BACKGROUND: Insight into the pathophysiology of inflammatory skin diseases, especially at the proteomic level, is severely hampered by the lack of adequate in situ data.
OBJECTIVE: Characterize lesional and nonlesional skin of inflammatory skin diseases using skin microdialysis.
METHODS: Skin microdialysis samples from patients with atopic dermatitis (AD, n=6), psoriasis vulgaris (PSO, n=7) or prurigo nodularis (PN, n=6), as well as healthy controls (n=7) were subjected to proteomics and multiplex cytokine analysis. Single-cell RNA sequencing of skin biopsy specimens was used to identify the cellular origin of cytokines.
RESULTS: Among the top 20 enriched GO annotations, NAD metabolic process, regulation of secretion by cell, and pyruvate metabolic process were elevated in microdialysates from lesional AD skin compared with both nonlesional skin and controls. The top 20 enriched KEGG pathways in these three groups overlapped almost completely. In contrast, nonlesional skin from patients with PSO or PN and control skin showed no overlap with lesional skin in this KEGG pathway analysis. Lesional skin from patients with PSO, but not AD or PN, showed significantly elevated protein levels of MCP-1 compared to nonlesional skin. IL-8 was elevated in lesional vs nonlesional AD and PSO skin, whereas IL-12p40 and IL-22 were higher only in lesional PSO skin. Integrated single-cell RNA-seq data revealed identical cellular sources of these cytokines in AD, PSO and PN.
CONCLUSIONS: Based on microdialysate, proteomic data of lesional PSO and PN skin, but not lesional AD skin, differed significantly from those of nonlesional skin. IL-8, IL-22, MCP-1 and IL-12p40 might be suitable markers for minimally invasive molecular profiling.

Aberrant metabolism is a hallmark of malignancies including gliomas. Intracranial microdialysis enables the longitudinal collection of extracellular metabolites within CNS tissues including gliomas and can be leveraged to evaluate changes in the CNS microenvironment over a period of days. However, delayed metabolic impacts of CNS injury from catheter placement could represent an important covariate for interpreting the pharmacodynamic impacts of candidate therapies. Intracranial microdialysis was performed in patient-derived glioma xenografts of glioma before and 72 h after systemic treatment with either temozolomide (TMZ) or a vehicle. Microdialysate from GBM164, an IDH-mutant glioma patient-derived xenograft, revealed a distinct metabolic signature relative to the brain that recapitulated the metabolic features observed in human glioma microdialysate. Unexpectedly, catheter insertion into the brains of non-tumor-bearing animals triggered metabolic changes that were significantly enriched for the extracellular metabolome of glioma itself. TMZ administration attenuated this resemblance. The human glioma microdialysate was significantly enriched for both the PDX versus brain signature in mice and the induced metabolome of catheter placement within the murine control brain. These data illustrate the feasibility of microdialysis to identify and monitor the extracellular metabolome of diseased versus relatively normal brains while highlighting the similarity between the extracellular metabolome of human gliomas and that of CNS injury.

BACKGROUND: Mass spectrometry (MS)-based cerebrospinal fluid (CSF) proteomics is an important method for discovering biomarkers of neurodegenerative diseases. CSF serves as a reservoir for interstitial fluid (ISF), and extensive communication between the two fluid compartments helps to remove waste products from the brain.
METHODS: We performed proteomic analyses of both CSF and ISF fluid compartments using intracerebral microdialysis to validate and detect novel biomarkers of Alzheimer\'s disease (AD) in APPtg and C57Bl/6J control mice.
RESULTS: We identified up to 625 proteins in ISF and 4,483 proteins in CSF samples. By comparing the biofluid profiles of APPtg and C57Bl/6J mice, we detected 37 and 108 significantly up- and downregulated candidates, respectively. In ISF, 7 highly regulated proteins, such as Gfap, Aldh1l1, Gstm1, and Txn, have already been implicated in AD progression, whereas in CSF, 9 out of 14 highly regulated proteins, such as Apba2, Syt12, Pgs1 and Vsnl1, have also been validated to be involved in AD pathogenesis. In addition, we also detected new interesting regulated proteins related to the control of synapses and neurotransmission (Kcna2, Cacng3, and Clcn6) whose roles as AD biomarkers should be further investigated.
METHODS: This newly established combined protocol provides better insight into the mutual communication between ISF and CSF as an analysis of tissue or CSF compartments alone.
CONCLUSIONS: The use of multiple fluid compartments, ISF and CSF, for the detection of their biological communication enables better detection of new promising AD biomarkers.

