Tissue disposition of cadmium and nutritional metals in mice with a reduced functioning BCRP transporter
Creators: name: Stradford, Christopher Shareif Jackson
Publisher: name: No Publisher Supplied
Year: 2024

description: This thesis will explore the tissue distribution of the toxic metal cadmium and its interplay with a prominent efflux transporter. The main transporter covered in this thesis is the BCRP transporter. Otherwise known as the breast cancer resistance protein, the BCRP transporter was shown to reduce the accumulation of cadmium in different types of tissues. Cadmium has no beneficial biological purpose in the body and can result in negative effects such as kidney failure and liver dysfunction. Although the target organs of toxicity are mainly the kidneys and liver, cadmium has also been known to accumulate in the testis, and small intestinal tract. This thesis studies the mouse wild type Bcrp variant and compares it to the Q140K variant, which is genetically modified to mimic the reduced functionality of the human Q141K BCRP transporter in mice, in order to compare how effective they are in eliminating cadmium from tissues. Inductively Coupled Plasma Mass Spectrometry (ICPMS) was used to identify which tissues accumulate cadmium and quantify absolute concentrations in target tissues. The purpose of this study was to understand the role of the Bcrp transporter in decreasing cadmium bioaccumulation, and to analyze cadmium’s distribution within specific organs in a C57BL/6 male mouse model. In-vitro and in-vivo experiments have helped in understanding that transporters might either reduce or increase cadmium bioaccumulation and toxicity in the body. To test the role of the human Q141K variant in vivo, wild-type C57BL/6J mice were modified by CRISPR to contain the same nonsynonymous polymorphism at position 140 (i.e., Q140K). Tissues from mice with the Q140K Bcrp variant have lower Bcrp protein expression, and therefore reduced transport activity compared to the wild-types. Thirty-two mice were split into control and CdCl2-dosed groups for both WT and Q140K genotypes. The Cd-dosed groups were provided MQ water spiked with 50ppm of CdCl2 for drinking while the control groups were provided regular MQ water for 14 days. The Cd-exposed groups had a significant increase in body weight compared to the control groups. ICPMS was used to quantify cadmium, manganese, zinc, and copper. Results showed a significant increase of cadmium concentrations in the testis, liver, and kidneys of the Q140K mice, while there was a significant decrease in both cadmium in the plasma of Q140K mice. Cadmium showed no significant differences within the small intestinal tract between WT and Q140K mice. Zinc showed a significant increase in the liver of Q140K mice, and a significant decrease in the plasma of WT mice. Manganese showed a significant decrease in the liver and duodenum for Q140K, and a significant decrease in the liver for WT mice. Selenium showed a significant in both plasma and testis, as well as a significant increase in the kidneys for Q140K. There were no significant changes for copper. Multiple transporters are involved in the uptake and efflux of cadmium. RNA sequencing was used to compare the Bcrp transporter to other proteins previously studied that might contribute to cadmium clearance or cadmium toxicity. RNAseq data from liver samples were analyzed and showed an increase of cadmium binding proteins metallothionein, lipocalin-2, and transferrin in the cadmium-treated Q140K mice compared to the cadmium-treated WT group. There was a decrease in the mRNA levels of the heat shock proteins Hspa1a, Hspa1b, and Hspa4l in the cadmium-treated Q140K group compared to the WT. Zinc transporters Znt1 and ZIP14 were increased in the livers of Cd-treated Q140K mice, while ZIP10 mRNA decreased compared to the WT group. Quantitative PCR data of metallothionein also show an increase in the cadmium-treated Q140K group and western blot data show a decrease of Bcrp protein and an increase of HO-1 protein in the Q140K group compared to the WT group following administration of CdCl2. Clinical chemistry data showed no significant difference between WT exposed and Q140K exposed groups for BUN, ALT, ALP, creatinine, calcium, phosphorus, albumin, cholesterol, or bilirubin. Glucose has a significant difference with the cadmium exposed WT group having higher levels than the control WT group, and a similar but non-significant trend between the Q140K groups.The BCRP transporter plays a major role in reducing the accumulation of cadmium in the body. The reduced activity in the Q140K variant alters the activity of other transporters that play a role in cadmium transport, and the transport of other metals. With cadmium concentrations higher in the Q140K mice compared to the wild type group, this could mean that humans with a reduced functioning BCRP variant could be at a higher risk of developing cadmium toxicity than other mammals, and more research needs to be done to reduce the negative effects that cadmium accumulation causes.