Mobilization and removing of cadmium from kidney by GMDTC utilizing renal glucose reabsorption pathway

Abstract

Chronic exposure to cadmium compounds (Cd(2+)) is one of the major public health problems facing humans in the 21st century. Cd(2+) in the human body accumulates primarily in the kidneys which leads to renal dysfunction and other adverse health effects. Efforts to find a safe and effective drug for removing Cd(2+) from the kidneys have largely failed. We developed and synthesized a new chemical, sodium (S)-2-(dithiocarboxylato((2S,3R,4R,5R)-2,3,4,5,6 pentahydroxyhexyl)amino)-4-(methylthio) butanoate (GMDTC). Here we report that GMDTC has a very low toxicity with an acute lethal dose (LD50) of more than 10,000mg/kg or 5000mg/kg body weight, respectively, via oral or intraperitoneal injection in mice and rats. In in vivo settings, up to 94% of Cd(2+) deposited in the kidneys of Cd(2+)-laden rabbits was removed and excreted via urine following a safe dose of GMDTC treatment for four weeks, and renal Cd(2+) level was reduced from 12.9μg/g to 1.3μg/g kidney weight. We observed similar results in the mouse and rat studies. Further, we demonstrated both in in vitro and in animal studies that the mechanism of transporting GMDTC and GMDTC-Cd complex into and out of renal tubular cells is likely assisted by two glucose transporters, sodium glucose cotransporter 2 (SGLT2) and glucose transporter 2 (GLUT2). Collectively, our study reports that GMDTC is safe and highly efficient in removing deposited Cd(2+) from kidneys assisted by renal glucose reabsorption system, suggesting that GMDTC may be the long-pursued agent used for preventive and therapeutic purposes for both acute and chronic Cd(2+) exposure.

Keywords: Cadmium decorporation; Cadmium induced renal dysfunction; Chelating agent; GMDTC; Renal glucose reabsorption pathway.

Conflict of interest statement

Conflict interests

GMDTC is under protection by the patent, ZL 200510035377 to X.T.

Copyright © 2016 Elsevier Inc. All rights reserved.

Figures

Fig. 1

GMDTC synthesis and acute toxicity assessment. A). Simplified synthesis steps of Sodium (S)-2-(dithiocarboxylato((2S,3R,4R,5R)-2,3,4,5,6 pentahydroxyhexyl)amino)-4-(methylthio)butanoate (GMDTC). B). The schematic structure of the GMDTC-Cd complex was created by coordination chemistry software (molecular formula: NaCdC24H43O14N2S6). C). The body weight of mice (C-1) and rats (C-2) was shown following gavage administration of 10.1 g/kg (23.3 mmol/kg) GMDTC at 3, 7 and 14 days. D). The body weight of mice (D-1) and rats (D-2) was shown followingi.p. injection of 5.1 g/kg (11.8 mmol/kg) GMDTC at 3, 7 and 14 days.

Fig. 2

GMDTC’s effect in removing Cd2+ from kidneys. Panel A, Animal models of sub-chronic Cd2+ intoxication. Cd2+ levels were significantly increased in kidneys of Cd2+-laden animals (A-1). Urinary β2-microglobulin level was significantly increased in Cd2+-laden animals (A-2); panel B, GMDTC’s effect in removing Cd2+ from kidneys of mice and rats. Renal Cd2+ levels in mice (B-1) and rats (B-2) were significantly reduced following 4-weeks GMDTC treatment. EDTA at 0.25 mmol/kg was included as a control; panel C, GMDTC’s effect in removing Cd2+ from kidneys of rabbits. A significantly reduced renal Cd2+ level was observed within a week of GMDTC treatment (C-1). EDTA at 0.25 mmol/kg was included as a control. Renal Cd2+ levels were further reduced in a time-depend manner (C-2). * P < 0.05 & **P < 0.01.

Fig. 3

SGLT2 and GLUT2 transporters mediate the transportation of GMDTC and the GMDTC-Cd complex into and out of renal tubular cells. Panel A, in vitrostudy. HK-2 cells were treated with CdCl2, GMDTC, canagliflozin or phloretin or their combinations for 24 h, and cell viability was evaluated by MTT assay (A-1). The data was from three independent experiments; time course of the cytoplasmic Ca2+ levels of HK-2 cells post Cd2+ and/or GMDTC exposure when HK-2 cells were pre-incubated with canagliflozin or phloretin. Representative images under confocal laser scanning microscope were shown (A-2, scale bar = 5 μm); the inflorescence intensity of cytoplasmic Ca2+ was recorded under confocal laser scanning microscope and presented in A-3. The data was from three independent experiments, and error bar with standard deviations was removed for clear presentation. (* P< 0.05 & ** P < 0.01, in comparison with GMDTC + Cd2+ group). Panel B, in vivo study. Canagliflozin pretreatment has a little impact on GMDTC’s effect in removing Cd2+ from kidney (B-1),n = 6; GMDTC’s effect in removing Cd2+ from kidney was compromised when Cd2+-laden mice were pretreated with phloretin (B-2),n = 6 (* P < 0.05 & ** P < 0.01).

Fig. 3

SGLT2 and GLUT2 transporters mediate the transportation of GMDTC and the GMDTC-Cd complex into and out of renal tubular cells. Panel A, in vitrostudy. HK-2 cells were treated with CdCl2, GMDTC, canagliflozin or phloretin or their combinations for 24 h, and cell viability was evaluated by MTT assay (A-1). The data was from three independent experiments; time course of the cytoplasmic Ca2+ levels of HK-2 cells post Cd2+ and/or GMDTC exposure when HK-2 cells were pre-incubated with canagliflozin or phloretin. Representative images under confocal laser scanning microscope were shown (A-2, scale bar = 5 μm); the inflorescence intensity of cytoplasmic Ca2+ was recorded under confocal laser scanning microscope and presented in A-3. The data was from three independent experiments, and error bar with standard deviations was removed for clear presentation. (* P< 0.05 & ** P < 0.01, in comparison with GMDTC + Cd2+ group). Panel B, in vivo study. Canagliflozin pretreatment has a little impact on GMDTC’s effect in removing Cd2+ from kidney (B-1),n = 6; GMDTC’s effect in removing Cd2+ from kidney was compromised when Cd2+-laden mice were pretreated with phloretin (B-2),n = 6 (* P < 0.05 & ** P < 0.01).

Fig. 4

Schematic diagram of Cd2+ decorporation from kidney by GMDTC.