Lipoprotein (a) up-regulates the expression of the plasminogen activator inhibitor 2 in human blood monocytes

Lipoprotein(a): Emerging insights and therapeutics

The strong association between lipoprotein (a) [Lp(a)] and atherosclerotic cardiovascular disease has led to considerations of Lp(a) being a potential target for mitigating residual cardiovascular risk. While approximately 20 % of the population has an Lp(a) level greater than 50 mg/dL, there are no currently available pharmacological lipid-lowering therapies that have demonstrated substantial reduction in Lp(a). Novel therapies to lower Lp(a) include antisense oligonucleotides and small-interfering ribonucleic acid molecules and have shown promising results in phase 2 trials. Phase 3 trials are currently underway and will test the causal relationship between Lp(a) and ASCVD and whether lowering Lp(a) reduces cardiovascular outcomes. In this review, we summarize emerging insights related to Lp(a)'s role as a risk-enhancing factor for ASCVD, association with calcific aortic stenosis, effects of existing therapies on Lp(a) levels, and variations amongst patient populations. The evolving therapeutic landscape of emerging therapeutics is further discussed.

Sex-specific immune-inflammatory markers and lipoprotein profile in patients with anhedonia with unipolar and bipolar depression

BACKGROUND

Anhedonia is a core symptom in patients with unipolar and bipolar depression. However, sex-specific markers reflecting biological heterogeneity are lacking. Emerging evidence suggests that sex differences in immune-inflammatory markers and lipoprotein profiles are associated with anhedonia.

METHODS

The demographic and clinical data, immune-inflammatory markers (CD3, CD4, and CD8), and lipoprotein profiles [TC, TG, LDL-C, HDL-C, lipoprotein(a) Lp (a)] of 227 patients with unipolar and bipolar depression were collected. The Hamilton Depression Rating Scale (HAMD) and Snaith-Hamilton Pleasure Scale (SHAPS) were used to assess depression and anhedonia symptoms. Data were analyzed using ANOVA, logistic regression, and receiver operating characteristic curves.

RESULTS

Male patients in the anhedonia group had higher levels of CD3, CD4, and CD8, and lower levels of Lp (a) than the non-anhedonia group, while no significant difference was identified in female patients with and without anhedonia. Logistic regression analysis showed that CD3, CD4, CD8, and Lp (a) levels were associated with anhedonia in male patients. Furthermore, the combination of CD3, CD4, CD8, and Lp (a) had the strongest predictive value for distinguishing anhedonia in male patients than individual parameters.

CONCLUSIONS

We identified sex-specific associations between immune-inflammatory markers, lipoprotein profiles, and anhedonia in patients with unipolar and bipolar depression. The combination of CD3, CD4, CD8, and Lp (a) might be a possible biomarker for identifying anhedonia in male patients with unipolar and bipolar depression.

Lipoprotein(a) in Atherosclerotic Diseases: From Pathophysiology to Diagnosis and Treatment

Lipoprotein(a) (Lp(a)) is a low-density lipoprotein (LDL) cholesterol-like particle bound to apolipoprotein(a). Increased Lp(a) levels are an independent, heritable causal risk factor for atherosclerotic cardiovascular disease (ASCVD) as they are largely determined by variations in the Lp(a) gene (LPA) locus encoding apo(a). Lp(a) is the preferential lipoprotein carrier for oxidized phospholipids (OxPL), and its role adversely affects vascular inflammation, atherosclerotic lesions, endothelial function and thrombogenicity, which pathophysiologically leads to cardiovascular (CV) events. Despite this crucial role of Lp(a), its measurement lacks a globally unified method, and, between different laboratories, results need standardization. Standard antilipidemic therapies, such as statins, fibrates and ezetimibe, have a mediocre effect on Lp(a) levels, although it is not yet clear whether such treatments can affect CV events and prognosis. This narrative review aims to summarize knowledge regarding the mechanisms mediating the effect of Lp(a) on inflammation, atherosclerosis and thrombosis and discuss current diagnostic and therapeutic potentials.

A method for lipoprotein (a) Isolation from a small volume of plasma with applications for clinical research

High levels of circulating Lipoprotein (a) [Lp(a)] are an independent risk factor for CVD. One of the major limitations to investigating Lp(a) biology is the need for large volumes of plasma (4-10 mL) for its isolation. We developed an isolation technique requiring only 0.4 mL of plasma yielding an enriched Lp(a) fraction suitable for compositional and functional studies. We collected plasma from patients (n = 9) in EDTA presenting to our Center for Preventive Cardiology for CVD risk management and with circulating Lp(a) > 66 mg/dL. 0.4 mL of plasma was added to 90 µL of potassium bromide (1.33 g/mL) and subjected to our two-step density-gradient ultracentrifugation method. The first step separates VLDL and LDL from the Lp(a) and HDL fractions and the second step further separates VLDL from LDL and Lp(a) from HDL. Lp(a) is then dialyzed for up to 24 h in potassium phosphate buffer. We performed cholesterol gel electrophoresis, immunoblotting and LC-MS/MS proteomics on isolated lipoprotein fractions to confirm fraction enrichment. Functional studies including Lp(a)-dependent induction of macrophage gene expression and cholesterol efflux inhibition were performed on isolated Lp(a) to confirm its preserved bioactivity. Lp(a) yields (264 ± 82.3 µg/mL on average) correlated with Lp(a) plasma concentrations (r2 = 0.75; p < 0.01) and represented the relative distribution of circulating apo(a) isoforms. Proteomic analyses confirm lipoprotein fraction separation. Functional integrity was confirmed by the findings that isolated Lp(a) inhibited plasminogen-dependent cholesterol efflux in HEK293T cells expressing ABCA1 and increased expressions of Il1b, Nos2 and Ccl2. We developed a small-volume isolation technique for Lp(a) suited for a range of applications used in biomedical research. The use of this technique circumvents volume-dependent limitations and expands our ability to investigate the mysteries of this deleterious lipoprotein.

