular proliferation, and apoptotic cell death. The era of gaseous molecules in biomedical research and human diseases initiated with the discovery that the endothelial cell-derived relaxing factor was identical to the gaseous molecule nitric oxide (NO). The discovery that endogenously produced gaseous molecules such as NO and now CO can impart potent physiological and biological effector functions truly represented a paradigm shift and unraveled new avenues of intense investigations. This review covers the molecular and biochemical characterization of HOs, with a discussion on the mechanisms of signal transduction and gene regulation that mediate the induction of HO-1 by environmental stress. Furthermore, the current understanding of the functional significance of HO shall be discussed from the perspective of each of the metabolic by-products, with a special emphasis on CO. Finally, this presentation aspires to lay a foundation for potential future clinical applications of these systems.

Synthetic heteroprostanoids of A- and E-types as novel non-comprehensive inhibitors of adenylyl cyclase in rat hepatocytes

Treatment of rat hepatocyte plasma membranes with five novel synthetic heteroprostanoids of A- and E-types significantly decreased basal activity of adenylyl cyclase. Inhibition of forskolin-stimulated activity of the enzyme was seen as well. The maximal effective concentration for all substances tested was found at approximately 5x10(-6)-1x10(-5) M. The values of half maximal concentration (IC50) for all prostanoids were at the region of 0.7-1.1 microM. Prostanoids belonging to cyclopentenone group A (U-39, U-26) were less active than analogs of 11-deoxy-PGE1 (TA-227, TA-280, and TA-239). The strongest inhibitory effect of adenylyl cyclase activity (more than 3 times) was determined in the presence of prostanoid TA-227 possessing hydrophobic 15-phenyl ring and isoxazol group in omega-chain. The investigation of AC activity in the presence of different concentrations of prostanoids and varying concentrations of Mg x ATP has demonstrated that a non-comprehensive mechanism with particular effect takes place in case of AC inhibition by the heteroprostanoids.

Heme oxygenase and cyclooxygenase in the central nervous system: A functional interplay

Heme oxygenase (HO) and cyclooxygenase (COX) are two hemeproteins involved in the regulation of several functions in the nervous system. Heme oxygenase is the enzyme responsible for the degradation of heme into ferrous iron, carbon monoxide (CO), and biliverdin, the latter being further reduced in bilirubin (BR) by biliverdin reductase. Heme oxygenase-derived CO is a gaseous neuromodulator and plays an important role in the synaptic plasticity, learning and memory processes, as well as in the regulation of hypothalamic neuropeptide release, whereas BR is an endogenous molecules with antioxidant and anti-nitrosative activities. Cyclooxygenase is considered a pro-inflammatory enzyme as free radicals and prostaglandins (PGs) are produced during its catalytic cycle. Although PGs are also involved in a variety of physiologic conditions including angiogenesis, hemostasis, or regulation of kidney function, upregulation of COX and increase in PGs levels are a common feature of neuroinflammation. In the brain, a functional interplay exists between HO and COX. Heme oxygenase regulates COX activity by reducing the intracellular heme content or by generating CO, which stimulates PGE(2) release. Increased levels of PGs, free radicals, and the associated oxidative stress serve in the brain as a trigger for the induction of HO isoforms which increases cellular antioxidant defenses to counteract oxidative damage. The importance of the interaction between HO and COX in the regulation of physiologic brain functions, and its relevance to neuroprotective or neurodegenerative mechanisms are discussed.

PGE1analog alprostadil induces VEGF and eNOS expression in endothelial cells

Endothelial nitric oxide synthase (eNOS), VEGF, and hypoxia-inducible factor 1-α (HIF-1α) are important regulators of endothelial function, which plays a role in the pathophysiology of heart failure (HF). PGE1analog treatment in patients with HF elicits beneficial hemodynamic effects, but the precise mechanisms have not been investigated. We have investigated the effects of the PGE1analog alprostadil on eNOS, VEGF, and HIF-1α expression in human umbilical vein endothelial cells (HUVEC) using RT-PCR and immunoblotting under normoxic and hypoxic conditions. In addition, we studied protein expression by immunohistochemical staining in explanted hearts from patients with end-stage HF, treated or untreated with systemic alprostadil. Alprostadil causes an upregulation of eNOS and VEGF protein and mRNA expression in HUVEC and decreases HIF-1α. Hypoxia potently increased eNOS, VEGF, and HIF-1α synthesis. The alprostadil-induced upregulation of eNOS and VEGF was prevented by inhibition of MAPKs with PD-98056 or U-0126. Consistently, the expression of eNOS and VEGF was increased, and HIF-1α was reduced in failing hearts treated with alprostadil. The potent effects of alprostadil on endothelial VEGF and eNOS synthesis may be useful for patients with HF where endothelial dysfunction is involved in the disease process.

