Characterization of plasma membranes and rough endoplasmic reticulum of synovial cells cultured from rheumatoid arthritis patients

Two-dimensional electrophoresis of synovial tissue, synovial fluid and serum in patients with rheumatoid arthritis and related diseases

Using the technique of two-dimensional (2D) electrophoresis with consecutive silver staining, we investigated samples of serum, synovial fluid and synovial tissue obtained from 19 patients suffering from rheumatoid arthritis (RA) or non-RA arthritis. From these experiments we have drawn the following conclusions. 2D electrophoresis of serum, synovial fluid and synovial tissue extracts taken from patients suffering from joint diseases is a reproducible method. Repeated runs of the same sample reveal an essentially constant protein spot pattern. The time period between surgery and tissue preparation did not influence the number of protein spots when less than 15 h was involved. The protein spot number is always lower in synovial fluid than in either synovial tissue or serum in RA and non-RA patients. The mean value for the number of spots is 68 for the inflamed tissue irrespective of the cause of arthritis (RA and non-RA group taken together) and 47 for the control group. This difference is significant. We were able to definitely identify 7 spots in the tissue extract. We did not find RA-specific protein spots in either serum, synovial fluid or tissue extracts from the synovial membrane. The only significant difference between RA patients and either non-RA or control group patients concerning the protein spot pattern is the increased size of the immunoglobulin spot (mainly IgG) in RA. In addition, we discuss possible reasons for failure of the 2D electrophoresis technique to detect disease-specific protein patterns.

Decreased NA+, K+-ATPase activity in erythrocyte membrane from rheumatoid arthritis patients

The activity of the plasma membrane Na+/K+-ATPase and cellular sodium (Nai) and potassium (Ki) content were analysed in RBCs from 15 rheumatoid arthritis (RA) and 30 reference subjects (11 healthy controls, 12 osteoarthritis and 7 gouty patients). Na+/K+-ATPase activity was determined by measuring the inorganic phosphate (Pi) released by incubation in a reaction medium in the presence and absence of K ions or ouabain. Nai and Ki were measured with an ion-selective electrode analyser on the hemolysates, after washing the RBCs in 110 mM MgCl2. The Na/K-ATPase activity was significantly lower in RA patients than in both healthy controls and patients with osteoarthritis or gout. A slight but significant increase in Nai was observed in rheumatoid subjects. It is hypothesized that the decrease in the Na+/K+-ATPase activity in RA may be the result of a defective expression of membrane proteins, which is probably related to the altered cell sensitivity observed.

Etiology of rheumatoid arthritis

Definite genetic associations with immunological cooperative HLA-D(R) antigens have been demonstrated for rheumatoid arthritis (RA). Microbial etiology has not been proven, but some hope for the supporters of this view is still given by small viruses, plasmids of enteric bacteria or perhaps oncogen-like DNA-sequences. Yet, electrophoretical analysis of membrane proteins or surface glycoproteins of RA synovial cells does not show any differences compared to reference cells. Autoimmunity to several tissue elements has been demonstrated, but most of it is of secondary nature. Antigenicities of type II and III collagens are probably only contributory factors for HLA-DR4 positive individuals. Proteoglycans or minor cartilage collagens have not been extensively studied, so far. Endocrine, dietary or psychological influences might be triggering events for otherwise 'preloaded' individuals.