The Synthesized Plant Metabolite 3,4,5-Tri-O-Galloylquinic Acid Methyl Ester Inhibits Calcium Oxalate Crystal Growth in a Drosophila Model, Downregulates Renal Cell Surface Annexin A1 Expression, and Decreases Crystal Adhesion to Cells.

The plant metabolite 3,4,5-tri-O-galloylquinic acid methyl ester (TGAME, compound 6) was synthesized, and its potential effect on calcium oxalate monohydrate (COM) crystal binding to the surface of Madin-Darby canine kidney cells type I (MDCKI) and crystal growth in a Drosophila melanogaster Malpighian tubule (MT) model were investigated. Membrane, cytosolic, and total annexin A1 (AxA1), α-enolase, and heat shock protein 90 (HSP90) amounts were examined by Western blot analysis after subcellular fractionation, then confirmed by immunofluorescence staining of cultured cells. Pretreatment of MDCKI cells with TGAME for up to 6 h significantly diminished COM crystal binding in a concentration-dependent manner. TGAME significantly inhibited AxA1 surface expression by immunofluorescence microscopy, whereas intracellular AxA1 increased. Western blot analysis confirmed AxA1 expression changes in the membrane and cytosolic fractions of compound-treated cells, whereas whole cell AxA1 remained unchanged. TGAME also significantly decreased the size, number, and growth of calcium oxalate (CaOx) crystals induced in a Drosophila melanogaster MT model and possessed a potent antioxidant activity in a DPPH assay.

Insulin and SGK1 reduce the function of Na+/monocarboxylate transporter 1 (SMCT1/SLC5A8).

SMCTs move several important fuel molecules that are involved in lipid, carbohydrate, and amino acid metabolism, but their regulation has been poorly studied. Insulin controls the translocation of several solutes that are involved in energetic cellular metabolism, including glucose. We studied the effect of insulin on the function of human SMCT1 expressed in Xenopus oocytes. The addition of insulin reduced α-keto-isocaproate (KIC)-dependent 22Na+ uptake by 29%. Consistent with this result, the coinjection of SMCT1 with SGK1 cRNA decreased the KIC-dependent 22Na+ uptake by 34%. The reduction of SMCT1 activity by SGK1 depends on its kinase activity, and it was observed that the coinjection of SMCT1 with S442D-SGK1 (a constitutively active mutant) decreased the KIC-dependent 22Na+ uptake by 50%. In contrast, an SMCT1 coinjection with K127M-SGK1 (an inactive mutant) had no effect on the KIC-dependent Na+ uptake. The decreasing SMCT1 function by insulin or SGK1 was corroborated by measuring [1-14C]acetate uptake and the electric currents of SMCT1-injected oocytes. Previously, we found that SMCT2/Slc5a12-mRNA, but not SMCT1/Slc5a8-mRNA, is present in zebrafish pancreas (by in situ hybridization); however, SLC5a8 gene silencing was associated with the development of human pancreatic cancer. We confirmed that the mRNA and protein of both transporters were present in rat pancreas using RT-PCR with specific primers, Western blot analysis, and immunohistochemistry. Additionally, significant propionate-dependent 22Na+ uptake occurred in pancreatic islets and was reduced by insulin treatment. Our data indicate that human SMCT1 is regulated by insulin and SGK1 and that both SMCTs are present in the mammalian pancreas.