ExcelMale
Menu
Home
What's new
Latest activity
Forums
New posts
Search forums
What's new
New posts
Latest activity
Videos
Lab Tests
Doctor Finder
Buy Books
About Us
Men’s Health Coaching
Log in
Register
What's new
Search
Search
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Navigation
Install the app
Install
More options
Contact us
Close Menu
Forums
Testosterone Replacement, Low T, HCG, & Beyond
Testosterone Basics & Questions
FT using TruT vs Dialysis methods
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="madman" data-source="post: 163649" data-attributes="member: 13851"><p>Forgive me for being harsh but what is it that you seem to be pig headed too here!</p><p></p><p>It has been explained numerous times to you and you just keep making brain dead statements!</p><p></p><p>It is not just based of TT..... it is TT, SHBG, Albumin.....and if you could grasp the reason why at higher TT/SHBG levels that FT levels only decline modestly.....is because as shown in the newer research regarding SHBG:T binding it was discovered that the binding affinities of the two sites <span style="color: rgb(184, 49, 47)">(two binding sites on the SHBG dimer) </span>are not identical.</p><p></p><p><span style="color: rgb(0, 0, 0)"><strong>"</strong></span><strong>SHBG dimer exhibits conformational allostery in binding testosterone"</strong></p><p></p><p><strong>"Recent studies of testosterone binding to SHBG using modern biophysical techniques suggest that <span style="color: rgb(44, 130, 201)">SHBG circulates as a homodimer and that there is complex allosteric interaction between the two binding sites on the SHBG dimer, such that </span><span style="color: rgb(184, 49, 47)">the binding affinities of the two sites are not identical </span>(34)"</strong></p><p></p><p></p><p></p><p></p><p><strong><span style="color: rgb(184, 49, 47)">TruT</span></strong></p><p><strong>*This algorithm is based on experimental data demonstrating that testosterone’s binding to SHBG is a multi-step process involving an allosteric interaction between the two binding sites on the SHBG dimer.</strong></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p><strong>*</strong> <span style="color: rgb(26, 188, 156)">highlighted in green- </span><span style="color: rgb(0, 0, 0)"><strong>refer to</strong></span><span style="color: rgb(26, 188, 156)"> <strong>the linear law-of-mass-action model/equation Vermueulen</strong> </span><strong><span style="color: rgb(26, 188, 156)">(cFTV)</span></strong></p><p></p><p><strong>*</strong><span style="color: rgb(44, 130, 201)">highlighted in blue- </span><span style="color: rgb(0, 0, 0)"><strong>refer to</strong></span><span style="color: rgb(44, 130, 201)"><strong> the new Multi-step Dynamic Binding Model with Complex Allostery (TruT calculated)</strong> </span></p><p></p><p></p><p></p><p><strong>[0302] <span style="color: rgb(26, 188, 156)">The current equations based on homogenous SHBG:T interaction (equal affinity of T for each of the monomers within SHBG dimer and without allostery in SHBG dimers) proposed by Vermeulen and others (13, 17) are based on the assumption that each SHBG dimer binds two testosterone molecules, and that each of the two binding sites on SHBG dimer has similar binding constants (data not shown).</span></strong> <strong><span style="color: rgb(26, 188, 156)">It is demonstrated herein that the current model of testosterone binding to SHBG that has formed the basis of the law-of-mass-action equation is erroneous; the free testosterone levels derived from these equations display substantial discrepancy from the values obtained by </span></strong><span style="color: rgb(26, 188, 156)"><strong>equilibrium dialysis (18).</strong> </span><strong><span style="color: rgb(44, 130, 201)">Based on binding isotherms, ligand depletion experiments, and isothermal titration calorimetry (ITC), we provide experimental evidence of complex allostery between the binding sites on the two SHBG monomers in the presence of the ligand. Based on this new model of testosterone binding to SHBG, described herein is a novel algorithm for the calculation of free testosterone, applied it to samples derived from randomized testosterone trials in men and women, and compared the results with those obtained using </span></strong><span style="color: rgb(44, 130, 201)"><strong>equilibrium dialysis.