follow the teachings of his master and also use the resources recommended in the process.
This has resulted in abysmal dependence on imported reagents using very scarce foreign reserves which impacts negatively on the economies of developing nations especially Sub-Saharan African countries.
But the economies of these countries has nosedived in the past decades leading to skyrocketing cost of these imported histology laboratory reagents.
Most of these imported dyes are synthetic in nature which has been found to be detrimental to human health in one way or the other.
In order to frontally address the developmental needs of their countries, histology researchers and scientists must now look inwards for local alternatives to the foreign imported reagents so as to conserve foreign reserves, create employment opportunities, industrial growth and shoring up the compedium of natural dyes that could be applied in the histological demonstration of tissue components.
Theses natural dyes are safe, cheap, eco-friendly, and biodegradable.
This paper focuses on the use of natural dyes from plant extract, different methods of extraction and recent discoveries in the applications of these dyes in histological demonstration of tissues.
Various parts of plants such as roots, stems, leaves, flowers, fruits and seeds are used for dye extraction. Some plants may have more than one color depending on which part of the plant one uses. The color yield and shade of the color a plant produces vary according to time of the year the plant is picked, how it is grown, soil conditions, etc. Before extraction, the parts of the plants are collected and generally shade- dried in air or sun -dried. Then the grinding is carried out to break down the material into very small pieces or powder using the manual or electric grinding machines. Optimum conditions of extraction are determined by varying extraction parameters such as type of solvents, time of extraction, ratio between plant material and solvent, temperature and pH which depend on the properties of particular dye components (Prabhu and Bhute, 2012).
After extraction, the extracts are generally filtered through various filters such as cheesecloth, cotton wool or paper filter. The filtrates may be freshly used (normally aqueous extract) or
further evaporated of solvent, washing and drying to get purified dye. There are mainly four methods used in extraction of natural dyes (Samanta and Konar, 2011).
Methods of extraction of natural dyes include:
1. Aqueous extraction
2. Extraction by non-aqueous and other solvent assisted system
3. Extraction by acid or alkaline assisted system
4. Extraction by other methods e.g. ultrasound assisted and enzyme assisted extraction
Natural dyes often need mordants to enhance their staining capabilities. These mordants could chemical or natural in nature.
Histological Uses of Natural Dyes: Recent DevelopmentsThe following locally available dyes has been used of recent in the histological demonstration of tissue components:
Hibiscus sabdariffa20% aqeuous extract of H. sabdariffa was used by Eman Hashim (2006) to stain tissues in albino mice as eosin substitute in the Haematoxylin and Eosin technique.
5% H. sabdariffa aqeous solution mordanted with ferric chloride was used as haematoxylin substitute in the H&e technique by Benard (2008) on formalin fixed, paraffin embedded appendix and lymph node tissues.
Egbujo et. al., (2008) prepared aqueous extract of H. sabdariffa with alum and iron mordants to stain testicular biopsies. Iron-mordanted H. sabdariffa solution gave best results.
Ibnouf et.al assessed the staining quality of H. sabdariffa on formalin fixed, paraffin embedded renal tissue and found out that 5% aqueous extract of the dye gave best results.
Curcuma LongaYellow staining of collagen was demonstrated by Avwioro et. al (2006) by using extract of Curcuma longa. Ethanolic extract of Curcuma longa was used as counter stain for haemtoxylin stained sections of testes by Bassey et. al (2011).
Sorghum bicolorShades of pinkish-yellow staining of collagen was demonstrated by Avwioro et. al.,(2007) by using Sorghum bicolor leaf extract.
The histomorphology of selected histological tissues were assessed using alcoholic extract of Sorghum bicolor by Omoowo et. al., (2014).
Extract of kola nut was used as eosin substitute in rat tissues by Shehua et. al., (2012).
With progress made so far, hope arises in the horizon for developing countries that resources locally available to them can be useful in the histological demonstration of tissues which could lead to conservation of foreign reserves and progressive development of their economies. However, the issue of standardization, climatic variations, and cultivation methods need to be evaluated.
REFERENCESAvwioro, O.G., Onwuka, S.K., Moody, J.O., Agbedahunsi, J.M., Oduola, T., Ekpo, O.E. and Oladele, A.A. 2007. Curcuma longa extract as a histological dye for collagen fibres and red blood cells. J. Anat. 210: 600–603.
Avwioro, OG, Aloamaka, CP, Oduola, T and Komolafe, AO (2006). Collagen and muscle stains obtained from Sorghum bicolor. Sc. J. Clin. Lab. Invest. 66: 161-168.
Benard SA, (2008): Iron-Roselle: A Progressive nuclear Stain Substitute For Hematoxylin; The Journal of Histotechnology/Vol.31.No.2 :57-59/june.
Egbujo E. C., Adisa O. J. and Yahaya, A. B 2008. A study of the staining effect of Roselle (Hibiscus sabdariffa) on the histologic section of the testis. Int. J. Morphol. 26(4): 927-930.
Hashim, E.A. 2006. The use of watery extract of kujarat flowers Hibiscus Sabdariffa as a natural histological stain. Iraqi J. Med. Sci. 5(1): 29-33.
Omoowo BT, Bankole JK, Muhammed AO, Benard SA, Afolabi OO (2014). Histomorphological assessment of the extract of the stalk of Sorghum bicolor as counter stain. African Journal of Cellular Pathology 2:69-74
Prabhu, K. H. and Bhute, A.S. 2012. Plant based natural dyes and mordnats: A review. J. Nat. Prod. Plant Resour. 2(6):
Samanta, A.K. and Konar, A. (cited 7 November 2013) 2011. Dyeing of textiles with natural dyes. Available
from: http://www.intechopen.com/ books/natural-dyes
Shehua, S.A., Sonfada, M.L., Danmaigoro, A., Umar, A.A., Hena, S.A. and Wiam, I.M. 2012. Kola nut (Cola acuminata)
extract as a substitute to histological tissue stain eosin. Sci. J. Vet. Adv. 1(2): 33-37.