Gas Bubble Disease model to study the pathophysiology of Decompression Sickness

Abstract

INTRODUCTION: Decompression sickness (DCS) occurs when the partial pressure of dissolved gases in the organism exceeds the ambient pressure, resulting in gas bubbles in circulation and tissues [1]. Gas bubble disease (GBD) is a pathology widely described in fish living in large dams where the supersaturation of the water with dissolved gases is responsible for significant mortalities [2]. Considering the similarities in gas bubble formation [3,4] and applying the replacement principle, GBD in fish could be an alternative model to experimental DCS in mammals. Here, we studied the clinical and pathological findings in fish with GBD and the relationship between some biochemical factors and the abundance of gas bubbles. METHODS: A low-pressure vessel (max. 3 ATA) coupled to a pressurized aquarium (max. 0.5 bar) was designed to produce supersaturated water. Pressurized air was injected and forced into dissolution by constant recirculation through a dissolution tube composed of small-diameter porous materials. Goldfish (Carassius auratus) (n=12) were individually introduced in the pressurized aquarium and exposed to 112±5% supersaturation for 18h. The control group (n=12) was also introduced individually in the pressurized aquarium, but with non-supersaturated water. Clinical signs were constantly monitored. All fish were euthanized after 18h and a pathological study was performed, including a gas score method [5]. Samples of heart, ventral aorta, posterior kidney, and gills of 6 fish from each group were placed in RNA-later for RTqPCR study of HSP70, HSP90, ET-1 and ICAM-1. Correlation studies were carried out with biomarkers and total gas score of each animal. RESULTS: GBD group showed clinical signs consistent with severe GBD such as erratic movements, loss of buoyancy along with severe congestion, hemorrhages, and gas bubbles in the fins. Pathological findings of GBD were a massive presence of macroscopic and microscopic gas bubbles systemically distributed, and associated lesions such as haemorrhages and congestion affecting gills, heart, and posterior kidney, among others, similarly to DCS. High total gas score values were observed, although with some individual variability. HSP70 showed a statistically significant expression increase in the four organs. HSP90 was significantly increased in gills and heart. HSP70 in gills correlated with the total gas score (gas bubble amounts). CONCLUSIONS: The GBD model displayed a severe presence of intravascular and extravascular gas bubbles systemically distributed, similar to DCS. Fish with severe GBD showed an increase in HSPs, mainly HSP70, and a positive correlation of this marker with gas score in gills, showing its strength as a marker of gas embolism, as previously described. Therefore, these results validate the GBD model to study further the pathophysiological pathways activated by gas bubbles, being a useful alternative model to increase the knowledge of DCS.