Search

We present a case of a 48-year-old woman with a fortuitous discovery of macrocytic anemia and thrombocytopenia. Serum folate and vitamin B12 levels were normal. However, due to the presence of indirect signs of cobalamin deficiency, such as elevated homocysteine and methylmalonic acid, and signs of dyserythropoiesis on the bone marrow aspirate, pernicious anemia was suspected. Vitamin B12 dosage was repeated finding fluctuating but always normal results. Anti-intrinsic factor antibodies were present at a very high level, explaining the fluctuations and the interference found on the assay using competitive binding chemiluminescence (CBLA). Serum vitamin B12 dosage by electrochemiluminescence, a method described as not interfering with intrinsic factor antibodies, showed a collapsed vitamin B12 level. Measurement of vitamin B12 with CBLA after adsorption of immunoglobulins in the sample using protein G SepharoseTM, confirmed the interference of the cobalamin assay with autoantibodies. This case illustrates the difficulties regarding the analysis and standardization of the vitamin B12 assay for the diagnosis of pernicious anemia.

Traditionally, low-density lipoprotein (LDL) are separated with respect to their size, density and apolipoprotein composition. Fractionation of LDL according to their electrical charge is also interesting as modified LDL have been implicated in the onset of atherosclerosis. This review discusses possible mechanisms underlying charge heterogeneity of human plasma LDL, such as oxidation, glycation, conjugation with aldehydes, carbamylation and changes in sialic acid content and protein composition.

The role of plasma LDL in atherogenesis is now well established. Cholesteryl ester accumulation within macrophages leads to foam cell formation, an early atherosclerotic process. In vitro, foam cell formation scarcely ever occurs in the presence of native LDL. Modification of these lipoproteins is necessary for their binding to macrophage scavenger receptors. In vitro modifications reported have involved chemical reactions, physical mechanisms, enzymatic reactions, cellular interactions and association with macromolecules. In vivo, they can occur by glycation or desialylation, smoking or by hemodynamic interactions. Alterations of the physicochemical properties of LDL are induced by oxidation and include an increase in their density and their net electronegative charge, changes in lecithin composition, polyunsaturated fatty acid peroxidation of lipids and apolipoprotein B100 degradation. Apolipoprotein B100 fragmentation leads to an impairment of uptake through LDL receptors, while uptake through macrophage scavenger receptors is enhanced. Modified LDL have also other particularities such as cytotoxicity, chemotactism for circulating monocytes, inhibition of resident macrophage mobility, vasoconstriction, perturbation of the arachidonic acid cascade, involvement in haemostasis and immune mechanisms. Hypotheses concerning the role of modified LDL, in particular oxidized LDL, in atherogenesis open new therapeutic prospects.