4. Effects of vitamin E in hemodialysis patients


A schematic representation of mechanisms leading to these effects of vitamin E in hemodialysis patients is displayed in Figure 2.

### 4.1. Antioxidant agent

Increased reactive oxygen species (ROS) production was observed in hemodialysis patients, in response to inflammation and extracorporeal membranes. Markers of lipid peroxidation are increased in these patients, while catalase and superoxide dismutase activity are decreased.

5-lipoxygenase branch of the arachidonate cascade is only responsible for membrane peroxidation, oxidative stress, and apoptosis of leucocytes in hemodialysis patients.

Figure 2. Effects of vitamin E on hemodialysis patients.

these patients because of its increased phosphorus and/or potassium content. Table 1 displays vitamin E containing foods which are allowed (A), allowed with restricted portions size (ARP),

Vitamin E is a lipophilic vitamin. Hemodialysis membranes remove only hydrophilic substances, so that alpha-tocopherol cannot be cleared by hemodialysis. It should be unlikely that vitamin E levels should be low in these patients as long as the intake is adequate, but abnor-

Tocopherol is metabolized to carboxyethyl-hydroxychromans (CEHC), which are watersoluble compounds excreted by the kidneys. These metabolites accumulate in uremic patients, but as they are water soluble, they might be removed by dialysis membranes also. This could be an explanation for the results of a study from USA that found that even though CEHC levels increased after 30 days of alpha-tocopherol supplementation, they did not increase any

A reduction of vitamin E in cellular membranes has been noted in HD patients, suggesting that a decreased uptake of alpha-tocopherol by different tissues is happening, but the mechanism is not known. Some studies showed a disproportion between plasma tocopherol and lipids, as well as a low level of gamma-tocopherol and CEHC accumulation in patients undergoing

A schematic representation of mechanisms leading to these effects of vitamin E in hemodialy-

Increased reactive oxygen species (ROS) production was observed in hemodialysis patients, in response to inflammation and extracorporeal membranes. Markers of lipid peroxidation are increased in these patients, while catalase and superoxide dismutase activity are decreased.

5-lipoxygenase branch of the arachidonate cascade is only responsible for membrane peroxi-

dation, oxidative stress, and apoptosis of leucocytes in hemodialysis patients.

or not allowed (NA) in patients undergoing chronic hemodialysis [4–6].

malities in absorption and metabolism of alpha-tocopherol have been reported.

3.2. Metabolism and clearance

34 Vitamin E in Health and Disease

more with further treatment [4, 7].

4. Effects of vitamin E in hemodialysis patients

chronic hemodialysis.

• antioxidant agent • antiatherosclerotic

• hypolipidemic

4.1. Antioxidant agent

• ameliorates recurrent muscle cramps

• reduces erythropoietin doses

sis patients is displayed in Figure 2.

Vitamin E might directly inhibit 5-lipoxygenase in peripheral blood monocytes and partially control the lipid peroxidation and oxidative stress [8, 9].

Early studies showed that vitamin E acts as a scavenger for ROS in hemodialysis patients. Other researchers found that gamma-tocopherol is a detoxifier of peroxynitrile radicals. More recent in vitro studies found that vitamin E-coated dialysis membranes reduce intracellular ROS in monocytes and maintain normal activity of Cu/Zn superoxide dismutase [4, 10–12].

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide (NO) synthase and it is increased in hemodialysis patients. Vitamin E acts as an inhibitor of ADMA and increases the activity of NO synthase [13, 14].

Pertosa et al. demonstrated that vitamin E-coated dialysis membranes reduce activation of Jun N-terminal kinase [15].
