Influence of age on plasma osmolality: a community study

Age-related changes on physicochemical properties of the artificial vitreous humor: A practical tool for enhancing ex vivo studies

The vitreous humor (VH) is a hydrophilic, jelly-like ocular fluid, which is located in the posterior chamber of the eye. The rheological, structural, and chemical properties of VH change significantly during aging, which further causes eye-associated diseases and could be a potential indicator for various diseases. In this study, artificial VH (A-VH) samples were created by taking into account different age groups to observe age-related changes in the physicochemical properties of these samples. This study aimed to measure the physicochemical properties of age-dependently prepared A-VH samples to determine the changes with aging in the physicochemical properties of A-VH samples. Phosphate-buffered saline (PBS)-based A-VH samples were prepared in three types representing adult, middle-aged, and elder individuals. Age-related changes in physicochemical properties (surface tension, osmolality, pH, relative viscosity, density, and refractive index) were analyzed by related equipment. The A-VH samples, prepared using PBS, showed strong similarity to authentic VH in terms of physicochemical properties. While the age-related changes studies have revealed some discrepancies between age-dependently prepared A-VH samples in terms of surface tension, osmolality, relative viscosity, and pH with high correlation coefficients (r2 > 0,94), density and refractive index values did not show any significant differences and correlation between types of A-VH representing 3 age groups. In conclusion, age-dependent A-VH samples were created successfully to use ex vivo method development studies, and the influence of aging on the physicochemical properties of VH was demonstrated as well.

High-Resolution Micro-object Separation by Rotating Magnetic Chromatography

The development of new technologies for the separation, selection, and isolation of microparticles such as rare target cells, circulating tumor cells, cancer stem cells, and immune cells has become increasingly important in the last few years. Microparticle separation technologies are usually applied to the analysis of disease-associated cells, but these procedures often face a cell separation problem that is often insufficient for single specific cell analyses. To overcome these limitations, a highly accurate size-based microparticle separation technique, herein called "rotating magnetic chromatography", is proposed in this work. Magnetic nanoparticles, placed in a microfluidic separation channel, are forced to move in well-defined trajectories by an external magnetic field, colliding with microparticles that are in this way separated on the basis of their dimensions with high accuracy and reproducibility. The method was optimized by using fluorescein isothiocyanate-modified polystyrene particles (chosen as a reference standard) and then applied to the analysis of cancer cells like Hep-3B and SK-Hep-1, allowing their fast and high-resolution chromatographic separation as a function of their dimensions. Due to its unmatched sub-micrometer cell separation capabilities, RMC can be considered a break-through technique that can unlock new perspectives in different scientific fields, that is, in medical oncology.

The effects of aging on biosynthetic processes in the rat hypothalamic osmoregulatory neuroendocrine system

Elderly people exhibit a diminished capacity to cope with osmotic challenges such as dehydration. We have undertaken a detailed molecular analysis of arginine vasopressin (AVP) biosynthetic processes in the supraoptic nucleus (SON) of the hypothalamus and secretory activity in the posterior pituitary of adult (3 months) and aged (18 months) rats, to provide a comprehensive analysis of age-associated changes to the AVP system. By matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis, we identified differences in pituitary peptides, including AVP, in adult and aged rats under both basal and dehydrated states. In the SON, increased Avp gene transcription, coincided with reduced Avp promoter methylation in aged rats. Based on transcriptome data, we have previously characterized a number of novel dehydration-induced regulatory factors involved in the response of the SON to osmotic cues. We found that some of these increase in expression with age, while dehydration-induced expression of these genes in the SON was attenuated in aged rats. In summary, we show that aging alters the rat AVP system at the genome, transcriptome, and peptidome levels. These alterations however did not affect circulating levels of AVP in basal or dehydrated states.

An in vitro model of skeletal muscle volume regulation

INTRODUCTION

Hypertonic media causes cells to shrink due to water loss through aquaporin channels. After acute shrinkage, cells either regulate their volume or, alternatively, undergo a number of metabolic changes which ultimately lead to cell death. In many cell types, hypertonic shrinkage is followed by apoptosis. Due to the complex 3D morphology of skeletal muscle and the difficulty in obtaining isolated human tissue, we have begun skeletal muscle volume regulation studies using the human skeletal muscle cell line TE671RD. In this study we investigated whether hypertonic challenge of the human skeletal muscle cell line TE671RD triggered cell death or evoked a cell volume recovery response.

METHODS

The cellular volume of TE671RD cells was calculated from the 2D surface area. Cell death was assessed by both the trypan blue live/dead assay and the TUNEL assay.

RESULTS

Medium osmolality was increased by addition of up to 200 mM sucrose. Addition of 200 mM sucrose resulted in mean cell shrinkage of 44±1% after 30 mins. At later time points (2 and 4 hrs) two separate cell subpopulations with differing mean cell volume became apparent. The first subpopulation (15±2% of the total cell number) continued to shrink whereas the second subpopulation had an increased cell volume. Cell death was observed in a small proportion of cells (approximately 6-8%).

