In the latest Quest tagged: , , , , , , ,

In the latest Quest

Posted by in Health, Physics & Maths, Science in Society

HIV: who would have thought…

I used to think of HIV/AIDS as something that is very far removed from me and I don’t personally know anybody who is living with HIV. By Gillian Arendse.

This naive view of my lived experience was changed during my years as a lecturer. I was asked by a first year student to accompany her for an HIV-test. My first reaction was … ‘why do you want to go for a test?’ The answer? … not something I expected. ‘Well, I went out last night and found myself this morning in a bed that’s NOT mine. As a matter of fact; I don’t really know what happened last night.’

Suddenly I was awakened to the fact that HIV is all around us. People from all walks of life are at risk. The Joint United Nations Program on HIV/AIDS (UNAIDS) estimated in 2007 that there were 5.6 million people living with HIV/AIDS in South Africa (UNAIDS/World Health Organisation Report on the global HIV/AIDS epidemic 2009).

I have since left academia and I’m currently employed at iThemba LABS in Cape Town. iThemba LABS is a national research facility administered by the National Research Foundation committed to unleash South African potential through knowledge creation, innovation and human capacity building. The facility’s core activities are related to fundamental research, the provision of particle beams used for particle radiotherapy and the production of radionuclides.

Radiation and HIV

A recent discussion with one of my colleagues, Dr Kobus Slabbert, made me aware of the link between radiation and HIV. Dr Slabbert is the head of the Medical Radiation group at iThemba LABS, and spearheads research into the biological effects of radiation. It is known from clinical experience that the normal tissue tolerance to radiotherapy treatment is considerably less in HIV-positive individuals and it is assumed that these patients are more sensitive to ionising radiation when they receive radiation as part of cancer therapy. This enhanced sensitivity to radiation exposure could have significant implications not only for the treatment plans of HIV-positive patients, but also for workers who are exposed to radiation, specifically mine workers.

Radiosensitivity of cells in relation to HIV status is an essential area of research for radiation medicine applications because of the high prevalence of HIV infections in South Africa. South Africa is a country with an emerging economy that already has a large radiation industry in operation. As a result, South African workers use a wide range of radioactive sources and electronic equipment, which produces ionising radiation for many different applications. So it is a real possibility that radiation workers in South Africa could be over exposed to ionising radiation. As ionising radiation can induce cancer, such radiation workers require regular monitoring to make sure that they are in safe working environments.

HIV-infected individuals now survive longer as a result of antiretroviral treatment. This means that, statistically, 40% run the risk of developing cancer during the course of their lives, and many will require radiation therapy.

Cancers such as Kaposi’s sarcoma, non-Hodgkin’s lymphoma, and cervical cancer, are considered AIDS-related cancers. However, there are several additional cancers, referred to as non-AIDS-defining cancers, that are also more prevalent in HIV-infected persons. These include Hodgkin’s disease, anal cancer, lung cancer, non-melanomatous skin cancer, cancers of the head and neck, conjunctival cancer, multiple myeloma, leukaemias and testicular germ cell tumours.

The LINAC  – this apparatus delivers radiation treatment to cancer patients.

iThemba LABS

Surgical treatment can be limited for cancer patients infected by HIV because of the risk of  infection by other pathogens. Thus radiotherapy is a mainstay of localised treatment for tumours in patients who are HIV positive.

There have been several studies reporting on the enhanced sensitivity to radiation therapy in HIV/AIDS patients. Also laboratory investigations have provided further evidence to support the clinical observations of higher sensitivity to radiotherapy in AIDS patients with Kaposi’s sarcoma.

Dr Slabbert and his co-workers undertook a study of the chromosomal radiosensitivity of HIV-positive individuals; the results of which was published in the International Journal of Radiation Biology in 2010. The main aim is to be able to predict, before starting radiotherapy, the response of HIV patients to ionising radiation.

The basic idea is to use blood samples to detect and monitor the radiation damage. This sounds simple enough, but remember that the typical size of a white blood cell is 10 mm. To put that into perspective – the typical thickness of your hair is 100 mm. So if you take a single strand of hair you need to divide that into 10 strands! The conclusion; you’ll probably need some fancy equipment to be able to see things; something like a microscope.

Examining blood samples under a microscope.

iThemba LABS

The exposure of the body to radiation results in the fragmentation of the chromosomes in cells. These fragments are left in the cytoplasm after cell division and appear as micronuclei.

The micronuclei can be seen under a microscope.

iThemba LABS

The numbers of these micronuclei provides an indication of the sensitivity of the individual to the radiation exposure.

Technical detail

Blood cell cultures were prepared in plastic flasks and then irradiated with X-rays at room temperature. For this, 6 MV X-rays from a medical linear accelerator (Siemens Healthcare, Erlangen, Germany) was used. This accelerator is routinely employed for clinical radiotherapy. Following irradiation white blood cells (T-lymphocytes) were cultured for three days to show levels of radiation damage. This was quantified using fluorescence microscopy to be able to identify dividing cells as well as the formation of micronuclei in each cell.

What the research showed

The figure below shows the difference in micronuclei formation for individuals who are HIV-positive compared to those who are HIV-negative.

This graph shows the difference in micronuclei formation for individuals who are HIV-positive compared to those who are HIV-negative.

HIV-positive individuals showed a significantly higher in vitro chromosomal radiosensitivity compared to HIV-negative individuals for all radiation doses studied. Although this study was performed on a small group of individuals and can be seen as a pilot study, observations are clear and suggest that radiotherapy treatments of HIV-positive individuals need some adjustments to prevent the overt tissue reactions in HIV-positive individuals. However, before this data can be used to adjust radiotherapy treatment planning, we need further investigations to quantify the dose modifying influence of HIV on different individuals.

Further studies are needed to elucidate the molecular mechanism underlying the radiosensitivity of HIV-positive individuals.

It is clear however, that there is so much more that we don’t know; so many questions that we need to answer. For the moment I can only conclude that there is more to HIV than I ever imagined.

This article is based on: Baeyens A et al. Chromosomal radiosensitivity of HIV positive individuals. International Journal of Radiation Biology. 2010; 86: 1 – 9

Gillian Arendse is a physicist by training and is now the communications officer for iThemba LABS.