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1.
Cogn Emot ; : 1-8, 2024 May 09.
Article En | MEDLINE | ID: mdl-38722266

The perception of meaningful patterns in random arrangements and unrelated events takes place in our everyday lives, coined apophenia, synchronicity, or the experience of meaningful coincidences. However, we do not know yet what predicts this phenomenon. To investigate this, we re-analyzed a combined data set of two daily diary studies with a total of N = 169 participants (mean age 29.95 years; 54 men). We investigated if positive or negative affect (PA, NA) predicts the number of meaningful coincidences on the following day (or vice versa). By means of a cross-lagged multilevel modelling approach (Bayesian estimation) we evaluated with which of two theoretical assumptions the data are more in line. First, if meaningful coincidences are facilitated by a broader and more flexible thinking style, PA should positively predict meaningful coincidences at the following day. However, if the experience of meaningful coincidences signifies a strategy to cope with negative feeling states, NA should predict the experience of meaningful coincidences during the following day. In favour of a more flexible thinking style, we found that PA predicted the number of perceived coincidences the following day. We did not find any effect for NA, and therefore, no evidence arguing for the coping mechanism hypothesis of meaningful coincidences.

2.
Biol Psychol ; 186: 108760, 2024 Feb.
Article En | MEDLINE | ID: mdl-38331345

Intermittent fasting has been associated with diverse physical and psychological health benefits. According to previous research, fasting-induced alterations in psychophysiological functioning should facilitate the accurate detection of an internal bodily signal (like the heart), which is referred to as interoceptive accuracy. In two within-subjects studies we aimed to examine whether an intermittent fasting protocol (i) evokes distinct autonomic nervous system changes in the laboratory and (ii) improves (objectifiable) interoceptive accuracy and sensibility (i.e., the subjective belief in perceiving bodily signals) in everyday life. Study 1 (N = 36) found increasing heart rate variability (precisely, the root mean square of successive differences; RMSSD) accompanied by a more vascular than myocardial response following a 16 h fast. Study 2 (N = 40) applied an ecological momentary assessment design including intermittent fasting (8 h normal eating followed by 16 h fasting) and normal eating (24 h normal eating) for three consecutive days each. Findings suggested a tendency toward higher interoceptive accuracy and sensibility during the fasting regimen, which was particularly pronounced in individuals exhibiting lower RMSSD. Together, findings suggest that (short-term) fasting seems to facilitate momentary attention to organismic cues due to alterations in autonomic nervous system function.


Interoception , Humans , Interoception/physiology , Heart , Autonomic Nervous System , Fasting , Heart Rate/physiology , Awareness/physiology
3.
Int J Psychophysiol ; 196: 112277, 2024 Feb.
Article En | MEDLINE | ID: mdl-38065411

BACKGROUND: Feeling safe and secure has been proposed to dampen autonomic arousal and buffer threat responses. In a previous study, we could show that momentary ratings of subjective safety were associated with elevated heart rate variability (specifically, root mean square of successive differences; RMSSD) and lower heart rate in everyday life, thus suggesting a health-protective role of feeling safe. METHODS: This study aimed to replicate this effect in a sample of N = 79 adults, applying Bayesian statistics with prior effects of the original study. RESULTS: Using an ecological momentary assessment (EMA) across three days we could replicate the effect of lower heart rate and higher RMSSD in moments when participants felt more safe. In accordance with the original study, we could also show that the effect on heart rate were independent of RMSSD, thus suggesting a contribution of sympathetic activity to this effect. CONCLUSION: The findings confirm the connection between momentary feelings of safety and cardiac regulation, thus substantiating research on the health-protective role of psychological safety.


