Emerging engineered magnetic nanoparticulate probes for molecular MRI of atherosclerosis : how far have we come?

Atherosclerosis is a chronic, progressive, immunoinflammatory disease of the large and medium-sized arteries, and a major cause of cardiovascular diseases. Atherosclerosis often progresses silently for decades until the occurrence of a major catastrophic clinical event such as myocardial infarction, cardiac arrest and stroke. The main challenge in the diagnosis and management of atherosclerosis is to develop a safe, noninvasive technique that is accurate and reproducible, which can detect the biologically active high-risk vulnerable plaques (with ongoing active inflammation, angiogenesis and apoptosis) before the occurrence of an acute clinical event. This Journal Article reviews the events involved in the pathogenesis of atherosclerosis in light of recently advanced understanding of the molecular pathogenesis of the disease. Next, we elaborate on the interesting developments in molecular MRI, by describing the recently engineered magnetic nanoparticulate probes targeting clinically promising molecular and cellular players/processes, involved in early atherosclerotic lesion formation to plaque rupture and erosion.

Aortic intima-media thickness measured by trans-abdominal ultrasound as an early life marker of subclinical atherosclerosis

Atherosclerosis is a chronic inflammatory process that begins in early life. Improved identification of markers of early atherosclerosis via neonatal aortic intima-media thickness (aIMT) measurement may allow the development of interventions to prevent or reduce later cardiovascular disease.

Zinc doped ferrite magnetic resonance imaging contrast agent for atherosclerosis

 This project focuses on the development of zinc doped ferrite nanoparticle based MRI contrast agents with enhanced contrast and site-specific targeting for atherosclerosis diagnosis. The engineered nanocomplexes developed were validated through MRI scans using rat models with potential for multimodal imaging and effective therapy.

Changes in abdominal obesity and age-related macular degeneration: the atherosclerosis risk in communities study

OBJECTIVE: To examine the association between changes in waist-hip ratio (WHR), a measure of abdominal obesity, and age-related macular degeneration (AMD). METHODS: A total of 12 515 persons from a population-based cohort study, aged 45 to 64 years in 1987 to 1989, were followed up over 6 years. The percentage change in WHR during follow-up was ranked into sex-specific deciles; an increase in WHR was defined as the top 10% of change and a decrease in WHR as the bottom 10%. The association of increased or decreased WHR and presence of AMD at follow-up was determined using logistic regression adjusting for potential confounders. RESULTS: The average change in WHR was an increase of 2%, ranging from a decrease of 44% to an increase of 102%. A decrease in WHR of 3% or more was associated with 29% lower odds of any AMD (odds ratio = 0.71; 95% confidence interval, 0.52-0.97). This effect was most pronounced among obese participants at baseline, where a decrease in WHR was associated with 59% lower odds of AMD (odds ratio = 0.41; 95% confidence interval, 0.20-0.82). CONCLUSIONS: Middle-aged persons who had a 3% or greater reduction in WHR over time were less likely to have AMD, particularly among those who were initially obese.

Engineered atherosclerosis-specific zinc ferrite nanocomplex-based MRI contrast agents

BACKGROUND: Cardiovascular diseases are the most prevalent cause of morbidity and mortality affecting millions of people globally. The most effective way to counter cardiovascular complications is early diagnosis and the safest non-invasive diagnostic approach is magnetic resonance imaging (MRI). In this study, superparamagnetic ferrite nanoparticles doped with zinc, exhibiting highly enhanced saturation magnetization and T2 and computed tomography (CT) contrast were synthesized. These nanoparticles have been strategically engineered using bovine lactoferrin (Lf), polyethylene glycol (PEG), and heat shock protein (Hsp)-70 antibody specifically targeting atherosclerosis with potential therapeutic value. The nanocomplexes were further validated in vitro to assess their cytotoxicity, internalization efficiency, effects on cellular proliferation and were assessed for MRI as well as X-ray CT in ex vivo Psammomys obesus rat model.

