Indian scientists pooh-pooh doubts over curcumin

Scientists in India are dismissing a new report¹ that debunks the medicinal value of curcumin, the substance that gives the age-old Indian spice turmeric (Curcuma longa) its trademark bright yellow colour.

The review in a reputed journal attracted a great deal of attention in India with its conclusion that curcumin "does not satisfy any of the tenets of medicinal chemistry properties to qualify as a drug for any application". There’s no evidence, the report said, that curcumin has any specific therapeutic benefits. Noting that much effort and funding has been "wasted" on curcumin research to find a new drug, the authors hoped their report will alert scientists about the futility of pursuing further research.

Leading Indian biochemist Govindarajan Padmanabhan, at the Indian Institute of Science (IISc) in Bengaluru, strongly refutes this conclusion. "The review is a huge dampener considering that over 10,000 papers have been published and there are over 120 clinical trials using curcumin, under various stages of progress," Padmanabhan, who has worked extensively on curcumin, told Nature India .

"Even if 1% of the published papers make sense, it would still be a sizeable number to warrant against passing a negative verdict on the whole field," he said.

Admitting that curcumin may not manifest properties which a medicinal chemist would look for, and so cannot come under the category of a classical drug, he said it shows potential as an adjunct drug and acts through mechanisms that “defy the classical tenets dearly held by medicinal chemists”.

"Curcumin works as an excellent adjunct drug in malaria as shown in our mice experiments," he said. A combination of curcumin with the antimalarial drug arteether ensured almost 100% survival of the animals infected with Plasmodium berghei (the murine malaria parasite), while the control animals died in six or seven days.

"At the time of publication of these results in 2012, we had data from 200 mice obtained over a 4 year period," he said. In another study, the curcumin-arteether combination "completely cured the animals of cerebral malaria."

Padmanabhan points out that in clinical trials elsewhere, curcumin formulations were found effective in patients with rheumatoid arthritis and in cases with chronic pulmonary obstructive disease that leads to coronary artery disease.

Curcumin does suffer from poor bioavailability and rapid metabolism, admits Padmanabhan. "But by virtue of its ability to function as an immunomodulator, it has the potential to serve as an adjunct drug to treat infectious diseases and provide long-term protection. This is especially relevant in cases where a vaccine is not available. While, a cautionary approach is welcome, summary dismissal of an entire area of research is like throwing the baby with bath water."

Gautam Desiraju, a structural chemist at the Indian Institute of Science says curcumin as a molecule is different from turmeric as a medicinal product. “Drug is different from a preventive. Allopathy is different from Ayurveda and other native medicinal systems.” To describe research in curcumin as a waste, would therefore not be looking at it from a holistic approach, he cautions. “Curcumin is being used in India for 1000 years and more. People are not stupid. Not over such a length of time,” he points out.

Sankaran Valiathan, a cardiac surgeon who heads the India government’s task force on Ayurvedic biology is equally critical of the report. Noting that turmeric is used in many herbal formulations of Ayurveda, the traditional Indian system of medicine, he says medicinal chemists make the mistake of supposing that the therapeutic effect of Ayurvedic treatment is "brought about by a new chemical entity or molecular drug in the formulation. “This is an over-simplification made by reductionists who refuse to recognize that their molecular supposition has no support in Ayurveda,” he adds.