GB2460056A - Compositions comprising omega-6 fatty acids for use in treating schistosomiasis - Google Patents

Abstract

A composition comprising an omega-6 unsaturated fatty acid for use in the treatment of schistosomiasis (also known as bilharzias, bilharziosis, or snail fever) is disclosed. The omega-6 unsaturated fatty acid is preferably arachidonic acid. The composition may further comprise an omega-3 unsaturated fatty acid such as docosahexaenoic acid. Methods of treatment using the aforementioned compositions are also claimed, along with a pharmaceutical composition comprising an omega-6 unsaturated fatty acid and an omega-3 unsaturated fatty acid.

Description

COMPOSITIONS AND METHODS FOR THE PREVENTION AND

TREATMENT OF SCHISTOSOMIASIS

The invention relates to novel prophylactic and therapeutic compositions for the prevention and treatment of schistosorniasis mansoni and haematobium and to related methods of prophylaxis and therapy.

Schistosomiasis (also known as bilharzia, bilharziosis or snail fever) is a parasitic disease caused by several species of fluke of the genus Schistosoma. It is most commonly found in Asia, Africa and South America, especially in areas with water that is contaminated with freshwater snails which may carry the parasite. Schistosomiasis is considered the second most important parasitic infection after malaria in terms of public health and economic impact, affecting 207 million people in the developing world, with 779 million, mostly children, at risk of the infection [1]. Schistosomiasis is caused by the platyhelminth worms of the genus Schistosoma, trematodes that live in the bloodstream of humans and animals. Schistosomes have a typical trematode vertebrate-invertebrate I ifecycle. Three species (Schistosoma mansoni, S. haematobium and S. japonicum) account for the majority of human infections. Free-swimming larvae (cercariae) break out of infected snail tissues into the water, swimming actively until dying or penetrating the unbroken skin of humans or animals, the definitive host, where they change into schistosomula. During the first 24 hr after infection, nearly 90% of S. mansoni and S. haematobium schistosomula are present only in the blood-free, lymph-free epidermis. The majority of schistosomula are found in the dermis only after 48 hr, and they appear to reach the dermal vessels around 72 hr after infection. Once in the blood capillaries, the schistosomula are carried passively by the blood flow until reaching the right heart and then the lungs. Depending on the species, schistosomula stay inside the pulmonary capillaries from 3 to 16 days, where they change into much longer and slender organisms, a shape that enables them to traverse the thin pulmonary capillaries to the left heart and the systemic circulation.

Following this period, the larvae make their way to the liver via the splanchnic vasculature. Upon reaching the liver, schistosomula start feeding and growing by active cell division. Once they reach maturity, between 28-35 days post-infection, the worms start pairing. The paired adults migrate out of the liver, with the male carrying the female, to where they will finally reside at the mesenteric veins (S. mansoni), or at the pelvic venous plexus and veins around the bladder (S. haematobium). Eggs deposited daily in massive numbers must traverse the walls of the blood venules to enter the lumen of the intestine or bladder, and are then excreted with the faeces or urine. The morbidity associated with schistosomiasis results from the immunologic io reactions to egg-derived antigens, as well as the mechanical and toxic irritation caused by eggs trapped in the wall of blood vessels. Some of the more common pathological changes seen in chronic schistosomiasis infections include bleeding into the intestine or urinary system, liver and spleen enlargement and periportal fibrosis. A connection between the chronic urinary form of schistosomiasis and bladder cancer is suspected [2,3].

Since the 1970's, developments in the field of chemotherapy have changed the ways of schistosomiasis control from reducing transmission by targeting the intermediate snail host, to reducing morbidity of the definitive host. Since the beginning of the 20th century, many schistosomicidal drugs have been tried and used without encouraging results until metrifonate (effective against S. haematobium) and oxamniquine (effective against S. mansoni) were introduced in the 1970's. When praziquantel was introduced soon afterwards, it immediately proved much superior to any other schistosomicidal drug and quickly became the drug of choice in most endemic areas. Although oxamniquine is still being used in South America where S. mansoni is widely endemic, metrifonate has been removed from the World Health Organization (WHO) list of essential drugs [4].