Association between COVID-19 Diagnosis and Coronary Artery Thrombosis: A Narrative Review

Coronavirus disease 2019 is characterized by its severe respiratory effects. Data early on indicated an increased risk of mortality in patients with cardiovascular comorbidities. Early reports highlighted the multisystem inflammatory syndrome, cytokine storm, and thromboembolic events as part of the disease processes. The aim of this review is to assess the association between COVID-19 and its thrombotic complications, specifically related to the cardiovascular system. The role of neutrophil extracellular traps (NETs) is explored in the pathogenesis of the disease. The structure and anatomy of the virus are pivotal to its virulence in comparison to other α and β Coronaviridae (HCoV-229E, HCoV-OC43, HCoV-229E, HCoV-NL63, HCoV-OC43, and HCoV-HKU1). In particular, the host interaction and response may explain the variability of severity in patients. Angio tensin-converting enzyme 2 (ACE2) activation may be implicated in the cardiovascular and throm bogenic potential of the disease. The virus may also have direct effects on the endothelial lining affecting hemostasis and resulting in thrombosis through several mechanisms. Dipyridamole may have a therapeutic benefit in NET suppression. Therapeutic avenues should be concentrated on the different pathophysiological steps involving the virus and the host.

Associations of Genetically Predicted Lp(a) (Lipoprotein [a]) Levels With Cardiovascular Traits in Individuals of European and African Ancestry

BACKGROUND

Lp(a) (lipoprotein [a]) levels are higher in individuals of African ancestry (AA) than in individuals of European ancestry (EA). We examined associations of genetically predicted Lp(a) levels with (1) atherosclerotic cardiovascular disease subtypes: coronary heart disease, cerebrovascular disease, peripheral artery disease, and abdominal aortic aneurysm and (2) nonatherosclerotic cardiovascular disease phenotypes, stratified by ancestry.

METHODS

We performed (1) Mendelian randomization analyses for previously reported cardiovascular associations and (2) Mendelian randomization-phenome-wide association analyses for novel associations. Analyses were stratified by ancestry in electronic Medical Records and Genomics, United Kingdom Biobank, and Million Veteran Program cohorts separately and in a combined cohort of 804 507 EA and 103 580 AA participants.

RESULTS

In Mendelian randomization analyses using the combined cohort, a 1-SD genetic increase in Lp(a) level was associated with atherosclerotic cardiovascular disease subtypes in EA-odds ratio and 95% CI for coronary heart disease 1.28 (1.16-1.41); cerebrovascular disease 1.14 (1.07-1.21); peripheral artery disease 1.22 (1.11-1.34); abdominal aortic aneurysm 1.28 (1.17-1.40); in AA, the effect estimate was lower than in EA and nonsignificant for coronary heart disease 1.11 (0.99-1.24) and cerebrovascular disease 1.06 (0.99-1.14) but similar for peripheral artery disease 1.16 (1.01-1.33) and abdominal aortic aneurysm 1.34 (1.11-1.62). In EA, a 1-SD genetic increase in Lp(a) level was associated with aortic valve disorders 1.34 (1.10-1.62), mitral valve disorders 1.18 (1.09-1.27), congestive heart failure 1.12 (1.05-1.19), and chronic kidney disease 1.07 (1.01-1.14). In AA, no significant associations were noted for aortic valve disorders 1.08 (0.94-1.25), mitral valve disorders 1.02 (0.89-1.16), congestive heart failure 1.02 (0.95-1.10), or chronic kidney disease 1.05 (0.99-1.12). Mendelian randomization-phenome-wide association analyses identified novel associations in EA with arterial thromboembolic disease, nonaortic aneurysmal disease, atrial fibrillation, cardiac conduction disorders, and hypertension.

CONCLUSIONS

Many cardiovascular associations of genetically increased Lp(a) that were significant in EA were not significant in AA. Lp(a) was associated with atherosclerotic cardiovascular disease in four major arterial beds in EA but only with peripheral artery disease and abdominal aortic aneurysm in AA. Additionally, novel cardiovascular associations were detected in EA.

Expert position statements: comparison of recommendations for the care of adults and youth with elevated lipoprotein(a)

PURPOSE OF REVIEW

Summarize recent recommendations on clinical management of adults and youth with elevated lipoprotein(a) [Lp(a)] who are at-risk of or affected by cardiovascular disease (CVD).

RECENT FINDINGS

There is ample evidence to support elevated Lp(a) levels, present in approximately 20% of the general population, as a causal, independent risk factor for CVD and its role as a significant risk enhancer. Several guidelines and position statements have been published to assist in the identification, treatment and follow-up of adults with elevated levels of Lp(a). There is growing interest in Lp(a) screening and strategies to improve health behaviors starting in youth, although published recommendations for this population are limited. In addition to the well established increased risk of myocardial infarction, stroke and valvular aortic stenosis, data from the coronavirus pandemic suggest adults with elevated Lp(a) may have a particularly high-risk of cardiovascular complications. Lp(a)-specific-lowering therapies are currently in development. Despite their inability to lower Lp(a), use of statins have been shown to improve outcomes in primary and secondary prevention.

SUMMARY

Considerable differences exist amongst published guidelines for adults on the use of Lp(a) in clinical practice, and recommendations for youth are limited. With increasing knowledge of Lp(a)'s role in CVD, including recent observations of COVID-19-related risk of cardiovascular complications, more harmonized and comprehensive guidelines for Lp(a) in clinical practice are required. This will facilitate clinical decision-making and help define best practices for identification and management of elevated Lp(a) in adults and youth.

Deficiency of plasminogen activator inhibitor-2 results in accelerated tumor growth

BACKGROUND

Upregulation of the plasminogen activation system, including urokinase plasminogen activator (uPA), has been observed in many malignancies, suggesting that co-opting the PA system is a common method by which tumor cells accomplish extracellular matrix proteolysis. PAI-2, a serine protease inhibitor, produced from the SERPINB2 gene, inhibits circulating and extracellular matrix-tethered uPA. Decreased SERPINB2 expression has been associated with increased tumor invasiveness and metastasis for several types of cancer. PAI-2 deficiency has not been reported in humans and PAI-2-deficient (SerpinB2-/- ) mice exhibit no apparent abnormalities.