Autonomic Nervous System , Emotions , Adult , Humans , Bayes Theorem , Heart Rate/physiology
4.
Conscious Cogn ; 117: 103621, 2024 01.
Article En | MEDLINE | ID: mdl-38113709

Knowing when perceiving inner bodily signals better and when perceiving them worse is a health relevant but understudied dimension of interoception. Therefore, the present study assessed interoceptive metacognition (IMC) as the skill to adequately monitor interoceptive accuracy in the cardiac domain. We used the Graz Ambulatory Interoception task (GRAIT), which applied two intervals of the heartbeat tracking task 12 times a day for 3 days in total to n = 66 participants. We assessed IMC as the relative correspondence between interoceptive accuracy and the subjective confidence ratings. We found that 6 % of the total IMC variance was due to person, which was assessed reliable (RKRn=0.81). Furthermore, the between-person variation of IMC was negatively associated with the MAIA (especially attention regulation and self-regulation). People who believe that they are aware of their interoceptive experiences (MAIA) showed lower IMC. This study advocates the assessment of interoception in everyday life.


Interoception , Metacognition , Humans , Awareness/physiology , Attention , Interoception/physiology , Heart Rate/physiology
5.
Am Psychol ; 2023 Nov 16.
Article En | MEDLINE | ID: mdl-37971840

Research indicated an association of acute and chronic physical activity with creative ideation performance. However, no study to date applied ecologically valid ambulatory methods with the potential to generalize these positive relationships to everyday life contexts. This study assessed acute and chronic physical activity (i.e., number of steps assessed via acceleration sensors) as well as creative ideation performance (in the verbal and figural domain) with an ecological momentary assessment approach in a sample of 157 young adults. We found that both single bouts of walking and walking regularly were associated with more original verbal ideas. Positive affect did not mediate this association; however, for figural creativity, the indirect path of acute physical activity via acute positive affect was significant. Although the relationship between walking and creativity seems to be domain-specific, the study findings suggest that the positive effects of physical activity on creativity transfer to everyday life contexts. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

6.
Nutrients ; 15(19)2023 Sep 22.
Article En | MEDLINE | ID: mdl-37836395

Recent evidence on the association between vitamin D and cognition in mentally healthy individuals is inconsistent. Furthermore, the link between vitamin D and cognitive ability in individuals with bipolar disorder has not been studied yet. Thus, we aimed to investigate the association between 25-hydroxyvitamin D (25(OH)D), 24,25 dihydroxyvitamin D (24,25(OH)2D, the vitamin D metabolite ratio (VMR) and cognition in a cohort of euthymic patients with bipolar disorder. Vitamin D metabolites were measured simultaneously by liquid-chromatography tandem mass-spectrometry in serum samples from 86 outpatients with bipolar disorder and 93 healthy controls. Neither the inactive precursor 25(OH)D, nor the primary vitamin D catabolite 24,25(OH)2D, or the vitamin D metabolite ratio were significantly associated with the domains "attention", "memory", or "executive function" in individuals with bipolar disorder and healthy controls. Further, no vitamin D deficiency effect or interaction group × vitamin D deficiency was found in the cognitive domain scores. In summary, the present study does not support vitamin D metabolism as a modulating factor of cognitive function in euthymic BD patients. Considering the current study's cross-sectional design, future research should expand these results in a longitudinal setting and include additional aspects of mental health, such as manic or depressive symptoms, long-term illness course and psychopharmacological treatment.


Bipolar Disorder , Vitamin D Deficiency , Humans , Bipolar Disorder/complications , Bipolar Disorder/psychology , Cross-Sectional Studies , Vitamin D , Cognition , Vitamins
7.
Psychoneuroendocrinology ; 158: 106381, 2023 12.
Article En | MEDLINE | ID: mdl-37688892

