Patients suffering from bladder pain syndrome/Interstitial cystitis (BPS/IC) have vascular fragility, reflected by the waterfall bleeding following bladder distention. Vascular endothelial growth factor (VEGF) is a molecule involved in vasculogenesis and angiogenesis. In addition VEGF also participates in the pathophysiology of pain. VEGF was shown to be increased in the lamina propria of BPS/IC bladders. However, urinary VEGF levels has been reported to be similar between BPS/IC and controls.
VEGF can bind to membrane VEGF receptors or to their soluble forms. VEGF membrane receptors include 3 subtypes: VEGFR1, VEGFR2 and VEGFR3. VEGFR1 occurs in sensory neurons and in monocyte/macrophages. VEGFR2 is expressed by endothelial cells. VEGFR1 and VEGFR2 receptors can also be found in urothelial cells.
VEGFR-2 mediates almost all of the known cellular responses to VEGF, like angiogenesis and increases vascular permeability. VEGFR1 promotes inflammation and pain, mainly by modulating VEGFR-2 signalling. Moreover, VEGFR1 soluble form act as a buffer, sequestering VEGF from binding to the membrane receptors. VEGFR-3 is associated with lymphangiogenesis and, since it seems to have no role in pain control, was not a subject of our study.
In the present work, we hypothesised that the sVEGFR1 can be detected in the urine of BPS/IC patients.

The urine of 18 healthy control subjects and of 18 BPS/IC patients from a urine bank was analysed by ELISA to measure the urinary levels of VEGF (Enzo, ENZ-KIT156-001; detection limit 4.712 pg/ml), VEGFR1 (Abcam, ab195210; detection limit - 0.391 ng/ml) and VEGFR2 (Abcam, ab213476; detection limit - 117 pg/ml).
As VEGFR1 and R2 occur in the membrane of urothelial cells, the urine samples were centrifuged and only the supernatant was used. 
Results are presented has mean values ± sd. T test was used for comparisons. Confidence intervals (CI) are presented. Whenever CI includes 0, the null hypothesis is not discarded.

The urinary levels of VEGF in controls and BPS/IC patients were 10.18±0.24 pg/ml and 10.28±0.26 pg/ml, respectively (p=0.241). The 95% CI ranges [-0.07013,0.2707].
The urinary levels of sVEGFR1 in centrifuged urine were 9.64±7.36 ng/ml while in patients were 3.96±3.88 ng/ml of sVEGFR1 (p=0.0044). The 95% CI ranges [-6.916,-1.387] discards the null hypothesis. 
A post hoc analysis showed that 67% of BPS/IC patients had less than 6 ng/ml of VEGFR1. These patients were older than the remaining (49±9 vs 39±5 years). 
VEGFR2 was not detected in the urine of controls and patients.

The presence of VEGFR1 in centrifuged samples indicates that the receptor detected belongs to the soluble form. 
Our exploratory study showed a marked decrease in the urinary levels of sVEGFR 1. This results may reflect a reduction on VEGF sequestration by the VEGFR1 soluble form, which may leave VEGF free to activate the membrane attached receptors, leading to angiogenesis, pain, inflammation and urothelial changes.
 This decrease seems to be age-dependent. The levels of urinary VEGF do not seem to reflect the tissue VEGF changes previously reported.

Urinary sVEGFR1 may be a potential BPS/IC biomarker for patient phenotyping and a potential target for future treatments.