IISc study reveals toxic effects of widely used herbal plants

Folk healers in North-East use plants to treat infections, cancer

Plants have been used as a traditional medicine from ancient times. The 2015 Nobel Prize in Medicine for the discovery of Artemisinin from a plant extract is an epitome of the potential benefits of plants. However, certain commonly used medicinal plants can be toxic to human health, too.

Researchers at the Indian Institute of Science (IISc) have shown that the concept of herbal medicines being totally safe is a myth and their properties need to be thoroughly investigated for toxic properties.

In a recent study, the researchers examined the toxic effects of a common medicinal plant, scientifically known as Millettia pachycarpa (MP). In Manipur, the plant is commonly referred to as ‘Ngamuyai’.

This plant is widely used in the North-East states for treating intestinal worm infections and cancer by local folk healers. Besides, the juice extract of the crushed root and seeds of the plant is extensively used as fish poison to catch fishes, which increases the chances of the extract making its way into human diet.

In the wake of the widespread use of Millettia pachycarpa, the findings of the study raises concern. “We have shown that M. pachycarpa is very toxic, only a few microgram concentration is enough for causing toxicity, particularly for developing fauna,” says Prof Upendra Nongthomba, who led the study.

In this study, zebrafish embryos were subjected to five different concentrations of M. pachycarpa from six hours post-fertilisation until 120 hours post-fertilisation.

The embryos’ morphology was then examined under a stereomicroscope. The researchers found that the mortality rates of embryos exposed to M. pachycarpa were significantly greater than the control. As little as 4.28 ug/ml aqueous extract of M. pachycarpa (AEMP) was sufficient to kill 50 per cent of zebrafish embryos at 96 hours post-fertilisation.

Exposure of zebrafish embryos to below lethal doses induced severe developmental deformities: edema (swelling) of the membranes in the embryo, delayed hatching and reduction in heartbeat. In some embryos, reduced growth rate, swim bladder deficiency, muscle deformities and eye defects were observed. The researchers further explored the mechanisms behind increased developmental deformities.

They could observe a high number of dead cells in the heart, brain and eyes of the fish treated with the plant. Further tests suggested that the cell death was not natural but caused by toxic properties of  the plant.

Nongthomba is an associate professor at the Department of Molecular Reproduction, Development and Genetics, IISc Bengaluru. The others who contributed to the study included Debasish Roy, a research scholar in Nongthomba’s lab, and collaborators Thangal Yumnamcha, and M Damayanti Devi from Manipur University.

A paper on this study appeared online in the journal ‘Toxicological & Environmental Chemistry’ early this month.