Novel aspects of vitamin C in epoetin response

Restless Legs Syndrome in Chronic Kidney Disease- a Systematic Review

Objectives

The objective of this review is to provide updated information on the epidemiology, correlating factors and treatment of chronic kidney disease associated restless legs syndrome (CKD-A-RLS) in both adult and pediatric population.

Materials and Methods

We have reviewed the Medline search and Google Scholar search up to May 2022, using key words restless legs syndrome, chronic kidney disease and hemodialysis and kidney transplant. The reviewed articles were studied for epidemiology, correlating factors, as well as pharmacologic and non-pharmacologic treatment options.

Results

Our search revealed 175 articles, 111 were clinical trials or cross- sectional studies and 64 were review articles. All 111 articles were retrieved and studied in detail. Of these, 105 focused on adults and 6 on children. A majority of studies on dialysis patients reported a prevalence between 15-30%, which is notably higher than prevalence of RLS in general population (5-10%). The correlation between presence of CKD-A-RLS with age, gender, abnormalities of hemogram, iron, ferritin, serum lipids, electrolytes and parathyroid hormones were also reviewed. The results were inconsistent and controversial. Limited studies have reported on the treatment of CKD-A-RLS. Non-pharmacological treatment focused on the effect(s) of exercise, acupuncture, massage with different oils and infra-red light whereas, pharmacologic treatment options include the effects of dopaminergic drugs, Alpha2-Delta ligands (gabapentin and pregabalin), vitamins E and C, and intravenous iron infusion.

Conclusion

This updated review showed that RLS is two to three times more common in patients with CKD compared to the general population. More patients with CKD-A-RLS demonstrated increased mortality, increased incidence of cardiovascular accident, depression, insomnia and impaired quality of life than those with CKD without RLS. Dopaminergic drugs such as levodopa, ropinirole, pramipexole and rotigotine as well as calcium channel blockers (gabapentin and pregabalin) are helpful for treatment of RLS. High quality studies with these agents are currently underway and hopefully confirm the efficacy and practicality of using these drugs in CKD-A-RLS. Some studies have shown that aerobic exercise and massage with lavender oil can improve symptoms of CKD-A- RLS suggesting that these measures can be useful as adjunct therapy.

Low-dose ferrous bisglycinate chelate supplementation in chronic kidney disease and hemodialysis patients

BACKGROUND

Provision of parenteral or oral iron supplementation can restore iron stores and maintain stable hemoglobin levels in chronic kidney disease (CKD) and hemodialysis (HD) patients. The route for oral or intravenous (IV) administration of iron depends on the acuity of anemia, costs, and patient tolerance. IV iron can restore iron stores rapidly but also carries higher risks for allergy and infection. Oral iron supplementation is limited by high gastrointestinal adverse effects.

METHODS

We conducted an open-label trial to study the efficiency of a film-coated iron supplementation tablet, which contains ferrous bisglycinate chelate, vitamin C, and folic acid, in CKD stage 3b to 4 and HD patients.

RESULTS

Twenty-seven HD patients and 20 CKD patients participated this study. After a 16-week intervention, low-dose ferrous bisglycinate chelate improved serum iron concentration (67.8 vs 87.2 mg/dL, p = 0.04) and transferrin saturation (24.7% vs 31.3%, p = 0.03) in stage 3 to 4 CKD patients, restored iron loss, and maintained stable hemoglobin levels in HD patients. No GI upset events were reported.

CONCLUSION

Ferrous bisglycinate chelate is a well-tolerated oral iron supplementation for CKD and HD patients.

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.

Iron sucrose and ferric carboxymaltose: no correlation between physicochemical stability and biological activity

Intravenous iron preparations, like iron sucrose (IS) and ferric carboxymaltose (FCM) differ in their physicochemical stability. Thus differences in storage and utilization can be expected and were investigated in a non-clinical study in liver parenchyma HepG2-cells and THP-1 macrophages as models for toxicological and pharmacological target cells. HepG2-cells incorporated significant amounts of IS, elevated the labile iron pool (LIP) and ferritin and stimulated iron release. HepG2-cells had lower basal cellular iron and ferritin content than THP-1 macrophages, which showed only marginal accumulation of IS and FCM. However, FCM increased the LIP up to twofold and significantly elevated ferritin within 24 h in HepG2-cells. IS and FCM were non-toxic for HepG2-cells and THP-1 macrophages were more sensitive to FCM compared to IS at all concentrations tested. In a cell-free environment redox-active iron was higher with IS than FCM. Biostability testing via assessment of direct transfer to serum transferrin did not reflect the chemical stability of the complexes (i.e., FCM > IS). Effect of vitamin C on mobilisation to transferrin was an increase with IS and interestingly a decrease with FCM. In conclusion, FCM has low bioavailability for liver parenchyma cells, therefore liver iron deposition is unlikely. Ascorbic acid reduces transferrin-chelatable iron from ferric carboxymaltose, thus effects on hepcidin expression should be investigated in clinical studies.

