Inborn defects in N-acetylglutamate (NAG) synthase (NAGS) cause a reduction of NAG, an essential cofactor for the initiation of the urea cycle. As a consequence, blood ammonium concentrations are elevated, leading to severe neurological disorders. The orphan drug N-carbamoylglutamate (NCG; Carbaglu), efficiently overcomes NAGS deficiency. However, not much is known about the transporters involved in the uptake, distribution, and elimination of the divalent organic anion NCG. Organic anion-transporting polypeptides (OATPs) as well as organic anion transporters (OATs) working in cooperation with sodium dicarboxylate cotransporter 3 (NaDC3) accept a wide variety of structurally unrelated drugs. To test for possible interactions with OATPs and OATs, the impact of NCG on these transporters in stably transfected human embryonic kidney-293 cells was measured. The two-electrode voltage-clamp technique was used to monitor NCG-mediated currents in Xenopus laevis oocytes that expressed NaDC3. Neither OATPs nor OAT2 and OAT3 interacted with NCG, but OAT1 transported NCG. In addition, NCG was identified as a high-affinity substrate of NaDC3. Preincubation of OAT4-transfected human embryonic kidney-293 cells with NCG showed an increased uptake of estrone sulfate, the reference substrate of OAT4, indicating efflux of NCG by OAT4. In summary, NaDC3 and, to a lesser extent, OAT1 are likely to be responsible for the uptake of NCG from the blood. Efflux of NCG across the luminal membrane into the tubular lumen probably occurs by OAT4 completing renal secretion of this drug.

Patients with type 2 diabetes (T2D) are threatened by excessive cardiovascular morbidity and mortality. While accelerated arterial stiffening may represent a critical mechanistic factor driving cardiovascular risk in T2D, specific therapies to contain the underlying diabetic arterial remodeling have been elusive. The present translational study investigates the role of microRNA-29b (miR-29b) as a driver and therapeutic target of diabetic aortic remodeling and stiffening. Using a murine model (db/db mice), as well as human aortic tissue samples, we find that diabetic aortic remodeling and stiffening is associated with medial fibrosis, as well as fragmentation of aortic elastic layers. miR-29b is significantly downregulated in T2D and miR-29b repression is sufficient to induce both aortic medial fibrosis and elastin breakdown through upregulation of its direct target genes COL1A1 and MMP2 thereby increasing aortic stiffness. Moreover, antioxidant treatment restores aortic miR-29b levels and counteracts diabetic aortic remodeling. Concluding, we identify miR-29b as a comprehensive—and therefore powerful—regulator of aortic remodeling and stiffening in T2D that moreover qualifies as a (redox-sensitive) target for therapeutic intervention.

Inborn defects in the carbamoylphosphate synthase 1 (CPS1) cause a reduction of N‐acetylglutamate (NAG), an essential cofactor for the function of the urea cycle, and consequently elevated blood levels of the neurotoxic ammonia. N‐carbamoylglutamate (carglumic acid, carbaglu®, NCG) is a structural analog of NAG that can substitute for NAG on CPS1, thereby reactivating the urea cycle and finally reducing blood ammonia levels. The renal clearance of NCG exceeds the glomerular filtration rate suggesting an active secretion process in kidney proximal tubules. The kidneys are known to express organic anion transporting polypeptides (OATPs) and organic anion transporters (OATs). OATs work in cooperation with sodium‐dicarboxylate transporters (NaDCs) thereby mediating the exit of many drugs. The impact of NCG on several human OATPs, OATs, and NaDCs stably transfected in HEK293 cells was tested. From the transporters tested, OAT1, OATP1B3, and NaDC3 interacted with NCG. Sodium‐ and concentration‐dependent NCG‐mediated currents were measured in Xenopus laevis oocytes expressing NaDC3. NCG was identified as a high affinity substrate of NaDC3 with a KM of 27.5 µM. This value equals the plasma concentration of succinate, the lead substance of NaDC3 and as well as the plasma concentration of patients treated with NCG. Competition of succinate and NCG on NaDC3 may result in reduced renal clearance of drugs.

Mögliche Transporter für Resorption, Verteilung und Elimination von NCG 4.4.2 hNaDC3 im Rahmen der Ausweitung der NCG-Anwendung .