Concentrations In Peripheral Tissues Research Articles

Microdialysis as a tool for antibiotic assessment in patients with diabetic foot: a review.

Diabetic foot is a serious late complication frequently caused by infection and ischaemia. Both require prompt and aggressive treatment to avoid lower limb amputation. The effectiveness of peripheral arterial disease therapy can be easily verified using triplex ultrasound, ankle-brachial/toe-brachial index examination, or transcutaneous oxygen pressure. However, the success of infection treatment is difficult to establish in patients with diabetic foot. Intravenous systemic antibiotics are recommended for the treatment of infectious complications in patients with moderate or serious stages of infection. Antibiotic therapy should be initiated promptly and aggressively to achieve sufficient serum and peripheral antibiotic concentrations. Antibiotic serum levels are easily evaluated by pharmacokinetic assessment. However, antibiotic concentrations in peripheral tissues, especially in diabetic foot, are not routinely detectable. This review describes microdialysis techniques that have shown promise in determining antibiotic levels in the surroundings of diabetic foot lesions.

Design principles of the paradoxical feedback between pancreatic alpha and beta cells

Mammalian glucose homeostasis is controlled by the antagonistic hormones insulin and glucagon, secreted by pancreatic beta and alpha cells respectively. These two cell types are adjacently located in the islets of Langerhans and affect each others’ secretions in a paradoxical manner: while insulin inhibits glucagon secretion from alpha cells, glucagon seems to stimulate insulin secretion from beta cells. Here we ask what are the design principles of this negative feedback loop. We systematically simulate the dynamics of all possible islet inter-cellular connectivity patterns and analyze different performance criteria. We find that the observed circuit dampens overshoots of blood glucose levels after reversion of glucose drops. This feature is related to the temporal delay in the rise of insulin concentrations in peripheral tissues, compared to the immediate hormone action on the liver. In addition, we find that the circuit facilitates coordinate secretion of both hormones in response to protein meals. Our study highlights the advantages of a paradoxical paracrine feedback loop in maintaining metabolic homeostasis.

Thyroid hormone status affects expression of daily torpor and gene transcription in Djungarian hamsters (Phodopus sungorus)

Thyroid hormones (TH) play a key role in regulation of seasonal as well as acute changes in metabolism. Djungarian hamsters (Phodopus sungorus) adapt to winter by multiple changes in behaviour and physiology including spontaneous daily torpor, a state of hypometabolism and hypothermia. We investigated effects of systemic TH administration and ablation on the torpor behaviour in Djungarian hamsters adapted to short photoperiod. Hyperthyroidism was induced by giving T4 or T3 and hypothyroidism by giving methimazole (MMI) and sodium perchlorate via drinking water. T3 treatment increased water, food intake and body mass, whereas MMI had the opposite effect. Continuous recording of body temperature revealed that low T3 serum concentrations increased torpor incidence, lowered Tb and duration, whereas high T3 serum concentrations inhibited torpor expression. Gene expression of deiodinases (dio) and uncoupling proteins (ucp) were analysed by qPCR in hypothalamus, brown adipose tissue (BAT) and skeletal muscle. Expression of dio2, the enzyme generating T3 by deiodination of T4, and ucps, involved in thermoregulation, indicated a tissue specific response to treatment. Torpor per se decreased dio2 expression irrespective of treatment or tissue, suggesting low intracellular T3 concentrations during torpor. Down regulation of ucp1 and ucp3 during torpor might be a factor for the inhibition of BAT thermogenesis. Hypothalamic gene expression of neuropeptide Y, propopiomelanocortin and somatostatin, involved in feeding behaviour and energy balance, were not affected by treatment. Taken together our data indicate a strong effect of thyroid hormones on torpor, suggesting that lowered intracellular T3 concentrations in peripheral tissues promote torpor.

