Qualitative metabolomics profiling of serum and bile from dogs with gallbladder mucocele formation

Abstract

Mucocele formation is characterized by secretion of abnormally thick mucus by the gallbladder epithelium of dogs that may cause obstruction of the bile duct or rupture of the gallbladder. The disease is increasingly recognized and is associated with a high morbidity and mortality. The cause of gallbladder mucocele formation in dogs is unknown. There is a strong breed predisposition and affected dogs have a high incidence of concurrent endocrinopathy or hyperlipidemia. These observations suggest a significant influence of both genetic and metabolic factors on disease pathogenesis. In this study, we investigated a theory that mucocele formation is associated with a syndrome of metabolic disruption. We surmised that a global, untargeted metabolomics approach could provide unique insight into the systemic pathogenesis of gallbladder mucocele formation and identify specific compounds as candidate biomarkers or treatment targets. Moreover, concurrent examination of the serum and hepatic duct bile metabolome would enable the construction of mechanism-based theories or identification of specific compounds responsible for altered function of the gallbladder epithelium. Abnormalities observed in dogs with gallbladder mucocele formation, including a 33-fold decrease in serum adenosine 5’-monophosphate (AMP), lower quantities of precursors required for synthesis of energy transporting nucleotides, and increases in citric acid cycle intermediates, suggest excess metabolic energy and a carbon surplus. Altered quantities of compounds involved in protein translation and RNA turnover, together with accumulation of gamma-glutamylated and N-acetylated amino acids in serum suggest abnormal regulation of protein and amino acid metabolism. Increases in lathosterol and 7α-hydroxycholesterol suggest a primary increase in cholesterol synthesis and diversion to bile acid formation. A number of specific biomarker compounds were identified for their ability to distinguish between control dogs and those that formed a gallbladder mucocele. Particularly noteworthy was a significant decrease in quantity of biologically active compounds that stimulate biliary ductal fluid secretion including adenosine, cAMP, taurolithocholic acid, and taurocholic acid. These findings support the presence of significant metabolic disruption in dogs with mucocele formation. A targeted, quantitative analysis of the identified serum biomarkers is warranted to determine their utility for diagnosis of this disease. Finally, repletion of compounds whose biological activity normally promotes biliary ductal secretion should be examined for any therapeutic impact for resolution or prevention of mucocele formation.

Prevalence and impact of cholecystitis on outcome in dogs with gallbladder mucocele

“…Gallbladder mucocele formation has emerged as a substantial biliary disease in dogs over the last 10 years . The syndrome remains elusive in its etiology, clinical and histopathological progression, medical therapy versus surgery in dogs that are subclinical, and the optimal time for surgery in dogs that are systemically ill. Shetland Sheepdogs, Cocker Spaniels, Miniature Schnauzers, Pomeranians, and Chihuahuas appear to be consistently overrepresented for the development of GBM; however, a genetic link has not yet been established . There is a high incidence of hyperadrenocorticism, hypothyroidism, and hyperlipidemia in dogs with GBM.…”

“…There is a high incidence of hyperadrenocorticism, hypothyroidism, and hyperlipidemia in dogs with GBM. It is not known if these associations are causal or if they merely heighten the risk of an already susceptible dog . It is speculated that these comorbid conditions can cause gallbladder paresis resulting in biliary stasis and cholecystitis .…”

“…Moreover, severe gallbladder distension with inspissated bile may eventually lead to pressure necrosis of the wall and focal accumulation of inflammation. Dogs with GBM have a high incidence of concurrent hyperadrenocorticism, hypothyroidism, and hyperlipidemia . These metabolic disturbances cause immune dysregulation in various species and may contribute to the development of, or magnify, cholecystitis (infectious and sterile) in dogs with GBM .…”

Fearful dogs have increased plasma glutamine and γ-glutamyl glutamine

“…γ-Glu Gln has been characterized in several mammalian tissues 51 as well as in human plasma 52 and CSF 52 , 53 . Aberrations in γ-Glu Gln levels have been observed in the CSF of schizophrenic patients 53 , in the plasma and CSF of hyperammonemic patients 52 , and in the serum of dogs with gallbladder mucocele formation 54 . The increased plasma γ-Glu Gln in fearful dogs may be partially explained by the simultaneous elevation in plasma glutamine abundance.…”

Tryptophan metabolism is differently regulated between large and small dogs

“…Metabolomics has been used extensively in model organisms to understand aging and longevity (e.g., Fuchs et al 2010;Hoffman et al 2014;Houtkooper et al 2011), as well as non-human primates (Hoffman et al 2018b;Hoffman et al 2016) and humans (Darst et al 2019;Menni et al 2013). Previous research has suggested that individual dog breeds show different metabolomic profiles (Lloyd et al 2016;Nicholatos et al 2019;Viant et al 2007) and that metabolomic profiles change in response to diet and obesity (Forster et al 2018;Soder et al 2017), as well as with specific diseases (e.g., Gookin et al 2018;Hasegawa et al 2014;Minamoto et al 2015). Dogs of varying sizes have been shown to have different levels of circulating amino acids (Middleton et al 2017), as well as different metabolomic profiles (Nicholatos et al 2019).…”