Linseed or flax (Linum usitatissimum) is a herbaceous annual plant of Lineaceae family. It is an important oilseed and fiber crop. The oil is edible and also due to its quick drying property is used for the preparation of paints, varnishes, printing ink, oil cloth, soap, patent leather and water proof fabrics. In the ayurvedic system of medicine, the seeds of linseed have been used in treatment of biliousness, backache, inflammations, ulcers, urinary discharges, eye troubles, leprosy and epilepsy. According to Unani system of medicine, seeds are mucilaginous, diuretic, aphrodisiac, galactagogue, emmenagogue, and useful in treatment of cough and kidney troubles. Bark and leaves are good for gonorrhoea. Oil from seeds removes biliousness. It is claimed to be useful in loss of appetite, internal wounds and ringworm [1]. Recent studies indicate that flaxseed is the major source of lignan. Phytoestrogens of the lignan type are widely distributed in plant-derived food items and are believed to protect against hormone-dependent cancer. The richest known dietary source of lignan is flaxseed or linseed. Flaxseed has been reported to contain glycosides of secoisolariciresinol as the major lignan, together with small amounts of matairesinol, isolariciresinol, and pinoresinol. Flaxseed is also a good source of alpha-linolenic acid which is an n-3 fatty acid.
Prasad (1999) in his study on rabbit claimed that secoisolariciresinol isolated from flaxseed reduce hypercholesterolemic atherosclerosis and that this effect was associated with a decrease in serum cholesterol, LDL-C, and lipid peroxidation product and an increase in HDL-C and antioxidant reserve [2]. Flaxseed has been demonstrated to inhibit human breast cancer growth and metastasis and down-regulated expression of insulin-like growth factor and epidermal growth factor receptor [3]. Another study on rat suggested that exposure to flaxseed or its purified lignan during suckling inhibits chemically induced mammary tumorigenesis [4]. Dietary supplementation of flaxseed was also found to inhibit the growth and development of prostate cancer in the transgenic adenocarcinoma mouse prostate model [5].
The study carried out in the Department of Zoology, University of Rajasthan, India demonstrated that oral administration of linseed oil for 20 days has not caused any toxic effect on mice. The values of GSH, GSSG, GSH-Px and Phospatase were significantly not different in oil treated group from normal group. The activities of antioxidant enzymes, GSH-Px and alkaline phosphatase were significantly inhibited following cyclophosphamide exposure. However, the levels of GSSG and acid phosphatase were augmented following drug administration. Linseed treatment lowered the blood GSH levels, as well as GSH-Px and alkaline phosphatase activities in comparison to non-treated group, statistically significant at p<0.001 level. The cyclophosphamide-caused increase in the acid phosphatase activity and GSSG level was significantly (p<0.001) prevented in linseed treated group. A profound decline in GSH/GSSG ratio was reported in cyclophosphamide-treated mice. However, linseed treated group showed near the normal level.
Cyclophosphamide is a commonly used chemotherapeutic drug and well-known mutagen and clastogen. It is an alkylating agent, producing the highly active carbonium ion, which reacts with the extremely electron-rich area of nucleic acids and proteins. Results obtained from this study indicate that the linseed oil renders protection against cyclophosphamide-induced oxidative stress. Oxidative stress refers to the cytotoxic consequence of reactive oxygen byproducts: superoxide anions and hydroxyl radicals which are generated as metabolites of normal and aberrant metabolic processes that utilize molecular oxygen. Oxidative stress cause devastating effect on the functional state of the membrane because it alters membrane fluidity, typically decreasing it and thereby allowing ions such as Ca++ to leak into the cell. Therefore, the preservation of cellular membrane integrity depends on protection or repair mechanism capable of neutralizing oxidative reactions. In present study the inhibition of cyclophosphamide induced depletion of GSH level in the linseed-treated animals suggests that linseed oil may scavenge the free radicals formed during oxidative stress. GSH, with its sulfhydryl group, functions in the maintenance of sulfhydryl groups of other molecules (especially proteins), as a catalyst for disulfide exchange reactions, and in the detoxification of foreign compounds, hydrogen peroxide and free radicals. When GSH acts as a reducing agent, its SH becomes oxidized and forms a disulfide link with other molecules of GSH. GSSG, in turn, can be reduced to GSH by the action of GSSG reductase, in a reaction using NADPH. NADPH is recycled by glucose-6 phosphate dehydrogenase via the pentose phosphate pathway, which is particularly important in red blood cells.
