Katherine Chabot

Agreement of bioelectric impedance analysis and dual-energy X-ray absorptiometry for body composition evaluation in adults with cystic fibrosis

Malnutrition in cystic fibrosis (CF) is associated with increased mortality and can lead to fat-free (FFM) and fat mass (FM) loss. Dual-energy X-ray absorptiometry (DXA) is used and validated to measure FFM and FM. DXAs high cost has led to the utilization of less costly techniques such as bioelectrical impedance analysis (BIA). The aim of this study was to determine the agreement of FFM, FM and %FM measurements taken with DXA and BIA in adults with CF. We measured FFM, FM and %FM in 34 adults with CF with a leg-to-leg BIA and an iDXA and determined agreement using Bland-Altman analysis. While DXA and BIA measurements were well correlated (r > 0.8), mean biases between both methods were between 8 and 11%. BIA underestimated FM and %FM and overestimated FFM. In a clinical research setting where these measurements are used to phenotype patients, BIA cannot replace DXA.

A semi-automated mass spectrometric immunoassay coupled to selected reaction monitoring (MSIA-SRM) reveals novel relationships between circulating PCSK9 and metabolic phenotypes in patient cohorts.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a key regulator of circulating low density lipoprotein cholesterol (LDL-C) levels. Besides its full-length mature form, multiple variants of PCSK9 have been reported such as forms that are truncated, mutated and/or with posttranslational modifications (PTMs). Previous studies have demonstrated that most of these variants affect PCSK9s function and thereby LDL-C levels. Commercial ELISA kits are available for quantification of PCSK9, but do not allow discrimination between the various forms and PTMs of the protein. To address this issue and given the complexity and wide dynamic range of the plasma proteome, we have developed a mass spectrometric immunoassay coupled to selected reaction monitoring (MSIA-SRM) for the multiplexed quantification of several forms of circulating PCSK9 in human plasma. Our MSIA-SRM assay quantifies peptides spanning the various protein domains and the S688 phosphorylation site. The assay was applied in two distinct cohorts of obese patients and healthy pregnant women stratified by their circulating LDL-C levels. Seven PCSK9 peptides were monitored in plasma samples: one in the prodomain prior to the autocleavage site at Q152, one in the catalytic domain prior to the furin cleavage site at R218, two in the catalytic domain following R218, one in the cysteine and histidine rich domain (CHRD) and the C-terminal peptide phosphorylated at S688 and unmodified. The latter was not detectable in sufficient amounts to be quantified in human plasma. All peptides were measured with high reproducibility and with LLOQ and LOD below the clinical range. The abundance of 5 of the 6 detectable PCSK9 peptides was higher in obese patients stratified with high circulating LDL-C levels as compared to those with low LDL-C (p < 0.05). The same 5 peptides showed good and statistically significant correlations with LDL-C levels (0.55 < r < 0.65; 0.0002 ⩽ p ⩽ 0.002), but not the S688 phosphorylated peptide. However, this phosphopeptide was significantly correlated with insulin resistance (r = 0.48; p = 0.04). In the pregnant women cohort, none of the peptides were associated to LDL-C levels. However, the 6 detectable PCSK9 peptides, but not PCSK9 measured by ELISA, were significantly correlated with serum triglyceride levels in this cohort. Our results also suggest that PCSK9 circulates with S688 phosphorylated at high stoichiometry. In summary, we have developed and applied a robust and sensitive MSIA-SRM assay for the absolute quantification of all PCSK9 domains and a PTM in human plasma. This assay revealed novel relationships between PCSK9 and metabolic phenotypes, as compared to classical ELISA assays.

Glucose Fluctuations are Not Modulated by the Proportion of Calories from Macronutrients or Spontaneous Total Energy Expenditure in Adults with Cystic Fibrosis

OBJECTIVES To determine the modifiable factors affecting glucose variability in people with cystic fibrosis (CF). CF-related diabetes (CFRD) is the most common complication of CF, and its presence increases morbidity and mortality in patients. Patients with CF (with and without CFRD) have potentially harmful glucose fluctuations and glucose excursions when compared to healthy adults. Carbohydrate intake and exercise have been shown to affect glycemia. Therefore, our hypothesis was that the proportion of energy from carbohydrates and total energy expenditure (TEE) would influence glucose fluctuations in adults with CF. METHODS A cross-sectional study involved 36 patients with CF, in whom continuous glucose monitoring systems were installed. Glucose fluctuations were then quantified using 3 indexes: mean amplitude of glucose excursions, standard deviation and coefficient of variation. Patients filled out a 3-day food diary to quantify energy intake and the proportions of calories from carbohydrates, fats and proteins, and they wore Sensewear Armbands to estimate spontaneous TEE and footsteps walked. Glucose tolerance status was determined using oral glucose tolerance tests. RESULTS Patients with CF with normal and impaired glucose tolerance had fewer glucose fluctuations than patients with CFRD (p<0.05). However, linear regression models used to determine whether nutrition or energy expenditure affects glucose fluctuations demonstrated that energy, the proportion of carbohydrates, of fat and of protein, TEE or the number of footsteps walked did not affect glucose fluctuation indexes (p>0.05). CONCLUSIONS TEE and the proportion of energy from carbohydrates did not affect glucose fluctuations in adults with CF.

