* FOR PRESERVATION PURPOSES ONLY * Credit: Tim Sandle

Many people who pass away from severe emphysema are found, at the time of autopsy, to have black lungs. The discoloured lungs are most strongly associated with people who have smoked heavily or worked in certain industries.

Now medical researchers have a clue as to what causes the black colour. Studies led by David Corry and Farrah Kheradmand, both of Baylor College of Medicine have found that the black material is made up of an insoluble nanoparticulate of carbon. These tiny specks are result of the incomplete combustion of organic material. An example is with tobacco. The particles are around 30 and 40 nanometers in size. A nanometer is one billionth of a meter in length.

Many of the particles are found in the dendritic cells (dendritic cells are a type of human antigen-presenting cell). The particles are small enough to break strands of DNA inside these cells.

Taking the nanoparticle carbon black material from deceased humans and placing controlled amounts into the noses of mice led to the experimental mice developing emphysema. This highlighted the fact that the tiny particles are hazardous to human health.

The studies showed, unsurprisingly, that the more particles that an animal is exposed to then the worse the effects. The findings also showed that smaller particles do more harm than larger ones.

A burning cigarette has a temperature of between 800 to 920oC; this is hot enough to cause carbon black particle formation. This effect is not only linked to tobacco, for people who work in certain industries, such as the processing of rubber or plastic face a similar hazard. This could lead to new risk assessments being performed. The key risk is that once someone has inhaled a sufficient level of particles, the particles cannot be removed from the lungs and the risk of ill-health is very real.

It might be possible one day to develop drugs to deal with the particles. However, in the meantime, the best measures are to minimize exposure.

The researchers have produced two papers that explain the findings. The first is in eLife, in a paper titled: “Nanoparticulate carbon black in cigarette smoke induces DNA cleavage and Th17-mediated emphysema”.

The second is published in Nature Immunology, which is headed: “The microRNA miR-22 inhibits the histone deacetylase HDAC4 to promote TH17 cell–dependent emphysema”.