Udo Seedorf

Expression of ATP binding cassette‐transporter ABCG1 prevents cell death by transporting cytotoxic 7β‐hydroxycholesterol

Oxysterols result from cholesterol by enzymatic or oxidative processes. Some exert cytotoxic effects leading to necrosis or apoptosis. Detoxification of these compounds mainly occurs in the liver and requires transport from peripheral tissues towards it. Some ATP‐binding cassette transporters are involved in export of cytotoxic compounds. In the current study, we investigated whether ABC transporter family member G1 (ABCG1) may be involved in oxysterol transport, since its gene expression is highly responsive to oxysterol loading. TetOff HeLa cells stably expressing ABCG1 showed decreased mass uptake of 7β‐hydroxycholesterol (7β‐HC) whereas that of other physiologically relevant oxysterols was unaffected. Application of 7β‐HC to ABCG1 expressing cells induced hyperpolarization of mitochondrial membrane potential and production of reactive oxygen species, indicating energy consumption by the ATP‐binding cassette transporter when it is activated by its correct substrate. Our study points to detoxification as one of potential cellular functions of ABCG1. We assume that ABCG1 protects against 7β‐HC‐induced cell death, an important role in prevention of neurodegenerative and cardiovascular disease.

Interaction between periodontal disease and atherosclerotic vascular disease – Fact or fiction?

C-reactive protein (CRP) level is associated with the 10-year risk of an atherosclerotic vascular disease (ASVD), suggesting presence of systemic inflammation probably long before ASVD is present. Where, however, does this systemic inflammation come from? One active area of research has been the study of dental infection and various forms of periodontal disease (PD), both of which are highly prevalent in populations at risk for ASVD. Recent data show that ASVD and PD interact with each other via systemic release of specific pro- and anti-inflammatory cytokines, small signal molecules and enzymes which modulate initiation and progression of the chronic inflammatory reaction involved in both diseases. In addition, periodontal pathogens were identified within atherosclerotic lesions and thrombi isolated from myocardial infarction patients. LDL cholesterol, a strong risk factor for ASVD, is also associated with PD; and statins, used to treat ASVD, are also active to prevent or reduce PD. Finally, there is growing evidence for common genetic susceptibility factors involved in both diseases. These findings support commonalities with respect to the pathogenic mechanisms involved in both inflammatory diseases. Conversely, a causative relationship cannot yet be concluded in the absence of data from large longitudinal cohort and randomized controlled intervention trials.

Expression and functional characterization of ABCG1 splice variant ABCG1(666).

The ATP‐binding cassette transporter ABCG1 mediates the transport of excess cholesterol from macrophages and other cell types to high density lipoprotein (HDL) but not to lipid‐depleted apolipoprotein AI. Several splice variants which may have different functions have been identified in mammals. In the current study, we characterized the human splice variant ABCG1(666), which differs from full‐length ABCG1(678) by absence of an internal segment of 12 amino acids (VKQTKRLKGLRK). Accordingly spliced ABCG1 transcripts were detected in macrophages and liver in approximately twofold higher amounts than the alternatively spliced ABCG1 form encoding full‐length ABCG1. We used transient and stable expression of ABCG1(666) fusion proteins to characterize glycosylation, subcellular localization, molecular interaction and functions of this ABCG1 variant. It could be demonstrated that ABCG1(666) is located at the cell surface and has the ability to form cholesterol transport competent homodimers which affect cellular cholesterol export in a similar manner as previously characterized forms of ABCG1. Our results support that ABCG1(666) may in fact be the most prominent form of functional ABCG1 expressed in the human.

Impact of lipoprotein(a) levels and apolipoprotein(a) isoform size on risk of coronary heart disease

Observational and genetic studies have shown that lipoprotein(a) [Lp(a)] levels and apolipoprotein(a) [apo(a)] isoform size are both associated with coronary heart disease (CHD) risk, but the relative independence of these risk factors remains unclear. Clarification of this uncertainty is relevant to the potential of future Lp(a)‐lowering therapies for the prevention of CHD.

