Cytidine deaminase activity as a measure of acute inflammation in rheumatoid arthritis

Proof-of-principle studies on a strategy to enhance nucleotide imbalance specifically in cancer cells

Highly specific and potent inhibitors of dihydroorotate dehydrogenase (DHODH), an essential enzyme of the de novo pyrimidine ribonucleotide synthesis pathway, are in clinical trials for autoimmune diseases, viral infections and cancer. However, because DHODH inhibitors (DHODHi) are immunosuppressants they may reduce the anticancer activity of the immune system. Therefore, there may be a need to improve the therapeutic index of DHODHi in cancer patients. The aim of this study was to find strategies to protect activated T cells from DHODHi and to identify cancer types hypersensitive to these inhibitors. First, we observed that like uridine supplementation, adding cytidine to the culture medium protects T cells from DHODH blockage. Next, we identified tumor types with altered expression of pyrimidine ribonucleotide synthesis enzymes. In this regard, we detected that the expression of cytidine deaminase (CDA), which converts cytidine into uridine, is low in an important proportion of cancer cell lines and consistently low in neuroblastoma samples and in cell lines from neuroblastoma and small cell lung carcinoma. This suggested that in the presence of a DHODHi, an excess of cytidine would be deleterious for low CDA expressing cancer cell lines. We show that this was the case (as could be seen almost immediately after treatment) when cells were cultured with fetal bovine serum but, was significantly less evident when cultures contained human serum. One interesting feature of CDA is that aside from acting intracellularly, it is also present in human plasma/serum. Altogether, experiments using recombinant CDA, human serum, pharmacologic inhibition of CDA and T cell/cancer cell co-cultures suggest that the therapeutic index of DHODHi could be improved by selecting patients with low-CDA expressing cancers in combination with strategies to increase cytidine or the cytidine/uridine ratio in the extracellular environment. Collectively, this proof-of-principle study warrants the discovery of agents to deplete extracellular CDA.

Lethal toxicities after capecitabine intake in a previously 5-FU-treated patient: why dose matters with dihydropryimidine dehydrogenase deficiency

Dihydropryimidine dehydrogenase (DPD) deficiency is a pharmacogenetic syndrome associated with severe or lethal toxicities with oral capecitabine. Usually, patients with history of 5-FU-based therapy with no signs for life-threatening toxicities are considered as not DPD-deficient individuals who can be safely treated next with capecitabine if required. Here we describe the case of a woman originally treated with standard FEC100 protocol for metastatic breast cancer with little severe toxicities but grade-3 mucosities that were quickly resolved by symptomatic treatment. When switched to capecitabine + vinorelbine combo, extremely severe toxicities with fatal outcome were unexpectedly observed. Pharmacogenetic investigations were performed on cytidine deaminase and DPYD, and showed that this patient was heterozygous for the 2846A>T mutation on the DPYD gene. DPD phenotyping (i.e., uracil plasma levels >250 ng/ml, dihydrouracil/uracil ratio <0.5) confirmed that this patient was profoundly DPD deficient. Differences in fluoropyrimidine dosing between FEC100 (i.e., 500 mg/m² 5-FU) and capecitabine (i.e., 2250 mg daily) could explain why initial 5-FU-based protocol did not lead to life-threatening toxicities, whereas capecitabine rapidly triggered toxic death. Overall, this case report suggests that any toxicity, even when not life threatening, should be considered as a warning signal for possible underlying profound DPD deficiency syndrome, especially with low-dose protocols.

The Emerging Role of Cytidine Deaminase in Human Diseases: A New Opportunity for Therapy?

The recycling activity of cytidine deaminase (CDA) within the pyrimidine salvage pathway is essential to DNA and RNA synthesis. As such, CDA deficiency can lead to replicative stress, notably in Bloom syndrome. Alternatively, CDA also can deaminate cytidine and deoxycytidine analog-based therapies, such as gemcitabine. Thus, CDA overexpression is often associated with lower systemic, chemotherapy-related, adverse effects but also with resistance to treatment. Considering the increasing interest of CDA in cancer chemoresistance, the aims of this review are to describe CDA structure, regulation of expression, and activity, and to report the therapeutic strategies based on CDA expression that recently emerged for tumor treatment.

