Is mizoribine a new therapeutic agent for Sjögren's syndrome?

The geoepidemiology of Sjögren's syndrome

Sjogren's syndrome (SS) is a slowly progressing autoimmune disease, affecting predominantly middle-aged women, with a female to male ratio reaching 9:1. It is characterized by lymphocytic infiltration of the exocrine glands, mainly the lacrimal and salivary glands, resulting in reduced secretory functions and oral and ocular dryness. The syndrome can present alone as primary SS (pSS) or in the context of underlying connective tissue disease as secondary SS (sSS). While the pathogenesis of the disease remains elusive, environmental, genetic and hormonal contributors seem to be involved. Over the last years, compelling evidence has suggested a pivotal role of the epithelium in orchestrating the immune response in the histopathological lesion of Sjogren's syndrome and the term "autoimmune epithelitis" has been proposed as an etiological term. Although the clinical manifestations of pSS patients are mainly those of an autoimmune exocrinopathy, almost half of patients develop extraglandular disease, which may be manifested either by epithelial lymphocytic invasion of lung, liver, or kidney (resulting in interstitial nephritis) or by skin vasculitis, peripheral neuropathy, glomerulonephritis, and low C4 levels. The latter reflect immune-complex mediated disease and confer increased risk for lymphoma development.

Usefulness of initial histological features for stratifying Sjogren's syndrome responders to mizoribine therapy

OBJECTIVES

To evaluate the response of patients with SS to mizoribine therapy in relation to histological features of minor salivary glands.

METHODS

Forty patients definitely diagnosed as having SS were treated with mizoribine (150 mg/day). Thirty-four untreated patients matched for age, baseline salivary secretion, etc., served as controls. Salivary secretion volume (measured by the Saxon test) and serum IgG level were measured before and after 24 weeks of treatment. Each histological finding (lymphocytic infiltration, acinar atrophy and intralobular fibrosis) was graded at baseline and the therapeutic responses were compared with the grade at 24 weeks in both the groups.

RESULTS

There was a significant increase of the salivary secretion volume after treatment with mizoribine as compared with the untreated control group. The effect of mizoribine on salivary secretion was more marked in patients having moderate lymphocytic infiltration and moderate or less severe acinar atrophy and intralobular fibrosis at baseline.

CONCLUSIONS

Mizoribine was clinically effective in patients with SS whose minor salivary glands had moderate cell infiltration and were free of intralobular fibrosis. The drug was less effective in patients who presented intralobular fibrosis. Histological evaluation of the minor salivary glands may serve to predict the response of SS patients to mizoribine therapy.