Research Article: Levels of 8-OxodG Predict Hepatobiliary Pathology in Opisthorchis viverrini Endemic Settings in Thailand

Date Published: July 31, 2015

Publisher: Public Library of Science

Author(s): Prasert Saichua, Anna Yakovleva, Christine Kamamia, Amar R. Jariwala, Jiraporn Sithithaworn, Banchob Sripa, Paul J. Brindley, Thewarach Laha, Eimorn Mairiang, Chawalit Pairojkul, Narong Khuntikeo, Jason Mulvenna, Paiboon Sithithaworn, Jeffrey M. Bethony, John Pius Dalton.

Abstract: Opisthorchis viverrini is distinct among helminth infections as it drives a chronic inflammatory response in the intrahepatic bile duct that progresses from advanced periductal fibrosis (APF) to cholangiocarcinoma (CCA). Extensive research shows that oxidative stress (OS) plays a critical role in the transition from chronic O. viverrini infection to CCA. OS also results in the excision of a modified DNA lesion (8-oxodG) into urine, the levels of which can be detected by immunoassay. Herein, we measured concentrations of urine 8-oxodG by immunoassay from the following four groups in the Khon Kaen Cancer Cohort study: (1) O. viverrini negative individuals, (2) O. viverrini positive individuals with no APF as determined by abdominal ultrasound, (3) O. viverrini positive individuals with APF as determined by abdominal ultrasound, and (4) O. viverrini induced cases of CCA. A logistic regression model was used to evaluate the utility of creatinine-adjusted urinary 8-oxodG among these groups, along with demographic, behavioral, and immunological risk factors. Receiver operating characteristic (ROC) curve analysis was used to evaluate the predictive accuracy of urinary 8-oxodG for APF and CCA. Elevated concentrations of 8-oxodG in urine positively associated with APF and CCA in a strongly dose-dependent manner. Urinary 8-oxodG concentrations also accurately predicted whether an individual presented with APF or CCA compared to O. viverrini infected individuals without these pathologies. In conclusion, urinary 8-oxodG is a robust ‘candidate’ biomarker of the progression of APF and CCA from chronic opisthorchiasis, which is indicative of the critical role that OS plays in both of these advanced hepatobiliary pathologies. The findings also confirm our previous observations that severe liver pathology occurs early and asymptomatically in residents of O. viverrini endemic regions, where individuals are infected for years (often decades) with this food-borne pathogen. These findings also contribute to an expanding literature on 8-oxodG in an easily accessible bodily fluid (e.g., urine) as a biomarker in the multistage process of inflammation, fibrogenesis, and infection-induced cancer.

Partial Text: Over 750 million people (10% of the human population) are at risk of infection with food-borne trematodes, with more than 40 million people currently infected with one of three of these parasites: Clonorchis sinensis, Opisthorchis felineus, and Opisthorchis viverrini [1, 2]. O. viverrini is considered the most important of these food-borne trematodes due to its well-documented association with hepatobiliary pathologies that include advanced periductal fibrosis (APF) [3, 4] and intrahepatic cholangiocarcinoma (CCA) [5–10]. In Northeastern Thailand (Isaan), uncooked cyprinoid fish, which is the intermediate host for the parasite, are a staple of the diet, with O. viverrini infecting an estimated 10 million people in Isaan alone [8]. While infection with O. viverrini can be eliminated by chemotherapy (praziquantel), regional culinary practices result in rapid re-infection after treatment, often leading to life-long infection with the parasite [5, 7, 11] and the highest incidence of CCA in the world (85 per 100,000) [7].

O. viverrini-infected individuals with advanced periductal fibrosis (APF) as determined by abdominal ultrasound had markedly elevated levels of urinary 8-oxodG compared to O. viverrini-infected individuals without APF. Moreover, the concentrations of 8-oxodG in the urine of individuals with APF were comparable to the highly elevated levels of this oxidatively modified DNA lesion in individuals with O. viverrini-induced CCA [28, 31–33]. These results clearly suggest that elevated levels of this metabolite in urine are indicative of hepatobiliary fibrogenesis and tumorogenesis from chronic O. viverrini infection. Moreover, levels of 8-oxodG in the urine of O. viverrini infected individuals with APF or CCA individuals corroborated the ‘gold’ standard diagnostics used to detect both of these hepatobiliary pathologies in a dose-dependent manner: e.g., the highest 50 unit increment of 8-oxodG (200 units) indicated an increased risk of diagnosis of APF or CCA by 354% and 408%, respectively, compared to individuals with no detectable levels of urinary 8-oxodG. Furthermore, the risk models used to evaluate the utility of 8-oxodG as a biomarker were also used to identify the diagnostically relevant levels of 8-oxodG in the urine of study participants. The identification of these diagnostic threshold levels of urinary 8-oxodG, if corroborated in additional larger scale validation studies, would have important implications for urine 8-oxodG as diagnostic tool in field settings, with special significance in resource-limited settings, since they establish benchmarks that may be used to identify individuals at-risk of CCA and refer them for further testing (e.g., confirmatory abdominal ultrasound diagnosis) and preventive chemotherapy.

The findings herein confirm previous observations that severe hepatobiliary disease occurs early and asymptomatically among residents in O. viverrini endemic areas. A simple, non-invasive assay targeting 8-oxodG in urine would be of profound benefit to populations in Southeast Asia, especially in the resource-limited settings of the Mekong Basin region countries of Thailand, Laos and Cambodia, where the incidence of O. viverrini-induced CCA is the highest in the world [7]. The future plan for the candidate biomarker includes moving to a verification step to test its accuracy in a larger sample size [58].



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