OBJECTIVES

We investigated the role of PAI-2 deficiency on tumor growth and metastasis.

METHODS

To explore the long-term impact of PAI-2 deficiency, a cohort of SerpinB2-/- mice were aged to >18 months, with spontaneous malignancies observed in 4/9 animals, all of apparently vascular origin. To further investigate the role of PAI-2 deficiency in malignancy, SerpinB2-/- and wild-type control mice were injected with either B16 melanoma or Lewis lung carcinoma tumor cells, with markedly accelerated tumor growth observed in SerpinB2-/- mice for both cell lines. To determine the relative contributions of PAI-2 from hematopoietic or nonhematopoietically derived sources, bone marrow transplants between wild-type C57BL/6J and SerpinB2-/- mice were performed.

RESULTS AND CONCLUSIONS

Our results suggest that PAI-2 deficiency increases susceptibility to spontaneous tumorigenesis in the mouse, and demonstrate that SerpinB2 expression derived from a nonhematopoietic compartment is a key host factor in the regulation of tumor growth in both the B16 melanoma and Lewis lung carcinoma models.

Lipoprotein(a) and Its Potential Association with Thrombosis and Inflammation in COVID-19: a Testable Hypothesis

PURPOSE OF REVIEW

The COVID-19 pandemic has infected over > 11 million as of today people worldwide and is associated with significant cardiovascular manifestations, particularly in subjects with preexisting comorbidities and cardiovascular risk factors. Recently, a predisposition for arterial and venous thromboses has been reported in COVID-19 infection. We hypothesize that besides conventional risk factors, subjects with elevated lipoprotein(a) (Lp(a)) may have a particularly high risk of developing cardiovascular complications.

RECENT FINDINGS

The Lp(a) molecule has the propensity for inhibiting endogenous fibrinolysis through its apolipoprotein(a) component and for enhancing proinflammatory effects such as through its content of oxidized phospholipids. The LPA gene contains an interleukin-6 (IL-6) response element that may induce an acute phase-type increase in Lp(a) levels following a cytokine storm from COVID-19. Thus, subjects with either baseline elevated Lp(a) or those who have an increase following COVID-19 infection, or both, may be at very high risk of developing thromboses. Elevated Lp(a) may also lead to acute destabilization of preexisting but quiescent atherosclerotic plaques, which might induce acute myocardial infarction and stroke. Ongoing studies with IL-6 antagonists may be informative in understanding this relationship, and registries are being initiated to measure Lp(a) in subjects infected with COVID-19. If indeed an association is suggestive of being causal, consideration can be given to systematic testing of Lp(a) and prophylactic systemic anticoagulation in infected inpatients. Therapeutic lipid apheresis and pharmacotherapy for the reduction of Lp(a) levels may minimize thrombogenic potential and proinflammatory effects. We propose studies to test the hypothesis that Lp(a) may contribute to cardiovascular complications of COVID-19.

Lipoprotein(a) in clinical practice: New perspectives from basic and translational science

Elevated plasma concentrations of lipoprotein(a) (Lp(a)) are a causal risk factor for coronary heart disease (CHD) and calcific aortic valve stenosis (CAVS). Genetic, epidemiological and in vitro data provide strong evidence for a pathogenic role for Lp(a) in the progression of atherothrombotic disease. Despite these advancements and a race to develop new Lp(a) lowering therapies, there are still many unanswered and emerging questions about the metabolism and pathophysiology of Lp(a). New studies have drawn attention to Lp(a) as a contributor to novel pathogenic processes, yet the mechanisms underlying the contribution of Lp(a) to CVD remain enigmatic. New therapeutics show promise in lowering plasma Lp(a) levels, although the complete mechanisms of Lp(a) lowering are not fully understood. Specific agents targeted to apolipoprotein(a) (apo(a)), namely antisense oligonucleotide therapy, demonstrate potential to decrease Lp(a) to levels below the 30-50 mg/dL (75-150 nmol/L) CVD risk threshold. This therapeutic approach should aid in assessing the benefit of lowering Lp(a) in a clinical setting.

Lipoprotein(a) and its role in inflammation, atherosclerosis and malignancies

Lipoprotein (a) (Lp(a)) is a modified low-density lipoprotein (LDL) particle with an additional specific apolipoprotein (a), covalently attached to apolipoprotein B‑100 of LDL by a single thioester bond. Increased plasma Lp(a) level is a genetically determined, independent, causal risk factor for cardiovascular disease.

The precise quantification of Lp(a) in plasma is still hampered by mass-sensitive assays, large particle variation, poor standardization and lack of assay comparability.

The physiological functions of Lp(a) include wound healing, promoting tissue repair and vascular remodeling. Similarly to other lipoproteins, Lp(a) is also susceptible for oxidative modifications, leading to extensive formation of pro-inflammatory and pro-atherogenic oxidized phospholipids, oxysterols, oxidized lipid-protein adducts in Lp(a) particles, that perpetuate atherosclerotic lesion progression and intima-media thickening through induction of M1-macrophages, inflammation, autoimmunity and apoptosis. The oxidation-specific epitopes of modified lipoproteins are major targets of pre-immune, natural IgM antibodies, that may attenuate the pro-inflammatory and pro-atherogenic effects of Lp(a).

Although the data are still insufficient, recent studies suggest a potential anti-neoplastic role of Lp(a).

Lipoprotein(a) hyperlipidemia as cardiovascular risk factor: pathophysiological aspects

Lipoprotein (a) [Lp(a)] is a modified LDL particle with an additional apolipoprotein [apo(a)] protein covalently attached by a thioester bond. Multiple isoforms of apo(a) exist that are genetically determined by differences in the number of Kringle-IV type-2 repeats encoded by the LPA gene. Elevated plasma Lp(a) is an independent risk factor for cardiovascular disease.

The phenotypic diversity of familial Lp(a) hyperlipidemia [Lp(a)-HLP] and familial hypercholesterolemia [FH], as defined risks with genetic background, and their frequent co-incidence with additional cardiovascular risk factors require a critical revision of the current diagnostic and therapeutic recommendations established for isolated familial Lp(a)-HLP or FH in combination with elevated Lp(a) levels.

