Arsenic exposure may damage children’s immunity for life

Muhammad Nabil

Long-term arsenic exposure from early childhood can cause permanent genetic-level damage to children’s ability to fend off diseases, new icddr,b study suggests.

Immunity of arsenic-exposed children has shown similar characteristics like aged people, suggesting that certain cells of their immune system have ‘started growing older and become weaker’; the signs of onset of this change was detectable as early as at 9 years of age.

Infographic: Inamul Shahriar / Muhammad Nabil / icddr,b

The findings published in Toxicological Sciences investigated whether prolonged arsenic exposure from fetal life to early childhood causes immunodeficiency or weakening of the ability to fight diseases, by examining certain biomarkers or health status indicators in the human body.

Researchers followed up arsenic exposure in unborn children and then at 4.5 and 9 years of age after birth.

Then they examined Telomeres – a protective region at the end of human chromosomes that are truncated each time the human cells divide and multiply over time as we age normally. The 2009 Nobel Prize in medicine was awarded for discovering how telomeres protect chromosomes.

“Shorter length of these telomeres in immune cells indicates earlier aging of immune cells thereby reducing their capacity to fight infections/diseases,” observes Dr Rubhana Raqib, icddr,b senior scientist and senior author of the study, supported by Swedish Research Council, SIDA.

“Our study found that the arsenic-exposed children had shortened telomere length which indicates that arsenic toxicity may have negatively influenced their immune function. These children at only 9 years of age may have lesser ability to fight different diseases, similar to a scenario seen in older people,” explains Ms Tania Mannan, the first author of the study and a PhD student under the supervision of Dr Raqib.

There is a natural decline of immunity in aged people to defend infectious diseases and the risk of chronic diseases such as cancer also increase with aging. What is unusual in these arsenic-exposed children is that they have shown the same characteristics that will make them more susceptible to such diseases because of the low host defence properties as seen in aged people.

The study also examined whether arsenic exposure affects the function of a gland known as Thymus, located above the lungs in the human body. It produces certain T-cells that contribute to fighting diseases as part of the immune system. Existing icddr,b research has already shown that arsenic exposure reduces the size and function of thymus in infants, which naturally results in weaker immunity.

A region in these T cells called ‘signal joint T-cell receptor excision circles’ or simply sjTRECs is also a biomarker of thymus function ). sjTREC level in the human body may reduce when a person’s defense system weakens to defend diseases.

Dr Raqib went on to explain, “Children in the recent study being exposed to arsenic since their fetal lives, have shown decreased sjTREC concentrations. It reflects immunodeficiency or damage to their immune system, similar to  that seen in diseases like HIV-infection/AIDS or the way chemotherapy weakens immune system of cancer patients.”

 

Toxic effects are well-known. What’s next?

The poisonous effects of arsenic on human body is already well-established in many research.

In Bangladesh, some 20-40 million people are reportedly exposed to arsenic poisoning through drinking water. Despite the fact that it claims around 40,000 lives annually, the issue has gone off the radar.

The new study may help strengthen advocacy around arsenic poisoning as it has for the first time shown the how arsenic affects the building blocks of life for children at such an early age, which was previously not clearly known.

“We now know that it does not only cause cancer and death by slow-poisoning but may cause damage to children for life even though they survive,” observes Dr Raqib, who is part of a new research exploring whether intake of selenium-rich lentils could neutralise arsenic concentrations in human body.

Selenium, an essential micronutrient available in food, has the ability to bind with arsenic in the human bile and help remove it from the body through the excreta, as shown in animal- models, says Ms Evana Akhtar, senior research officer at icddr,b and the paper's co-author undertaking her PhD under the supervision of Dr Raqib.

Published in the Trials, the study, supported by Grand Challenges Canada and Global Institute of Food Security (GIFS), Canada, a collaborative study of Dr Raqib with Canadian scientists, Professor Judit Smits and Professor Albert Vandenberg, plans to feed naturally produced selenium-rich lentils grown in Saskatchewan provinces in Canada to arsenic-exposed people in Bangladesh as part of their regular diet.

“If our results are affirmative to show depleting arsenic deposit in the human body, it will pave way towards a cost-effective solution for a persisting health problem killing thousands in Bangladesh,” observes Dr Raqib.