The parts of a cell that produce energy are called mitochondria (Mt). These can be damaged by HIV as well as prolonged exposure to anti-HIV drugs, particularly some nucleoside analogues. To help doctors diagnose Mt toxicity, laboratory measurements of the levels of lactic acid and bicarbonate in blood samples are useful. More specific and direct techniques include performing a liver (or other tissue/organ) biopsy to obtain cells whose Mt can be visually examined under a microscope or assessing the DNA content of Mt. However, these are cumbersome and not usually performed outside of the setting of a research study. Simple and less invasive tests would be useful.
To this end, a team of researchers including Dr. Matthias Banasch at St. Josef Hospital in Bochum, Germany, appears to have developed a simple breath test for assessing Mt toxicity in PHAs—by measuring carbon dioxide levels in exhaled breath. According to the results of their study, the breath test can detect Mt damage in the liver of PHAs even when levels of lactic acid in the blood are within standard ranges.
Dr. Banasch and colleagues recruited 50 participants as follows:
- 10 HIV negative, healthy people (2 females, 8 males)
- 40 PHAs (6 females, 34 males)
The PHAs were further subdivided into three groups:
- 12 who had never been exposed to anti-HIV drugs
- 15 HAART users
- 13 HAART users who had lipodystrophy
Researchers gave the participants a certain formulation of the amino acid methionine, which is used by Mt. Thirty minutes after taking the supplement, researchers collected the participants' breath from time to time as follows:
Participants would otherwise breathe normally, but at 10-minute intervals exhaled air was collected when participants exhaled a deep breath into a glass tube and again for every 10 minutes for two hours. This was then analysed.
The particular formulation of methionine used in the German experiment was 13C-methionine, which is also known as a "tracer." Although not radioactive, this formulation of methionine can be detected by instruments, so its metabolic path through the body can be followed. Methionine is broken down in Mt and carbon dioxide (CO2) is produced. Instruments measure the level of 13C02 in exhaled breath. When Mt are not working properly, methionine is not broken down through normal chemical reactions and the body's output of 13C02 is reduced. The greater the extent of Mt damage, the lower the levels of the 13C02 in breath samples.
As expected, healthy, HIV negative participants had the least degree of liver damage, followed by healthy PHAs not taking HAART. Mt toxicity was greatest, according to the breath test results, in PHAs on HAART with signs of lipodystrophy. These differences between the groups in this study were statistically significant; that is, not likely due to chance alone.
Additionally, Dr. Banasch and colleagues assessed levels of Mt DNA from the white blood cells of participants. The pattern of results with this test was similar to those seen with the breath test.
The breath test is a relatively simple and non-invasive tool that could be done in many hospitals. Dr. Banasch's next step would likely be to conduct another study comparing breath test results to those from liver biopsies, in healthy people as well as others with Mt toxicity. This validation is important because liver biopsies are considered the "gold standard" when assessing Mt toxicity in that organ.
1. Banasch M, Goetze O, Hollborn I, et al. Non-invasive 13C-methionine breath test detects distinct hepatic mitochondrial dysfunction in HIV-infected patients with normal serum lactate. International Workshop on Adverse Drug Reactions and Lipodystrophy in HIV. 2004 October 25-28;6th: Abstract No. 25.
2. Milazzo L, Piazza M, Sangaletti O, et al. 13C-methionine breath test: a novel method to detect antiretroviral drug-related mitochondrial toxicity. J Antimicrob Chemother. 2005 Jan;55(1):84-9.