Sickle cell disease is a genetic, hereditary disease that attacks red blood cells and deforms them (Pliya, 1994). It is due to a point mutation of the gene coding for the synthesis of the β chain of hemoglobin. This results in the replacement of glutamic acid by valine (André and Marc, 1988). Abnormal hemoglobin (Hbs) deforms red blood cells that take the form  of  a  lunar  crescent  (sickle cell). These sickle cells block the fine vessels of certain organs: lungs, eye, brain, etc., hence the clinical manifestations of sickle cell disease (Pliya, 1994). Sickle cell anemia modifies the membrane flexibility of erythrocytes making them more sensitive and fragile against free radicals. In black Africa, sickle cell disease is one of the leading causes of infant mortality; almost  95% of children die before the age of 4 (Tshilolo et al., 2019; Mamounata et al., 2006). In Niger, the prevalence of sickle cell trait is between 18 and 22% (Issaka, 2012). This justifies the creation of the National Reference Center for Sickle Cell Disease (CNRD) in August 2009 (Issaka, 2012).

Recently conducted survey on the screening and management of medicinal plants in four localities of Niger through the traditional practitioners revealed that 110 species in 89 genera and 47 families are used in the tradItional pharmacopoeia, among them plants with potential effect against sickle cell disease (Mounkaila et al., 2017). The work of Souchet and Louis (2013) reported that in West Africa, 93 species are potential plants with effect against sickle cell disease. Among them Cajanus cajan, Carica papaya, Piper guineense, Pterocarpus osun, Sorghum bicolor, Syzygium aromaticum, Zanthoxylum zanthoxyloides, Justicia secunda, Moringa oleifera and Vinga unguiculata seem to be the most promising species for sickle cell disease treatment.

Plants are naturally sourcing of various bioactive compounds thought with various health benefits such as prevention of blood sickle cell disease. Plant metabolites can be divided into primary metabolites associated with nutrition and secondary metabolites, which perform several functions like interaction between a plant and its environment, and also involves in many drug formulation or preparation (Uko et al., 2019). Secondary metabolites included a group of compounds known as phenolic (Raji et al., 2019). In Africa, medicinal plants have a good reputation, as nearly 75% of the population uses these plants for their medical care (Grosse et al., 2011; Mamounata et al., 2006). Nigeriens use traditional medicine more than the modern, because of the low monthly income of parents of sickle cell patients and the high cost of modern medicine (Karl Rachid, 2013). This study aimed to identify, through an ethnobotanical survey in the region of Niamey (Niger), the medicinal plants used for the treatment of sickle cell disease and carry out the phytochemical screening of these plants.

Niamey region is located at the extreme West of Niger Republic where the National Reference Center for Sickle Cell Disease created in 2009 is located; and at the same time the place where the survey was conducted with the patients or their parents of CNRD but also with traditional healers (Issaka, 2012). The data collection was carried out using an ethnobotanical survey through a direct interview. To carry out this survey, two questionnaires were prepared for sickle cell patients and traditional healers. The questions have been translated into local languages, Hausa and Zarma (the two most spoken languages in Niamey region). The inventory survey questions were mainly focused on the anti-sickle cell plants, the manifestations of the disease, the parts of the plants used and the methods of drug preparation. The names of the plants listed are given in vernacular languages and for each plant species, a sample was collected for identification  and  phytochemical  study.

The identification of the plants species was carried out by the Biology Laboratory of the Faculty of Science and Technology, Abdou Moumouni University of Niamey, with help of Niger Republic national plant nomenclature and Professor Mahamane Saadou. In total, fifty-three (53) sickle cell patients (28 female and 25 male) from the CNRD and seven (7) all-male traditional healers were questioned for ethnobotanical survey. As for the patients, the survey focus more on the age of the patient, sex, origin, electrophoresis, type of hemoglobin, age of diagnosis of the disease, major symptoms of the disease, names of plants used, parts of plants, method of preparation, and locality of plants.

Chemical characterization

The plants organs depending on the part needed were collected from 15 to 30^th December, 2013 during the day in the Tillabery (Niger) region at 115 km far from Niamey and 527 km away from Ouagadougou Burkina Faso. The plants were authenticated by a botanist professor Mahamane Saadou, Department of Biology at the Faculty of Science and Technology, Abdou Moumouni University of Niamey, Niger and were given voucher numbers from HI/011 to HI/039. After harvesting the different parts of the plant’s materials, they were then cleaned and dried in an aerated area at room temperature for two weeks. The dried plant materials were grinded, sieved and the given powder were pulverized followed by extraction of the secondary metabolites using three different solvents petroleum ether, methanol and distilled water. Different chemical characterizations were performed as described in the work of Ronchetti and Russo (1971). The sterols and polyterpenes were characterized by the reaction of Liebermann, and the polyphenols content was determined through the reaction with ferric chloride (FeCl₃). The cyanidine reaction was used to characterize the flavonoids. The tannins, quinones and alkaloids content were determined using Stiasny, Bornstraëgen and Dragendorff's reagents, respectively. Picrosodium and foam test were used to characterize the cyanogenic glycosides and saponosides respectively.

Plant organs and prescription

The survey revealed 29 plant species distributed among 20 families used in the treatment of sickle cell disease. The results of the ethnobotany survey are summarized in Table 1. Capparidaceae and Rubiaceae are the most represented (10.34%), followed by Bombacaceae, Meliaceae, Combretaceae, Convolvulaceae and Anacardiaceae (6.89%). At the end, the least-mentioned families are Lilliaceae, Vitaceae, Cyperaceae, Asclepiadaceae, Cochlospermaceae, Malvaceae, Acanthaceae, Bignoniaceae, Scrophulariaceae, Caesalpiniaceae, Mimosaceae, Sterculiaceae and Poaceae (3.45%). Depending on the size of the organs used, the leaves are the most recommended (41%), followed by the leafy stems (17%), the barks of the trunk (14%), the roots (10%), root barks (7%), fruits and seeds (4%) and finally, pods (3%). Figure 1a shows the percentages of utilized plant organs. The massive use of leaves is explained by their richness in primary and secondary metabolites, through photosynthesis. Indeed,  plants ensure the synthesis and storage of these metabolites with their chlorophyllian pigment. Secondary metabolites have very important biological interests (N'Guessan et al., 2009) which justifies in general, the use of leaves by the traditional healers in the treatment of sickle cell disease.

The study thus revealed that the ethnobotanical surveys carried out among sickle cell patients and traditional healers has enabled identifying of many ways of handling sickle cell cases, based on twenty-nine (29) plant species distributed among twenty (20) families. Several organs of these plant species have been used in the drug preparation to cope with sickle cell crises. These are manifested through several symptoms such as joint pain, headache, stomach, edema and jaundice. The plant parts analysis highlighted compounds like sterols and polyterpenes, polyphenols, flavonoids, tannins, saponosides, alkaloids, quinones, cyanogenic glycosides and anthocyanins. Natural substances also provide a basis for potential new drugs used against several diseases, including sickle cell anemia. Moreover, herbal medicine can currently be considered as a way of relieving anemia in general and sickle cell disease in particular.

The authors have not declared any conflict of interests.

The authors are grateful to Dr Tondy Gani DJIBRILLA, Mr Mamoudou MOROU and Mr Hamza Kona MAYAKI for their kind assistance.