OAT3 inhibitors for Bumetanide - Probenecid, but also Aspirin, Chlorogenic acid (Coffee), Epicatechin (Cocoa, Cinnamon) and more.

Today’s post is about OAT3, highlighted by the green lines.
The interventions reduce renal excretion and raise plasma
concentration rather than directly improving transport across the BBB

Today’s post is a collaboration. Our reader Ling pointed out research trying to boost the bioavailability of bumetanide using something clever called an OAT3 inhibitor.  This would reduce the rate at which the body excretes bumetanide and thus potentially improve its therapeutic effect.

Petra, our reader from Greece, pointed out that in her son Bumetanide seemed to work better when taken with Greek coffee and that that Greek Grandpas like to take their diuretics with a steaming Greek coffee.

Most people, me included, automatically think caffeine when someone mentions coffee.

So I assumed that caffeine might be an OAT3 inhibitor and I did make some experiments on that basis. There is no research data to support caffeine as an OAT3 inhibitor.

Recently I was again looking for other potential Bumetanide boosters.  The obvious one is called Probenecid.  Probenecid is used to treat gout because it lowers uric acid.

Aspirin has some odd effects; low dose aspirin will raise uric acid, but high dose aspirin will lower it. Aspirin is an OAT3 inhibitor.

OATs are a very niche subject, to add to the confusion sometimes you are better looking for SLC22A8, the gene that encodes the transporter. 

There was an earlier post on this subject, which showed that many NSAIDs inhibit OAT3, including Knut’s favourite Ponstan. They are not so well suited to continued use.

Boosting Bumetanide with an OAT3 Inhibitor?

At the end of my little investigation I figured it out; there are many OAT3 inhibitors available, including some in your kitchen.  

Key points on OAT3 (Organic Anion Transporter 3)

If you want to increase the peak concentration and indeed the half-life of a drug that is excreted from the body by OAT3 (organic anion transporter 3), an OAT inhibitor is what you need.

The drug Probenecid is by far the best known OAT3 inhibitor and it is very potent. It has long been to boost the performance of penicillin type antibiotics to treat tough bacterial infections.

Probenecid, if available, may very well be the ideal bumetanide booster.

For adults a simple option is Greek/Turkish coffee. I see little downside as long as you can handle the caffeine. The Greeks live a long time and drink plenty of coffee.

For those who do not like caffeine you can go to active components within the coffee, which seem to be the chlorogenic acids (1,3- and 1,5-dicaffeoylquinic acid). They are sold as a weight loss supplement, the long established version is the French-made Svetol, but there are now others. They still contain 2- 3% caffeine.

Epicatechin, found in cinnamon, dark chocolate and high flavanol cocoa is another OAT3 inhibitor. Cocoavia, made by Mars, is used by some readers of this blog. Cocoa flavanols do clever things with nitric oxide (NO) and have been shown to improve mild cognitive impairment (MCI) and heart health by improving blood vessel elasticity.

Catechins are flavanols belonging to a family of closely related compounds, such as epicatechin, epigallocatechin, epicatechin gallate (EGC), and epigallocatechin gallate (EGCG). They are all slightly different. Catechin itself is not an OAT3 inhibitor; EGCG may or may not be.

Low dose aspirin is likely the cheapest OAT3 inhibitor. It also increases peripheral circulation, which could benefit some. Low dose aspirin has the downside of a small bleeding risk, mainly in old people, and there is a risk of Reye’s syndrome if given during/after a viral infection.

I think for adults a Greek coffee may be the best. For people who have a profound benefit from Bumetanide, I think they should look into Probenecid.

Personally I think Svetol is worth a try.

Coffee that has been extensively processed (just as we saw with cocoa) may not have the same chlorogenic acid content as the more gritty coffee used in the Balkans. Coffee consumption is actually associated with many neurological benefits, reducing the incidence of Parkinson’s and Alzheimer’s; the common mistake in research is the assumption that the effect must be from caffeine.

Source: Can coffee consumption lower the risk of Alzheimer’s disease and Parkinson’s disease? A literature review

  

The health effects of decaffeinated Coffee

My eureka moment in this post was reading about gout and coffee and then decaffeinated coffee. 

Coffee Itself, Not Caffeine, Reduces Risk of Gout 

Dietary supplementation with decaffeinated green coffee improves diet-induced insulin resistance and brain energy metabolism in mice. 

