Benign prostatic hyperplasia (BPH) and the resulting urethral obstruction and other lower urinary tract symptoms (LUTS) are common disorders of the ageing male. About 60 % of all men in the 40 to 50 decade already have an enlargement of the prostate and the prevalence continues to increase with age. Thus, BPH is becoming more and more clinically relevant. However, current pharmacotherapeutics are resulting in some undesireable side effects and often fail in their efficacy.

The problem in developing new drugs is largely due to the fact that not every single signalling pathway in the prostate is fully understood, including the signalling pathways of the neurohypophyseal hormone oxytocin. The function and mode of action of oxytocin, especially the contractile effects on smooth muscles cells in the male reproductive tract have been in the focus of researchers for over 60 years, but there is still no medication that would interfere with the oxytocin signalling pathways.

Therefore, the aim of our study was to investigate the effect of the new, potent and highly selective oxytocin receptor (OTR) antagonist cligosiban on human prostate tissue. To date, there have been no studies investigating cligosiban on prostatic tissue.

The human prostate samples used for the experiments were collected from informed patients undergoing transurethral resection of the prostate (TURP) with the approval of the local Ethics Committee.

Small strips were carefully prepared from the human prostate samples using fine surgical tools. The maximum size of the strips was 5 x 0.5 x 0.5 mm³ (length x width x thickness).

After embedding our samples in rat collagen (1), live imaging experiments were performed. Dishes with the tissue were positioned under transmitted light and images were taken with a 10-fold magnification at a time interval of 2 s.

Two films were recorded from each human prostate tissue, where we always started by filming a “no treatment period” to record spontaneous prostate contractions. 
The experimental set-up, film duration and the final concentrations of the additions were as follows:
-   First film:        no treatment period (10 min), oxytocin addition (10 min) (0.5 µM), cligosiban addition (10 min) (40 µM), 
                             vitality check with KCl (80 mM).
-   Second film:   no treatment period (10 min), cligosiban addition (10 min) (40 µM), oxytocin addition (10 min) (0.5 µM), 
                             vitality check with KCl (80 mM).

Image processing and montage of the images into a short film were done using Fiji (ImageJ).

For analysis a newly developed version of the Wiggle Index was used (2). The index allowed us to quantify and compare the sum of movements of the whole tissue in different sections of the experiment and showed us how each pixel evolves over time. 
This pixel evolution could be visualised in heat maps. These made it possible to determine exactly which specific areas of the tissue were moving more or less relative to the rest of the tissue and allowed us to display the area of interest in only one image. Besides this, the program measured the fold change relative to baseline (and any other addition) and expressed the data as a population distribution.

Tissue was only included in the analysis if it showed response to the vitality check with KCl and if both filming runs were reactive with tissue from only one patient.

All data were analysed with frequency distribution and non-linear regression using GraphPad.

1. We could visualize spontaneous contractions and the movement changes after the addition of oxytocin and cligosiban in human prostate tissue.

2. For analysis, a newly developed version of the Wiggle Index was used giving information about contraction frequency and amplitude in the entire tissue over time in all pixels (see Study design, materials and methods).

3. Spontaneous contractions were significantly increased by oxytocin (p = 0.0227) (n = 7).

4. The oxytocin-induced contractions were significantly inhibited by addition of the OTR antagonist cligosiban (p < 0.0001) (n = 7).

5. Cligosiban, when given before oxytocin, did not alter spontaneous contractions 
(p = 0.7588) (n = 7), but inhibited the oxytocin effects afterwards (p = 0.9523) (n = 7).

Based on the results, it is evident that oxytocin is able to increase contractions in the human prostate via the OTR.

The OTR antagonist cligosiban is able to inhibit the oxytocin-induced contractions. Besides this, oxytocin is also not able to induce an effect for a long time period after tissue treatment with cligosiban. This is in agreement with the knowledge that cligosiban leads to internalization of the OTR and also has a long half-life (about 12 h) (3). Thus, cligosiban would be well suited as a pharmacotherapeutic for BPH patients due to its long-term effect.

Spontaneous contractions in the prostate may be important for the mixture of the prostatic secretion to avoid possible calcification. Since cligosiban did not affect the spontaneous contractions in the prostate, it can be assumed that the OTR antagonist has no negative influence on the basic movements of the prostate outside ejaculation.

The oxytocin inhibitor cligosiban could be a promising therapeutic option to treat BPH in the future.

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