Praziquantel (PZQ) is an isoquinoline-pyrazine derivative, which is highly effective against larval and adult worms but less effective against juvenile parasites. Use of PZQ as a chemotherapeutic agent may be the most cost-effective short term method of reducing prevalence and intensity of all species of human schistosomiasis. However, mass treatment campaigns using PZQ have proved expensive to maintain and insufficient for the elimination of morbidity as a public health problem. This is due to the difficulty in treating all infected individuals, and more importantly, those people who have been chemotherapeutically cured may rapidly become re-infected, as infected snails and cercariae will still be present in their water supplies, and costly re-treatment campaigns must be repeated. Additionally, evidence of emerging drug resistance and a low efficacy of PZQ have been reported in Egypt and Senegal [5]. Moreover, the possibility that PZQ elicits polymerization of host actin cannot be entirely precluded [6,7].

io In view of the foregoing, it is imperative to develop effective new drugs for treatment and also prevention of schistosome infection. The present invention fulfils this objective by providing a therapeutic and prophylactic composition comprising arachidonic acid.

Developing and adult schistosomes are covered by the tegument, a 2-4 pm thick syncytium. The innermost membrane of the tegument is a conventional membrane (the basal membrane), whereas the outer membrane on the syncytium is trilaminate in cercariae. By about three hours after penetration, the trilaminate outer membrane of the cercariae is gradually replaced by a unique heptalaminate membrane, widely believed to provide protection against elements of the host immune system. Notably, the surface membrane at developing and adult schistosomes/host interface consists of two tightly apposed bilayers, the inner and outer bilayers, each of which is composed of inner and outer leaflets [8].

As with conventional plasma membranes, proteins are embedded in schistosome outer and inner lipid bilayers among phosphoglycerides, cholesterol and sphingomyelin molecules [9]. In contrast to conventional plasma membranes, proteins in the schistosome outer lipid bilayer are concealed, hidden, and totally inaccessible to host antibodies providing an effective immune evasion mechanism.

The present inventors have previously suggested that schistosome antigenic molecules are concealed by confinement in lipid-rich sites of the outer membrane and have shown that this can be overcome in vitro by incubating schistosomula in corn oil, whereby sequestered antigenic molecules become exposed [10]. However, surmounting the schistosome immune evasion mechanism in vivo, under natural conditions, remains difficult.

Treatment of ex vivo lung-stage schistosomula with methyl-n-cyclodextrin (MBCD), a highly specific cholesterol-binding ligand, led to considerable binding of specific antibodies to the outer membrane surface [11], supporting the hypothesis that cholesterol contributes to the restriction of divalent antibody binding by keeping outer membrane lipid in an immobile rigid state. Treatment of S. mansoni larvae with MBCD elicited cholesterol depletion which was accompanied by an increase in specific antibody binding in the indirect membrane immunofluorescence test (IF), supporting a role for cholesterol in sequestration of surface membrane antigens of S. mansoni lung-stage schistosomula [12]. However, despite almost complete depletion of cholesterol from the outer membrane of S. haematobium larvae by MBCD, no increase in specific antibody binding in IF was evident, implying that cholesterol is not responsible for masking surface membrane antigens of S. haematobium lung-stage larvae.