Lp(a) assays still suffer from poor standardization, comparability and particle variation. Further evaluation of the current biomarkers and establishment of novel comorbidity biomarkers are necessary for extended risk assessment of cardiovascular disease in FH or Lp(a)-HLP and to better understand the pathophysiology and to improve patient stratification of the Lp(a) syndrome complex.

Lp(a) promotes vascular remodeling, increased lesion progression and intima media thickening through induction of M1-macrophages, antiangiogenic effects (e.g. vasa vasorum) with secretion of the antiangiogenic chemokine CXCL10 (IP10) and CXCR3 mediated activation of Th1- and NK-cells.

In addition inhibition of serine proteases causing disturbances of thrombosis/ hemostasis/ fibrinolysis, TGFb-activation and acute phase response (e.g. CRP, anti-PL antibodies) are major features of Lp(a) pathology. Anti-PL antibodies (EO6 epitope) also bind to oxidized Lp(a).

Lipoprotein apheresis is used to reduce circulating lipoproteins in patients with severe FH and/or Lp(a)-HLP, particularly with multiple cardiovascular risks who are intolerant or insufficiently responsive to lipid-lowering drugs.

Lipoprotein (a) and other Lipid Profile in Patients with Thrombotic Stroke: Is it a Reliable Marker?

BACKGROUND

Cerebrovascular disease (CVD) and coronary heart disease (CHD) cause 40%-50% of deaths in developed countries with CVD causing 10%-12% of deaths. Though increased Lipoprotein (a) is a risk factor in developing CHD, its role is poorly defined in etiopathogenesis of CVD.

AIMS

To find the association of lipoprotein (a) and lipid profile in thrombotic stroke patients after acute phase.

SETTINGS AND DESIGN

The study was conducted at Kasturba Medical College, Manipal. Twenty one cases of thrombotic stroke and 18 cases of age and sex matched controls were taken for the study. Informed consent was taken from both case and control.

MATERIALS AND METHODS

Overnight fasting sample was collected from both case and control. Serum was separated and parameters such as total cholesterol, triglycerides, high density lipoproteins-C, low density lipoprotein-C, lipoprotein (a), fasting blood sugars were estimated.

STATISTICAL ANALYSIS

Data were analyzed by SPSS software, Student's t-test, standard deviation (SD), and standard error of mean (SEM), P-value <0.05 is considered to be significant.

RESULTS

In this study, we found no statistical significant differences in serum lipid and lipoprotein (a) profile between controls and thrombotic stroke patients.

CONCLUSIONS

Highest frequency (38%) of stroke was found in the age group of 7080 years. There were other associated risk factors such as diabetes in five cases (24%), hypertension in nine cases (43%), and family history of stroke in four cases. However, further studies are required to evaluate the importance of serum Lp(a) estimation in the assessment as a risk factor for thrombotic stroke.

Plasminogen activator inhibitor type 2: still an enigmatic serpin but a model for gene regulation

Plasminogen activator inhibitor type-2 (PAI-2; SERPINB2) is an atypical member of the Ov-serpin family of serine protease inhibitors. While it is an undisputed inhibitor of urokinase and tissue-type plasminogen activator in the extracellular space and on the cell surface, the weight of circumstantial evidence suggests that PAI-2 also fulfills an intracellular role which is independent of plasminogen activator inhibition and indeed may not even involve protease inhibition at all. More and more data continue to implicate a role for PAI-2 in many settings, the most recent associating it as a modulator of the innate immune response. Further to the debates concerning its physiological role, there are few genes, if any, that display the regulation profile of the PAI-2 gene: PAI-2 protein and mRNA levels can be induced in the order of, not hundred-, but thousand-folds in a process that is controlled at many levels including gene transcription and mRNA stability while an epigenetic component is also likely. The ability of some cells, including monocytes, fibroblasts, and neurons to have the capacity to increase PAI-2 synthesis to such high levels is intriguing enough. So why do these cells have the capacity to synthesize so much of this protein? While tantalizing clues continue to be revealed to the field, an understanding of how this gene is regulated so profoundly has provided insights into the broader mechanics of gene expression and regulation.

The plasminogen activator inhibitor 2 transcript is destabilized via a multi-component 3' UTR localized adenylate and uridylate-rich instability element in an analogous manner to cytokines and oncogenes

Plasminogen activator inhibitor type 2 (PAI-2; SERPINB2) is a highly-regulated gene that is subject to both transcriptional and post-transcriptional control. For the latter case, inherent PAI-2 mRNA instability was previously shown to require a nonameric adenylate-uridylate element in the 3' UTR. However, mutation of this site was only partially effective at restoring complete mRNA stabilization. In the present study, we have identified additional regulatory motifs within the 3' UTR that cooperate with the nonameric adenylate-uridylate element to promote mRNA destabilization. These elements are located within a 74 nucleotide U-rich stretch (58%) of the 3' UTR that flanks the nonameric motif; deletion or substitution of this entire region results in complete mRNA stabilization. These new elements are conserved between species and optimize the destabilizing capacity with the nonameric element to ensure complete mRNA instability in a manner analogous to some class I and II adenylate-uridylate elements present in transcripts encoding oncogenes and cytokines. Hence, post-transcriptional regulation of the PAI-2 mRNA transcript involves an interaction between closely spaced adenylate-uridylate elements in a manner analogous to the post-transcriptional regulation of oncogenes and cytokines.