CONCLUSION

We have established that a substantial proportion of TE671RD cells respond to hypertonic challenge with RVI, but that these cells are resistant to hypertonicity triggered cell death.

Moderate-intensity intermittent work in the heat results in similar low-level dehydration in young and older males

Older individuals may be more susceptible to the negative thermal and cardiovascular consequences of dehydration during intermittent work in the heat. This study examined the hydration, thermal, and cardiovascular responses to intermittent exercise in the heat in 14 Young (Y, Mean ± SE; 25.8 ± 0.8 years), Middle-age (MA, 43.6 ± 0.9 years), and Older (O, 57.2 ± 1.5 years) healthy, non-heat acclimated males matched for height, mass, body surface area, and percent body fat. Rectal temperature (Tre), heart rate (HR), local sweat rate (LSR), and hydration indices were measured during 4 × 15-min moderate to heavy cycling bouts at 400 W heat production, each followed by a 15-min rest period, in Warm/Dry (35°C, 20% relative humidity [RH]) and Warm/Humid (35°C, 60% RH) heat. No differences were observed between the age groups for Tre, Tre change, HR, LSR, mass change, urine specific gravity, and plasma protein concentration in either condition, irrespective of the greater level of thermal and cardiovascular strain experienced in the Warm/Humid environment. Plasma volume changes (Dry Y: -5.4 ± 0.7, MA: -6.2 ± 0.9, O: -5.7 ± 0.9%, Humid Y: -7.3 ± 1.0, MA: -7.9 ± 0.8, O: -8.4 ± 1.0%) were similar between groups, as were urine specific gravity and plasma protein concentrations. Thus, physically active Young, Middle-age, and Older males demonstrate similar hydration, thermal, and cardiovascular responses during moderate- to high-intensity intermittent exercise in the heat.

Clinical assessment of dehydration in older people admitted to hospital: what are the strongest indicators?

Due to an absence of published primary data, this study explores dehydration prevalence and the change in physiological parameters frequently used to assess dehydration (fluid deficit) in older hospitalized people, as no standard measurement method exists. This observational longitudinal cohort study recruited 43 people aged 60 years or over, voluntarily admitted to a tertiary teaching hospital's Geriatric and Rehabilitation Unit (GARU). Over 40 clinical, hematological and urinary biochemical parameters employed by medical officers during dehydration assessment, identified through literature, interviews and focus group were investigated. Short-term weight changes, intra- and inter-rater repeatability of dehydration assessments were completed to assess validation and precision of the clinician's clinical dehydration assessment. Systolic blood pressure drop on standing, sternal skin turgor, tongue dryness and body mass index (BMI) were associated with hydration status; demonstrated clinically meaningful differences between groups. BMI negatively confounded the association between dehydration and systolic blood pressure drop on standing. Physical, rather than biochemical, parameters more often identified mild dehydration. The findings challenge common expectations of hematological and physiological measurement changes occurring in older people clinically assessed as dehydrated and emphasize the need to adjust for potential confounders during exploration of the associations of clinical parameters with dehydration status.

Early identification of hypovolemia using total body resistance measurements in long-term care facility residents

BACKGROUND

Clinical management of fluid imbalance continues to be a major challenge in the long-term care industry. A proactive method of recognizing hypovolemia (reduced total body fluid) in its early stages is greatly needed.

OBJECTIVES

The goals of this research were 3-fold: (1) to determine the mean total body resistance(TBR) of an unmatched population of long-term care facility (LTCF) residents and correlate increased levels of TBR with evidence of fluid imbalance; (2) to identify patients at risk for hypovolemia by using TBR measurements as an objective guide; and (3) to suggest nursing practices designed to increase hydration in LTCF residents.

METHODS

Two pairs of electrocardiograph-type electrodes were placed on the right humeral-carpal junction and at the level of the right lateral malleolus of each patient. A 50-kHz signal was introduced to the outer electrode of each pair; the inner electrode detected variation of the resistance to the signal as a function of ionic conduction through the electrolyte content of body fluids. Resistance, reactance, and phase angle were measured.

RESULTS

The medical records of patients in 26 LTCFs (17 urban, 9 rural) in north-central and east Texas were reviewed during 2001. The mean age of the 1225 study patients (754 women, 471 men) was 76 years; mean height was 165.8 cm, and mean body weight was 71.9 kg. The mean TBR (right wrist-right ankle) for men and women was 504.81 ohms. Based on this measurement and a measurement of 629 ohms in residents judged to be hypovolemic on the basis of abnormal clinical laboratory data, patients with a wrist-ankle resistance >550 ohms were considered at risk for hypovolemia and possibly clinically significant dehydration. Subsequent measurements of TBR revealed a reduction consistent with levels in the normal range.