Penicillin is available in both an oral (penicillin V) and intravenous formulation (penicillin G), theoretically allowing for a safe transition between the two. However, the use of oral penicillin remains a topic of debate due to low and variable bioavailability. This study aimed to assess the time for which the free penicillin concentration exceeded targeted minimum inhibitory concentrations for Staphylococcus aureus and Streptococcus species (0.125, 0.25, and 0.5 mg/L) in cancellous bone and subcutaneous tissue after intravenous penicillin and oral penicillin administration. 12 female pigs (68-75 kg) were assigned, according to local standard clinical regimes, to either intravenous penicillin (1.2 g) or oral penicillin (0.8 g) treatment every 6 h over an 18 h period. Microdialysis catheters were placed for sampling in tibial cancellous bone and adjacent subcutaneous tissue. Data was dynamic/continually collected in the first dosing interval (0-6 h), simulating a prophylactic situation, and the third dosing interval (12-18 h), simulating a therapeutic setting. Plasma samples were collected for reference. For all investigated targets, intravenous treatment resulted in a longer mean time above relevant minimum inhibitory concentrations in cancellous bone during the first dosing interval, and in both cancellous bone and subcutaneous tissue during the third dosing interval compared to oral treatment. With clinically relevant dosing, intravenous penicillin provides superior exposure compared to oral penicillin in both a prophylactic and therapeutic setting.

BACKGROUND: Brain energy metabolism is often disturbed after acute brain injuries. Current neuromonitoring methods with cerebral microdialysis (CMD) are based on intermittent measurements (1-4 times/h), but such a low frequency could miss transient but important events. The solution may be the recently developed Loke microdialysis (MD), which provides high-frequency data of glucose and lactate. Before clinical implementation, the reliability and stability of Loke remain to be determined in vivo. The purpose of this study was to validate Loke MD in relation to the standard intermittent CMD method.
METHODS: Four pigs aged 2-3 months were included. They received two adjacent CMD catheters, one for standard intermittent assessments and one for continuous (Loke MD) assessments of glucose and lactate. The standard CMD was measured every 15 min. Continuous Loke MD was sampled every 2-3 s and was averaged over corresponding 15-min intervals for the statistical comparisons with standard CMD. Intravenous glucose injections and intracranial hypertension by inflation of an intracranial epidural balloon were performed to induce variations in intracranial pressure, cerebral perfusion pressure, and systemic and cerebral glucose and lactate levels.
RESULTS: In a linear mixed-effect model of standard CMD glucose (mM), there was a fixed effect value (± standard error [SE]) at 0.94 ± 0.07 (p < 0.001) for Loke MD glucose (mM), with an intercept at - 0.19 ± 0.15 (p = 0.20). The model showed a conditional R2 at 0.81 and a marginal R2 at 0.72. In a linear mixed-effect model of standard CMD lactate (mM), there was a fixed effect value (± SE) at 0.41 ± 0.16 (p = 0.01) for Loke MD lactate (mM), with an intercept at 0.33 ± 0.21 (p = 0.25). The model showed a conditional R2 at 0.47 and marginal R2 at 0.17.
CONCLUSIONS: The established standard CMD glucose thresholds may be used as for Loke MD with some caution, but this should be avoided for lactate.

