Prof. Debabrata Dash (sitting) and Nitesh Singh were able to easily disintegrate blood clots by combining photothermal ablation with streptokinase (a drug-dissolving drug) at 30-50 times less than the therapeutic dosage.

It is now possible to remove blood clots in a less risky way, thanks to research carried out by scientists at the Institute of Medical Sciences, Banaras Hindu University, Varanasi.

A team led by Prof. Debabrata Dash from the Department of Biochemistry  has for the first time used photothermal therapy using near-infrared (NIR) laser and NIR-absorbing gold nanorods to disintegrate freshly formed clots and clots formed a few hours ago. The disintegration of clots was accelerated when the therapy was combined with clot-dissolving drugs given at 30-50 times less than the therapeutic dosage. The results were published in the journal Nano Research.

There is an inherent risk of severe bleeding, haemorrhagic stroke and embolism when clot-dissolving drugs such as streptokinase are used at therapeutic dosages.  So the drug is generally administered only under medical supervision.

“Though we have studied freshly formed clot and clots that are a few hours old, the combination therapy should be effective even for aged clots,” says Prof. Dash, who is the corresponding author of the paper. “Since the near-infrared laser can penetrate up to a few centimetres depth, it can be used for treating blood clots present in superficial veins.”

How it works

When a clot forms, fibrin monomers are held together by weak noncovalent bonds. After some time, the clotting factor XIII forms covalent bonds that cross-links the monomers and stabilises the clot.

“We reasoned that heat supplied locally to the clot should loosen the noncovalent interaction between fibrin strands, thus facilitating reduction in the clot mass,” says Prof. Dash.

Heat (50-55 degree C) supplied locally to the clot for 45 minutes using near-infrared laser and gold nanorods led to nearly 18 per cent reduction in the clot mass. Since anti-fibrin antibodies are ligated on the surface of gold nanorods, the nanoparticles would get attached to the fibrin-rich blood clots when injected into the blood. So the heating would largely be localised to the area where the clot is present.

Photothermal ablation used in combination with low-dose of streptokinase led to nearly 21 per cent lysis in fresh clots.“We focussed on non-covalent interaction. When we exposed the fibrin to near-infrared laser, heat generated locally led to disruption of the non-covalent bonds resulting in loosening of the strands and a reduction in the size of the clot. This allows clot-busting drugs like streptokinase to easily get inside the clot and break it down,” says Nitesh Singh from the Department of Biochemistry, Institute of Medical Sciences at BHU and the first author of the paper.

In the case of in vitro studies, photothermal ablation used in combination with low-dose of streptokinase led to nearly 20 per cent lysis in clots that were more than three hours old; the disintegration was 21 per cent in the case of fresh clots.  Since pressure from flowing blood is seen in arteries and veins the extent of clot disintegration should be higher when thermal ablation and chemotherapy is combined with fluid pressure seen in blood vessels. Indeed, nearly 41 per cent disintegration under arterial blood flow pressure and 19.5 per cent under venous pressure condition were seen in in vitro studies.

The team replicated the study in mice. Freshly induced clots in the femoral vein of mice were irradiated with laser and treated with sub-therapeutic dose of streptokinase. From being completely occluded, normal blood flow in the vein was restored after the combination treatment. “Vein tissues examined under microscope showed ‘significant reduction’ in the extent of blockage after laser irradiation. Clot clearance improved further when combination treatment was used,” says Singh.

“Our work on mice was to test if the combination therapy was effective against clots. We will be studying the amount of clot reduction in future studies,” Singh says.