Veterinary Medicine

Mayumi Ishizuka

Exploring the Mechanism by which Animals Protect Their Bodies against Toxic Chemicals

Mayumi Ishizuka , Professor

Graduate School of Veterinary Medicine (Laboratory of Toxicology)

High school : Ibaraki Prefectural Mito First Senior High School

Academic background : Doctorate from Hokkaido University

Research areas
Research keywords
xenobiotic-metabolizing enzyme, environmental pollutant, wild animals

What is your goal?

Our daily lives are full of chemicals. We are constantly taking various chemicals into our body, from food, the environment, and drugs. However, chemicals we unintentionally take in through our everyday lives do not always have a favorable effect on our body. When viruses or bacteria invade our body, the immune system functions within our body prevent the body from getting ill as a result of these invaders. So how does our body fight against the “toxic chemicals” we ingest on a daily basis?

When chemicals are taken into the body, if they are immediately excreted from the body via urine and feces, there is less time for the chemical to affect the body. In the event that the toxic chemical is of a structure that is difficult for the body to excrete, the structure thereof undergoes chemical changes which make it easier to metabolically excrete. This is a biological defense mechanism against chemicals. Specifically, mammalian livers have a variety of xenobiotic-metabolizing enzymes that are required for this biological defense against chemicals, so the liver plays an important role in protecting the body from venom.

Do all animals have such a biological defense system? The answer is "Yes." However, the mechanism thereof differs depending on the animal. This is referred to as species specificity, with sensitivity to chemicals differing widely among species. Our goal is to discover this mechanism behind protecting the bodies of not only humans but also various animals, thereby determining what animal is more vulnerable to what chemicals, i.e., their sensitivity to chemicals.


What kind of equipment do you use and what kind of experiments do you conduct?

Image 1. Sampling river sediment in the Republic of Zambia

At the School of Veterinary Medicine, our study subjects cover a wide variety of animals. Specifically, while wild animals are exposed to various environmental pollutants throughout their lives, as humans are, hardly any light has been shed on the impact of these pollutants on wild animals compared with the impact thereof on humans. Thus, in order to investigate what kinds of chemicals wild animals are exposed to and the impact thereof, we carry out fieldwork to collect various samples from wild animals, from feces to blood and organs. From Japan to as far afield as Africa, we ourselves actually go and investigate the impact on animals living there along with the local status of environmental pollution.

Image 2. Blood sampling from a giraffe in Kenya

With the collected samples, we make full use of various analyzers to analyze the chemicals to which animals are exposed and which accumulate in these animals. In analyzing the chemicals, we identify them based on the characteristics that chemicals possess. Chemicals are separated using high-performance liquid chromatography or gas chromatography, after which they are identified with detecting devices such as mass spectrometers. Various pollutants are detected from domestic and overseas wild animals including chlorinated organic compounds such as PCB and agricultural chemical DDT which are problematic due to their persistence in the environment, polycyclic aromatics such as benzopyrene which occurs as a result of burning oil and is problematic due to the carcinogenicity thereof, and heavy metals which are problematic due to the diffusion caused by ore deposit mining. Wild animals making their habitat in African countries abundant in nature are no exception.

Moreover, in order to analyze the biological effect of chemicals, samples with as much information on the living body as possible are necessary. Therefore, to keep samples fresh, our laboratory has a -30℃ freezer room, in addition to a number of -160℃ liquid nitrogen and -80℃ freezers. In addition, in order to elucidate the xenobiotic-metabolizing enzymes that wild animals possess to fight against chemicals, molecules related to xenobiotic metabolism are analyzed at the genetic level. With this purpose, devices to amplify genes and DNA sequencers to determine gene sequences are used. Furthermore, based on the obtained genetic information, genes are synthesized to cells and incorporated, leading to artificial expression, thereby allowing the function of the molecule to be determined.


What is your next goal?

The impact of chemicals is difficult to visualize and easily overlooked unless it becomes a matter of life and death. While there is a wide variety of sensitivity to chemicals depending on species specificity, hardly any light has been shed on the level of species specificity and the molecules attributed thereto except in humans and experimental animals. We aim to elucidate the reality of what is happening in animals in chemically contaminated fields from a scientific perspective.