Georgios Christou

The Metabolic Role of Retinol Binding Protein 4: An Update

Retinol binding protein 4 (RBP(4)) is regarded as a novel cardiometabolic risk factor, which is secreted mainly by the hepatocytes and also by the adipose tissue. RBP(4) has been shown to induce insulin resistance, and plasma RBP(4) values are increased in type 2 diabetes mellitus, obesity, metabolic syndrome, and cardiovascular disease. Moreover, it has been found that circulating RBP(4) decreases during medical interventions that result in amelioration of the metabolic profile, such as diet, exercise, oral antidiabetic drugs, and hypolipidemic agents. However, only few of the RBP(4)-related studies have investigated whether RBP(4) constitutes a causal factor of the above-mentioned metabolic conditions. Importantly, circulating RBP(4) is influenced by some nonmetabolic conditions, such as renal failure, acute illness, injury, and liver failure. Thus, further studies investigating the metabolic roles of RBP(4) should be carefully planned, taking into account the effects of nonmetabolic conditions on circulating RBP(4).

The role of adiponectin in renal physiology and development of albuminuria

Adiponectin is secreted by the adipose tissue and is downregulated in states of obesity and insulin resistance. There is a growing body of evidence indicating that adiponectin has renoprotective effects and protects against the development of albuminuria in rodent experiments. Adiponectin crossing the glomerular filtration barrier possibly inhibits inflammation, fibrosis and oxidative stress in kidneys through activation of AMP-activated protein kinase. Moreover, microalbuminuria is a well established early sign of progressive cardiovascular and renal disease, even in subjects with preserved glomerular filtration rate. Studies investigating the relationship between serum adiponectin levels and urinary albumin excretion rate (UAE) have yielded conflicting data and the mechanisms underlying the interplay between adiponectin and albuminuria remain to be elucidated. This article constitutes a critical review attempting to clarify any remaining confusion about this matter. Furthermore, this article examines the clinical significance of adiponectin-albuminuria interplay, suggesting that adiponectin is possibly involved in the development of albuminuria that is associated with obesity, diabetes and cardiovascular disease and may mediate, at least in part, the actions of medical treatments that influence UAE, such as angiotensin-converting-enzyme inhibitors, angiotensin II receptor blockers, thiazolidinediones, fenofibrate and diet. Further studies to investigate more thoroughly the renoprotective role of adiponectin in the human setting should be carefully planned, focusing on causality and the possible influence of adiponectin on the development of albuminuria in specific clinical settings.

A comparison between experienced and inexperienced video game players’ perceptions

In this article we examine the relationship between usability, hedonic attributes and general appeal of two types of video games, first-person shooters, and massively multi-player online role playing games. Through the use of a successful example of a game from each genre, we examine the perceptions of both inexperienced and experienced players of each game, and draw conclusions on comparisons. We find that playing experience only affects usability and appeal perceptions, while type of game played not only affects usability and appeal, but also hedonic perceptions as well. We also find that the perception of appeal by players of a video game in the context of this study can be predicted from a linear combination of the same players’ perceptions of hedonic attributes and usability. We translate these findings into suggestions for game designers and developers.

Challenges of designing for sociability to enhance player experience in Massively Multi-player Online Role-playing Games

Massively Multi-player Online Role-playing Games (MMORPGs) have become a popular leisure activity. It has been suggested that the reason for their popularity is that they offer a new ‘third-place’ for people to socialise. However, designing for sociability in these games has been shown to be a challenge. In this article, we discuss the results of an online survey that was directed towards game design researchers and professionals. We then present a subsequent discussion on the results of the survey at a Special Interest Group (SIG) held at CHI 2011. Through analysis of the findings of the survey and the discussion, we propose six requirements that facilitate the design of MMORPGs: In-game Communication, Off-game Communication, Empathy, Grouping and Rewards, World Design, and Designed Relationships. We state that it is not necessary to add all the proposed requirements in the design of such games, but we also caution that a game that does not include any of the requirements presented here cannot belong to this genre. We discuss limitations of this work, and offer future research directions that result from this work.

The interplay between immersion and appeal in video games

A 2i?2 study on immersion and appeal of video games is presented.Immersion and appeal are found to be highly related.Immersion is found to be unaffected by playing experience.Appeal is found to be affected both by game played and playing experience. Immersion and appeal are considered to be necessary constituents of the player experience. In this article their relationship is examined through a 2i?2 factorial study (n=173) in the context of two games, a first-person shooter and a massively multi-player online role-playing game, and in the context of two types of players: experienced players who have never played the game in one of the genres in question, and experienced players who have played one of the games in question. It is found that immersion and appeal are linearly correlated, and the repercussions of this finding are discussed.

High density lipoprotein is positively correlated with the changes in circulating total adiponectin and high molecular weight adiponectin during dietary and fenofibrate treatment.

