Iron Therapy in Chronic Kidney Disease: Days of Future Past

Anemia affects millions of patients with chronic kidney disease (CKD) and prompt iron supplementation can lead to reductions in the required dose of erythropoiesis-stimulating agents, thereby reducing medical costs. Oral and intravenous (IV) traditional iron preparations are considered far from ideal, primarily due to gastrointestinal intolerability and the potential risk of infusion reactions, respectively. Fortunately, the emergence of novel iron replacement therapies has engendered a paradigm shift in the treatment of iron deficiency anemia in patients with CKD. For example, oral ferric citrate is an efficacious and safe phosphate binder that increases iron stores to maintain hemoglobin levels. Additional benefits include reductions in fibroblast growth factor 23 levels and the activation of 1,25 dihydroxyvitamin D. The new-generation IV iron preparations ferumoxytol, iron isomaltoside 1000, and ferric carboxymaltose are characterized by a reduced risk of infusion reactions and are clinically well tolerated as a rapid high-dose infusion. In patients undergoing hemodialysis (HD), ferric pyrophosphate citrate (FPC) administered through dialysate enables the replacement of ongoing uremic and HD-related iron loss. FPC transports iron directly to transferrin, bypassing the reticuloendothelial system and avoiding iron sequestration. Moreover, this paper summarizes recent advancements of hypoxia-inducible factor prolyl hydroxylase inhibitors and future perspectives in renal anemia management.

Effect of hypoxia-inducible factor-prolyl hydroxylase inhibitors on anemia in patients with CKD: a meta-analysis of randomized controlled trials including 2804 patients

Hypoxia-inducible factor-prolyl hydroxylase inhibitors (HIF-PHIs) are orally active first-in-class new generation drugs for renal anemia. This extensive meta-analysis of randomized controlled trials (RCTs) was designed to provide clear information on the efficacy and safety of HIF-PHIs on anemia in chronic kidney disease (CKD) patients. Searches included PubMed, Web of Science, Ovid MEDLINE, and Cochrane Library database up to October 2019. RCTs of patients with CKD comparing HIF-PHIs with erythropoiesis-stimulating agents (ESAs) or placebo in the treatment of anemia. The primary outcome was hemoglobin change from baseline (Hb CFB); the secondary outcomes included iron-related parameters and the occurrence of each adverse event. 26 trials in 17 articles were included, with a total of 2804 dialysis or patients with CKD. HIF-PHIs treatment produced a significant beneficial effect on Hb CFB compared with the placebo group (MD, 0.69; 95% CI, 0.36 to 1.02). However, this favored effect of HIF-PHIs treatment was not observed in subgroup analysis among trials compared with ESAs (MD, 0.06; 95% CI, -0.20 to 0.31). The significant reduction in hepcidin by HIF-PHIs was observed in all subgroups when compared with the placebo group, whereas this effect was observed only in NDD-CKD patients when compared with ESAs. HIF-PHIs increased the risk of nausea (RR, 2.20; 95% CI, 1.06 to 4.53) and diarrhea (RR, 1.75; 95% CI, 1.06 to 2.92). We conclude that orally given HIF-PHIs are at least as efficacious as ESAs treatment to correct anemia short term in patients with CKD. In addition, HIF-PHIs improved iron metabolism and utilization in patients with CKD.

A Single-Dose, Open-Label, Randomized, Two-Way Crossover Study in Healthy Japanese Participants to Evaluate the Bioequivalence and the Food Effect on the Pharmacokinetics of Daprodustat

