Differential low density lipoprotein receptor-dependent formation of eicosanoids in human blood-derived monocytes

Mapping the link between cardiac biomarkers and chronic periodontitis: A clinico-biochemical study

Background:

Various risk factors are coupled with atherosclerotic complications, such as myocardial infarction and stroke. Periodontitis is considered one of them.

Aims and Objectives:

The objective of the study is to compare and correlate the occurrences of periodontitis with serum levels of cardiac-biomarkers in patients with coronary heart-disorders.

Materials and Methods:

Of 70 individuals diagnosed with coronary artery diseases, 32 patients with chronic periodontitis constituted the test group, 31 without chronic periodontitis constituted the control group. Cardiac-biomarkers analyzed were Troponin T, Troponin I, Myoglobin; low density lipoprotein (LDL), high-density lipoprotein, very LDL (VLDL), total cholesterol (TC), and highly sensitive C-reactive protein (Hs-CRP). Periodontal characteristics were drawn from the plaque index (PI) and gingival index, probing depth (PD), clinical attachment loss, and periodontal inflammatory surface area (PISA).

Statistical Analysis:

In order to separate any association between cardiac biomarkers and clinical parameters of periodontitis, detailed statistical analysis through independent t-test and Pearson test of correlation was done.

Results:

Statistically significant differences were seen not only in PI, PD, and PISA between both the groups (P < 0.05), but also between various cardiac parameters of test and control groups (P < 0.001). Positive relations were seen in the test group, between cardiac biomarkers such as TC, VLDL, Hs-CRP, and Troponin T with periodontal parameters such as PD and PISA.

Conclusion:

The study reveals, a strong association between periodontitis and diseases of cardiovascular nature, highlighting the need for awareness and timely medical interventions to prevent periodontitis from scaling up and interfering with the risk of cardiovascular problems.

Lysosomal lipid hydrolysis provides substrates for lipid mediator synthesis in murine macrophages

Degradation of lysosomal lipids requires lysosomal acid lipase (LAL), the only intracellular lipase known to be active at acidic pH. We found LAL to be expressed in murine immune cells with highest mRNA expression in macrophages and neutrophils. Furthermore, we observed that loss of LAL in mice caused lipid accumulation in white blood cells in the peripheral circulation, which increased in response to an acute inflammatory stimulus. Lal-deficient (-/-) macrophages accumulate neutral lipids, mainly cholesteryl esters, within lysosomes. The cholesteryl ester fraction is particularly enriched in the PUFAs 18:2 and 20:4, important precursor molecules for lipid mediator synthesis. To investigate whether loss of LAL activity affects the generation of lipid mediators and to eliminate potential systemic effects from other cells and tissues involved in the pronounced phenotype of Lal-/- mice, we treated macrophages from Wt mice with the LAL-specific inhibitor LAListat-2. Acute inhibition of LAL resulted in reduced release of 18:2- and 20:4-derived mediators from macrophages, indicating that lipid hydrolysis by LAL is an important source for lipid mediator synthesis in macrophages. We conclude that lysosomes should be considered as organelles that provide precursor molecules for lipid mediators such as eicosanoids.

Effects of the total replacement of fish-based diet with plant-based diet on the hepatic transcriptome of two European sea bass (Dicentrarchus labrax) half-sibfamilies showing different growth rates with the plant-based diet

Background

Efforts towards utilisation of diets without fish meal (FM) or fish oil (FO) in finfish aquaculture have been being made for more than two decades. Metabolic responses to substitution of fishery products have been shown to impact growth performance and immune system of fish as well as their subsequent nutritional value, particularly in marine fish species, which exhibit low capacity for biosynthesis of long-chain poly-unsaturated fatty acids (LC-PUFA). The main objective of the present study was to analyse the effects of a plant-based diet on the hepatic transcriptome of European sea bass (Dicentrarchus labrax).

Results

We report the first results obtained using a transcriptomic approach on the liver of two half-sibfamilies of the European sea bass that exhibit similar growth rates when fed a fish-based diet (FD), but significantly different growth rates when fed an all-plant diet (VD). Overall gene expression was analysed using oligo DNA microarrays (GPL9663). Statistical analysis identified 582 unique annotated genes differentially expressed between groups of fish fed the two diets, 199 genes regulated by genetic factors, and 72 genes that exhibited diet-family interactions. The expression of several genes involved in the LC-PUFA and cholesterol biosynthetic pathways was found to be up-regulated in fish fed VD, suggesting a stimulation of the lipogenic pathways. No significant diet-family interaction for the regulation of LC-PUFA biosynthesis pathways could be detected by microarray analysis. This result was in agreement with LC-PUFA profiles, which were found to be similar in the flesh of the two half-sibfamilies. In addition, the combination of our transcriptomic data with an analysis of plasmatic immune parameters revealed a stimulation of complement activity associated with an immunodeficiency in the fish fed VD, and different inflammatory status between the two half-sibfamilies. Biological processes related to protein catabolism, amino acid transaminations, RNA splicing and blood coagulation were also found to be regulated by diet, while the expression of genes involved in protein and ATP synthesis differed between the half-sibfamilies.