Genetic Susceptibility Contributing to Periodontal and Cardiovascular Disease

Periodontal disease (PD) and coronary artery disease (CAD) are common diseases characterized by an overaggressive inflammatory response to diverse stimuli. Whereas PD leads to destruction of the tooth-supporting structures, CAD is a chronic inflammatory condition ultimately causing myocardial infarction via narrowing and occluding of blood vessels. Classical twin studies led to the conclusion that both complex diseases have a similar degree of heritability and that a significant fraction of the genetic factors accounting for this heritability is shared. Recent genome-wide association and large-scale candidate gene studies highlight that variations in >50 genes are associated with premature CAD, while variations in only 4 genes showing nominally significant associations with aggressive periodontitis and/or chronic periodontitis have so far been identified. Remarkably, 3 of the PD loci (75%) show shared associations with CAD (ANRIL/CDKN2B-AS1, PLG, CAMTA1/VAMP3), suggesting involvement of common pathogenic mechanisms. In this critical review, we highlight recent progress in identifying genetic markers and variants associated with PD, present their overlap with CAD, and discuss functional aspects. In addition, we answer why a significant fraction of the heritability of PD is still missing, and we suggest approaches that may be taken to close the gap.

3β,5α,6β-Cholestanetriol and 25-hydroxycholesterol accumulate in ATP-binding cassette transporter G1 (ABCG1)-deficiency

OBJECTIVE Oxysterols are oxidized derivatives of sterols that have cytotoxic effects and are potent regulators of diverse cellular functions. Efficient oxysterol removal by the sub-family G member 1 of the ATP-binding cassette transporters (ABCG1) is essential for cell survival and control of cellular processes. However, the specific role of ABCG1 in the transport of various oxysterol species has been not systematically investigated to date. Here, we examined the involvement of ABCG1 in the oxysterol metabolism by studying oxysterol tissue levels in a mouse model of Abcg1-deficiency. METHODS AND RESULTS Analysis of lung tissue of Abcg1(-/-) mice on a standard diet revealed that 3β,5α,6β-cholestanetriol (CT) and 25-hydroxycholesterol (HC) accumulated at more than 100-fold higher levels in comparison to wild-type mice. 24S-HC and 27-HC levels were also elevated, but were minor constituents. A radiolabeled assay employing regulable ABCG1-expressing HeLa cell lines revealed that 25-HC export to albumin was dependent on functional ABCG1 expression and could be blocked by an excess of unlabeled 25-HC or 27-HC. In this cell line, 25-HC at low doses triggered mitochondrial membrane potential, and reactive oxygen species production, which are both indirect indicators of cellular energy expenditure. CONCLUSION Our results suggest that 25-HC and CT are physiologic substrates for ABCG1. Excessive accumulation of these oxysterols may explain the increased rate of cell death and the inflammatory phenotype observed in Abcg1-deficient animals and cells.

Chronic oral infection: An emerging risk factor of cerebral small vessel disease

Chronic oral infections (gingivitis/periodontitis) have been associated with age-related diseases such as diabetes, coronary heart disease, and acute ischemic stroke. In addition, imaging surrogates of cerebrovascular ischemia beyond acute ischemic stroke (i.e., silent strokes and brain white matter hyperintensities) may also be associated with chronic oral infections. The pathology underlying lacunar strokes and brain white matter hyperintensities (WMH) relates to small vessel disease in the brain. In this review, we highlight recent progress in exploring potential associations of oral infections with cerebral small vessel disease and its surrogates (silent strokes, white matter hyperintensities) and clinical sequelae (i.e., vascular dementia). Recent evidence suggests that periodontitis aggravates cerebral small vessel disease and increases lacunar stroke risk. Moreover, periodontitis interacts with Alzheimers disease to increase the severity of clinical dementia and to accelerate its manifestations. The results suggest that periodontitis may be an emerging risk factor of small vessel disease-associated cerebrovascular disorders and that the risk increase may be mediated by the systemic inflammation resulting from chronic oral infections. Large cohort studies employing state-of-the-art magnetic resonance techniques to identify specific cerebral pathologies as a function of time, oral health status, and systemic inflammation are needed to further substantiate the hypothesis.