Daprodustat is a prolyl hydroxylase inhibitor that stimulates erythropoiesis in a manner similar to the natural response to hypoxia, whereby inhibition of hypoxia inducible factor (HIF) prolyl-4-hydroxylases by daprodustat ultimately results in increased levels of HIF-responsive genes. Daprodustat is under development as an emerging new class of agents for the treatment of anemia associated with chronic kidney disease (CKD). This was a single-center, single-dose, open-label, randomized, 2-way crossover study in healthy Japanese male participants consisting of 2 parts. The primary objective was to evaluate the bioequivalence (BE) between daprodustat tablet strengths (part 1) and to evaluate the food effect on the pharmacokinetics (PK) of daprodustat (part 2). A total of 64 healthy Japanese male participants were enrolled; 52 participants were included in part 1 and 12 in part 2. BE was demonstrated between the daprodustat 2-mg tablet and the daprodustat 4-mg tablet. A standard CKD meal did not have a large effect on the PK parameters of daprodustat after a single oral dose of daprodustat 4 mg. Administration of single oral doses of daprodustat 4 mg was generally well tolerated in the healthy Japanese participants, and no new safety signals were identified without regard to food.

Erythropoietin and a hypoxia-inducible factor prolyl hydroxylase inhibitor (HIF-PHDi) lowers FGF23 in a model of chronic kidney disease (CKD)

Iron-deficiency anemia is a potent stimulator of the phosphaturic hormone Fibroblast growth factor-23 (FGF23). Anemia, elevated FGF23, and elevated serum phosphate are significant mortality risk factors for patients with chronic kidney disease (CKD). However, the contribution of anemia to overall circulating FGF23 levels in CKD is not understood. Our goal was to investigate the normalization of iron handling in a CKD model using the erythropoiesis stimulating agents (ESAs) Erythropoietin (EPO) and the hypoxia-inducible factor prolyl hydroxylase inhibitor (HIF-PHDi) FG-4592, on the production of, and outcomes associated with, changes in bioactive, intact FGF23 ("iFGF23"). Our hypothesis was that rescuing the prevailing anemia in a model of CKD would reduce circulating FGF23. Wild-type mice were fed an adenine-containing diet to induce CKD, then injected with EPO or FG-4592. The mice with CKD were anemic, and EPO improved red blood cell indices, whereas FG-4592 increased serum EPO and bone marrow erythroferrone (Erfe), and decreased liver ferritin, bone morphogenic protein-6 (Bmp-6), and hepcidin mRNAs. In the mice with CKD, iFGF23 was markedly elevated in control mice but was attenuated by >70% after delivery of either ESA, with no changes in serum phosphate. ESA treatment also reduced renal fibrosis markers, as well as increased Cyp27b1 and reduced Cyp24a1 mRNA expression. Thus, improvement of iron utilization in a CKD model using EPO and a HIF-PHDi significantly reduced iFGF23, demonstrating that anemia is a primary driver of FGF23, and that management of iron utilization in patients with CKD may translate to modifiable outcomes in mineral metabolism.

Iron Regulation by Molidustat, a Daily Oral Hypoxia-Inducible Factor Prolyl Hydroxylase Inhibitor, in Patients with Chronic Kidney Disease

BACKGROUND/AIMS

The current treatment for anemia associated with chronic kidney disease (CKD) includes the administration of erythropoiesis stimulating agents (ESAs) combined with iron supplementation. Molidustat, a hypoxia-inducible factor prolyl hydroxylase inhibitor, has potential to treat anemia associated with CKD through increased erythropoietin production and improved iron availability. Here, we report the effect of molidustat on iron metabolism.

METHOD

Parameters of iron metabolism were monitored in three 16-week, randomized, controlled, phase 2 studies assessing the safety and efficacy of molidustat in the treatment of anemia associated with CKD in different populations: treatment-naïve and previously ESA-treated patients not on dialysis, and previously ESA-treated patients on hemodialysis. Iron supplementation was left at the discretion of the investigator.

RESULTS

In treatment-naïve patients not on dialysis, transferrin saturation (TSAT), hepcidin, ferritin, and iron concentrations decreased with molidustat, whereas total iron binding capacity (TIBC) increased. Similar results were observed in previously ESA-treated patients not on dialysis, although changes in those parameters were larger in treatment-naïve than in previously ESA-treated patients. In previously ESA-treated patients receiving hemodialysis, hepcidin concentration and TIBC remained stable with molidustat, whereas TSAT and ferritin and iron concentrations increased. Generally, similar trends were observed in secondary analyses of subgroups of patients not receiving iron supplementation.

