The Effect of Cadmium on the Cardiac Development of Embryonic Zebrafish
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Transcript of The Effect of Cadmium on the Cardiac Development of Embryonic Zebrafish
Aaliyah Williams
The Effect of Cadmium on the Cardiac Development of Embryonic Zebrafish
Aaliyah Williams
Niles North High School 2015
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Table of Contents
Acknowledgements 3 Purpose/Hypothesis 4 Review of Literature 510 Procedure 11 Materials 12 Variables 13 Results 1418 Conclusion 19 References 20
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Acknowledgements
I would like to acknowledge my teacher, Ms.Camel, who guided me throughout my project and kept me on the right track.
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Purpose/Hypothesis
Hypothesis: If zebrafish embryos are exposed to varying concentrations of cadmium then their hearts will
exhibit developmental defects. Zebrafish treated with higher concentrations of cadmium will
have a higher heart rate and a larger ratio of distance between sinus venosus and bulbus
arteriosus(heart chambers) to body length of the zebrafish embryo.
Purpose: To investigate if there are morphological and functional defects of the zebrafish heart due to
varying concentrations of exposure to the environmental toxicant cadmium, in the early stages of
development.
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Review of Literature
By: Aaliyah Williams Camel Period 9
There are numerous chemicals in our environment that can be considered toxic, but are
hard to completely avoid, such as the chemical cadmium. Cadmium is an environmental toxicant
that has been shown to have many health related side effects. Cadmium, like many other toxic
metals, has been suspected of causing a high amount of reactive oxygen species (ROS), thus
leading to oxidative stress damage associated with the development of many diseases and aging.
The overproduction of ROS can lead to damage in proteins, DNA, lipid function and even cell
death. This overproduction of ROS can lead to diseases, such as cardiovascular disease. Since it
is very difficult to observe the effect of cadmium on actual organs, such as the heart, many
scientists have began to use zebrafish as a model because of its similarity to the human heart.
Cadmium is a toxic chemical that is nonessential to biological processes and there is
usually low levels of exposure in our environment, but there are still multiple ways one is
exposed to cadmium. Humans may be exposed to cadmium through cigarette smoke inhalation
due to tobacco plants high absorption of cadmium. “It has been reported that one cigarette
contains about 1 2 µg of cadmium and that about 10% of the cadmium content is inhaled when
the cigarette is smoked”(ICDA n.d). Also, workers in the industry sector are highly susceptible
to cadmium exposure, workers usually in the manufacturing and construction field. Workers are
exposed through the making of batteries, plastics, coatings, and solar panels, and smelting of
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metals. landfill operations, recycling of electronic parts or plastics (OSHA n.d) . Another
common source of cadmium exposure is exposure through ingestion of food. “In general, leafy
vegetables such as lettuce and spinach, potatoes and grains, peanuts, soybeans, and sunflower
seeds contain high levels of cadmium, approximately 0.05 0.12 mg cadmium/kg.” Exposure to
cadmium is also possible through its presence in water sources near industries emitting cadmium.
The exposure of water to cadmium puts aquatic life at risk, possibly contaminating food
supply(WHO 2010).
When cadmium enters the human body, it accumulates in the body throughout a person’s
lifetime making it very dangerous. It’s halflife is actually 1730 years in a human being. Once
cadmium is uptaken from the lung or gastrointestinal tract, is is transported by proteins, such as
Albumin. Usually, the cadmium that is attached to the Albumin is taken up by the liver, thus
inducing the synthesis of metallothionein. Then the metallothionein bound cadmium appears in
the blood plasma. Since cadmium has a low molecular weight, the cadmiummetallothionein is
efficiently filtered through the glomeruli and taken up by the tubules (Haschek 2013).
Cadmium exposure may result in overproduction of ROS(reactive oxidative species).
ROS is generated by prooxidants, thus inducing oxidative stress. ROS and consist of free
radicals and reactive species and breakdown products of lipids proteins, nucleic acids and
carbohydrates made by them. Free radicals can be positively,negatively or neutrally charged and
contain unpaired electrons. The most common and most important free radicals are superoxide
anion, free hydroxyl radical and nitric oxide that are able to produce other free radicals from
unsaturated fatty acids mostly. These free radicals have aggressive characteristics that allow
them to take electrons from other molecules or give away their unpaired electron in order to
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maintain stability. They are commonly known for this ability to fragment other molecules and
are produced from the cellular membrane mitochondria , lysosomes, nucleus, cytoplasm,
peroxisomes, and endoplasmic reticulum. These free radicals can play an important role
physiologically, but can also lead to the development of chronic inflammatory diseases when in
excess(Singh). Oxidative stress is defined as a continuous imbalance between antioxidants and
prooxidants, that can result in damage to cells. ROS as previously discussed before, is an
oxidant that may be overproduced by the mitochondrial respiratory chain. The ROS creates
oxidative stress damage that can be visually represented in Figure 1. Oxidative stress is caused
by ROS due to it being overly reactive “causing breaks and mutation in DNA, by inactivating
proteins and enzymes, by oxidizing sugars, and by inducing lipid peroxidation among the
polyunsaturated fatty acids of lipoproteins or of the cell membrane”(Probiox).