The exposure of otherwise masked apical membrane antigens in S. mansoni lung-stage larvae by treatment with corn oil, reported in [10], has been attributed to unsaturated fatty acids (FA) [13]. However, unsaturated FA did not appear to induce exposure of schistosomular surface membrane antigens via extraction of surface membrane cholesterol as previously suggested. Worm recovery in infected mice was affected by the unsaturated FA content of their diet [13], leading the authors to propose a role for FA in the natural attrition of larvae in vivo. One hypothesis put forward in [13-15] was that unsaturated FA might elicit larval surface membrane antigen exposure via their ability to stimulate tegument-associated neutral sphingomyelinase (nSMase), documented in [16-19]. However, it was acknowledged that unsaturated FA interact with several plasma membrane-associated proteins beside nSMase so that the molecular basis for the action of unsaturated FA remains unproven. Furthermore, there is no information as yet regarding the effect of unsaturated FA on antigen exposure on the surface membranes of adult S. mansoni or S. haematobium worms.

It has subsequently been proposed that equilibrium in sphingomyelin breakdown and biosynthesis may be the mechanism by which lung-stage S schistosomula expose proteins at the host-parasite interface to nutrient, but not to antibody [14]. However, there has not yet been any demonstration that nSMase activation-mediated breakdown of sphingomyelin in the outer membranes of developing and adult schistosomes will lead to their attrition.

The present invention arises from the inventors' finding that arachidonic acid (AA) kills lung-stage schistosomula and adult schistosomes in vitro and produces highly significant reduction in worm burden in infected mice, when given orally.

Accordingly, the invention provides the use of a composition comprising one or more omega-6 (w-6) unsaturated fatty acids in the is prevention or treatment of schistosomiasis. An exemplary omega-6 unsaturated fatty acid for use in a composition according to the invention is arachidonic acid.

Arachidonic acid (AA) is an omega-6 fatty acid: 20:4(w-6). It is a carboxylic acid with a 20-carbon chain and four cis double bonds; the first double bond is located at the sixth carbon from the omega end. It is also termed all-cis 5,8,11,14-eicosatetraenoic acid. The chemical structure of AA is represented below: w H6' Arachidonic acid is a polyunsaturated fatty acid that is present in the phospholipids (especially phosphatidylethanolamine, phosphatidylcholine and phosphatidylinositides) of membranes of the body's cells, and is abundant in the brain. It is a precursor in the production of eicosanoids: the prostaglandins, thromboxanes, prostacycline and the leukotrienes (through enzymes including cyclooxygenase, lipoxygenase and peroxidase).

The four cis double bonds of AA are the source of its flexibility, keeping the pure fatty acid liquid, even at sub-zero temperatures, and helping to give mammalian cell membranes their correct fluidity at physiological temperatures. The double bonds are also the key to the propensity of arachidonic acid to react with molecular oxygen. This can happen nonenzymatically, contributing to oxidative stress, or through the actions of three types of oxygenase: cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 [20,21].

Proposing intake of exogenous AA could be met with awe, as AA may be metabolized to end products that produce pain and inflammation, namely the prostaglandins (COX pathway), which are mediators of the vascular phases of inflammation, are potent vasodilators, and increase vascular permeability; prostacycline (vasodilator and reduces platelet aggregation); thromboxane (increases vasoconstricton and platelet aggregation); and leukotrienes (LOX pathway) that are important mediators of inflammation.

Leukotrienes cause vasoconstriction, but increase microvascular permeability.

They are important mediators of bronchial asthma. They cause leukocyte adherence to the vascular endothelium and activate the leucocytes to secrete their enzymes. They contract smooth muscle, especially in the bronchi and blood vessels. A great concern is the fact that exogenous AA is acted upon by COX and LOX enzymes, many of which are located on the endoplasmic reticulum or nuclear membrane [20]. Accordingly, AA has not previously been considered for prevention or treatment of schistosomiasis or any other parasitic disease.

Nevertheless, the present inventors have embarked on use of AA for schistosomiasis therapy in the knowledge that AA is an essential constituent of membrane lipids, and is the base material used by the body to synthesize a key series of hormones referred to collectively as dienolic prostag land ins (PG) that include the prostaglandins PGE2 and PGF2a. Proper development of the brain, retina and other body tissues depends upon provision of AA either directly in the diet or through synthesis from linoleic acid (LA). Additionally, AA is an essential fatty acid, which is consumed in small amounts in our regular diets. It is found mainly in lean meat, egg yolks and some fish oils.

