Increased circulating levels of tissue kallikrein in systemic sclerosis correlate with microvascular involvement

Abstract

Background: In systemic sclerosis (SSc) the lack of an angiogenic response to hypoxia may be due to inappropriate synthesis of angiogenic and angiostatic factors. Tissue kallikrein (t-kallikrein), regulating the kallikrein-kinin system and acting on the microcirculation, is a potent angiogenic agent, and kallistatin is its natural inhibitor.

Objective: To evaluate, in patients with SSc, t-kallikrein and kallistatin levels and their correlation with clinical features and measures of microvascular involvement.

Patients and methods: Serum levels of t-kallikrein and kallistatin (ELISA) and t-kallikrein skin expression (immunohistochemistry) were studied in patients with SSc, and evaluated for subset (dSSc or lSSc), clinical and immunological features, and microvascular involvement (ulcers, telangiectasias, nailfold videocapillaroscopy).

Results: Circulating levels of t-kallikrein were higher in SSc than in controls (p<0.001). T-kallikrein did not differ between lSSc and dSSc, although it was higher in lSSc than in controls (p<0.001).T-kallikrein levels were higher in patients with early and active capillaroscopic pattern than in those with late pattern (p = 0.019 and 0.023). Patients with giant capillaries and capillary microhaemorrhages had higher t-kallikrein concentrations than patients with architectural derangement (p = 0.04). No differences in kallistatin levels were detected between patients with SSc and controls, or between lSSc and dSSc. In early SSc skin, the presence of t-kallikrein was found in endothelial and in perivascular inflammatory cells, while no staining in skin of advanced SSc was detected.

Conclusion: T-kallikrein levels are increased in patients with SSc, particularly in lSSc, and are associated with early and active capillaroscopic patterns. T-kallikrein may play a part in SSc microvascular changes.

Figure 1

The kallikrein-kinin system (KKS) and its putative actions in SSc. T-kallikrein cleaves kinins (bradykinin and lysil-bradykinin) from low molecular weight kininogen (LMWK) and high molecular weight kininogen (HMWK). Kinins released from the vascular endothelium interact with B₁ receptors (constitutively expressed) and B₂ receptors (induced by tissue damage and inflammation) of endothelial and vascular smooth muscle cells. Kinins are rapidly inactivated mainly by angiotensin converting enzyme (ACE, kininase II). EC, endothelial cells.

Figure 2

T-kallikrein levels in SSc, lSSc, dSSc, and controls. *Significantly higher versus controls.

Figure 3

(A) T-kallikrein levels in SSc according to capillaroscopic pattern (early versus active versus late); *significantly higher in early and active versus controls. (B) T-kallikrein levels according to single capillaroscopic changes (patients with giants capillaries and microhaemorrhages versus patients with architectural derangement of capillaries); *significantly higher in the group with haemorrhages and giant capillaries than in the group with architectural derangement.

Figure 4

Skin sections. Immunostaining for t-kallikrein with diaminobenzidine revelation and Mayer's haematoxylin counterstaining. (A) Control: vessels with positive endothelial cells (arrows); (B) early SSc: small vessels show t-kallikrein staining in endothelial cells and in perivascular inflammatory infiltrate (arrow); (C) advanced SSc: no immunostaining for t-kallikrein is detected in the vessel wall.