Figure 1. Mechanisms of oxidative stressinduced cell damage(Agarwal 2005).
The effects of Cadmium have been researched throughout many studies, and recently a
connection between cardiovascular disease and cadmium exposure has been hypothesized due to
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increased ROS production . Researchers have performed a systematic review of epidemiologic
studies and have concluded that there is reason to suspect that cadmium may be a risk factor of
cardiovascular disease. Their experimental evidence suggests that this connection is due to
cadmium initiating and progressing atherosclerosis due to its ability to raise the blood pressure.
“Cadmium may increase reactive oxygen species formation and interfere with antioxidative
stress responses by binding metallothionein , a low molecular weight protein that regulates zinc
homeostasis and acts as a free radical scavenger”. The study also explains a correlation between
cadmium and blood pressure, a side effect of Cardiovascular Disease. This systematic review
supports the theory that Cadmium is responsible for ROS production, leading to oxidative stress,
potentially creating a causal relationship between cadmium and cardiovascular disease
(TellezPlaza).
Many researchers use a zebrafish model in order to examine the cardiovascular system.
Figure 2 shows a visual representation of the heart development of zebrafish during the 5 hour
post fertilization phase through the 48 hour post fertilization phase.
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Figure 2. Heart development of zebrafish(Stainier 2001).
The ventricular end of the heart tube assembles first, then the the atrial end develops. At 24 hpf,
the tube lies along the anterioposterior axis with the atrial end to the left of the midline. At 30
hpf, visibly distinct ventricular and atrial chambers form. At 36 hpf, the heart undergoes looping
morphogenesis and, by 48 hpf, functional valves are formed(Stainier 2001). During
embryogenesis of zebrafish, the heart is the first organ to fully develop and function. Even
though the heart is able to function and is developed it will not be essential to the embryos ability
to live until after several days. This is because the connection of circulation has not developed
yet prevent full blood circulation. Since the heart is not essential during the early stages of
development, zebrafish embryos are great models because they are able to survive without
cardiac function because they’re oxygen is delivered by diffusion than the cardiovascular system.
The heart has 4 chambers , sinus venosus, atrium, ventricle, and bulbus arteriosus, in
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zebrafish(Hu 2011).The embryonic zebrafish heart has the same electrical excitation as the
human heart. It has pulses generated in the sinoatrial node, propagated through the atrium,
pausing in the atrioventricular node, and then sent to the ventricle. A regular resting heart beat is
usually between 6090 beats per minute for humans, but for zebrafish a heart rate is usually
between 120180 beats per minute, which is relatively similar to humans.(De Luca 2014).
The zebrafish heart is a great model because it consists of mammalian traits allowing it to serve
as a model for human heart development. The zebrafish and humans both have a closed
cardiovascular system, so their developments are extremely similar. It is an ideal model to be
studied because during its stage as an embryo it is transparent easily allowing observation under
a dissecting microscope(Hu 2011).
The toxic effects of cadmium and its role in the development of diseases is very
important to investigate because of the high chances of exposure to cadmium. It is known that
cadmium is toxic, but researchers are not aware of the direct effects relating to diseases such as
cardiovascular disease. Exposure to cadmium could explain the development of various diseases
that many are diagnosed with unexpectedly. A sudden high rate of certain diseases that may be
related to cadmium exposure may help to detect when their is a higher than normal cadmium
exposure in certain areas. If cadmium is a potential cause for some diseases, then the method of
treatment could be altered in order to ensure a better result and halt any further cadmium
exposure.
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Procedure: Part I
1. Label the petri dishes depending on the concentration of cadmium chloride(0 mg/L, 0.25 mg/L, 0.50 mg/L, 1.0 mg/L) that the embryos will be exposed to.
2. Separate the alive embryos from the dead ones using forceps. Then rinse the alive ones.
3. Transfer embryos into 20 miniature petri dishes(6 embryos per petri dish). Place petri dishes in cooler and keep at 28 degrees celsius.
4. Using the balance mass out 0.25 mg, 0.50 mg, 1 mg of cadmium chloride and mix into 1 L of water to make cadmium solutions.
5. Distribute 120 hatched zebrafish (24 hpf) embryos into 10 sixwell microplates in 3 mL of fish water with differing cadmium concentrations and 30 embryos per concentration group(0 mg/L, .25 mg/L, .5 mg/L, 1 mg/L) for 18 hours. 30 zebrafish embryos will only contain .1% DMSO and fish water(0 mg/L).