OBJECTIVE: Previous research suggests differential effects of participant-selected (PS) vs. researcher-selected (RS) music on emotional responses to music listening. This study investigates whether such selection strategies, as well as gender, influence (1) stress and (2) mood responses. Additionally, we examine the role of (3) stimulus-induced emotions and (4) emotion regulation strategies. METHODS: Participants (N = 61) listened to auditory stimuli (PS music, RS music, sound of lapping water (LW); randomized) on three days and underwent a cold pressor test (CPT) while listening. Stress parameters (subjective acute stress, heart rate, parameter RMSSD, salivary alpha-amylase, salivary cortisol), mood dimensions (calmness, valence, energetic arousal), emotions, and emotion regulation strategies were measured. Multilevel and mediation analyses were conducted. RESULTS: (1) There were no direct effects of selection strategy or gender on stress responses, but interaction effects indicated that women showed the strongest subjective stress response and the longest HR recovery with PS music, while men showed the lowest HR response to the CPT with PS music. (2) No mood differences emerged between PS and RS music overall. Women showed stronger variability in calmness overall as well as perceived higher arousal when listening to PS music compared to men. (3) Higher stimulus-induced anger in men compared to women and with LW compared to PS was associated with lower calmness and valence, while no consistent pattern emerged for the stress responses. (4) Women scored higher on reappraisal, associated with a decrease in parasympathetic activity, whereas men scored higher on suppression, associated with an increase in endocrine activity. CONCLUSIONS: Music selection and gender appear to have no direct impact on stress and mood responses overall, although men tend to benefit more from self-selected music than women. Our findings provide first indications that avoiding music stimuli that induce anger may facilitate mood management via music. Furthermore, finding alternative emotion regulation strategies to the strategy of suppression may be a helpful approach to improve music-based stress management.


Music , Salivary alpha-Amylases , Female , Humans , Male , Affect , Arousal/physiology , Auditory Perception/physiology , Emotions/physiology , Music/psychology
8.
Health Commun ; : 1-11, 2023 Sep 27.
Article En | MEDLINE | ID: mdl-37753620

Although it is clear that people experience physiological arousal in anticipation of news-focused medical consultations, our knowledge of people's experiences during and throughout these consultations is scarce. We examine interbeat interval responses (IBI) of patients and doctors during real-life medical consultations to understand how the experiences of both parties change throughout these encounters and whether they differ from each other. We also examine how the type of news delivered affects responses. We measured the IBI responses of patients and their oncologists throughout 102 consultations in which providers delivered news (classified as good, bad, or status quo) to patients about a recent computerized tomography scan. We observed two distinct phases of consultations: an initial "news" delivery phase and a subsequent "information" phase. During the news phase, on average, patients' IBI responses rapidly increased-indicating less autonomic arousal over time - whereas doctors' responses did not change over time. In contrast, throughout the information phase, on average, both patients' and doctors' responses remained steady. During the information phase, responses differed based on news type: on average, status quo consultations involved an increase in autonomic arousal, whereas good and bad news consultations involved no changes. Lastly, we observed significant variability in patients' responses during both phases. In sum, on average, patients (but not doctors) experience decreases in autonomic arousal while news is being delivered, suggesting that anticipatory distress regarding these consultations wanes quickly. However, our results also indicate that patients' experiences vary from one another, and future research should focus on factors explaining this variability.

9.
Int J Psychophysiol ; 192: 80-90, 2023 10.
Article En | MEDLINE | ID: mdl-37574020

We present a novel ambulatory method, the Graz Ambulatory Interoception Task (GRAIT), to assess the accuracy of interoceptive beliefs (AccIB). This method captures both between- and within-person variations of AccIB by having participants counting perceived heartbeats in daily life. Reliability analyses showed high between-person (RkR = 0.99) and moderate within-person reliability (RCn = 0.62). Validity was supported by associations with an established laboratory task (r = 0.87). Within-person associations revealed that interoceptive sensibility, heart rate variability, and states of low arousal coupled with positive affect were linked to AccIB. Study 2 replicated these findings and showed a relationship between AccIB and self-control in everyday life, highlighting the importance of cardiac interoception and its relevance for health.