Decaffeinated Green Coffee Bean Extract Attenuates Diet-Induced Obesity and Insulin Resistance in Mice

So then it was a question of finding what in coffee could be the OAT3 inhibitor. At which point I found a very insightful paper that tells you everything, once you realise that:

Coffee = chlorogenic acids  = 1,3- and 1,5-dicaffeoylquinic acid

Interaction of Natural Dietary and Herbal Anionic Compounds and Flavonoids with Human Organic Anion Transporters 1 (SLC22A6), 3 (SLC22A8), and 4 (SLC22A11)

Five compounds, 1,3- and 1,5-dicaffeoylquinic acid, ginkgolic acids (15 : 1) and (17 : 1), and epicatechin, significantly inhibited hOAT3 transport under similar conditions

3.2. Inhibition of hOAT3 by Natural Anionic Compounds and Flavonoids

Human OAT3 expressing cells showed about 4-fold greater accumulation of ES as compared to background control cells ( versus  pmol mg 10  , resp.). Similar to hOAT1, hOAT3-mediated ES uptake was completely (>96% inhibition) blocked by probenecid (Figure 4). Five of the compounds, 1,3- and 1,5-dicaffeoylquinic acid, epicatechin, and ginkgolic acids (15 : 1) and (17 : 1), significantly inhibited hOAT3-mediated transport at 50-fold excess (Figure 4). 1,3-Dicaffeoylquinic acid and ginkgolic acid (17 : 1) exhibited 41% inhibition, while 30–35% reduction of hOAT3-mediated ES uptake was observed for 1,5-dicaffeoylquinic acid, epicatechin, and ginkgolic acid (15 : 1). Catechin, 18β-glycyrrhetinic acid, and ursolic acid failed to produce significant inhibition. Based on the level of inhibition observed, values for all of these compounds would be greater than 50 μM, much higher than clinically relevant concentrations (Table 1). Therefore, further dose-response studies were not performed.

Lay off the Lycopene?

Lycopene does the opposite of what we want. Too much lycopene may lower the effectiveness of a drug that is excreted via OAT3. 

2.29. Lycopene

Lycopene is a carotenoid pigment found in tomato [94]. Lycopene from dietary sources has been shown to reduce the risk of some chronic diseases including cancer and cardiovascular disorders [95]. The administration of lycopene significantly normalized the kidney function and antioxidant status of CSP-treated animals. Furthermore, lycopene also increased the expression of the organic anion and cation transporters (OAT and OCT, resp.) including OAT1, OAT3, OCT1, and OCT2 in the renal tissues [96–98]. In addition, lycopene also decreased the renal efflux transporters (multidrug resistance-associated protein [MRP]-2 and MRP4) levels and induced Nrf2 activation, which activated the antioxidant defense system [99]. Furthermore, lycopene protected against CSP-induced renal injury by modulating proapoptotic Bax and antiapoptotic Bcl-2 expressions and enhancing heat shock protein (HSP) expression [97].

https://www.hindawi.com/journals/omcl/2016/4320374/                                                                                                                  

Aspirin

I actually started out this post by looking at what dose of aspirin might be effective in inhibiting OAT3.  We do know that Aspirin is indeed an OAT3 inhibitor.  

Aspirin and probenecid inhibit organic anion transporter 3

I did find the answer, but along the way you do end up having to look at uric acid. 

Uric acid is taken up by OAT1 and OAT3 from the blood and reabsorbed into renal tubular cells via URAT1 Uric acid is taken up by OAT1 and OAT3 from the blood and reabsorbed into renal tubular cells via URAT1Uric acid is taken up by OAT1 and OAT3 from the blood and reabsorbed into renal tubular cells via URAT1. 

Uricosuric drugs increase the excretion of uric acid in the urine, thus reducing the concentration of uric acid in blood plasma. 

In general, uricosuric drugs act on as urate transporter 1 (URAT1). URAT1 is the central mediator in the transport of uric acid from the kidney into the blood.  By their mechanism of action, some uricosurics (such as  probenecid) increase the blood plasma concentration of certain other drugs and their metabolic products  – this is their effect on OAT3.

Probenecid is a medication that increases uric acid excretion in the urine.

Atorvastatin is a so-called secondary uricosuric. High dose aspirin should also be called a secondary uricosuric.

Antiuricosuric drugs raise serum uric acid levels and lower urine uric acid levels. These drugs include all diuretics and low dose aspirin. 

Low dose aspirin inhibits OAT1 and OAT3 which reduces urate secretion, but high dose aspirin inhibits URAT1 and reduces urate re absorption. This is sometimes known as the biphasic effect.