Conclusions

Overall, the combined gene expression, compositional and biochemical studies demonstrated a large panel of metabolic and physiological effects induced by total substitution of both FM and FO in the diets of European sea bass and revealed physiological characteristics associated with the two half-sibfamilies.

Characteristics of inflammation common to both diabetes and periodontitis: are predictive diagnosis and targeted preventive measures possible?

Diabetes and periodontitis are chronic inflammatory disorders that contribute to each others' severity and worsen each others' prognosis. Studies have shown that patients with diabetes are at increased risk of developing periodontitis, and that diabetics with untreated periodontitis have more difficulty controlling serum glucose. Periodontal treatment that reduces gingival inflammation aids in the control of hyperglycemia. Periodontitis is accompanied by gingival bleeding and the production of an inflammatory exudate termed gingival crevicular fluid (GCF) that arises from the inflamed gingival tissues surrounding the teeth. GCF contains byproducts of connective tissue degradation, enzymes from host and bacterial cells, cytokines and other inflammatory mediators, and has been studied for screening blood glucose and for biomarkers of both diabetes and periodontitis. This review focuses on the inter-relationship between diabetes and periodontitis and the biomarkers common to both these diseases that may enable earlier detection, targeted preventive measures and individualized therapeutic intervention of these chronic conditions.

Suppression of Macrophage Eicosanoid Synthesis by Atherogenic Lipoproteins Is Profoundly Affected by Cholesterol-Fatty Acyl Esterification and the Niemann-Pick C Pathway of Lipid Trafficking

Atheroma macrophages internalize large quantities of lipoprotein-derived lipids. While most emphasis has been placed on cholesterol, lipoprotein-derived fatty acids may also play important roles in lesional macrophage biology. Little is known, however, about the trafficking or metabolism of these fatty acids. In this study, we first show that the cholesterol-fatty acyl esterification reaction, catalyzed by acyl-CoA:cholesterol acyltransferase (ACAT), competes for the incorporation of lipoprotein-derived fatty acids into cellular phospholipids. Furthermore, conditions that inhibit trafficking of cholesterol from late endosomes/lysosomes to the endoplasmic reticulum (ER), such as the amphipathic amine U18666A and the Npc1+/- mutation, also inhibit incorporation of lipoprotein-derived fatty acids into phospholipids. The biological relevance of these findings was investigated by studying the suppression of agonist-induced prostaglandin E(2) (PGE(2)) and leukotriene C(4)/D(4)/E(4) production during lipoprotein uptake by macrophages, which has been postulated to involve enrichment of cellular phospholipids with non-arachidonic fatty acids (NAAFAs). We found that eicosanoid suppression was markedly enhanced when ACAT was inhibited and prevented when late endosomal/lysosomal lipid trafficking was blocked. Moreover, PGE(2) suppression depended entirely on acetyl-LDL-derived NAAFAs, not on acetyl-LDL-cholesterol, and was not due to decreased cPLA(2) activity per se. These data support the following model: lipoprotein-derived NAAFAs traffic via the NPC1 pathway from late endosomes/lysosomes to a critical pool of phospholipids. In competing reactions, these NAAFAs can be either esterified to cholesterol or incorporated into phospholipids, resulting in suppression of eicosanoid biosynthesis. In view of recent evidence suggesting dysfunctional cholesterol esterification in late lesional macrophages, these data predict that such cells would have highly suppressed eicosanoid synthesis, thus affecting eicosanoid-mediated cell signaling in advanced atherosclerosis.

Dentistry and the medically compromised patient

Certain medical conditions and their accompanying drug treatment do have an impact upon oral structures and the delivery of dental care. Recent evidence suggests that oral health could be a significant risk factor for coronary artery disease. Many medical conditions can affect dental care are often over-stated and lack an evidence base. Examples include the need for antibiotic cover in patients at risk from infective endocarditis and the necessity to provide supplementary corticosteroids for those patients on longterm steroid therapy. By contrast, certain systematic drug treatments can have a profound affect on the oral tissue. The most obvious is drug-induced gingival overgrowth. Drugs frequently implicated in this unwanted effect include phenytoin, ciclosporin and the calcium channel blockers. Several risk factors for drug-induced overgrowth have been identified and include age, sex, peridontal variables and a range of drug pharmacokinetic variables. The relationship between oral health and coronary artery disease opens up a potentially new vista for the delivery of oral care. Although the association is convincing, casualty has not been established. If casualty for this relationship can be confirmed then the delivery of dental care and the promotion of oral health will receive a significant impetus.

