Cutaneous Microdialysis: Is it Worth the Sweat?

Water and hemoglobin modulated gelatin-based phantoms to spectrally mimic inflamed tissue in the validation of biomedical techniques and the modeling of microdialysis data

SIGNIFICANCE

Tissue simulating phantoms are an important part of validating biomedical optical techniques. Tissue pathology in inflammation and oedema involves changes in both water and hemoglobin fractions.

AIM

We present a method to create solid gelatin-based phantoms mimicking inflammation and oedema with adjustable water and hemoglobin fractions.

APPROACH

One store-bought gelatin and one research grade gelatin were evaluated. Different water fractions were obtained by varying the water-to-gelatin ratio. Ferrous stabilized human hemoglobin or whole human blood was added as absorbers, and the stability and characteristics of each were compared. Intralipid® was used as the scatterer. All phantoms were characterized using spatial frequency domain spectroscopy.

RESULTS

The estimated water fraction varied linearly with expected values (R2  =  0.96 for the store-bought gelatin and R2  =  0.99 for the research grade gelatin). Phantoms including ferrous stabilized hemoglobin stayed stable up to one day but had methemoglobin present at day 0. The phantoms with whole blood remained stable up to 3 days using the store-bought gelatin.

CONCLUSIONS

A range of physiological relevant water fractions was obtained for both gelatin types, with the stability of the phantoms including hemoglobin differing between the gelatin type and hemoglobin preparation. These low-cost phantoms can incorporate other water-based chromophores and be fabricated as thin sheets to form multilayered structures.

Advances in the bioanalytical study of drug delivery across the skin

The study of a drug's dermal penetration profile provides important pharmaceutical data for the rational development of topical and transdermal delivery systems because the skin is a broadly used delivery route for local and systemic drugs and a potential route for gene therapy and vaccines. Monitoring drug penetration across the skin and quantifying its levels in different skin layers have been constant challenges due to the detection limitations of the available techniques, as well as the inherent interference in this tissue. This review explores and discusses several bionalytical methods that are indispensable tools to study drugs across the skin. In addressing the main topic, we structure the review highlighting the skin as an important route of drug administration and its structure, skin membrane models most used and its properties, in vitro and in vivo assays most used in the study of drug delivery to the skin, the techniques for processing the skin for subsequent analysis by bioanalytical methods that have a theoretical and practical approach showing its applicability, limitations and also including examples of its use. This review has a comprehensive approach in order to help researchers design their experiments and update the applicability and advances in this area of expertise.

In vivo microdialysis sampling of adipokines CCL2, IL-6, and leptin in the mammary fat pad of adult female rats

Adipocytes from white adipose tissue secrete cytokines and other bioactive proteins which are collectively termed adipokines. Adiposity has been linked with increased breast cancer risk as adipokines secreted by adipocytes significantly affect epithelial cells from which breast cancer arises. Measurement of extracellular adipokine concentrations that would be involved in signaling through mammary tissue is therefore of importance. In this work, microdialysis sampling was used to collect adipokines from the interstitial space of the mammary fat pad of female rats under isoflurane anesthesia. The adipokines CCL2 (MCP-1), leptin and IL-6 were quantified from dialysate samples and compared to total tissue concentrations surrounding the implanted probes. After three hours of microdialysis sampling at 1 μL min(-1), the respective median values for these adipokines in dialysate samples were approximately 175 pg mL(-1) (CCL2), 150 pg mL(-1) (IL-6) and 750 pg mL(-1) (leptin). Adipokine protein levels from dialysates were an order of magnitude lower than levels obtained directly from mammary tissue. However, the adipokine concentrations between excised tissue surrounding the microdialysis sampling probes and control tissue without implants did not differ. This work demonstrates the utility of microdialysis sampling to quantify mammary gland adipokine levels, with relevance to understanding mammary physiology.

Clinical applicability of dOFM devices for dermal sampling

BACKGROUND

Sampling the dermal interstitial fluid (ISF) allows the pharmacokinetics and pharmacodynamics of dermatological drugs to be studied directly at their site of action. Dermal open-flow microperfusion (dOFM) is a recently developed technique that can provide minimally invasive, continuous, membrane-free (thus unfiltered) access to the dermal ISF. Herein, we evaluate the clinical applicability and reliability of novel wearable dOFM devices in a clinical setting.