Therapeutic intradermal delivery of tumor necrosis factor-alpha antibodies using tip-loaded dissolvable microneedle arrays

Tumor necrosis factor-alpha (TNF-α) specific antibodies (anti-TNF-α Ab) have been shown to be potent TNF inhibitors and effective therapeutics for a range of inflammatory diseases. Typically, these drugs are administered systemically, but systemic dosing sufficient to achieve locally effective concentrations in peripheral tissues has been associated with systemic immunosuppression and related adverse events. Here, we evaluated the use of tip-loaded dissolvable microneedle arrays (MNAs) for localized intradermal delivery of anti-TNF-α Ab. MNAs with obelisk shape microneedles that incorporate the antibody cargo in the needle tips were created from carboxymethylcellulose (CMC) using a micromilling/spin-casting fabrication method. We found that anti-TNF-α Ab integrated into MNAs using this room temperature fabrication process maintained conformationally dependent TNF-α binding activity. Further, these MNAs efficiently delivered anti-TNF-α antibodies to the dermis of human skin with clinically applicable release profiles. To evaluate MNA delivered anti-TNF-α Ab function, we applied anti-TNF-α Ab containing MNAs to established psoriasiform lesions on the skin of mice. MNA anti-TNF-α Ab treatment reduced key biomarkers of psoriasiform inflammation including epidermal thickness and IL-1β expression. Taken together, these results demonstrate efficient and biologically effective MNA delivery of anti-TNF-α Ab to the intradermal microenvironment of the skin in mice and humans, and support the development of MNA mediated antibody delivery for clinical applications. Statement of SignificanceTumor necrosis factor-alpha (TNF-α) specific antibodies (anti-TNF-α Ab) have been shown to be potent TNF inhibitors and effective therapeutics for a range of inflammatory diseases. Typically, these drugs are administered systemically, but systemic dosing sufficient to achieve locally effective concentrations in peripheral tissues has been associated with systemic immunosuppression and related adverse events. Here we demonstrate efficient and biologically effective MNA delivery of anti-TNF-α Ab to the intradermal microenvironment of the skin in mice and humans. These results support the development of MNA mediated antibody delivery of therapeutic antibodies for clinical applications.

Population pharmacokinetics meets microdialysis: Benefits, pitfalls and necessities of new analysis approaches for human microdialysis data

Pharmacokinetic (PK) data originating from human microdialysis studies have by now most commonly been analysed using noncompartmental analysis or the standard two-stage population approach. During the last decades, additional modelling strategies for PK data have been developed, which also seem apt for the analysis of microdialysis data. The present opinion article gives an overview of the three approaches of nonlinear mixed-effects (NLME) modelling, physiologically-based pharmacokinetic (PBPK) modelling and a combined population PBPK modelling approach (PPBPK) as well as their application within the field of microdialysis in humans. Potential benefits and pitfalls of the different approaches will be outlined and exemplified, complemented by modelling prerequisites to be met on the part of principal investigators, bioanalysts and documentalists involved in a microdialysis study.In summary, the combination of microdialysis as the method of choice for measuring unbound drug concentrations in peripheral tissues and the presented modelling strategies seems a promising way to enhance the understanding of drug disposition at the target site of drugs and might thus contribute to a more rational use of medicines.

The disposition of thioperamide, a histamine H3-receptor antagonist, in rats.

An HPLC method using an ovomucoid-conjugated column has been developed for measurement of thioperamide, a histamine H3 antagonist, with a minimum quantitation limit of 0.05 micrograms mL-1. The assay was used to study the disposition of thioperamide in rats. After bolus intravenous administration of thioperamide (10 mg kg-1), the plasma concentration decreased monoexponentially with a half-life of 26.9 min. The apparent total body clearance of thioperamide from rat plasma was 74.6 mL min-1 kg-1. Although thioperamide was quickly transferred to various tissues, its concentrations in peripheral tissues were higher than that in the brain. However, the brain regional tissue/plasma ratios of thioperamide increased continuously after its injection.

Short chain fatty acids may elicit an innate immune response from preadipocytes: A potential link between bacterial infection and inflammatory diseases

