- Jul 27, 2010
 
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Here's a potentially very relevant paper reporting that NSAIDs (pain-killers such as aspirin and paracetamol) inhibit transport of salbutamol across bronchial epithelium by effects on organic cation transporters (OCTs):
http://sci-hub.la/10.3109/02770903.2013.773518
There are several very important implications here. First, use of these drugs, by blocking uptake of salbutamol into the lungs, would reduce the effects of inhaling, perhaps resulting in a need to take more than the usual dose. Second, if the salbutamol is retained in the lungs for a period of time, it could build up, so that when it finally passes into the blood and then the kidneys, would be at increased concentration. The third implication is that NSAID inhibition of OCTs would also be a mechanism by which these drugs could reduce salbutamol excretion by the kidneys, since OCTs are present in renal proximal tubules, and thought to play a major role in excretion of many drugs. This paper reports effects of NSAIDs on OCTs in proximal tubule cells:
http://sci-hub.la/10.3109/02770903.2013.773518
This may be what Froome's team is looking at in trying to construct a renal impairment defense. There's still a big jump between lab studies and a credible in vivo mechanism. Both of these studies were carried out using cell cultures. The first study, on bronchial epithelium, used concentrations of NSAIDs that the authors concede are far higher than in vivo plasma concentrations following the usual doses. The second study did not directly demonstrate an effect on salbutamol transport, but on a much simpler cation, tetraethylammonium. The effects were quite modest, and in fact their data suggest that at physiological doses there wouldn't be any effect at all. It should also be noted that this study transfected the transporters into the cells, i.e., inserted the appropriate gene. I think this was done to maximize the amount of transporter, so that it would be easier to detect changes produced by the NSAIDs.
I'm just speculating here, of course, but Froome may claim that after the crash on stage 12, he took paracetamol or some other NSAID or NSAID-like pain-killer for several days. The argument would be that this reduced uptake of salbutamol both in his lungs and in the kidneys, leading to elevated concentrations in the lungs and plasma. When he stopped taking the analgesic, this backlog of salbutamol was excreted.
This would require more than a week of analgesic, though, which seems unlikely, unless Froome wants to claim he was treating some additional problem. Also, of course, Froome has crashed before, as no doubt have other riders who take salbutamol, not to mention that pain-killers might be taken for some other problem. In any case, as supporting evidence, he would want to show that all his urine samples during this previous time period showed very low levels of salbutamol. And if he gave a blood sample at any point during that period, plasma concentration would be very informative. Though as noted before, all of this information has limited usefulness if Froome can't demonstrate how much salbutamol he was inhaling during this period.
			
			http://sci-hub.la/10.3109/02770903.2013.773518
There are several very important implications here. First, use of these drugs, by blocking uptake of salbutamol into the lungs, would reduce the effects of inhaling, perhaps resulting in a need to take more than the usual dose. Second, if the salbutamol is retained in the lungs for a period of time, it could build up, so that when it finally passes into the blood and then the kidneys, would be at increased concentration. The third implication is that NSAID inhibition of OCTs would also be a mechanism by which these drugs could reduce salbutamol excretion by the kidneys, since OCTs are present in renal proximal tubules, and thought to play a major role in excretion of many drugs. This paper reports effects of NSAIDs on OCTs in proximal tubule cells:
http://sci-hub.la/10.3109/02770903.2013.773518
This may be what Froome's team is looking at in trying to construct a renal impairment defense. There's still a big jump between lab studies and a credible in vivo mechanism. Both of these studies were carried out using cell cultures. The first study, on bronchial epithelium, used concentrations of NSAIDs that the authors concede are far higher than in vivo plasma concentrations following the usual doses. The second study did not directly demonstrate an effect on salbutamol transport, but on a much simpler cation, tetraethylammonium. The effects were quite modest, and in fact their data suggest that at physiological doses there wouldn't be any effect at all. It should also be noted that this study transfected the transporters into the cells, i.e., inserted the appropriate gene. I think this was done to maximize the amount of transporter, so that it would be easier to detect changes produced by the NSAIDs.
I'm just speculating here, of course, but Froome may claim that after the crash on stage 12, he took paracetamol or some other NSAID or NSAID-like pain-killer for several days. The argument would be that this reduced uptake of salbutamol both in his lungs and in the kidneys, leading to elevated concentrations in the lungs and plasma. When he stopped taking the analgesic, this backlog of salbutamol was excreted.
This would require more than a week of analgesic, though, which seems unlikely, unless Froome wants to claim he was treating some additional problem. Also, of course, Froome has crashed before, as no doubt have other riders who take salbutamol, not to mention that pain-killers might be taken for some other problem. In any case, as supporting evidence, he would want to show that all his urine samples during this previous time period showed very low levels of salbutamol. And if he gave a blood sample at any point during that period, plasma concentration would be very informative. Though as noted before, all of this information has limited usefulness if Froome can't demonstrate how much salbutamol he was inhaling during this period.
				
		
			