Andrea Petróczi

Fuzzy communities and the concept of bridgeness in complex networks

We consider the problem of fuzzy community detection in networks, which complements and expands the concept of overlapping community structure. Our approach allows each vertex of the graph to belong to multiple communities at the same time, determined by exact numerical membership degrees, even in the presence of uncertainty in the data being analyzed. We create an algorithm for determining the optimal membership degrees with respect to a given goal function. Based on the membership degrees, we introduce a measure that is able to identify outlier vertices that do not belong to any of the communities, bridge vertices that have significant membership in more than one single community, and regular vertices that fundamentally restrict their interactions within their own community, while also being able to quantify the centrality of a vertex with respect to its dominant community. The method can also be used for prediction in case of uncertainty in the data set analyzed. The number of communities can be given in advance, or determined by the algorithm itself, using a fuzzified variant of the modularity function. The technique is able to discover the fuzzy community structure of different real world networks including, but not limited to, social networks, scientific collaboration networks, and cortical networks, with high confidence.

Methodological considerations regarding response bias effect in substance use research: Is correlation between the measured variables sufficient?

Efforts for drug free sport include developing a better understanding of the behavioural determinants that underline doping with an increased interest in developing anti-doping prevention and intervention programmes. Empirical testing of both is dominated by self-report questionnaires, which is the most widely used method in psychological assessments and sociology polls. Disturbingly, the potential distorting effect of socially desirable responding (SD) is seldom considered in doping research, or dismissed based on weak correlation between some SD measure and the variables of interest. The aim of this report is to draw attention to i) the potential distorting effect of SD and ii) the limitation of using correlation analysis between a SD measure and the individual measures. Models of doping opinion as a potentially contentious issue was tested using structural equation modeling technique (SEM) with and without the SD variable, on a dataset of 278 athletes, assessing the SD effect both at the i) indicator and ii) construct levels, as well as iii) testing SD as an independent variable affecting expressed doping opinion. Participants were categorised by their SD score into high- and low SD groups. Based on low correlation coefficients (<|0.22|) observed in the overall sample, SD effect on the indicator variables could be disregarded. Regression weights between predictors and the outcome variable varied between groups with high and low SD but despite the practically non-existing relationship between SD and predictors (<|0.11|) in the low SD group, both groups showed improved model fit with SD, independently. The results of this study clearly demonstrate the presence of SD effect and the inadequacy of the commonly used pairwise correlation to assess social desirability at model level. In the absence of direct observation of the target behaviour (i.e. doping use), evaluation of the effectiveness of future anti-doping campaign, along with empirical testing of refined doping behavioural models, will likely to continue to rely on self-reported information. Over and above controlling the effect of socially desirable responding in research that makes inferences based on self-reported information on social cognitive and behavioural measures, it is recommended that SD effect is appropriately assessed during data analysis.

Misleading measures in Vitamin D analysis: a novel LC-MS/MS assay to account for epimers and isobars

BackgroundRecently, the accuracies of many commercially available immunoassays for Vitamin D have been questioned. Liquid chromatography tandem mass spectrometry (LC- MS/MS) has been shown to facilitate accurate separation and quantification of the major circulating metabolite 25-hydroxyvitamin-D3 (25OHD3) and 25-hydroxyvitamin-D2 (25OHD2) collectively termed as 25OHD. However, among other interferents, this method may be compromised by overlapping peaks and identical masses of epimers and isobars, resulting in inaccuracies in circulating 25OHD measurements. The aim of this study was to develop a novel LC-MS/MS method that can accurately identify and quantitate 25OHD3 and 25OHD2 through chromatographic separation of 25OHD from its epimers and isobars.MethodsA positive ion electrospray ionisation (ESI) LC-MS/MS method was used in the Multiple Reaction Monitoring (MRM) mode for quantification. It involved i) liquid-liquid extraction, ii) tandem columns (a high resolution ZORBAX C18 coupled to an ULTRON chiral, with guard column and inlet filter), iii) Stanozolol-D3 as internal standard, and iv) identification via ESI and monitoring of three fragmentation transitions. To demonstrate the practical usefulness of our method, blood samples were collected from 5 healthy male Caucasian volunteers; age range 22 to 37 years and 25OHD2, 25OHD3 along with co-eluting epimers and analogues were quantified.ResultsThe new method allowed chromatographic separation and quantification of 25OHD2, 25OHD3, along with 25OHD3 epimer 3-epi-25OHD3 and isobars 1-α-hydroxyvitamin-D3 (1αOHD3), and 7-α-hydroxy-4-cholesten-3-one (7αC4). The new assay was capable of detecting 0.25 ng/mL of all analytes in serum.ConclusionsTo our knowledge, this is the first specific, reliable, reproducible and robust LC-MS/MS method developed for the accurate detection of 25OHD (Vitamin D). The method is capable of detecting low levels of 25OHD3 and 25OHD2 together with chromatographic separation from the co-eluting epimers and isobars and circumvents other instrumental/analytical interferences. This analytical method does not require time-consuming derivatisation and complex extraction techniques and could prove very useful in clinical studies.