Determinants of the interindividual variability in serum cytidine deaminase activity of patients with solid tumours

AIMS

Cytidine deaminase (CDA) activity in cancer patients' serum has been proposed as a predictive biomarker for efficacy and toxicity of nucleoside analogues. However, discrepant results about its predictive value have been reported due to the high interindividual variability in CDA activity. This study aimed at identifying determinants of this interindividual variability.

METHODS

From December 2014 to November 2015, 183 patients were prospectively included. Serum CDA activity, biological and clinical characteristics as well as five common single nucleotide polymorphisms (SNPs) in the CDA gene (c.-451C > T, c.-92A > G, c.-33_-31delC, c.79A > C, c.435 T > C) were analysed. Associations between clinical characteristics, pharmacogenetic variants and CDA activity were univariately tested. P < 0.1-candidate variables were analysed through a multivariate analysis. The association between CDA activity and toxicity was assessed for the 56 gemcitabine-treated patients. Intraindividual variability in CDA activity was explored in six pancreatic cancer patients treated with gemcitabine.

RESULTS

Median CDA activity was 3.97 U mg^-1 (range 1.53-15.49 U mg^-1 ). A univariate analysis showed that CDA activity was statistically associated with Eastern Cooperative Oncology Group performance status, mild or severe malnutrition, inflammatory syndrome, leucocyte count, neutrophil count, albumin, C-reactive protein and -c.-33_-31delC single nucleotide polymorphism. A multivariate analysis identified that only neutrophil count (P < 0.0001) and severe malnutrition (P = 0.0278) were independently associated with CDA activity. Low CDA activity (<2 U mg^-1 ) was not statistically associated with severe gemcitabine-related toxicities (P = 0.16). A decrease in CDA activity was observed during the longitudinal follow-up of six pancreatic cancer patients treated with gemcitabine (P = 0.03).

CONCLUSIONS

These results suggest that neutrophil count and malnutrition should be considered for the interpretation of pretherapeutic CDA activity.

Cytidine deaminase enzymatic activity is a prognostic biomarker in gemcitabine/platinum-treated advanced non-small-cell lung cancer: a prospective validation study

Background

Cytidine deaminase (CDA) plays a crucial role in the degradation of gemcitabine. In our previous retrospective study, CDA enzymatic activity was the strongest prognostic biomarker of the activity and efficacy of platinum/gemcitabine combinations. The aim of this prospective study was to validate the prognostic role of CDA activity in the first-line treatment of advanced non-small-cell lung cancer.

Methods

A total of 124 untreated patients received standard doses of platinum/gemcitabine. CDA activity was baseline measured in plasma samples by spectrophotometric assay.

Results

Using the median CDA level as cut-off, in the patients with high versus low CDA activity the response rate was 25.0% (95% CI, 14.7–37.8) and 54.1% (95% CI, 40.8–66.9), P = 0.0013; the 6-month progression rate was 34.5% (95% CI, 22.6–46.6) and 54.1% (95% CI, 40.9–65.6), HR = 2.01 (95% CI, 1.32–3.06), P < 0.001; the 1-year survival rate was 23.3% (95% CI, 13.6–34.6) and 57.3% (95% CI, 43.9–68.6), HR = 2.20 (95% CI, 1.46–3.34), P = 0.0002, respectively. CDA activity resulted to be an independent prognostic factor for progression and survival at multivariate analysis.

Conclusions

This study validated prospectively the prognostic role of the CDA activity and should prompt larger and adequately designed randomised prospective studies to establish the predictive impact of this test in improving the outcome of selected patients.

