Abstract

A number of studies have demonstrated that geophagia can be beneficial and harmful. However, toxicological aspects of this earth, soil, clay eating habit are not fully investigated. In addition, low levels of antioxidants have been observed in pre-eclamptic women. Still, the molecular mechanism implicated oxidative stress in geophagia inducing pre-eclampsia has not been elucidated. Despite its absorbent properties in detoxifying phytotoxin, lowering the incidence of nausea, natural clay still remains toxic for human consumption in normal and long term conditions. Our previous studies have shown the implication of oxidative stress in pre-eclampsia characterized by maternal hypertension. Biomarkers of oxidative stress such as lipid peroxides (LPO), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GPX) and 8-OHdG correlated with the extent of oxidative stress in pre-eclampsia. Fenton reaction induced by the presence of iron produces a more powerful reactive oxygen species (OH radical) which may contribute to the exacerbation of this status; while, clay eating is believed to protect pregnant women from pre-eclampsia by inhibiting iron uptake from gastrointestinal environment and so reducing the risk of production of OH radical during pregnancy where iron deficiency has been observed, it may be harmful however in iron overload conditions. We have demonstrated that cellular hepato-carcinoma can be indeed induced in rats being iron-loaded by ferrocene supplementation of their diet. Taking into account this possibility, we are postulating that during pre-eclamptic pregnancy, a number of factors including oxidative stress, activated macrophages and activation of xanthine oxidase (XO) can exacerbate this pregnancy complication. In addition, the availability of free iron from soil may as catalytic trace element involve in Harber-Weiss and Fenton reactions producing more ROS/RNS and especially OH radical. We are therefore suggesting that the subsequent activation of the nuclear factor NF-kB by ROS/RNS generated from activated macrophages stimulates the induction of COX-2. This enzymatic induction leading to the expression of inflammatory cytokines could be one of the molecular mechanisms underlying pre-eclamptic conditions. Supplementation of zinc or eating clay containing zinc could overcome such pregnancy complication.

Key words: Geophagia, pregnancy, molecular mechanism, oxidative stress, Haber-Weiss and Fenton reactions, superoxide dismutase (SOD), glutathione peroxidase (GPX), OH radical, 8-hydroxyl deoxyguanosine (8-OHdG).

Abbreviation

CAT, Catalase; Fe, iron; FOX, ferrous xylenol orange; H₂O_2, hydrogen peroxide; SOD, superoxide dismutase; GPx, glutathione peroxidise; GSH, reduced glutathione; GSSG, oxidized glutathione; GRx, glutathione reductase; TAS, total antioxidant status; Hb, haemoglobin; LOO^‾, lipid radical; LOO^•; alkoxyl radical; LOOH, lipid hydroperoxides; LPO, lipid peroxide; MDA, malondialdehyde; NADH, nicotinamide adenine dinucleotide reduced form; O₂^●-, superoxide anion; ^●OH, hydroxyl radical; 8-OHdG, 8-hydroxy-deoxyguanosine; ROS, reactive oxygen species; RNS, reactive nitrogen species; MSR, methionine sulphoxide reductase; AST, aspartate aminotrnasferase; ALT, alanine aminotransferase; ABTS, 2, 2’-azino-di-[3-ethylbenzthiazoline sulphonate]; ORAC, oxygen radical absorbance capacity; Cox-2, cyclo-oxygenase, Nf-kB, nuclear factor kappa B; HELLP, haemolysis, elevated liver enzymes, low platelet count; WHO, World Health Organization.