Enabling drug formulations are often required to ensure sufficient absorption after oral administration of poorly soluble drugs. While these formulations typically increase the apparent solubility of the drug, it is widely acknowledged that only molecularly dissolved, i.e., free fraction of the drug, is prone for direct absorption, while colloid-associated drug does not permeate to the same extent. In the present study, we aimed at comparing the effect of molecularly and apparently (i.e., the sum of molecularly and colloid-associated drug) dissolved drug concentrations on the oral absorption of a poorly water-soluble drug compound, Alectinib. Mixtures of Alectinib and respectively 50 %, 25 %, 12.5 %, and 3 % sodium lauryl sulfate (SLS) relative to the dose were prepared and small-scale dissolution tests were performed under simulated fed and fasted state conditions. Both the molecularly and apparently dissolved drug concentrations were assessed in parallel using microdialysis and centrifugation/filtration sampling, respectively. The data served as the basis for an in vitro-in vivo correlation (IVIVC) and as input for a GastroPlusTM physiologically-based biopharmaceutics model (PBBM). It was shown that with increasing the content of SLS the apparently dissolved drug in FeSSIF and FaSSIF increased to a linear extent and thus, the predicted in vivo performance of the 50 % SLS formulation, based on apparently dissolved drug, would outperform all other formulations. Against common expectation, however, the free (molecularly dissolved) drug concentrations were found to vary with SLS concentrations as well, yet to a minor extent. A systematic comparison of solubilized and free drug dissolution patterns at different SLS contents of the formulations and prandial states allowed for interesting insights into the complex dissolution-/supersaturation-, micellization-, and precipitation-behavior of the formulations. When comparing the in vitro datasets with human pharmacokinetic data from a bioequivalence study, it was shown that the use of molecularly dissolved drug resulted in an improved IVIVC. By incorporating the in vitro dissolution datasets into the GastroPlusTM PBBM, the apparently dissolved drug concentrations resulted in both, a remarkable overprediction of plasma concentrations as well as a misprediction of the influence of SLS on systemic exposure. In contrast, by using the molecularly dissolved drug (i.e., free fraction) as the model input, the predicted plasma concentration-time profiles were in excellent agreement with observed data for all formulations under both fed and fasted conditions. By combining an advanced in vitro assessment with PBBM, the present study confirmed that only the molecularly dissolved drug, and not the colloid-associated drug, is available for direct absorption.

It has been suggested that sodium-glucose cotransporter 2 (SGLT2) inhibitors have cardioprotective effects during myocardial ischemia/reperfusion (I/R) independent of glucose-lowering action. However, the effects of SGLT2 inhibitors on structural damage to cardiomyocytes in the ischemic region during I/R remain unknown. We applied a microdialysis technique to the heart of anesthetized rats and investigated the effects of an SGLT2 inhibitor, dapagliflozin, on myocardial interstitial myoglobin levels in the ischemic region during coronary occlusion followed by reperfusion. Dapagliflozin was administered systemically (40 μg/body iv) or locally via a dialysis probe (100 μM and 1 mM) 30 min before coronary occlusion. In the vehicle group, coronary occlusion increased the dialysate myoglobin concentration in the ischemic region. Reperfusion further increased the dialysate myoglobin concentration. Intravenous administration of dapagliflozin reduced dialysate myoglobin concentration during ischemia and at 0-15 min after reperfusion, but local administration (100 μM and 1 mM) did not. Therefore, acute systemic administration of dapagliflozin prior to ischemia has cardioprotective effects on structural damage during I/R.

(R,S)-ketamine (ketamine) has rapid and sustained antidepressant (AD) efficacy at sub-anesthetic doses in depressed patients. A metabolite of ketamine, including (2R,6R)-hydroxynorketamine ((6)-HNKs) has been reported to exert antidepressant actions in rodent model of anxiety/depression. To further understand the specific role of ketamine\'s metabolism in the AD actions of the drug, we evaluated the effects of inhibiting hepatic cytochrome P450 enzymes on AD responses. We assessed whether pre-treatment with fluconazole (10 and 20 mg/kg, i. p.) 1 h prior to ketamine or HNKs (10 mg/kg, i. p.) administration would alter behavioral and neurochemical actions of the drugs in male BALB/cJ mice with a highly anxious phenotype. Extracellular microdialysate levels of glutamate and GABA (Gluext, GABAext) were also measured in the medial prefrontal cortex (mPFC). Pre-treatment with fluconazole altered the pharmacokinetic profile of ketamine, by increasing both plasma and brain levels of ketamine and (R,S)-norketamine, while robustly reducing those of (6)-HNKs. At 24 h post-injection (t24 h), fluconazole prevented the sustained AD-like response of ketamine responses in the forced swim test and splash test, as well as the enhanced cortical GABA levels produced by ketamine. A single (2R,6R)-HNK administration resulted in prevention of the effects of fluconazole on the antidepressant-like activity of ketamine in mice. Overall, these findings are consistent with an essential contribution of (6)-HNK to the sustained antidepressant-like effects of ketamine and suggest potential interactions between pharmacological CYPIs and ketamine during antidepressant treatment in patients.

