HIGH-DENSITY LIPOPROTEINS REDUCE THE INTESTINAL DAMAGE ASSOCIATED WITH ISCHEMIA/REPERFUSION AND COLITIS

Molecular Mechanisms Underlying Intestinal Ischemia/Reperfusion Injury: Bioinformatics Analysis and In Vivo Validation

Background

Intestinal ischemia/reperfusion (I/R) injury is a serious clinical complication. This study aimed to explore the hub genes and pathways of intestinal I/R injury.

Material/Methods

GSE96733 from the GEO website was extracted to analyze the differentially expressed genes (DEGs) of intestinal I/R injured and sham-operated mice at 3 h and 6 h after surgery. The DAVID and STRING databases were used to construct functional enrichment analyses of DEGs and the protein–protein interaction (PPI) network. In Cytoscape software, cytoHubba was used to identify hub genes, and MCODE was used for module analysis. Testing by qRT-PCR detected the expression of hub genes in intestinal I/R injury. Western blot analysis detected the key proteins involved with the important pathways of intestinal I/R injury.

Results

IL-6, IL-10, CXCL1, CXCL2, and IL-1β were identified as critical upregulated genes, while IRF7, IFIT3, IFIT1, Herc6, and Oasl2 were identified as hub genes among the downregulated genes. The qRT-PCR testing showed the expression of critical upregulated genes was significantly increased in intestinal I/R injury (P<0.05), while the expression of hub downregulated genes was notably reduced (P<0.05). The proteins of CXCL1 and CXCR2 were upregulated following intestinal I/R injury (P<0.05) and the CXCL1/CXCR2 axis was involved with intestinal I/R injury.

Conclusions

The results of the present study identified IL-6, IL-10, CXCL1, CXCL2, IL-1β, IRF7, IFIT3, IFIT1, Herc6, and Oasl2 as hub genes in intestinal I/R injury and identified the involvement of the CXCL1/CXCR2 axis in intestinal I/R injury.

High-Density Lipoproteins Decrease Proinflammatory Activity and Modulate the Innate Immune Response

Atherosclerosis, a chronic inflammatory disease of the arterial wall, is the leading cause of cardiac disorders and stroke. The onset and progression of these diseases are linked with the inflammatory response, especially NLRP3 inflammasome activation, inducing the production of proinflammatory cytokines, such as interleukin 1β (IL-1β). Because high-density lipoproteins (HDLs) have shown significant antiatherogenic and anti-inflammatory properties, we evaluated their immunomodulatory activity in response to cholesterol crystals and other innate immune activators. Human primary monocyte-derived macrophages, THP-1 cells, and murine macrophages were stimulated to activate NLRP3 inflammasome and other pattern recognition receptors, in the presence or absence of HDL. Then, HDL immunomodulatory effects were evaluated through IL-1β and IL-6 production by enzyme-linked immunosorbent assay. Furthermore, in vivo HDL anti-inflammatory effects were evaluated in a murine model of peritoneal inflammatory infiltration. HDLs have an immunomodulatory effect on different cellular models, including peripheral blood mononuclear cells, THP-1 cells, and murine macrophages, by affecting the activity of innate immunity sensors, such as Toll-like receptors (TLRs), dectin-1, and inflammasomes. HDL reduces the proinflammatory role of cholesterol crystals, nigericin, and other NLRP3 and AIM2 inflammasome agonists, and several TLR agonists, leading to a decreased production of IL-1β and IL-6. The results suggest that HDLs are highly important in the regulation of the innate immune response and may have a beneficial role in controlling diseases associated with the inflammatory response.

