Colorant extracted from turmeric can be useful for combating dengue
FAPESP/DICYT A compound extracted from the roots of turmeric (Curcuma longa L.), a plant that belongs to the ginger family (Zingiberaceae) and is also known as Indian saffron, has been successfully tested by researchers in the city of São Carlos, São Paulo State, as a weapon against larvae of the mosquito species that transmits dengue virus.
The research is being conducted at the Optics and Photonics Research Center (CEPOF), one of the Research, Innovation and Dissemination Centers (RIDCs) funded by Fapesp. The lead investigator of the project is Vanderlei Bagnato, a professor at the University of São Paulo (USP).
“Curcumin, one of the substances that give turmeric its orange color, has natural photodynamic properties. In the presence of light, it stimulates the production of reactive oxygen species, which are highly toxic,” Bagnato said.
The larvae of Aedes aegypti are transparent and are therefore particularly sensitive to photodynamic effects. The pigment accumulates in the insect’s gut after being swallowed with the water in which the larvae breed. When activated by light, it stimulates the production of singlet oxygen molecules, which cause fatal damage to digestive tract tissue.
A similar principle has been used in experimental applications of photodynamic therapy designed to target tumor cells and infectious agents.
In partnership with PDT Pharma, a local pharmaceutical firm, the CEPOF group is also conducting three separate clinical trials to evaluate the effectiveness of the curcumin-based colorant to combat nail fungus, for oral decontamination, and in the treatment of venous ulcers.
In vitro experiments performed at the University of São Paulo’s São Carlos Institute of Physics (IFSC-USP) have already shown that the compound is effective at killing microorganisms.
Over the past two years, as part of Larissa Marila de Souza’s research for her master’s degree in biotechnology at the Federal University of São Carlos (UFSCar), the use of curcumin against A. aegypti has been tested under the supervision of Bagnato and Cristina Kurachi, a professor at IFSC-USP, in collaboration with Natalia Inada, a researcher at IFSC-USP.
“So far we have only performed laboratory experiments, using a standardized controlled system. The aim is to determine the lowest concentration required to kill the larvae without harmful effects on the environment,” Inada said.
The researchers are comparing the effects of photodynamic therapy using sunlight, ordinary white light, and blue LED light. In the most successful trial, 100 por cent of the larvae that were present in the sample died after eight hours of exposure to sunlight. Mortality rates began to increase after the first two hours. The colorant was used at a concentration of 15 micrograms per milliliter of water.
“The best result observed was with sunlight, which is very welcome because it wouldn’t be economically feasible to install lamps to bathe all of the mosquito’s natural breeding grounds in artificial light,” Inada said. “Another important result is that mortality was high even on overcast days, from which it can be concluded that the breeding ground doesn’t have to be in direct sunlight for the method to work.”
According to Inada, exposure to sunlight for 24 hours was sufficient to completely break down the colorant into smaller molecules, whose toxicity is now being studied by the researchers.
“Before conducting field trials to test our findings in the mosquito’s natural breeding grounds, we must be totally sure that the substances resulting from curcumin’s photochemical fragmentation are harmless to other organisms, such as algae, fish, humans and domestic animals, that may come into contact with the water in which the larvae breed,” Inada said.
Souza is conducting preliminary toxicity studies with bean sprouts and oligochaete worms, which are freshwater organisms that A. aegypti larvae often feed upon. The research group is prospecting for partners with whom they can perform trials in larger, more complex species.
“The curcumin-based compound degrades in 24 hours, so if used to combat dengue it would have to be applied to breeding grounds fairly frequently. Testing of the proposal’s feasibility requires interest on the part of the public health authorities,” Bagnato said.
The process used to extract curcumin pigment from turmeric powder was developed in partnership with researchers at UFSCar, who belong to the CEPOF group and PDT Pharma.
“We used solvents to obtain a mixture of curcumin and similar substances called curcuminoids, such as monodemethoxycurcumin and bisdemethoxycurcumin. But the raw extract isn’t suitable for use as a photosensitizer because it’s contaminated by several other organic substances from the plant, so intensive purification is needed,” explained Kleber Thiago de Oliveira, a chemistry professor at UFSCar.
According to Oliveira, the extraction and purification of the natural product would be too costly for use on a large scale. To address this problem, UFSCar’s Photosensitizing Heterocyclic Compound Synthesis Group developed a method of producing synthetic curcumin with the same chemical structure as the natural pigment.
“This synthetic curcumin can be produced on a large scale and it’s also more sustainable,” Oliveira said. “The absence of other curcuminoids hasn’t significantly diminished the molecule’s activity in our ongoing studies. On the contrary, the use of synthetic curcumin has enhanced the experiments’ dynamism, breadth, versatility and reproducibility.”