Cardiovascular diseases and periodontology

BACKGROUND

Cardiovascular diseases represent a widespread heterogeneous group of conditions that have significant morbidity and mortality. The various diseases and their treatments can have an impact upon the periodontium and the delivery of periodontal care.

AIM

In this paper we consider three main topics and explore their relationship to the periodontist and the provision of periodontal treatment.

METHOD

The areas reviewed include the effect of cardiovascular drugs on the periodontium and management of patients with periodontal diseases; the risk of infective endocarditis arising from periodontal procedures; the inter-relationship between periodontal disease and coronary artery disease.

RESULTS AND CONCLUSIONS

Calcium-channel blockers and beta-adrenoceptor blockers cause gingival overgrowth and tooth demineralisation, respectively. Evidence suggests that stopping anticoagulant therapy prior to periodontal procedures is putting patients at a greater risk of thromboembolic disorders compared to the risk of prolonged bleeding. The relationship between dentistry and infective endocarditis remains a controversial issue. It would appear that spontaneous bacteraemia arising from a patient's oral hygiene practices is more likely to be the cause of endocarditis than one-off periodontal procedures. The efficacy of antibiotic prophylaxis is uncertain (and unlikely to be proven), and the risk of death from penicillin appears to be greater than the risk of death arising from infective endocarditis. Finally, the association between periodontal disease and coronary artery disease has been explored and there seem to be many issues with respect to data handling interpretation. Many putative mechanisms have been suggested; however, these only further highlight the need for intervention studies.

Does increased leukotriene B4 in type 1 diabetes result from elevated cholesteryl ester transfer protein activity?

Elevated cholesteryl ester transfer protein (CETP) activity has been reported in type 1 diabetic subjects and may be one cause of the high incidence of macrovascular complications in these patients. LDL delivers arachidonic acid (AA), in the form of cholesteryl ester (CE), to cells such as monocytes and fibroblasts, as precursor for eicosanoid synthesis. We discovered that AA content in LDL CE was significantly correlated with CETP activity, even after controlling for CETP concentration, in type 1 diabetic children. The production of LTB(4), a potent chemotactic and pro-inflammatory factor which plays a role in atherogenesis, has been shown to be increased in type 1 diabetic patients. We hypothesized that in these subjects, increased AA content in LDL CE, resulting from increased CETP activity and transient hyperinsulinemia, may lead to enhanced synthesis of LTB(4) and subsequently the higher incidence of cardiovascular disease.

Oral health and heart disease

Over the past ten years, a body of evidence has accumulated to suggest that aspects of oral health, particularly the extent and severity of periodontal disease, may be associated with an increased risk of coronary heart disease (CHD). This evidence should be seen against the background of a more general interest in the role of chronic infections in vascular disease. There have, for example, been suggestions of associations between CHD and a range of bacterial and viral agents, including H. pylori, C. pneumoniae, and cytomegalovirus, which are involved in persistent infections at various sites around the body. Reviews of the evidence for the causality of these relationships between CHD and specific organisms have been inconclusive. By comparison, periodontal disease is related to a wide and complex range of organisms rather than a single species and although the nature of the relationship is still inconclusive, the evidence for its validity still persists to some degree. A brief synopsis of the epidemiological studies to date and their outcomes is shown in Table 1.

Amplification of extracellular nucleotide-induced leukocyte(s) degranulation by contingent autocrine and paracrine mode of leukotriene-mediated chemokine receptor activation