METHODS

Physicians inserted 141 membrane-free dOFM probes into the dermis of 17 healthy and psoriatic volunteers and sampled dermal ISF for 25 h by using wearable push-pull pumps. The tolerability, applicability, reproducibility, and reliability of multiple insertions and 25 h continuous sampling was assessed by pain scoring, physician feedback, ultrasound probe depth measurements, and 25 h-drift and variability of the sodium relative recovery.

RESULTS

Insertion pain was moderate and decreased with each additional probe. Probe insertion was precise, although slightly deeper in lesional skin. The wearable push-pull pump enabled uninterrupted ISF sampling over 25 h with low variability. The relative recovery was drift-free and highly reproducible.

CONCLUSION

dOFM sampling devices are tolerable and reliable for prolonged continuous dermal sampling in a multiprobe clinical setting. These devices should enable the study of a wide range of drugs and their biomarkers in the skin.

Iontophoresis of a 13 kDa protein monitored by subcutaneous microdialysis in vivo

Background: The purpose of this study was to optimize parameters pertaining to microdialysis technique so as to make this method feasible for evaluating transdermal transport of macromolecules. Results: Microdialysis experiments were performed in vivo using hairless rats with daniplestim as the model protein. Two perfusion fluids – phosphate-buffered saline (PBS) and 3% dextran in PBS – were evaluated with respect to their effect on sample volume retrieval and recovery of the target protein from the microdialysis probe. Incorporation of dextran-60 in the perfusion fluid reduced fluid loss to 10% as opposed to 34% in the absence of dextran-60. Improvement in daniplestim recovery was also seen with dextran-PBS (56.5 ± 10.3%) as the perfusion fluid than with PBS alone (26.7±4.5%). Conclusion: Subcutaneous levels of daniplestim were measured following iontophoresis after improving recovery and minimizing fluid loss from the microdialysis probe.

Are cutaneous microdialysis cytokine findings supported by end point biopsy immunohistochemistry findings?

Insertion of a cutaneous microdialysis catheter into normal dermis has been shown to induce the production of IL1b, IL6 and IL8 in an innate response to minimal trauma. In the present study, skin biopsy for immunohistochemistry has been performed at the site of the microdialysis catheter to compare the findings with that of the microdialysis findings 24 h after insertion. Of the three named cytokines, concordance between the two investigated technologies was highest for IL8 (100%) followed by IL6 (70%) and IL1b (50%). For seven other pro-inflammatory and T cell-relevant cytokines studied, concordance ranged between 50% and 80%. The total number of positive (microdialysis or immunofluorescence) findings was similar between the two methodologies. Technical and biological phenomenon can explain the differences. We conclude that both methodologies illustrate important features of tissue biology and that a combination of the two methods in clinical research can provide the chronology of soluble mediator participation and the more classic, but also more invasive, biopsy-based methodology at a point which constitutes the end of the observation period. We conclude further that at the 24-h time period here studied, microdialysis catheters are still functional and thus capable of producing relevant data which can be corroborated and extended by the "end point biopsy".

Does chewing coca leaves influence physiology at high altitude?

Andean Indians have used coca leaves (Erythroxylon coca and related species) for centuries to enhance physical performance. The benefits and disadvantages of using coca leaf have been a subject of many political debates. The aim of this study was to investigate the effects of chewing coca leaves on biochemical and physiological parameters. Cutaneous microdialysis catheters were used to estimate systemic biochemical changes. We subjected 10 healthy adult males (local residents) in Cajamarca (Peru, altitude 2700 m) to a standardised exercise routine on a stationary cycle ergometer. The blood pressure, oxygen saturation (digital), pulse, VO2 max and ECG (Holter monitor) were recorded before the exercise. Cutaneous microdialysis catheters were introduced in the forearm. The subjects were given to chew 8 g of coca leaves with a small amount of lime. They were then placed on the cycle ergometer for 20 min. Blood pressure, oxygen saturation, pulse, ECG and VO2 max were recorded. Pyruvate, glucose, lactate, glycerol and glutamate levels were estimated. Oxygen saturation, blood pressure, and pulse rate did not show any significant changes between the two groups. Glucose levels showed hyperglycaemic response. Glycerol, Lactate and Pyruvate increased. Glutamate remained unchanged. Similar changes were not seen in the controls. These results suggest that coca leaves have blocked the glycolytic pathway of glucose oxidation resulting in accumulation of glucose and pyruvate. The energy requirement for exercise is being met with beta-oxidation of fatty acids. The glycerol released was also getting accumulated since its pathway for oxidation was blocked. These experimental findings suggest that chewing coca leaves is beneficial during exercise and that the effects are felt over a prolonged period of sustained physical activity.