Protective Effects of HDL Against Ischemia/Reperfusion Injury

Several lines of evidence suggest that, besides being a strong independent predictor of the occurrence of primary coronary events, a low plasma high density lipoprotein (HDL) cholesterol level is also associated with short- and long-term unfavorable prognosis in patients, who have recovered from a myocardial infarction, suggesting a direct detrimental effect of low HDL on post-ischemic myocardial function. Experiments performed in ex vivo and in vivo models of myocardial ischemia/reperfusion (I/R) injury have clearly shown that HDL are able to preserve cardiac function when given before ischemia or at reperfusion; the protective effects of HDL against I/R injury have been also confirmed in other tissues and organs, as brain and hind limb. HDL were shown to act on coronary endothelial cells, by limiting the increase of endothelium permeability and promoting vasodilation and neoangiogenesis, on white blood cells, by reducing their infiltration into the ischemic tissue and the release of pro-inflammatory and matrix-degrading molecules, and on cardiomyocytes, by preventing the activation of the apoptotic cascade. Synthetic HDL retains the cardioprotective activity of plasma-derived HDL and may become a useful adjunctive therapy to improve clinical outcomes in patients with acute coronary syndromes or undergoing coronary procedures.

Anti-inflammatory Function of High-Density Lipoproteins via Autophagy of IκB Kinase

BACKGROUND & AIMS

Plasma levels of high-density lipoprotein (HDL) cholesterol are frequently found decreased in patients with inflammatory bowel disease (IBD). Therefore, and because HDL exerts anti-inflammatory activities, we investigated whether HDL and its major protein component apolipoprotein A-I (apoA-I) modulate mucosal inflammatory responses in vitro and in vivo.

METHODS

The human intestinal epithelial cell line T84 was used as the in vitro model for measuring the effects of HDL on the expression and secretion of tumor necrosis factor (TNF), interleukin-8 (IL-8), and intracellular adhesion molecule (ICAM). Nuclear factor-κB (NF-κB)-responsive promoter activity was studied by dual luciferase reporter assays. Mucosal damage from colitis induced by dextran sodium sulphate (DSS) and 2,4,6-trinitrobenzenesulfonic acid (TNBS) was scored by colonoscopy and histology in apoA-I transgenic (Tg) and apoA-I knockout (KO) and wild-type (WT) mice. Myeloperoxidase (MPO) activity and TNF and ICAM expression were determined in intestinal tissue samples. Autophagy was studied by Western blot analysis, immunofluorescence, and electron microscopy.

RESULTS

HDL and apoA-I down-regulated TNF-induced mRNA expression of TNF, IL-8, and ICAM, as well as TNF-induced NF-κB-responsive promoter activity. DSS/TNBS-treated apoA-I KO mice displayed increased mucosal damage upon both colonoscopy and histology, increased intestinal MPO activity and mRNA expression of TNF and ICAM as compared with WT and apoA-I Tg mice. In contrast, apoA-I Tg mice showed less severe symptoms monitored by colonoscopy and MPO activity in both the DSS and TNBS colitis models. In addition, HDL induced autophagy, leading to recruitment of phosphorylated IκB kinase to the autophagosome compartment, thereby preventing NF-κB activation and induction of cytokine expression.

CONCLUSIONS

Taken together, the in vitro and in vivo findings suggest that HDL and apoA-I suppress intestinal inflammation via autophagy and are potential therapeutic targets for the treatment of IBD.

Deletion of scavenger receptor A gene in mice resulted in protection from septic shock and modulation of TLR4 signaling in isolated peritoneal macrophages

Scavenger receptor A (Sra), also known as macrophage scavenger receptor 1 (Msr1), is a surface glycoprotein preferentially present in macrophages that plays a primary role in innate immunity. Previous studies have shown that Sra is a modifier gene for the response to bacterial LPS in mice at the level of IL-10 production, in particular. In the present study, we found that Sra(-/-) mice are more resistant to septic shock induced by cecal ligation and puncture than wild-type C57BL/6 J (B6) mice. In addition, Sra(-/-) mice displayed initial elevated high density lipoprotein (HDL) circulating levels. Naïve peritoneal macrophages (PMs) were isolated from Sra(-/-) mice to understand the possible protective mechanism. Incubation of these cells with LPS was found to modulate TLR4 signaling, leading to a reduction in IL-10 and IL-6 mRNA levels, but not TNF-α expression, at low concentrations of LPS in comparison with PMs isolated from B6 mice. No differences were found in LPS binding between PMs derived from Sra(-/-) or B6 mice. The lack of Sra binding to LPS was confirmed after transfection of Chinese hamster ovary (CHO) cells with the Sra gene. The contribution of Sra to the outcome of sepsis may be a combination of changes in TLR4 signaling pathway and elevated levels of HDL in circulation, but also LPS toxicity.