Effects of cyclopentenone prostaglandins on the expression of heme oxygenase-1 in MCF-7 cells

Cyclopentenone prostaglandins (cyPGs) are produced by dehydration of precursor molecules. The cyPGs are reported to have proapoptotic effects in a variety of cell types. However, cyPGs, particularly 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), can also exert cytoprotective effects at relatively low concentrations. The cytoprotective activity of cyPGs appears to be mediated by the reactive alpha,beta-unsaturated carbonyl group located in the cyclopentene ring. In this study, we investigated the effect of cyPGs on the expression of heme oxygenase-1 (HO-1), a ubiquitous stress-responsive enzyme that catalyzes oxidative cleavage of heme to form iron, carbon monoxide, and biliverdin. Treatment of the human breast cancer cell line (MCF-7) with 15d-PGJ(2) resulted in a concentration- and time-dependent increase in the expression of HO-1, whereas prostaglandin A(2) (PGA(2)) and the non-PG derivative 2-cyclopenten-1-one failed to induce HO-1 expression at the protein level. RT-PCR revealed that the expression of HO-1 mRNA was induced at 6 h by 15d-PGJ(2) at 10 microM. However, PGA(2) induced HO-1 mRNA expression at a higher concentration (30 microM). 2-Cyclopenten-1-one did not induce the expression of HO-1 mRNA at all. Likewise, 15d-PGJ(2) treatment for 6 h led to phosphorylation of Akt/protein kinase B (PKB) to a greater extent than that achieved with PGA(2). Thus, the induction of HO-1 expression and the activation of Akt/PKB by 15d-PGJ(2) and PGA(2) are likely to confer cytoprotective or antiapoptotic effects exerted by these cyPGs.

Unique Properties of Polyphenol Stilbenes in the Brain: More than Direct Antioxidant Actions; Gene/Protein Regulatory Activity

The 'French Paradox' has been typically associated with moderate consumption of wine, especially red wine. A polyphenol 3,4',5-trihydroxy-trans-stilbene (a member of the non-flavonoids family), better known as resveratrol, has been purported to have many health benefits. A number of these valuable properties have been attributed to its intrinsic antioxidant capabilities, although the potential level of resveratrol in the circulation is likely not enough to neutralize free radical scavenging. The brain and the heart are uniquely vulnerable to hypoxic conditions and oxidative stress injuries. Recently, evidence suggests that resveratrol could act as a signaling molecule within tissues and cells to modulate the expression of genes and proteins. Stimulation of such proteins and enzymes could explain some the intracellular antioxidative properties. The modulation of genes could suffice as an explanation of some of resveratrol's cytoprotective actions, as well as its influence on blood flow, cell death, and inflammatory cascades. Resveratrol stimulation of the expression of heme oxygenase is one example. Increased heme oxygenase activity has led to significant protection against models of in vitro and in vivo oxidative stress injury. Resveratrol could provide cellular resistance against insults; although more work is necessary before it is prescribed as a potential prophylactic in models of either acute or chronic conditions, such as stroke, amyotrophic lateral sclerosis, Parkinson, Alzheimer, and a variety of age-related vascular disorders.

Characterization of rat heme oxygenase-3 gene. Implication of processed pseudogenes derived from heme oxygenase-2 gene

Heme oxygenase (HO) is an enzyme responsible for the physiological degradation of heme to produce iron, CO and biliverdin. The released iron is recycled and represents the major source of this metal in heme homeostasis. A putative role as messenger in a signaling pathway is suggested for CO. Biliverdin, together with bilirubin, may function as an antioxidant. Thus far, three isoforms of HO, HO-1, HO-2 and HO-3 have been described. While HO-1 and HO-2 have been extensively investigated, HO-3 is still an elusive and poorly understood isoform. In this study, we examined the structure of the rat HO-3 gene with genomic PCR. However, we failed to isolate the reported HO-3 gene but, instead, found two HO-3-related genes, tentatively named HO-3a and HO-3b, whose sequences differed slightly from each other. Neither gene had any introns and consisted only of exon 2 through 5 of the HO-2 gene, though their sequences were not completely identical with that of HO-2. A stop codon was introduced within the coding regions of these genes due to frame-shift. The nucleotide sequence of their 5'-upstream region largely agreed with long interspersed nuclear element 3. No HO-3-related mRNAs were amplified by RT-PCR, and no HO-3-related proteins were detected in tissues by Western blot analysis. Our results suggested that there are no functional HO-3 genes in rat and that the HO-3a and HO-3b genes are processed pseudogenes derived from HO-2 transcripts.