Modulation of growth control mechanisms critical to atherogenesis

The principal lesion characteristic of atherosclerosis is the plaque. This lesion mainly consists of smooth muscle cells, connective matrix and large amounts of extracellular lipids. Smooth muscle cell hyperplasia is an integral event in atherosclerotic plaque formation and the resultant occlusion of blood vessels. These abnormal cell proliferations are primarly caused by defects in the autocrine and/or paracrine growth regulation. A novel mechanism critical to atherogenesis introduced in the present study is gap junctional mediated growth control. The atherogen-induced effects on gap junctional communication between human smooth muscle cells are described in chapters 2,3 and 4. The role of autocrine growth stimulation in atherogenesis is shown by the demonstration of the presence of activated transforming genes in atherosclerotic lesions (chapter 5) and the cell transforming potential of (atherogenic) low density lipoproteins (LDL) as shown in chapter 6. Chapter 5 also demonstrated that several transforming genes may be present in human plaque DNA, one of them being PDGF-A (platelet-derived growth factor chain A). The expression of the latter gene can be modulated by oxidized LDL (chapter 7).The present investigation provides additional evidence for the hypothesis that autocrine production of growth modulating factors may contribute to the characteristic abnormal smooth muscle growth in atherogenesis. We demonstrated that lipoproteins with atherogenic potential, such as LDL, in contrast to the non-atherogenic HDL, are able to transform fibroblasts in vitro. Genetical alteration of intimal cells present in atherosclerotic lesions was demonstrated using DNA-mediated transfection techniques. It could be demonstrated that human aortic plaque DNA contains active transforming genes, as PDGF-A. This is in agreement with studies by Penn et al. (1986) and Ahmed et al. (1990), showing transforming genes in human coronary artery plaques. Even DNA of cultured human atherosclerotic plaque cells appeared to have cell transforming capacities (Parkes et al., 1991). Only Yew et al. (1989) could not demonstrate a transforming potential of human plaque DNA. The variable results obtained sofar might indicate that different mechanisms are involved. It should be stressed in this respect that in all these studies pooled plaque samples were used and it should be realized that the transforming potential is not necessarily present in each plaque. The observed transforming potential of plaque DNA supports very well the monoclonal hypothesis of Benditt and Benditt (1973). They observed that atherosclerotic lesions start as singular focal masses containing monoclonality and suggested that these masses were in general similar to benign tumors as observed in other tissues. However, it has been argued that apparent monoclonality could also arise because of strong selection pressure favoring a subpopulation of cells, although findings of transforming genes, such as PDGF-A, present in atherosclerotic lesions and the transforming potential of atherogens indicate the opposite. Additional arguments in favor of the monoclonal hypothesis are that tumor initiators like chemical mutagens and promutagens (Albert et al., 1975; Bond et al., 1981), radiation (Gold, 1961) and oncogenic viruses (Minick et al., 1979) can induce atherosclerotic lesions in laboratory animals. Hence, molecular alterations underlying the proliferation of smooth muscle cells could show resemblance to the molecular events, which are critical in the development of cancer.The current view on atherosclerosis is based on the "response to injury" hypothesis, implying a paracrine stimulation of smooth muscle growth as a result of injury of endothelium (Ross, et al., 1976; Ross, 1981). Most of the studies of experimental atherogenesis are implemented in the framework with this hypothetical model. Support for this hypothesis is based on the following observations. Atherosclerotic lesions can be induced in experimental animals by endothelial denudation and factors derived from platelets can induce smooth muscle growth in vitro. Injury to arterial endothelium by mechanical, chemical, toxic, viral, or immunological agents caused endothelial denudation, and was followed by platelet adhesion and aggregation, with consequent release of platelet-derived growth factors (PDGF), in turn leading to migration into and proliferation of smooth muscle cell in the intima and secretion of connective tissue components. Over the years, the hypothesis has been modified (Ross, 1990). First of all, it became apparent that actual denudation was not a consistent early feature of atherosclerosis (Davies et al., 1976). Secondly, platelet adherence is neither necessary nor sufficient to cause the lesions (Schwartz and Reidy, 1987). Presently, the view is: a. the endothelium can respond to a variety of stimuli, by subtle changes in function (endothelial dysfunction) and/or by the induction of new endothelium properties; thus non- denuding injury may be important in initiating the lesions of atherosclerosis and b. platelets are not the sole initiators of smooth muscle proliferation, since growth promoting and growth inhibitory factors secreted by other cell types, including macrophages and endothelial cells, may modulate smooth muscle growth.However, not all observations made can be explained by