6. Transfer zebrafish from microplates to depression glass slides and examine under dissecting microscope .
7. Using a timer, count the beats per minute of each of the zebrafish embryo’s heart for 30 seconds(multiply to get beats per minute) .
8. Return zebrafish embryos to petri dishes filled with fish water. Part II(At 72 hpf of the zebrafish embryos):
1. Using a pipette place a drop of 2% methylcellulose inside of the wells. 2. Examine under a dissecting microscope under room temperature. 3. Count the number of embryos that have died and those that are still alive. 4. Take pictures of the the embryos under the dissecting microscope.
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a.Examine morphological changes. Measure the distance between SABA, and the body length of the embryo.
Materials: ● 10 6well Microplates ● 120 Zebrafish Embryos ● 25 g Cadmium Chloride Solution ● Dissecting Microscope ● Methylcellulose ● Stopwatch ● 3 mL Pipette(Automatic Pipette) ● DMSO(1%),Depression slides ● 3 Micro Dissection Forceps ● 30 Petri dishes ● Computer ● Motic 2.0 ● Face Mask ● Gloves ● Goggles ● Balance
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Variables Independent Variables:
● Cadmium Concentrations(0 mg/L, 0.25 mg/L ,0.50 mg/L , 1 mg/L) Dependent Variables:
● Heart Rate(Beats Per Minute) ● Distance Between SABA/Body Length
Control:
● 0 mg/L CdCl2 Controlled Variables:
● Temperature ● Amount of Cadmium Solution ● Number of embryos within each experimental group ● Amount of Hours Post Fertilization(hpf) data was recorded ● Hours of cadmium exposure ● Amount of Hours Post Fertilization cadmium was introduced to embryos
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Results: Data: Figure 1.
Figure 1. visually compares the heart beats per minute of zebrafish embryos 48 hours post fertilization after exposure to cadmium. Figure 5. Zebrafish Heart Rate After Exposure to Varying Concentrations of Cadmium Chloride
Embryos 0 mg/L CdCl2
0.25 mg/L CdCl2
0.50 mg/L CdCl2 1 mg/L CdCl2
1 128 152 178 204
2 138 153 166 198
3 142 168 182 194
4 134 158 178 202
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5 146 168 174 192
6 130 170 168 190
7 126 160 176 204
8 138 164 182 196
9 124 168 174 188
10 154 154 176 198
11 132 172 166 190
12 136 162 182 208
13 143 156 174 197
14 128 166 178
15 138 162
16 132 168
17 144 162
18 136
19 142
20 140
21 134
22 132
23 128
24 136
Figure 5. gives the heart beats per minute for the zebrafish embryos in the experimental groups. Figure 6. Average Heart Rate(Beats Per Minute) of Zebrafish Embryos Treated with Varying Concentrations of Cadmium
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0 mg/L CdCl2 0.25 mg/L CdCl2
0.50 mg/L CdCl2
1.0 mg/L CdCl2
135.875 162.5294118 175.2857143 197 Figure 6. shows the average of the ratio of SABA/ Body Length. Figure 3. Mortality Rates(%) of Zebrafish Embryos after Cadmium Chloride Exposure at Varying Hours of Postfertilization Concentration of Cadmium Chloride 24 hpf 48 hpf 72 hpf
0 mg/L 6.67% 23.33% 43.33%
.25 mg/L 13.33% 53.33% 60.00%
.50 mg/L 10.00% 56.67% 66.67%
1 mg/L 6.67% 63.33% 73.33%
Figure 3. has the percentages of zebrafish embryos that died during each interval of hours post fertilization. Zebrafish were treated with cadmium after 24 hours post fertilization. Figure 4. The Distance Between the Sinus Venosus and Bulbus Arteriosus of the Zebrafish Embryo Heart 0 mg/L CdCl2 0.25 mg/L CdCl2 0.5 mg/L CdCl2 1 mg/L CdCl2
0.09 0.14 0.16 0.24
0.14 0.15 0.19 0.26
0.1 0.16 0.2 0.22
0.12 0.17 0.22 0.24
0.11 0.18 0.16 0.22
0.16 0.17 0.21 0.24
0.14 0.15 0.19 0.21
0.13 0.19 0.18 0.25
0.09 0.14 0.17
0.12 0.15 0.23
0.14 0.18
0.08 0.12
0.15
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0.13
0.11
0.14
0.17
Figure 4. gives the ratios of the heart chambers SABA. Figure 2.
Figure 2. shows the ratio of the distance between the heart chambers, sinus venosus and bulbus arteriosus, of the zebrafish embryo heart to the body length of the embryo. Figure 7.The Average Ratios of the Distance Between the Sinus Venosus and Bulbus Arteriosus of the Zebrafish Embryo Heart:
Concentration 0 mg/L CdCl2 0.25 CdCl2 0.50 mg/L CdCl2 1.0 mg/L
Ratios 0.1247058824 0.1583333333 0.191 0.235
Figure 7. shows the average ratios of SABA/body length of zebrafish embryos.