RESULTS: Optimized zinc doped ferrite nanoparticles (Zn0.4Fe2.6O4) with enhanced value of maximum saturation magnetization value on 108.4 emu/g and an average diameter of 24 ± 2 nm were successfully synthesized. Successfully incorporation with bovine lactoferrin, PEG and Hsp-70 (70 kDa) antibody led to synthesis of spherical nanocomplexes (size 224.8 nm, PDI 0.398). A significantly higher enhancement in T2 (p < 0.05, 1.22-fold) and slightly higher T1 (1.09-fold) and CT (1.08-fold) contrast compared to commercial ferrite nanoparticles was observed. The nanocomplexes exhibited effective cellular internalization within 2 h in both THP-1 and Jurkat cells. MRI scans of contrast agent injected animal revealed significant arterial narrowing and a significantly higher T2 (p < 0.05, 1.71-fold) contrast in adult animals when compared to juvenile and control animals. The excised heart and aorta agar phantoms exhibited weak MRI contrast enhancement in juvenile animal but significant contrast enhancement in adult animal specifically at the aortic arch, descending thoracic aorta and iliac bifurcation region with X-ray CT scan. Histological investigation of the contrast agent injected aorta and heart confirmed site target-specific accumulation at the atherosclerotic aortic arch and descending thoracic aorta of the adult animal with severely damaged intima full of ruptured microatheromas.

CONCLUSION: Overall, the study demonstrates the strategic development of nanocomplex based bimodal MRI and CT contrast agents and its validation on Psammomys obesus for atherosclerosis diagnostics.

Early-life markers of atherosclerosis using aortic and carotid intima-media thickness: an assessment of methods to account for child size

Background.—Distinguishing pathological from physiological relationships between vessel size and aortic intima-media thickness (aIMT) is an important challenge, especially in growing children. We examined the relationship between childhood vessel diameter and aIMT and assessed common analytic approaches used to address this relationship.Methods.—We analyzed aIMT in two population-derived cohorts; 6-week-old infants and 19-year-olds. We simulated datasets in which we assumed a simple physiological relationship between vessel diameter and aIMT, and then superimposed possible pathological effects on aIMT; (a) intrauterine growth retardation, (b) macrosomia and (c) both intrauterine growth retardation and macrosomia. Using simulated datasets and cohorts, we evaluated analytic strategies including those in which the relationship between vessel diameter and aIMT was (a) ignored, (b) adjusted for by dividing aIMT by weight, or (c) adjusted for using varying regression techniques.Results.—aIMT was found to increase in proportion to vessel diameter in both cohorts (138 μm/mm at 6 weeks and 52 μm/mm at 19 years of age). Simply dividing aIMT by weight produced negative associations with weight across all datasets. By contrast, adjusting for vessel diameter as a covariate enabled accurate distinction of the direction of the association between aIMT and weight in all simulated datasets. These results were replicated in the cohort studies for both aIMT and carotid intima-media thickness.Conclusion.—There is a physiological relationship between vessel diameter and aIMT. Simply dividing aIMT by weight may lead to incorrect assumptions regarding the relationship between weight and aIMT. However, the physiological relationship is appropriately estimated by including vessel diameter as a covariate in regression.

Phytoestrogens : end of a tale?

Phytoestrogens are plant‐derived hormone‐like diphenolic compounds of dietary origin that are present at high levels in plasma of subjects living in areas with low atherosclerosis and cancer incidence. The term phytoestrogen is commonly applied to the soy isoflavones genistein, daidzein and glycitein. As outlined in a previous review article in this journal by Adlercreutz and Mazur 1, these compounds are weakly estrogenic and appear to influence the cardiovascular system, the production, metabolism and biological activity of sex‐hormones, as well as malignant cell proliferation, differentiation and angiogenesis. Recently skepticism has developed concerning the true potential of phytoestrogens to beneficially modify these processes. A critical analysis of the early findings from supplementing the diet with soy protein has failed to confirm phytoestrogens as the responsible agent for beneficial cardiovascular effects, be it by way of lipid reduction, vasodilation or lipoprotein oxidation. Furthermore, contrasting data have been reported on the potential of phytoestrogens to prevent hormone‐dependent cancers (e.g. breast and prostate) and to successfully treat post‐menopausal complaints, an indication for which they are widely used. These potentially negative findings have led health authorities in several countries to suggest maximum daily intake levels for phytoestrogens. There is now growing interest in the use of soy products containing low levels of phytoestrogens and in research on other phytoestrogen free legumes such as lupin.