So low dose aspirin will increase plasma uric acid, but high dose aspirin has the same effect as Probenecid, it lowers plasma uric acid levels.

So Aspirin and Probenecid both affect URAT1 and OAT3. 

Source: Effects on Uric Acid Metabolism of the Drugs except the Antihyperuricemics

At what dose is Aspirin an OAT3 inhibitor?

If we just want aspirin to inhibit OAT3 and not inhibit URAT1, what dose is effective? Fortunately this has been answered in the research. The typical low dose of aspirin (75mg) used preventatively in older people is OAT3 inhibiting, it raises plasma uric acid.  

THE EFFECT OF MINI-DOSE ASPIRIN ON RENAL FUNCTION AND URIC ACID HANDLING IN ELDERLY PATIENTS

Salicylate

Salicylic acid and its derivatives are the most prescribed analgesic, antipyretic, and anti-inflammatory agents. Salicylates have a “paradoxical effect” on the handling of uric acid by the kidney. The action of salicylates on uric acid excretion depends on the dose of salicylates. At doses of less than 2.5 g/day, salicylates cause the retention of uric acid by blocking the tubular secretion of uric acid, while at dose of higher than 3 g/day, they cause increased urinary excretion of uric acid [70]. Mini-dose aspirin, even at a dosage of 75 mg/day, caused a decrease in uric acid excretion and raised serum uric acid level [71]. It has been suggested that the “paradoxical effect” of salicylate can be explained by two modes of salicylate interaction with URAT1: (1) acting as an exchange substrate to facilitate uric acid reabsorption, and (2) acting as an inhibitor for uric acid reabsorption [72]. Low dose of salicylate interact with OAT1/OAT3, the uric acid secreters [73].

Low dose aspirin leads to decreased renal excretion of uric acid and raised serum uric acid levels, which can cause a gout attack in those predisposed to this condition.

High doses of aspirin lower serum uric acid concentration.

Reye’s Syndrome

In children aspirin is very rarely used because of the risk of Reye’s syndrome. Reye’s syndrome causes severe liver and brain damage. It is a type of severe mitochondrial failure that can occur after a viral infection like flu or chickenpox, but it almost only occurs when aspirin has been prescribed. Nobody knows for sure the exact mechanism of the disease.

So do not give aspirin to children with a viral infection.  We already know to avoid paracetamol/acetaminophen (Tylenol in the US) in babies/children and people with autism. Paracetamol/acetaminophen depletes the body’s key antioxidant GSH. 

If someone overdoses on Paracetamol/acetaminophen you give them a high dose of NAC to prevent death. 

Conclusion

Given how long it takes to develop new drugs, I think that improving the pharmokinetics of bumetanide is a pretty obvious thing to do. 

Diamox is an OAT3 inhibitor and our reader Agnieszka found it beneficial only when administered along with Bumetanide.

Strong coffee is an OAT3 inhibitor and this was found to enhance bumetanide by Petra’s son with Asperger’s.

Cinnamon which contains epicatechin, another OAT3 inhibitor, did seem to be helpful in Monty who also takes bumetanide.

I suspect Diamox may be the most potent OAT3 inhibitor of those three

The interesting OAT3 inhibitors seem to be:-

·        Probenecid

·        Low dose aspirin

·        Epicatechin (cocoa, cinnamon ..)

·        Chlorogenic acids (coffee and decaffeinated green coffee extracts) 

Cinnamon, high flavanol cocoa and indeed coffee (minus the caffeine) have numerous health benefits.

Note that Catechin has no effect on OAT3. EGCG was not tested but in other studies has been shown it does affect.

Interactions of green tea catechins with organic anion-transporting polypeptides.

The logical next step would be to improve bumetanide transport across the blood brain barrier.

Boosting Bumetanide with an OAT3 Inhibitor?

Today’s post was prompted by our reader Ling, who highlighted research suggesting another way to improve the potency of bumetanide, a drug many readers have found reduces the severity of autism.

Sometime a little extra boost is necessary

There is an ongoing debate in the literature about how poorly bumetanide crosses into the brain and whether the theoretical chloride-lowering benefit can actually take place in humans.  Well for many readers of this blog, we know the answer.

Nonetheless there are efforts underway to improve the potency of bumetanide in neurological disorders. There is a prodrug called BUM5 which has been shown to reverse types of seizure that bumetanide could not, due to much greater potency in the brain.