Tissue AA pools originate from the diet, and from hepatic and extrahepatic desaturation-elongation of dietary LA. In humans who ingest 0.2-0.3 g of AA and 10-20 g of LA per day on a Western diet the formation of AA from LA exceeds the dietary supply of AA [21]. Most evidence supports that ingestion of moderate amounts of AA is not disadvantageous. In a series of studies, humans ingested a diet containing 1.7 g of AA per day for 50 days, and were then extensively studied. DietaryAA at these levels nearly doubled AA levels in the plasma phospholipids and cholesteryl ester. AA mainly replaced LA, which was reduced by 20%. Some increases in AA in platelets, red blood cells, and tissue lipids were also found, but no significant increase in AA was seen in adipose tissue triglycerides and phospholipids. The plasma free fatty acids showed a small but statistically significant rise in the AA level. No harmful effects could be proven during the studies, although an increased production of eicosanoids was observed [21-23].

A possible association of AA with cancer, particularly prostate and colon cancer development, has been reported [24]. However, it is important to note that this is essentially a result of daily consumption of very large amounts of unsaturated fatty acids-containing food, or could be due to enhanced desaturase activity upon linoleic and linolenic acid [24].

In case possible inflammatory effects elicited by administration of AA remain a concern, it may be noted that ingestion of w-3 essential fatty acids, namely eicosapentaenoic acid (EPA) entirely protects from any inflammatory effect AA might elicit, by displacement, competitive inhibition and direct counteraction [25]. Docosahexaenoic acid (DHA) was reported to have an effect similar to EPA [26,27]. DHA is an omega-3 essential fatty acid, 22:6(w- 3). Chemically, DHA is a carboxylic acid with a 22-carbon chain and six cis double bonds; the first double bond is located at the third carbon from the omega end. It is also termed all-cis-docosa-4,7,10,13,16,19-hexaenoic acid.

Infant formulas containing AA (ARASCO�) and DHA have recently been produced (Martek Biosciences Corporation, Columbia, MD, USA). Using controlled fermentation conditions, Martek Biosciences obtains arachidonic acid (AA) from the soil fungus Mortierella alpina, and docosahexaenoic acid (DHA) from the non-photosynthetic marine micro-algae Crypthecodinium cohnii, products of proven entire safety [28].

Accordingly, the composition of the invention preferably further comprises one or more omega-3 (w-3) unsaturated fatty acids such as eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA). Preferably, the omega-3 unsaturated fatty acid is DHA. The omega-3 unsaturated fatty acid protects the patient from any possible undesired inflammatory effects elicited by the omega-6 unsaturated fatty acid.

Compositions comprising an omega-6 unsaturated fatty acid (e.g. AA) and, preferably, an omega-3 unsaturated fatty acid (e.g. DHA), as described herein, may conveniently be administered orally and are useful for the is prevention and treatment of schistosomiasis (e.g. schistosorniasis mansoni and haematobium).

The compositions described herein (i) protect hosts from developing disease following exposure to cercariae of Schistosoma sp. (eg. S. mansoni or S. haematobium), via attrition of migrating schistosomula, and (ii) treat infected hosts via killing of both male and female adult worms. As used herein, the term "attrition" means destruction, usually manifested as a reduction in the number of viable parasites.

Accordingly, the composition of the invention can be used prophylactically, to prevent the development of schistosomiasis in individuals who have been, or are at risk of being, exposed to cercariae, or therapeutically, to treat individuals with parasitologically confirmed infection.

For prophylactic use, the individuals (hosts or potential hosts) are treated (i.e. the composition is administered) prior to, or during the first weeks of, exposure. For therapeutic use, hosts are treated for 1 to 4 weeks until no eggs are detected in stool (or urine) by thorough analysis on 3 consecutive days. The distinction between prophylactic and therapeutic use is not hard and fast since it will not always be apparent whether an individual is infected.