Insulin induces monocytic CXCL8 secretion by the mitogenic signalling pathway

Oral glucose uptake alters the function of immune cells and an elevation of systemic CXCL8 was described. Monocytes secrete high amounts of CXCL8 and therefore it was analyzed whether glucose or insulin upregulate monocytic CXCL8 release. Incubation of monocytes with insulin for 2h induced CXCL8 mRNA and secretion whereas glucose had no effect. Inhibition of the phosphatidylinositol 3-kinase by wortmannin or the mammalian target of rapamycin by rapamycin did not influence insulin-mediated CXCL8 induction. In contrast, blockage of the ERK-specific MAP kinase MEK with PD98059, that prevents phosphorylation of ERK1/ERK2, abrogated insulin-induced CXCL8 release in primary monocytes. To investigate the in vivo effect of oral glucose uptake, monocytes of healthy probands were isolated in the fasted state and 2h after glucose ingestion and CXCL8 mRNA and protein were increased in the latter. CXCL8 was also higher when determined in the cell lysate of leukocytes 2h after glucose uptake whereas plasma CXCL8 levels were significantly reduced. In summary, these data indicate that oral glucose uptake in insulin-sensitive adults is associated with elevated monocytic and reduced systemic CXCL8.

E-LDL upregulates TOSO expression and enhances the survival of human macrophages

Uptake of modified lipoproteins by macrophages causes foam cell formation and promotes atherosclerosis. Atherogenic lipoproteins are cytotoxic and induce cell death under certain conditions but may also enhance macrophage survival. Macrophages treated with enzymatically modified LDL (E-LDL) were subjected to GeneChip analysis and the antiapoptotic gene TOSO was found induced. TOSO mRNA is upregulated and apoptosis is reduced in E-LDL but not in oxidized LDL (Ox-LDL) loaded macrophages. FLIP(L) abundance was suggested to mediate the antiapoptotic properties of TOSO; however, FLIP(L) was not changed. Ox-LDL is internalized predominantly by scavenger receptors such as CD36 while E-LDL particles are preferentially internalized by Fc- and complement-receptor dependent phagocytosis and internalization of phagobeads by macrophages upregulates TOSO. In COS-7 cells however, phagocytotic activity was not affected by TOSO. These data indicate that E-LDL-generated foam cells are protected from cell death most likely through the expression of TOSO by a FLIP(L) independent mechanism.

Fibrinolysis, inflammation, and regulation of the plasminogen activating system

The maintenance of a given physiological process demands a coordinated and spatially regulated pattern of gene regulation. This applies to genes encoding components of enzyme cascades, including those of the plasminogen activating system. This family of proteases is vital to fibrinolysis and dysregulation of the expression pattern of one or more of these proteins in response to inflammatory events can impact on hemostasis. Gene regulation occurs on many levels, and it is apparent that the genes encoding the plasminogen activator (fibrinolytic) proteins are subject to both direct transcriptional control and significant post-transcriptional mechanisms. It is now clear that perturbation of these genes at either of these levels can dramatically alter expression levels and have a direct impact on the host's response to a variety of physiological and pharmacological challenges. Inflammatory processes are well known to impact on the fibrinolytic system and to promote thrombosis, cancer and diabetes. This review discusses how inflammatory and other signals affect the transcriptional and post-transcriptional expression patterns of this system, and how this modulates fibrinolysis in vivo.

Lipoprotein (a) and risk of ischemic stroke in young adults

Lipoprotein (a) [Lp(a)] is a LDL-particle linked to apoprotein (a) [apo(a)]. High Lp(a) plasma level is a risk factor for coronary heart disease and, in older men, for ischemic stroke. The role of Lp(a) as a risk factor for ischemic stroke in young adults is uncertain.

METHODS

Lp(a) concentration was prospectively measured in 100 consecutive patients with acute ischemic stroke (58 men and 42 women) aged 18-55 years, and in 100 controls matched for age and gender.

RESULTS

The distribution of Lp(a) concentration was skewed toward the highest and median tertiles in male patients. In multivariate logistic regression analyses adjusting on classical risk factors for ischemic stroke and lipid variables, Lp(a) concentration in the highest and medium tertiles compared with the lowest tertile was significantly associated with ischemic stroke in men (OR 3.55, 95% CI 1.33-9.48, p = 0.012), but was not in women (OR 0.42, 95% CI 0.14-1.26, p = 0.12). Although large vessel atherosclerosis was more common in men than in women, there were no differences in Lp(a) concentration according to the cause of ischemic stroke.

CONCLUSION

Among subjects aged 18-55 years, a slightly elevated Lp(a) concentration was strongly and independently associated with ischemic stroke in men, but not in women. Further studies are required to elucidate the mechanisms underlying this gender-specific association.

Reciprocal upregulation of urokinase plasminogen activator and its inhibitor, PAI-2, by Borrelia burgdorferi affects bacterial penetration and host-inflammatory response

The mammalian plasminogen activation system (PAS) is a complex system involved in multiple physiological and pathological processes. Borrelia burgdorferi interacts with certain components of the PAS. Here we further investigate this interaction to determine its effect on bacterial dissemination and host cell migration in vitro. We show that stimulation of monocytic cells with B. burgdorferi induces the transient production and secretion of urokinase plasminogen activator (uPA), shortly followed by its physiological inhibitor, plasminogen activator inhibitor-2 (PAI-2). Mono Mac 6 (MM6) cells as well as peripheral blood monocytes enhanced transmigration of B. burgdorferi across a barrier coated with fibronectin mediated by uPA. Moreover, the induction of PAI-2 or the addition of recombinant PAI-2 did not have a significant effect on the uPA-potentiated transmigration of B. burgdorferi. In contrast, the induction of PAI-2 by B. burgdorferi resulted in significantly diminished invasion by monocytic cells across a reconstituted basement membrane (matrigel), which could be partially restored by treatment with purified uPA. These results show that the PAS plays a twofold role in the pathogenesis of B. burgdorferi infection, both by enhancing bacterial dissemination and by diminishing host-cell inflammatory migration.

