Pregnenolone/aspirin can block cellular estrogen uptake, PUFA promotes it

haidut

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I have posted in the past about the "obscure" estrogen estrone sulfate (E1S) and its role as a biomarker of both onset and progression of breast, colon, prostate, endometrial, and many other cancers. Despite its major role in cancer development, E1S remains known to mainstream medicine as simply an "inactive" estrogen precursor, relevant only to menopausal women. The role as a precursor is certainly true - i.e. cells can synthesize E1 and E2, as needed, using E1S as a precursor and the body does seem to be using E1S as a long-term storage reservoir of estrogen. Thus, blood levels of E1S have been proposed as a reliable biomarker of whole-body estrogenic tone, since it can (and it is) easily converted to the "active" estrogens E1 and E2. Conversely, interventions aimed at lowering E1S levels have been proposed as viable methods for preventing and potentially treating the types of cancer E1S is involved in. Lowering E1S uptake into the cells would also likely be therapeutic as it basically deprives the cell of this estrogenic precursor that the cell can turn into the more active estrogens E1 and E2. As it turns out, anions such as E1S are subject to a so-called "active transport", which can be controlled (blocked or enhanced) and this would lead to changes in the cellular levels of E1S. The transporter of E1S is something called the organic anion transporter protein (OATP) family, and it seems to control the transport/levels of others important steroids, especially cortisol.

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.633.3124&rep=rep1&type=pdf
Demonstration of a Probenecid-Inhibitable Anion Exchanger Involved in the Release of Cortisol and cAMP and in the Uptake of p-Aminohippurate in Bovine Adrenocortical Cells

There is a closely-related family of transporters known as the cation organic transport protein (OCTN/OCTP), which are responsible for transporting/controlling carnitine inside the cell, and I have written about them in the past in regards to substances such as Meldnium/Mildronate, aspirin, quinine, etc. Anyways, back to E1S and OATP. It turns out that a number of molecules is capable of inhibiting this protein as well. The study below demonstrates that the PUFA metabolites known as prostaglandins strongly increased E1S cellular uptake. Conversely, the abundant endogenous steroid pregnenolone-sulfate (PS) (and to a much smaller degree, DHEA-S) was capable of inhibiting E1S update into the cell and thus depriving the cell of its major estrogen precursor used to synthesize the active estrogens. Importantly, at concentrations of 50 uM/L PS inhibited E1S uptake by about 80%. Now, every cell can synthesize estrogen de-novo, without using E1S as a precursor. However, studies have shown that the de-novo pathway is energetically very expensive and as long as the cell has access to pre-formed precursors such as E1S it prefers to use them instead of synthesizing E1 and E2 from scratch using cholesterol as a precursor. Overall, about 90% of the active estrogens inside the cell are derived from E1S and only 10% are synthesized de-novo from cholesterol and other precursors. Thus, if one inhibits significantly the E1S uptake into the cell, this has the effect of drastically reducing the estrogenic tone of a cell/organism. That means that the cheap and widely available aspirin and PS are functional anti-estrogens and can be used similarly to known anti-estrogenic drugs such as the SERM class or aromatase inhibitors (AI). The study corroborates this hypothesis by demonstrating that OATP expression in breast cancer cells is more than 100-fold higher than in healthy cells, ensuring a major role for E1S (and its uptake inhibitors) in breast cancer. If cortisol uptake into the cell is indeed controlled to a large degree by the same transporter as for E1S, this suggests that pregnenolone and aspirin may also be useful in conditions driven by excess cortisol such as Cushing syndrome/disease, diabetes, sarcopenia, osteoporosis/osteopenia, mental diseases (especially depression, and bipolar disorder), dementias, liver diseases, etc.

Identification of Steroid Sulfate Transport Processes in the Human Mammary Gland

"...There are also epidemiological data to support an association between the circulating concentrations of hormones and prohormones, including E1S and DHEAS, and the eventual risk of developing breast cancer, especially in the postmenopausal years (14, 15). This link implies that steroids in their sulfated, anionic form gain access to the intracellular milieu and can determine the extent of exposure to downstream, biologically active hormones. Sulfated steroid conjugates carry a net negative charge at physiological pH levels, and as such, their transfer across cell membranes is carrier mediated. Steroid sulfates have been identified as substrates for distinct members of two organic anion carrier gene families: the organic anion transporting polypeptide (OATP) superfamily, classified within the solute carrier 21A gene family (SLC21A) (16) and the organic anion transporter (OAT) family, encoded by the solute carrier 22A (SLC22A) genes (17)."

"...In cis-inhibition studies with 5 mol/liter [3H]-E1S, DHEAS showed a dose-dependent effect that reached statistical significance at 50 umol/liter (Fig. 5A). Another adrenally derived steroid hormone precursor, pregnenolone sulfate, was a more potent inhibitor and significantly inhibited E1S uptake to 50% and 20% of control values at 10 umol/liter and 50 umol/liter, respectively. Other pregnenolone derivatives, 17-OH pregnenolone sulfate and 21-OH pregnenolone sulfate, inhibited uptake to a moderate degree at the higher concentration tested (Fig. 5B). The unconjugated forms of pregnenolone, 17-OH pregnenolone and 21-OH pregnenolone, exerted no effect when tested at 10 mol/liter (data not shown)."

