Discrepancies between dihydropyrimidine dehydrogenase phenotyping and genotyping: What are the explanatory factors?

AIM: Dihydropyrimidine dehydrogenase (DPD) deficiency can be detected by phenotyping (measurement of plasma uracil [U], with U ≥ 16 µg/L defining a partial deficiency) and/or by genotyping (screening for the four most frequent DPYD variants). We aimed to determine the proportion of discrepancies between phenotypic and genotypic approaches and to identify possible explanatory factors. METHODS: Data from patients who underwent both phenotyping and genotyping were retrospectively collected. Complementary genetic analyses (genotyping of the variant c.557A>G and DPYD sequencing) were performed for patients with U ≥ 16 µg/L without any common variants. The characteristics of patients classified according to the congruence of the phenotyping and genotyping approaches were compared (Kruskal-Wallis test), and determinants of U levels were studied in the whole cohort (linear model). RESULTS: Among the 712 included patients, phenotyping and genotyping were discordant for 12.5%, with 63 (8.8%) having U ≥ 16 µg/L in the absence of a common variant. Complementary genetic investigations marginally reduced the percentage of discrepancies to 12.1%: Among the nine additional identified variants, only the c.557A>G variant, carried by three patients, had been previously reported to be associated with DPD deficiency. Liver dysfunction could explain certain discordances, as ASAT, ALP, GGT and bilirubin levels were significantly elevated, with more frequent liver metastases in patients with U ≥ 16 µg/L and the absence of a DPYD variant. The impact of cytolysis was confirmed, as ASAT levels were independently associated with increased U (p < 0.001). CONCLUSION: The frequent discordances between DPD phenotyping and genotyping approaches highlight the need to perform these two approaches to screen for all DPD deficiencies.

Non-linearity in lipase assays: A multicentric comparison on different analysers.

OBJECTIVES: Non-linearity in lipase assays and the ensuing gaps in results distribution have been described on Roche analysers, but have yet to be studied on other analysers. DESIGN AND METHODS: Eighteen lithium-heparinized plasma pools of lipase activities decreasing from 1700 to <4 U/L were prepared for multicentric evaluation on several analysers. Non-linearity was modelled as the difference between the polynomial regression of lipase activities depending on relative dilutions over the primary measuring range, and the linear regression of the same variables above the manufacturer's limit of linearity (MLL). Gaps in lipase distribution resulting from non-linearity were graphically evidenced through histograms. Upper limits of gaps were calculated, which are lipase activities where non-linearity biases no longer impact the diluted lipase results. RESULTS: MLLs and lipase (U/L) calculated at MLL (%biases versus MLL) were respectively: 1200 and 1124 (-6.3%) on the Architect C16000 (Abbott); 300 and 248 (-17.3%) on the Cobas c503 (Roche); 1500 and 1458 (-2.8%) on the Dimension Vista (Siemens); and 700 and 659 (-5.9%) on the Atellica CH930 (Siemens). Using Sentinel Lipase reagents on Abbott analysers, these measurements were respectively: 300 and 294 (-2.0%) on the Architect C16000, and 300 and 298 (-0.7%) on the Alinity. Setting Randox Lipase reagents on the Alinity, MLL and lipase at MLL were 953 and 776 (-18.6%), respectively. CONCLUSIONS: Considering the desirable (±14.2 %) and optimal (±7.1 %) allowable total error for lipase (EFLM/EuBIVAS), biases at manufacturer's limit of linearity were acceptable, except for Roche Cobas c503 method and Randox method on Abbott Alinity.

Inhibition of Vascular Endothelial Cadherin Cleavage Prevents Elastic Fiber Alterations and Atherosclerosis Induced by Intermittent Hypoxia in the Mouse Aorta.

Intermittent hypoxia (IH), the major feature of obstructive sleep apnea syndrome (OSAS), induces atherosclerosis and elastic fiber alterations. VE-cadherin cleavage is increased in OSAS patients and in an IH-cellular model. It is mediated by HIF-1 and Src-tyr-kinases pathways and results in endothelial hyperpermeability. Our aim was to determine whether blocking VE-cadherin cleavage in vivo could be an efficient strategy to inhibit deleterious IH-induced vascular remodeling, elastic fiber defects and atherogenesis. VE-cadherin regulation, aortic remodeling and atherosclerosis were studied in IH-exposed C57Bl/6J or ApoE-/-mice treated or not with Src-tyr-kinases inhibitors (Saracatinib/Pazopanib) or a HIF-1 inhibitor (Acriflavine). Human aortic endothelial cells were exposed to IH and treated with the same inhibitors. LDL and the monocytes transendothelium passage were measured. In vitro, IH increased transendothelium LDL and monocytes passage, and the tested inhibitors prevented these effects. In mice, IH decreased VE-cadherin expression and increased plasmatic sVE level, intima-media thickness, elastic fiber alterations and atherosclerosis, while the inhibitors prevented these in vivo effects. In vivo inhibition of HIF-1 and Src tyr kinase pathways were associated with the prevention of IH-induced elastic fiber/lamella degradation and atherogenesis, which suggests that VE-cadherin could be an important target to limit atherogenesis and progression of arterial stiffness in OSAS.