STUDY ON THE ROLE OF CADMIUM AS A 2

STUDY ON THE ROLE OF CADMIUM AS A CAUSATIVE AGENT OF MISCARRIAGE : 

STUDY ON THE ROLE OF CADMIUM AS A CAUSATIVE AGENT OF MISCARRIAGE

A ThesisSubmitted to the Medical Research Institute : 

By Naela Aly Mohamed Diab A ThesisSubmitted to the Medical Research Institute

INTRODUCTION : 

INTRODUCTION

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Pregnancy represents one of the most important processes in biology. It starts by the union of egg and sperm at fertilization . Embryonic implantation occurs one week later and consists of three consecutive phases, namely apposition, adhesion and invasion.

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Fig. (34) Redox regulation of spermatogenesis and fertilization Redox regulation of spermatogenesis and fertilization. During the spermatogenesis process, histones are converted to protamines via transition proteins in sperm nuclei. The maturation of spermatozoa proceeds in the epididymis. Oxidation mediated by sulfoxidase is involved in the packaging of chromatin into the small nucleus via disulfide bridge formation between protamines. After fertilization, the sperm head expands to the male pronucleus by reducing the disulfide bond in the oocyte

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Spontaneous abortion is highly frustrating for both patients and physicians. Recurrent pregnancy loss, defined as three or more consecutive pregnancy losses before of gestation, has been reported to affect of women in the reproductive age group. 20 weeks 0.5% - 3%

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There is profound emotional and psychological stress associated with recurrent abortion. Women experience moderate to severe grief and have feelings of guilt or anxiety accompanying abortions. The families find it difficult to cope with the situation and these women may require psychotherapeutic support at times.

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Early anatomical and histopathological studies have almost exclusively focused on abnormal villous development in early pregnancy failure. There is now clear evidence, that miscarriages are a placentation disorder which is mainly characterized by; a thinner and fragmented trophoblast shell reduced cytotrophoblast invasion of the endometrium incomplete plugging of the lumen at the tips of the spiral arteries, leading to premature onset of the maternal circulation throughout the entire placenta.

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The causative factors associated with recurrent pregnancy loss can be varied and multiple. The factors reported in literature are genetic abnormalities, uterine anomalies, autoimmune diseases, infectious diseases, endocrinopathies, sperm DNA fragmentation and sperm meiotic alteration. In about 50-60% of recurrent pregnancy losses, a causative factor cannot be identified and are therefore classified as idiopathic.

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Environmental pollution is one of the ever surging problems receiving careful attention in our country, as well as in the world. As a result of industrial development, many chemical substances have generated pollution in air, water and soil.

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A considerable amount of heavy metals remained inert in the deeper parts of the earth until 20th century. When these metals began to be used in industries, they spread and condensed more in the environment. Heavy metals are more or less toxic elements. They can be carried through soil-plant-animal-human cycle in increasing concentrations.

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It has been evidenced, that environmental pollutants play an important role in the manifestations of severe reproductive-associated disorders. Among them, an environmental pollutant, namely cadmium has contributed to several deleterious effects.

AIM OF WORK : 

AIM OF WORK

The aim of the present study was endeavored to investigate the association between non-occupational cadmium exposure and the occurrence of recurrent abortion. : 

The aim of the present study was endeavored to investigate the association between non-occupational cadmium exposure and the occurrence of recurrent abortion.

SUBJECTS AND METHODS : 

SUBJECTS AND METHODS

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A total of one hundred and twenty women were recruited from the Prenatal Genetic Diagnosis Clinic of the National Research Centre in Dokki, Giza. The study subjects were divided into four groups. Group I included thirty women, who had never experienced any miscarriage before and were therefore considered controls. Group II, III and IV involved 27, 23 and 40 subjects with a history of one, two and three or more miscarriages, respectively.

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A questionnaire was done to the four studied groups considering age, socioeconomic standard, life style, occupation and residence. In addition, an obstetric history pointing to the number of previous pregnancies and miscarriages was taken. The obstetric history of the selected study subjects excluded other factors, which could be interpreted as a cause of miscarriage, such as infectious diseases involving Toxoplasmosis, Rubella, Cytomegalovirus and Herpes (TORCH), anatomical obstetric complications, immunological factors and hereditary chromosomal aberrations.