Therapy of hyper-Lp(a)

Lipoprotein (a) [Lp(a)] appears to be one of the most atherogenic lipoproteins. It consists of a low-density lipoprotein (LDL) core in addition to a covalently bound glycoprotein, apolipoprotein (a) [apo(a)]. Apo(a) exists in numerous polymorphic forms. The size polymorphism is mediated by the variable number of kringle-4 Type-II repeats found in apo(a). Plasma Lp(a) levels are determined to more than 90% by genetic factors. Plasma Lp(a) levels in healthy individuals correlate significantly high with apo(a) biosynthesis and not with its catabolism. There are several hormones known to have a strong impact on Lp(a) metabolism. In certain diseases, such as kidney disease, Lp(a) catabolism is impaired leading to up to fivefold elevations. Lp(a) levels rise with age but are otherwise influenced only little by diet and lifestyle. There is no safe and efficient way of treating individuals with elevated plasma Lp(a) concentrations. Most of the lipid-lowering drugs have either no significant influence on Lp(a) or exhibit a variable effect in patients with different forms of primary and secondary hyperlipoproteinemia. There is without doubt a strong need to concentrate on the development of specific medications to selectively target Lp(a) biosynthesis, Lp(a) assembly and Lp(a) catabolism. So far only anabolic steroids were found to drastically reduce Lp(a) plasma levels. This class of substance cannot, of course, be used for treatment of patients with hyper-Lp(a). We recommend that the mechanism of action of these drugs be studied in more detail and that the possibility of synthesizing derivatives which may have a more specific effect on Lp(a) without having any side effects be pursued. Other strategies that may be of use in the development of drugs for treatment of patients with hyper-Lp(a) are discussed in this review.

Quo vadis haemapheresis. Current developments in haemapheresis

The techniques of haemapheresis originated in the development of centrifugal devices separating cells from plasma and later on plasma from cells. Subsequently membrane filtration was developed allowing for plasma-cell separation. The unspecificity of therapeutic plasma exchange led to the development of secondary plasma separation technologies being specific, semi-selective or selective such as adsorption, filtration or precipitation. In contrast on-line differential separation of cells is still under development. Whereas erythrocytapheresis, granulocytapheresis, lymphocytapheresis and stem cell apheresis are technically advanced, monocytapheresis may need further improvement. Also, indications such as erythrocytapheresis for the treatment of polycythaemia vera or photopheresis though being clinically effective and of considerable importance for an appropriate disease control are to some extent under debate as being either too costly or without sufficient understanding of the mechanism. Other forms of cell therapy are under development. Rheohaemapheresis as the most advanced technology of extracorporeal haemorheotherapy is a rapidly developing approach contributing to the treatment of microcirculatory diseases and tissue repair. Whereas the control of a considerable number of (auto-) antibody mediated diseases is beyond discussion, the indication of apheresis therapy for immune complex mediated diseases is quite often still under debate. Detoxification for artificial liver support advanced considerably during the last years, whereas conclusions on the efficacy of septicaemia treatment are debatable indeed. LDL-apheresis initiated in 1981 as immune apheresis is well established since 24 years, other semi-selective or unspecific procedures, allowing for the elimination of LDL-cholesterol among other plasma components are also being used. Correspondingly Lp(a) apheresis is available as a specific, highly efficient elimination procedure superior to techniques which also eliminate Lp(a). Quality control systems, more economical technologies as for instance by increasing automation, influencing the over-interpretation of evidence based medicine especially in patients with rare diseases without treatment alternative, more insight into the need of controlled clinical trials or alternatively improved diagnostic procedures are among others tools ways to expand the application of haemapheresis so far applied in cardiology, dermatology, haematology, immunology, nephrology, neurology, ophthalmology, otology, paediatrics, rheumatology, surgery and transfusion medicine.

Cytoplasmic and nuclear interaction between Rb family proteins and PAI-2: a physiological crosstalk in human corneal and conjunctival epithelial cells

Extracellular plasminogen activator inhibitor type-2 (PAI-2) is a potent inhibitor of urokinase-type plasminogen activator (u-PA) and also acts as a multifunctional protein. However, the biological activity of intracellular PAI-2, as well as its intracellular targets, until now remain an enigma. Here, we show that pRb2/p130 and Rb1/p105, but not p107, interact with PAI-2 in both the cytoplasm and nucleus of normal primary human corneal and conjunctival epithelial cells. We provided the first in vivo evidence that a specific fragment of the PAI-2 promoter is bound simultaneously by pRb2/ p130, PAI-2, E2F5, histone deacetylase 1 (HDAC1), DNA methyltransferase 1 (DNMT1), and histone methyltransferase (SUV39H1), in normal primary human corneal epithelial cells, and by pRb2/p130, PAI-2, E2F5, HDAC1, and DNMT1, in normal primary human conjunctiva epithelial cells. Our results strongly indicate a physiological interaction between pRb family members and PAI-2, suggesting the hypothesis that pRb2/p130 and PAI-2 may cooperate in modulating PAI-2 gene expression by chromatin remodeling, in normal corneal and conjunctival cells.

The adiponectin paralog CORS-26 has anti-inflammatory properties and is produced by human monocytic cells

The adiponectin paralog CORS-26 (collagenous repeat-containing sequence of 26kDa protein) is a member of the C1q/TNF-alpha molecular superfamily. CORS-26 is a secreted protein and baculovirus-produced CORS-26 released in the supernatant of insect cells forms stable trimers. Adiponectin exerts anti-inflammatory effects in LPS-treated monocytic cells and CORS-26 also reduces IL-6 and TNF-alpha secretion but does not increase IL-10. Suppression of NFkappaB signalling may explain the anti-inflammatory actions of CORS-26. Furthermore CORS-26 protein was detected in human monocytic and dendritic cells. The present data demonstrate for the first time that CORS-26 forms trimers, exerts anti-inflammatory properties and that it is expressed in monocytic cells. Therefore CORS-26 may provide a new target for pharmacological drugs in inflammatory diseases like the metabolic syndrome.

The undecided serpin

Plasminogen activator inhibitor type-2 (PAI-2) is a nonconventional serine protease inhibitor (serpin) with unique and tantalizing properties that is generally considered to be an authentic and physiological inhibitor of urokinase. However, the fact that only a small percentage of PAI-2 is secreted has been a long-standing argument for alternative roles for this serpin. Indeed, PAI-2 has been shown to have a number of intracellular roles: it can alter gene expression, influence the rate of cell proliferation and differentiation, and inhibit apoptosis in a manner independent of urokinase inhibition. Despite these recent advances in defining the intracellular function of PAI-2, it still remains one of the most mysterious and enigmatic members of the serpin superfamily.