An enzymatic assay for high-throughput screening of cytidine-producing microbial strains

Cytidine is an industrially useful precursor for the production of antiviral compounds and a variety of industrial compounds. Interest in the microbial production of cytidine has grown recently and high-throughput screening of cytidine over-producers is an important approach in large-scale industrial production using microorganisms. An enzymatic assay for cytidine was developed combining cytidine deaminase (CDA) and indophenol method. CDA catalyzes the cleavage of cytidine to uridine and NH3, the latter of which can be accurately determined using the indophenol method. The assay was performed in 96-well plates and had a linear detection range of cytidine of 0.058-10 mM. This assay was used to determine the amount of cytidine in fermentation flasks and the results were compared with that of High Perfomance Liquid Chromatography (HPLC) method. The detection range of the CDA method is not as wide as that of the HPLC, furthermore the correlation factor of CDA method is not as high as that of HPLC. However, it was suitable for the detection of large numbers of crude samples and was applied to high-throughput screening for high cytidine-producing strains using 96-well deep-hole culture plates. This assay was proved to be simple, accurate, specific and suitable for cytidine detection and high-throughput screening of cytidine-producing strains in large numbers of samples (96 well or more).

Cytidine deaminase in polymyalgia rheumatica and elderly onset rheumatoid arthritis

Serum cytidine deaminase (CD) as a marker of inflammatory disease was assessed in 44 patients and 47 controls to differentiate polymyalgia rheumatica (PMR) from elderly onset rheumatoid arthritis (EORA). The patients were divided into four groups: PMR with and without synovitis and seropositive and seronegative EORA. No statistically significant differences were found when serum CD levels of seropositive EORA patients were compared with serum CD of PMR patients without synovitis, neither when serum CD levels of all PMR patients were compared with a seronegative EORA group, nor when serum CD levels of PMR patients with synovitis were compared with those with EORA. Nevertheless, statistically significant differences were detected between EORA's serum CD levels and the control group (p=0.023). This difference was 10% when comparing CD levels of PMR patients with the control group (p=0.070). We did not demonstrate that serum CD levels could be a useful tool to differentiate PMR from EORA, but these findings could nevertheless reflect the presence of an inflammatory disease.

Serum adenosine deaminase and cytidine deaminase activities in patients with systemic lupus erythematosus

We evaluated serum total adenosine deaminase, its isoenzymes adenosine deaminase-1 and adenosine deaminase-2, and cytidine deaminase activities in 24 patients with active systemic lupus erythematosus, and in 26 healthy control subjects, and found the means +/- SD values to be 21.38 +/- 5.96 IU/l, 3.74 +/- 2.12 IU/l, 17.72 +/- 5.02 IU/l and 17.89 +/- 4.62 IU/l, respectively in the patients, and 14.97+/- 4.71 IU/l, 4.01 +/- 1.35 IU/l, 10.91 +/- 3.91 IU/l and 7.39 +/- 3.97 IU/l, respectively in the control subjects. When compared to the healthy controls, serum total adenosine deaminase, adenosine deaminase-2 and cytidine deaminase levels were significantly higher (p<0.001) in systemic lupus erythematosus patients, but the decrease of adenosine deaminase-1 level was not statistically significant (p>0.05). The increased adenosine deaminase-2 may be of macrophage origin. It closely correlated with clinical signs of active systemic lupus erythematosus. The membranes of polymorphonuclear neutrophils may be damaged, and cytidine deaminase may be released into serum. In conclusion, serum total adenosine deaminase, adenosine deaminase-2 and cytidine deaminase activities may serve as useful indicators for evaluating disease activity in patients with active systemic lupus erythematosus.

Changes in biochemical markers of joint tissue metabolism in a randomized controlled trial of glucocorticoid in early rheumatoid arthritis

OBJECTIVE

To determine the effects of low-dose prednisolone on joint tissue metabolism in early rheumatoid arthritis (RA).

METHODS

In addition to a range of biochemical markers of cartilage, bone and synovial tissue turnover, levels of pro-matrix metalloproteinase 3 (pro-MMP-3), pro-MMP-1, and cytidine deaminase (CD) were measured in serum from 79 of 128 patients with early RA who took part in the Arthritis and Rheumatism Council Low-Dose Glucocorticoid Study. Serum concentrations of joint tissue metabolites on treatment and off treatment were compared using Student's t-test.

