• Effect of Cadmium Exposure on the Transport System of Organic Cation Transporters and Multidrug and Toxin Extrusion Proteins (OCTs/MATEs)

      Yang, Hong; Shu, Yan, Ph.D. (2019)
      The universal pollution by cadmium (Cd) in our agricultural land and the prevalence of cigarette smoking make the environmental Cd exposure an unneglectable human health concern. While the mechanism of cadmium accumulation has been extensively studied, no explicit mechanism has been reported regarding the elimination of cadmium from the body. On the other hand, whereas Cd exposure has been correlated with a variety of diseases, little is known pertaining to its effect on drug disposition and response in patients. Thus, we aim to delineate the mechanism of cadmium elimination and detoxification and to gain new insights into its effect on xenobiotic disposition and response. The OCTs/MATEs transport system are pair of transporter proteins highly expressed at the basolateral and apical membrane of hepatocytes and renal proximal tubules respectively. Recently, Cd has been identified as a substrate of OCTs, while we determined that MATEs could reduce the toxicity of Cd by serving as its efflux transporters in vitro. In addition, knockout of Mate1 in mice kidney resulted in higher renal toxicity in both chronic and acute Cd intoxication studies. We found that Cd was an inducer of OCT activity while an inhibitor towards MATEs in cells. Consistently, Cd exposure could lead to accumulation of the substrates of these transporters in mouse liver and kidney. Being focused on human (h) OCT2 and MATE1, our mechanistic studies revealed that hOCT2, as compared to hMATE1, was more active in trafficking between the plasma membrane and the cytoplasmic storage pool. Cd exposure could trigger the formation of a protein complex consisting of AKT2, calmodulin and AS160, which could then selectively facilitate the phosphorylation of AKT2 at T309, and initiate the translocation of hOCT2 to the plasma membrane. Altogether, our findings have identified MATE transporters as new contributors for Cd detoxification, and provided foundation to uncover environmental Cd as a previously unrecognized factor for the broad variation in drug disposition and response.
    • Novel WNT/beta-catenin Signaling Pathway Inhibitors for the Treatment of Metabolic Disorders

      Obianom, Obinna N.; Shu, Yan, Ph.D. (2018)
      The WNT/β-catenin signaling (β-cat) pathway is critical for embryonic development and tissue homeostasis. For this reason, alterations in the β-cat pathway are associated with many ailments including metabolic disorders, which may result from defects in the energy metabolism. The contribution of β-cat pathway to energy metabolism has become a subject of many investigations following the identification of polymorphisms in β-cat pathway components that predispose individuals to type-2-diabetes. Current evidence suggests that downregulation of the β-cat pathway activity may help treat metabolic disorders. Given these findings, the overarching goal of this thesis was to discover and develop novel β-cat pathway inhibitors and to examine their efficacy on glucose and lipid metabolism. We started with an FDA approved anthelmintic, pyrvinium, which is a potent inhibitor of the β-cat pathway. Our results showed that pyrvinium improved glucose tolerance by inhibiting glucose output, hepatic lipid accumulation and activating the AMPK pathway. Despite these beneficial effects, pyrvinium is unsuitable for repurposing to use orally in the treatment of metabolic disorders due to its almost zero bioavailability and other unspecific toxic effects in mice at higher doses. Based on the structure of pyrvinium, we decided to discover new potent β-cat pathway inhibitors with lower toxicity and improved bioavailability. Our screening of more than 150 newly synthesized pyrvinium derivatives led to the discovery of YW1128 as such a candidate having the aforementioned properties. Administration of YW1128 led to decreased lipid accumulation and improved glucose tolerance in the mice fed with high fat diet. Previous studies had suggested a critical role of hepatic β-cat pathway in determining the whole body metabolic homeostasis. So we next sought to achieve a selective delivery of the new derivatives to the liver without having significant disposition in other tissues. We performed a proof-of-concept study where we took advantage of high expression of organic cation transporter 1 (OCT1) in the liver to modify the compounds that were not specifically permeable to OCT1 expressing cells. We inserted a biguanide, which is a major backbone of several OCT1 substrates, into these compounds and showed that they became highly permeable to cells overexpressing OCT1. This suggests that insertion of the biguanide moiety into YW1128 may be an approach to improve its selective liver targeting. In conclusion, this thesis uncovered the efficacy by small molecule inhibition of β-cat pathway in the treatment of metabolic disorders and established that incorporating a biguanide moiety to the compounds may serve as a strategy to achieve selective liver targeting.