Extracellular nucleotide-induced stimulation and activation of peripheral blood leukocytes and subsequent degranulation play a critical role in immediate-type hypersensitivity reaction and other inflammatory diseases. The extracellular nucleotides stimulate a P2Y receptor(s) on human PMN with the pharmacological profile similar to that of the P2Y2 receptor. Upon activation of P2Y2, arachidonic acid, formed from the membrane bound lipids by phospholipase A2, which subsequently metabolized by 5-lipoxygenase to form the leukotrienes. Of the several leukotrienes generated, LTB(4) is a potent pro-inflammatory chemokine. Upon its release LTB(4) binds to the PMN in a paracrine manner and also other leukocytes such as monocytes at the site of vascular injury, leading to an accelerated rate of degranulation. It is known that LTA(4) formed in the 5-lipoxygenase pathway in PMN could be released from PMN by receptor-mediated transport. Upon its release, the monocytes, erythrocytes, platelet, endothelial or smooth muscle cells can take up LTA(4). The endogenous LTA(4) hydrolase form the LTB(4) from LTA(4) in erythrocytes, platelet, endothelial or smooth muscle cells. As in PMN, LTB(4) is released from these cells via receptor-mediated transport to the extracellular milieu. Thus, released LTB(4) most likely acts as potentially accelerating factor in PMN and MN degranulation through its receptor-specific binding. It is not known whether any LTB(4) receptor exists in cytoplasm in any given cell type and also, the existence of any other signaling cascade for the extracellular nucleotide-induced leukocyte degranulation. Thus, it is convincing that the extracellular nucleotides released from the activated platelets and other damaged cell types exacerbate the inflammatory response by leukotriene generation. In turn the leukotriene will act in both autocrine and paracrine manner to amplify the degranulation processes in leukocytes invoked by extracellular nucleotides.

Exercise shifts the platelet aggregation modulatory role from native to mildly oxidized low-density lipoprotein

PURPOSE

The role of low-density lipoprotein (LDL) lipid peroxides in strenuous exercise-induced changes in platelet function was studied in 30 patients (male/female = 22/8) aged 30-62 yr (mean +/- SD = 508).

METHODS

All subjects were subjected to a treadmill exercise test, using the standard Bruce protocol. Blood samples were collected pre-, peak, and 10 min postexercise to assess hematological and biochemical parameters and platelet aggregation. Ex vivo whole blood platelet aggregation during treadmill exercise was assessed in 10 subjects by adding mildly oxidized LDL.

RESULTS

Preexercise, a correlation existed between plasma thromboxane (TX) levels and plasma LDL cholesterol or beta-thromboglobulin (beta-TG) levels (r = 0.48, P < 0.05: r = 0.47, P < 0.05, respectively), whereas, at peak exercise, TX and beta-TG levels increased, but no correlation was seen. At peak exercise, platelets showed hyperaggregability in terms of maximal amplitude and reaction slope (P < 0.001 and P < 0.01, respectively). In contrast to the increase in plasma lipid peroxide levels seen during peak exercise (P < 0.05), LDL lipid peroxides decreased during exercise, this decrease reaching a statistical significance at 10 min postexercise (P < 0.05). In addition, the ex vivo addition of mildly oxidized LDL (10 mg protein x L(-1)) to peak exercise blood resulted in a significant attenuation of platelet aggregation and a decrease in TX release. At 10 min postexercise, a correlation was seen between LDL lipid peroxides and TX levels (r = 0.78, P < 0.001) or beta-TG levels (r = 0.68, P < 0.005).

CONCLUSION

These results suggest that LDL lipid peroxides play a role in modulating and attenuating platelet aggregation during strenuous exercise.

CD14-dependent internalization and metabolism of extracellular phosphatidylinositol by monocytes

We report that membrane CD14 (mCD14), a cell surface receptor found principally on leukocytes, can mediate the uptake and metabolism of extracellular phosphatidylinositol (PtdIns). mCD14 facilitates PtdIns internalization, targeting it to intracellular sites where, following stimulation with a calcium ionophore, it can be acted upon by cytosolic phospholipase A(2). The [(14)C]arachidonate released from mCD14-acquired [(14)C]arachidonyl-PtdIns is either esterified to triacylglycerol and retained in the cell or secreted as free arachidonate or leukotrienes. Although less than 10% of the arachidonate-derived lipids secreted from endogenous cellular stores are 5-lipoxygenase metabolites, over one-half of the secreted (14)C-lipids derived from mCD14-acquired PtdIns are hydroxyeicosatetraenoic acids or leukotriene B(4). mCD14 may allow these highly active blood cells to acquire and use extracellular PtdIns as a source of arachidonate for leukotriene synthesis.

Effects of low density and high density lipoproteins isolated from non-insulin dependent diabetic patients on prostaglandin secretion by mouse macrophage cell line P388D1