HDL-replacement therapy: mechanism of action, types of agents and potential clinical indications

HDL-replacement therapy is a promising new treatment strategy involving the acute administration of HDL to rapidly stabilize patients at imminent risk for developing a myocardial infarction, such as those with acute coronary syndrome. This review will first focus on the anti-atherogenic mechanisms for HDL, such as the stimulation of the reverse cholesterol transport pathway, and then discuss the other potential beneficial biological effects of HDL on atherosclerosis. The various types of HDL-replacement therapies that are being investigated and developed will be reviewed and ongoing clinical trials and other possible clinical indications for HDL-replacement therapy besides the prevention of myocardial infarction will also be described. Finally, HDL-replacement therapy will be put into perspective by summarizing the current gaps in our knowledge of HDL metabolism and identifying challenges for future research in this area.

Proteomic analysis of the winter-protected phenotype of hibernating ground squirrel intestine

The intestine of hibernating ground squirrels is protected against damage by ischemia-reperfusion (I/R) injury. This resistance does not depend on the low body temperature of torpor; rather, it is exhibited during natural interbout arousals that periodically return hibernating animals to euthermia. Here we use fluorescence two-dimensional difference gel electrophoresis (DIGE) to identify protein spot differences in intestines of 13-lined ground squirrels in the sensitive and protected phases of the circannual hibernation cycle, comparing sham-treated control animals with those exposed to I/R. Protein spot differences distinguished the sham-treated summer and hibernating samples, as well as the response to I/R between summer and hibernating intestines. The majority of protein changes among these groups were attributed to a seasonal difference between summer and winter hibernators. Many of the protein spots that differed were unambiguously identified by high-pressure liquid chromatography followed by tandem mass spectrometry of their constituent peptides. Western blot analysis confirmed significant upregulation for three of the proteins, albumin, apolipoprotein A-I, and ubiquitin hydrolase L1, that were identified in the DIGE analysis as increased in sham-treated hibernating squirrels compared with sham-treated summer squirrels. This study identifies several candidate proteins that may contribute to hibernation-induced protection of the gut during natural torpor-arousal cycles and experimental I/R injury. It also reveals the importance of enterocyte maturation in defining the hibernating gut proteome and the role of changing cell populations for the differences between sham and I/R-treated summer animals.

Anti-inflammatory and cardioprotective activities of synthetic high-density lipoprotein containing apolipoprotein A-I mimetic peptides

Apolipoprotein A-I (apoA-I) mimetic peptides may represent an alternative to apoA-I for large-scale production of synthetic high-density lipoproteins (sHDL) as a therapeutic agent. In this study, the cardioprotective activity of sHDL made with either L37pA peptide or its d-stereoisomer, D37pA, was compared to sHDL made with apoA-I. The peptides were reconstituted with palmitoyl-oleoyl-phosphatidylcholine, which yielded sHDL particles comparable to apoA-I sHDL in diameter, molecular weight, and alpha-helical content. Pretreatment of endothelial cells with either peptide sHDL reduced tumor necrosis factor alpha-stimulated vascular cell adhesion molecule-1 expression to the same extent as apoA-I sHDL. In an isolated rat heart model of ischemia/reperfusion (I/R) injury, L37pA and D37pA sHDL significantly reduced postischemic cardiac contractile dysfunction compared to the saline control, as indicated by a 49.7 +/- 6.4% (L37pA; P < 0.001) and 53.0 +/- 9.1% (D37pA; P < 0.001) increase of left ventricular-developed pressure (LVDP) after reperfusion and by a 45.4 +/- 3.4% (L37pA; P < 0.001) and 49.6 +/- 2.6% (D37pA; P < 0.001) decrease of creatine kinase (CK) release. These effects were similar to the 51.3 +/- 3.0% (P < 0.001) increase of LVDP and 51.3 +/- 3.0 (P < 0.001) reduction of CK release induced by apoA-I sHDL. Consistent with their cardioprotective effects, all three types of sHDL particles mediated an approximate 20% (P < 0.001) reduction of cardiac tumor necrosis factor alpha (TNFalpha) content and stimulated an approximate 35% (P < 0.05) increase in postischemic release of prostacyclin. In summary, L37pA and D37pA peptides can form sHDL particles that retain a similar level of protective activity as apoA-I sHDL on the endothelium and the heart; thus, apoA-I mimetic peptides may be useful therapeutic agents for the prevention of cardiac I/R injury.

