Introduction

Spirulina (Arthrospira), a filamentous, multicellular microalga, is a ubiquitous organism that was used as food in Mexico 400 years ago during the Aztec civilization. It is still being used as food by the Kanembu tribe in the Republic of Chad where it is sold as dried bread called "dihe."1 Although it was first isolated by Turpin in 1827 from the freshwater stream, species of Spirulina (Spirulina platensis, Spirulina maxima, Spirulina fusiformis) have been found in variety of environments: soil, sand, marshes, brackish water, sea water, and fresh water. This alga is a rich source of proteins, vitamins, amino acids, minerals, and other nutrients. It is considered as a valuable additional food source of some macro- and micronutrients including high quality protein, iron, gamma-linolenic fatty acid, carotenoids, vitamins B1, and B2. It is also used to derive additives in pharmaceuticals and foods. During Spirulina cultivation in open reservoirs and especially in closed photo bioreactors, its biomass may be additionally enriched with some trace elements such as iron, iodine, selenium, zinc, copper, manganese, and chromium in high bioavailable form.

In spite of the fact that the chemical composition of Spirulina varies widely when grown in open reservoirs, its efficiency in treatment and prophylaxis of different diseases is proved in a variety of experimental test systems and clinical trials. Over the past few years, however, it has been found to have many additional pharmacological properties. It has been experimentally proven, in vivo and in vitro, that it is effective to treat certain allergies, anemia, cancer, hepatotoxicity, viral and cardiovascular diseases, hyperglycemia, hyperlipidemia, immunodeficiency, and inflammatory processes, among others. Several of these activities are attributed to Spirulina itself or to some of its components including fatty acids omega-3 or omega-6, beta-carotene, alpha-tocopherol, phycocyanin, phenol compounds, and a recently isolated complex, Ca-Spirulan (Ca-SP)2

It is a well-known fact that reactive oxygen species (ROS) are involved in a diversity of important pathological processes in medicine including inflammation and neurodegenerative diseases, atherosclerosis, and cancer. There has been a global resurgence for alleviation of chronic diseases. The use of synthetic antioxidants has decreased because of their suspected activity as promoters of carcinogenesis as well as a general consumer rejection of synthetic food additives. The phenolic compounds in the plants are known to possess antioxidant activities in biological systems, however the antioxidant activities of algae are still being characterized. This chapter encompasses information on antioxidant effects of Spirulina and their implications in a multitude of oxidative pathologies.

MORPHOLOGY, BIOCHEMISTRY, AND CHEMICAL COMPOSITION OF SPIRULINA

Spirulina is a multicellular, filamentous cyanobacterium. Under the microscope, Spirulina appears as blue-green filaments composed of cylindrical cells arranged in unbranched, helicoidal trichomes (Figure 5.1). The filaments are motile, gliding along their axis, and heterocysts are absent. The helical shape of the trichome is characteristic of the genus but the helical parameters (i.e., pitch length and helix dimensions) vary with the species,3,4 or may be induced by changing the environmental conditions.5 Electron microscopy of ultra thin sections of S. platensis revealed that the cell wall is composed of possibly four layers. The most external or outer membrane layer (L-IV) is composed of material arranged linearly in parallel with the trichome axis and is considered analogous to that present in the cell wall of gram-negative bacteria. Layer III is possibly composed of protein fibrils wound helically around the trichomes, whereas the peptidoglycan-containing layer (L-II) folds

FIGURE 5.1 Morphology of Spirulina: (a) Optical microscopy of S. platensis. (b) Scanning electron micrograph of S. platensis. (c) Scanning electron micrograph of trichrome of S. platensis. (d) Scanning electron micrograph of nonaxenic of S. platensis. (Redrawn from Ciferri et al., 1983.)

towards the inside of the filament, giving rise, together with a putative fibrillar inner L-I, to the septum separating the cells. The most prominent cytoplasmic structure is the system of thylakoids originating from the plasmalemma but quite distinct from the well-evident mesosomes.4,6

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