However, because the composition of the invention is effective against both migrating schistosomula and adult worms (male and female), the same composition is effective for prevention and for treatment of schistosomiasis.

In a further aspect, the invention provides the use of a composition as described herein in the manufacture of a medicament for the treatment of sch istosom iasis.

In another aspect, the invention provides a method for the treatment and/or prevention of schistosomiasis which comprises the step of administering a composition as described herein.

io In yet another aspect, the invention provides a pharmaceutical composition comprising an omega-6 unsaturated fatty acid and, preferably, an omega-3 unsaturated fatty acid, and one or more pharmaceutically acceptable carriers, binders or excipients. Preferably, the pharmaceutical composition comprises arachidonic acid as the omega-6 unsaturated fatty acid and docosahexaenoic acid as the omega-3 unsaturated fatty acid. Preferably, the pharmaceutical preparation is in unit dosage form, such as tablets or capsules.

Preferred features of different aspects of the invention are as to each other mutatis mutandis.

The invention derives from the inventors' initial observation of the in vitro killing effect of 5-10 mM pure AA (Sigma) on lung-stage schistosomula and adult schistosomes, incubated in 50% fetal calf serum in RPMI medium to simulate the in vivo situation. The inventors then attempted to reach this concentration in vivo in BALB/c and C57BL/6 mice via a single oral ingestion of pure AA (Sigma) at 7 days (targeting the lung-stage larvae) or 35-40 days (targeting the adult worms) following infection with 100-150 infective cercariae of S. mansoni or S. haematobium. Highly significant reduction in worm burden was obtained in five consecutive experiments.

The inventors then proceeded to elevate the plasma AA concentration in BALB/c and C57BL/6 mice, this time via feeding mice with approximately 6.4 mg AA and 3.2 mg DHA/day in normal rodent food mixed at a ratio of 2:1 with Nestle� Good Start� Supreme DHA and ARA. In 6 independent experiments, comprising BALB/c or C57BL/6 mice, highly significant reduction in both male and particularly female worm counts was recorded in every trial.

Based on the above findings, work is underway to devise a formulation containing appropriate amounts of AA together with DHA, and begin preclinical studies in parasite-free and Schistosoma-infected volunteers, prior to marketing and widespread utilization.

The invention will now be illustrated by way of the following non-limiting

examples.

io Example 1: In vitro Findings Exposure of ex vivo lung stacie larvae of S. mansoni or S. haematobium to 10-20 pM AA in fetal calf serum (FCS)-free medium led to larval attrition within less than 60 mm of incubation at 37°C. Since our aim was to target larvae within the host, in vivo, 2 experiments were set up whereby larvae were incubated at 37°C in 100% FCS and exposed to 0, 0.6, 1.25, 2.5, 5.0 and 10.0 mM AA (Sigma), and examined for viability and contractility every 30 mm for a 6 hr observation period. For up to 2 hr, 1.0 mM and 5 mM AA were not lethal. However, with longer exposure time, concentrations> 1.25 mM led to attrition of all larvae. It was concluded that in vivo exposure of migrating larvae to 1.0-5.0 mM AA for 3-4 hr may well lead to significant reduction in worm survival and recovery.

A total of 4 experiments were set up using adult S. mansoni and S. haematobium worms incubated at 37°C in 50% FCS in RPMI-1 640 medium to approximate the in vivo situation, but exposed to 0, 1.0, 5, 10, and 20.0 mM AA. The results indicated, for the first time in the literature, that incubation of adult worms for 2 hr in the presence of 10.0 mM AA led to their attrition, S. haematobium being more sensitive than S. mansoni, and females more than males.

Based on this study, in vivo studies were conducted with the aim of provoking increase in experimental host plasma AA concentration to 10 mM, for 2 hr or more.