Lipoprotein(a) as a risk factor for atherosclerosis and thrombosis: mechanistic insights from animal models

Evidence continues to accumulate from epidemiological studies that elevated plasma concentrations of lipoprotein(a) [Lp(a)] are a risk factor for a variety of atherosclerotic and thrombotic disorders. Lp(a) is a unique lipoprotein particle consisting of a moiety identical to low-density lipoprotein to which the glycoprotein apolipoprotein(a) [apo(a)] that is homologous to plasminogen is covalently attached. These features have suggested that Lp(a) may contribute to both proatherogenic and prothrombotic/antifibrinolytic processes and in vitro studies have identified many such candidate mechanisms. Despite intensive research, however, definition of the molecular mechanisms underlying the epidemiological data has proven elusive. Moreover, an effective and well-tolerated regimen to lower Lp(a) levels has yet to be developed. The use of animal models holds great promise for resolving these questions. Establishment of animal models for Lp(a) has been hampered by the absence of this lipoprotein from common small laboratory animals. Transgenic mice and rabbits expressing human apo(a) have been developed and these have been used to: (i) examine regulation of apo(a) gene expression; (ii) study the mechanism and molecular determinants of Lp(a) assembly from LDL and apo(a); (iii) demonstrate that apo(a)/Lp(a) are indeed proatherogenic and antifibrinolytic; and (iv) identify structural domains in apo(a) that mediate its pathogenic effects. The recent construction of transgenic apo(a) rabbits is a particularly promising development in view of the excellent utility of the rabbit as a model of advanced atherosclerosis.

Lipoprotein(a): new insights into mechanisms of atherogenesis and thrombosis

Lipoprotein(a) (Lp[a]) continues to be a controversial molecule regarding its role in human vascular disease. Although the physiologic role of this molecule is still unclear, novel discoveries within the last few years have suggested numerous mechanisms whereby Lp(a) may contribute to atherosclerosis and its complications in human subjects. These effects may differentially occur in vascular tissue and circulating blood compartments. A complex interplay between tissue-specific effects is probably more relevant to the pathogenicity of this molecule than one single effect alone. This review briefly describes the structure of Lp(a) in relation to its biochemical function, summarizing the current literature on various pathophysiologic mechanisms of Lp(a)-induced vascular disease and the role of cell and tissue-specific effects in promoting atherogenesis and thrombosis.

Cell-cell contacts trigger programmed necrosis and induce cyclooxygenase-2 expression

Necrosis was induced by cell-cell contacts of human dermal fibroblasts in three-dimensional culture. Dramatic induction of cyclooxygenase-2 (COX-2) expression was found throughout these necrotizing cell clusters, whereas no increase in expression of apoptosis markers was seen. The cells were rapidly committed to necrosis, and the process could not be reversed by allowing them to spread and adhere on a solid substrate. Induction of COX-2 expression was accompanied by greatly enhanced production of the prostaglandins E(2), I(2), and F(2alpha). When applied exogenously on necrotizing clusters, these prostaglandins delayed cell clustering and further enhanced COX-2 expression. Abolishing prostaglandin production by NS-398 or indomethacin reduced cell membrane damage (as measured by lactate dehydrogenase release into the culture medium). We also identified alpha-enolase-mediated plasminogen activation as the major extracellular proteolytic executor of necrotic cell death. In contrast to inhibition of COX-2, inhibition of plasminogen activation failed to inhibit membrane damage associated with necrosis. Intracellular proteolysis, by caspases, was shown to take part in COX-2 induction. Taken together, our results indicate that cell-cell contacts induce an actively programmed necrotic process that functionally involves COX-2, a known hallmark of inflammation and cancer.

Lipoprotein (a) downregulates lysosomal acid lipase and induces interleukin-6 in human blood monocytes

The association of elevated lipoprotein (a) (Lp(a)) with an increased risk for coronary events is clearly established. This increased risk may in part be due to the activation of monocytes as major cells involved in atherogenesis. High concentrations of plasma Lp(a) were shown to influence the gene expression of human blood monocytes and in the present study we demonstrate a reduced abundance of the lysosomal acid lipase (LAL) mRNA in monocytes of patients with coronary disease and selective Lp(a) hyperlipidemia. This is also supported by in vitro studies where purified Lp(a) but not low-density lipoprotein (LDL) was shown to downregulate mRNA levels of the LAL in control monocytes. A correlation of Lp(a) serum levels and the proinflammatory cytokine IL-6 was recently also described. Therefore, we investigated whether Lp(a) is capable to enhance the release of this acute phase cytokine from human blood monocytes. Purified Lp(a) led to an increased secretion of IL-6, but not TNF-alpha arguing against a general activation of these cells. The association of reduced LAL activity with the premature development of coronary artery disease has been demonstrated in patients with hypercholesterolemia, and in the present study we show for the first time that LAL expression is suppressed in monocytes from patients with Lp(a) hyperlipidemia and by purified Lp(a). In addition, increased levels of IL-6 also predict future cardiovascular events and IL-6 secretion was also induced by purified Lp(a).

Lipoprotein(a) and the atherothrombotic process: mechanistic insights and clinical implications

Although many epidemiologic studies have pointed at an association between plasma levels of lipoprotein(a) (Lp(a)) and cardiovascular risk, the data obtained have been conflicting because of a number of factors, particularly those dealing with plasma storage, lack of assay standardization, population sample size, age, gender, ethnic variations, and variable disease endpoints. Moreover, the attention has been primarily focused on whole Lp(a), with relatively less emphasis on its constituent apolipoprotein(a) and on the apolipoprotein B100-containing lipoprotein, mainly low-density lipoprotein (LDL), to which apolipoprotein(a) is linked. According to recent studies, small-size apolipoprotein(a) isoforms may represent a cardiovascular risk factor either by themselves or synergistically with plasma Lp(a) concentration. Moreover, the density properties of the LDL moiety may have an impact on Lp(a) pathogenicity. It has also become apparent that Lp(a) can be modified by oxidative events and by the action of lipolytic and proteolytic enzymes with the generation of products that exhibit atherothrombogenic potential. The role of the O-glycans linked to the inter-kringle linkers of apolipoprotein(a) is also emerging. This information is raising the awareness of the pleiotropic functions of Lp(a) and is opening new vistas on pathogenetic mechanisms whose knowledge is essential for developing rational therapies against this complex cardiovascular pathogen.

