Irradiation for haematology studies

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The text on this page is taken from an informal compilation of opinions of contributors to the online VOLE List. As such, they are not peer reviewed and may contain differences of opinion. Those wishing to contact the list may contact Adrian Smith.

I am wondering if any of you are working with groups who are doing lethal irradiation in mice with reconstitution specifically for the investigation of the haematological system (long term studies to look at possible development of leukaemia, lymphoma and myeloma) and if so whether you use antibiotics post irradiation and if so what and for how long.

The issue has come up because we don't routinely use antibiotics in animals on irradiation protocols other than when we have identified specific issues with a reconstituting cell line. We have a new researcher working in the haematology field who is unhappy with our approach as he considers that it is standard to give antibiotics for his type of haematological studies and wants us to prove he shouldn't (whereas I think he should prove he needs them if others don't, since the use of antibiotics clinically is discouraged unless it is required). I accept that, as he is not reconstituting a full cell set, there could be increased risk and I clearly don't want to lose animals/ cause an increase in welfare issues - but I am reluctant to change from our usual position of not giving antibiotics without some evidence that it is "standard" for these types of study or (better still) there is some evidence that it is required (rather than being told that "everyone gives antibiotics" when I can name several establishments who don't).

I don’t think antibiotics are needed for as long as the facility is clean and the mice handled accordingly. In fact, I suspect antibiotics may contribute to furthering the floral displacement and the post irradiation diarrhoea. However, I couldn’t quantify how the microbiome changes with versus without antibiotics; and whether this impacts the weight loss or the leukaemia model in itself. I’ve never a chance to do a side by side comparison, and I wish I could have done that.

This conversation comes up quite a bit with researchers, who are adamant that they need to give the mice antibiotics around the time of irradiation. On enquiry, there doesn't seem to be a (researcher) consensus as to:

* when to start / finish the antibiotic (range 0-7 days beforehand) and when to finish - similar timescale.

* which drug is given and the dose (some of the calculations for drug "dissolved" in water would be way below a therapeutic dose) and there's no evidence about drug stability once diluted. Bottles are not changed more frequently!

* exactly what it is they are preventing/treating - it's usually "gram negatives" but of course there are quite a lot of other microbes in the intestines too..

For these reasons and general lack of hard evidence, I'm somewhat skeptical about the use of antibiotics for irradiated mice, and would always advise against their use, on the basis that we shouldn't use them where there isn't proven need and you may do more harm than good by altering the mouse's normal flora.

In addition to ensuring the sterile environment, it's also worth taking care that the mice who are going to be irradiated are well-grown (>8 weeks old) and in good body condition before you start. Fractioning the dose helps; also to ensure that the mice are reconstituted within a couple of hours.

Ensure that they take a baseline bodyweight and monitor any that look ill in the danger period 7-12 days post irradiation. We tend to leave the mice in peace and not to weigh unless the mice show clinical signs, then daily weights if this is the case. Providing mash and gels helps if you're worried.

Here is something that may not have been widely read but may be helpful when talking to investigators about responsible antibiotic use. Although research is not a huge user of antibiotics, all involved have a part to play in good stewardship.

Another possible approach is to encourage the re-establishment of gut flora with commercial probiotics, or gavaging with faecal slurry made up from the animals own faeces taken just before irradiation. Of course coprophagic mice will normally do this for themselves, but if inappetent they might not, and the faeces post irradiation could be altered. Anyone got data on this?

It can be quite challenging to change the strategy in some PIs; for many of our leukemic models, many researchers would still prefer the use of antibiotics as they are really concerned on the effects of bacterial translocation across the gut, and they also mention the translational relevance of such treatments. Two things to consider are the strain specifics (our GA LM models are far more susceptible to side effects) and poor recovery.

I faced a similar situation years ago with a group that was losing NSG mice even with 'routine antibiotics'. To convince them, I did necropsies to show them the severe gut problems after radiation. We set up a pilot study with different housing conditions and compared a bit of good nursing care to their usual leave-them-alone approach. Within a week the researchers were persuaded that the mice needed to be checked frequently, kept warm, offered mash within easy reach, and given fluid support if they got too dehydrated (radiation sickness).