Polyunsaturated fatty acid supplementation reverses cystic fibrosis-related fatty acid abnormalities in CFTR-/- mice by suppressing fatty acid desaturases.

Cystic fibrosis patients and model systems exhibit consistent abnormalities in metabolism of polyunsaturated fatty acids that appear to play a role in disease pathophysiology. Recent in vitro studies have suggested that these changes are due to overexpression of fatty acid desaturases that can be reversed by supplementation with the long-chain polyunsaturated fatty acids docosahexaenoate and eicosapentaenoate. However, these findings have not been tested in vivo. The current study aimed to test these results in an in vivo model system, the CFTR(-/-) knockout mouse. When compared with wild-type mice, the knockout mice exhibited fatty acid abnormalities similar to those seen in cystic fibrosis patients and other model systems. The abnormalities were confined to lung, ileum and pancreas, tissues that are affected by the disease. Similar to in vitro models, these fatty acid changes correlated with increased expression of Δ5- and Δ6-desaturases and elongase 5. Dietary supplementation with high-dose free docosahexaenoate or a combination of lower-dose docosahexaenoate and eicosapentaenoate in triglyceride form corrected the fatty acid abnormalities and reduced expression of the desaturase and elongase genes in the ileum and liver of knockout mice. Only the high-dose docosahexaenoate reduced histologic evidence of disease, reducing mucus accumulation in ileal sections. These results provide in vivo support for the hypothesis that fatty acid abnormalities in cystic fibrosis result from abnormal expression and activity of metabolic enzymes in affected cell types. They further demonstrate that these changes can be reversed by dietary n-3 fatty acid supplementation, highlighting the potential therapeutic benefit for cystic fibrosis patients.

Risk management in the clinical laboratory.

Clinical laboratory tests play an integral role in medical decision-making and as such must be reliable and accurate. Unfortunately, no laboratory tests or devices are foolproof and errors can occur at pre-analytical, analytical and post-analytical phases of testing. Evaluating possible conditions that could lead to errors and outlining the necessary steps to detect and prevent errors before they cause patient harm is therefore an important part of laboratory testing. This can be achieved through the practice of risk management. EP23-A is a new guideline from the CLSI that introduces risk management principles to the clinical laboratory. This guideline borrows concepts from the manufacturing industry and encourages laboratories to develop risk management plans that address the specific risks inherent to each lab. Once the risks have been identified, the laboratory must implement control processes and continuously monitor and modify them to make certain that risk is maintained at a clinically acceptable level. This review summarizes the principles of risk management in the clinical laboratory and describes various quality control activities employed by the laboratory to achieve the goal of reporting valid, accurate and reliable test results.

DHA and EPA reverse cystic fibrosis-related FA abnormalities by suppressing FA desaturase expression and activity.

Patients and models of cystic fibrosis (CF) exhibit consistent abnormalities of polyunsaturated fatty acid composition, including decreased linoleate (LA) and docosahexaenoate (DHA) and variably increased arachidonate (AA), related in part to increased expression and activity of fatty acid desaturases. These abnormalities and the consequent CF-related pathologic manifestations can be reversed in CF mouse models by dietary supplementation with DHA. However, the mechanism is unknown. This study investigates this mechanism by measuring the effect of exogenous DHA and eicosapentaenoate (EPA) supplementation on fatty acid composition and metabolism, as well as on metabolic enzyme expression, in a cell culture model of CF. We found that both DHA and EPA suppress the expression and activity of Δ5- and Δ6-desaturases, leading to decreased flux through the n-3 and n-6 PUFA metabolic pathways and decreased production of AA. The findings also uncover other metabolic abnormalities, including increased fatty acid uptake and markedly increased retroconversion of DHA to EPA, in CF cells. These results indicate that the fatty acid abnormalities of CF are related to intrinsic alterations of PUFA metabolism and that they may be reversed by supplementation with DHA and EPA.

Increased Δ5- and Δ6-desaturase, cyclooxygenase-2, and lipoxygenase-5 expression and activity are associated with fatty acid and eicosanoid changes in cystic fibrosis.