the "response to injury" hypothesis, including the findings that (intimal) smooth muscle cells themselves can secrete and can respond to growth modulating factors and the cell transforming potential of plaque DNA as demonstrated above, thus implying an involvement of autocrine growth stimuli. A good candidate for autocrine growth factor stimulation of smooth muscle cells is PDGF-A. High transcript levels of this transforming gene were detected in intimal cells of human atherosclerotic lesions (Libby et al., 1988; Wilcox et al., 1988). The present study showed that PDGF-A was identified as one of the transforming genes present in human plaque DNA and the expression of this gene can be induced by LDL (oxidized). HDL, a protective lipoprotein to atherosclerosis, did not modulate PDGF-A transcript levels in smooth muscle cells. While both oxidized LDL as well as PDGF-A transcripts are detected in atherosclerotic lesions this molecular mechanism could play a role in atherogenesis.Furthermore, the present study provides strong evidence that disturbance of intercellular communication is another mechanism, which is probably important in the etiology of atherosclerosis. It is shown that compounds with atherogenic potential inhibit communication between human smooth muscle cells. The potency to modulate cell-cell communication correlates well with their atherogenic potential. For example, low density lipoproteins (LDL) in oxidized form and cholesterol oxidation products inhibited cell-cell communication. A non-atherogenic lipoprotein as high density lipoprotein (HDL) did not influence gap junctional communication between human smooth muscle cells. Otherwise, growth factors like PDGF and EGF can modulate cell-to-cell communication (Maldonado et al., 1988; Madhukar et al., 1989). This would imply that both paracrine and autocrine growth factor production are involved in atherogenesis, in which their influence on the gap junctional mediated growth control mechanism is a vital step in atherogenesis. At this stage, disruption of intercellular communication results in an uninhibited multiplication of these cells leading to the formation of (monoclonal) atherosclerotic lesions.The main conclusion of the present study is that the three phenomena 1) production of growth modulating factors by vascular cells, including endothelium, monocytes, platelets and smooth muscle cells 2) DNA modification (e.g. PDGF-A) of smooth muscle cells 3) loss of intercellular communication together are important factors in the process of atherosclerosis. The two main theories on atherosclerosis, the "monoclonal" and the "response to injury" theory, are compatible in many respects and can be fit into one unifying hypothesis as described in Fig. 8.1The figure shows that one of the earliest events in atherosclerosis is an increased adhesion of monocytes to what appears to be intact arterial endothelium, a phenomenon which can be well demonstrated using scanning electron microscopy (Faggiotto et al., 1984). In this process lipid factors like hypercholesteraemia and other factors as IL-1 or TNF (which introduces adhesion molecules. on endothelial cells) are important triggers. As a consequence of monocyte emigration, there is focally increased permeability to LDL and macromolecules (Territo et al., 1984; Gerrity et al., 1979). An altered endothelial function (dysfunction) causing increased permeability may also be induced by risk factors such as hypertension, hyperlipidaemia, smoking, immunological factors, stress and diabetes mellitus (Reidy, 1985; Sieffert et al., 1981; Gordon et al., 1981, Munro and Cotran, 1988). In this way the agents present in the bloodstream (such as LDL) accumulate and are modified in the arterial wall and thereafter exert their effects locally on vascular cells.The next important step could be DNA modification(s) of smooth muscle cells as shown by the presence of transforming genes, as PDGF-A, in lesion DNA and the effects of the atherogenic LDL on cell transformation. This defect of an autocrine growth regulation is followed by another vital growth control mechanism, the gap junctional communication. Communication between human smooth muscle cells has been modified by several atherogens, like LDL (oxidized) and oxysterols. In case of impairement of both growth regulation mechanisms clonal growth may occur.The processes described on the left side of the scheme are consistent with the paracrine proliferation mechanism of "the response to injury" theory of Ross (1990). The first trigger in this process is a dysfunction of the endothelium. This process introduces the adhesion and aggregation of platelets and/or monocytes to the endothelium, which results in a release of growth modulating factors as platelet-derived growth factor. At this stage, paracrine growth stimulating factors do not yet cause abnormal smooth muscle growth, because autonomous growth of cells still is controlled by gap junctional communication with surrounding cells. Only when growth factors (and atherogens) inhibit gap junctional communication abnormal smooth muscle cell proliferation occurs. Thus, inhibition of gap junctional intercellular communication could play a predominant role in the onset of atherogenesis.A better understanding of these growth modulating processess will improve the possibility to study the possible atherogenic properties of chemicals within the framework of toxicological research