Short chain fatty acids (SCFAs) such as acetate, propionate and butyrate are produced by bacterial fermentation of dietary fiber. The highest concentrations of SCFAs in the body are found in the colon. Elevated dietary acetate has been shown to have anti-inflammatory effects in mouse models of colitis and inflammatory diseases in peripheral tissues. The details of how dietary SCFAs stimulate reduced inflammation in peripheral tissues have not been determined. I suggest that SCFA concentrations in peripheral tissues are generally not sufficient to locally produce a significant anti-inflammatory effect from immune cells. Moreover it is possible that elevated SCFA levels in peripheral tissues may actually stimulate an inflammatory response. The hypothesis is presented that preadipocytes and other cells with immune function such as fibroblasts in peripheral tissues elicit an inflammatory innate immune response when exposed to SCFAs at millimolar concentrations. A role for SCFAs in activating an immune response in preadipocytes is possible given the expression of a SCFA receptor in these cells, the demonstration that adipocytes and preadipocytes have immunity related functions, the observation that 2 mM SCFAs stimulated the expression of monocyte chemoattractant protein-1 (MCP-1) mRNA from 3T3-L1 preadipocytes and that concentrations of SCFAs can reach elevated levels at sites of bacterial infection. A SCFA-induced inflammatory response from preadipocytes and other cells with immune function, such as fibroblasts, may provide a further contributing factor linking bacterial infection to the development of insulin resistance and the severity of inflammatory diseases such as atherosclerosis.

Quantitative determination and tissue distribution of human 11β-hydroxysteroid dehydrogenase, hexose-6-phosphate dehydrogenase, glucose-6-phosphate transporter, glucocorticoid receptor and mineralocorticoid receptor mRNAs.

Glucocorticoid (GC) concentrations in peripheral tissues are precisely regulated by 11β-hydroxysteroid dehydrogenase (HSD) isozymes. When considering the physiological effects of GC in various tissues, quantitative determination of these isozymes and other components involved in corticosteroid signaling is important and informative. We thus performed comprehensive determination of the expression of these mRNAs in a wide range of human tissues. An absolute comparison of mRNA expression of human 11β-HSD isozymes, hexose-6-phosphate dehydrogenase (H6PDH), glucose-6-phosphate transporter (G6PT), glucocorticoid receptors (GRs), and mineralocorticoid receptor (MR) was performed by real-time RT-PCR. Human 11β-HSD type 1 mRNA was strongly expressed in the liver and placenta at comparatively high levels. H6PDH was expressed at low copy number, and comparatively high expression was observed in the kidney, testis, and ovary. G6PT expression was ubiquitous, but marked expression was observed in the liver, kidney, small intestine, and colon. GRα was also ubiquitously expressed at relatively high levels, which were approximately 10-fold higher than those of MR, whereas GRβ levels were below the detection limit in all tissues. 11β-HSD type 2 was predominantly expressed in the kidney, small intestine and colon; however, copy numbers of these transcripts showed a nearly identical pattern to type 1. MR was observed in various tissues examined, but was not fully correlated to the distribution of 11β-HSD type 2. The present quantitative results were partially consistent with previous studies. This quantification method can thus provide valuable information for understanding the physiological effects and physiological roles of glucocorticoid in humans.

A pilot study testing whether concentrations of levofloxacin in interstitial space fluid of soft tissues may serve as a surrogate for predicting its pharmacokinetics in lung

Recent observations indicate that pharmacokinetics of β-lactam antibiotics in the lung can be predicted by the use of concentration versus time profiles in peripheral soft tissues. If this observation is transferred to other classes of antimicrobials, measurement of antimicrobial concentrations in peripheral tissues would enable prediction of the pharmacokinetics of antimicrobials at the site of the respiratory tract infection. We set out to test the hypothesis that concentrations of the fluoroquinolone levofloxacin in the respiratory tract can be predicted on the basis of knowledge of its pharmacokinetics in peripheral soft tissues. After administration of a single intravenous dose of 500 mg of levofloxacin, microdialysis was used to describe the concentration versus time profiles of levofloxacin in the interstitial space fluid of lung tissue of patients ( n = 5) undergoing elective lung surgery. These data were compared with the concentration versus time courses in the interstitial space fluid of skeletal muscle and subcutaneous adipose tissue of healthy volunteers ( n = 7). The median AUC 0–∞ of free levofloxacin in lung (2267 mg × min/L, 1980–2355) was about 2-fold and 1.5-fold lower compared with skeletal muscle (4381 mg × min/L, range 1720–8195) and adipose tissue (3492 mg × min/L, range 1323–6420) of healthy controls, respectively. Concentrations in the interstitial space fluid of the lung were descriptively lower compared with corresponding concentrations in peripheral soft tissues. This is in contrast to previous observations made for the class of β-lactam antibiotics, and indicates that pharmacokinetics of levofloxacin derived from soft tissues may not be used uncritically for prediction of levofloxacin concentrations in the interstitium of the lung.