The French bumetanide researchers are themselves looking to develop a more potent drug.

Ling highlighted a recent paper that suggested using an old drug called Probenecid to increase the concentration of bumetanide in the brain (and plasma) threefold.

This is not a new idea, during World War Two when antibiotics were in short supply, the same drug Probenecid was used to increase the potency of antibiotics to reduce how much you needed to give patients.

Pharmacodynamics

What we want to do is increase the concentration of bumetanide in the brain and ideally increase the half-life.  Both should increase its effect.

The recent research shows that in mice Probenecid does indeed have the effect we want, but humans are not mice.

A very old study looked at the effect in humans of Probenecid on a very similar diuretic called furosemide.

Pharmacodynamic analysis of the furosemide-probenecid interaction in man

The graph above shows that probenecid had a dramatic effect on the potency of the diuretic. Consider the area under the curves lines.  The area is a proxy for the effect of the drug (but it is a log scale).  After eight hours the furosemide alone has gone to zero, whereas when probenecid is added it is as potent as furosemide was alone after 90 minutes.

The recent study highlighted by Ling:-

The organic anion transport inhibitor probenecid increases brain concentrations of the NKCC1 inhibitor bumetanide.

Bumetanide is increasingly being used for experimental treatment of brain disorders, including neonatal seizures, epilepsy, and autism, because the neuronal Na-K-Cl cotransporter NKCC1, which is inhibited by bumetanide, is implicated in the pathophysiology of such disorders. However, use of bumetanide for treatment of brain disorders is associated with problems, including poor brain penetration and systemic adverse effects such as diuresis, hypokalemic alkalosis, and hearing loss. The poor brain penetration is thought to be related to its high ionization rate and plasma protein binding, which restrict brain entry by passive diffusion, but more recently brain efflux transporters have been involved, too. Multidrug resistance protein 4 (MRP4), organic anion transporter 3 (OAT3) and organic anion transporting polypeptide 2 (OATP2) were suggested to mediate bumetanide brain efflux, but direct proof is lacking. Because MRP4, OAT3, and OATP2 can be inhibited by probenecid, we studied whether this drug alters brain levels of bumetanide in mice. Probenecid (50 mg/kg) significantly increased brain levels of bumetanide up to 3-fold; however, it also increased its plasma levels, so that the brain:plasma ratio (~0.015-0.02) was not altered. Probenecid markedly increased the plasma half-life of bumetanide, indicating reduced elimination of bumetanide most likely by inhibition of OAT-mediated transport of bumetanide in the kidney. However, the diuretic activity of bumetanide was not reduced by probenecid. In conclusion, our study demonstrates that the clinically available drug probenecid can be used to increase brain levels of bumetanide and decrease its elimination, which could have therapeutic potential in the treatment of brain disorders.

Supporting research on organic anion transporters

As is often the case, there is already a wealth of research that we can draw on and it does indeed look like an OAT3 inhibitor should modify the pharmacodynamics of bumetanide in a very helpful way. But questions do remain.

POTENT INHIBITORS OFHUMAN ORGANIC ANION TRANSPORTERS 1 AND 3 FROM CLINICAL DRUG LIBRARIES:DISCOVERY AND MOLECULAR CHARACTERIZATION

Identification of hOAT1 and hOAT3 inhibitors from drug libraries

The NIH Clinical Collection (NCC) and NIH Clinical Collection 2 (NCC2) drug libraries used for HTS consisted respectively of 446 and 281 small molecules (727 total) approved for clinical use or having a history of use in human clinical trials. The clinically tested compounds in the NCC and NCC2 libraries are highly drug-like with known safety profiles. At the indicated concentrations, 92 compounds resulted in 50 % decrease in hOAT1-mediated 6-CF transport, whereas 262 compounds resulted in 50 % decrease in hOAT3-mediated 6-CF transport (Fig. 2). All of the 92 hOAT1 inhibitors were also inhibitors for hOAT3 but with a different potency. Among the 262 inhibitors for hOAT3, 8 compounds were specific for hOAT3 (Table 1), i.e., they lacked appreciable inhibitory activity for hOAT1. For example, stiripentol inhibited hOAT3 with an IC₅₀ of 27.6 ±1.28 μM, but it barely had any effect on hOAT1 (not shown). These inhibitors for hOAT1 and hOAT3 included classes of anti-inflammatory, antiseptic/anti-infection, antineoplastic, steroid hormones, cardiovascular, antilipemic, CNS, gastrointestinal, respiratory and reproductive control drugs.