Denitrification in an oligotrophic estuary: a delayed sink for riverine nitrate

Estuaries are often seen as natural filters of riverine nitrate, but knowledge of this nitrogen sink in oligotrophic systems is limited. We measured spring and summer dinitrogen production (denitrification, anammox) in muddy and non-permeable sandy sediments of an oligotrophic estuary in the northern Baltic Sea, to estimate its function in mitigating the riverine nitrate load. Both sediment types had similar denitrification rates, and no anammox was detected. In spring at high nitrate loading, denitrification was limited by likely low availability of labile organic carbon. In summer, the average denitrification rate was similar to 138 mu mol N m(-2) d(-1). The corresponding estuarine nitrogen removal for August was similar to 1.2 t, of which similar to 93% was removed by coupled nitrification-denitrification. Particulate matter in the estuary was mainly phytoplankton derived (> 70% in surface waters) and likely based on the riverine nitrate which was not removed by direct denitrification due to water column stratification. Subsequently settling particles served as a link be tween the otherwise uncoupled nitrate in surface waters and benthic nitrogen removal. We suggest that the riverine nitrate brought into the oligotrophic estuary during the spring flood is gradually, and with a time delay, removed by benthic denitrification after being temporarily ` trapped' in phytoplankton particulate matter. The oligotrophic system is not likely to face eutrophication from increasing nitrogen loading due to phosphorus limitation. In response, coupled nitrification-denitrification rates are likely to stay constant, which might increase the future export of nitrate to the open sea and decrease the estuary's function as a nitrogen sink relative to the load.Peer reviewe

Amnion formation in the mouse embryo: the single amniochorionic fold model

<p>Abstract</p> <p>Background</p> <p>Despite the detailed knowledge obtained over the last decade on the molecular regulation of gastrulation in amniotes, the process of amnion development has been poorly described and illustrated in mice, and conflicting descriptions exist. Understanding the morphogenesis and development not only of the early mouse embryo, but also of its extraembryonic tissues, is crucial for correctly interpreting fate-mapping data and mouse mutants with gastrulation defects. Moreover, the recent isolation from amnion of cells with stem cell features further argues for a better understanding of the process of amnion formation. Here, we revisit the highly dynamic process of amnion formation in the mouse. Amnion development starts early during gastrulation and is intimately related to the formation of the exocoelom and the expansion of the amniotic fold. The authoritative description involves the fusion of two amniotic folds, a big posterior and a smaller anterior fold. We challenged this 'two amniotic folds' model by performing detailed histomorphological analyses of dissected, staged embryos and 3D reconstructions using historical sections.</p> <p>Results</p> <p>A posterior fold of extraembryonic ectoderm and associated epiblast is formed early during gastrulation by accumulation of extraembryonic mesoderm posterior to the primitive streak. Previously called the "posterior amniotic fold", we rename it the "amniochorionic fold" (ACF) because it forms both amnion and chorion. Exocoelom formation within the ACF seems not to involve apoptosis within the mesoderm. The ACF and exocoelom expand without disrupting the anterior junction of epiblast, extraembryonic ectoderm and visceral endoderm. No separate anterior fold is formed; its absence was confirmed in 3D reconstructions. Amnion and chorion closure is eccentric, close to the anterior margin of the egg cylinder: we name it the "anterior separation point".</p> <p>Conclusions</p> <p>Here, we reconcile previous descriptions of amnion formation and provide new nomenclature, as well as an animation, that clarify and emphasize the arrangement of the tissues that contribute to amnion development and the dynamics of the process. According to our data, the amnion and the chorion are formed by a single amniochorionic fold initiated posteriorly. Finally, we give an overview on mutant mouse models with impaired amnion development.</p