Tissue distribution of protease resistant prion protein in variant Creutzfeldt-Jakob disease using a highly sensitive immunoblotting assay

Variant Creutzfeldt-Jakob disease (vCJD) has a pathogenesis distinct from other forms of human prion disease: disease-related prion protein (PrP(Sc)) is readily detectable in lymphoreticular tissues. Quantitation of risk of secondary transmission, and targeting of risk reduction strategies, is limited by lack of knowledge about relative prion titres in these and other peripheral tissues, the unknown prevalence of preclinical vCJD, and a transmission barrier which limits the sensitivity of bioassay. We aimed to improve immunoblotting methods for high sensitivity detection of PrP(Sc) to investigate the distribution of PrP(Sc) in a range of vCJD tissues. We obtained tissues at necropsy from four patients with neuropathologically confirmed vCJD and from individuals without neurological disease. Tissues were analysed by sodium phosphotungstic acid precipitation of PrP(Sc) and western blotting using high sensitivity enhanced chemiluminescence. We could reliably detect PrP(Sc) in the equivalent of 50 nL 10% vCJD brain homogenate, with a maximum limit of detection equivalent to 5 nl. PrP(Sc) could be detected in tissue homogenates when present at concentrations 10(4)-10(5) fold lower than those reported in brain. Tonsil, spleen, and lymph node were uniformly positive for PrP(Sc) at concentrations in the range of 0.1-15% of those found in brain: the highest concentrations were consistently seen in tonsil. PrP(Sc) was readily detected in the retina and proximal optic nerve of vCJD eye at levels of 2.5 and 25%, respectively of those found in brain. Other peripheral tissues studied were negative for PrP(Sc) with the exception of low concentrations in rectum, adrenal gland, and thymus from a single patient with vCJD. vCJD appendix and blood (Buffy coat fraction) were negative for PrP(Sc) at this level of assay sensitivity. We have developed a highly sensitive immunoblot method for detection of PrP(Sc) in vCJD tissues that can be used to provide an upper limit on PrP(Sc) concentrations in peripheral tissues, including blood, to inform risk assessment models. Rectal and other gastrointestinal tissues should be further investigated to assess risk of iatrogenic transmission via biopsy instruments. Ophthalmic surgical instruments used in procedures involving optic nerve and the posterior segment of the eye, in particular the retina, might represent a potential risk for iatrogenic transmission of vCJD. Tonsil is the tissue of choice for diagnostic biopsy and for population screening of surgical tissues to assess prevalence of preclinical vCJD infection within the UK and other populations.

Elevated sorbitol concentration in the cerebrospinal fluid of patients with mood disorders.

This study was undertaken to test the hypothesis that a specific pathophysiological mechanism of diabetic neuropathy, namely increased polyol pathway flux, could be operative in patients with bipolar and unipolar mood disorders. Numerous studies have shown abnormalities of carbohydrate metabolism, including high rates of diabetes mellitus, in patients with mood disorders. Several studies have found that peripheral neuropathy is a risk factor for depression in diabetics. Furthermore, increased polyol pathway flux results in elevated sorbitol concentrations in peripheral tissues and cerebrospinal fluid (CSF) of diabetics with neuropathy. The purpose of this study was to determine whether sorbitol concentration is elevated in the CSF of non-medically ill patients with mood disorders. Lumbar punctures were performed on 30 subjects - 10 with bipolar mood disorder, 10 with unipolar mood disorder, and 10 age-matched normal controls, and CSF sorbitol concentrations were measured, using a gas chromatographic-mass spectroscopic technique. The mean+/-standard deviation of CSF sorbitol concentrations differed among the three groups as follows: bipolar (22.9+/-4.6 micromoles/l) > unipolar (19.0+/-2.8 micromoles/l)>normal control (15. 6+/-1.9 micromoles/l). One-way ANOVA showed significant (P=0.0002) differences among the three groups. Post-hoc tests indicated a significant (P<0.05) difference between bipolars and normal controls, bipolars and unipolars, and unipolars and normal controls. Further investigation is needed to determine the pathophysiological significance of this novel finding of elevated sorbitol concentration in the CSF of patients with mood disorders.