The measurement of GLUT4 translocation in 3T3-L1 adipocytes

Type 2 diabetes (T2D) is one of the fastest growing threats to human health in westernised and developing countries and is associated with central obesity, atherosclerosis, dyslipidaemia, hyperinsulinaemia and  hypertension. Insulin resistance, defined as a diminished response to ordinary levels of circulating insulin in one or more peripheral tissues, is an integral feature of T2D pathophysiology. This includes an impairment of insulin to inhibit hepatic glucose output and to stimulate glucose disposal into muscle and fat. While insulin is responsible for a number of specific biological responses, stimulation of glucose transport is critical for the maintenance of glucose homeostasis. The primary mechanism for insulin stimulation of glucose uptake into muscle and fat is the translocation of glucose transporter 4 (GLUT4) to the cell surface from intracellular storage vesicles within the cell. A major advantage in focussing on insulin regulation of glucose transport is that this represents the endpoint of multiple upstream signalling pathways. This chapter describes the measurement of GLUT4 translocation in cultured cells and its potential application for both  mechanistic and therapeutic studies.

Chemistry and health of olive oil phenolics

The Mediterranean diet is associated with a lower incidence of atherosclerosis, cardiovascular disease, and certain types of cancer. The apparent health benefits have been partially attributed to the dietary consumption of virgin olive oil by Mediterranean populations. Most recent interest has focused on the biologically active phenolic compounds naturally present in virgin olive oils. Studies (human, animal, in vivo and in vitro) have shown that olive oil phenolics have positive effects on certain physiological parameters, such as plasma lipoproteins, oxidative damage, inflammatory markers, platelet and cellular function, and antimicrobial activity. Presumably, regular dietary consumption of virgin olive oil containing phenolic compounds manifests in health benefits associated with a Mediterranean diet. This paper summarizes current knowledge on the physiological effects of olive oil phenolics. Moreover, a number of factors have the ability to affect phenolic concentrations in virgin olive oil, so it is of great importance to understand these factors in order to preserve the essential health promoting benefits of olive oil phenolic compounds.

Biological activities of phenolic compounds present in virgin olive oil

The Mediterranean diet is associated with a lower incidence of atherosclerosis, cardiovascular disease, neurodegenerative diseases and certain types of cancer. The apparent health benefits have been partially ascribed to the dietary consumption of virgin olive oil by Mediterranean populations. Much research has focused on the biologically active phenolic compounds naturally present in virgin olive oils to aid in explaining reduced mortality and morbidity experienced by people consuming a traditional Mediterranean diet. Studies (human, animal, in vivo and in vitro) have demonstrated that olive oil phenolic compounds have positive effects on certain physiological parameters, such as plasma lipoproteins, oxidative damage, inflammatory markers, platelet and cellular function, antimicrobial activity and bone health. This paper summarizes current knowledge on the bioavailability and biological activities of olive oil phenolic compounds.

Temporal expression of heat shock proteins 60 and 70 at lesion-prone sites during atherogenesis in ApoE-deficient mice

In the study, we investigate whether the expressions of heat shock protein (hsp)60 (a potential autoantigen) and the stress-inducible form of cytoprotector hsp70 are correlated with the development of atherosclerotic lesions in the aortic tree of apolipoprotein E–deficient (apoE^-/-) mice. The apoE^-/- mouse model is advantageous because the stress-inducible form of hsp70 is not constitutively expressed in mice, unlike primates; hence, tissues under stress can be clearly defined. Both mammalian hsps were detected newly expressed (before mononuclear cell infiltration) on aortic valves and endothelia at lesion-prone sites of 3-week-old apoE^-/- mice. In 8- and 20-week-old mice, they were strongly and heterogeneously expressed in early to advanced fibrofatty plaques, with levels correlating with lesion severity. Expression was markedly downregulated in advanced collagenous, acellular, calcified plaques of 40- and 69-week-old mice and was absent in control aortas of normocholesterolemic wild-type (apoE^+/+) mice. Western blot analysis of tissue homogenates confirmed the temporal expression of the hsps. Double immunostaining revealed that both hsps were expressed by lesional endothelial cells, macrophages, smooth muscle cells, and CD3⁺ T lymphocytes. This study provides evidence that hsp60 and hsp70 are temporally expressed on all major cell types in lesion-prone sites during atherogenesis, suggesting that few cells escape the toxic environment of the atherosclerotic plaque.

