**a. Docosahexaenoic acid (DHA)**

involved in the production of pro-oxidants leading to apoptosis and tissular damage. Con‐ versely, the production of immunosuppressive cytokine IL-10 with anti-inflammatory

Thus, the severe and recurrent respiratory inflammation ultimately leads to excessive activated neutrophils and macrophages, which contribute to the generation of free radicals. Further‐ more, defects in the Cystic Fibrosis Transmembrane Regulator (CFTR) can directly affect transport and glutathione homeostasis, while maldigestion and malabsorption related to exocrine pancreatic insufficiency impair the absorption of fat-soluble vitamins and antioxi‐ dants. It has been suggested that the chloride channel CFTR also regulates glutathione, disturbing the balance between pro- and anti-oxidants and promoting oxidative stress, which may play an important role in Cystic Fibrosis Related Diabetes, a serious complication

Although the cause of CF is well established, the pathogenesis of this progressive multisyste‐ mic disease is not yet fully understood. In fact, the broad spectrum of phenotypes and severity in CF patients that carry the same combination of mutations suggests additional environmental

The CFTR dysfunction in the pancreas causes exocrine pancreatic insufficiency in almost 90% of patients with CF. This leads to fat malabsorption, which explains the difficulty to gain or at least maintain weight, and the high incidence of fat-soluble-vitamins and antioxidant (vita‐ mins A, E, and D and carotenoids) deficiency, and also essential-fatty-acids deficiency. Obviously, the reduced availability of dietary antioxidants may further increase oxidative stress in CF patients, which apparently plays an important role in multiorgan pathophysiology

Consequently, the products of lipid peroxidation, which are markers of oxidative stress, have been detected in exhaled breath condensate, as well as in blood and urine of CF patients. Thus products of lipid peroxidation are unstable molecules that can reach distant sites to exert various effects, including activation of the fibroblast cells in the presence of inflammation,

Nutrition plays an essential role in the survival and quality of life of CF patients. CF patients have high caloric requirements due to an increased resting energy expenditure (REE), bacterial infection, and malabsorption. REE is higher in CF patients with a more severe phenotype. Lung function and nutritional status are closely correlated, and the severe weight loss can lead to a decrease in lean body mass, with consequences for respiratory muscles. There is a significant correlation between growth retardation and the severity of pulmonary involvement [4]. Recently, Yen et al. found that greater weight at age four years is associated with greater height, better pulmonary function, fewer complications of CF, and better survival through the age of 18 years. Furthermore, greater weight for age in the peripubertal period is associated, on

properties is reduced or even suppressed [1].

74 Cystic Fibrosis in the Light of New Research

which further increases oxidative stress [3].

**2. Management of oxidative stress in cystic fibrosis**

or genetic factors.

of CF.

associated with a dramatic increase in morbidity and mortality [2].

Essential fatty acid (EFA) imbalance has been identified in CF patients and is characterized by a decrease in docosahexaenoic acid (DHA) and linoleic acid and an increase in arachidonic acid (AA) [7]. These characteristics were mainly attributed to intestinal malabsorption due to exocrine pancreatic insufficiency. In the last few years, new mechanisms have been proposed, such as intensification of the b-oxidation of polyunsaturated fatty acids (PUFAs), inadequate dietary EFA consumption, the possibility of an intrinsically defective EFA metabolism in CF epithelial cells, an increase in the production of proinflammatory eicosanoids, a rise in the peroxidation of PUFAs, and finally an impairment of desaturases or hepatic lipase activity [8].

It has been observed that long-term intake of the daily mixtures of fatty acids (eicosapentae‐ noic, docosahexaenoic, linoleic and γ-linolenic acid) at a low dose has a positive effect on lung function and inflammation in adult CF patients. The total number of exacerbations after a year of supplementation was reduced, while the lean-body-mass and lung-function parameters measured by spirometry were increased. In addition, supplementation led to improved parameters of oxidation, inflammation (IgG and IgM) and other clinical parameters [9]. 8 isoprostane, a free-radical product of lipid peroxidation which is a consequence of oxidative stress, appears to be a prognostic factor in deterioration of lung function in a short time in patients infected with *Burkholderia cenocepacia*. The measured concentration of 8-isoprostane in exhaled breath condensate of 24 patients did not show any significant relationship with the clinical parameters during a one- and three-year study [10].