</strong> </span></p><p></p><p><strong>[0354]</strong> Circulating free testosterone (FT) levels have been used widely in the diagnosis and treatment of hypogonadism in men. Due to experimental complexities in FT measurements, the Endocrine Society expert panel has recommended the use of calculated FT (cFT) as an appropriate approach for estimating FT.<strong> <span style="color: rgb(26, 188, 156)">It is demonstrated herein that the prevailing model of testosterone's binding to SHBG, which assumes that each SHBG dimer binds two testosterone molecules and that the two binding sites on SHBG have similar binding affinity, provides values of free testosterone that differ substantially from those obtained using equilibrium dialysis.</span></strong></p><p></p><p><strong>[0359]</strong> <strong><span style="color: rgb(26, 188, 156)">The current model of testosterone's binding to SHBG assumes that each SHBG dimer binds two testosterone molecules, and that each of the two binding sites on SHBG dimer has similar binding affinity. Equations to determine FT were proposed by Vermeulen and others (Rosner et al 2007, Sodergard et al 1982, Vermeulen et al 1971, Mazer 2009)(Sodergard et al 1982, Vermeulen et al 1971). We show here that the prevailing model of testosterone's binding to SHBG is erroneous. </span></strong><span style="color: rgb(44, 130, 201)"><strong>The data from equilibrium dialysis and isothermal titration calorimetry (ITC) experiments provide evidence for ligand modulated allosteric interaction between the binding sites on the two SHBG monomers.</strong> </span></p><p></p><p><strong>[0368]</strong><span style="color: rgb(184, 49, 47)"><strong> Various molecular models of testosterone's binding to SHBG were numerically tested using LabVIEW™ (National Instruments, Austin, Tex.) toolkit (Zakharov et al 2012) (available on the world wide web at code.google.com/p/labview-biochemical-framework/). Parameter estimation for the models was performed as described previously (Zakharov et al 2012). Numerical correction for the equilibrium dialysis was incorporated as a part of every simulation model.</strong></span> <strong><span style="color: rgb(26, 188, 156)">Since some of the models and equations (Sodergard et al 1982, Vermeulen et al 1999, Nanjee and Wheeler 1985) were developed essentially before the confirmation of the 2 binding sites per SHBG dimer (Avvakumov et al 2001) we adjusted SHBG concentration by the factor of 2 for these models.</span></strong></p><p></p><p><strong><span style="color: rgb(26, 188, 156)"><strong>[0376] The simplest of the SHBG T interaction models is Vemeulens model, assuming that each binding site interacts with T with the same affinity, regardless of the other binding site occupancy (FIG. 6, model A).</strong> </span></strong></p><p></p><p><strong>[0387]</strong> <strong><span style="color: rgb(184, 49, 47)">Relation between Percent FT with Total Testosterone and SHBG.</span><span style="color: rgb(44, 130, 201)"> Intra-dimer complex allostery suggests that SHBG can regulate FT fraction over a wide range of total testosterone concentrations without getting saturated.</span></strong> <strong><span style="color: rgb(44, 130, 201)">Indeed, it was found that percent FT calculated using the new model changed very modestly over a wide range of total testosterone concentrations.</span></strong> <strong><span style="color: rgb(26, 188, 156)">In contrast, the Vermeulen's equation suggests a negative relation between percent FT and total testosterone.