A non-invasive breath test to measure key aspects of liver function

INTRODUCTION

The liver plays a key role in human health, broadly responsible for metabolism, detoxification and protein synthesis. Dysfunction of the liver is associated with many conditions including obesity, diabetes, cardiovascular disease, kidney disease, and autoimmune conditions like lupus, as well as diseases of the liver (e.g. alcohol related liver disease).

Traditionally, liver function is measured with ‘liver function tests’ (LFTs) using blood samples taken in primary care settings. However, many of these are not true measures of how well the liver is performing its key functions instead they simply measure liver cell damage. Other tests report on the synthesis of key proteins (e.g. albumin), or natural products of liver degradation. However, these processes can be affected by multiple other factors, such as nutritional status and some kidney conditions, which can mask true changes in liver function. Additionally, some biomarkers take time to change in response to liver damage.

A key liver function is extracting compounds from the blood stream and metabolizing them to less harmful and more excretable forms. No regularly used liver function test currently measures this. Our new LIBRA® Liver Function Test allows for this to be measured with a convenient non-invasive breath test suitable for clinic and home use.

We know that liver function can improve in individuals with liver impairment, for example, with lifestyle changes and other interventions. Due to the non-invasive nature of the test, practical administration at home is possible. The LIBRA Liver Function test is therefore well-suited to analysing changes in liver function longitudinally to monitor for treatment success, or deterioration in liver metabolic function.

What is liver metabolic activity, and why is it important to look at?

The liver is the body’s major site of detoxification; it processes drugs, toxins and other small molecules into more excretable forms. The enzymes responsible are found in hepatocytes. In conditions where the liver is damaged (e.g. cirrhosis) we know there is reduced function of a variety of enzymes – due to both loss of hepatocytes and reduced enzyme transcription (1). For example, alcohol dehydrogenase is known to be reduced in liver disease (2). This reduced function contributes to the negative health outcomes of liver disease.

While loss of hepatocytes and reduced enzyme levels are features of late-stage liver disease, alterations in liver metabolic activity can also be seen in early-stage liver disease like MASH (3) and in other acute conditions – for example sepsis, liver inflammation, and ischemia (4).

What is Hepatic Extraction, and why is it important to look at?

For a compound to be metabolised in hepatocytes, it must first get there. Hepatic extraction relates to the ability of the liver to remove a compound from the blood to get it to the enzymes that then degrade it.

Changes in liver structure and blood flow are present in late-stage liver conditions like cirrhosis, which affects hepatic extraction, as well as earlier stage disease, including MASH and even obesity (5). Other conditions that affect blood flow to, and from the liver (e.g. heart failure) (6) can also impact hepatic extraction.

How is the LIBRA Liver Function Test Performed?

The LIBRA Liver Function Test is simple to use and can be performed in the home environment as well as in the clinic – in the morning is ideal – see Figure 1 for an overview.

After a short fast, the LIBRA oral solution is taken by the patient (this is sweetened for palatability) and contains ingredients widely found in food and confirmed to be safe (GRAS). After around 25 minutes, simple instructions for use direct participants to collect a breath sample. The LIBRA analytes are collected, concentrated and stabilised from the breath using specialised materials inside the collection device, enabling the collected breath samples to be sent using standard postal services at room temperature. They are analysed in the Owlstone Breath Analysis laboratory post-collection.

How does the LIBRA Liver Function Test Work?

The food safe compounds in the LIBRA oral solution are absorbed from the gut and processed in the liver. For some of these compounds, the rate of metabolism is dependent on the actual functional levels of certain liver enzymes – i.e related directly to liver metabolic activity. Other LIBRA compounds are more dependent on the access to the sites where they are metabolised – i.e. their levels in blood and rate of metabolism are related to the extent of hepatic extraction, which is influenced by liver structure and blood flow (shown in figure 2).

By analysing the levels of the LIBRA oral solution compounds and their metabolites in breath* at an appropriate point after ingestion of the LIBRA solution, we can get a measure of liver metabolism and hepatic extraction. This can be:

• compared between timepoints in the same person to understand changes in their personal liver function
• compared between different patient groups to compare levels of liver function in them
• compared to our reference ranges to get a read out of how well the liver is functioning versus e.g. healthy people or people with confirmed liver disease

* The levels of the LIBRA compounds found in breath are proportional to the concentration levels in blood – similar to the principles of an alcohol breathalyser