New research led by scientists from Imperial College London explains why around half of people with asthma experience a 'late phase' of symptoms several hours after exposure to allergens. The findings, published in the journal Thorax, could lead to better treatments for the disease.
An estimated 300 million people suffer from asthma, and the prevalence is rising. Symptoms are commonly triggered by allergens in the environment, such as pollen and dust mites. These stimuli can cause the airways to tighten within minutes, causing breathing difficulties which range from mild to severe. Many sufferers also experience a 'late asthmatic response' three to eight hours after exposure to allergens, causing breathing difficulties which can last up to 24 hours.
In the early asthmatic response, the allergen is recognised by mast cells, which release chemical signals that cause the airways to narrow. In contrast, the mechanism behind the late phase has remained unclear.
In research on mice and rats, the Imperial team have now found evidence that the late asthmatic response happens because the allergen triggers sensory nerves in the airways. These nerves activate reflexes which trigger other nerves that release the neurotransmitter acetylcholine, which causes the airways to narrow. If the findings translate to humans, it would mean that drugs that block acetylcholine called anticholinergics could be used to treat asthma patients that experience late phase responses following exposure to allergens.
Steroids are the main treatments for asthma prescribed now, but they are not effective for all patients. A recent clinical trial involving 210 asthma patients found that the anticholinergic drug tiotropium improved symptoms when added to a steroid inhaler, but the reason for this was unexplained.
"Many asthmatics have symptoms at night after exposure to allergens during the day, but until now we haven't understood how this la
|Contact: Sam Wong|
Imperial College London