RESULTS

Levels of the keratan sulfate epitope, 5D4, and glycosaminoglycan (GAG) were similar on and off treatment. However, the levels of synovium-derived markers, hyaluronate (HA) and N-propeptide of type III procollagen (PIIINP), were reduced by 23.9% (P < 0.01) and 25.2% (P < 0.001), respectively, during treatment with prednisolone. Serum osteocalcin (OC) was reduced by 25.8% (P < 0.001), while the levels of CD and pro-MMP-3 increased by 31.2% (P < 0.01) and 53.7% (P < 0.001) during prednisolone treatment compared with the off-treatment period.

CONCLUSION

Low-dose prednisolone had no significant effect on markers of cartilage turnover (GAG, 5D4) in early RA, suggesting that early erosions do not involve cartilage surfaces. The reduction in the markers of bone turnover (OC) and synovial tissue turnover (HA and PIIINP) support the general view that prednisolone reduces synovitis and suppresses bone turnover.

Re-evaluation of the colorimetric assay for cytidine deaminase activity

This study re-evaluated the colorimetric assay for cytidine deaminase (CTD), and showed that the optimum conditions were pH 7.5, 37 degrees C, and up to 24 h. In addition, this method was found to require protein precipitation. Following these modifications, intra-assay and inter-assay coefficients of variation were below 5 per cent, indicating that the assay was highly reliable. CTD activity was determined in 282 serum samples from 206 normal pregnant women by the incubation of 100 microliters of serum and 400 microliters of 1.4 mmol/l cytidine substrate for 16 h at 37 degrees C. Following protein precipitation, the ammonia liberated during conversion was measured by a colorimetric procedure. The mean (+/- SD) CTD activity was 7.31 +/- 2.50 U at 3-12 weeks of gestation, 8.70 +/- 2.12 U at 13-24 weeks, 7.59 +/- 2.25 U at 25-36 weeks, and 7.29 +/- 2.16 U at 37-42 weeks. High levels of CTD activity were found in patients with abruptio placentae and amnionitis associated with intrauterine fetal death (IUFD). The increase in CTD activity was noted from 3 days to 1 week before the confirmation of IUFD. The placenta contains extremely high levels of CTD, but cord serum does not. Thus, the excessive elevation of CTD activity was probably derived from progressive placental damage. This modified CTD assay was concluded to be simple and reliable, and may perhaps be useful in detecting pregnancy disorders.

Cytidine deaminase activity in abnormal pregnancy

OBJECTIVE

To determine the usefulness of cytidine deaminase (CTD) activity in the prediction of abnormal pregnancy and the prognosis of fetal outcome.

METHOD

The CTD activities in 367 pregnant women and 17 placentas and their cord sera were determined. The CTD activity was estimated to determine the amount of ammonia liberated during conversion of cytidine into uridine. The Kruskal-Wallis test and paired t-test were employed for statistical comparisons.

RESULT

The placentas contained extremely high levels of CTD activity, but the cord serum did not. The mean value of CTD activity in abnormal pregnancy women was significantly higher than in normal pregnancy women. The two cases with a CTD activity of 40 U or more had the worst infant prognosis.

CONCLUSION

The CTD activity in abnormal pregnancies was excessively elevated due to a damaged placenta under progressive deterioration. This CTD assay was simple and had predictive value for the prognosis of an infant of an abnormal pregnancy.

Morphological evidence that activated polymorphs circulate in the peripheral blood of patients with rheumatoid arthritis