Interoception , Humans , Heart Rate/physiology , Interoception/physiology , Reproducibility of Results , Arousal , Awareness/physiology
11.
Neuropsychologia ; 177: 108416, 2022 12 15.
Article En | MEDLINE | ID: mdl-36343705

Creative metacognitive monitoring represents the ability to accurately evaluate the quality of own ideas during idea generation. To the best of our knowledge, this study presents the first EEG investigation of creative metacognitive monitoring in the brain, using data, of 100 participants, who generated single, original uses of common objects (alternate uses task). After each response, participants subjectively rated the creative quality of their idea. Additionally, five independent external judges rated the creative quality of all ideas. The correspondence between the subjective and the external performance ratings served as a measure of monitoring accuracy. We applied a generalized linear mixed effects model to investigate effects of creative metacognitive monitoring and creative potential on EEG activity in the alpha band at idea and person level. Participants with both higher monitoring skills and higher creative potential showed stronger alpha power decreases at parietal/occipital sites during creative idea generation and evaluation. Interestingly, only more creative people with lower metacognitive monitoring skills showed the expected alpha power increases at parietal/occipital sites during both phases. Furthermore, metacognitive monitoring skills were associated with lower frontal and temporal/central alpha power during idea evaluation (compared to generation) at the person level. This pattern of findings seems to suggest that less internal attention, less memory load, and increased sensory processing are associated with more effective and accurate monitoring of the creative process. This study sheds first light on the brain mechanisms underlying the interplay of creative metacognitive monitoring skills and creative potential.


Metacognition , Humans , Metacognition/physiology , Electroencephalography , Creativity , Brain/physiology , Brain Mapping
12.
Int J Psychophysiol ; 182: 231-239, 2022 12.
Article En | MEDLINE | ID: mdl-36374747

Feeling safe has been suggested to reflect a state of beneficial autonomic regulation, which might facilitate physical and mental health. We aimed to examine the relationship between the perception of safety in everyday life and cardiac activity (heart rate, heart rate variability) via ecological momentary assessment (EMA). Sixty participants volunteered in a 3-day EMA protocol with parallel recordings of the ECG and subjective ratings of safety. Higher experienced safety in everyday life was associated with better sleep quality, being at home (vs. other locations), being surrounded by close others, as well as more positive and less negative social interactions, thus suggesting valid assessment. Moreover, perceived safety was positively associated with heart rate variability, although this association vanished when controlling for heart rate. Conversely, perceived safety was significantly negatively associated with heart rate, even after controlling for heart rate variability. Findings suggest that feeling safe is associated with attenuated cardiac activity and this effect is probably mediated by sympathetic nervous system activity.


Ecological Momentary Assessment , Emotions , Humans , Autonomic Nervous System , Heart Rate/physiology
13.
Front Psychol ; 13: 964206, 2022.
Article En | MEDLINE | ID: mdl-36186395

Psychometrically sound instruments that assess temporal dynamics of creative abilities are limited. The Ambulatory Battery of Creativity (ABC) is designed to assess creative ideation performance multiple times in everyday life and was proven to capture the intra-individual dynamic of creative abilities reliably and validly. The present ambulatory study aimed to replicate and extend the psychometric evidence of the novel ABC. Sixty-nine participants worked on the ABC during a 5-day ambulatory assessment protocol. Each day, participants completed six randomly presented items of the verbal and the figural ABC. Matching previous psychometric analyses, the results indicated good between-person (≥0.80) and good within-person (≥0.72) reliability. Furthermore, evidence for between-person and within-person validity of the ABC was obtained. Performance in the verbal and the figural ABC were interrelated and correlated with an independent measure of creative potential. The verbal ABC was further associated with openness, self-reported creative behavior, creative activities, and creative achievements, thus providing additional evidence of construct validity, especially for the verbal ABC. Finally, the verbal and the figural ABC yielded convincing within-person validity: Longer response times and higher subjective originality ratings were associated with more original ideas. This replication and extension of the ABC's psychometric properties indicates that it enables a reliable and valid assessment of moment-to-moment fluctuations of creative ideation abilities in everyday life, which may facilitate the investigation of exciting new research questions related to dynamic aspects of creative ability.