</span></strong> <strong><span style="color: rgb(44, 130, 201)">Furthermore, as SHBG concentrations increase, percent FT calculated using our new model shows only a modest decline</span></strong> <strong><span style="color: rgb(44, 130, 201)">in contrast</span> <span style="color: rgb(26, 188, 156)">to the marked decline in percent FT calculated using Vermeulen's equation.</span></strong></p><p></p><p></p><p></p><p></p><p>key points being:</p><p></p><p><strong><span style="color: rgb(44, 130, 201)">*Intra-dimer complex allostery suggests that </span><span style="color: rgb(184, 49, 47)">SHBG can regulate FT fraction over a wide range of total testosterone concentrations without getting saturated.</span></strong></p><p></p><p><strong><span style="color: rgb(44, 130, 201)">*Indeed, it was found that </span><span style="color: rgb(184, 49, 47)">percent FT calculated using the new model changed very modestly over a wide range of total testosterone concentrations.</span></strong></p><p></p><p><strong><span style="color: rgb(44, 130, 201)">*Furthermore, </span><span style="color: rgb(184, 49, 47)">as SHBG concentrations increase, percent FT calculated using our new model shows only a modest decline</span></strong> <strong><span style="color: rgb(26, 188, 156)">in contrast to the marked decline in percent FT calculated using Vermeulen's equation.</span></strong></p><p></p><p></p><p></p><p></p><p>Here is the big flaw in the outdated calculated FT methods based off of linear law-of-mass action models:</p><p></p><p><strong><span style="color: rgb(26, 188, 156)"><strong>[0376] The simplest of the SHBG T interaction models is Vemeulens model, assuming that </strong></span><span style="color: rgb(184, 49, 47)"><strong>each binding site interacts with T with the same affinity, regardless of the other binding site occupancy</strong></span><span style="color: rgb(26, 188, 156)"><strong> (FIG. 6, model A).</strong></span></strong></p><p></p><p></p><p></p><p></p><p>Regarding the TruT model/algorithm:</p><p></p><p><strong>[0390] The new dynamic model leads to the reconsideration of several dogmas related to testosterone's binding to SHBG and has important physiologic and clinical implications. First, the fraction of circulating testosterone which is free is substantially greater (2.9±0.4%)</strong> <strong>than has been generally assumed (% cFTV 1.5±0.4%)</strong>.<strong> <span style="color: rgb(44, 130, 201)">Second, percent FT is not significantly related to total testosterone over a wide range of total testosterone concentrations. However, the percent FT declines as SHBG concentrations increase, </span></strong><span style="color: rgb(184, 49, 47)"><strong>although it does not decline as precipitously as predicted by the Vermeulen's model.</strong></span><span style="color: rgb(44, 130, 201)"><strong> Due to the allostery between the two binding sites, </strong></span><span style="color: rgb(184, 49, 47)"><strong>SHBG is able to regulate FT levels in much larger dynamic range.</strong> </span></p></blockquote><p></p>
[QUOTE="madman, post: 163649, member: 13851"] Forgive me for being harsh but what is it that you seem to be pig headed too here! It has been explained numerous times to you and you just keep making brain dead statements! It is not just based of TT..... it is TT, SHBG, Albumin.....and if you could grasp the reason why at higher TT/SHBG levels that FT levels only decline modestly.....is because as shown in the newer research regarding SHBG:T binding it was discovered that the binding affinities of the two sites [COLOR=rgb(184, 49, 47)](two binding sites on the SHBG dimer) [/COLOR]are not identical. [COLOR=rgb(0, 0, 0)][B]"[/B][/COLOR][B]SHBG dimer exhibits conformational allostery in binding testosterone"[/B] [B]"Recent studies of testosterone binding to SHBG using modern biophysical techniques suggest that [COLOR=rgb(44, 130, 201)]SHBG circulates as a homodimer and that there is complex allosteric interaction between the two binding sites on the SHBG dimer, such that [/COLOR][COLOR=rgb(184, 49, 47)]the binding affinities of the two sites are not identical [/COLOR](34)"[/B] [B][COLOR=rgb(184, 49, 47)]TruT[/COLOR] *This algorithm is based on experimental data demonstrating that testosterone’s binding to SHBG is a multi-step process involving an allosteric interaction between the two binding sites on the SHBG dimer.