"...Unexpectedly, the naturally occurring cyclopentenone PGA1, which is derived from PGE1, increased OATP-B-mediated [3 H]-E1S transport (Fig. 7A). The PGA1-mediated stimulation was detectable after 15 sec and was maximal at 1 min (Fig. 7B). No further stimulation occurred when transport was measured at longer intervals or when cells were preincubated with PGA1 (data not shown). A more marked stimulation was observed at lower substrate concentrations (500 nmol/liter) with both 100 nmol/liter and 1 mol/liter (Fig. 7B). PGA2, a second cyclopentenone prostanoid derived from PGE2, also enhanced E1S uptake at similar concentrations. However, PGJ2, a third cyclopentenone PG, which differs from the PG of the A series by the position of the reactive electrophilic carbon, had no effect (Fig. 7C). "

"...To establish whether widely used breast cancer cell lines expressed OATP carriers and could serve as in vitro models for additional studies of steroid sulfate transport, the mRNA expression of OATP-B, OATP-D, and OATP-E was measured in MCF-7, T47D, and MDA-MB-453 cell lines. For comparison, the expression levels in the OATP-B stably transfected CHO cells as well as in the Hep-G2 cell line, which reportedly expresses both OATP-B and OATP-E (34), are given. None of the breast cancer lines examined gave detectable signals for OATP-B above background levels (Table 2). Conversely, when standardized for expression in Hep-G2 cells, our studies identified MCF-7 as the cell line with the highest expression of OATP-E (13-fold higher than Hep-G2), whereas the MDA-MB-453 and T47-D cell lines express 10-fold and 100- fold less, respectively. Although no standard cell line was available for OATP-D, MCF-7 again expressed the highest levels of OATP D mRNA (approximately 100-fold more than T47-D and 500-fold more than MDA-MB-453) (Table 2). "
 

Lollipop2

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Wow…important. Surprised no one commented on this study. For post menopausal women this is so important to know especially how easily the takes up Estrone sulfate not just estradiol. Progesterone and DHEA seem so important in face of an environment so high in xenoestrogens and phytoestrogens. The PUFA connection is obvious to us on RPF; amazing to find in the study. What a great find @haidut! Thanks for sharing.
 

Regina

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I have posted in the past about the "obscure" estrogen estrone sulfate (E1S) and its role as a biomarker of both onset and progression of breast, colon, prostate, endometrial, and many other cancers. Despite its major role in cancer development, E1S remains known to mainstream medicine as simply an "inactive" estrogen precursor, relevant only to menopausal women. The role as a precursor is certainly true - i.e. cells can synthesize E1 and E2, as needed, using E1S as a precursor and the body does seem to be using E1S as a long-term storage reservoir of estrogen. Thus, blood levels of E1S have been proposed as a reliable biomarker of whole-body estrogenic tone, since it can (and it is) easily converted to the "active" estrogens E1 and E2. Conversely, interventions aimed at lowering E1S levels have been proposed as viable methods for preventing and potentially treating the types of cancer E1S is involved in. Lowering E1S uptake into the cells would also likely be therapeutic as it basically deprives the cell of this estrogenic precursor that the cell can turn into the more active estrogens E1 and E2. As it turns out, anions such as E1S are subject to a so-called "active transport", which can be controlled (blocked or enhanced) and this would lead to changes in the cellular levels of E1S. The transporter of E1S is something called the organic anion transporter protein (OATP) family, and it seems to control the transport/levels of others important steroids, especially cortisol.

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.633.3124&rep=rep1&type=pdf
Demonstration of a Probenecid-Inhibitable Anion Exchanger Involved in the Release of Cortisol and cAMP and in the Uptake of p-Aminohippurate in Bovine Adrenocortical Cells

There is a closely-related family of transporters known as the cation organic transport protein (OCTN/OCTP), which are responsible for transporting/controlling carnitine inside the cell, and I have written about them in the past in regards to substances such as Meldnium/Mildronate, aspirin, quinine, etc. Anyways, back to E1S and OATP. It turns out that a number of molecules is capable of inhibiting this protein as well. The study below demonstrates that the PUFA metabolites known as prostaglandins strongly increased E1S cellular uptake. Conversely, the abundant endogenous steroid pregnenolone-sulfate (PS) (and to a much smaller degree, DHEA-S) was capable of inhibiting E1S update into the cell and thus depriving the cell of its major estrogen precursor used to synthesize the active estrogens. Importantly, at concentrations of 50 uM/L PS inhibited E1S uptake by about 80%. Now, every cell can synthesize estrogen de-novo, without using E1S as a precursor. However, studies have shown that the de-novo pathway is energetically very expensive and as long as the cell has access to pre-formed precursors such as E1S it prefers to use them instead of synthesizing E1 and E2 from scratch using cholesterol as a precursor. Overall, about 90% of the active estrogens inside the cell are derived from E1S and only 10% are synthesized de-novo from cholesterol and other precursors. Thus, if one inhibits significantly the E1S uptake into the cell, this has the effect of drastically reducing the estrogenic tone of a cell/organism. That means that the cheap and widely available aspirin and PS are functional anti-estrogens and can be used similarly to known anti-estrogenic drugs such as the SERM class or aromatase inhibitors (AI). The study corroborates this hypothesis by demonstrating that OATP expression in breast cancer cells is more than 100-fold higher than in healthy cells, ensuring a major role for E1S (and its uptake inhibitors) in breast cancer. If cortisol uptake into the cell is indeed controlled to a large degree by the same transporter as for E1S, this suggests that pregnenolone and aspirin may also be useful in conditions driven by excess cortisol such as Cushing syndrome/disease, diabetes, sarcopenia, osteoporosis/osteopenia, mental diseases (especially depression, and bipolar disorder), dementias, liver diseases, etc.

