Increased transferrin protects from thrombosis in Chuvash erythrocytosis

Increased Transferrin Concentrations Are Not Associated With Thrombosis in People Living at High Altitude

Background

Bolivian Andean Aymara highlanders, living at 4,000 m for 14,000 years, have evolved genetic adaptations to hypoxia. These include EGLN1 encoding prolyl hydroxylase 2 (PHD2), a regulator of transferrin transcription. Transferrin level increases in hypoxia and iron deficiency. Contrasting reports indicate that elevated transferrin is associated with experimentally induced thrombosis in mice undergoing short-stay at high altitude, but with decreased thrombosis in a congenital disorder of hypoxia-sensing.

Methods

A retrospective study was conducted in people living at high altitude (3,650 - 4,150 m). We analyzed serum transferrin concentration and thrombosis history in Aymara patients with high-altitude erythrocytosis (n = 149, median age 55 years, female gender 30%, iron deficiency 23%) or high-altitude anemia (n = 137, median age 43 years, female gender 86%, iron deficiency 57%).

Results

The median transferrin concentration was 339 mg/dL in erythrocytosis patients versus 310 mg/dL in anemia patients (P = 0.037); it was 367 mg/dL in iron deficient versus 312 mg/dL in iron replete patients (P < 0.001). Thrombosis history was present in 13% of erythrocytosis and 8% of anemia patients (P = 0.25) and was present in 16% of iron deficient and 7% of iron replete patients (P = 0.017). After adjustment for erythrocytosis and iron deficiency in multivariate regression analysis, the mean (95% confidence interval) transferrin concentration was 277 (237 - 316) mg/dL in 30 patients with thrombosis history versus 324 (306 - 341) mg/dL in 256 patients without thrombosis history (P = 0.018). Similar trends occurred for the subgroups of arterial thrombosis history (P = 0.044) and venous thrombosis history (P = 0.22).

Conclusions

In individuals with extreme environmental hypoxia, we found no evidence that increased transferrin is associated with increased thrombosis history. Rather, we observed a trend to decreased thrombosis history with increased transferrin levels.

Growing concerns about using hypoxia-inducible factor prolyl hydroxylase inhibitors for the treatment of renal anemia

Hypoxia-inducible factor prolyl hydroxylase inhibitors (HIF-PHIs) have emerged as a novel therapeutic class for treating anemia in patients with chronic kidney disease. Small molecule analogs of α-ketoglutarate (AKG), an essential substrate for 2-oxoglutarate-dependent dioxygenases (2-OGDDs), including prolyl hydroxylase domain proteins (PHDs), inhibit PHDs pharmacologically and thereby prevent HIF degradation. HIF stabilization alleviates anemia through several stimulatory effects on erythropoiesis, but it also affects the expression of many anemia-unrelated genes whose protein products exert important functions in vivo. Therefore, the pleiotropic effects of HIF stabilization under normoxic conditions deserve to be examined in more detail. Specifically, we believe that particular attention should be given to epigenetic modifications among the various AKG-based metabolic systems that may be altered by HIF-PHIs. It is noteworthy that AKG has been reported to exert health-protective actions. AKG-based metabolic systems include enzymes associated with the tricarboxylic acid cycle and amino acid metabolism, as well as 2-OGDD-mediated processes, which play important roles in many biological reactions. In this review, we examine the multifaceted effects of HIF-PHIs, encompassing not only their on-target effect of HIF stabilization but also their off-target inhibitory effects on various AKG-based metabolic systems. Furthermore, we examine its potential relevance to cardiovascular complications, based on clinical and animal studies suggesting its involvement in vascular calcification, thrombogenesis and heart failure. In conclusion, although HIF-PHIs offer a promising avenue for anemia treatment in CKD patients, their broader impact on multiple biological systems raises substantial concerns. The intricate interplay between HIF stabilization, AKG competition and cardiovascular complications warrants extensive, long-term investigations to ensure the safety and usefulness of HIF-PHIs in clinical practice.

Targeting Pro-Oxidant Iron with Exogenously Administered Apotransferrin Provides Benefits Associated with Changes in Crucial Cellular Iron Gate Protein TfR in a Model of Intracerebral Hemorrhagic Stroke in Mice

We have previously demonstrated that the post-stroke administration of iron-free transferrin (apotransferrin, ATf) is beneficial in different models of ischemic stroke (IS) through the inhibition of the neuronal uptake of pro-oxidant iron. In the present study, we asked whether ATf is safe and also beneficial when given after the induction of intracerebral hemorrhage (ICH) in mice, and investigated the underlying mechanisms. We first compared the main iron actors in the brain of IS- or collagenase-induced ICH mice and then obtained insight into these iron-related proteins in ICH 72 h after the administration of ATf. The infarct size of the IS mice was double that of hemorrhage in ICH mice, but both groups showed similar body weight loss, edema, and increased ferritin and transferrin levels in the ipsilateral brain hemisphere. Although the administration of human ATf (hATf) to ICH mice did not alter the hemorrhage volume or levels of the classical ferroptosis GPX4/system xc- pathways, hATf induced better neurobehavioral performance, decreased 4-hydroxynonenal levels and those of the second-generation ferroptosis marker transferrin receptor (TfR), and restored the mRNA levels of the recently recognized cytosolic iron chaperone poly(RC) binding protein 2. In addition, hATf treatment lowered the ICH-induced increase in both endogenous mouse transferrin mRNA levels and the activation of caspase-2. In conclusion, hATf treatment provides neurobehavioral benefits post-ICH associated with the modulation of iron/oxidative players.