Dermatotoxins and Gastrointestinal toxins in African Waters

Dermatotoxins and Gastrointestinal toxins are toxins that affects the skin and mucous membranes, and causes allergy-type reactions such as rashes, eye/nose/throat irritation, and asthma, as well as headaches, fever, and gastroenteritis (nausea, stomach cramps, vomiting, diarrhea) most times leading to tissue necrosis. Examples include lyngbyatoxin and lipopolysaccharide endotoxins.
Cyanobacteria are group of prokaryotic and autotrophic microorganisms that contain the photosynthetic pigments (Chlorophyll a, carotenois, phycobilins and phycoerythrin in some species). From what we know, over 2,500 species have been identified, mainly related to ecosystems of surface waters, consisting both freshwater and marine (Cavalier-Smith, 2002; Oren, 2011). Over 80 species have been recognized and are able to synthesize toxic metabolites which shows activity especially against the endothermic vertebrates ( Kabziński, 2005). These chemical compounds include alkaloids, cyclic peptides and lipopolysaccharides with a wide range of health effects: hepatotoxic, neurotoxic, cytotoxic as well as dermatotoxic (van Apeldoorn, 2007).
The dermatotoxic group of chemical compounds produced by Cyanobacteria are characterized into LyngbyatoxinsLyngbyatoxins (LA) are indole alkaloids, their name was taken from a cyanobacteria genus Lyngbya belonging to the order Oscillatoria (Bridgeman, 2010). Lyngbyatoxin-a has a skin tumour promoting activity similar to 12-O-tetradecanoylphorbol-13-acetate (TPA) based on the activation of protein kinase C (PKC) as a result of replacing endogenous activator of this enzyme (1,2 diacyloglycerol). Several literatures in Medical science described several confirmed cases of significant lyngbyatoxins effects on humans having direct contact with water resources with high occurrence of Lyngbya. The most common symptoms noticed involved skin and are usually defined as “seaweed dermatitis” (Izumi,1987). It’s a skin rash caused by direct contact with a poisonous type of seaweed (alga). Symptoms frequently observed include: skin burns (10.5%), skin itching (23%), skin blistering (2.2%), Redness of the skin (10.5%), and swollen skin (0.8%) (Osborne, 2007). Consumption of water contaminated by lyngbyatoxin leads to oesophagus inflammation and digestive tract (Chorus, 1999).

Aplysiatoxin and debromoaplysiatoxin


Aplysiatoxin (AT) and debromoaplysiatoxin (DAT) belong to phenolic bislactones. They have a molecular mass of 671 Da and 592 Da, respectively (Rao et al.,2002). Several experimental studies on dermatotoxins revealed the potential negative impact of aplysiatoxin and debromoaplysiatoxin on mammals health. In mice for example both toxins caused severe ear irritation (Fujiki et al.,1982). Inhibition of epidermal growth factor (EGF) (10 times higher for aplysiatoxin) (Horowitz,1983) and activation of ornithine decarboxylase in human skin cells was observed (Fujiki,1983). It was reported by (Osborne et al.,2010) that direct contact with water contaminated with aplysia and debromoaplysiatoxin caused acute skin irritation, rashes and blisters.

Lipopolysaccharides


Lipopolysaccharides (LPS) are mostly present in cyanobacterium cell wall. They usually form complexes with proteins and phospholipids. So far, there are very few publications on impact of cyanobacterium LPS on human health and its mode of action remains unclear (Fujiki et al.,1982). This is due to the deadlock or complications in distinguishing the symptoms caused only by lipopolysaccharides and caused by secondary metabolites synthesized by bloom formimg cyanpbacteria. Therefore, the whole range of symptoms were attributed to lipopolysaccharides such as: skin (Codd,1994; National Rivers Authority,1999) and eye (Steffensed,1999;Queensland Water Quality Task Force, 1992) irritation, Allergic rhinitis (Codd, 1995), respiratory problems (Ressom,1994), headaches and dizziness (Weckesser,1974), blistering of mucous membranes and fever (Rapala et al.,2002).

THE SITUATION IN AFRICA


South Africa has 497 large reservoirs, each with a capacity in excess of one million cubic metres, in addition to over 150,000 smaller reservoirs and farm dams (Basson et al., 1997). South Africa is unique amongst Southern Hemisphere countries in having most of its principal metropolitan areas located on the watersheds of river catchments. The rivers draining away from these watersheds have the dual burden of providing water supplies and transporting waste material most of which enters downstream water storage reservoirs. Because most South African reservoirs are located downstream of urban and metropolitan areas, these reservoirs becomes progressively more enriched.
Modern agricultural practices significantly add to this environmental burden, with pesticides and fertilizers washing into rivers or leaching into groundwater (Walmsley, 2000). Freshwater pollution (in the form of Chemical Oxygen Demand) is estimated to be 4.74 tonne/km3 while the average phosphorous concentration in the natural water resources of South Africa (as orthophosphate) has been estimated at 0.73 mg/litre (Nationmaster.com, 2003). These values indicate that South Africa’s freshwater resources are excessively enriched and are considered to be moderately to highly eutrophic.
Eutrophication is generally indicated by accumulation of metabolic products (e.g. hydrogen sulphide in deep waters), discolouration or turbidity of water (resulting in low or poor light penetration), deterioration in the taste of water, depletion of dissolved oxygen and an enhanced occurrence of cyanobacterial bloom-forming species.
Arguably the most alarming characteristic of the blue green algae is the ability of most of the species to produce a range of extremely effective, low-molecular-weight cyanotoxins (Carmichael, 1992). These cyanotoxins are grouped according to the physiological systems, organs, tissues or cells that are primarily affected. The table below shows the cyanobacterial toxins particularly dermatotoxins and irritatant toxins of the most dominant species in South Africa, their functions and mechanisms of action.

Previous reviews or investigations have shown that dermatotoxic metabolites synthesized by cyanobacteria in human health is still not clear. Therefore, knowledge of the above substances is based mainly on studies of animal models. Described cases reveals negative impact of dermatotoxins on human skin, even during a short period of exposure. (Poitr, 2012). Long term exposure to dermatotoxins can lead to promotion of carcinogenesis. In the case of massive occurrence of bloom forming cyanobacteria (even species not producing toxic metabolites) there is a risk of exposure to lipopolysaccharide(LPS) which in a few reports seems to have an irritant effect on human skin (Poitr, 2012).


References

 

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