The impact of temperature on vascular function in connection with vascular laser treatment

Abstract

Pulsed dye lasers are used effectively in the treatment of psoriasis with long remission time and limited side effects. It is, however, not completely understood which biological processes underlie its favorable outcome. Pulsed dye laser treatment at 585-595 nm targets hemoglobin in the blood, inducing local hyperthermia in surrounding blood vessels and adjacent tissues. While the impact of destructive temperatures on blood vessels has been well studied, the effects of lower temperatures on the function of several cell types within the blood vessel wall and its periphery are not known. The aim of our study is to assess the functionality of isolated blood vessels after exposure to moderate hyperthermia (45 to 60°C) by evaluating the function of endothelial cells, smooth muscle cells, and vascular nerves. We measured blood vessel functionality of rat mesenteric arteries (n=19) by measuring vascular contraction and relaxation before and after heating vessels in a wire myograph. To this end, we elicited vascular contraction by addition of either high potassium solution or the thromboxane analogue U46619 to stimulate smooth muscle cells, and electrical field stimulation (EFS) to stimulate nerves. For measurement of endothelium-dependent relaxation, we used methacholine. Each vessel was exposed to one temperature in the range of 45-60°C for 30 seconds and a relative change in functional response after hyperthermia was determined by comparison with the response per stimulus before heating. Non-linear regression was used to fit our dataset to obtain the temperature needed to reduce blood vessel function by 50% (Half maximal effective temperature, ET50). Our findings demonstrate a substantial decrease in relative functional response for all three cell types following exposure to 55°C-60°C. There was no significant difference between the ET50 values of the different cell types, which was between 55.9°C and 56.9°C (P>0.05). Our data show that blood vessel functionality decreases significantly when exposed to temperatures between 55°C-60°C for 30 seconds. The results show functionality of endothelial cells, smooth muscle cells, and vascular nerves is similarly impaired. These results help to understand the biological effects of hyperthermia and may aid in tailoring laser and light strategies for selective photothermolysis that contribute to disease modification of psoriasis after pulsed dye laser treatment.

Keywords: Blood vessels; Endothelial cells; Hyperthermia; Smooth muscle cells; Vascular nerves; Wire myography.

Fig. 1

Diagram of the distribution of rats and illustration of the technical procedure for the wire-myograph experiment

Fig. 2

Confocal images (A. and B.) of a rat mesenteric artery with endothelium (lectin, red), nuclei of the smooth muscle cells (dapi, blue), and nerves (PGP-9.5, green). A. shows a mid-section of the artery segment, B. shows the maximum intensity projection of the z-stack. Scale bars indicate 100 μm

Fig. 3

Example of raw wire myography data showing the force in milliNewton (mN) produced by the arteries before and after temperature exposure that lasted 30 seconds. Baseline values upon stimuli were recorded for all vessels after which they were exposed to a designated temperature, after which stimuli were repeated. Active force data was obtained by subtracting the baseline response from the maximum force value (indicated by red lines). The plots indicate that KPSS maintained reproducible contraction at around 15 mN for temperatures up to 50°C. In most cases, contraction by U46619 shows a strong decline at temperatures higher than 46°C. For electrical field stimulation (EFS) incomplete relaxation in-between stimulation was observed at 55°C and the complete absence of EFS-contraction occurred at 60°C

Fig. 4

Impaired functionality of rat mesenteric arteries after hyperthermia. The figure displays the least squares regression fit (line), with each point representing the mean ± SEM of the ratio before and after heating. Control groups were subjected to 37°C conditions. The graphs show a grey-dotted line at 0.5 at which the intersection represents the ET50: The temperature at which vessel function is decreased by 50%. The goodness of fit (R2) and the 95% confidence intervals for the ET50 are indicated for each stimulus. The graphs represent distinct stimuli: KPSS, U46619, methacholine, and electrical field stimulation, each chosen to target specific cell types within the artery