Schematic representation of 10 knockout variants used in the systems model.

<p>Knockouts shown in blue account for passive diffusion, those shown in green account for active absorption from apical side and those shown in red account for active absorption from basolateral side in the gut. In case of knockout 1 passive diffusion in the upper proximal gut was knocked out, in knockout 3 active absorption on the apical side of the lower proximal gut was knocked out and in knockout 4 active absorption on the basolateral side of the lower proximal gut was knocked out.</p

Simulation profiles of BHB in blood against empirical data at two dose levels for knockout of active absorption process along subcomponents of the gut.

<p>Simulation profiles of BHB in blood against empirical data at two dose levels for knockout of active absorption process along subcomponents of the gut.</p

Schematic of the systems model for the absorption and catabolism of the ketone monoester following oral administration.

<p>Solid arrows represent mass transfer, uptake and flux. Dashed arrows represent reactions or productions. Dash-dot arrows represent feedback. Green ovals represent monocarboxylate (or sodium monocarboxylate) transport proteins (MCTs). State 37 denoting ‘Other’ represents the compounds such as glucose and insulin that have a feedback effect on endogenous ketogenesis.</p

An <i>In Silico</i> Knockout Model for Gastrointestinal Absorption Using a Systems Pharmacology Approach - Development and Application for Ketones

<div><p>Gastrointestinal absorption and disposition of ketones is complex. Recent work describing the pharmacokinetics (PK) of d-β-hydroxybutyrate (BHB) following oral ingestion of a ketone monoester ((<i>R</i>)-3-hydroxybutyl (<i>R</i>)-3-hydroxybutyrate) found multiple input sites, nonlinear disposition and feedback on endogenous production. In the current work, a human systems pharmacology model for gastrointestinal absorption and subsequent disposition of small molecules (monocarboxylic acids with molecular weight < 200 Da) was developed with an application to a ketone monoester. The systems model was developed by collating the information from the literature and knowledge gained from empirical population modelling of the clinical data. <i>In silico</i> knockout variants of this systems model were used to explore the mechanism of gastrointestinal absorption of ketones. The knockouts included active absorption across different regions in the gut and also a passive diffusion knockout, giving 10 gut knockouts in total. Exploration of knockout variants has suggested that there are at least three distinct regions in the gut that contribute to absorption of ketones. Passive diffusion predominates in the proximal gut and active processes contribute to the absorption of ketones in the distal gut. Low doses are predominantly absorbed from the proximal gut by passive diffusion whereas high doses are absorbed across all sites in the gut. This work has provided mechanistic insight into the absorption process of ketones, in the form of unique <i>in silico</i> knockouts that have potential for application with other therapeutics. Future studies on absorption process of ketones are suggested to substantiate findings in this study.</p></div

A single deterministic simulated time course of blood BHB concentrations.

<p>Simulations (blue dotted line) overlaid on empirical data (red dashed lines; Mean ± SEM) at two dose levels (192 mg/kg and 573 mg/kg) of the ketone monoester. The dashed green line at bottom of each graph represents lower limit of quantification of BHB in blood.</p

Simulation profiles of BHB in blood against empirical data at two dose levels for knockout of each sub-component (passive and active transport knockout) of the gut.

<p>Simulation profiles of BHB in blood against empirical data at two dose levels for knockout of each sub-component (passive and active transport knockout) of the gut.</p

Simulation profiles of BHB in blood against empirical data at two dose levels for knockout of regions and the processes in the gut.

<p>Knockout of processes (passive and active transport) along the length of the gut (upper panel) and knockout of regions (proximal and distal) of the gut (lower panel) at two doses.</p

Simulation profiles of BHB in blood against empirical data at two dose levels for knockout of passive diffusion along subcomponents of the gut.

<p>Simulation profiles of BHB in blood against empirical data at two dose levels for knockout of passive diffusion along subcomponents of the gut.</p

Time-concentration curves for plasma L-arginine concentrations before and after infusion of 12 g L-arginine (solid line) or saline (broken line) for patients 1 to 5.

<p>X-axis = time in hours, y-axis = L-arginine concentration in mg/L.</p

Pharmacokinetic parameter values estimated in the patients with severe malaria compared to those from moderately severe malaria [15].

<p>The moderate severe malaria parameter estimates are derived from the best model without considering covariates (for comparison with the current parameter estimates).</p><p>Baseline = base+gradient(1)*<i>time</i>+gradient(2)*<i>time</i>². Where <i>time</i> represents time post-start of L-arginine infusion.</p><p>CL = clearance, V1 = central volume of distribution, V2 = peripheral volume of distribution, Q = intercompartmental clearance, BSV = between subject variability which was assumed to be log-normally distribution and expressed as a %, σ = residual variability (standard deviation).</p