Differences in neuropsychiatric symptoms between nursing home residents with young-onset dementia and late-onset dementia

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Agreement between oral contraceptive users and prescribers: implications for case-control studies

Case-control studies examining the effects of oral contraceptives (OC) are prone to misclassification bias due to errors in assessment of OC use. Concern about inaccurate exposure histories has increased since current studies require women to recall OC use over prolonged periods of time. In preparation for a case-control study of breast cancer and OC use, an investigation was carried out to assess agreement between women's lifetime histories of OC use (covering a period of up to 20 years) and prescribers' records. OC histories were obtained during personal interview with 218 women who had used OC at some point in their lives (127 breast cancer patients, 91 controls). Recall was aided by an album with color photographs of all OC marketed in the Netherlands from 1962 onwards (n = 65), and a calendar that covered the women's life span from date of birth to menopause. The participants were asked for the names of all physicians who prescribed OC for them. The rate of response from the prescribers was high (94%), but only half of the forms provided useful information. Patient-prescriber agreement on brand names (including dosage) was 70%. About half of the women agreed with their prescribers on starting dates to within less than a year's difference. Approximately the same percentage of agreement was found for stopping dates. Multiple linear regression indicated that agreement on brand names and dates of usage was lower for women of low socioeconomic status, for healthy women (as compared to breast cancer patients) and for periods of pill use that had to be recalled from the more distant past. Agreement on total duration of use was high enough to permit testing of a moderately strong duration-response relationship in a case-control study

Time trends in psychotropic drug prescriptions in Dutch nursing home residents with dementia between 2003 and 2018

Objective: Several European studies investigated the trends in psychotropic drug prescriptions (PDPs) among nursing home (NH) residents and reported a decline in antipsychotics prescriptions. Since the Dutch long-term care system differs from other European systems (e.g. higher threshold for NH admission and trained elderly care physicians), this study explores the trends in PDPs in Dutch NH residents with dementia. Methods: The study used data from nine studies, comprising two cross-sectional studies, one cohort study, and six cluster-randomized controlled trials, collected in Dutch NHs between 2003 and 2018. With multilevel logistic regression analysis, NHs as a random effect, we estimated the trends in PDPs overall and for five specific psychotropic drug groups (antipsychotics, antidepressants, anxiolytics, hypnotics, and anti-dementia drugs), adjusting for confounders: age, gender, severity of dementia, severity of neuropsychiatric symptoms, and length of stay in NHs. Results: The absolute prescription rate of antipsychotics was 37.5% in 2003 and decreased (OR = 0.947, 95% CI [0.926, 0.970]) every year. The absolute prescription rate of anti-dementia drugs was 0.8% in 2003 and increased (OR = 1.162, 95% CI [1.105, 1.223]) per year. The absolute rate of overall PDPs declined from 62.7% in 2003 to 40.4% in 2018. Conclusions: Among Dutch NH residents with dementia, the odds of antipsychotics prescriptions decreased by 5.3% per year while the odds of anti-dementia drug prescriptions increased by 16.2%. There were no distinct trends in antidepressants, anxiolytics, and hypnotics prescriptions. However, overall PDPs were still high. The PDPs in NH residents remain an issue of concern