Patients with cystic fibrosis consistently demonstrate selective abnormalities in essential fatty acid concentrations, including decreased linoleate (LA) and docosahexaenoate (DHA), with variably increased arachidonate (AA). These changes appear important for the pathophysiology of the disease. However, the mechanisms of these changes are not clearly understood. The current study demonstrates that metabolism of LA and alpha linolenate (LNA) to AA and eicosapentaenoate (EPA), respectively, are significantly increased in two different cell culture models of cystic fibrosis. These changes correlated with increased expression of fatty acid Δ5- and Δ6-desaturases, key enzymes in this metabolic pathway. In contrast, cystic fibrosis cells showed decreased metabolism of AA and EPA to docosapentaenoate (DPA) and docosahexaenoate (DHA), respectively, although metabolism of 22:5n-3 to DHA was relatively unchanged. In addition, the expression and activity of both cyclooxygenase-2 and lipoxygenase-5 was markedly increased in these cells. Taken together, these findings are consistent with the conclusion that the diminished LA and increased AA in cystic fibrosis result from increased metabolism of LA, while the observed decrease in DHA is at least partly due to decreased elongation and desaturation beyond EPA.

Increased elongase 6 and Δ9-desaturase activity are associated with n-7 and n-9 fatty acid changes in cystic fibrosis.

Patients with cystic fibrosis, caused by mutations in CFTR, exhibit specific and consistent alterations in the levels of particular unsaturated fatty acids compared with healthy controls. Evidence suggests that these changes may play a role in the pathogenesis of this disease. Among these abnormalities are increases in the levels of n-7 and n-9 fatty acids, particularly palmitoleate (16:1n-7), oleate (18:1n-9), and eicosatrienoate or mead acid (20:3n-9). The underlying mechanisms of these particular changes are unknown, but similar changes in the n-3 and n-6 fatty acid families have been correlated with increased expression of fatty acid metabolic enzymes. This study demonstrated that cystic fibrosis cells in culture exhibit increased metabolism along the metabolic pathways leading to 16:1n-7, 18:1n-9, and 20:3n-9 compared with wild-type cells. Furthermore, these changes are accompanied by increased expression of the enzymes that produce these fatty acids, namely Δ5, Δ6, and Δ9 desaturases and elongases 5 and 6. Taken together, these findings suggest that fatty acid abnormalities of the n-7 and n-9 series in cystic fibrosis are as a result, at least in part, of increased expression and activity of these metabolic enzymes in CFTR-mutated cells.

The SLAM family member CD48 (Slamf2) protects lupus-prone mice from autoimmune nephritis.

Polymorphisms in the SLAM family of leukocyte cell surface regulatory molecules have been associated with lupus-like phenotypes in both humans and mice. The murine Slamf gene cluster lies within the lupus-associated Sle1b region of mouse chromosome 1. Non-autoreactive C57BL/6 (B6) mice that have had this region replaced by syntenic segments from other mouse strains (i.e. 129, NZB and NZW) are B6 congenic strains that spontaneously produce non-nephritogenic lupus-like autoantibodies. We have recently reported that genetic ablation of the SLAM family member CD48 (Slamf2) drives full-blown autoimmune disease with severe proliferative glomerulonephritis (CD48GN) in B6 mice carrying 129 sequences of the Sle1b region (B6.129CD48(-/-)). We also discovered that BALB/c mice with the same 129-derived CD48-null allele (BALB.129CD48(-/-)) have neither nephritis nor anti-DNA autoantibodies, indicating that strain specific background genes modulate the effects of CD48 deficiency. Here we further examine this novel model of lupus nephritis in which CD48 deficiency transforms benign autoreactivity into fatal nephritis. CD48GN is characterized by glomerular hypertrophy with mesangial expansion, proliferation and leukocytic infiltration. Immune complexes deposit in mesangium and in sub-endothelial, sub-epithelial and intramembranous sites along the glomerular basement membrane. Afflicted mice have low-grade proteinuria, intermittent hematuria and their progressive renal injury manifests with elevated urine NGAL levels and with uremia. In contrast to the lupus-like B6.129CD48(-/-) animals, neither BALB.129CD48(-/-) mice nor B6 × BALB/c F1.129CD48(-/-) progeny have autoimmune traits, indicating that B6-specific background genes modulate the effect of CD48 on lupus nephritis in a recessive manner.