14.
Internet Interv ; 30: 100571, 2022 Dec.
Article En | MEDLINE | ID: mdl-36105006

Introduction: While online consultations have shown promise to be a means for the effective delivery of high-quality mental healthcare and the first implementations of these digital therapeutic contacts go back nearly two decades, uptake has remained limited over the years. The onset of the COVID-19 pandemic dramatically altered this relative standstill and created a unique turning point, with a massive amount of both professionals and clients having first hands-on experiences with technology in mental healthcare. Objective: The current study aimed to document the uptake of online consultations and explore if specific characteristics of mental health professionals across and beyond Europe could predict this. Methods: An international survey was designed to assess mental health professionals' (initial) experiences with online consultations at the onset of the pandemic: their willingness to make use of them and their prior and current experiences, alongside several personal characteristics. Logistic mixed-effects models were used to identify predictors of the use of online consultations, personal experience with this modality, and the sense of telepresence. Results: A total of 9115 healthcare professionals from 73 countries participated of which about two-thirds used online consultations during the initial COVID-19 outbreak. The current study identifies multiple determinants relating to the use and experience of online consultations, including the professionals' age, experience with the technology before the outbreak, the professional context, and training. Conclusions: Despite strong evidence supporting the relevance of training in digital mental health, this is clearly still lacking. Nevertheless, the COVID-19 pandemic presented a first, and potentially transformative, experience with online consultations for many healthcare professionals. The insights from this study can help support professionals and, importantly, (mental) healthcare organisations to create optimal circumstances for selective and high-quality continued use of online consultations.

15.
Sports Med Open ; 8(1): 62, 2022 May 06.
Article En | MEDLINE | ID: mdl-35523914

BACKGROUND: Physical activity is a health-relevant lifestyle factor associated with various benefits on physical and mental health. Several meta-analyses indicated effects of acute and chronic physical activities on elementary cognitive functions such as executive control processes, memory, and attention. Meta-analytic evidence on the effects of physical activity on creative idea generation, which involves a conglomerate of these elementary cognitive functions, is largely missing. OBJECTIVE: A twofold approach was used to evaluate (1) if there is an association between habitual physical activity and creative ideation and (2) if physical activity interventions (acute and chronic) enhance creative ideation performance. METHODS: Multilevel meta-analytic methods were applied to (1) evaluate the cross-sectional association between creative ideation performance and measures of habitual physical activity and (2) the effect of physical activity on creative ideation performance. Indicators of creative ideation (fluency, flexibility, originality, elaboration, or composite score), creativity domain (verbal, figural), population (adults, children), gender, study quality, and publication year served as moderator variables for both meta-analyses. Analyses of intervention studies additionally examined the moderator variables study design (between, within), time of measurement (during, after), and implementation of intervention (acute, chronic). RESULTS: The applied meta-analytic multilevel analysis indicated a medium effect for cross-sectional studies (r = 0.22, SE = 0.06, p = 0.002, 95% CI [0.10-0.34]) based on 17 effects sizes from seven studies. The pooled effects of 28 intervention studies, providing 115 effect sizes, indicated a medium effect size of Hedges' g = 0.47 (SE = 0.09, p < 0.001, 95% CI [0.30-0.65]). Furthermore, a stronger effect was observed for chronic interventions of several days or weeks in comparison with acute interventions of one single bout. CONCLUSION: This study adds important new meta-analytic evidence on the beneficial role of physical activity beyond mental and physical health outcomes: Physical activity has a positive impact on creative ideation, which expands the literature on the role of physical activity in more elementary cognitive functions such as executive control, memory, and attention. Moderator analyses suggested that chronic interventions showed stronger effects than single bouts of physical activity. Rigorously conducted randomized controlled intervention studies and more cross-sectional studies are needed to broaden the evidence in this nascent field of research.

