Brief Report

Acid Phosphatase in Human Synovial Fluid

By CAROL Smm AND DAVID HAMEAMAN

YNOVIAL MEMBRANE lining cells show acid phosphatase activity in S granules that are thought to be lysosomes.’ In rheumatoid arthritis, the lining cells show markedly increased acid phosphatase activity.’ This observa- tion led us to compare acid phosphatase activity in synovial fluids from nor- mal and arthritic joints with the thought that in rheumatoid arthritis, lyso- some of lining cells might release their contained hydrolytic enzymes into synovial effusions. There appears to be no previous study of the occurrence of acid phosphatase in synovial fluid, although activities of a number of other enzymes have been measured: glucuronidase,2 pepsin and trypsin? amylase and lipase,’ peroxidase,s alkaline phosphatase and transaminases8

METHODS Patients in the following groups were studied: 1) “Normal” subjects were those apparently free of joint disease. This group included

3) Patients with rheumatoid arthritis, as defined by the criteria of the American Rheuma-

3) Patients with a miscellaneous group of joint diseases:

one patient with carcinoma of the prostate with extension beyond the capsule.

tism A~sociation.~

Traumatic arthritis Pulmonary osteoarthropathy Degenerative osteoarthritis Arthritis with psoriasis Acute rheumatic fever Effusion due to tumor in the joint cavity Gout

Acid phosphatase (AP) activity was measured in synovial fluid from the knee, and in serum obtained at the same time. Three pleural fluids and three cerebrospinal fluids were also studied. All determinations were done within 30-60 minutes. The method of Andersch and Sczapinskis was used with paranitrophenyl phosphate (Sigma) as substrate. By this method the maximum normal level of serum AP is 0.63 units for males and 0.56 units for females.

Cell counts and differential counts were carried out on synovial fluids within three hours after collection. Protein and hyaluronate determinations were done on most synovial fluids using methods described e1sewhere.S

RESULTS

Of six “normal” synovial fluids studied, four showed AP levels within nor- mal limits, and two showed elevation of AP twice the maximum normal adult

F T ~ the Department of Medicine, Albert Einstein College of Mediche cmd Bronx Municipal Hospital Center, New York, N . Y.

‘Supported Graduate Training Grant 2A-5082, N a t i d I & t e of Arthritis and Metabolic Disease#, and by a grant from the New York State Chapter, Arthritis and Rh.6-u- matism Folmdatim. One of the aunhws (0. H.) is Markk Scholar in Medical Science.

411

ARTHRITIS & RHEUMATISM, VOL. 5, No. 4 (AUGUST), 1962

412 SMITH AND HAMERMAN

Table l.-Synovial Fluid Acid Phosphatuse Levels

VOI. Cells PMNL (ml.) (per mm.3) %

Acid Phosphatase (units) Protein Gm. % Syn. Fluid Serum

Normal

Cancer of prostate Rheumatoid

arthritis (rt) (It)

Degen. osteo. Traum. arth. Arth. with psor. Pulm. osteoarth. Tumor Rheum. fever Gout

4 5 2 2% 4 1.5

30' 8'

25 18" 80' 15 20 10' 9*

80 ' 20' 11 4

18 30 30 55 11 8

1,900 600

1,500 90

220 44

11,075 2,300 1,500 1,CEO

36,700 38,300 46,700 18,300 3,200

24,000 20,000 16,600

360 2,300

78,600 1,400

70 600

33,000

8 14 75 2

55 4

46 25 40 55 86 92 70 55 67 55 62 44 30 8

88 30 10 50 86

2.7 1.15 0.30

2.5 0.62 2.4 0.33 2.8 1.20 1.8 0.50

4.10 2.36 3.43 0.62 3.43 0.58 4.80 1.10 4.50 2.30

6.40 3.20 3.60 4.20 2.84 5.70 0.80 3.80 2.05 6.0 3.20

2.85 0.53

3.80 0.63 3.30 4.70 2.60 0.52 2.60 0.30 6.00 0.72 4.40 5.70

0.50 0.55 0.50 6.27

0.47 0.45

0.62 0.52 0.60

0.49

0.60 0.45 0.58 0.41

0.60 0.42 0.43

'These patients had positive serum latex agglutination tests.

serum level (table 1). It is of particular interest that a normal value for AP was found in synovial fluid obtained from the normal knee of a patient with carcinoma of the prostate whose serum AP was markedly increased.

Synovial fluids from patients with rheumatoid arthritis generally showed AP levels much greater than normal. The serum AP of these patients was normal, as would tye expected. Fluids obtained from subjects with joint pathology other than rheumatoid arthritis showed normal values for AP ex- cept for high levels in fluids from a patient with psoriasis and arthritis, and from a patient with gout.

Elevation of synovial fluid AP levels was accompanied by findings in these fluids compatible with synovitis: increased volume of synovial fluid, high white cell count, many polymorphonuclear leukocytes ( PMNL ) and elevated protein concentration.