Identification of Steroid Sulfate Transport Processes in the Human Mammary Gland

"...There are also epidemiological data to support an association between the circulating concentrations of hormones and prohormones, including E1S and DHEAS, and the eventual risk of developing breast cancer, especially in the postmenopausal years (14, 15). This link implies that steroids in their sulfated, anionic form gain access to the intracellular milieu and can determine the extent of exposure to downstream, biologically active hormones. Sulfated steroid conjugates carry a net negative charge at physiological pH levels, and as such, their transfer across cell membranes is carrier mediated. Steroid sulfates have been identified as substrates for distinct members of two organic anion carrier gene families: the organic anion transporting polypeptide (OATP) superfamily, classified within the solute carrier 21A gene family (SLC21A) (16) and the organic anion transporter (OAT) family, encoded by the solute carrier 22A (SLC22A) genes (17)."

"...In cis-inhibition studies with 5 mol/liter [3H]-E1S, DHEAS showed a dose-dependent effect that reached statistical significance at 50 umol/liter (Fig. 5A). Another adrenally derived steroid hormone precursor, pregnenolone sulfate, was a more potent inhibitor and significantly inhibited E1S uptake to 50% and 20% of control values at 10 umol/liter and 50 umol/liter, respectively. Other pregnenolone derivatives, 17-OH pregnenolone sulfate and 21-OH pregnenolone sulfate, inhibited uptake to a moderate degree at the higher concentration tested (Fig. 5B). The unconjugated forms of pregnenolone, 17-OH pregnenolone and 21-OH pregnenolone, exerted no effect when tested at 10 mol/liter (data not shown)."

"...Unexpectedly, the naturally occurring cyclopentenone PGA1, which is derived from PGE1, increased OATP-B-mediated [3 H]-E1S transport (Fig. 7A). The PGA1-mediated stimulation was detectable after 15 sec and was maximal at 1 min (Fig. 7B). No further stimulation occurred when transport was measured at longer intervals or when cells were preincubated with PGA1 (data not shown). A more marked stimulation was observed at lower substrate concentrations (500 nmol/liter) with both 100 nmol/liter and 1 mol/liter (Fig. 7B). PGA2, a second cyclopentenone prostanoid derived from PGE2, also enhanced E1S uptake at similar concentrations. However, PGJ2, a third cyclopentenone PG, which differs from the PG of the A series by the position of the reactive electrophilic carbon, had no effect (Fig. 7C). "

"...To establish whether widely used breast cancer cell lines expressed OATP carriers and could serve as in vitro models for additional studies of steroid sulfate transport, the mRNA expression of OATP-B, OATP-D, and OATP-E was measured in MCF-7, T47D, and MDA-MB-453 cell lines. For comparison, the expression levels in the OATP-B stably transfected CHO cells as well as in the Hep-G2 cell line, which reportedly expresses both OATP-B and OATP-E (34), are given. None of the breast cancer lines examined gave detectable signals for OATP-B above background levels (Table 2). Conversely, when standardized for expression in Hep-G2 cells, our studies identified MCF-7 as the cell line with the highest expression of OATP-E (13-fold higher than Hep-G2), whereas the MDA-MB-453 and T47-D cell lines express 10-fold and 100- fold less, respectively. Although no standard cell line was available for OATP-D, MCF-7 again expressed the highest levels of OATP D mRNA (approximately 100-fold more than T47-D and 500-fold more than MDA-MB-453) (Table 2). "
Yay! Pregnenolone and aspirin is my favorite goto combo. Great for getting through hurricanes too!
 

Inaut

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Yay! Pregnenolone and aspirin is my favorite goto combo. Great for getting through hurricanes too!
Been thinking about you and the other Floridians in our community. Sending you blessings :)
 
OP
haidut

haidut

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Wow…important. Surprised no one commented on this study. For post menopausal women this is so important to know especially how easily the takes up Estrone sulfate not just estradiol. Progesterone and DHEA seem so important in face of an environment so high in xenoestrogens and phytoestrogens. The PUFA connection is obvious to us on RPF; amazing to find in the study. What a great find @haidut! Thanks for sharing.