Modifying the anti-inflammatory effects of high-density lipoprotein

The anti-inflammatory effects of high-density lipoproteins (HDL) are well documented and include inhibition of low-density lipoprotein (LDL) oxidation, reduction of inflammatory cytokines and vascular leukocyte adhesion molecules, and participation in innate immunity. However, certain conditions, including coronary disease, diabetes mellitus, systemic inflammation, and a diet high in saturated fat, are associated with modification of HDL such that it paradoxically enhances LDL oxidation and/or vascular inflammation. Treatment with statins and/or apolipoprotein A1 mimetic peptides improves HDL's anti-inflammatory functions, and these as well as other medications may represent a novel pathway through which to target atherosclerosis.

High-density lipoproteins: a therapeutic target for atherosclerotic cardiovascular disease

Despite great progress being made during the last two decades in cardiovascular disease prevention, especially by lowering low-density lipoprotein-cholesterol with statins, cardiovascular events continue to occur. Plasma high-density lipoprotein (HDL) exerts multiple protective effects on the arterial wall, through promotion of reverse cholesterol transport, prevention of endothelial dysfunction and inhibition of lipid oxidation. Therapeutic interventions raising plasma HDL levels or directly mimicking its beneficial effects represent the next frontier in the prevention and treatment of cardiovascular disease.

Functionally defective high-density lipoprotein: a new therapeutic target at the crossroads of dyslipidemia, inflammation, and atherosclerosis

High-density lipoproteins (HDL) possess key atheroprotective biological properties, including cellular cholesterol efflux capacity, and anti-oxidative and anti-inflammatory activities. Plasma HDL particles are highly heterogeneous in physicochemical properties, metabolism, and biological activity. Within the circulating HDL particle population, small, dense HDL particles display elevated cellular cholesterol efflux capacity, afford potent protection of atherogenic low-density lipoprotein against oxidative stress and attenuate inflammation. The antiatherogenic properties of HDL can, however be compromised in metabolic diseases associated with accelerated atherosclerosis. Indeed, metabolic syndrome and type 2 diabetes are characterized not only by elevated cardiovascular risk and by low HDL-cholesterol (HDL-C) levels but also by defective HDL function. Functional HDL deficiency is intimately associated with alterations in intravascular HDL metabolism and structure. Indeed, formation of HDL particles with attenuated antiatherogenic activity is mechanistically related to core lipid enrichment in triglycerides and cholesteryl ester depletion, altered apolipoprotein A-I (apoA-I) conformation, replacement of apoA-I by serum amyloid A, and covalent modification of HDL protein components by oxidation and glycation. Deficient HDL function and subnormal HDL-C levels may act synergistically to accelerate atherosclerosis in metabolic disease. Therapeutic normalization of attenuated antiatherogenic HDL function in terms of both particle number and quality of HDL particles is the target of innovative pharmacological approaches to HDL raising, including inhibition of cholesteryl ester transfer protein, enhanced lipidation of apoA-I with nicotinic acid and infusion of reconstituted HDL or apoA-I mimetics. A preferential increase in circulating concentrations of HDL particles possessing normalized antiatherogenic activity is therefore a promising therapeutic strategy for the treatment of common metabolic diseases featuring dyslipidemia, inflammation, and premature atherosclerosis.