We have previously shown that low-density (LDL) and high-density (HDL) lipoprotein from healthy subjects can promote in vitro prostaglandin (PG) release by murine macrophages. In this pilot study, we have measured PG production induced by lipoproteins of six diabetic patients with poor metabolic control, compared to five healthy controls. Plasma lipoprotein levels were similar in both groups. Lipoprotein fractions were purified by sequential ultracentrifugation. After lipoprotein incubation with cells, supernatants were extracted and PG quantified by HPLC. In presence of LDL, in control subjects, there was an increase in total PG production, mainly due to thromboxane B2 (TxB2). In diabetic patients, the secretion pattern was similar. In presence of HDL, in control subjects, total PG secretion was also increased, but it was balanced between TxB2 and prostacyclin. In diabetic patients, at low HDL concentration (10 mg/l) the secretion was mainly due to TxB2, while at higher HDL concentrations (100 mg/l). the secretion was balanced between TxB2 and prostacyclin. Comparison of means of areas under curve for the two groups studied showed that LDL increased all PG secretion in diabetic patients compared to controls (P < 0.05 for PGF2alpha), while HDL increased all PG secretion in controls compared to diabetic patients, except PGF2alpha. Our work suggests a key role of LDL in TxB2 secretion in diabetic patients, which is a major proaggregant and vasoconstrictive agent. There was also an increased secretion of all PG in diabetic patients.

PGE2, IL-1 beta, and TNF-alpha responses in diabetics as modifiers of periodontal disease expression

Diabetes mellitus is a systemic disease that affects more than 12 million people in the United States and represents a risk factor for periodontitis with odds ratios of 2.1 to 3.0. New data support the concept that in diabetes-associated periodontitis, the altered host inflammatory response plays a critical role. We have recently examined the gingival crevicular fluid (GCF) mediator level, monocytic secretion, and clinical presentation of 39 insulin-dependent diabetes mellitus (IDDM) patients and 64 non-diabetic patients with various degrees of periodontal health and disease. First, we found that there was an unexpected high level of GCF mediators among the IDDM subjects, even in the gingivitis and mild periodontitis patients. Furthermore, the GCF and monocytic mediator responses were obviously bimodal in distribution with respect to periodontal status. Gingivitis patients and mild periodontitis patients represented one low response group, and the moderate and severe periodontitis subjects the high response group. Accordingly, these 4 periodontal subgroups were pooled to form 2 main groups for analyses--group A (AAP Types I-II) and group B (AAP Types III-IV). Diabetics had significantly higher GCF levels of both PGE2 and IL-1 beta when compared to non-diabetic controls with similar periodontal status. Within the diabetic group, the GCF levels of these inflammatory mediators were almost 2-fold higher in group B subjects when compared to diabetics from group A. Among diabetics, GCF TNF-alpha levels were only marginally detectable and no significant difference was found between group A and group B patients. Insulin-dependent diabetic patients with gingivitis or mild periodontitis (group A) and moderate to severe periodontitis (group B) have abnormal monocytic inflammatory secretion in response to LPS challenge from Porphyromonas gingivalis (P. gingivalis) as compared to non-diabetic periodontal patients. Data suggest that the diabetic state results in a significantly upregulated monocytic secretion of PGE2 (4.2-fold), IL-1 beta (4.4-fold), and TNF-alpha (4.6-fold) when compared to non-diabetic controls. Within diabetics, LPS dose-response curves demonstrated that monocytes from group B patients secreted approximately 3 times more PGE2 and 6.2 times more TNF-alpha than those from group A; however, there was no significant difference in monocytic IL-1 beta secretion between the 2 diabetic groups. This upregulated monocytic trait is thought to exist independently of the presence of severe periodontal disease since, in non-diabetic patients with adult periodontitis, Gram-negative bacterial infections alone are not sufficient to elicit a systemic hyperresponsive monocytic trait. Between group A and group B diabetics, there was no significant difference in metabolic control as expressed by mean level of glycosylated hemoglobin (HbA1c). In conclusion, our data suggest that diabetic patients have exaggerated inflammatory responses when compared to non-diabetic controls. Furthermore, within diabetics, individuals with moderate to severe periodontitis (group B) have significantly elevated monocytic secretion of PGE2 and TNF-alpha upon LPS challenge and significantly higher GCF levels of PGE2 and IL-1 beta when compared to patients with gingivitis or mild periodontal disease (group A). Thus, we suggest that insulin-dependent diabetes mellitus is a significant risk factor for more severe periodontal disease because, as compared to non-diabetics, diabetic subjects react with an abnormally high degree of inflammation to an equivalent bacterial burden.

The pathobiology of periodontal diseases may affect systemic diseases: inversion of a paradigm

A new paradigm for the pathobiology of periodontitis is presented, and the manner in which periodontitis may relate to susceptibility for certain systemic diseases such as cardiovascular disease and preterm labor is described. Periodontitis is caused by a small group of Gram-negative bacteria present on the tooth root surfaces as bioffilms. Lipopolysaccharide (LPS) and other substances gain access to the gingival tissues, initiate and perpetuate immunoinflammation, resulting in production of high levels of proinflammatory cytokines. These induce production of matrix metalloproteinases which destroy the connective tissues of the gingiva and periodontal ligament, and prostaglandins which mediate alveolar bone destruction. Periodontitis may enhance susceptibility to systemic diseases in several ways. LPS and viable Gram-negative bacteria from the biofilms and proinflammatory cytokines from the inflamed periodontal tissues may enter the circulation in pathogenic quantities. In addition, periodontitis and certain systemic diseases, such as cardiovascular disease, share risk factors including tobacco smoking, male gender, race/ethnicity, stress, and aging.