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All control and aborters in this study were investigated by the following parameters. 1- Graphite Furnace Atomic Absorption Spectroscopy (GF-AAS) assay of blood cadmium. 2- ELISA assay of serum ferritin. 3- Estimation of plasma malondialdehyde (MDA) concentration. 4- Colorimetric determination of whole blood reduced glutathione (GSH) concentration. 5- Enzymatic estimation of the glutathione peroxidase (GPx) enzyme activity in whole blood. 6-Determination of plasma carnosine by ion-exchange amino acid analyzer. 7- ELISA assay of plasma 8-hydroxy-2deoxyguanosine concentration. 8- Estimation of serum progesterone concentration.

RESULTS AND DISCUSSION : 

RESULTS AND DISCUSSION

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Studies on cadmium (Cd) first started in 1950 – 1960s with the occurrence of Itai-Itai disease in Japan. Itai-Itai disease was found to be an endemic cadmium poisoning, resulting by dietary exposure, especially via rice; the typical clinical picture of which was kidney dysfunction leading to loss of calcium, resulting in frequent bone fractures.

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Cd is a heavy metal, that is dispersed throughout the modern environment, mainly as a result of pollution from a variety of sources. This is why the Agency for Toxic Substances and Disease Registry has listed Cd among the top seven of the 275 most hazardous substances in the environment .

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Cadmium gets into soil from the use of fertilizers and as a result of zinc-mining processes, in which cadmium is a discarded impurity. In Egypt, many industries are located in Cairo and Giza. Women in this study were living in Cairo and Giza; both places are known to have plants and factories emitting industrial fumes. Cadmium pollution from industrial waste might be also expected in the River Nile, which distributes cadmium remnants into homes through drinking water

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Dietary Cd is a growing concern, since it constitutes the main exposure source for non – occupationally exposed individuals. Cigarette smoke is known to constitute another significant source of the body cadmium burden.

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A number of mechanisms of cadmium toxicity have been suggested, including ionic and molecular mimicry, interference with cell adhesion and signaling, oxidative stress, apoptosis, genotoxicity and cell cycle disturbance. Although the overall effect of cadmium on any cell or tissue is likely to be due to a synergism of several mechanisms, it is possible, that one mechanism will predominate in a specific cell type .

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There are two aspects of cadmium toxicity, both of which are well documented clinically. Interactions between iron and cadmium appear to be implicated in both these effects.

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One is the interference with iron absorption by cadmium, which is illustrated by the development of microcytic, hypochromic anaemia as a result of cadmium exposure. The other is the effect of iron status on cadmium toxicity, which is best portrayed by the illness, ITAI-ITAI (bone lesions and anaemia), described in Japan in individuals drinking water of high cadmium content.

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It appears, that cadmium in some way blocks the transferrin cycle within the cell. In addition, the binding of cadmium to mucosal ferritin was shown to interfere with the subsequent deposition of iron within the molecule. It has been suggested, that cadmium binds to catalytic sites necessary for oxidation and deposition of ferritin iron

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These findings confirmed and represented a very good interpretation to the results of the current study, which elucidated, that the three studied groups of aborter women were exposed to the environmental cadmium pollution, which induced impairment of iron storage, as well as microcytic, hypochromic anaemia manifested by a highly significant decrease in the level of serum ferritin associated with a highly significant decrease in their MCV, as well as MCH. It is admirable to note, that there was an inverse correlation between serum ferritin and cadmium body burden.

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A large body of work exists outlining the effects of cadmium on gametogenesis in both males and females, and implicating its compounds in early embryolethality and implantation failure. In addition, animal studies have shown a wide range of anomalies following exposure at specific stages of embryogenesis and emerging evidence has indicated, that cadmium may also be linked to pathological processes in late pregnancy and in the early postnatal period, causing third trimester complications and minor but significant problems in the offspring of exposed individuals. Thus, cadmium has the potential to affect reproduction and development in many different ways, and at every stage of the reproductive process.

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A large body of work exists outlining the effects of cadmium on gametogenesis in both males and females, and implicating its compounds in early embryolethality and implantation failure.

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In addition, animal studies have shown a wide range of anomalies following exposure at specific stages of embryogenesis and emerging evidence has indicated, that cadmium may also be linked to pathological processes in late pregnancy and in the early postnatal period, causing third trimester complications and minor but significant problems in the offspring of exposed individuals. Thus, cadmium has the potential to affect reproduction and development in many different ways, and at every stage of the reproductive process.

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Effects on the testis include disruption of the blood-testis barrier due to adverse effects on cell adhesion, oxidative stress and necrosis at higher experimental doses. Incorporation into chromatin of the developing spermatozoa has also been described .

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In the ovary, oocyte development is inhibited, steroidogenesis reduced and ovarian haemorrhage and necrosis supervene at higher cadmium doses. Cumulus expansion and possibly oocyte pick-up by the tubal epithelium are also hampered, probably by interference with normal junction formation.