[/B] [B]*[/B] [COLOR=rgb(26, 188, 156)]highlighted in green- [/COLOR][COLOR=rgb(0, 0, 0)][B]refer to[/B][/COLOR][COLOR=rgb(26, 188, 156)] [B]the linear law-of-mass-action model/equation Vermueulen[/B] [/COLOR][B][COLOR=rgb(26, 188, 156)](cFTV)[/COLOR][/B] [B]*[/B][COLOR=rgb(44, 130, 201)]highlighted in blue- [/COLOR][COLOR=rgb(0, 0, 0)][B]refer to[/B][/COLOR][COLOR=rgb(44, 130, 201)][B] the new Multi-step Dynamic Binding Model with Complex Allostery (TruT calculated)[/B] [/COLOR] [B][0302] [COLOR=rgb(26, 188, 156)]The current equations based on homogenous SHBG:T interaction (equal affinity of T for each of the monomers within SHBG dimer and without allostery in SHBG dimers) proposed by Vermeulen and others (13, 17) are based on the assumption that each SHBG dimer binds two testosterone molecules, and that each of the two binding sites on SHBG dimer has similar binding constants (data not shown).[/COLOR][/B] [B][COLOR=rgb(26, 188, 156)]It is demonstrated herein that the current model of testosterone binding to SHBG that has formed the basis of the law-of-mass-action equation is erroneous; the free testosterone levels derived from these equations display substantial discrepancy from the values obtained by [/COLOR][/B][COLOR=rgb(26, 188, 156)][B]equilibrium dialysis (18).[/B] [/COLOR][B][COLOR=rgb(44, 130, 201)]Based on binding isotherms, ligand depletion experiments, and isothermal titration calorimetry (ITC), we provide experimental evidence of complex allostery between the binding sites on the two SHBG monomers in the presence of the ligand. Based on this new model of testosterone binding to SHBG, described herein is a novel algorithm for the calculation of free testosterone, applied it to samples derived from randomized testosterone trials in men and women, and compared the results with those obtained using [/COLOR][/B][COLOR=rgb(44, 130, 201)][B]equilibrium dialysis.[/B] [/COLOR] [B][0354][/B] Circulating free testosterone (FT) levels have been used widely in the diagnosis and treatment of hypogonadism in men. Due to experimental complexities in FT measurements, the Endocrine Society expert panel has recommended the use of calculated FT (cFT) as an appropriate approach for estimating FT.[B] [COLOR=rgb(26, 188, 156)]It is demonstrated herein that the prevailing model of testosterone's binding to SHBG, which assumes that each SHBG dimer binds two testosterone molecules and that the two binding sites on SHBG have similar binding affinity, provides values of free testosterone that differ substantially from those obtained using equilibrium dialysis.[/COLOR][/B] [B][0359][/B] [B][COLOR=rgb(26, 188, 156)]The current model of testosterone's binding to SHBG assumes that each SHBG dimer binds two testosterone molecules, and that each of the two binding sites on SHBG dimer has similar binding affinity. Equations to determine FT were proposed by Vermeulen and others (Rosner et al 2007, Sodergard et al 1982, Vermeulen et al 1971, Mazer 2009)(Sodergard et al 1982, Vermeulen et al 1971). We show here that the prevailing model of testosterone's binding to SHBG is erroneous. [/COLOR][/B][COLOR=rgb(44, 130, 201)][B]The data from equilibrium dialysis and isothermal titration calorimetry (ITC) experiments provide evidence for ligand modulated allosteric interaction between the binding sites on the two SHBG monomers.[/B] [/COLOR] [B][0368][/B][COLOR=rgb(184, 49, 47)][B] Various molecular models of testosterone's binding to SHBG were numerically tested using LabVIEW™ (National Instruments, Austin, Tex.) toolkit (Zakharov et al 2012) (available on the world wide web at code.google.com/p/labview-biochemical-framework/). Parameter estimation for the models was performed as described previously (Zakharov et al 2012). Numerical correction for the equilibrium dialysis was incorporated as a part of every simulation model.