Purified peripheral blood polymorphonuclear leucocytes (PMNs) from patients with rheumatoid arthritis (RA) have been found to differ from purified PMNs from normal subjects in ways that are consistent with their prior activation. However, it is currently contentious whether activated PMNs really circulate in patients with RA, or whether they are produced as an in vitro artefact of purification. Recently developed rapid leucocyte fixation and preparation technique showed that the proportion of polarised (activated) PMNs (36.9 (24.7)%, mean (SD); n = 31) was increased relative to that in control subjects (8.1 (5.6)%; n = 12). Serum cytidine deaminase levels, a biochemical marker of PMN lysis, were also increased in patients with RA (11.59 (7.26) U/ml) compared with those in controls (6.82 (3.78) U/ml), but the proportion of polarised PMNs and the levels of cytidine deaminase activity were unrelated to clinical assessments of inflammatory disease activity. Twelve patients who were not receiving drugs or who were receiving only non-steroidal anti-inflammatory drugs (NSAIDs) had more polarised PMNs than 19 patients receiving second line treatment in addition to NSAIDs (patients receiving NSAIDs, 49.6 (25.9)%; patients receiving second line treatment, 27.5 (21.1)%). Fluorescence activated cytometric analysis of CR1 and CR3 expression on PMNs from a randomly selected subgroup of patients with RA showed that the serum level of cytidine deaminase activity was correlated positively with the expression of CR1 (the C3b receptor) on the cell surface and that the proportion of polarised PMNs was positively correlated with the expression of CR3 (or CD11b/CD18), the iC3b receptor that is upregulated on activation. It is suggested that the polarised PMNs which circulate in blood samples from patients with RA represent cells which have been activated but not yet marginated, or activated cells which have marginated but subsequently returned to the circulating pool.

The measurement of nucleoside deaminases by high performance liquid chromatography and their use in clinical chemistry

The measurement of the nucleoside deaminases--cytidine deaminase, guanosine deaminase and adenosine deaminase--by reversed phase high performance liquid chromatography is reviewed. The clinical value of assaying the enzyme activity is discussed for each of these enzymes. Both cytidine deaminase and adenosine deaminase measurements have proven clinical value, although the use of the assay of cytidine deaminase in the diagnosis of pre-eclampsia is probably not helpful.

Cytidine deaminase activity, C reactive protein, histidine, and erythrocyte sedimentation rate as measures of disease activity in psoriatic arthritis

Cytidine deaminase activity, C reactive protein, histidine, and erythrocyte sedimentation rate were measured in 36 subjects with psoriatic arthritis of varying disease duration and severity. Although cytidine deaminase activity may provide an integrated measure of synovial inflammation in rheumatoid arthritis, neutrophil accumulation in psoriatic plaques compromises this measure in psoriatic arthritis. Low histidine concentrations confirm that this amino acid provides a non-specific index of synovial inflammation. In psoriatic arthritis high C reactive protein concentrations seem to be associated with extensive joint destruction. In this study the erythrocyte sedimentation rate was found to be the best laboratory guide to clinical disease activity in psoriatic arthritis.

Evaluation of a simple method for the measurement of cytidine deaminase in serum and comparison with a reference method

This study was designed to evaluate a cytidine deaminase (CD) assay modified to allow results to be achieved within one working day. Inter-batch variation for samples of mean (SD) CD activity, 10.2 (1.0) units, 17.5 (1.2) units and 31.7 (1.7) units were, 9.8%, 6.9% and 5.4% respectively (n = 26). The reference range (3.2-13.2 U) was similar in males and females and was independent of age. There was close correlation with a reference method (r = 0.96). The mean difference between methods was 2.7 U and the limits of agreement were -1.7 to 7.1 U. The results indicate that the short assay technique can produce results that are sufficiently accurate and precise to be clinically useful.

Cytidine deaminase activity in synovial fluid of patients with rheumatoid arthritis: relation to lactoferrin, acidosis, and cartilage proteoglycan release

It is claimed that cytidine deaminase activity reflects local granulocyte turnover or activity in the synovial fluid of patients with rheumatoid arthritis, but cytidine deaminase is not a granulocyte specific enzyme. Lactoferrin is a granulocyte specific protein that is released from the secondary granulae during activation. We measured cytidine deaminase activity and lactoferrin concentrations in 33 rheumatic synovial fluid samples. Cytidine deaminase activity and lactoferrin concentrations correlated closely, indicating that both analyses reflect similar events in the joint-that is, result in their release from granulocytes. Cytidine deaminase activity and granulocyte concentrations correlated less closely, suggesting that there are additional factors besides the cell number which contribute to this release. Joint acidosis may be one such factor, as pH and cytidine deaminase activity correlated inversely. There was no association with synovial fluid proteoglycan concentrations, a marker of cartilage degradation.

