OBJECTIVE--Increased concentrations of lipid peroxidation products have been described in the serum and synovial fluid from patients with rheumatoid arthritis. A large proportion of the unsaturated lipids in human extracellular fluids is a component of low density lipoprotein (LDL). The oxidative modification of LDL, and its subsequent uptake by macrophages, has been implicated in the pathogenesis of atherosclerosis, but not of rheumatoid arthritis. This study aimed to assess whether oxidatively modified LDL was present in the rheumatoid synovium. METHODS--A polyclonal antiserum raised in rabbits against oxidised LDL (o-LDL) was used to perform an immunohistochemical study of a series of synovial biopsy specimens from patients with rheumatoid arthritis. RESULTS--Collections of positively stained macrophages, arranged in a linear fashion and with the morphological characteristics of foam cells--that is, 9fatty streaks9, were identified around blood vessels within the intimal connective tissue. In addition, scattered, positively stained foam cells were present in association with deposits of fibrin. These staining patterns were absent from control synovial membranes (traumatic knee injuries). CONCLUSIONS--The findings in all rheumatoid patients studied suggest that atherosclerosis and rheumatoid arthritis have analogous pathogenetic features.
A promising approach to study lipid peroxidation pathology is antibodies recognizing aldehydes which react with and became bound to amino acid side chains of proteins. We present in this study the characterization of several monoclonal antibodies which recognize 4-hydroxynonenal (HNE) modified proteins. Six out of 20 antibodies recognizing HNE modified BSA were able to detect HNE-protein adducts in peroxidized liver microsomes. Two of these antibodies were selected and characterized. Both antibodies could also detect HNE-protein adducts in oxidized low density lipoprotein. They exhibit no detectable cross reaction with proteins modified by malonaldehyde, nonanal, nonenal and 4-hydroxyhexenal. Protein bound 4-hydroxyoctenal and 4-hydroxydecenal were recognized to some extent. Further characterization revealed that the two antibodies are highly selective for HNE bound to histidine with only some cross reaction to HNE bound to lysine and cysteine. Preliminary quantitative ELISA-analysis showed that oxidized microsomes and oxidized LDL contain 12 nmol and 3 nmol HNE-histidine per mg protein respectively.
alpha-Tocopherol (alpha-T), an important anti-oxidant of plasma lipoproteins and cell membranes, is secreted from liver together with very-low-density lipoproteins into the blood stream. Other serum lipoprotein classes gain alpha-T by exchange and transfer processes. We show here that the lipoprotein-free d > 1.22 g/ml fraction of human or pig serum increases the exchange rate of alpha-T by a factor of 2-4 as compared with spontaneous exchange/transfer. The alpha-T exchange/transfer (alpha-TET) activity was purified by multiple-step column chromatography. It gave a single band in PAGE with an apparent molecular mass of 75 kDa, and was found to be identical with the phospholipid transfer protein (PLTP). PLTP catalysed alpha-T exchange between different lipoprotein classes, as well as the transfer of alpha-T from artificial liposomes to high-density lipoproteins. The alpha-TET activity measured with a newly developed assay in ten healthy people was 2.45 +/- 0.88 nmol.ml-1.h-1.alpha-TET activity was negatively correlated with plasma low-density lipoprotein-cholesterol (r = -0.75; P < 0.01). It is concluded that human PLTP catalyses exchange/transfer processes of alpha-T between lipid compartments. This factor may be of relevance in atherogenesis and tumour initiation and growth.
