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Glycoproteins as markers of inflammation in rheumatic disorders.
Glycoproteins (GP) are one of the many acute phase proteins (APP) present in serum. Their presence and levels in the blood are a non-specific measure of the disease activity. ESR is the most commonly performed laboratory test for this purpose. Greactive protein, transferrin, ceruloplasmin, albumin, a1-antitrypsin have been similarly used.[6] The present study was undertaken to evaluate the utility of glycoproteins as a measure of the disease activity and inflammation in rheumatic disorders. GPs were studied in patients with rheumatoid arthritis (RA), juvenile rheumatoid arthritis (JRA) and osteoarthritis (OA). These were compared with normal healthy controls.
Forty-five patients of RA, eight of JRA, fifteen of osteoarthritis and fifty normal healthy adults were studied. As per the ARA criteria,[12] twenty-eight were definite, seven were classical and ten were probable cases of RA. The healthy controls were mainly medical students and technicians. Venous blood was collected after an overnight fast. Following investigations were carried out apart from routine haemogram and biochemistry: (1) Total serum protein concentration was estimated by Biuret method using bovine albumin as a standard. (2) Serum hexose, hexosamine and fucose were estimated by the method of Winzler (1955).[25] (3) Sialic acid by the method of Hess et al (1957).[10] (4) Paper electrophoresis was carried out in barbital buffer, pH 8.6 of ionic strength 0.075. A current of 1.5 milliamps for each strip was applied and allowed to run for 1618 hours. The strips were stained with bromophenol blue and evaluated by elution of the dye. (5) Glycoprotein electrophoresis was carried out in barbital buffer pH 8.6 of ionic strength 0.05. A current of 2.5 milliamps per cm was applied and allowed to run for five hours. The strips were stained with periodic acid-schiff's stain and quantitated with a densitometer.
[Table - 1] depicts the levels (mean ± S.D.) of ESR and some glycoproteins in normal individuals and in patients with R.A., O.A., and J.R.A. The Table also shows the correlation between the various parameters. [Table - 2] shows the mean levels of serum total proteins alongwith their fractions as obtained by the electrophoresic technique. [Table - 3] depicts the serum hexose levels and its various fractions as seen on the electrophoretic patterns.
Most glycoproteins contain mannose, galactose, fucose and in some instances glucose as the carbohydrate moiety. Several derivatives of neuraminic acid often referred to as Sialic acid are also glycoprotein compounds. Glycoproteins are found in greatest concentration in animal fluids like plasma and urine and also in connective tissue. Spiro in 1959 established that liver is the major organ involved in the normal synthesis of glycoproteins.[19] Interleukin-1, a polypeptide induces amongst other things increased synthesis of acute phase proteins. All the four glycoproteins were significantly elevated in sera of patients with RA and JRA. As against this, sera from patients of OA showed minimal but statistically insignificant elevations. Glycoproteins may, thus be able to differentiate an inflammatory arthritis from a degenerative, non-inflammatory arthritis. The results are in agreement with those of many other workers.[3], [13], [15],[16],[17], [23], [24] High levels of hexosamine in RA cases have been reported.[1], [6], [14], [18], [20] Dutt[8] suggested that rise of GPs in the absence of any other obvious sign of tissue destruction may be the earliest arthrogenic index. Carter et al[2] found increased sialic acid levels in R.A. Coburn et al[4] found that sialic acid estimation was helpful both in estimating the degree of rheumatic activity and also in evaluating the efficacy of therapeutic agents. ESR was significantly elevated in R.A. and JRA and slightly but insignificantly in O.A. [Table - 1]. There was a positive correlation of ESR with all the four GPs studied, the best correlation being with hexosamine, followed by sialic acid, fucose and hexose in that order. [Table - 2] shows the results of serum protein fractions in controls, R.A., JRA and OA. There was a significant decrease in serum albumin with highly significant elevation of a2 and total globulin (p< 0.001) and significant elevation of a1-globulin (p< 0.05) in R.A. O.A. sera showed an insignificant change. All these changes are consistent with an inflammatory process in R.A., J.R.A. and relative lack of inflammation in O.A. These results are in agreement with other workers.[5], [7], [9], [21], [22] Since glycoproteins are associated with all protein fractions, it was interesting to study serum glycoprotein fractions (hexose-bound). [Table - 3] shows that there was a significant decrease in albumin-bound hexose with significant elevation in a1 and a2 bound hexose levels in sera of patients with R.A. and J.R.A. O.A. patients showed changes in the same direction, but the results were not statistically significant. These results are consistent with those of others.[11], [13] Thus, serum GPs (hexose, fucose, sialic acid, hexosamine) or protein-bound glycoproteins are a useful index of inflammation. Additionally, they bear a significant correlation with ESR. It is not possible to say from this data if they are a better index or if they can be used as alternatives to ESR or other APP. It is now known that some inflammation is present in OA. Possibly, the degree of inflammation as well as the number of joints affected in OA, keen the aberrations in APP within levels of statistical insignificance. It would be interesting to study these parameters in OA patients with significant inflammatory activity.
The authors thank the Dean, Topiwala National Medical College, Bombay, 400 008, for allowing to publish this article.
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