Examples 2-7: In vivo Studies Example 2: A single oral ingestion of pure AA during the parasite lung stage migration (approximate plasma concentration 12.0 mM) stage led to significant reduction in worm burden, pointing to AA anti-schistosomiasis prophylactic potential.

Pure AA: all cis 5,8,11,14-eicosatetraenoic acid; FW 304.47; density: 0.922 gm/mI; approximately 3.0 M (Sigma Chemical Co., catalogue number: A9673). Note: The average total blood volume of a mouse is about 77-80 mI/kg (0.077-0.080 mI/gm) [29], i.e., about 2.0 ml for a 25 gram mouse.

A total of 20 young female BALB/c mice were exposed to 140 14 cercariae of S. mansoni, and then distributed at random in 2 separate cages.

Cage # 1 (Control Group), 10 mice; Cage # 2 (LS targeting) 10 mice, each received on day 7 post-infection a single oral injection of 100 p1 Sunflower (Slight, Egypt) oil containing 10 p1 AA (Sigma, 3.0 M) (ca plasma concentration 12.0 mM AA). Worm burden was assessed 42 days after infection.

Table 1. Anti-schistosomiasis mansoni prophylactic potential of a single AA oral dose in BALB/c mice.

Mean� SD Control mice AA-treated mice P Percent (lung worm targeting) protection Totalwormburden 61�17 37�10 0.0020 39.3% Male worm burden 37 � 8 22 � 7 0.0009 40.5% Female woun burden 26 � 9 16 � 5 0.0050 38.4% Example 3. A single oral injection of pure AA, to reach 30 mM plasma concentration targeting the parasite adult stage led to significant decrease in worm and egg burden in BALB/c mice, pointing to AA anti-schistosomiasis therapeutic potential.

A total of 22 young female BALB/c mice were exposed to 127 8 cercariae of S. mansoni, and then distributed at random in 2 separate cages.

Cage # 1 (Control Group), 11 mice and Cage # 2 (adult worm targeting) 11 mice, each received on day 35 post-infection a single oral injection of 100 p1 Sunflower (Slight, Egypt) oil containing 20 p1 AA (Sigma) (ca plasma concentration 30.0 mM AA).

Table 2. Anti-schistosomiasis mansoni therapeutic potential of a single AA oral dose in BALB/c mice.

Mean � SD Control mice AA-treated mice P Percent (adult worm targeting) protection Totalworrnburden 58�19 36�7 0.007 37.9% Male wormburden 34�10 22�4 0.005 35.3% Female woun burden 25 � 10 14 � 4 0.0 18 41.6% Livereggburden 18150�5587 12000�4123 0.035 22.8% Small intestine egg burden 20777 � 6755 14166 � 5269 0.032 3 1.8% Example 4. A single oral injection of pure AA, to reach 30 mM plasma concentration, protects BALB/c mice infected with Schistosoma haematobium, via reducing worm, particularly female worm, burden.

A total of 22 young female BALB/c mice were exposed to 232 i-14 cercariae of S. haematobium, and then distributed at random in 2 separate cages. Cage # 1 (Control Group), 11 mice and Cage # 2 (adult worm targeting) 11 mice, each received on week 10 (day 70) post-infection a single oral injection of 100 p1 Sunflower (Slight, Egypt) oil containing 20 p1 AA (Sigma) (ca plasma concentration 30.0 mM AA). On day of perfusion, 2 weeks later, 7 control mice were moribund, and 4 dead, whereas all AA-treated mice were perfectly alive and healthy.

Table 3. Anti-schistosomiasis haematobium therapeutic potential of a single AA oral dose in BALB/c mice.