Vitamin C supplementation does not improve hypoxia-induced erythropoiesis

Hypoxia induces reactive oxygen species production. Supplements with antioxidant mixtures can compensate for the decline in red cell membrane stability following intermittent hypobaric hypoxia by decreasing protein and lipid oxidation. We aimed to determine whether supplementation with vitamin C is implicated in the regulation of erythropoiesis and in the oxygen-carrying capacity of the blood, and also whether antioxidant supplementation prevents the oxidative stress associated to intermittent hypoxia. Twenty-four male Wistar rats were randomly divided into four experimental groups: normoxia control (n=6), normoxia + vitamin C (n=6), hypoxia control (12 h pO(2) 12%/12 h pO(2) 21%) (n=6), and hypoxia + vitamin C (n=6). Animals were supplemented with vitamin C at a dose of 250 mg·kg(-1)·day(-1) for 21 days. Red blood cell count, hemoglobin, hematocrit, reticulocytes, erythropoietin, and oxidative stress parameters such as malondialdehyde and protein oxidation in plasma were analyzed at two different time points: basal sample (day zero) and final sample (day 21). Similar RBC, Hb, Hct, and Epo increments were observed in both hypoxic groups regardless of the vitamin C supplementation. There was no change on MDA levels after intermittent hypoxic exposure in any experimental group. However, we found an increase in plasma protein oxidation in both hypoxic groups. Vitamin C does not affect erythropoiesis and protein oxidation in rats submitted to intermittent hypoxic exposure.

The effect of intravenous ascorbic acid in hemodialysis patients with normoferritinemic anemia

Background

Hemodialysis (HD) patients with functional iron deficiency often develop resistance to recombinant human erythropoietin (rhEPO). Recent studies have shown that intravenous ascorbic acid (IVAA) administration could override rhEPO resistance in HD patients. This study was undertaken to test the effects of IVAA in HD patients with normoferritinemic functional iron deficiency accompanied by EPO-hyporesponsive anemia.

Methods

Fifty-eight HD patients with normoferritinemic anemia (between 100 and 500 μg/L) were included and divided into the control (N=25) and IVAA (N=33) groups. IVAA patients received 500 mg of IVAA with each dialysis session for 3 months and an additional 4-month follow-up after the end of the therapy.

Results

Twenty patients had a response to IVAA with a significant increase in hemoglobin level (Hgb>1.0 g/dL) and reduction of weekly rhEPO dosage compared with the control group after 3 months of treatment (P<0.05). Compared with non-responders, transferrin saturation (TSAT) was significantly decreased in the responders group (26±11 vs. 35±14%, P<0.05) on baseline data. There was a significant increase in serum iron and TSAT (baseline vs. 3 months, serum iron 57±22 vs. 108±22 μg/dL, TSAT 26±11 vs. 52±7%, P<0.05) and a decrease in serum ferritin (377±146 vs. 233±145 ng/mL, P<0.05) in the responders group (N=20), but no significant changes in the control and non-responders groups (N=13) at 3-month treatment.

Conclusion

IVAA can be a potent and effective adjuvant therapy for HD patients with rhEPO-resistant normoferritinemic anemia. In addition, IVAA can reduce the dosage of rhEPO for anemia correction.

Vitamin C affects the expression of hepcidin and erythropoietin receptor in HepG2 cells

BACKGROUNDS

Hepcidin modulates the de novo absorption of iron from the duodenum and the recycling of iron released from the reticuloendothelial system. In patients with chronic renal failure, administration of higher doses of erythropoietin (EPO) or vitamin C (Vit C) can correct the functional iron deficiency. While EPO-regulated hepcidin expression within hepatocytes has been recently identified, the relation between vitamin C with hepcidin expression is still uncertain.

METHODS

Hepcidin-producing HepG2 cells (a human liver carcinoma cell line) were cultured with 50- to 100-μg/mL vitamin C or 0.25- to 1.0-U/mL EPO for 6 hours. Reverse transcription polymerase chain reaction was performed for quantitative measurements of hepcidin, EPO, and EPO receptor (EPOR) expression.

RESULTS

EPO and vitamin C inhibited hepcidin expression within HepG2 cells; the EPO effect was dose dependent. EPO downregulated EPOR and vitamin C and upregulated EPOR. However, vitamin C had little effect on the expression of EPO.

CONCLUSIONS

EPO is capable of downregulating EPOR when it acts early. Vitamin C directly inhibits hepcidin expression within HepG2 cells. Moreover, by enhancing EPOR production, vitamin C may correct the downregulating EPOR from EPO, which has additional effect with EPO in treating anemia.