Differential leukotriene constrictor responses in human atherosclerotic coronary arteries

BACKGROUND

Leukotrienes are a class of biologically active lipids that have potent effects on the heart. To assess their role in coronary artery disease, we compared the contractile responses of leukotriene C4 (LTC4) and leukotriene D4 (LTD4) and their binding activity in both atherosclerotic and nonatherosclerotic human coronary arteries. We also studied expression of the enzymes that control their formation to understand how the 5-lipoxygenase (5-LO) pathway is activated in the coronary arteries.

METHODS AND RESULTS

The capacity of leukotrienes to affect coronary vessel tone and the influence of atherosclerosis was tested in organ baths. Leukotriene receptors were examined by autoradiography, and antibody binding to the various enzymes responsible for their formation was assessed by use of immunocytochemistry. Nonatherosclerotic coronary artery ring segments were unresponsive to LTC4 and LTD4. In contrast, LTC4 and LTD4 induced concentration-dependent contractions in atherosclerotic coronary arteries. Specific [3H]-LTC4 but not LTD4 binding to atherosclerotic coronary artery was evident, with no evidence of specific binding of [3H]-leukotrienes to nonatherosclerotic coronary artery. High-resolution autoradiography identified specific [3H]-LTC4 binding sites to smooth muscle cell and to regions of intimal proliferation and plaque. Cells showing positive antibody binding to 5-LO, FLAP (5-lipoxygenase activating protein), and leukotriene A4 hydrolase were also present in the coronary arteries and had a similar distribution to macrophages.

CONCLUSIONS

Atherosclerosis is associated with a specific leukotriene receptor(s) capable of inducing hyperreactivity of human epicardial coronary arteries in response to LTC4 and LTD4.

LDL stimulates chemotaxis of human monocytes through a cyclooxygenase-dependent pathway

Monocyte migration into the vessel wall is an early step in atherogenesis. Even though a number of chemotactic factors have been identified, the regulation of the chemotactic response is not clearly understood. As the release of arachidonic acid has been implicated in monocyte chemotaxis, we studied the influence of LDL, which can supply this fatty acid to cells, on the chemotactic mobility of monocytes. Migration of human monocytic U937 cells was abolished by a 30-hour incubation in medium containing lipoprotein-depleted 10% fetal calf serum. Thereafter, human VLDL, LDL, acetyl LDL, methyl LDL, HDL, free cholesterol, linoleic acid, oleic acid, or arachidonic acid was added. At the end of varying incubation periods (0.5 to 8 hours), chemotaxis, viability, and cellular cholesterol content were measured. In the same experimental setting we also studied the effects of the pharmacological agents chloroquine, indomethacin, and acetylsalicylic acid on LDL-mediated chemotaxis. Chemotaxis was restored by LDL in a dose- and time-dependent manner starting at concentrations as low as 5 micrograms/mL and at incubations as brief as 30 minutes. The other lipoproteins tested (VLDL, HDL, acetyl LDL, and methyl LDL) as well as free cholesterol had no comparable effect on chemotaxis. Viability and total cholesterol content did not differ among the groups. Simultaneous incubation of cells with chloroquine, indomethacin, and acetylsalicylic acid reduced restitution of chemotaxis by LDL by 71%, 82%, and 68%, respectively. In contrast, the agents had only slight inhibitory effects on the chemotactic mobility of serum-fed control cells. Incubation with linoleic acid showed a 60% restoration of chemotaxis, whereas arachidonic acid stimulated chemotaxis by 140% compared with the positive control. Preincubation of LDL with the monoclonal antibody MB47 directed against LDL resulted in a significantly reduced migratory response. The data suggest a novel cyclooxygenase-dependent regulatory mechanism of chemotaxis by LDL.