Mission impossible? Regulatory and enforcement issues to ensure safety of dietary supplements

Dietary supplements are widely used across all ages and user groups and constitute a considerable business sector in most developed countries. Hazards relating to concentration, composition, individual contaminants and supplement interactions present an increasing public health concern. The aim of this paper is to review the literature for reported supplement contaminations (occurs in ca 25% of supplements, with anabolic steroids being the most common) and complement these findings with notifications logged in the EUs Rapid Alert System for Food and Feed (RASFF) through imports or market surveillance, typically logged for poor quality control issues. Notifications in the RASFF have steadily increased by sixfold for supplements in the past 7 years with the USA and China being the major transgressors. Finland and Italy lead in detections, mainly notifying unpermitted substances and contaminants in sexual-enhancing or weight-loss supplements. This paper highlights the paucity of enforcement. Regulating supplements as a foodstuff and not a medicine, coupled with the fact that a significant proportion of the supplement market is distributed via the Internet (hence absent from routine border control and surveillance), make ensuring and enforcing safety a very challenging task. The need for better quality control, compliance and public awareness is evident.

Gateway to doping? Supplement use in the context of preferred competitive situations, doping attitude, beliefs, and norms.

Nutritional supplement (NS) use is widespread in sport. This study applied an integrated social cognitive approach to examine doping attitudes, beliefs, and self‐reported doping use behavior across NS users (n = 96) and nonusers (n = 116). Following ethical approval, 212 competitive athletes (age mean = 21.4, s = 4.5; 137 males) completed self‐reported measures of doping‐related social cognitions and behaviors, presented in an online format where completion implied consent. Significantly more NS users (22.9%) reported doping compared with nonusers (6.0%; U = 4628.0, P < 0.05). NS users presented significantly more positive attitudes toward doping (U = 3152.0, P < 0.05) and expressed a significantly greater belief that doping is effective (U = 3152.0, P < 0.05). When presented with the scenario that performance‐enhancing substances are effective and increase the possibility of winning, NS users were significantly more in favor of competing in situations that allow doping (U = 3504.5, P < 0.05). In sum, doping use is three‐and‐a‐half times more prevalent in NS users compared with nonusers. This finding is accompanied by significant differences in doping attitudes, norms, and beliefs. Thus, this article offers support for the gateway hypothesis; athletes who engage in legal performance enhancement practices appear to embody an “at‐risk” group for transition toward doping. Education should be appropriately targeted.

Determination of metal ion content of beverages and estimation of target hazard quotients: a comparative study

This is a correction to the following paper: Hague T, Petroczi A, Andrews PR, Barker J, Naughton DP: Determination of metal ion content of beverages and estimation of target hazard quotients: a comparative study. Chem Central J 2008, 2:13.