Cholinergic disruptions underlie attentional deficits following traumatic brain injury (TBI). Yet, drugs specifically targeting acetylcholinesterase (AChE) inhibition have yielded mixed outcomes. Therefore, we hypothesized that galantamine (GAL), a dual-action competitive AChE inhibitor and α7 nicotinic acetylcholine receptor (nAChR) positive allosteric modulator, provided chronically after injury, will attenuate TBI-induced deficits of sustained attention and enhance ACh efflux in the medial prefrontal cortex (mPFC), as assessed by in vivo microdialysis. In Experiment 1, adult male rats (n = 10-15/group) trained in the 3-choice serial reaction time (3-CSRT) test were randomly assigned to controlled cortical impact (CCI) or sham surgery and administered GAL (0.5, 2.0, or 5.0 mg/kg; i.p.) or saline vehicle (VEH; 1 mL/kg; i.p) beginning 24-h post-surgery and once daily thereafter for 27 days. Measures of sustained attention and distractibility were assessed on post-operative days 21-25 in the 3-CSRT, following which cortical lesion volume and basal forebrain cholinergic cells were quantified on day 27. In Experiment 2, adult male rats (n = 3-4/group) received a CCI and 24 h later administered (i.p.) one of the three doses of GAL or VEH for 21 days to quantify the dose-dependent effect of GAL on in vivo ACh efflux in the mPFC. Two weeks after the CCI, a guide cannula was implanted in the right mPFC. On post-surgery day 21, baseline and post-injection dialysate samples were collected in a temporally matched manner with the cohort undergoing behavior. ACh levels were analyzed using reverse phase high-performance liquid chromatography (HPLC) coupled to an electrochemical detector. Cortical lesion volume was quantified on day 22. The data were subjected to ANOVA, with repeated measures where appropriate, followed by Newman-Keuls post hoc analyses. All TBI groups displayed impaired sustained attention versus the pooled SHAM controls (p\'s < 0.05). Moreover, the highest dose of GAL (5.0 mg/kg) exacerbated attentional deficits relative to VEH and the two lower doses of GAL (p\'s < 0.05). TBI significantly reduced cholinergic cells in the right basal forebrain, regardless of treatment condition, versus SHAM (p < 0.05). In vivo microdialysis revealed no differences in basal ACh in the mPFC; however, GAL (5.0 mg/kg) significantly increased ACh efflux 30 min following injection compared to the VEH and the other GAL (0.5 and 2.0 mg/kg) treated groups (p\'s < 0.05). In both experiments, there were no differences in cortical lesion volume across treatment groups (p\'s > 0.05). In summary, albeit the higher dose of GAL increased ACh release, it did not improve measures of sustained attention or histopathological markers, thereby partially supporting the hypothesis and providing the impetus for further investigations into alternative cholinergic pharmacotherapies such as nAChR positive allosteric modulators.

OBJECTIVE: The interstitial fluid of tissues is the effect site for antibiotics targeting extracellular pathogens. Microdialysis studies investigating these concentrations in muscle and subcutaneous tissue have reported notable variability in tissue penetration. This study aimed to comprehensively summarise the existing data on interstitial fluid penetration in these tissues and to identify potential factors influencing antibiotic distribution.
METHODS: A literature review was conducted, focusing on subcutaneous and intramuscular microdialysis studies of antibiotics in both adult healthy volunteers and patients. Random-effect meta-analyses were used to aggregate effect size estimates of tissue penetration. The primary parameter of interest was the unbound penetration ratio, which represents the ratio of the area under the concentration-time curve in interstitial fluid relative to the area under the concentration-time curve in plasma, using unbound concentrations.
RESULTS: In total, 52 reports were incorporated into this analysis. The unbound antibiotic exposure in the interstitial fluid of healthy volunteers was, on average, 22% lower than in plasma. The unbound penetration ratio values were higher after multiple dosing but did not significantly differ between muscle and subcutaneous tissue. Unbound penetration ratio values were lower for acids and bases compared with neutral antibiotics. Neither the molecular weight nor the logP of the antibiotics accounted for the variations in the unbound penetration ratio. Obesity was associated with lower interstitial fluid penetration. Conditions such as sepsis, tissue inflammation and tissue ischaemia were not significantly associated with altered interstitial fluid penetration.
CONCLUSIONS: This study highlights the variability and generally lower exposure of unbound antibiotics in the subcutaneous and intramuscular interstitial fluid compared with exposure in plasma. Future research should focus on understanding the therapeutic relevance of these differences and identify key covariates that may influence them.