Thanks. I think combining pregnenolone and aspirin is synergistic, and Peat seems to be recommending this combo to people when they ask him for recommendations for estrogen-dominant males. For women, he seems to favor progesterone, but when the question is about men he often comes back with this combo recommendation, and has also given it in the context of high cortisol so pregnenolone being able to block cortisol uptake (as I hinted in my post) is looking more and more plausible.
 
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haidut

haidut

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Yay! Pregnenolone and aspirin is my favorite goto combo. Great for getting through hurricanes too!

Yep, my most often used combo too, usually with some niacinamide and policosanol as well. Niacinamide also has antiestrogenic effects, as does policosanol.
 

Regina

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Yep, my most often used combo too, usually with some niacinamide and policosanol as well. Niacinamide also has antiestrogenic effects, as does policosanol.
Thank you!!
I've got it all on hand. Much needed for the coming days. :muscle:
 

DennisX

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Yep, my most often used combo too, usually with some niacinamide and policosanol as well. Niacinamide also has antiestrogenic effects, as does policosanol.
So are saying that resveratrol, a SIRT1 activator, is is estrogenic and should be avoided?
 

Steve

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Do you feel anything when taking a pregnenolone/aspirin combo, or do you just go on faith that it's having a good effect?
 
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haidut

haidut

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So are saying that resveratrol, a SIRT1 activator, is is estrogenic and should be avoided?

Oh yeah, it is a stilbenoid, and they are all estrogenic. It is structurally similar to the infamous DES and probably just as estrogenic.

Another infamous drug, Vioxx, that killed many people and was pulled from the market is also a stilbenoid and the way it killed people (clots, heart attacks, strokes, etc) strongly suggests it is estrogenic as that is what estrogen does.

David Sinclair, the Harvard professor who started the resveratrol hype, sold his company Sirtris (producing a synthetic, more potent version of resveratrol) to GSK for $700mil. In a few years GSK closed Sirtris down due to failed clinical trials - i.e. several people died in the groups taking the synthetic resveratrol chemical.

SIRT1 is heavily involved in cancer as it promotes fatty acid oxidation.

Finally, Peat actually wrote an entire article on resveratrol and its "benefits".
 

J.R.K

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Oh yeah, it is a stilbenoid, and they are all estrogenic. It is structurally similar to the infamous DES and probably just as estrogenic.

Another infamous drug, Vioxx, that killed many people and was pulled from the market is also a stilbenoid and the way it killed people (clots, heart attacks, strokes, etc) strongly suggests it is estrogenic as that is what estrogen does.

David Sinclair, the Harvard professor who started the resveratrol hype, sold his company Sirtris (producing a synthetic, more potent version of resveratrol) to GSK for $700mil. In a few years GSK closed Sirtris down due to failed clinical trials - i.e. several people died in the groups taking the synthetic resveratrol chemical.

SIRT1 is heavily involved in cancer as it promotes fatty acid oxidation.

Finally, Peat actually wrote an entire article on resveratrol and its "benefits".
An excellent find @haidut, aspirin and pregnenalone are an emergency combo I like as well, but I do like pregnenalone on a regular basis as well.
If I am not mistaken Metformin is also a stilbenoid as well, presumably with similar caveats to resveratrol. I thought I had read in one of Dr Peats newsletters that resveratrol, acetaminophen, Metformin which are proposed to raise heme oxygenase, which raises carbon monoxide, which is once again activating stress hormone systems to combat inflammation in short term stress situations, but long term use has a cumulative degenerating effect.
 

DennisX

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OK thanks. What about this new SIRT6 activator made from Fucus Vesiculosus marketed by DoNotAge. Is it estrogenic or worse?
 

J.R.K

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Oh yeah, it is a stilbenoid, and they are all estrogenic. It is structurally similar to the infamous DES and probably just as estrogenic.

Another infamous drug, Vioxx, that killed many people and was pulled from the market is also a stilbenoid and the way it killed people (clots, heart attacks, strokes, etc) strongly suggests it is estrogenic as that is what estrogen does.

David Sinclair, the Harvard professor who started the resveratrol hype, sold his company Sirtris (producing a synthetic, more potent version of resveratrol) to GSK for $700mil. In a few years GSK closed Sirtris down due to failed clinical trials - i.e. several people died in the groups taking the synthetic resveratrol chemical.

SIRT1 is heavily involved in cancer as it promotes fatty acid oxidation.

Finally, Peat actually wrote an entire article on resveratrol and its "benefits".
An excellent find @haidut, aspirin and pregnenalone are an emergency combo I like as well, but I do like pregnenalone on a regular basis as well.
If I am not mistaken Metformin is also a stilbenoid as well, presumably with similar caveats to resveratrol. I thought I had read in one of Dr Peats newsletters that resveratrol, acetaminophen, Metformin which are proposed to raise heme oxygenase.
 