Relative contribution of muscle and liver insulin resistance to dysglycemia in postmenopausal overweight and obese women: A MONET group study

OBJECTIVES The relative contribution of muscle and liver insulin resistance (IR) in the development of dysglycemia and metabolic abnormalities is difficult to establish. The present study aimed to investigate the relative contribution of muscle IR vs. liver IR to dysglycemia in non-diabetic overweight or obese postmenopausal women and to determine differences in body composition and cardiometabolic indicators associated with hepatic or muscle IR. MATERIAL AND METHODS Secondary analysis of 156 non-diabetic overweight or obese postmenopausal women. Glucose tolerance was measured using an oral glucose tolerance test. Whole-body insulin sensitivity (IS) was determined as glucose disposal rate during a euglycemic-hyperinsulinemic clamp. Muscle and liver IR have been calculated using Abdul-Ghani et al. OGTT-derived formulas. Participants body compositions as well as cardiometabolic risk indicators were also determined. RESULTS Overall, 57 (36.5%) of patients had dysglycemia, among them 25 (16.0%); 21 (13.5%); 11 (7.1%) had impaired fasting glycemia, impaired glucose tolerance and combined glucose intolerance respectively. Fifty-three (34.0%) participants were classified as combined IS while on the opposite 51 participants (32.7%) were classified as combined IR and 26 (16.7%) participants had either muscle IR or liver IR. For similar body mass index and total fat mass, participants with liver IR were more likely to have lower whole-body IS, dysglycemia and higher visceral fat, liver fat index, triglycerides and alanine aminotransferase than participants with muscle IR. CONCLUSION In the present study, the presence of liver IR is associated with a higher prevalence of dysglycemia, ectopic fat accumulation and metabolic abnormalities than muscle IR.

Intravenous catheters induce a local inflammatory response

Aim Chronic inflammation has been associated to the development of cardiometabolic dysfunctions. The use of an intravenous (IV) catheter is highly recommended for physiology testing. Yet, the presence of an IV catheter triggers local inflammation that does not reflect systemic inflammatory status. The aim of this study was to assess the effect of an IV catheter on serum concentrations of IL‐6, IL‐8 and hsCRP in a fasting state and after a high‐fat meal known to trigger low‐grade inflammation. Methods Twenty‐two healthy subjects (7 men, 15 women) were included in this study. The trial included 2 visits. After an overnight fast, a venous catheter was inserted into an antecubital vein. A first blood sample was collected through this catheter at T = 0 min. On each visit, participants were requested either to drink only water for the whole duration of the test (WO test), or to consume a high‐fat meal (HFM). Blood samples were collected through the catheter at T60, T120, T180 and T300 min. Additional venous punctures were performed on the contralateral arm at T180 and T300 min. Serum inflammatory mediators were measured at each time point of both interventions. Results When serum was collected by venous punctures, IL‐6 concentrations remained unchanged during both WO and HFM tests (Ptime = 0.15 and Ptime = 0.23, respectively), whereas the concentrations increased progressively over time when serum was collected through the catheter (Ptime < 0.001). The high‐fat meal had no additional effect on IL‐6 levels (Pmeal = 0.27) neither in serum collected by venous puncture nor in serum collected through the catheter. Serum IL‐8 and hsCRP concentrations did not vary over time, and were influenced neither by the meal type nor by the blood collection method. Conclusion The insertion of an indwelling catheter is associated with a local inflammatory response possibly mediated by IL‐6 but not IL‐8. This inflammatory response was not enhanced by a pro‐inflammatory high‐fat meal. HighlightsThe use of an IV catheter induced a local inflammatory response mediated by IL‐6.This inflammatory response was not enhanced by a pro‐inflammatory high‐fat meal.The IV catheter distorts the assessment of inflammation in physiology testing.