Pleural fluids containing the same number of PMNL as normal synovial fluids, and normal cerebrospinal fluids, usually showed lower AP levels than normal synovial fluid: 0.15, 0.30, 0.38 units in pleural fluids, and 0.20, 0.20, 0.25 units in cerebrospinal fluids.

DISCUSSION The acid phosphatase (AP) level of normal synovial ffuid is similar to or

slightly higher than that of normal serum. Despite high AP activity in the

ACID PHOSPHATASE IN HUMAN SYNOVIAL FLUID 413

serum from a patient with prostatic carcinoma, a normal AP was found in synovial fluid from the patient’s normal knee. This is additional evidence of the normal synovial membrane’s control of the passage of proteins from the serum into the synovial fluid.g In nine of ten patients with rheumatoid ar- thritis, synovial fluid AP levels were increased while serum levels were normal. Elevated levels of AP in synovial effusions appear to be associated with high white cell counts and increased numbers of PMNL in these fluids. In the synovial effusions from patients with a miscellaneous group of joint disease, high AP levels were found only in those fluids with a high white cell count. Leukocytes can be shown to be a source of AP, for when these cells are ruptured by freeze-thawing, a high content of AP is found in the supw- natant fluid. Moreover, studies by Cohn and HirschlO showed granules (lyso- somes) with AP activity in the cytoplasm of rabbit PMNL. Another enzyme believed to be present in lysosomes, B glucuronidase, was found elevated in the synovial effusions in rheumatoid arthritis and also correlated with the number of PMNL in these fluids.2

Thus the high AP levels in effusions associated with active synovitis can most likely be attributed to increased numbers of PMNL in these ffuids. The large number of lysosomes in synovial membrane lining cells in rheumatoid arthritis may also contribute to the high AP levels in these effusions. One implication of increased activity of hydrolytic (lysosomal) enzymes in syno- vial effusions stems from the ability of some of these enzymes to cause dis- solution of the matrix of cartilageall Presumably, the matrix of articular cartilage could also be digested, particularly since it is thought to receive nutrients from the synovial fluid.12 The further possibility that these hy- drolytic enzymes degrade synovial fluid hyaluronate is under study.

SUMMARY

I) Acid phosphatase (AP) activity is present in normal synovial fluids. 2) A marked increase in AP activity occurs in synovial effusions in rheumatoid arthritis. 3) The high leukocyte count in these effusions is thought to be the major source of increased AP activity. 4) Increased numbers of lysosomes in synovial membrane lining cells in rheumatoid arthritis may also contribute to the elevated AP levels in synovial effusions.

REFERENCES 1. Hamerman, D., Barland, P., Stephens,

M.: Comparative histology and metabolism of synovial tissue in nor- mal and arthritic joints. In Mills, L. C., and Moyer, J. H., eds.: Inflam- mation and Diseases of Connective Tissue. Philadelphia, W. B. Saun- ders, 1961, p. 158.

2. Jacox, R. F., and Feldmahn, A.: Varia- tions of beta glucuronidase concen- tration in abnormal human synovial fluid. J. Clin. Invest. 34:263, 1955.

3. Vartio, T.: Proteolytic enzymes of syn-

ovial fluid. Ann. med. exper. et biol. Fenniae 38:94, 1960.

4. Podkaminsky, N. A,: Ober Fermente in der Synovia und deren Bedeutung. Arch. klin. Chir. 165:383, 1931.

5. Ropes, M., and Bauer, W.: Synovial Fluid Changes in Joint Disease. Har- vard Univ. Press, Cambridge, Mass., 1953, p. 9.

6. Salomone, G., and Quartini, U.: Attivite fostfastasica alcalina nei liquidi artico- lari umani. Boll. Soc. ital. biol. sper. 37:41, 1961.

414 SMITH AND H A M "

7. Ropes, M., Bennett, G. A., Cobb, S., Jacox, R., and Jessar, R.: 1958 Re- vision of diagnostic criteria for rheu- matoid arthritis. Bull. Rheumat. Dis. 9:175, 1958.

8. Andersch, M. A., and Szypinski, A. G.: Use of p-nitrophenyl phosphate as the substrate in determination of serum acid phosphatase. Am. J. Qin. Path. 17:571, 1947.

9. Sandson, J., and Hamerman, D.: Non- dialyzable hexose of human synovial

fluid. J. Clin. Invest. 39:782, 1960. 10. Cohn, Z. A., and Hirsch, J. G.: Isola-

tion and properties of the specific cytoplasmic granules of rabbit poly- morphonuclear leukocytes. J. Exper. Med. 112:983, 1960.

11. Dingle, J. T.: Lysosomal enzymes and the degradation of cartilage matrix. Proc. Roy. Soc. Med. 55:109, 1962.

12. Ekholm, R.: Nutrition of articular cartilage; a radioautographic study. Acta anat. 24:329, 1955.

Carol Smith, B.S., Fourth-year Medical Student, Albert Ein- stein College of Medicine, New York City

David Harnemn, M . D., Associate Professor of Medicine, Albert Einstein College of Medicine, N e w York City.