Greyhounds used to test drug delivery

Sifei Han, Luojuan Hu, Gracia, Tim Quach, Jamie S. Simpson, Glenn A. Edwards, Natalie L. Trevaskis, and Christopher J. H. Porter Lymphatic Transport and Lymphocyte Targeting of a Triglyceride Mimetic Prodrug Is Enhanced in a Large Animal Model: Studies in Greyhound Dogs

Associated Institution(s): Monash Institute of Pharmaceutical Sciences, Monash University, Victoria and Charles Sturt University, NSW

The Experiment

Ten male greyhounds were used in an experiment to test the delivery of drugs to the lymphatic system and then killed.

The thoracic lymph duct was cannulated (tube inserted) to six of the dogs. After recovery, an intravenous catheter was inserted into the cephalic vein to enable blood sampling. Drugs were then administered orally via capsule and the dogs were given water. Lymph was then collected continuously (10 hours post dosing). At the end of the sampling period the dogs were killed with pentobarbitone.

Another 4 dogs had no lymph duct cannulation surgery but the drug was administered via IV infusion or orally. They were killed after two hours and their lymph nodes were collected for study.

The paper recorded that 2 of the dogs pulled out their thoracic lymph duct cannulas at 1.5 and 5.5 hours post prodrug dosing.

The research, funded by tax payer’s dollars by way of NHMRC and ARC grants, did little to progress human health and indeed the researchers state that “direct comparison of free MPA plasma levels and plasma levels of MPA associated with glycerides such as re-esterified 2-MPA-TG is not possible since each species will have different systemic pharmacokinetics (e.g., volume of distribution and clearance).”

In fact the differences between dogs and humans should have been enough reason not to fund this project.  The NHMRC and ARC when assessing the application should have known and the researchers should have known when devising such an experiment that physiological differences exist between dogs and humans particularly in relation to gastro intestinal (GI) physiology which makes extrapolation unreliable.

  • The canine gastric emptying rate is a dog is lower than in a human.
  • Canine gastric pH is higher than that of a human
  • Intestinal dimensions vary between dogs and humans – for example the length of a dog’s small intestine is half the length of a human’s and therefore there is a faster transit time of drugs in dogs as compared to humans.
  • Dogs secrete bile salts at a higher rate than humans

The researchers themselves state that rats, used routinely as models to study lymphatic drug transfer, differ in GI physiologically between other species such as dogs and humans and yet the researchers want to keep undertaking studies comparing different species to give them misguided confidence in extrapolating to humans.

Humane Research Australia asks why the researchers are using conscious greyhounds only to confirm rat studies.  This research can only make assumptions at best, and at worst is totally unreliable when translating to humans.

HRA now calls on the federal government funding bodies to no longer fund these types of out-dated, unreliable animal experiments.

Replacements (Alternatives)

Various in vitro models can serve as an alternative to in vivo models for studying lymphatic drug transport. 

In the intestinal permeability model, Caco-2 cells are used to evaluate intracellular lipoprotein-lipid assembly and to examine the effect of lipids and lipidic excipients on incorporation of drug with lipoproteins in lymphatic transport. In one in vitro model, Gershkovich and Hoffman described a correlation between the degree of ex vivo incorporation of a drug into chylomicrons and the extent of intestinal lymphatic drug transport.(2) According to a lipolysis model described by Dahan and Hoffman, in vivo drug absorption could be predicted by evaluating drug release from a lipid-based drug delivery system and estimating precipitation of the drug during lipolysis.(3)Holm and Hoest reported an in silico method that established a quantitative relationship between the molecular structure and amount of drug transferred from the intestinal to the lymphatic system.(4) using the computer program VolSurf.

Cost-Benefit Analysis:

HRA received the following advice from a medical expert:

"The papers found, collectively combining computer modelling with some very nice in vitro (cellular) models shows that alternatives are available, and in this context, with the “Code” as the guiding document, should not have been approved (i.e. alternatives are available). In fact, the researchers themselves developed an in vitro component (in vitro digestion of compounds by lipases) that could have meshed with the other previous studies identified.

Given human application was suggested as the ultimate benefit, systematic reviews should have been conducted (a) to see if large animal studies on this question have been performed previously, and (b) whether human drug studies, with the TG-based drugs used in the greyhound, had been attempted previously – namely, was the study needed? Also, if yes, more studies were required, were the small number of animals adequate to generate statistically and biologically meaningful results?

The physiological/anatomical differences highlighted between dogs and humans are also powerful, suggesting that the translation to humans will be most likely to fall in the 90% animal studies that don’t translate, rather that the 5 – 10% that do succeed. If the study was done to improve dog health, maybe it could be justified, but it clearly states that a human context inspired this study.

For the above reasons, in the context of balancing benefit with animal welfare, the greyhound study cannot be justified.”

Funding

National Health & Medical Research Council and the Australian Research Council.

What You Can Do

Please direct a letter to the National Health and Medical Research Council, and the ARC (details of each below) demanding that in the future no animal experiment such as this be funded and instead moneys be devoted to medical research that is relevant to human health.  Ask them to set up funding specifically for non-animal research.

National Health and Medical Research Council
GPO Box 1421
Canberra ACT 2601
Email: nhmrc@nhmrc.gov.au

Australian Research Council
GPO Box 2702
Canberra ACT 2601
Email:info@arc.gov.au 

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References

  1. Han, S., Hu, L. Gracia, Quach,T.,  Simpson,J.S.,  Edwards,G.A., Trevaskis, N.L. and Porter, CJH. Mol. Pharmaceutics 2016 113, 3351-3361 Lymphatic Transport and Lymphocyte Targeting of a Triglyceride Mimetic Prodrug Is Enhanced in a Large Animal Model: Studies in Greyhound Dogs
  2. Gershkovich P1, Hoffman A.  Eur J Pharm Sci. 2005 Dec;26(5):394-404. Uptake of lipophilic drugs by plasma derived isolated chylomicrons: linear correlation with intestinal lymphatic bioavailability.
  3. Dahan A, Hoffman A. J Control Release. 2008 Jul 2; 129(1):1-10. Rationalizing the selection of oral lipid based drug delivery systems by an in vitro dynamic lipolysis model for improved oral bioavailability of poorly water soluble drugs.
  4. Holm R1, Hoest J.  Int J Pharm. 2004 Mar 19;272(1-2):189-93. Successful in silico predicting of intestinal lymphatic transfer.


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