Impact of Sampling and Cellular Separation on Amino Acid Determinations in Drosophila Hemolymph

Extracellular Fluid Collection and Analysis of Drosophila melanogaster Brain Tissue with μ-Low-Flow Push-Pull Perfusion (μLFPP)

The development of methods to generate quantitative chemical content information from precise tissue locations is needed to understand fundamental cellular and tissue physiology. This work describes a method to perfuse the extracellular fluid of fly brains in vivo using μ-low-flow push-pull perfusion (μLFPP) for quantitative chemical content determinations. Miniaturization of push-pull perfusion probe designs allowed the development of methods for probe tip placement into and sampling from the fruit fly's brain. Perfusate analysis identified and quantified arginine, octopamine, histidine, taurine, glycine, glutamate, and aspartate. The perfusate data did not exhibit any statistical differences based on sex. The perfusate analysis was compared to hemolymph samples to confirm probe placement in fly brain tissues. The appearance of probe placement into the brain space was confirmed with the following observations. Hemolymph and perfusate samples were found to contain analytes unique to each sample type. Quantitated levels of perfusate were not a simple dilution of hemolymph content. Further, the discovery of perfusates with composition similar to both hemolymph and brain perfusate when damage was intentionally inflicted supports the observation that perfusates are distinct from hemolymph. The analysis of perfusate collected for greater than an hour of sampling exhibits the possibility of monitoring applications. Altogether, this work demonstrates the viability of performing μ-low-flow push-pull perfusion for in vivo studies of fly brain tissues to identify and quantitate neurotransmitter content.

Quantifying Sample Collection and Processing Impacts on Fiber-Based Tear Fluid Chemical Analysis

Purpose

Noninvasive analyses of tear fluid from humans and animal models in clinical and research settings most commonly use absorbent material for collection and processing. Still, the impact of these analytical techniques on tear chemical analyses remains largely unknown. The purpose of this study was to quantify the impacts of phenol red thread fiber-based tear sample collection and processing on the primary amine content.

Methods

Human tears were collected by placing the folded end of phenol red thread on the palpebral conjunctiva of the right eye for 20 seconds. The wetted thread was then processed using elution or extraction, and capillary electrophoresis with light-emitting diode-induced fluorescence detection was used for analysis and quantitation.

Results

Distinct processing methods impacted tear analysis differently. Primary amines adsorbed onto the thread partitioned in a chromatographic manner and thus any single portion of the wetted thread might not be representative of the whole sample. Quantitative assessment of five small molecule standards after on-thread processing showed significant overestimation of the actual concentration, with increased accuracy for larger volume samples. Yet collection of larger tear volumes introduced error in volume determination owing to evaporation and reduced small molecule separation resolution.

Conclusions

These results indicated that absorption-based tear fluid collection and processing significantly alter chemical content analysis, suggesting that the impacts of methods used should be regularly evaluated to standardize results drawn from different studies.

Translational Relevance

This study identifies potential inconsistencies and inaccuracies in tear analyses that are widespread across the published literature and clinical care.