Mean � SD Control mice AA-treated mice P Percent (adult worm targeting) protection Totalwoimburden 16�3 11�7 0.0381 31.2% Male worm burden 9 � 3 7 � 4 NS Female worm burden 6 � 2 3 � 2 0.0003 50.0% Example 5. Feeding BALB/c mice with approximately 6 mg AAlmouse/day for 15 days at the beginning (targeting the parasite lung stage) or end (targeting the parasite adult stage) of a 42 day S. mansoni infection period, did not lead to the slightest harmful change in host survival, activity, plasma lipid concentrations, while was associated with a highly significant reduction in both male and female S. mansoni worms, pointing to the anti-schistosomiasis prophylactic and therapeutic potential of AA-enriched food.

AA-DHA/Milk. Nestle� Good Start� Supreme DHA and ARA (AA) is an ideal formula choice. DHA and ARA nutrients naturally found in breast milk that support babies' brain and eye development, levels of DHA and ARA are recommended by nutrition experts.

Good Start Supreme DHA and ARA DHA level + : 0.32% = 320 mg/i 00 g ARA level + : 0.64% = 640 mg/i 00 g Conventional rodent food was mixed at a ratio of 2:1 with AA-DHNMiIk, hereafter named AA food, and given to test mice ad libitum for the specified time period. Mice usually consume 3 gram food/mouse/day, i.e., approximately 1 gram AA-DHA/Milk = 6.4 mg AA and 3.2 mg DHNday. This means reaching plasma concentration of 10 mM, if the food is taken within a reasonable period of time, and not throughout the day as is inevitable in rodents.

A total of 24 BALB/c mice were exposed, via tail exposure, to 98.1 -- 9.5 cercariae of S. mansoni, and then distributed into 3 groups of 8 mice each. Control mice received normal Diet. Mice treated with AA and targeting the parasite lung stage were given AA food for the first 15 days (against early stages). Mice treated with AA and targeting the adult stage were given AA-food for the last 15 days of a total of 42 days infection.

Table 4. Anti-schistosomiasis mansoni prophylactic and therapeutic potential of feeding BALB/c mice AA-enriched food for a 15 days period.

Mean womi burden � SD Control mice AA-treated mice AA-treated mice (lung stage targeting) (adult worm targeting) Totalwormburden 21.0�4.1 9.6�4.7 8.8�5.9 P (2-tailed) 0.0002 0.0003 Percent Reduction 54.2% 5 8.0% Male wonn burden 11.0 � 2.2 5.6 � 2.4 5.5 � 3.2 P (2-tailed) 0.0003 0.0009 Percent Reduction 49.0% 50.0% Female worm burden 10.0 � 2.6 3.8 � 2.2 3.2 � 3.0 P (2-tailed) 0.000 1 0.0002 Percent Reduction 62.0% 68.0% Example 6. Feeding C57BL/6 mice with approximately 6 mg AAlmouse/day for 15 days at the beginning (targeting the parasite lung stage) or end (targeting the parasite adult stage) of a 42 day S. mansoni infection period, did not lead to the slightest harmful change in host survival, activity, plasma lipid concentrations, while was associated with a highly significant reduction in both male and female S. mansoni worms, pointing to the anti-schistosomiasis prophylactic and therapeutic potential of AA-enriched food.

A total of 30 C57BL/6 mice were exposed, via tail exposure, to 98.1 -- 9.5 cercariae of S. mansoni, and then distributed into 3 groups of 10 mice each. Control mice received normal Diet. Mice treated with AA and targeting the parasite lung stage were given AA food for the first 15 days (against early stages). Mice treated with AA and targeting the adult stage were given AA-food for the last 15 days of a total of 42 days infection.

Table 5. Anti-schistosomiasis mansoni prophylactic and therapeutic potential of feeding C57BL/6 mice AA-enriched food for a 15 days period.