CONCLUSIONS

Molidustat is a potential alternative to standard treatment of anemia associated with CKD, with a different mechanism of action. In patients not receiving dialysis, molidustat increases iron availability. In patients receiving hemodialysis, further investigation is required to understand fully the mechanisms underlying iron mobilization associated with molidustat.

Chronic cigarette smoke exposure induces systemic hypoxia that drives intestinal dysfunction

Crohn's disease (CD) is a chronic inflammatory disease of the gastrointestinal tract (GIT). Cigarette smoke (CS) exposure and chronic obstructive pulmonary disease (COPD) are risk factors for CD, although the mechanisms involved are poorly understood. We employed a mouse model of CS-induced experimental COPD and clinical studies to examine these mechanisms. Concurrent with the development of pulmonary pathology and impaired gas exchange, CS-exposed mice developed CD-associated pathology in the colon and ileum, including gut mucosal tissue hypoxia, HIF-2 stabilization, inflammation, increased microvasculature, epithelial cell turnover, and decreased intestinal barrier function. Subsequent smoking cessation reduced GIT pathology, particularly in the ileum. Dimethyloxaloylglycine, a pan-prolyl hydroxylase inhibitor, ameliorated CS-induced GIT pathology independently of pulmonary pathology. Prior smoke exposure exacerbated intestinal pathology in 2,4,6-trinitrobenzenesulfonic acid-induced (TNBS-induced) colitis. Circulating vascular endothelial growth factor, a marker of systemic hypoxia, correlated with CS exposure and CD in mice and humans. Increased mucosal vascularisation was evident in ileum biopsies from CD patients who smoke compared with nonsmokers, supporting our preclinical data. We provide strong evidence that chronic CS exposure and, for the first time to our knowledge, associated impaired gas exchange cause systemic and intestinal ischemia, driving angiogenesis and GIT epithelial barrier dysfunction, resulting in increased risk and severity of CD.

The prolyl 4-hydroxylase inhibitor GSK360A decreases post-stroke brain injury and sensory, motor, and cognitive behavioral deficits

There is interest in pharmacologic preconditioning for end-organ protection by targeting the HIF system. This can be accomplished by inhibition of prolyl 4-hydroxylase (PHD). GSK360A is an orally active PHD inhibitor that has been previously shown to protect the failing heart. We hypothesized that PHD inhibition can also protect the brain from injuries and resulting behavioral deficits that can occur as a result of surgery. Thus, our goal was to investigate the effect of pre-stroke surgery brain protection using a verified GSK360A PHD inhibition paradigm on post-stroke surgery outcomes. Vehicle or an established protective dose (30 mg/kg, p.o.) of GSK360A was administered to male Sprague-Dawley rats. Initially, GSK360A pharmacokinetics and organ distribution were determined, and then PHD-HIF pharmacodynamic markers were measured (i.e., to validate the pharmacological effects of the GSK360A administration regimen). Results obtained using this validated PHD dose-regimen indicated significant improvement by GSK360A (30mg/kg); administered at 18 and 5 hours prior to transient middle cerebral artery occlusion (stroke). GSK360A exposure and plasma, kidney and brain HIF-PHD pharmacodynamics endpoints (e.g., erythropoietin; EPO and Vascular Endothelial Growth Factor; VEGF) were measured. GSK360A provided rapid exposure in plasma (7734 ng/ml), kidney (45–52% of plasma level) and brain (1–4% of plasma level), and increased kidney EPO mRNA (80-fold) and brain VEGF mRNA (2-fold). We also observed that GSK360A increased plasma EPO (300-fold) and VEGF (2-fold). Further assessments indicated that GSK360A reduced post-stroke surgery neurological deficits (47–64%), cognitive dysfunction (60–75%) and brain infarction (30%) 4 weeks later. Thus, PHD inhibition using GSK360A pretreatment produced long-term post-stroke brain protection and improved behavioral functioning. These data support PHD inhibition, specifically by GSK360A, as a potential strategy for pre-surgical use to reduce brain injury and functional decline due to surgery-related cerebral injury.