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The clinical implications of the effects of cadmium on oocyte maturation, oocyte pick up and development of preimplantation embryo through to implantation are obvious and has been demonstrated to reduce the possibility of a successful pregnancy.

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Cadmium exposure has previously been shown to target the trophoblast cells of the placenta and result in various toxic responses: lysosomal vesiculation, nuclear chromatin clumbing, nucleolar changes and mitochondrial calcification.

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The majority of metallothionein, a low molecular weight, cysteine rich, metal-binding protein, induced in placenta perfused with cadmium is localized to stromal and endothelial cells. Induction of metallothionein occurs to a lesser extent in trophoblast cells, which makes them inherently susceptible to cadmium-induced toxicity.

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During pregnancy, this reduced production of MT by the trophoblast may be clinically relevant in the decreased steroidogenesis induced by cadmium, since syncytiotrophoblast cells are in direct contact with the maternal blood and are responsible for the production of many hormones, associated with pregnancy.

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Other injurious effects on the placenta include inhibition of trophoblastic invasion and adjusted handling of nutritive metals have also been identified.

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Cadmium has been found to induce oxidative stress in gestation. This is evidenced by the reduced antioxidant parameters and the elevated oxidant markers observed in our study subjects.

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The observed decrease in GSH might be a result of : *Its utilization in the scavenging of free radicals. *Its utilization in the synthesis of MT. *Its ability to form conjugates with toxic metals, like Cd and harmful endogenous compounds, like MDA.

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The decrease GPx may be due to: *The formation of a chemical complex between Cd and Se at its active site. *Decreased transcription of the genes, that encode GPx, as well as posttranscriptional effects. *Depletion of cellular GSH, a necessary cofactor for GPx.

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The decreased plasma carnosine may be due to: *Its activity as a transition metal ion chelator. *Its role in scavenging free radicals and MDA.

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Accumulation of toxic metals in placental tissue may result in abnormal placental function, leading to impaired transport of essential metals, such as zinc, copper, Se and iron.

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This undesirable condition leads to an imbalance between toxic and essential metals in favour of the formers, with detrimental effects on enzymatic protective systems, such as Se-dependent GPx and Cu-Zn-dependent SOD, which require these essential metals as cofactors.

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The presence of heavy metals in placentas may be detrimental for placental GPx and SOD activities and as a result the fetus is subjected to some degree of oxidative stress, which may result in potential damage.

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The process of lipid peroxidation has been implicated as one of the primary events in oxidative cellular damage and has been reported to interfere with normal intrauterine development, causing placental endothelial cell injury, vasoconstriction and a reduction in placental perfusion mediated by an imbalance between thromboxane and prostacyclin.

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Lipid peroxidation has long been considered as the primary mechanism for Cd toxicity. Although, its peroxidative mechanism is a controversial matter, as Cd does not undergo redox cycling and does not participate in the Fenton reaction.

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It has been reported, that the increase in lipid peroxidation could be the consequence of a direct effect of Cd, a Cd-induced displacement of redox metal ions or a decrease in GSH content

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Recurrent pregnancy loss may be caused by oxidative damage to macromolecules and DNA and ROS-induced signal transduction for various genes are some of the underlying factors leading to recurrent abortion.

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Histogram for 8-OH-2-deoxyguanosine Correlation curve between Cd and 8-OH-2-deoxyguanosine Correlation curve between MDA and 8-OH-2-deoxyguanosine Correlation curve between 8-OH-2-deoxyguanosine and GSH Correlation curve between 8-OH-2-deoxyguanosine and GPx Correlation curve between 8-OH-2-deoxyguanosine and carnosine

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The principal mechanisms for Cd genotoxicity and mutagenecity are: *Generation of ROS *Inhibition of DNA repair *Depletion of GSH *Suppression of apoptosis

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Whereas apoptosis is thought to be important for normal placental development, it may also be involved in the pathological conditions associated with this organ.

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Apoptic cells have been identified in both the maternal and fetal compartments of the placenta during normal pregnancy. The presence of these cells may be related to the stage of placental development, including the attachment and invasion of the trophoblast, spiral artery transformation, trophoblast differentiation and turn over and parturition.

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Apoptosis has also been shown to play an important role in promoting maternal immune tolerance to paternal antigens expressed by trophoblast cells. In complicated pregnancies, such as preeclampsia or IUGR , a greater incidence of trophoblast apoptosis has been observed, suggesting that alterations in the regulation of trophoblast apoptosis may contribute to the pathophysiology of these diseases