OBJECTIVEThe investigation of the relationship between high density lipoprotein (HDL) and adiponectin.DESIGNThirty-seven obese or overweight [body mass index ≥27 Kg/m2], hypertriglyceridemic patients underwent one of the following interventions for 3 months: 1) Low-calorie diet (n=19), 2) Low-calorie diet plus fenofibrate (n=18).RESULTSCirculating total adiponectin did not change significantly in the low-calorie diet group. However, in the subgroup of patients whose high density lipoprotein cholesterol (HDL-C) decreased over the first month of diet, a statistically significant reduction of the circulating total adiponectin was observed (p=0.010), while in the subgroup of patients whose HDL-C increased over the latter 2 months of the diet, an increase in circulating total adiponectin over the 2 months was found (p=0.043). The percentage change of HDL-C over the first month of diet was positively correlated with the percentage change of circulating total adiponectin (r=0.579, p=0.019). The percentage change of HDL-C over the 3 months of diet was positively correlated with the percentage changes of circulating total adiponectin (r=0.527, p=0.030) and high molecular weight (HMW) adiponectin (r=0.524, p=0.031). The change in circulating total adiponectin over the first month of diet was positively correlated with the HDL-C at 1 month (r=0.606, p=0.013). The change in HMW adiponectin over the 3 months of diet was positively correlated with the HDL-C at 3 months (r=0.602, p=0.011). The percentage change of circulating HMW adiponectin over the first month of fenofibrate treatment was positively correlated with the percentage change of HDL-C (r=0.594, p=0.012).CONCLUSIONSHDL is positively correlated with the changes in circulating adiponectin during dietary and fenofibrate treatment.

The Current Role of Omega-3 Fatty Acids in the Management of Atrial Fibrillation.

Background: The main dietary source of omega-3 polyunsaturated fatty acids (n-3 PUFA) is fish, which contains eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). In the present manuscript, we aimed to review the current evidence regarding the clinical role of n-3 PUFA in the prevention of atrial fibrillation (AF) and the possible underlying mechanisms. Methods: A literature search based on PubMed listings was performed using “Omega-3 fatty acids” and “atrial fibrilation” as key search terms. Results: n-3 PUFA have been shown to attenuate structural atrial remodeling, prolong atrial effective refractory period through the prevention of reentry and suppress ectopic firing from pulmonary veins. Dietary fish intake has been found to have no effect on the incidence of AF in the majority of studies. Circulating DHA has been consistently reported to be inversely associated with AF risk, whereas EPA has no such effect. The majority of studies investigating the impact of n-3 PUFA supplementation on the incidence of AF following cardiac surgery reported no benefit, though most of them did not use n-3 PUFA pretreatment for adequate duration. Studies using adequate four-week pretreatment with n-3 PUFA before cardioversion of AF showed a reduction of the AF incidence. Conclusions: Although n-3 PUFA have antiarrhythmogenic properties, their clinical efficacy on the prevention of AF is not consistently supported. Further well-designed studies are needed to overcome the limitations of the existing studies and provide robust conclusions.

The changes in plasma retinol-binding protein 4 levels are associated with those of the apolipoprotein B-containing lipoproteins during dietary and drug treatment.

We investigated the association between retinol-binding protein 4 (RBP4) and apolipoprotein B (ApoB)-containing lipoproteins. Obese or overweight, hypertriglyceridemic patients underwent the following interventions for 3 months: (1) Diet (n = 20), (2) Diet + fenofibrate (n = 18), (3) Diet + rimonabant (n = 8). Circulating RBP4 decreased during dietary treatment. The percentage change in RBP4 was positively correlated with the percentage changes in very-low density lipoprotein cholesterol (r = .570, P = .02), low-density lipoprotein cholesterol ([LDL-C]; r = .605, P = .01), ApoB (r = .705, P = .007), and small dense LDL-C ([sdLDL-C]; r = .872, P < .001). The percentage change in RBP4 was the best predictor of the percentage changes in sdLDL-C and ApoB. Rimonabant treatment reduced RBP4, whereas fenofibrate increased RBP4 during the first month of therapy followed by a subsequent decrease. In conclusion, RBP4 may significantly influence the metabolic pathways responsible for changes in ApoB lipoprotein subspecies, thus RBP4 may be associated with cardiovascular disease risk.

CODEIN - A NEW NOTATION FOR GOMS TO HANDLE EVALUATIONS OF REALITY BASED INTERACTION STYLE INTERFACES

We propose a new diagrammatic notation system for Goals, Operators, Methods, Selection rules (GOMS), called Codein, with extensions to support the evaluation of Reality Based Interaction Styles. The proposed notation gives added power to GOMS to model and evaluate the task completion time of parallel actions during the performance of a task, something that was previously only possible using CPM-GOMS, which is far more complicated to use. Codeins evaluative power is verified through an experiment. The first condition of the experiment compares the completion time predicted by a GOMSL model, a Codein model, and the actual completion time of participants in a direct manipulation task. The second compares the completion time of participants in a Tangible User Interface task with predictions by a GOMSL model and a Codein model. Predicted task times by Codein in both conditions come close to the actual experimental results.

Challenges in evaluating usability and user experience of reality-based interaction

This workshop aims to further the understanding of the challenges relating to the evaluation methods of usability and user experience that are specific to Reality-Based Interaction (RBI), and to identify effective practical responses to these challenges. The emergence of Post-WIMP interfaces has led to new ways of interacting with technologies. However, there are still no integrated ways of evaluating the usability and user experience of these interfaces. Developers and designers are left to discover their own metrics and evaluation methods. This approach presents problems, in that the metrics used in each case may provide results that are neither valid nor meaningful. For this reason, the time is ripe to integrate the methods that have been developed for evaluating interfaces that belong to the RBI umbrella. The measures and techniques will then be turned into a framework that enables designers of RBI interfaces to select appropriately existing methods and tools to evaluate systematically the usability and user experience of their prototypes and products. Reusing and adapting validated evaluation approaches can not only avoid reinventing the wheel and wasting time but also further improve and consolidate these approaches. Such a framework will also provide a basis for comparison between designs of RBI interfaces in different application contexts.