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. The concept that herbal medicines are totally safe is a myth and their properties need to be thoroughly investigated.
In a recent study, IISc researchers examined the toxic effects of a common medicinal plant, scientifically known as Millettia pachycarpa (MP). In the state of Manipur, the plant is commonly referred to as “Ngamuyai”. This plant is widely used in the North-eastern states of India 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 raise a call of concern.
“We have shown that M. pachycarpa is very toxic, only few microgram concentration is enough for causing toxicity, particularly for developing fauna”, says Prof. Upendra Nongthomba, who led the study.
The researchers used zebrafish as a model system to systematically investigate the toxic effects of M. pachycarpa. As zebrafish development and genetic set-up is very similar to other vertebrates, including humans, the insights gained from the study are largely applicable to higher organisms. Zebrafish embyros are transparent, develop quickly and reproduce at a high rate, making them ideal for toxicological studies.
In this study, zebrafish embryos were subjected to five different concentrations of M. pachycarpa from six hours post fertilization until 120 hours post fertilization. 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% of zebrafish embryos at 96 hours post fertilization. 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 AEMP. Further tests suggested that the cell death was not natural but caused by toxic properties of AEMP.
When asked about the societal implications of the study, Dr. Nongthomba says, “There should be a framework for the usage of plants or plant extracts for killing animals or for treatment of diseases. Usage of the plant for killing fishes should be looked into as it can cause not only killing of the fishes, but may also harm aquatic animals.”
The plant kingdom is brimming with potentially beneficial unexplored resources. The current study highlights the importance of scientific investigation to reveal the hidden benefits or side effects of medicinal plants.
About the authors
Upendra Nongthomba is an Associate Professor at the Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore. Debasish Roy is a research scholar in his lab. Collaborators Thangal Yumnamcha, and M. Damayanti Devi are at Manipur University.
The paper appeared online in the journal Toxicological & Environmental Chemistry earlier this month.