Christian Ramakers

Despite the central role of quantitative PCR (qPCR) in the quantification of mRNA transcripts, most analyses of qPCR data are still delegated to the software that comes with the qPCR apparatus. This is especially true for the handling of the fluorescence baseline. This article shows that baseline estimation errors are directly reflected in the observed PCR efficiency values and are thus propagated exponentially in the estimated starting concentrations as well as 'fold-difference' results. Because of the unknown origin and kinetics of the baseline fluorescence, the fluorescence values monitored in the initial cycles of the PCR reaction cannot be used to estimate a useful baseline value. An algorithm that estimates the baseline by reconstructing the log-linear phase downward from the early plateau phase of the PCR reaction was developed and shown to lead to very reproducible PCR efficiency values. PCR efficiency values were determined per sample by fitting a regression line to a subset of data points in the log-linear phase. The variability, as well as the bias, in qPCR results was significantly reduced when the mean of these PCR efficiencies per amplicon was used in the calculation of an estimate of the starting concentration per sample.

OBJECTIVE: The aim was to examine the effects of a Mindfulness-Based Stress Reduction (MBSR) intervention on cardiovascular and cortisol activity during acute stress. METHOD: Eighty-eight healthy community-dwelling individuals reporting elevated stress levels were randomly assigned to the MBSR protocol or a waitlist control group. Before and after the intervention period they participated in a laboratory stress protocol consisting of mental arithmetic and speech tasks. Laboratory measurements included continuous cardiovascular parameters (heart period, heart rate variability, and systolic and diastolic blood pressure [SBP and DBP]), and salivary cortisol. RESULTS: Compared to the control group and controlling for age, sex, body mass index, and beta-blockers, the MBSR group showed larger pre- to postintervention decreases in overall SBP (F(1, 58) = 4.99, p = .029, partial η² = .08) and DBP (F(1, 58) = 11.09, p = .002, partial η² = .16). In addition, the MBSR group exhibited smaller SBP and DBP stress-related changes from pre- to postintervention (F(2, 116) = 4.89, p = .012, partial η² = .08; F(2, 116) = 6.07, p = .007, partial η² = .10, respectively). No effects were obtained on other physiological measures. CONCLUSION: MBSR may help reducing blood pressure levels and blood pressure reactivity to stress.

Background Observational studies suggest that adequate dietary potassium intake (90–120 mmol/day) may be renoprotective, but the effects of increasing dietary potassium and the risk of hyperkalemia are unknown. Methods This is a prespecified analysis of the run-in phase of a clinical trial in which 191 patients (age 68±11 years, 74% males, 86% European ancestry, eGFR 31±9 ml/min per 1.73 m 2 , 83% renin-angiotensin system inhibitors, 38% diabetes) were treated with 40 mmol potassium chloride (KCl) per day for 2 weeks. Results KCl supplementation significantly increased urinary potassium excretion (72±24 to 107±29 mmol/day), plasma potassium (4.3±0.5 to 4.7±0.6 mmol/L), and plasma aldosterone (281 [198–431] to 351 [241–494] ng/L), but had no significant effect on urinary sodium excretion, plasma renin, BP, eGFR, or albuminuria. Furthermore, KCl supplementation increased plasma chloride (104±3 to 105±4 mmol/L) and reduced plasma bicarbonate (24.5±3.4 to 23.7±3.5 mmol/L) and urine pH (all P <0.001), but did not change urinary ammonium excretion. In total, 21 participants (11%) developed hyperkalemia (plasma potassium 5.9±0.4 mmol/L). They were older and had higher baseline plasma potassium. Conclusions In patients with CKD stage G3b–4, increasing dietary potassium intake to recommended levels with potassium chloride supplementation raises plasma potassium by 0.4 mmol/L. This may result in hyperkalemia in older patients or those with higher baseline plasma potassium. Longer-term studies should address whether cardiorenal protection outweighs the risk of hyperkalemia. Clinical trial number: NCT03253172