Neurologic and Inflammatory Manifestations in Sjögren’s Syndrome: The Role of Tryptophan/kynurenine Pathway

Abstract

For decades, neurologic and other extra glandular manifestations have been described in Sjögren’s syndrome (SS). More recently, neuropathic, psychological and cognitive alterations are being considered part of the disease. The lacrimal glands (LG), the ocular surface (OS), salivary glands (SG) and the central nervous system (CNS) are integrated to modulate the autonomic functions and, not just those organs, but also the hippocampus, which is linked to the autonomic nervous system, and modulate behavior responses appears to be compromised in the SS. Recent studies confirm that the tryptophan/kynurenine pathway (TKP) can be stimulated by interferon-γ (IFN-γ) and other cytokines, activating the indoleamine-pyrrole 2,3-dioxygenase (IDO) in SS. This pathway interferes on serotonergic and glutamatergic neurotransmission, mostly in the hippocampus, and other structures of the CNS. Although not demonstrated, it is plausible that this constant interference induces clinical signs of SS, and contributes to the discrepancy between symptoms and signs, towards manifestations of hyperalgesia and depression in patients with SS. Therapeutic strategies are being reexamined and new options designed and tested to regulate the involved steps of the TKP. In the future, the application of this concept may offer a clue to the mosaic of manifestations of SS.