Lipoprotein(a): still an enigma?

PURPOSE OF REVIEW

Lipoprotein(a) belongs to the class of the most atherogenic lipoproteins. Despite intensive research - in the last year more than 80 papers have been published on this topic - information is still lacking on the physiological function of lipoprotein(a) and the site of its catabolism. Important advances have been made in the knowledge of these points, which may have some therapeutic implications.

RECENT FINDINGS

The association of high lipoprotein(a) values with an increase in risk for coronary events has been documented in further prospective studies. This increased risk may relate to recent findings that apolipoprotein(a) is produced in situ within the vessel wall. In addition, lipoprotein(a) binds and inactivates the tissue factor pathway inhibitor and induces plasminogen activator inhibitor type 2 expression in monocytes. A new antisense oligonucleotide strategy has been proposed which efficiently inhibits apolipoprotein(a) expression in vitro and in vivo. Apolipoprotein(a), however, suppresses angiogenesis and thus may interfere with the infiltration of tumor cells. Finally, the enzymatic activity leading to the formation of apolipoprotein(a) fragments in plasma and their catabolism have been further elucidated.

SUMMARY

We are still far away from understanding the pathways involved in lipoprotein(a) catabolism, and the physiological function of this lipoprotein. Recent findings, however, provide new insight into pathomechanisms in patients with increased lipoprotein(a) related to hemostasis, which may serve as a basis for designing new treatment strategies.

Expression profiling and comparative sequence derived insights into lipid metabolism

Expression profiling and genomic DNA sequence comparisons are increasingly being applied to the identification and analysis of the genes that are involved in lipid metabolism. Not only has genome-wide expression profiling aided in the identification of novel genes that are involved in important processes in lipid metabolism such as sterol efflux, but also the utilization of information from these studies has added to our understanding of the regulation of pathways that participate in the process. Coupled with these gene expression studies, cross-species comparison (a technique used to search for sequences that are conserved through evolution) has proven to be a powerful tool to identify important noncoding regulatory sequences and novel genes that are relevant to lipid biology. An example of the value of this approach was the recent chance discovery of a new apolipoprotein gene (that which encodes apolipoprotein AV) that has dramatic effects on triglyceride metabolism in mice and humans.

Microarrays in hematology

Microarrays are fast becoming routine tools for the high-throughput analysis of gene expression in a wide range of biologic systems, including hematology. Although a number of approaches can be taken when implementing microarray-based studies, all are capable of providing important insights into biologic function. Although some technical issues have not been resolved, microarrays will continue to make a significant impact on hematologically important research.

Characterisation of PAUSE-1, a powerful silencer in the human plasminogen activator inhibitor type 2 gene promoter

Plasminogen activator inhibitor type 2 (PAI-2) is a serine protease inhibitor traditionally regarded as a regulator of fibrinolysis and extracellular matrix degradation. More recently, PAI-2 has been implicated in diverse processes such as keratinocyte differentiation, cell death and viral pathogenesis. The PAI-2 promoter tightly regulates PAI-2 gene expression in a cell-specific manner and this control is mediated, in part, by the upstream silencer element, PAUSE-1. Here we have defined PAUSE-1 and investigated its activity as a silencer. A series of mutations were generated within the PAUSE-1 element and analysed for transcription factor binding and transcriptional silencing activity. These studies have defined the minimal functional PAUSE-1 element as TCTN(x)AGAN(3)T(4), where x = 0, 2 or 4. Examination of related elements present in other promoters, such as the human IFNbeta promoter, suggests that PAUSE-1 is a member of a family of universal silencers with the consensus sequence TCTN(x)AGA. UV crosslinking analyses determined that the PAUSE-1 binding protein was approximately 67 kDa. Insertion of PAUSE-1 into the heterologous (SV40) or the minimal PAI-2 promoters silenced transcription by 2.5-fold. These data show that PAUSE-1 acts as a powerful silencer of PAI-2 gene transcription and is likely to be important in the silencing of other genes as well.

DNA arrays in allergy and immunology

The DNA array technique allows the simultaneous analysis of multiple genes. This makes it an interesting tool for studies of gene expression in various diseases that are caused by or depend on multiple genes. DNA arrays are particularly applied to define certain immunological conditions such as allergic diseases. We summarize strategies on gene expression profiling of inflammatory disease and immunologically relevant cells using DNA array technology. Using DNA arrays, gene expression analysis of CD4+ T cells of allergy patients revealed interesting differences compared to healthy individuals, but also between different allergic conditions. This comparison demonstrated that T cells differed in their capacity to regulate peripheral tolerance, neuronal innervation, chemotaxis, neovascularization and epidermal growth. On the basis of these findings the DNA array technique appears to be especially interesting for the development of powerful diagnostic tools allowing fine specification and subtyping of allergic conditions, monitoring of therapy and of tailored therapy concepts.

The role of lipoprotein(a) in the pathogenesis of atherosclerotic cardiovascular disease and its utility as predictor of coronary heart disease events

Lipoprotein(a), is a highly heterogeneous lipoprotein, due to variations in the size of apolipoprotein(a), and the density of the apoB100-containing particles to which apo(a) is linked. Although high plasma levels of Lp(a) have been associated with an increased risk for atherosclerotic cardiovascular disease, the mechanism underlying this association is still largely undetermined, as is the potential role played by the particle's heterogeneity. Lp(a) pathogenicity may also be influenced by the action of environmental factors and post-translational events relating to oxidative processes, and the action of lipolytic and proteolytic enzymes. Complicating the study of Lp(a) are the competing methods for its quantification due to its complex structure, and the lack of standardized methodologies. The recognition that Lp(a) particles may not all be alike in atherogenic potential should encourage studies to identify genetic and nongenetic factors underlying its heterogeneity, in order to reach a better understanding of its actual impact on atherosclerotic cardiovascular disease.