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Data Analysis:
The mortality rate of the zebrafish embryos were recorded in figure 3. The percentage dead at
each interval of hour postfertilization(24, 48,72) is presented. The zebrafish embryos were
treated with cadmium at 24 hpf, so the 48 hpf and 72 hpf show the effects of the cadmium on
mortality. By the end of the experiment the mortality rates of the zebrafish were 43.33% for 0
mg/L CdCl2, 60.00% for 0.25 mg/L CdCl2, 66.67% for 0.50 mg/L CdCl2, 73.33% for 1.0 mg/L
CdCl2. The highest percent mortality rate was the 1.0 mg/L CdCl2 treatment group and the
lowest was the control treatment group. Figure 1. visually shows the heart beats per minute
recorded at 48 hours postfertilization for the different treatment groups. The average heart
beat for the control was 136 bpm, for 0.25 mg/L CdCl2 the average is 163 bpm, for 0.50 mg/L
CdCl2 the average 175 bpm, for 1.0 mg/L CdCl2 the average is 197 bpm. Figure 2 visually
shows the ratios of the distance between sinus venosus and bulbus arteriosus of the heart, to
its body. The graph shows a tendency of a higher ratio for the zebrafish embryos treated with
higher concentrations of cadmium chloride.
Experimental Error:
Although the concentrations of cadmium and amount of solution were precisely measured, a
difference in cadmium concentration and distribution may have taken place throughout the
trials. This may have caused vast differences within the cardiac development of zebrafish
embryos in the same experimental group. Also, error may have occurred through the counting
of zebrafish heart beats due to human eyes counting the beats per minute.
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Conclusion:
If zebrafish embryos are treated with varying concentrations of cadmium chloride
solution then their hearts will abnormally develop. The ratio of the distance between sinus
venosus and bulbus arteriosus of the heart and body length will be higher in embryos treated
with high amounts of cadmium chloride compared with the control group of 0 mg/L CdCl2. It
was also predicted that the heart rate of the embryos would be concentration dependent,
resulting in higher heart rates for larger concentration treatment of CdCl2. Based on
experimentation results, the original hypothesis was supported because as the cadmium
chloride concentration increased, so did the heart rate of the zebrafish embryos. The ratio of
SABA/body length also increased as concentrations increased showing a possible
morphological defect. The implications of this experiment involve exposing specific effects
toxic heavy metals such as cadmium. can not only have on zebrafish, but possibly on humans
due to our similarities. Discovering a causual relationship between cardiovascular disease
and cadmium exposure is very useful because it may explain sudden onsets of cardiovascular
disease cases and it can be used to even further understand the drastic effects of cadmium.
In order to improve this experiment, more trials with more zebrafish embryos would have to be
used due to the lack of quantity of zebrafish due to their high death rate within this
experiment, causing redesign of the experiment throughout the process. Also, further
research could include measuring the heart development of an actual fully developed
zebrafish and its heart function, so the full effects of cadmium can be observed.
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References: Chang, K., Hsu, C., & Liu, S. (2013). Cadmium Induces Apoptosis in Pancreatic βCells through a MitochondriaDependent Pathway: The Role of Oxidative StressMediated cJun NTerminal Kinase Activation. Plos One, 8(2)(Doi:10.1371/journal.pone.0054374). Retrieved October 26 , 2014. De Luca,Elisa. (2014). ZebraBeat: a flexible platform for the analysis of the cardiac rate in zebrafish embryos. Scientific Reports. 4898. Haschek, Wanda M.(2013). Handbook of Toxicologic Pathology:Elsevier Hu,Norman.(2000) Structure and Function of the Developing Zebrafish Heart. THE ANATOMICAL RECORD. 260:148157. ICDA (Ed.). (n.d.). Cadmium Exposure and Human Health. Retrieved October 30, 2014. OSHA. (n.d.). Safety and Health Topics | Cadmium. Retrieved November 2, 2014. WHO. (2010, January 1). Exposure to Cadmium: A Major Public Health Concern. Retrieved November 4, 2014. ProBiox. (n.d.). What is Oxidative Stress. Retrieved November 1, 2014. Agarwal et al. Reproductive Biology and Endocrinology 2005 3:28 Stainier, Didier Y. R.(January 2011). Zebrafish heart development. Nature Reviews Genetics 2 .3948. doi:10.1038/35047564 TellezPlaza, M., Jones, M., DominguezLucas, A., Guallar, E., & NavasAcien, A. (2013). Cadmium Exposure and Clinical Cardiovascular Disease: A Systematic Review. Current Atherosclerosis Reports, 15(10).
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