Determination of serum cytidine deaminase activity using ion-pair reversed-phase liquid chromatography

A rapid and sensitive assay for serum cytidine deaminase has been developed utilising ion-pair reversed-phase high-performance liquid chromatography. The addition of 1-octanesulphonic acid (OSA) caused the retention of cytidine and uridine to reverse and uridine, the minor component in the assay, to elute first. Cytidine, uridine and allopurinol (internal standard) were separated on a 5-micron Hypersil ODS column using 100 mM ammonium acetate with 1% (v/v) methanol and 1 mM OSA adjusted to pH 5.0. Detection was at 262 nm. Peak areas were linear from 7 pmol to 6 nmol injected (r = 0.99). Intra-assay variation was 7.8% (n = 10) and the correlation with a colorimetric assay was r = 0.78 (p less than 0.001).

Circadian rhythm of serum cytidine deaminase in patients with rheumatoid arthritis during rest and exercise

Circadian rhythm of serum cytidine deaminase and C reactive protein was assessed in 11 inpatients with rheumatoid arthritis who were crossed between 24 hours of bed rest and 24 hours of normal ward activity. Blood was taken at six hourly intervals and the results analysed by fitting sine waves with an assumed period of 24 hours to the measured concentrations. Cytidine deaminase after activity, but not at rest, showed circadian variation, with a 24 hour mean level of 17.4 units (normal 3-13 units) and an amplitude of 1.1 units. The circadian variation, defined as the curve's peak to trough difference as a percentage of the 24 hour mean, was 12.3% and occurred at 1208 hours. C reactive protein showed no significant circadian rhythm, in keeping with published findings. The timing of the peak in serum cytidine deaminase concentrations after a period of morning physiotherapy, but not during the bedrest morning, suggests that exercise accounts for the circadian rhythm, probably by increasing the lymphatic clearance from inflamed joints.

Determination of cytidine deaminase activity in synovial fluid by HPLC

A reversed-phase high-performance liquid chromatographic method for the determination of cytidine deaminase activity in synovial fluid is described. Diluted synovial fluid was incubated for 10 min at 56 degrees C with 0.4 mM cytidine. The protein in 5 vol of incubate was then precipitated using 1 vol of trichloroacetic acid (20% m/v) and the substrate, cytidine, and the product, uridine, were determined in the resultant supernatant. These substances were separated by reversed-phase HPLC using 0.05 M potassium dihydrogen orthophosphate (pH 6.5) containing methanol (3% v/v) and were detected at 280 nm. The enzyme activity was determined by measuring uridine formation. The effects of substrate concentration, pH and reaction temperature on uridine formation are described.

A double blind multicentre study of OM-8980 and auranofin in rheumatoid arthritis

The therapeutic efficacy of the immunomodulator OM-8980 in rheumatoid arthritis was compared with that of auranofin, an oral gold salt, in a double blind, randomised multicentre study lasting six months. Seventy patients were treated with auranofin and 75 with OM-8980. The patients of both groups improved significantly at three and six months for all the clinical parameters observed: Ritchie index, number of swollen joints, morning stiffness, pain, grip strength, intake of non-steroidal anti-inflammatory drugs, and erythrocyte sedimentation rate. No serious side effects were observed in either group. The patients receiving auranofin had more adverse reactions, mainly affecting the gastrointestinal system.

Serum cytidine deaminase levels after withdrawal of non-steroidal anti-inflammatory treatment in rheumatoid arthritis

Increases in joint inflammation in nine patients with rheumatoid arthritis were provoked by withdrawal of their non-steroidal anti-inflammatory drugs. Pain score, duration of morning stiffness, Ritchie articular index score, and the number of analgesic tablets consumed reached peaks after five, three, five, and five days respectively compared with values during six days of normal treatment. Changes in serum cytidine deaminase (believed to reflect polymorph turnover in inflamed joints) showed a different pattern, with a sharp peak after two days and a subsequent trough. Possible mechanisms for these differences are discussed.