On the origin of amniotic stem cells: of mice and men

A common characteristic of mammals is the development of extraembryonic supporting tissues and organs that are required for embryonic implantation, survival and development in utero. The amnion is the innermost extraembryonic membrane that eventually surrounds the fetus of amniotes, and contains the amniotic fluid. Next to its function in in utero development, the amnion has been shown to have an important potential for clinical applications. It is mainly used as a dressing to stimulate healing in skin and ocular wounds. Moreover, cells derived from the amniotic membrane and amniotic fluid have been reported to possess stem cell features, like pluripotent differentiation ability. Little is known about the early development of this membrane in humans. The mouse is a powerful genetic model organism that can be used to address the dynamics and the developmental origin of amnion and amnion-derived stem cells. Here, we discuss some fundamental differences in amnion development in the disc-shaped primate embryo and in the cup-shaped mouse embryo. We emphasize the consequences that this may have on the derivation of amniotic "stem" cells. After revision of the different isolation procedures of amniotic (fluid) derived "stem" cells from rodents, we reveal striking differences in the sources used to derive these cells across studies. The profound differences in the development of the extraembryonic membranes and cavities between primates and rodents may result in comparing cell types of different developmental origins, eventually leading to missinterpretations.status: publishe

Grip on challenging behaviour: a multidisciplinary care programme for managing behavioural problems in nursing home residents with dementia. Study protocol

Contains fulltext : 97945.pdf (publisher's version ) (Open Access)BACKGROUND: Behavioural problems are common in nursing home residents with dementia and they often are burdensome for both residents and nursing staff. In this study, the effectiveness and cost-effectiveness of a new care programme for managing behavioural problems will be evaluated. METHODS/DESIGN: The care programme is based on Dutch national guidelines. It will consist of four steps: detection, analysis, treatment and evaluation. A stepped wedge design will be used. A total of 14 dementia special care units will implement the care programme. The primary outcome is behavioural problems. Secondary outcomes will include quality of life, prescription rate of antipsychotics, use of physical restraints and workload and job satisfaction of nursing staff. The effect of the care programme will be estimated using multilevel linear regression analysis. An economic evaluation from a societal perspective will also be carried out. DISCUSSION: The care programme is expected to be cost-effective and effective in decreasing behavioural problems, workload of nursing staff and in increasing quality of life of residents. TRIAL REGISTRATION: The Netherlands National Trial Register (NTR). Trial number: NTR 2141

The Course of Quality of Life and Its Predictors in Nursing Home Residents With Young-Onset Dementia

OBJECTIVE: To explore the course of quality of life (QoL) and possible resident-related predictors associated with this course in institutionalized people with young-onset dementia (YOD). DESIGN: An observational longitudinal study. SETTING AND PARTICIPANTS: A total of 278 residents with YOD were recruited from 13 YOD special care units in the Netherlands. METHODS: Secondary analyses were conducted with longitudinal data from the Behavior and Evolution in Young-ONset Dementia (BEYOND)-II study. QoL was assessed with proxy ratings, using the Quality of Life in Dementia (QUALIDEM) questionnaire at 4 assessment points over 18 months. Predictors included age, gender, dementia subtype, length of stay, dementia severity, neuropsychiatric symptoms, and psychotropic drug use at baseline. Multilevel modeling was used to adjust for the correlation of measurements within residents and clustering of residents within nursing homes. RESULTS: The total QUALIDEM score (range: 0-111) decreased over 18 months with a small change of 0.65 (95% confidence interval -1.27, -0.04) points per 6 months. An increase in several domains of QoL regarding care relationship, positive self-image, and feeling at home was seen over time, whereas a decline was observed in the subscales positive affect, social relations, and having something to do. Residents with higher levels of QoL and more advanced dementia at baseline showed a more progressive decline in QoL over time. Sensitivity analyses indicated a more progressive decline in QoL for residents who died during the follow-up. CONCLUSION AND IMPLICATIONS: This study shows that although overall QoL in nursing home residents with YOD was relatively stable over 18 months, there were multidirectional changes in the QoL subscales that could be clinically relevant. Higher levels of QoL and more advanced stages of dementia at baseline predicted a more progressive decline in QoL over time. More longitudinal studies are needed to verify factors influencing QoL in YOD