Activation of Bovine Photoreceptor Guanylate Cyclase by S100 Proteins

S100 proteins are acidic calcium-binding proteins present in high concentration in the brain and at lower concentrations in peripheral tissues. Their function remains to be elucidated in many tissues. In this report we show for the first time that S100 proteins stimulate the bovine photoreceptor membrane guanylate cyclase. The extent of stimulation varied between the different S100 proteins with the S100b exhibiting the highest level of influence. The stimulation by all S100 proteins was calcium dependent, with the half-maximal stimulation occurring at about 35–40 μM calcium. These results suggest that in some cells S100 proteins can mediate calcium signals via cyclic GMP.

Theophylline kinetics in peripheral tissues in vivo in humans

Several biochemical and cellular effects have been described for methylxanthines under in vitro conditions. However, it is unknown, whether threshold concentrations required to exert these effects are attained in target tissues in vivo. We therefore employed the microdialysis technique for measuring theophylline concentrations in peripheral tissues under in vivo conditions. Following in vitro and in vivo calibration, microdialysis probes were inserted into the medial vastus muscle and into the periumbilical subcutaneous adipose layer of healthy volunteers. Following single oral dose administration of 300 mg or i.v. infusion of 240 mg theophylline, in vivo time courses of theophylline concentrations were monitored in tissues and plasma. Major pharmacokinetic parameters (cmax, tmax, AUC) were calculated for plasma and tissue time courses. The mean AUCtissue/AUCplasma-ratio was 0.56 (p.o.) and 0.55 (i.v.) for muscle and 0.55 (p.o.) and 0.72 (i.v.) for subcutaneous adipose tissue. We conclude that microdialysis provides important information on the distribution and the tissue pharmacokinetics of theophylline.

Interstitial fluid concentrations of glycerol, glucose, and amino acids in human quadricep muscle and adipose tissue. Evidence for significant lipolysis in skeletal muscle.

To determine the relationship between circulating metabolic fuels and their local concentrations in peripheral tissues we measured glycerol, glucose, and amino acids by microdialysis in muscle and adipose interstitium of 10 fasted, nonobese human subjects during (a) baseline, (b) euglycemic hyperinsulinemia (3 mU/kg per min for 3 h) and, (c) local norepinephrine reuptake blockade (NOR). At baseline, interstitial glycerol was strikingly higher (P < 0.0001) in muscle (3710 microM) and adipose tissue (2760 microM) compared with plasma (87 microM), whereas interstitial glucose (muscle 3.3, fat 3.6 mM) was lower (P < 0.01) than plasma levels (4.8 mM). Taurine, glutamine, and alanine levels were higher in muscle than in adipose or plasma (P < 0.05). Euglycemic hyperinsulinemia did not affect interstitial glucose, but induced a fall in plasma glycerol and amino acids paralleled by similar changes in the interstitium of both tissues. Local NOR provoked a fivefold increase in glycerol (P < 0.001) and twofold increase in norepinephrine (P < 0.01) in both muscle and adipose tissues. To conclude, interstitial substrate levels in human skeletal muscle and adipose tissue differ substantially from those in the circulation and this disparity is most pronounced for glycerol which is raised in muscle as well as adipose tissue. In muscle, insulin suppressed and NOR increased interstitial glycerol concentrations. Our data suggest unexpectedly high rates of intramuscular lipolysis in humans that may play an important role in fuel metabolism.

Dietary potassium effects on lithium concentration and toxicity in hamsters

Lithium can be toxic in rodents and human patients at concentrations within the therapeutic range for treatment of affective disorders. Diet containing supplemental potassium reduced lithium-induced weight loss in hamsters following daily injections of 3 mmol LiCl/kg for 7-10 days. Potassium supplementation also decreased lithium concentrations in peripheral tissues; but not in brain, after repeated lithium administration. Repeated lithium injection lowered the concentration of potassium in peripheral tissues, but tissue potassium was not restored by dietary potassium supplementation. Toxic effects of single injections of 1-10 mmol LiCl/kg were unaffected by dietary potassium. Lithium concentrations in plasma, brain, or peripheral tissues 6-hr after injection of 5 mmol LiCl/kg were also not altered by potassium diet. These data suggest that interactions between lithium and potassium diet differ in peripheral tissues compared to the central nervous system, and after acute versus chronic lithium administration.