**3. Antioxidants**

**2.4. Iron chelation therapy**

126 Pharmacology and Nutritional Intervention in the Treatment of Disease

Nowadays, DFO, DFP and deferasirox (DFX) are iron chelators of choice used for the treatment of β-thalassemia patients with iron overload. Their chemical structures are shown in Figure 4 [69-72]. DFO (Desferal®) is the first drug that was introduced in the 1970s to treat iron overload. The hexadentate chelator has an extremely high affinity for iron (III) (DFO : Fe = 1:1, Ka =1029) and a much lower affinity for other metal ions, such as zinc, calcium and magnesium [73]. DFO is poorly absorbed from the GI tract and rapidly excreted in the urine (plasma halflife of 5 - 10 minutes), it must be therefore administered parenterally; intravenously (*iv*), intramuscularly (*im*) or subcutaneously (*sc*) [8, 74]. However, the drug exhibits side effects including an elevated body iron burden, serious neurotoxicity and abnormalities of cartilage formation [75-78]. DFP (L1 or Ferriprox®), a synthetic bidentate chelator, has been the first orally active drug available for clinical use. A previous study demonstrated DFP decreased serum ferritin and liver iron concentrations in transfusion-dependent thalassemia patients [79]. Using magnetic resonance imaging (MRI) technique, DFP was able to reduce cardiac iron overload and improve cardiac function more effectively when compared to patients treated with DFO [80]. Recently, the Government Pharmaceutical Organization (GPO) of Thailand has manufactured and launched domestically produced DFP product (GPO-L-One®) for the treatment of Thai thalassemia patients with iron overload. This will make the in-house DFP cheaper and more available than the imported DFP. However, its side effects include nausea, vomiting, gastrointestinal disturbance, leucopenia and thrombocytopenia and zinc deficiency, as they are typically observed these side effects are being evaluated in the patients [81, 82]. DFX (ICL670 or Exjade®), a tridentate oral chelator with a high affinity and specificity for iron, has been clinically used for the treatment of transfusion-dependent thalassemia patients since 2003 [83-85]. Efficacy and safety of DFX uses have previously been evaluated and reported [83, 84, 86-88]. Common side effects of DFX are abdominal symptoms (usually diarrhea), skin

 **Pharmacology and Nutritional Intervention in the Treatment of Disease** 

and abnormalities of cartilage formation [75-78]. DFP (L1 or Ferriprox), a synthetic bidentate chelator, has been the first orally active drug available for clinical use. A previous study demonstrated DFP decreased serum ferritin and liver iron concentrations in transfusion-dependent thalassemia patients [79]. Using magnetic resonance imaging (MRI) technique, DFP was able to reduce cardiac iron overload and improve cardiac function more effectively when compared to patients treated with DFO [80]. Recently, the Government Pharmaceutical Organization (GPO) of Thailand has manufactured and launched

patients with iron overload. This will make the in-house DFP cheaper and more available than the imported DFP. However, its side effects include nausea, vomiting, gastrointestinal disturbance, leucopenia and thrombocytopenia and zinc deficiency, as they are typically observed these side effects are being evaluated in the patients [81, 82]. DFX (ICL670 or Exjade), a tridentate oral chelator with a high affinity and specificity for iron, has been clinically used for the treatment of transfusion-dependent thalassemia patients since 2003 [83-85]. Efficacy and safety of DFX uses have previously been evaluated and reported [83, 84, 86-88]. Common side effects of DFX are abdominal symptoms (usually diarrhea), skin

exanthems, elevated serum creatinine levels and renal tubular dysfunction [70].

) for the treatment of Thai thalassemia

12

**Figure 4** Chemical structures of DFO, DFP and DFX (Redrawn with modification from [89])

In the medical regimen, DFO must be subcutaneously infused in -thalassemia patients for extensive periods in order to achieve a negative iron balance, ranging from 8 to 12 hours, five to seven times per week, and at a daily dosage of 20 to 60 mg/kg body weight [72]. The patients experienced pain and swelling at the injection site, cumulatively leading to poor patient compliance [89, 90]. DFO chelation along with DFP or DFX has been designed to improve the efficacy and to diminish the adverse effects in the treated patients [91, 92]. Ideally, the iron chelator should be orally active, cheap and highly specific for iron, but not for other metal ions, and should freely penetrate into the target tissues, so as to get the

exanthems, elevated serum creatinine levels and renal tubular dysfunction [70].

**Figure 4.** Chemical structures of DFO, DFP and DFX (Redrawn with modification from [89])

Deferiprone Deferasirox

Deferrioxamine B mesylate

domestically produced DFP product (GPO-L-One®

Antioxidants can be defined as compounds that inhibit or delay, but do not completely prevent oxidation. There are two basic categories of antioxidants, namely synthetic and natural antioxidants.

#### **3.1. Synthetic antioxidants**

Mostly, the synthetic antioxidants that are widely used are phenolic compounds; for example, butylated hydroxyanisole, butylated hydroxytoluene, tertiary-butylhydroquinone and gallic acid (GA) derivatives.

#### **3.2. Natural antioxidants**

Natural antioxidants are found to be present in many sources such as plants, fungi, microor‐ ganism and even animal tissues. Phenolic compounds are also the majority group of natural antioxidants. The three important groups of antioxidant are tocopherols, flavonoids and phenolic acid. Natural antioxidants have been widely used in complementary and alternative medicines; in comparison, the synthetic antioxidants have reported signs of toxicological evidence and caution should be imposed in their use. Most importantly, some natural antioxidants are more potent, efficiency and safer than synthetic antioxidants.

