lp533401 and Renal-Insufficiency--Chronic

An increase in the peripheral synthesis of serotonin and kynurenine, observed during the chronic kidney disease (CKD) course, is negatively associated with bone health. Serotonin and kynurenine are connected by the common precursor, tryptophan. LP533401 is an inhibitor of peripheral serotonin synthesis. This study aimed to establish if the inhibition of serotonin synthesis by LP533401 may affect the kynurenine pathway activity in bone tissue and its potential consequence with regard to osteogenesis and bone mineral status. Nephrectomized rats were treated with LP533401 at a dose of 30 and 100 mg/kg daily for eight weeks. Tryptophan and kynurenine concentrations were determined, and tryptophan 2,3-dioxygenase (TDO) expression was assessed. We discovered the presence of a TDO-dependent, paracrine kynurenic system in the bone of rats with CKD. Its modulation during LP533401 treatment was associated with impaired bone mineral status. Changes in TDO expression affecting the kynurenine pathway activity were related to the imbalance between peripheral serotonin and 25-hydroxyvitamin D. There were also close associations between the expression of genes participating in osteoblastogenesis and activation of the kynurenine pathway in the bones of LP53301-treated rats. Our results represent the next step in studying the role of tryptophan metabolites in renal osteodystrophy.

Topics: Animals; Bone Diseases, Metabolic; Calcification, Physiologic; Kynurenine; Male; Mice; Osteoblasts; Osteogenesis; Paracrine Communication; Pyrimidines; Rats; Rats, Wistar; Renal Insufficiency, Chronic; Serotonin; Serotonin Agents; Tryptophan; Tryptophan Oxygenase; Vitamin D

Chronic kidney disease (CKD) is a pathological condition associated with renal osteodystrophy for which there are limited treatment options. Gut-derived serotonin (GDS) is one of the key signaling factors controlling the osteoblast proliferation. Previously, we shown that inhibition of GDS synthesis by LP533401 improved bone mineral status of rats with 5/6 nephrectomy-induced CKD model. Here, we investigated whether the use of LP533401 can modify GDS-dependent molecular pathway involved in osteoblast formation and bone mineralization in CKD rats. The 8-weeks of pharmacological manipulation after a complete CKD development reduced GDS and lead to the advantage of endogenous vitamin D [25(OH)D] over serotonin and parathyroid hormone (PTH) in rats treated with LP533401. The imbalance between GDS - 25(OH)D - PTH resulted in the intensified expression of cAMP- responsive element-binding protein (Creb), whereas the expression of myelocytomatosis oncogene (c-Myc) was simultaneously reduced. This lead to disruption of Foxo1- activating transcription factor 4 (Atf4) complex, and decrease in the expression of the major osteogenic markers. The weakening of excessive osteoblastogenesis was associated with better bone mineral status in all rats with CKD, and especially in LP533401-treated animals. In conclusion, the inhibition of GDS synthesis resulted in the mitigation of osteoblastogenesis observed in CKD, which translated into improvement of bone mineral status. This study provides key mechanistic insights into how modification of GDS-dependent molecular pathway affects bone mineral status in CKD and lays the groundwork for translating the role of functional serotonin signaling in the origin of impaired bone mineral status in patients with CKD.

Topics: Animals; Calcification, Physiologic; Disease Models, Animal; Male; Osteoblasts; Osteogenesis; Parathyroid Hormone; Pyrimidines; Rats; Rats, Wistar; Renal Insufficiency, Chronic; Serotonin; Serotonin Agents

Klotho is a key regulator of phosphate and Ca. We evaluated the effect of LP533401 therapy on Klotho-expression-dependent Ca. Treatment with LP533401 and its vehicle resulted in the inhibition of transient receptor potential vanilloid receptor subtypes 5 and 6 (TRPV5, TRPV6) and calbindin (CaBP-28k, CaBP-9k) expression. The compensatory acceleration in renal expression of Na+/Ca. The modulation of circulating serotonin and its relation to other regulators of calcium handling can play an important role in calcium homeostasis and bone integrity in CKD rats treated with LP533401.

Topics: Animals; Bone and Bones; Calcium; Chronic Kidney Disease-Mineral and Bone Disorder; Disease Models, Animal; Glucuronidase; Klotho Proteins; Male; Pyrimidines; Rats; Rats, Wistar; Renal Insufficiency, Chronic; Uremia; Vitamin D

LP533401 is an orally bioavailable small molecule that inhibits tryptophan hydroxylase-1, an enzyme responsible for the synthesis of gut-derived serotonin (GDS). Recently, we showed that increased GDS in rats with chronic kidney disease (CKD) affected bone strength and metabolism. We tested the hypothesis that treatment with LP533401 could reverse CKD-induced bone loss in uremia. Sixteen weeks after 5/6 nephrectomy, rats were randomized into untreated (CKD), treated with vehicle (VEH) and LP533401 at a dose of 30 or 100 mg/kg daily for 8 weeks. Treatment with LP533401 decreased serotonin turnover and restored bone mineral status, microarchitecture, and strength in CKD rats to the values observed in the controls. In parallel with the reduction of serotonin, serum phosphate levels also decreased, particularly in the LP533401, 100 mg/kg group. The mechanism underlying this phenomenon resulted from decreased expression of the renal VDR/FGF1R/Klotho/Npt2a/Npt2c axis, leading to elevated phosphate excretion in the kidneys. The elevated urinary phosphate excretion resulted in improved bone mineral status and strength in LP533401-treated rats. Unexpectedly, the standard VEH used in this model was able to reduce renal VDR/FGF1R/Klotho/Npt2a expression, leading to a compensatory increase in Npt2c mRNA levels, secondary disturbances in phosphate-regulated hormones and partial improvement in the mineral status of the trabecular bone. The decrease of serotonin synthesis together with the simultaneous reduction of renal Npt2a and Npt2c expression in rats treated with LP533401, 100 mg/kg led to an increase in 1,25(OH)

Topics: Animals; Bone Density; Disease Models, Animal; Kidney; Male; Nephrectomy; Phosphates; Pyrimidines; Rats; Rats, Wistar; Renal Insufficiency, Chronic; Serotonin; Sodium-Phosphate Cotransporter Proteins, Type II; Tryptophan Hydroxylase