Ildikó

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Yay! Pregnenolone and aspirin is my favorite goto combo. Great for getting through hurricanes too!
Yep, my most often used combo too, usually with some niacinamide and policosanol as well. Niacinamide also has antiestrogenic effects, as does policosanol.
I would need some input from you Haidut, i am postmenopausal since 51, have had total hysterectomy 3 years ago, 61 years old female. I am following Dr Peats advice on dieting trying to leave out pufa, normal weight, taking micronized progesterone, sometimes aspirin. I have tryed pregnenolone also but it gives me adrenaline surge/insomnia in the evening even taking 50 mg in the morning. When i stop taking it the insomnia goes away. The micronized progesterone is a huge help with sleeping, it is quite cheap in my country. I also take niacinamide when i remember. So, my question is why do i have insomnia from vitamine b3?
 
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haidut

haidut

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OK thanks. What about this new SIRT6 activator made from Fucus Vesiculosus marketed by DoNotAge. Is it estrogenic or worse?

This is not the topic of the thread. You can make a new thread about it and put the name of the chemical in the title so that people on the forum would see it and comment if they have use it or worked with it.
 
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haidut

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An excellent find @haidut, aspirin and pregnenalone are an emergency combo I like as well, but I do like pregnenalone on a regular basis as well.
If I am not mistaken Metformin is also a stilbenoid as well, presumably with similar caveats to resveratrol. I thought I had read in one of Dr Peats newsletters that resveratrol, acetaminophen, Metformin which are proposed to raise heme oxygenase, which raises carbon monoxide, which is once again activating stress hormone systems to combat inflammation in short term stress situations, but long term use has a cumulative degenerating effect.

I don't think Metformin is a stilbenoid, but it is definitely something to avoid. It has a black box warning that it can cause lactic acidosis, which is often lethal. Also, we now know that anything capable of raising lactic acid increases risk for cancer, despite most doctors laughing at such claims...but we even have direct studies showing it.

Acetaminophen raises serotonin and may have estrogenic effects as well. I would not use it, considering something like aspirin, quinine or an anti-serotonin drug are much safer ways to lower fever.
 
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haidut

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I would need some input from you Haidut, i am postmenopausal since 51, have had total hysterectomy 3 years ago, 61 years old female. I am following Dr Peats advice on dieting trying to leave out pufa, normal weight, taking micronized progesterone, sometimes aspirin. I have tryed pregnenolone also but it gives me adrenaline surge/insomnia in the evening even taking 50 mg in the morning. When i stop taking it the insomnia goes away. The micronized progesterone is a huge help with sleeping, it is quite cheap in my country. I also take niacinamide when i remember. So, my question is why do i have insomnia from vitamine b3?

Your post says it is pregnenolone that gives you insomnia, not niacinamide. If progesterone works well for you, then I'd take that, and maybe some niacinamide.
 

Ildikó

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Your post says it is pregnenolone that gives you insomnia, not niacinamide. If progesterone works well for you, then I'd take that, and maybe some niacinamide.
Thanks for your reply, i wrongly put in the last part of my question, i meant why does pregnenolone gives me insomnia.
I am fine with niacinamide.
So I just take micronized progesterone and niacinamide, does it have the same preventative action against postmenopausal breast cancer?
Do I have to cycle progesterone or is it ok if I just take a few days break?
Thank you!
 

RPDiciple

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@haidut do you have any idea why i struggle with penis getting less blood and just less viral if i take either aspirin, progesterone and or pregnenolone. No matter the dose or the combination. I know progesterone can have penis numming effects but all those three give me that. What can be the explenation? I have tested this very carefully as well with each one.
 

aliml

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"...OATP-B mediates E1S uptake when expressed in oocytes (19) and in HEK293 cells (31) with affinity constant (Km) values estimated to be 4–6 μmol/liter. However, the assignment of DHEAS as a substrate is equivocal, and the extent of its interaction with other steroids has not been investigated. The validity of the OATP-B stably transfected CHO expression system was first tested for E1S. Uptake was linear for 20 sec (Fig. 4A) and saturable with an apparent Km value of 5 μmol/liter and a maximum velocity (Vmax) value of 777 pmol/mg protein·min (Fig. 4B). In cis-inhibition studies with 5 μmol/liter [3H]-E1S, DHEAS showed a dose-dependent effect that reached statistical significance at 50 μmol/liter (Fig. 5A). Another adrenally derived steroid hormone precursor, pregnenolone sulfate, was a more potent inhibitor and significantly inhibited E1S uptake to 50% and 20% of control values at 10 μmol/liter and 50 μmol/liter, respectively. Other pregnenolone derivatives, 17-OH pregnenolone sulfate and 21-OH pregnenolone sulfate, inhibited uptake to a moderate degree at the higher concentration tested (Fig. 5B). The unconjugated forms of pregnenolone, 17-OH pregnenolone and 21-OH pregnenolone, exerted no effect when tested at 10 μmol/liter (data not shown)..."