Lipoproteins in inflammation and sepsis. I. Basic science

BACKGROUND

High-density lipoproteins (HDL) have been shown to bind and neutralize lipopolysaccharide (LPS) and are regarded as possible therapeutic agents for sepsis and conditions associated with local or systemic inflammation. However, in recent years, a multitude of possible immunomodulatory properties other than LPS neutralization have become evident.

DISCUSSION

This review highlights the advances in the understanding of how HDL is protective in both in vitro and in vivo inflammatory settings, including the ability of HDL to modulate adhesion molecule expression, upregulate endothelial nitric oxide synthase and counteract oxidative stress. Also, the active components of HDL and the recent discovery of novel lipid modulators of inflammation are discussed.

THALIDOMIDE TREATMENT REDUCES THE ALTERATION OF PARACELLULAR BARRIER FUNCTION IN MICE ILEUM DURING EXPERIMENTAL COLITIS

Small intestine permeability is frequently altered in inflammatory bowel diseases and may be caused by the translocation of intestinal toxins through leaky small intestine tight junctions (TJs) and adherence. Thus, the aim of the present study was to examine the effects of thalidomide treatment on the permeability and structure of small intestine TJs in an animal model of experimental colitis induced by dinitrobenzene sulfonic acid (DNBS). Four days after colitis induction with DNBS, the ileal TJs were studied by means of transmission electron microscopy using lanthanum nitrate and immunohistochemistry of occludin and zonula occludens 1. When compared with DNBS-treated mice, thalidomide-treated (200 mg/kg orally starting 30 min after the administration of DNBS) mice subjected to DNBS-induced colitis experienced a significantly reduced rate of the extent and severity of the histological signs of colon injury associated with a significant reduction of plasma and colon tumor necrosis factor alpha levels. After administration of DNBS to the mice induced a significant increase of ileal permeability was observed. Distal colitis in mice induced an increase of TJ permeability throughout the entire small intestine, and the extent of alterations correlates with colonic damage. In particular, we have observed that thalidomide treatment resulted in a significant reduction of the following: (1) the degree of colon injury, (2) the alteration of zonula occludens 1 and occludin localization (immunohistochemistry), and (3) intestinal permeability caused by DNBS in the colon. Taken together, our results clearly show that thalidomide treatment reduced small intestinal permeability in experimental colitis through the regulation of TJ protein.

Glutamine regulates the expression of proteins with a potential health-promoting effect in human intestinal Caco-2 cells

Glutamine is an essential amino acid for the enterocytes with respect to maintaining the gut mucosal integrity and function. This study was conducted to explore a molecular basis for the beneficial effects of glutamine on intestinal cells by searching for glutamine-dependent changes in the proteome. Caco-2 cells were exposed to different concentrations of L-glutamine with or without L-methionine sulfoximine, an inhibitor of the glutamine synthetase activity. 2-DE combined with MALDI-TOF-MS was used to identify proteins whose expression is changed by glutamine. To assess the relative protein synthesis rate, incorporation of L-[2H5]glutamine into individual proteins was monitored. The expression levels of 14 proteins changed significantly with the glutamine availability. Examples of differentially expressed proteins with potential health-promoting effects on the intestine are plasma retinol-binding protein, ornithine aminotransferase, apolipoprotein A-I, mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase, and acyl-CoA synthetase 5. Expression of these proteins was not changed by arginine deprivation. The differential change in the expression levels of the proteins was not correlated with their rate of synthesis, excluding an effect of glutamine depletion on general protein synthesis. Together, this study shows a gene-specific effect of glutamine on intestinal cells.

ROLE OF ENDOGENOUS PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR-α (PPAR-α) LIGANDS IN THE DEVELOPMENT OF GUT ISCHEMIA AND REPERFUSION IN MICE