Mean worm burden � SD Control mice AA-treated mice AA-treated mice (lung stage targeting) (adult woun targeting) Totalworrnburden 22.3 �9.5 12.7�5.1 8.1 �2.9 P(2-tailed) 0.011 0.001 Percent Reduction 43.0% 63.6% Male worm burden 13.3 � 5.5 7.0 � 3.2 4.6 � 2.5 P (2-tailed) 0.0057 0.00 12 Percent Reduction 47.3.0% 65.4.0% Femalewormburden 8.0�3.6 5.7 �2.8 3.3 � 1.1 P (2-tailed) NS 0.0022 Percent Reduction 28.7% 58.7% Example 7. Feeding C57BL/6 mice with approximately 6 mg AAlmouse/day for 3 weeks at the end (targeting the parasite adult stage) of a 70 day S. haematobium infection period, did not lead to the slightest harmful change in host survival, activity, plasma lipid concentrations, while was associated with a highly significant reduction in both male and female S. haematobium worms, pointing to the anti-schistosomiasis therapeutic potential of AA-enriched food.

A total of 20 C57BL/6 mice were exposed, via tail exposure, to 111 +10 cercariae of S. haematobium, and then distributed into 2 groups of 10 mice each. Control mice received normal Diet. Mice treated with AA and targeting the adult stage were given AA-food for the last 21 days of a total of 70 days infection.

Table 6. Anti-schistosomiasis haematobium therapeutic potential of feeding C57BL/6 mice AA-enriched food for a 3 week-period period.

Mean� SD Control mice AA-treated mice P Percent (adult worm targeting) protection Totalworrnburden 5.8�5.3 1.0�1.5 0.007 81.4% Male worm burden 4.0 � 3.6 0.4 � 0.8 0.002 89.9% Female worm burden 1.8 � 2.0 0.5 � 0.8 0.046 72.1% Example 8: Toxicity Studies It is of note to recall that we did not record the slightest mortality or decrease in viability, movement, feeding or any other change between AA-given and control mice in any one of the experiments described above.

Additionally, one and two weeks after treatment with AA-enriched formula, serum was obtained from test and control mice and assayed for levels of triglycerides, cholesterol, free fatty acids, liver and kidney enzymes activity, and antibody responses to schistosome antigens. No significant differences were recorded in any parameter between AA-and standard diet-.

fed mice, indicating entire lack of AA toxicity during the time of treatment.

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Claims (13)

1. CLAIMS1. Use of a composition comprising an omega-6 unsaturated fatty acid for the prevention or treatment of schistosomiasis.
2. 2. Use according to claim 1, in which the omega-6 unsaturated fatty acid is arachidonic acid.
3. 3. Use according to claim 1 or 2, in which the composition further io comprises an omega-3 unsaturated fatty acid.
4. 4. Use according to claim 3, in which the omega-3 unsaturated fatty acid is docosahexaenoic acid.
5. 5. Use according to any of claims 1 to 4, in which the composition is administered orally.
6. 6. Use according to any of claims 1 to 5, in which the schistosomiasis is schistosomiasis mansoni or schistosomiasis haematobium.
7. 7. Use according to any of claims 1 to 6, in which hosts are treated during the first weeks of exposure.
8. 8. Use according to any of claims 1 to 6, in which hosts with parasitologically confirmed infection are treated for a 1 to 4 week period until no eggs are detected in stool (or urine) by thorough analysis on 3 consecutive days.
9. 9. Use of a composition according to any of claims 1 to 4 in the manufacture of a medicament for the treatment of schistosomiasis.
10. 10. A method for the treatment and/or prevention of schistosomiasis which comprises the step of administering a composition according to any of claims 1 to 8.
11. 11. A pharmaceutical composition comprising an omega-6 unsaturated fatty acid and, preferably, an omega-3 unsaturated fatty acid, and one or more pharmaceutically acceptable carriers, binders or excipients.
12. 12. A pharmaceutical composition according to claim 11, comprising arachidonic acid and docosahexaenoic acid.
13. 13. A pharmaceutical composition according to claim 11 or claim 12 which is in unit dosage form such as tablet or capsule.