OATP-B In Vitro Inhibitors

InhibitorIC50 (μM)Ki (μM)Substrate used
Acemetacin0.1Dibromofluorescein
Atazanavir3.6Estrone sulfate
Atorvastatin0.09Dibromofluorescein
Atorvastatin0.4Estrone sulfate
Benzbromarone0.1Dibromofluorescein
Bicalutamide16.3Dibromofluorescein
Bicalutamide12.9Estrone sulfate
Bromsulphthalein1.7Estrone sulfate
Bromsulphthalein21.5Estrone sulfate
Bromsulphthalein6Estrone sulfate
Butylparaben44.3Dibromofluorescein
Calcitriol7.5Dibromofluorescein
Celecoxib13.7Dibromofluorescein
Cerivastatin66.2Estrone sulfate
Cyclosporine20Bromsulphthalein
Cyclosporine0.07Rosuvastatin
Darunavir26Estrone sulfate
D&C Orange No. 42.11Dibromofluorescein
Desogestrel30.3Dibromofluorescein
Diacerein19.98Dibromofluorescein
Didymin3.84',5'-dibromofluorescein
Diethylstilbestrol1.6Dibromofluorescein
Diflunisal12Dibromofluorescein
Dipyridamole2Dibromofluorescein
Doxazosin Mesylate15Dibromofluorescein
Drospirenone11.1Dibromofluorescein
Efavirenz9.6Estrone sulfate
Erlotinib0.07Dibromofluorescein
Estradiol2.7Dibromofluorescein
Estrone2.51.9Estrone sulfate
Ethinyl estradiol1.3Dibromofluorescein
Ezetimibe1.8Dibromofluorescein
FD&C Red No. 402.59Dibromofluorescein
Felodipine3.5Dibromofluorescein
Flutamide32.4Dibromofluorescein
Fluvastatin0.1Dibromofluorescein
Gemfibrozil8Rosuvastatin
Glimepiride1.6Dibromofluorescein
Glyburide1.9Dibromofluorescein
Hesperetin67.6Estrone sulfate
Hesperidin8.34',5'-dibromofluorescein
Hesperidin1.92Estrone sulfate
Indinavir3.93Estrone sulfate
Indomethacin16.3Dibromofluorescein
Irbesartan1.3Dibromofluorescein
Itraconazole24.8Dibromofluorescein
Kaempferol21.3Estrone sulfate
Ketoconazole5.7Dibromofluorescein
Latanoprost6.76Dibromofluorescein
Levothyroxine10.4Dibromofluorescein
Lopinavir0.72Estrone sulfate
Loratadine13.3Dibromofluorescein
Lornoxicam1.8Dibromofluorescein
Losartan8Dibromofluorescein
Lovastatin9.92Dibromofluorescein
Meloxicam1.59Estrone sulfate
MK-5710.2Bromsulphthalein
Montelukast1Bromsulphthalein
Montelukast0.38Dibromofluorescein
Naringenin49.2Estrone sulfate
Naringin6.94',5'-dibromofluorescein
Naringin4.63Estrone sulfate
Narirutin14.24',5'-dibromofluorescein
Nelfinavir0.9Estrone sulfate
Neohesperidin dihydrochalone20.1Dibromofluorescein
Nobiletin1.64',5'-dibromofluorescein
Norethindrone14.2Dibromofluorescein
Novobiocin3.4Dibromofluorescein
Olmesartan4.71Dibromofluorescein
Olsalazine2.8Dibromofluorescein
Oxybutynin27.79Dibromofluorescein
Paclitaxel25Bromsulphthalein
Phloretin1.31Estrone sulfate
Phloridzin23.2Estrone sulfate
Piroxicam35.42Dibromofluorescein
Prasurgel5.9Dibromofluorescein
Quercetin9.47Estrone sulfate
Quetiapine19.1Dibromofluorescein
Raloxifene7.4Dibromofluorescein
Raltitrexed70Pemetrexed
Repaglinide5.2Bromsulphthalein
Reserpine3.5Dibromofluorescein
Rifampicin90Bromsulphthalein
Rifampicin2.11.6Estrone sulfate
Rifamycin SV3Bromsulphthalein
Rifamycin SV32.3Estrone sulfate
Rifamycin SV2.7Estrone sulfate
Ritonavir6.34.8Estrone sulfate
Ritonavir2.2Estrone sulfate
Ronacaleret12Rosuvastatin
Rosiglitazone5.2Bromsulphthalein
Saquinavir5.34Estrone sulfate
Saquinavir4.6Estrone sulfate
Silibinin dihemisuccinate1Bromsulphthalein
Silymarin2.5Dibromofluorescein
Simvastatin9.4Dibromofluorescein
Simvastatin84.7Estrone sulfate
Sinensetin5.44',5'-dibromofluorescein
Sucrose monolaurate47.7Dibromofluorescein
Sulfasalazine2.7Dibromofluorescein
Tangeretin1.64',5'-dibromofluorescein
Ticagrelor4.8Dibromofluorescein
Ticagrelor2.12Estrone sulfate
Tipranavir0.2Dibromofluorescein
Tipranavir0.88Estrone sulfate
Tropesin0.03Dibromofluorescein
Vilazodone hydrochloride47.1Dibromofluorescein
Zafirlukast1.4Dibromofluorescein