The peroxisome proliferator-activated receptor-alpha (PPAR-alpha) is a member of the nuclear receptor superfamily of ligand-dependent transcription factors related to retinoid, steroid, and thyroid hormone receptors. The aim of the present study was to examine the effects of endogenous PPAR-alpha ligand on the development of gut ischemia and reperfusion injury. Splanchnic artery occlusion (SAO) shock was induced in mice by clamping both the superior mesenteric artery and the celiac artery for 30 min, followed thereafter by release of the clamp (reperfusion). At 60 min after reperfusion, animals were sacrificed for histological examination and biochemical studies. SAO-shocked WT mice developed a significant increase of ileum tissue, TNF-alpha, IL-1beta, myeloperoxidase activity, and marked histological injury. SAO shock was also associated with a significant mortality (0% survival at 24 h after reperfusion). Reperfused ileum tissue sections from SAO-shocked WT mice showed positive staining for P-selectin, ICAM-1, TNF-alpha, and IL-1beta. Absence of a functional PPAR-alpha gene in PPAR-alphaKO mice resulted in a significant augmentation of all the above-described parameters. Thus, endogenous PPAR-alpha ligands reduce the degree of ileum injury caused by ischemia and reperfusion.

High-Density Lipoprotein Function

Although high-density lipoproteins (HDL) possess many features that contribute to the association between elevated HDL cholesterol and protection from atherosclerosis, these lipoproteins may be modified in certain individuals and/or circumstances to become proinflammatory. The ability of HDL to inhibit or paradoxically to enhance vascular inflammation, lipid oxidation, plaque growth, and thrombosis reflects changes in specific enzyme and protein components. The anti-inflammatory and proinflammatory functional properties of HDL can now be assessed using cell-based and cell-free assays. Acute or chronic systemic inflammation and the metabolic syndrome appear to render HDL proinflammatory. In contrast, statins and experimental agents such as apolipoprotein A-1 mimetics render HDL more anti-inflammatory. Functional characterization of HDL is a promising method for enhanced assessment of cardiovascular risk and effectiveness of risk reduction.

Lipids for psychiatrists - an overview

Serum cholesterol is a major risk factor for cardiovascular disease. Total cholesterol, LDL cholesterol and triglycerides are positively related to cardiovascular disease, while HDL cholesterol has an inverse relationship. Measurement of lipids is essential in individuals with established cardiovascular disease or type 2 diabetes, and may also be carried out in healthy individuals as part of cardiovascular risk assessment. Lifestyle measures are important in cardiovascular disease prevention, but the mainstay of lipid lowering therapy is appropriate use of lipid lowering drugs. Total and LDL cholesterol are the primary targets for treatment, but consideration should also be given to raising HDL cholesterol and lowering triglycerides where appropriate. Statins are the most frequently used lipid lowering agents, but there is an important place for other drugs, including ezetimibe, fibrates and nicotinic acid.

Atheroprotective Effects of High-Density Lipoprotein-Associated Lysosphingolipids

Numerous epidemiological studies document an inverse relationship between plasma high-density lipoprotein (HDL) levels and the extent of atherosclerotic disease. The atheroprotective effects of HDL are more and more often seen in conjunction with the ability of HDL to restrict proinflammatory processes and thereby to carry out cytoprotection and organoprotection. Lysosphingolipids such as sphingosine 1 phosphate, sphingosylphosphorylcholine, and lysosulfatide are biologically active compounds that have recently been found to be associated with HDL particles. An increasing body of evidence suggests that several anti-inflammatory effects exerted by HDL can be attributed to the presence of lysosphingolipids in this lipoprotein fraction. In this review, we discuss the latest developments concerning the potential atheroprotective role of HDL-associated lysosphingolipids.

High-density lipoproteins as therapeutic targets

PURPOSE OF REVIEW

The concentration of cholesterol in HDL is an inverse predictor of future cardiovascular disease, with evidence mounting that therapies that increase HDL concentration are antiatherogenic. The best known antiatherogenic function of HDL particles relates to their ability to promote the efflux of cholesterol from cells. However, they also have antioxidant, antiinflammatory and antithrombotic properties.

RECENT FINDINGS

The past year has seen the publication of several papers that highlight a potential major protective role of HDL in states of acute inflammation. Papers showing extremely promising results using novel inhibitors of cholesteryl ester transfer protein as HDL-raising agents have also appeared. Finally, the discovery that ATP-binding cassette transporter G1 (ABCG1) transports cell cholesterol to large HDL particles in the extracellular space has largely reconciled apparent inconsistencies between basic research indicating that small, pre-beta-migrating HDL particles are the antiatherogenic components of HDL and epidemiological research that implicates larger HDL particles as the protective fraction.