Periodontal disease and cardiovascular disease

It is our central hypothesis that periodontal diseases, which are chronic Gram-negative infections, represent a previously unrecognized risk factor for atherosclerosis and thromboembolic events. Previous studies have demonstrated an association between periodontal disease severity and risk of coronary heart disease and stroke. We hypothesize that this association may be due to an underlying inflammatory response trait, which places an individual at high risk for developing both periodontal disease and atherosclerosis. We further suggest that periodontal disease, once established, provides a biological burden of endotoxin (lipopolysaccharide) and inflammatory cytokines (especially TxA2, IL-1 beta, PGE2, and TNF-alpha) which serve to initiate and exacerbate atherogenesis and thromboembolic events. A cohort study was conducted using combined data from the Normative Aging Study and the Dental Longitudinal Study sponsored by the United States Department of Veterans Affairs. Mean bone loss scores and worst probing pocket depth scores per tooth were measured on 1,147 men during 1968 to 1971. Information gathered during follow-up examinations showed that 207 men developed coronary heart disease (CHD), 59 died of CHD, and 40 had strokes. Incidence odds ratios adjusted for established cardiovascular risk factors were 1.5, 1.9, and 2.8 for bone loss and total CHD, fatal CHD, and stroke, respectively. Levels of bone loss and cumulative incidence of total CHD and fatal CHD indicated a biologic gradient between severity of exposure and occurrence of disease.

The arachidonic acid cascade, eicosanoids, and signal transduction

Eicosanoid biosynthesis in animal cells either results from agonist-stimulated phospholipase activation (endogenous pathway) or from lipoprotein receptor-mediated uptake and lysosomal lipid hydrolase-dependent release of AA (exogenous pathway) (see Fig. 1 for schematic representation). LDL stimulates eicosanoid formation through delivery of substrate AA to enzymes of oxidative AA metabolism. The classical LDL receptor is a control point of the effects of LDL AA on eicosanoid formation in different tissues: LDL AA metabolism occurs in several cell types of mesenchymal and epithelial origin and generates the formation of distinct eicosanoid patterns in each case. The LDL AA pathway does appear to couple directly to the PGH synthase reaction, whereas it does not couple directly to the 5-lipoxygenase reaction. We expect that a more complete characterization of the LDL unsaturated fatty acid pathway in different tissue will yield additional information on the biochemistry of lipoproteins, AA, and eicosanoids.

Involvement of 15-lipoxygenase in early stages of atherogenesis

The arachidonate 15-lipoxygenase which is expressed in atherosclerotic lesions is implicated in the oxidative modification of low density lipoproteins during atherogenesis. To obtain experimental in vivo evidence for this hypothesis, we analyzed the structure of oxygenated lipids isolated from the aorta of rabbits fed with a cholesterol-rich diet for different time periods and compared the pattern of oxygenation products with that isolated from low density lipoproteins treated in vitro with the pure rabbit 15-lipoxygenase and with oxygenated lipids isolated from advanced human atherosclerotic lesions. In early atherosclerotic lesions (12-wk cholesterol feeding), specific lipoxygenase products were detected whose structure was similar to those isolated from lipoxygenase-treated low density lipoproteins. The appearance of these products did coincide with the lipid deposition in the vessel wall. In later stages of atherogenesis (26-wk cholesterol feeding) the degree of oxidative modification of the tissue lipids did increase but the share of specific lipoxygenase products was significantly lower, suggesting an increasing overlay of the specific lipoxygenase products by nonenzymatic lipid peroxidation. In advanced human atherosclerotic lesions, large amounts of oxygenation products were detected whose structure suggests a nonenzymatic origin. These data suggest that the arachidonate 15-lipoxygenase is of pathophysiological importance during the early stages of atherogenesis. In later stages of plaque development nonenzymatic lipid peroxidation becomes more relevant.

Lipoprotein-dependent unsaturated fatty acid transport and metabolism in cultured cells

Our results can be summarized as follows. LDL stimulates eicosanoid formation through delivery of substrate AA to enzymes of oxidative AA metabolism. The classical LDL receptor controls the effect of LDL AA on eicosanoid formation. LDL AA metabolism occurs in several cell types of mesenchymal and epithelial origin and generates the formation of distinct eicosanoid patterns in a tissue-specific way. LDL inhibits the PGH synthase, and the LDL-dependent inhibition of the enzyme resembles the inhibition by unesterified AA. The LDL AA pathway does appear to couple directly to the PGH synthase reaction, but it does not appear to couple directly to the 5-lipoxygenase reaction. We expect that a more complete characterization of the LDL unsaturated fatty acid pathway in different tissues will yield additional information on the biochemistry of both lipoproteins and AA metabolism.