Forty-three CF patients were enrolled in a randomized double-blind placebo-controlled study with three fatty-acid blends containing mainly n-3 or n-6 FA, or saturated fatty acid acting as placebo [11]. After three months, in the omega-3 fatty-acid-supplemented group, a significant decrease in the inflammatory markers, erythrocyte sedimentation rate and IL-8 was reported. Another, longer-term study (17 participants) demonstrated a significant increase in essentialfatty-acid content in neutrophil membranes and a significant decrease in the leukotriene B4 to leukotriene B5 ratio in participants taking omega-3 supplements compared to the placebo [12].

### **b. Fat-soluble vitamins**

Supplementation of CF patients with vitamin E and β-carotene has been effective in preventing oxidative lung damage [13], as seen by a decrease in lipid peroxidation products. It is believed that these antioxidants have an important role in maintaining or restoring essential-fatty-acid status by protecting polyunsaturated fatty acid from oxidative degradation, as their supple‐ mentation augments levels of plasma polyunsaturated fatty acid.

### Carotenoids

Levels of plasma carotenoids such as β-carotene, β-cryptoxanthin, and total lycopene are significantly lowered in CF patients and this has been associated with higher susceptibility to lipid peroxidation. Rust et al. [14] examined the effect of long-term oral β-carotene supple‐ mentation in patients with CF. Patients of the CF supplementation group received 1 mg βcarotene/kg body weight/day (maximally 50 mg β-carotene/day). During high-dose treatment, a significant decrease in the MDA level and a correction of total antioxidative capacity was observed.

Renner et al. reported distinct clinical benefits from high-dose (1 mg/kg body weight/ day, maximum 50 mg/day) supplements. Their patients required significantly fewer antibiotics during the phase of high-dose β-carotene supplementation and showed a decrease in pulmo‐ nary exacerbations [15]. Lepage et al. reported that the two-month supplementation of CF patients with 4.42 mg β-carotene, three times per day, led to the normalization of increased MDA level and increased plasma β-carotene from 0.08 ± 0.03 to 3.99 ± 0.92 μM [16].

At the same time, toxicity issues have been raised for supplementation with water- miscible vitamin A formulations in CF patients, which may increase serum retinol and possible risk of CF-associated liver and bone complications [17]. However, β-carotene supplementation seems to be safe since it does not affect serum concentrations of other carotenoides and retinol [14]. Recent studies have analysed the use and safety of a new CF polyvitamin (AquADEKs ®), which comprises almost 90% vitamin A in retinol form. Patients on AquADEKs ® maintained a high level of serum β-carotene, but serum retinol was not above the normal levels. β-carotene levels were associated with lung function and better nutritional status [18,19], while lipid peroxidation markers were not affected [20].

### Vitamin E (α-tocopherol)

α-tocopherol acts as a membrane antioxidant closely associated with polyunsaturated fatty acids. Vitamin E's antioxidative properties might be helpful in reducing the negative effects of free radicals. Current recommended supplementation of vitamin E in CF patients only includes α-tocopherol. Supplementation with high levels of α-tocopherol alone may result in further imbalances in CF patients: such supplementation has been shown to deplete γtocopherol in the blood and tissues [21]. Papas et al. [16] evaluated vitamin E supplementation with mixed tocopherols. The increase in the blood of levels of γ-tocopherol may be particularly important for CF patients due to its function as a scavenger of reactive nitrogen species and its synergistic effects with α-tocopherol [22]. Cystic fibrosis is characterized by neutrophildominated airway inflammation. Activated neutrophils release oxidants, proteases, and cytokines, further sustaining and increasing the inflammatory response and causing direct injury to the lungs. Improved antioxidant capacity with γ-tocopherol, especially if present in the lungs, could potentially decrease oxidant-mediated damage and limit the cytokinemediated neutrophil recruitment. It has also been reported that reduced serum levels of vitamin E are associated with an increased rate of pulmonary exacerbations in CF [23].

### **c. Other vitamins and micronutrients**