Heavy metal ions in wines: meta-analysis of target hazard quotients reveal health risks

BackgroundMetal ions such as iron and copper are among the key nutrients that must be provided by dietary sources. Numerous foodstuffs have been evaluated for their contributions to the recommended daily allowance both to guide for satisfactory intake and also to prevent over exposure. In the case of heavy metal ions, the focus is often on exposure to potentially toxic levels of ions such as lead and mercury. The aim of this study is to determine target hazard quotients (THQ) from literature reports giving empirical levels of metal ions in table wines using the reference upper safe limit value. Contributions to the THQ value were calculated for seven metal ions along with total values for each wine.ResultsThe THQ values were determined as ranges from previously reported ranges of metal ion concentrations and were frequently concerningly high. Apart from the wines selected from Italy, Brazil and Argentina, all other wines exhibited THQ values significantly greater than one indicating levels of risk. The levels of vanadium, copper and manganese had the highest impact on THQ measures. Typical potential maximum THQ values ranged from 50 to 200 with Hungarian and Slovakian wines reaching 300. THQ values for a sample of red and white wines were high for both having values ranging from 30 to 80 for females based on a 250 mL glass per day.ConclusionThe THQ values calculated are concerning in that they are mainly above the safe level of THQ<1. It is notable that in the absence of upper safe limits, THQ values cannot be calculated for most metal ions, suggesting that further unaccountable risks are associated with intake of these wines.

Mercury, cadmium and lead contamination in seafood: a comparative study to evaluate the usefulness of Target Hazard Quotients.

The aim of this paper is to explore the applicability of Target Hazard Quotient (THQ) estimations to inform on seafood hazards through metal contamination. The food recall data set was collated by the Laboratory of the Government Chemist (LGC, UK) over the period from January to November 2007. Pearson chi-square goodness of fit test, nonparametric correlation (Kendall tau) and Kruskal-Wallis test were used. Descriptive statistics and statistical analyses were computed by using Excel and SPSS 15.0. The vast majority of food alerts/recalls owing to metal contamination occur in seafood and during the summer months. Only swordfish and shark containing produce received over 10 recalls which were mainly for mercury contamination. Seafood produce originating from only 3 countries had over 10 recalls owing to metal contamination (Spain 50; France 11 and Indonesia 11). Based upon the food alert/recall system, the application of THQ estimations of risk in cases of metal contamination of seafood is questionable as THQ implies frequent if not daily exposure over a lifetime. Infrequent recalls owing to metal contamination and the absence of patterns make it highly unlikely that an individual would be subject to multiple exposures to significant levels of metal ions in seafood.

Quantitative analysis of mephedrone using liquid chromatography tandem mass spectroscopy: Application to human hair

Recent abuse of designer drugs such as mephedrone has presented a requirement for sensitive, reliable and reproducible methods for the detection of these controlled drugs in different matrices. This study focuses on a fully developed validated method for the quantitative analysis of mephedrone and its two metabolites 4-methylephedrine and 4-methylnorephedrine in human hair. The calibration curve was found to be linear in the range 5-100 pg/mg for mephedrone and 10-150 pg/mg for 4-methylephedrine and 4-methylnorephedrine. The method was successfully validated for the intraday precision, interday precision, limit of detection, accuracy and extraction recovery. Five out of 154 hair samples were confirmed to be positive for mephedrone. Due to the structural similarities to other methcathinones and amphetamines, one can propose the metabolism for mephedrone based on a similar pathway that has been previously used for these psychoactive drugs. The outlined method can be valuable for the future detection of mephedrone and its two metabolites in hair.

Supplement use in sport: is there a potentially dangerous incongruence between rationale and practice?

BackgroundSupplement use by athletes is complex and research supports the alarming notion of misinformed decisions regarding supplements.HypothesisA frequent divergence between the type of supplements chosen by athletes and the rationale dictating the supplement use is hypothesized. Thus, a potentially dangerous incongruence may exist between rationale and practice.Testing the hypothesisIn the continued absence of reliable data on supplement use, an alternative approach of studying the reasons underlying supplement use in athletes is proposed to determine whether there is an incongruence between rationale and practice. Existing data from large scale national surveys can be used to investigate this incongruence.Implications of the hypothesisIn this report, analyses of distinctive patterns between the use and rationale for use of supplements among athletes are recommended to explore this potentially dangerous phenomenon.