The GSSG/GSH ratio may be a sensitive indicator of oxidative stress. GSH-Px is also the major antioxidative enzyme, which decomposes H2O2 to H2O molecules. By doing so, it reduces the formation of hydroxyl radicals. In present study, the cyclophosphamide-induced inhibition of GSH-Px and decrease in GSH/GSSG ratio is reported in mice blood. However, these are maintained to near the normal level in linseed-pretreated mice.
Present study revealed an increase in serum acid phosphatase activity after cyclophosphamide administration. Acid phosphatase is localized in cellular lysosomes. An enhanced Golgi activity and peroxidation of lysosomal membranes due to cyclophosphamide possibly resulted in the efflux of the enzymes and hence an increase in acid phosphatase levels. In present study, linseed pretreated mice shows near the normal level of GSH and acid phosphatase. In addition, alkaline phosphates activity decreased in cyclophosphamide-treated mice. Alkaline phosphatase plays an important role in maintenance of cellular permeability and acts on monophosphoesters. Damage to cell membrane caused by cyclophosphamide may be the reason for reduced activity of alkaline phosphatase. Alkaline phosphatase activity is also protected significantly in linseed-pretreated mice.
The protection afforded by linseed oil might be due to the antioxidative action of its important constituents, the lignans. Flaxseed contains glycosides of secoisolariciresinol as the major lignan, together with small amounts of matairesinol, isolariciresinol, and pinoresinol. The lignan like secoisolariciresinol and pinoresinol are reported to have strong antioxidant nature [6].
Endoh et al (2002) who demonstrated that flaxseed extract inhibit the carbon tetrachloride -induced decrease in the level of reduced glutathione in rat liver [7]. They have also reported that pretreatment of flaxseed extract protect against carbon tetrachloride-induced elevation of DNA strand breaks in the liver cells.
The present finding that linseed ameliorates the depletion of GSH, GSH-Px and alkaline phosphatase activities and reduces the level of GSSG and acid phosphatase in mice make it a potential preventive agent against oxidative stress.

References
[1] Oudhia P. Alsi (Linum usitatissimum) as medicinal herb in Chhattisgarh, India. 2003;  http://www.celestine-india.com/pankajoudhia
[2] Prasad K. Reduction of serum cholesterol and hypercholesterolemic atherosclerosis in rabbits by secoisolariciresinol diglucoside isolated from flaxseed. Circulation 1999; 99:1355-62.
[3] Chen J, Stavro PM, Thompson LU. Dietary flaxseed inhibits human breast cancer growth and metastasis and downregulates expression of insulin-like growth factor and epidermal growth factor receptor. Nutr Cancer 2002;43:187-92.
[4] Chen J, Tan KP, Ward WE, Thompson LU.Exposure to flaxseed or its purified lignan during suckling inhibits chemically induced rat mammary tumorigenesis. Exp Biol Med 2003; 228: 951-8.
[5] Lin X, Gingrich JR, Bao W, Li J, Haroon ZA, Demark-Wahnefried W. Effect of flaxseed supplementation on prostatic carcinoma in transgenic mice. Urology. 2002; 60:919-24.
[6] Harper A, Kerr DJ, Gescher A, Chipman JK. Antioxidant effects of isoflavonoids and lignans, and protection against DNA oxidation. Free Radic Res 1999;31:149-60.
[7] Endoh D, Okui T, Ozawa S, Yamato O, Kon Y, Arikawa J, Hayashi M. Protective effect of a lignan-containing flaxseed extract against CCl(4)-induced hepatic injury. J Vet Med Sci 2002; 64:761-5