[/B][/COLOR] [B][COLOR=rgb(26, 188, 156)]Since some of the models and equations (Sodergard et al 1982, Vermeulen et al 1999, Nanjee and Wheeler 1985) were developed essentially before the confirmation of the 2 binding sites per SHBG dimer (Avvakumov et al 2001) we adjusted SHBG concentration by the factor of 2 for these models.[/COLOR][/B] [B][COLOR=rgb(26, 188, 156)][B][0376] The simplest of the SHBG T interaction models is Vemeulens model, assuming that each binding site interacts with T with the same affinity, regardless of the other binding site occupancy (FIG. 6, model A).[/B] [/COLOR][/B] [B][0387][/B] [B][COLOR=rgb(184, 49, 47)]Relation between Percent FT with Total Testosterone and SHBG.[/COLOR][COLOR=rgb(44, 130, 201)] Intra-dimer complex allostery suggests that SHBG can regulate FT fraction over a wide range of total testosterone concentrations without getting saturated.[/COLOR][/B] [B][COLOR=rgb(44, 130, 201)]Indeed, it was found that percent FT calculated using the new model changed very modestly over a wide range of total testosterone concentrations.[/COLOR][/B] [B][COLOR=rgb(26, 188, 156)]In contrast, the Vermeulen's equation suggests a negative relation between percent FT and total testosterone.[/COLOR][/B] [B][COLOR=rgb(44, 130, 201)]Furthermore, as SHBG concentrations increase, percent FT calculated using our new model shows only a modest decline[/COLOR][/B] [B][COLOR=rgb(44, 130, 201)]in contrast[/COLOR] [COLOR=rgb(26, 188, 156)]to the marked decline in percent FT calculated using Vermeulen's equation.[/COLOR][/B] key points being: [B][COLOR=rgb(44, 130, 201)]*Intra-dimer complex allostery suggests that [/COLOR][COLOR=rgb(184, 49, 47)]SHBG can regulate FT fraction over a wide range of total testosterone concentrations without getting saturated.[/COLOR][/B] [B][COLOR=rgb(44, 130, 201)]*Indeed, it was found that [/COLOR][COLOR=rgb(184, 49, 47)]percent FT calculated using the new model changed very modestly over a wide range of total testosterone concentrations.[/COLOR][/B] [B][COLOR=rgb(44, 130, 201)]*Furthermore, [/COLOR][COLOR=rgb(184, 49, 47)]as SHBG concentrations increase, percent FT calculated using our new model shows only a modest decline[/COLOR][/B] [B][COLOR=rgb(26, 188, 156)]in contrast to the marked decline in percent FT calculated using Vermeulen's equation.[/COLOR][/B] Here is the big flaw in the outdated calculated FT methods based off of linear law-of-mass action models: [B][COLOR=rgb(26, 188, 156)][B][0376] The simplest of the SHBG T interaction models is Vemeulens model, assuming that [/B][/COLOR][COLOR=rgb(184, 49, 47)][B]each binding site interacts with T with the same affinity, regardless of the other binding site occupancy[/B][/COLOR][COLOR=rgb(26, 188, 156)][B] (FIG. 6, model A).[/B][/COLOR][/B] Regarding the TruT model/algorithm: [B][0390] The new dynamic model leads to the reconsideration of several dogmas related to testosterone's binding to SHBG and has important physiologic and clinical implications. First, the fraction of circulating testosterone which is free is substantially greater (2.9±0.4%)[/B] [B]than has been generally assumed (% cFTV 1.5±0.4%)[/B].[B] [COLOR=rgb(44, 130, 201)]Second, percent FT is not significantly related to total testosterone over a wide range of total testosterone concentrations. However, the percent FT declines as SHBG concentrations increase, [/COLOR][/B][COLOR=rgb(184, 49, 47)][B]although it does not decline as precipitously as predicted by the Vermeulen's model.[/B][/COLOR][COLOR=rgb(44, 130, 201)][B] Due to the allostery between the two binding sites, [/B][/COLOR][COLOR=rgb(184, 49, 47)][B]SHBG is able to regulate FT levels in much larger dynamic range.[/B] [/COLOR] [/QUOTE]
Insert quotes…
Verification
Post reply
Share this page
Facebook
Twitter
Reddit
Pinterest
Tumblr
WhatsApp
Email
Share
Link
Sponsors
Forums
Testosterone Replacement, Low T, HCG, & Beyond
Testosterone Basics & Questions
FT using TruT vs Dialysis methods
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
Accept
Learn more…
Top