Date Published: May 31, 2019
Publisher: Public Library of Science
Author(s): Yuri A. Lawrence, Blake C. Guard, Jörg M. Steiner, Jan S. Suchodolski, Jonathan A. Lidbury, Juan J. Loor.
Chronic hepatic disease can present a diagnostic challenge with different etiologies being associated with similar clinical and laboratory findings. The histopathological assessment of a liver biopsy specimen is usually required in order to make a definitive diagnosis and the availability of non-invasive prognostic biomarkers is limited. The emerging science of metabolomics is used to detect changes in endogenous low molecular weight metabolites in biological samples and offers the possibility of identifying noninvasive markers of disease. The objective of this study was to investigate differences in the urine metabolome between healthy dogs, dogs with chronic hepatitis, dogs with hepatocellular carcinoma, and dogs with a congenital portosystemic shunt. Stored urine samples from 10 healthy dogs, 10 dogs with chronic hepatitis, 6 dogs with hepatocellular carcinoma, and 5 dogs with a congenital portosystemic shunt were analyzed. The urine metabolome was analyzed by gas chromatography–quadrupole time of flight mass spectrometry and 220 known metabolites were identified. Principal component analysis and heat dendrogram plots of the metabolomics data showed clustering between groups. Random forest analysis showed differences in the abundance of various metabolites including putrescine, gluconic acid, sorbitol, and valine. Based on univariate statistics, 37 metabolites were significantly different between groups. In, conclusion, the urine metabolome varies between healthy dogs, dogs with chronic hepatitis, dogs with hepatocellular carcinoma, and dogs with a congenital portosystemic shunt. Further targeted assessment of these metabolites is needed to assess their diagnostic utility.
Chronic hepatic disease in dogs includes chronic hepatitis: idiopathic chronic hepatitis, copper-associated chronic hepatitis, drug-associated chronic hepatitis; lobar dissecting chronic hepatitis, and granulomatous chronic hepatitis, breed-associated metabolic errors, congenital portosystemic vascular anomalies, and hepatocellular carcinoma [1,2]. Differentiating these diseases can pose a diagnostic challenge due to the similarities of clinical signs and laboratory findings between different diseases. Although an early accurate diagnosis is important for an improved clinical outcome, achieving a definitive diagnosis can be cost prohibitive and invasive with the histological examination of a liver biopsy specimen regarded as the gold standard. The identification of non-invasive biomarkers that can reliably characterize chronic hepatic disease is desirable and could have clinical implications.
This study identified metabolic abnormalities in the urine of dogs diagnosed with chronic hepatitis, hepatocellular carcinoma, or a congenital portosystemic shunt with significant alterations in 37 of 220 named metabolites based on univariate data analysis. These metabolites are known to be involved in a variety of processes, including glutathione metabolism, nitrogen metabolism, arginine and proline metabolism, and fatty acid biosynthesis. Principle component analysis score plot allowed visualization of the data with dogs with hepatocellular carcinoma showing the clearest separation from healthy control dogs. Dogs with hepatocellular carcinoma were easily distinguished from healthy control dogs in hierarchical cluster analysis with the heatmap approach and overlapped with metabolites extracted in random forest analysis, which is based on a different algorithm. The results provide preliminary evidence for these metabolites to be used as biomarkers in disease classification.