16.
Front Psychiatry ; 13: 876344, 2022.
Article En | MEDLINE | ID: mdl-35573368

Slow breathing at 6 breaths per min (corresponding to ~ 0.1 Hz) has been found to benefit psychological and physical health. In this study, we aimed to examine if paced singing at 0.1 Hz has beneficial acute effects on physiological function as compared to slow breathing. Participants were randomized to one of four experimental interventions prior to performing a mental stress task: paced breathing at 0.1 Hz (n = 26), paced singing at 0.1 Hz (n = 26), spontaneous breathing (n = 24), or spontaneous singing (n = 25). Heart rate, heart rate variability in the low (LF-HRV) and high frequency (HF-HRV) domain, blood pressure and affective wellbeing were assessed. As expected, both paced breathing and paced singing resulted in elevated LF-HRV. Moreover, both singing groups evidenced increases in heart rate, blood pressure and positive affect, thus indicating elevated sympathetic activation. Breathing and singing at 0.1 Hz had no robust effect on cardiovascular stress reactivity. Findings suggest that paced singing could constitute a promising alternative to slow paced breathing as it increases cardiovascular coherence, although more studies are needed to elucidate whether slow breathing and/or singing could ameliorate acute stress responses.

17.
Sensors (Basel) ; 22(8)2022 Apr 11.
Article En | MEDLINE | ID: mdl-35458912

Several mobile devices have multiple sensors on board and interact with smartphones. This allows for a complex online evaluation of physiological data, important for interactive psychophysiological assessments, which targets the triggering of psychological states based on physiological data such as heart rate variability (HRV). However, algorithms designed to trigger meaningful physiological processes are rare. One exception is the concept of additional HRV reduction (AddHRVr), which aims to control for metabolic-related changes in cardiac activity. In this study we present an approach, based on data of a previous study, which allows algorithm settings to be derived that could be used to automatically trigger the assessment of psychosocial states by online-analysis of transient HRV changes in a sample of 38 firefighters. Settings of a static and a dynamic AddHRVr algorithm were systematically manipulated and quantified by binary triggers. These triggers were subjected to multilevel models predicting increases of objective stress during a period of 24 h. Effect estimates (i.e., odds) and bootstrap power simulations were calculated to inform about the most robust algorithm settings. This study delivers evidence that a dynamic AddHRVr algorithm can trigger transitions of stress, which should be further validated in future interactive psychophysiological assessments.


Firefighters , Algorithms , Emotions , Heart Rate/physiology , Humans , Psychophysiology
18.
Physiol Behav ; 245: 113676, 2022 03 01.
Article En | MEDLINE | ID: mdl-34919919

Recently, we reported on a rare manifestation of respiratory sinus arrhythmia (RSA), namely the "switched-off" RSA (Rassler et al., 2018), also called negative RSA (nRSA). It was found in a minority of healthy persons during elevated fMRI-related anxiety characterized by slow spontaneous breathing and synchronous slow beat-to-beat interval (RRI) oscillations. From 23 healthy scanner naïve participants of an fMRI study consisting of 4 resting states, we selected resting states with highest state anxiety (AS) from 10 participants (AS=24.6±2.5) and compared them to those with lowest AS of the same participants (AS=15.1±3.8, p<0.001). During elevated anxiety, the percentage of nRSA (nRSA%) was more than twice of RSA (p=0.045), while RSA prevailed during low anxiety. This indicates that nRSA might be related to elevated anxiety. Interestingly, nRSA was not only associated with slow RRI and breathing oscillations, but also occurred at "normal" breathing rates in the 0.20-0.35 Hz range. We often observed coupled RRI oscillations at 0.1 or 0.15 Hz and respiration at 0.3 Hz (rate ratio 1:3 or 1:2) with respiration-synchronous 0.3 Hz-wavelets in the RRI rhythm (termed "superposition") indicating a reduced dominance of the respiratory rhythm over the RRI rhythm. This novel finding is supported by the work of Perlitz et al., (2004) on a "0.15 Hz rhythm" in brainstem. The concept behind such a 1:n ratio is a pacemaker-like rhythm in the brainstem that "drives" the cardiac RRI signal and secondarily also respiration as reflected in the 1:n rate ratio.