**4. Potential antioxidants for use in thalassemias**

1) Inhibition of NAD(P)H oxidase activity:

and disrupts active NOX complex [100].

stricting peptide angiotensin II [102].

[103].

iron stores [104].

renal changes.

bioavailability in rat blood vessels [106].

Oxidative stress is not only a simple imbalance between the production and scavenging of ROS, but also a dysfunction of the enzymes involved in ROS production. Dysfunction of NOX, uncoupling endothelial nitric oxide synthase (eNOS), activation of xanthine oxidase (XO) and dysfunction of the mitochondria are underlying signs of oxidative stress; therefore, NOX is one of important therapeutic targets [99]. Pharmacological agents and approaches, as shown in Figure 5, can be implemented to relieve oxidative stress by the following mechanisms.

Antioxidants as Complementary Medication in Thalassemia

http://dx.doi.org/10.5772/57372

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1.1) Apocynin (methoxy-substituted catechol) is a natural compound that has a structure related to vanillin and exhibits anti-inflammatory activity, blocks an assembly of p47*phox* onto membrane complex, decreases production of superoxide, enhances production of nitric oxide

1.2) Chimeric peptides, such as polyethylene glycol-superoxide and NOX inhibitory peptide (gp91dstat), can inhibit association of p47*phox* with gp91*phox* [101] and synthesis of Angiotensin converting enzyme II (ACE-II) a dipeptidyl carboxy-peptidase that generates the vasocon‐

1.3) Compound S17834 (e.g. benzo(b)pyran-4-one) inhibits NOX activity and superoxide radical production and attenuates atherosclerotic lesions in apolipoprotein-E-deficient mice

1.4) Statins (e.g. simvastatin) are hydroxymethylglutaryl CoA (HMG CoA) reductase inhibitor hypocholesterolemic drugs that can prevent production of hydrogen peroxide and superoxide radicals, interfere with the renin-angiotensin-aldosterone system, and inhibit NOX activation and expression [99]. Currently, Zacharski and colleagues have demonstrat‐ ed that statins increased HDL/LDL ratios and reduced serum ferritin levels in subjects with advanced peripheral arterial disease. The results imply that statins may improve cardiovas‐ cular disease (CVD) outcomes, possibly by countering the pro-inflammatory effects of excess

1.5) ACE-II inhibitors (e.g. captopril, enalapril and quinapril) may act as antioxidants and down-regulate the vascular NOX system. Angiotensin II, through Angiotensin I (AT1) receptor activation, can induce vasoconstriction, cell growth, actions of pro-inflammatory cytokines and profibrogenic agents, and the production of vascular ROS, such as superoxide radicals [105]. Hence, the ACE-II inhibitors would lower ROS production and prevent vascular and

1.6) AT1 receptor antagonists (e.g. candesartan, losartan and irbesartan) reduce the expression of NOX enzyme components, resulting in lower superoxide levels and increased nitric oxide

1.7) Other blockers including calcium channel blocker (e.g. amlodipine, nifedipine and dihydropyridine), β-blocker (e.g. metoprolol, propranolol and nebivolol) and α-receptor blocker (e.g. doxazosin) can inhibit or interfere with functions of NOX activity [106, 107].


**Table 1.** Advantage and disadvantage of natural and synthetic antioxidants.

Advantages and disadvantages of the antioxidants are mentioned in Table 1. Most natural antioxidants are obtained in the diet from natural sources, especially from food of plant origin. Vegetables, fruits, and other foodstuffs are the best sources of these natural antioxidants. These antioxidants include vitamin C, vitamin E, carotenoids and polyphenol compounds. Antiox‐ idants that are derived from natural sources are preferred by consumers. This is due to concerns over the toxic and carcinogenic effects of the synthetic antioxidants. Phenolic compounds include a large class of phytochemicals with interesting biological properties. Recently, the roles of these natural compounds in counteracting the negative effects of ROS/RNS and maintaining the redox homeostasis of biological fluids have been reported. Commonly, antioxidants can neutralize potentially harmful ROS in the cells before they induce lipid and proteins oxidation. Antioxidants from plants are believed to be useful in preventing aging, atherosclerosis, cancer, peptic ulcer, liver diseases and other degenerative pathologies, such as cancer, diabetes, Alzheimer's and Parkinson's diseases.

Antioxidants are any substances that significantly delay or inhibit oxidation of the oxidized substrate. These can greatly reduce the adverse damage to oxidants by crumbling or scaveng‐ ing free radicals before they react with biological targets such as biomolecules, subcellular organelles, cells and tissues. The defense systems against the damage induced by ROS/reactive nitrogen species (RNS) fall into three categories: 1) preventive antioxidants that suppress free radical formation, 2) radical-scavenging antioxidants that inhibit initiation of chain reactions and intercept chain propagation and repair processes, and 3) adaptation to generate and transfer appropriate antioxidant enzymes. The hydrophilic antioxidants include vitamin C, uric acid, bilirubin, albumin, and the lipophilic antioxidants include vitamin E, ubiquinol and carotenoids. The radicals-scavenging antioxidant is described as a primary antioxidant, such as flavonoids and vitamin E (α-tocopherol), and the others that do not involve direct scavenge radical are secondary antioxidants.