OATP-B (organic anion transporting polypeptide B)

Aliases: OATP-B, OATPB, SLC21A9
Gene name: Solute carrier organic anion transporter family member 2B1 (SLCO2B1)

Summary

OATP2B1 is a ubiquitously expressed uptake transporter with broad substrate specificity. It mostly transports organic anionic endo- and xenobiotics, and its activity appears to be pH-dependent. OATP2B1 is primarily associated with the oral absorption of drugs, notably fexofenadine, whose PK is altered when intestinal OATPs and/or MDR1 are inhibited. Its expression in the liver and other tissues, as well as the results of in vitro studies, suggest a broader role in drug ADME, DDI, and toxicology; these aspects, however, are not well understood or characterized. The FDA and EMA guidances recommend evaluation of OATP drug interaction liabilities, but do not specifically recommend investigation of OATP2B1.

Localization

OATP2B1 is widely expressed in tissues including the sinusoidal membrane (blood side) of the hepatocyte, the apical membrane (gut side) of enterocytes, the basal membrane (fetal side) of the syncytiotrophoblasts, as well as the luminal membrane (blood side) of endothelial cells in brain, heart, and lung blood vessels [1-4]. OATP2B1 has been attributed tissue-specific physiological and pharmacological functions [5].

Function, physiology, and clinically significant polymorphisms

OATP2B1 is an organic anion uptake transporter with 12 predicted membrane-spanning domains. It exhibits pH dependency in that it seems to transport some substrates more efficiently at lower pH. Its substrate specificity appears somewhat more restricted than those of OATP1B1 and 1B3; however, it transports fexofenadine, statins, glibenclamide, glyburide, estrone 3-sulfate (E3S), dehydroepiandrosterone 3-sulfate (DHEAS), prostaglandin E2, thyroid hormones [6], and taurocholate.
The apparent pH dependency of transport may be important for the gastrointestinal transport of drug substrates such as fexofenadine, as pH varies substantially along the gastrointestinal tract [7, 8].
In the placenta and mammary gland, OATP2B1 plays a role in the uptake and recirculation of sulfate conjugates of steroid hormones, such as E3S and DHEAS [3, 9]. Additionally, OATP2B1 jointly with BCRP may be responsible for the transepithelial transport of E3S and DHEAS across the placenta [2].
OATP2B1 inhibitors include many organic anions, mono- and dicarboxylic acids [8, 10], steroid hormones and their derivatives [2], drugs such as rifamycin SV [11], pravastatin [8], cyclosporine, and gemfibrozil [12], as well as constituents of citrus juices [13] and herbal extracts [14]. Of the individual components of grapefruit juice, the polymethoxiflavone nobiletin was the most potent inhibitor of OATP2B1 [15], and in a screen of 22 antituberculosis drugs streptomycin and linezolid had the strongest inhibitory potential on OATP2B1 [16].
Sequence variation in the SLCO2B1 gene has been associated with altered transport activity of the protein in vitro [7, 17], and the clinical relevance of SLCO2B1 polymorphisms is slowly emerging. SNPs like the exonic rs12422149 and the intronic rs1077858 that influence the expression levels of the protein also affect the effectiveness of androgen deprivation therapy in prostate cancer. Higher expression of OATP2B1 correlates with increased uptake of DHEAS and subsequent resistance to therapy [18].
FXR, HNF1α, HNF3β, and HNF4α transcriptionally regulate OATP1B1, OATP1B3, and OATP2B1 by binding to the promoter region [19-22]. Besides being substrates of OATP2B1, the thyroid hormones thyroxine (T4) and triiodothyronine (T3) are also reported to be transcriptional regulators of the transporter via transactivation of the SLCO2B1 1b and the SLCO2B1 1e promoters [6].

