Effect of fasting status and other pre-analytical variables on quantitation of long-chain fatty acids in red blood cells

Lipoxygenase-derived oxylipins are enriched in anti-citrullinated protein antibody (ACPA)-positive individuals at risk for developing rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is typically preceded by an extended preclinical period where circulating autoantibodies, particularly anti-citrullinated protein antibodies (ACPA), are detectable in the absence of clinical arthritis. Increased dietary intake of anti-inflammatory omega-3 (ω3) polyunsaturated fatty acids (PUFA) has been shown to be associated with a lower the risk of developing incident RA in large epidemiological studies. It is currently not known how changes in fatty acid (FA) metabolism may impact on the progression towards RA in at-risk individuals. To begin to address this question, we profiled serum FAs and oxylipins in an established cohort of at-risk ACPA-positive first-degree relatives (FDR) of RA patients (N = 31), some of whom developed RA (N = 4), and compared their profile to ACPA-negative FDR from the same population (N = 10).

METHODS

Gas chromatography (GC) was used for FA quantitation. Oxylipins were extracted and quantified using high-performance liquid chromatography-tandem mass spectrometry (HPLC/MS/MS).

RESULTS

Although we did not detect any meaningful differences in overall FA content between ACPA + and ACPA - FDR, the levels of oxylipins derived from FA metabolism demonstrated significant differences between the two groups, with the ACPA + group demonstrating enrichment in circulating arachidonic acid- and eicosapentaenoic acid-derived molecules. Compared with the ACPA - FDR group, the ACPA + FDR, including those who progressed into inflammatory arthritis, displayed higher levels of LOX-derived oxylipins.

CONCLUSION

ACPA seropositivity in otherwise unaffected individuals at-risk for developing future RA based on family history (FDR) is associated with alterations in the serum oxylipin profile that suggests dysregulated LOX activity.

Quantitative analysis of ethanolamine plasmalogen species in red blood cells using liquid chromatography tandem mass spectrometry for diagnosing peroxisome biogenesis disorders

Plasmalogens are glycerophospholipids characterized by a vinyl-ether bond with a fatty alcohol at the sn-1 position, a polyunsaturated fatty acid at the sn-2 position, and a polar head at the sn-3 position, commonly phosphoethanolamine. Plasmalogens play crucial roles in several cellular processes. Reduced levels have been associated with Alzheimer's and Parkinson's disease progression. Markedly reduced plasmalogens are a classic feature of peroxisome biogenesis disorders (PBD) because plasmalogen synthesis requires functional peroxisomes. Particularly, severe plasmalogen deficiency is the biochemical hallmark of rhizomelic chondrodysplasia punctata (RCDP). Traditionally, plasmalogens are evaluated in red blood cells (RBCs) by gas-chromatography/mass-spectrometry (GC-MS), which cannot distinguish individual species. We developed a liquid-chromatography/tandem mass-spectrometry (LC-MS/MS) method to quantify eighteen phosphoethanolamine plasmalogens in RBCs to diagnose PBD patients, especially RCDP. Validation results showed a specific, robust, and precise method with broad analytical range. Age-specific reference intervals were established; control medians were used to assess plasmalogen deficiency in patients' RBCs. Clinical utility was also confirmed in Pex7 deficient mouse models recapitulating severe and milder RCDP clinical phenotypes. To our knowledge, this is the first attempt to replace the GC-MS method in the clinical laboratory. In addition to diagnosing PBDs, structure-specific plasmalogen quantitation could help understand disease pathogenesis and monitor therapy.

Inherited causes of exocrine pancreatic insufficiency in pediatric patients: clinical presentation and laboratory testing

Pediatric patients with exocrine pancreatic insufficiency (EPI) have symptoms that include abdominal pain, weight loss or poor weight gain, malnutrition, and steatorrhea. This condition can be present at birth or develop during childhood for certain genetic disorders. Cystic fibrosis (CF) is the most prevalent disorder in which patients are screened for EPI; other disorders also are associated with pancreatic dysfunction, such as hereditary pancreatitis, Pearson syndrome, and Shwachman-Diamond syndrome. Understanding the clinical presentation and proposed pathophysiology of the pancreatic dysfunction of these disorders aids in diagnosis and treatment. Testing pancreatic function is challenging. Directly testing aspirates produced from the pancreas after stimulation is considered the gold standard, but the procedures are not standardized or widely available. Instead, indirect tests are often used in diagnosis and monitoring. Although indirect tests are more widely available and easier to perform, they have inherent limitations due to a lack of sensitivity and/or specificity for EPI.

Establishing age-stratified red blood cell fatty acid reference ranges using model-based clustering and iterative application of the harris-boyd method

BACKGROUND

The current assessment of nutritional status and diagnosis of essential fatty acids deficiency (EFAD) utilizes the analysis of long-chain fatty acids (LCFAs) in serum or plasma; however, these concentrations do not represent habitual LCFA intake. LCFAs in red blood cells (RBCs) are less prone to intra-individual variability and exclude the need for fasting, which is unrealistic in pediatric populations. Our study objective was to characterize the RBC LCFA profiles in pediatric and adult reference populations and establish age-specific reference intervals (RIs).

METHODS

Twenty-one LCFAs in RBCs were measured in 523 pediatric and adult controls by gas chromatography-mass spectrometry. Model-based clustering was used to identify possible age subgroups. After removing outliers by the Tukey method, initial age subgroups were then compared using the Harris-Boyd method in an iterative manner. RIs (95%), with confidence intervals (90%), in the final age groups were established using parametric or non-parametric statistics.

RESULTS

Our data showed heterogeneous changes in the concentrations of most LCFAs and the EFAD biomarkers (mead acid, Triene/Tetraene ratio) during infancy. Model-based clustering identified six initial age subgroups per fatty acid, on average. Our application of the iterative Harris-Boyd method decreased the average number of age groups to three per fatty acid, with 13 total unique age cut-offs. Finally, using these age groups, we established age-specific RIs for 21 fatty acids, six group totals, and the Triene/Tetraene ratio.

CONCLUSION

Our study revealed significant age-dependent changes in RBC fatty acid profiles warranting separate pediatric and adults RIs. Model-based clustering and the iterative application of the Harris-Boyd method were successfully used to establish RBC fatty acid RIs for an objective assessment of long-term nutritional status in pediatric and adult populations.