Relationships between measures of fitness, physical activity, body composition and vascular function in children

Background : The prevalence of obesity and physical inactivity in Western countries has increased rapidly. Both are modifiable risk factors for cardiovascular disease. Atherosclerosis begins in childhood and endothelial dysfunction is its earliest detectable manifestation.

Methods : We assessed flow-mediated dilation (FMD) in 129 children (75 female; 10.3 + 0.3 yrs; 54 male; 10.4; 0.3 yrs). FMD was normalised for differences in the eliciting shear rate stimulus between subjects (SR_AUC). Fitness was assessed as peak oxygen uptake during an incremental treadmill exercise test (VO₂peak). Body composition was measured using a dual-energy X-ray absorptiometry (DEXA) scan. Physical activity (PA) was assessed using Actigraph accelerometers. The cohort was split into tertiles according to FMD% and also FMD% corrected for SR_AUC to gain insight into the determinants of vascular function.

Results : Across the cohort, significant correlations were observed between FMD%/SR_AUC and DEXA percentage fat (r = −0.23, p = 0.009) and percentage lean mass (r = 0.21, p = 0.008), and also with PA performed at moderate-to-high intensity (r = 0.363, p = 0.001). For children in the lowest FMD%/SR_AUC tertile, a stronger relationship with all PA measures was observed, particularly with high intensity PA (r = 0.572, P = 0.003). Regression analysis revealed that high intensity PA was the only predictor of impaired FMD%/SR_AUC.

Conclusions : These data suggest that traditional risk factors for CHD in adult populations impact upon vascular function in young people. Furthermore, it appears that individuals with impaired FMD may benefit from performing high intensity PA, whereas no relationships exist between FMD and lower intensities of PA or between PA and FMD in those subjects who possess preserved vascular function a priori.

Prevalence of vitamin D insufficiency and risk factors for type 2 diabetes and cardiovascular disease among African migrant and refugee adults in Melbourne

Migration to industrialised countries poses a “double whammy” for type 2 diabetes among sub-Saharan African migrant and refugee adults. This population group has been found to be at an increased risk of obesity and type 2 diabetes, which may be further aggravated by inadequate vitamin D status. Thus, this study aimed to describe the demographics of vitamin D insufficiency, obesity, and risk factors for type 2 diabetes among sub-Saharan African migrants and refugees aged 20 years or older living in Melbourne, Australia (n=49). Data were obtained by a questionnaire, medical assessment, and fasting blood samples. The mean serum 25-hydroxyvitamin D level was 27.3 nmol/L (95% CI: 22.2, 32.4 nmol/L); with 25-hydroxyvitamin D levels <50 nmol/L occurring in 88% of participants. Participants displayed a cluster of risk factors for type 2 diabetes and cardiovascular disease: 62% were overweight or obese, 47% had insulin resistance (HOMA-IR ≥2), 25% had low density lipoprotein cholesterol levels ≥3.5 mmol/L, 24.5% had high density lipoprotein cholesterol levels ≤1.03 mmol/L, 34.6% had borderline or high levels of total cholesterol (≥5.2 mmol/L), 18.2% had borderline or high levels of triglyceride (≥1.7 mmol/L), and 16% had hypertension (systolic blood pressure ≥140 mmHg or diastolic blood pressure ≥90 mmHg). These findings suggest that sub-Saharan African migrants and refugees may be at risk of type 2 diabetes and atherosclerosis-related diseases such as ischemic heart disease, stroke, and peripheral vascular disease. Well-designed vitamin D interventions that incorporate lifestyle changes are urgently needed in this sub-population.