Respiratory Sinus Arrhythmia , Anxiety/diagnostic imaging , Arrhythmia, Sinus , Heart Rate/physiology , Humans , Magnetic Resonance Imaging , Respiration
19.
Stress ; 25(1): 57-66, 2022 01.
Article En | MEDLINE | ID: mdl-34935585

Since medical communication can be perceived as stressful, the assessment of patients' physiological arousal and behavior during anamnesis interviews may lead to a better understanding of doctor-patient interactions. Therefore, the aim of this study was to test physiological arousal and word use in a laboratory anamnesis interview. In total, sixty-five participants with a mean age of 25.0 years were randomly assigned either to an experimental group (n = 35, 65.7% women) in which they underwent an anamnesis interview or to a control group (n = 30, 73.3% women). Physiological arousal was assessed by salivary cortisol, salivary alpha-amylase (sAA), heart rate (HR) and heart rate variability (HRV). Psychological arousal was assessed using the Positive and Negative Affect Schedule (PANAS). Anamnesis interviews were analyzed using the Linguistic Inquiry and Word Count text analysis tool (LIWC). Participants of the experimental group showed an increase of sAA, HR and negative affect (p's ≤.0.05). Moreover, higher cortisol area under the curve with respect to ground (AUCg) was associated with lesser use of positive emotion words during the interview and subsequent higher negative affect (p's <.05). These results indicate that talking about one's own and family's medical history in anamnesis interview induces physiological arousal. Our findings suggest that anamnesis interviews could not only induce higher negative affect, but also induce physiological arousal, underscoring the importance of good doctor-patient communication.


Laboratories , Salivary alpha-Amylases , Adult , Arousal/physiology , Female , Humans , Hydrocortisone , Male , Saliva , Stress, Psychological
20.
Front Genet ; 13: 1058668, 2022.
Article En | MEDLINE | ID: mdl-36685854

We aimed at extending the repertoire of high-quality miRNA normalizers for reverse transcription-quantitative PCR (RT-qPCR) of human plasma with special emphasis on the extremely guanine-cytosine-rich portion of the miRNome. For high-throughput selection of stable candidates, microarray technology was preferred over small-RNA sequencing (sRNA-seq) since the latter underrepresented miRNAs with a guanine-cytosine (GC) content of at least 75% (p = 0.0002, n = 2). miRNA abundances measured on the microarray were ranked for consistency and uniformity using nine normalization approaches. The eleven most stable sequences included miRNAs of moderate, but also extreme GC content (45%-65%: miR-320d, miR-425-5p, miR-185-5p, miR-486-5p; 80%-95%: miR-1915-3p, miR-3656-5p, miR-3665-5p, miR-3960-5p, miR-4488-5p, miR-4497 and miR-4787-5p). In contrast, the seven extremely GC-rich miRNAs were not found in the two plasma miRNomes screened by sRNA-seq. Stem-loop RT-qPCR was employed for stability verification in 32 plasma samples of healthy male Caucasians (age range: 18-55 years). In general, inter-individual variance of miRNA abundance was low or very low as indicated by coefficient of variation (CV) values of 0.6%-8.2%. miR-3665 and miR-1915-3p outperformed in this analysis (CVs: 0.6 and 2.4%, respectively). The eight most stable sequences included four extremely GC-rich miRNAs (miR-1915-3p, miR-3665, miR-4787-5p and miR-4497). The best-performing duo normalization factor (NF) for the condition of human plasma, miR-320d and miR-4787-5p, also included a GC-extreme miRNA. In summary, the identification of extremely guanine-cytosine-rich plasma normalizers will help to increase accuracy of PCR-based miRNA quantification, thus raise the potential that miRNAs become markers for psychological stress reactions or early and precise diagnosis of clinical phenotypes. The novel miRNAs might also be useful for orthologous contexts considering their conservation in related animal genomes.

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