Table 1

hOAT3-specific Inhibitors

Stiripentol	Cortisol succinate	Demeclocycline
Penciclovir	Ornidazole	Benazepril
Chlorpropamide	Artesunate

Table 2

Highly potent inhibitors for hOAT1 at peak plasma concentrations

Amlexanox	Telmisartan	Mefenamic Acid
Oxaprozin	Parecoxib Na	Meclofenamic Acid
Nitazoxanide	Ketoprofen
Ketorolac Tromethamine	Diflunisal

Table 3

Highly potent inhibitors for hOAT3 at peak plasma concentrations

Mefenamic Acid	Meclofenamic Acid	Pioglitazone
Oxaprozin	Nateglinide	Amlexanox
Ketorolac Tromethamine	Diflunisal	Nitazoxanide
Irbesartan	Valsartan	Telmisartan
Balsalazide	Ethacrynic Acid

We further increased the stringency of our selection criteria by incorporation of peak unbound plasma concentration of drugs since, for drugs tightly bound to plasma proteins, the free concentration in plasma is a better estimate of the drug level interfering with OAT transport function. Further screening using the peak unbound plasma concentration yielded three inhibitors of hOAT1 (Table 4) and seven inhibitors of hOAT3 (Table 5) with potency >95% inhibition.

Table 4

Highly potent inhibitors for hOAT1 at peak unbound plasma concentrations

Compounds	IC50 in COS-7 cells (μM)	Cmax (μM)	Cmax Unbound (Cu.p) (μM)	Cu.p/IC50
Oxaprozin	0.891±0.292	50116	5.01*	5.62
Mefenamic Acid	1.085±0.124	83.0*	8.30*	7.60
Ketorolac Tromethamine	0.653±0.130	9.5017	0.10017	0.150

Table 5

Highly potent inhibitors for hOAT3 at peak unbound plasma concentrations

Compounds	IC50 in COS-7 cells (μM)	Cmax (μM)	Cmax Unbound (Cu.p) (μM)	Cu.p/IC50
Nateglinide	0.860±0.0953	18.018	0.23019	0.270
Oxaprozin	0.870±0.0704	50116	5.01*	5.76
Nitazoxanide	0.154±0.0711	31.2▪	0.0300▪	0.200
Valsartan	0.250±0.143	14.820	0.85021	3.47
Ethacrynic Acid	0.662±0.261	30.922	0.600▲	0.910
Diflunisal	0.720±0.290	496▪	0.490▪	0.680
Mefenamic Acid	1.75±0.258	83.0*	8.30*	4.74

Regulatory Requirements

The FDA and EMA require that the drug interaction liability of this transporter be evaluated in vitro for drug candidates that are renally eliminated. OAT3 contributes to renal drug clearance and transporter – mediated renal drug interactions. Based on the in vitro substrate and inhibition data, decisions are made for OAT transporter–based clinical drug interaction trials, typically with probenecid.

Localization	Endogenous substrates	Substrates used experimentally	Substrate drugs	Inhibitors
Kidney, proximal tubule, basolateral membrane. Brain, choroid plexus and blood–brain barrier	prostaglandin, uric acids, bile acids; conjugated hormones	E3S, furosemide, bumetanide	NSAIDs, cefaclor, ceftizoxime	probenecid, novobiocin

FDA guidance on transporter related drug-drug interactions

APPENDIX A- Tables

Table 1. Major human transporters

Gene                  Aliases          Tissue                 Drug Substrate                  Inhibitor     

SLC22A6          OAT1       kidney,             acyclovir,                      probenecid

                                                                   adefovir,                      cefadroxil

    methotrexate,             cefamandole

    zidovudine                   cefazolin

SLC22A7          OAT2      liver, kidney    zidovudine                  

SLC22A8          OAT3     kidney, brain   cimetidine,                  probenecid

methotrexate             cefadroxil

zidovudine                  cefamandole

                                   cefazolin

Conclusion

This is a classic case where a little inexpensive experiment could be of huge value.  You just use adult volunteers to test the effect on bumetanide pharmacodynamics of a small number of OAT3 inhibitors.

There are now hundreds of kids in France who take bumetanide, meaning hundreds of parents who are probably more than willing to give up a day to sit in a clinic and give hourly blood samples, so their child might benefit.

Would this common sense approach be followed? Or would it be the case that it needs hundreds of thousands of dollars/euros to do a trial and we wait 3 years for the result?