Oral health and access to dental care – a comparison of elderly migrants and non-migrants in Germany

ABSTRACT Objectives: To compare oral health, access barriers to dental care, oral health behavior and oral hygiene behavior of elderly German residents with and without immigration background. Design: In this cross-sectional explorative study, a convenience sample (N = 112, age ≥ 60 years, 54% immigrants) was recruited in four dental practices in Hamburg, Germany. Oral health was assessed with Decayed/Missing/Filled Teeth (DMFT), Papillary Bleeding Index (PBI), and Approximal Plaque Index (API). Dental health was operationalized as number of decayed teeth, and poor oral hygiene based on a PBI ≥ 40%. Access barriers and oral health behavior were assessed with a standardized questionnaire. Results: While caries experience was similar in migrants and non-migrants (DMFT mean: 24.8 vs. 23.4, n.s.), significantly more teeth were decayed (5.3 vs. 2.1, p < 0.001), and API (55.3% vs. 33.0%, p = 0.002) and PBI (46.3% vs. 30.5%, p = 0.016) were significantly higher in migrants. After adjusting for age, sex, income, education, and number of teeth, migrants still had on average 3 decayed teeth more than non-migrants. However, impact of migration background on poor oral health changed from OR = 3.61 (p = 0.007) to OR = 1.05 (n.s.) after adjusting for confounders, mainly due to lower income in migrants. Fewer migrants had visited a dentist within the past 12 months, and migrants were less likely to have a regular dentist that they visit and more often indicated language or cost barriers than non-migrants. Conclusion: Elderly German migrants have higher treatment needs than non-migrants. Likely causes are poorer oral hygiene and lower utilization of dental care services. Specific prevention programs targeting migrants are warranted to improve oral health in this disadvantaged group.

Roles of Oral Infections in the Pathomechanism of Atherosclerosis

Oral infections occur frequently in humans and often lead to chronic inflammations affecting the teeth (i.e., caries), the gingival tissues surrounding the teeth (i.e., gingivitis and endodontic lesions), and the tooth-supporting structures (i.e., periodontitis). At least four basic pathogenic mechanisms have been proposed that involve oral inflammations in the pathogenesis of atherosclerosis: (1) low level bacteremia by which oral bacteria enter the blood stream and invade the arterial wall; (2) systemic inflammation induced by inflammatory mediators released from the sites of the oral inflammation into the blood stream; (3) autoimmunity to host proteins caused by the host immune response to specific components of oral pathogens; (4) pro-atherogenic effects resulting from specific bacterial toxins that are produced by oral pathogenic bacteria. In this narrative review, we summarize published experimental evidence related to these four mechanisms and discuss their impact on the pathogenesis of atherosclerosis.

Roles of the Chr.9p21.3 ANRIL locus in regulating inflammation and implications for anti-inflammatory drug target identification

Periodontitis (PD) is a common gingival infectious disease caused by an over-aggressive inflammatory reaction to dysbiosis of the oral microbiome. The disease induces a profound systemic inflammatory host response, that triggers endothelial dysfunction and pro-thrombosis and thus may aggravate atherosclerotic vascular disease and its clinical complications. Recently, a risk haplotype at the ANRIL/CDKN2B-AS1 locus on chromosome 9p21.3, that is not only associated with coronary artery disease / myocardial infarction (CAD/MI) but also with PD, could be identified by genome-wide association studies. The locus encodes ANRIL - a long non-coding RNA (lncRNA) which, like other lncRNAs, regulates genome methylation via interacting with specific DNA sequences and proteins, such as DNA methyltranferases and polycomb proteins, thereby affecting expression of multiple genes by cis and trans mechanisms. Here, we describe ANRIL regulated genes and metabolic pathways and discuss implications of the findings for target identification of drugs with potentially anti-inflammatory activity in general.