SUMMARY

The finding that ABCG1 promotes the efflux of cholesterol from cells to large HDL particles also provides powerful circumstantial evidence that cholesteryl ester transfer protein inhibition (which increases HDL size) may enhance, rather than reduce, cholesterol efflux, and thus inhibit the development of atherosclerosis.

Therapeutic approaches to raising plasma HDL-cholesterol levels

Epidemiologic data from the Framingham and Prospective Cardiovascular Munster studies, demonstrating an inverse correlation between the plasma concentration of HDLs and the incidence of cardiovascular disease, have driven research to explore precisely how HDLs confer this cardioprotective effect. HDLs are anti-inflammatory, antithrombogenic and have vasoactive effects, as well as being efficient cholesterol acceptors enabling the removal of cholesterol from peripheral tissues, all functions that are likely to protect the vasculature. The first part of this article will review the clinical evidence in support of the pleiotropic effects of HDLs, along with laboratory-based investigations of the molecular mechanisms of action. As the evidence of clinical benefits of raising plasma HDL concentration has increased, so has the number of strategies currently being considered to achieve this goal. The second part of this article will review three current strategies: infusion of HDL-like products, comparing physicopharmacologic characteristics of the two commercial products currently under trial; the use of fibrates to raise plasma HDLs (although fibrates primarily reduce triglyceride levels, certain derivatives are able to induce significant increases in plasma HDLs); and the use of drugs that inhibit cholesterol ester transfer protein (these drugs increase plasma HDL concentration either alone or as an adjunct therapy with statins). The clinical efficacy and mechanism of action of fibrates and inhibitors of cholesterol ester transfer protein will be reviewed.

WY 14643, A POTENT EXOGENOUS PPAR-?? LIGAND, REDUCES INTESTINAL INJURY ASSOCIATED WITH SPLANCHNIC ARTERY OCCLUSION SHOCK

The peroxisome proliferator-activated receptor-alpha (PPAR-alpha) is a member of the nuclear receptor superfamily of ligand-dependent transcription factors related to retinoid, steroid, and thyroid hormone receptors. WY 14643 is a potent PPAR-alpha ligand that modulates the transcription of target genes. The aim of this study was to investigate the effect of WY 14643 on the tissue injury caused by ischemia-reperfusion (I/R) of the gut. I/R injury of the intestine was caused by clamping both the superior mesenteric artery and the celiac trunk for 45 min, followed by release of the clamp, allowing reperfusion for 2 h or 4 h. This procedure results in splanchnic artery occlusion (SAO) shock. Rats subjected to SAO developed a significant fall in mean arterial blood pressure, and only 20% of the animals survived for the entire 4-h reperfusion period. Surviving animals were sacrificed for histological examination and biochemical studies. Rats subjected to SAO displayed a significant increase in tissue myeloperoxidase (MPO) activity, significant increases in plasma tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta levels, and marked injury to the distal ileum. Increased immunoreactivity to nitrotyrosine and polyadenosine diphosphate [ADP]-ribose (PAR) was observed in the ileum of rats subjected to SAO. Staining of sections of the ileum obtained from SAO rats with anti-intercellular adhesion molecule (ICAM-1) antibody or with anti-P-selectin antibody resulted in diffuse staining. Administration of WY 14643 (1 mg/kg i.v.) 30 min before the onset of gut ischemia significantly reduced the (a) fall in mean arterial blood pressure, (b) mortality rate, (c) infiltration of the reperfused intestine with polymorphonuclear neutrophils (MPO activity), (d) production of proinflammatory cytokines (TNF-alpha and IL-1beta), and (e) histological evidence of gut injury. Administration of WY 14643 also markedly reduced the nitrotyrosine formation, poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) activation, up-regulation of ICAM-1, and expression of P-selectin during reperfusion. These results demonstrate that the PPAR-alpha agonist WY 14643 significantly reduces I/R injury of the intestine.