Clinical significance

OATP2B1 in the gastrointestinal tract is involved in the oral absorption of drugs like fexofenadine (a substrate of OATP1A2, 2B1, and MDR1, amongst others) [23-26]. The oral PK of fexofenadine is altered by administration of fruit juices, which contain components that inhibit both drug transporters and drug-metabolizing enzymes. As fexofenadine is a substrate of drug transporters only, opposing roles for OATPs (facilitating absorption) and MDR1 (limiting absorption) have been proposed, although the precise contributions of these mechanisms are difficult to estimate [23]. A recent study of the pharmacokinetics (PK) of S- and R- fexofenadine enantiomers in individuals with a range of transporter genotypes indicated a strong association of OATP2B1 polymorphism with S- enantiomer PK and OATP2B1 polymorphs in combination with other transporter polymorphs with altered R- enantiomer PK [27]. This study not only indicates an important role for OATP2B1 in fexofenadine PK, but also illustrates the complexities of multiple transporters in multiple organs on drug PK. Grapefruit juice (at a concentration of 5%) inhibits the OATP2B1-mediated uptake of E3S by 80% [13]. On the other hand, grapefruit juice had no effect on the pharmacokinetics of glibenclamide in healthy subjects [28].
OATP1B1, OATP2B1, and OATP1B3 colocalize in the same membrane domain and have overlapping substrate and inhibitor profiles. OATP2B1 in the liver mediates the hepatic uptake of many xenobiotics, including bromosulfophthalein (BSP), benzylpenicillin, fexofenadine, glibenclamide, pravastatin, atorvastatin, rosuvastatin, and fluvastatin [3, 4, 7, 8, 13, 17, 29]. Net inhibition of hepatic OATPs results in significant changes in systemic exposure and toxicities [30-32]. The relative contribution of each transporter to net hepatic uptake is unknown for almost all drugs. It is a function not only of substrate/inhibitor affinity for each transporter, but also their relative functional expression in the liver, which will vary across the population. In practice, the contribution of OATP2B1 to the hepatic uptake of drugs has not been extensively studied; most investigators cite OATP1B1 and OATP1B3 as the primary hepatic drug uptake transporters involved in DDIs.
The clinical relevance of OATP2B1 in other tissues is even less well understood. OATP2B1 is expressed on the luminal side of enterocytes, and the experimental osteoporosis drug ronacaleret interfered with OATP2B1-mediated intestinal absorption of rosuvastatin [33]. Unlike DDIs involving hepatic OATP1Bs, this interaction decreased rather than increased rosuvastatin plasma exposure. OATP2B1 is also responsible for the intestinal uptake of the toxic irinotecan metabolite SN-38; thus, inhibition of intestinal OATP2B1 may help to prevent GI toxicity [34].
Overexpression of OATP2B1 has been detected in tumors of the colon, bone, breast, and prostate, as well as in gliomas. The elevated hormone uptake by OATP2B1 results in increased cell proliferation of hormone dependent tumors such as breast or prostate carcinomas. In these cases, inhibition of the transporter may be a viable strategy to inhibit tumor growth [35, 36].
Endogenous substratesIn vitro substrates used experimentallySubstrate drugsInhibitors
bile acids, steroid hormones, thyroid hormonescoproporphyrin III, E3S, DHEAS, bromosulfophthalein, rosuvastatinstatins, fexofenadine, glyburide, bosentan, rifampicin, aliskiren, erlotinib, balsalazide, olsalzine,
gavestinel,
tebipenem pivoxil, unaprostone,
gamithromycin
rifampin, cyclosporine,
naringin, hesperidin, streptomycin, linezolid, ronacaleret, sulfasalazine,
tropesin, asunaprevir, ritonavir, acemetacin,
benzbromarone, tipranavir, irbesartan, ezetimibe, ketoconazole
DRUGBANK IDNAMEACTIONSDETAILS
DB00655EstroneinhibitorDetails
DB01045RifampicininhibitorDetails
DB02746Phthalic AcidinhibitorDetails
DB03902Oxalic AcidinhibitorDetails
DB00627NiacininhibitorDetails
DB04398Lactic acidsubstrate-inhibitorDetails
DB04272Citric acidinhibitorDetails
DB03793Benzoic acidinhibitorDetails
DB03166Acetic acidsubstrate-inhibitorDetails
DB04216QuercetininhibitorDetails
DB03467NaringenininhibitorDetails
DB00770AlprostadilinhibitorDetails
DB11613Velpatasvirinhibitor-transporterDetails
DB05521TelaprevirinhibitorDetails
DB11591BilastineinhibitorDetails
DB13952Estradiol acetateinhibitorDetails
DB13953Estradiol benzoateinhibitorDetails
DB13954Estradiol cypionateinhibitorDetails
DB13955Estradiol dienanthateinhibitorDetails
DB13956Estradiol valerateinhibitorDetails
DB12319BenzbromaroneinhibitorDetails
DB08862CholecystokinininhibitorDetails
DB00975DipyridamoleinhibitorDetails
DB00530ErlotinibinhibitorDetails
DB01645GenisteininhibitorDetails
DB01167ItraconazoleinhibitorDetails
DB00451LevothyroxineinhibitorDetails
DB01149NefazodoneinhibitorDetails
DB00220NelfinavirinhibitorDetails
DB01051NovobiocininhibitorDetails
DB00554PiroxicaminhibitorDetails
DB00206ReserpineinhibitorDetails
DB09298SilibinininhibitorDetails
DB00795SulfasalazineinhibitorDetails
DB00759TetracyclineinhibitorDetails
DB00932TipranavirinhibitorDetails
DB00313Valproic acidinhibitorDetails
DB00224IndinavirinhibitorDetails
DB01232SaquinavirinhibitorDetails
DB00503RitonavirinhibitorDetails
DB11586Asunaprevirsubstrate-inhibitorDetails
DB05928DovitinibinhibitorDetails
DB11753RifamycininhibitorDetails
DB12978PexidartinibinhibitorDetails
DB01241GemfibrozilinhibitorDetails
DB01072AtazanavirinhibitorDetails
DB16226MaralixibatinhibitorDetails
DB11761TenapanorinhibitorDetails
 

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