Functionally abnormal monocytes in hypercholesterolemia

We investigated some functions of monocytes from 20 type IIa hypercholesterolemic (HC) and five homozygous familial hypercholesterolemic (FH) patients. Monocytes from the HC patients contained as much cholesterol and formed as much thromboxane B2 in response to N-formyl-methionyl-leucyl-phenylalanine (fMLP) or calcium ionophore A23187 as those from normal individuals. In contrast, the generation of prostaglandin E2 and 6-ketoprostaglandin F1 alpha in response to these agonists was 1.5-3 times normal, and that of leukotriene B4 was 40-60% of the normal value (p < 0.05 for all). Studies in which the combination of fMLP or A23187 with sodium arachidonate were employed suggested that these abnormalities were independent of the availability of the endogenous substrate for the lipoxygenase or cyclooxygenase enzymes. Quantitatively and qualitatively comparable abnormalities were found in monocytes from the five FH patients, and these were little affected when the patients' plasma cholesterol levels were almost normalized by low density lipoprotein apheresis. In keeping with the abnormalities in the eicosanoid metabolism, monocytes from HC patients exhibited a defective ability (p < 0.05) to generate O2-, the extent of which was correlated with the impaired formation of leukotriene B4. On the other hand, adhesion studies indicated that patients' cells exhibited an abnormally high ability to adhere to glass (p < 0.01). These data indicate the presence of functionally abnormal monocytes in hypercholesterolemia and suggest a direction to be followed to understand the importance of such cells in the premature atherosclerosis that occurs in these patients.

Angioplasty triggers intracoronary leukotrienes and lipoxin A4. Impact of aspirin therapy

BACKGROUND

Percutaneous transluminal coronary angioplasty (PTCA) is a widely used and important method of reperfusing coronary arteries. However, it is also associated with serious complications such as acute reocclusion and accelerated restenosis. The factors as well as the mechanisms involved in PTCA-associated complications remain to be fully elucidated. Because peptidoleukotrienes and lipoxins are potent vasoactive compounds, the formation of which is not inhibited by aspirin (ASA) treatment in vitro, it is possible that these eicosanoids are involved in PTCA-associated untoward events. To test this, we determined the intracoronary levels of peptidoleukotrienes and lipoxin A4 (LXA4) as well as thromboxane (TX) and 5S,12S-dihydroxyeicosatetraenoic acid (5S,12S-DiHETE; a product of double dioxygenation) after plaque rupture and evaluated the impact of ASA therapy.

METHODS AND RESULTS

PTCA was performed on 12 patients with coronary artery disease, six undergoing ASA therapy and six without ASA therapy, for at least 2 weeks before PTCA. By means of a technique that permitted sampling of intracoronary blood at the plaque site in situ, samples were taken immediately before and 10 seconds after initiation of plaque rupture. Lipoxygenase (LO)-derived products, including LXA4 and 5S,12S-DiHETE, and a marker of cyclooxygenase activity, i.e., TXB2, were quantitated after extraction and chromatography using deuterium-labeled internal standards and electron capture negative ion chemical ionization mass spectrometry. Peptidoleukotrienes (LTC4 and LTD4) were quantitated after reverse-phase high-performance liquid chromatography coupled with radioimmunoassay. Intracoronary blood taken before PTCA showed no detectable levels of these eicosanoids (the minimum limits of detection were within the picomole range). In contrast, each of these LO products was detected after PTCA. Patients undergoing ASA treatment showed elevated levels of each LO product examined compared with those not receiving ASA. Eicosanoid levels were (mean +/- SEM): LTC4, 7.10 +/- 1.22 ng/ml (ASA) versus 0.48 +/- 0.10 ng/ml; LTD4, 4.92 +/- 0.56 ng/ml (ASA) versus 1.17 +/- 0.48 ng/ml; LXA4, 24.98 +/- 4.11 ng/ml (ASA) versus 15.83 +/- 2.43 ng/ml; 5S,12S-DiHETE, 19.47 +/- 3.98 ng/ml (ASA) versus 11.98 +/- 1.83 ng/ml; TXB2, complete blockage (ASA) versus 31.04 +/- 7.38 ng/ml (p less than 0.05 for LTC4 and LTD4). To distinguish between dilatation of whole blood versus dilatation of whole blood and atheroma for contribution of eicosanoids, we also monitored their formation in Gore-tex grafts. Upon balloon inflation, TXB2 was generated, but LO products were not detected. In contrast, injection of platelet- and leukocyte-directed agonists within the graft led to both peptidoleukotriene and lipoxin formation.

CONCLUSIONS

The results indicate that PTCA triggers the intraluminal release of peptidoleukotrienes and LXA4 and that ASA therapy enhances their appearance in intracoronary blood. In addition, they provide direct evidence for LO products (LTC4, LTD4, and LXA4) in a local milieu in vivo. Moreover, the presence of the double dioxygenation product 5S,12S-DiHETE (a potential marker of 5- and 12-LO interactions) suggests that transcellular metabolic events can contribute to eicosanoid formation in vivo.