Circulating inhibitor bound elastase in patients with ankylosing spondylitis and rheumatoid arthritis and the influence of sulphasalazine treatment

The plasma concentration of granulocyte elastase in complex with alpha 1 proteinase inhibitor was determined in 42 patients with ankylosing spondylitis (AS) and 33 patients with rheumatoid arthritis (RA). Significantly raised levels of plasma elastase were found in patients with RA, whereas patients with AS had normal values. No correlation was seen between the elastase values and erythrocyte sedimentation rate (ESR), serum haptoglobin, immunoglobulins, or polymorphonuclear cell (PMN) count in either of the patient groups. A correlation was found between the Ritchie index and plasma elastase in patients with RA. After three months' treatment with sulphasalazine a clinical improvement was seen and this paralleled a reduction of the acute phase reaction in both patient groups. A reduction of the circulating elastase values was seen in the patients with RA, whereas no change was seen in patients with AS.

Adenosine deaminase activity in joint effusions

The activity of adenosine deaminase (ADA) was determined in serum and synovial fluid of 98 patients with joint effusions of various causes. Compared with osteoarthritis, there were significantly higher mean synovial fluid ADA activities in seropositive rheumatoid arthritis (p less than 0.01), chronic seronegative polyarthritis (p less than 0.001), juvenile chronic arthritis (p less than 0.001) and reactive arthritis (p less than 0.001). In inflammatory joint diseases higher mean ADA activities in synovial fluid than in serum were observed, indicating a local release of ADA by cells within the joints. ADA activity in synovial fluid correlated with general disease activity as measured by haemoglobin concentration and erythrocyte sedimentation rate, and may provide an additional measure of the degree of inflammation in joint diseases.

ELISA assays for IgM and IgG rheumatoid factors: their clinical correlations during therapy with slow-acting anti-rheumatic drugs

A longitudinal study of changes in rheumatoid factor levels and their correlations with other clinical and laboratory assessment of disease activity followed 45 rheumatoid arthritis patients during 12 months continuous therapy with gold and penicillamine. Rheumatoid factors were measured by the titred latex assay and by ELISA assays for IgM and IgG rheumatoid factor. The IgM ELISA assay correlated strongly with the titred latex assay and weakly with the IgG rheumatoid factor assay at 0, 6 and 12 months. All showed significant falls with treatment, and ELISA assays were not more sensitive indicators than the latex assay. Correlations of initial rheumatoid factor levels by all 3 assays to 34 other clinical and laboratory assessments showed that only a small number of weak correlations existed; there were more at 6 and 12 months, but still not many. Changes in rheumatoid factor levels over 0-6 months showed no significant correlation to changes in other variables. There were no more correlations with ELISA assays than with titred latex rheumatoid factor. We conclude that ELISA rheumatoid factor assays have no clinically relevant advantage over the titred latex assay when following rheumatoid patients treated with gold or penicillamine.

Determination of plasma cytidine deaminase activity by HPLC

Cytidine deaminase is an enzyme of nucleic acid metabolism, the measurement of which has been proposed as a useful test for the early detection of pre-eclamptic toxaemia in pregnancy. The enzyme converts the nucleoside cytidine to uridine, with the release of ammonia, and it is the measurement of this latter compound that forms the basis of the conventional methods for the assay of cytidine deaminase. The low activity of the enzyme requires long incubation times, which in turn increase the possibility of contamination by exogenous ammonia. We have developed a new method for determining cytidine deaminase activity, utilising high performance liquid chromatography to measure the production of uridine. This method uses much shorter incubation times and is unaffected by ammonia contamination. This paper describes the development of the method and its comparison with the established assay. The relative merits of each are discussed. Finally, the adaptation of incubation and chromatographic conditions, in order to measure other enzymes of nucleic acid metabolism which are of clinical interest, is briefly mentioned.