CONCLUSIONS

In these studies, TBR measurements correlated inversely with total body water and fluid compartments. Extracellular fluid compartments were found to be larger in females than in males, reflecting larger cellular mass in males. Total body resistivity was found to be higher in females than in males, which may have implications for body composition metrics. TBR provides a reference for comparison with both clinical and laboratory findings. The ability to identify LTCF residents at risk for hypovolemia, using noninvasive bedside measurements, may offer a definitive guideline for management of adequate fluid balance.

Osmotic regulation of cell function and possible clinical applications

Inflammation and immunosuppression can cause acute respiratory distress syndrome, multiple organ failure, and sepsis, all of which are lethal posttraumatic complications in trauma patients. Prevention of the inflammation and immunosuppression has been a main focus of trauma researcher for many years. Recently, hypertonic resuscitation has attracted attention as a possible therapeutic approach to counteract such deleterious immune responses in trauma patients. We have begun to understand how hypertonic fluids affect immune cell signaling, and a number of experimental and clinical studies have started to reveal valuable information on the clinical efficacy and the limitations of hypertonic resuscitation fluids. Knowledge of how osmotic cues regulate immune cell function will enable us to fully exploit the clinical potential of hypertonic resuscitation to reduce inflammatory and anergic complications in trauma patients.

Hypertonic stress increases T cell interleukin-2 expression through a mechanism that involves ATP release, P2 receptor, and p38 MAPK activation

Hypertonic stress (HS) can alter the function of mammalian cells. We have reported that HS enhances differentiated responses of T cells by increasing their ability to produce interleukin (IL)-2, a finding of clinical interest because hypertonic infusions may modulate immune function in patients. HS shrinks cells and mechanically deforms membranes, which results in ATP release from many cell types. Here we investigate if ATP release is an underlying mechanism through which HS augments T cell function. We found that mechanical stress and HS induced rapid ATP release from Jurkat T cells. HS and exogenous ATP mobilized intracellular Ca(2+), activated p38 MAPK, and increased IL-2 expression. Ca(2+) mobilization was attenuated in the presence of EGTA or by removal of extracellular ATP with apyrase. Adenosine did not increase IL-2 expression, as did ATP. Apyrase, inhibition of P2 receptors, or inhibition of p38 MAPK with SB203580 reduced the stimulatory effects of HS, indicating that HS enhances IL-2 expression through a mechanism that involves ATP release, P2 (perhaps P2X7) receptors, and p38 MAPK activation. We conclude that release of and response to ATP plays a key role in the mechanism through which hypertonic stress regulates the function of T cells.

Hypertonicity increases cAMP in PMN and blocks oxidative burst by PKA-dependent and -independent mechanisms

Hypertonic stress (HS) suppresses neutrophil (PMN) functions. We studied the underlying mechanism and found that HS rapidly (<1 min) increased intracellular cAMP levels by up to sevenfold. cAMP levels correlated with applied hypertonicity and the degree of neutrophil suppression. HS and cAMP-elevating drugs (forskolin and dibutyryl cAMP-acetoxymethyl ester) similarly suppressed extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase activation and superoxide formation in response to N-formylmethionyl-leucyl-phenylalanine (fMLP) stimulation. Inhibition of cAMP-dependent protein kinase A (PKA) with H-89 abrogated the suppressive effects of HS, restoring fMLP-induced ERK and p38 activation and superoxide formation. Inhibition of phosphodiesterase with 3-isobutyl-1-methylxanthine augmented cAMP accumulation and the suppressive effects of HS, while inhibition of adenylyl cyclase with MDL-12330A abolished these effects. These findings suggest that HS-activated cAMP/PKA signaling inhibits superoxide formation by intercepting fMLP-induced activation steps upstream of ERK and p38. In contrast to its effects in the presence of moderate hypertonicity levels (40 mM), H-89 was unable to rescue neutrophil functions from suppression by higher hypertonicity levels (100 mM), indicating that more severe HS suppresses neutrophils via secondary PKA-independent mechanisms.

Hypertonicity regulates the function of human neutrophils by modulating chemoattractant receptor signaling and activating mitogen-activated protein kinase p38

Excessive neutrophil activation causes posttraumatic complications, which may be reduced with hypertonic saline (HS) resuscitation. We tested if this is because of modulated neutrophil function by HS. Clinically relevant hypertonicity (10-25 mM) suppressed degranulation and superoxide formation in response to fMLP and blocked the activation of the mitogen activated protein kinases (MAPK) ERK1/2 and p38, but did not affect Ca2+ mobilization. HS did not suppress oxidative burst in response to phorbol myristate acetate (PMA). This indicates that HS suppresses neutrophil function by intercepting signal pathways upstream of or apart from PKC. HS activated p38 by itself and enhanced degranulation in response to PKC activation. This enhancement was reduced by inhibition of p38 with SB203580, suggesting that p38 up-regulation participates in HS-induced enhancements of degranulation. HS had similar effects on the degranulation of cells that were previously stimulated with fMLP, but had no effect on its own, suggesting that HS enhancement of degranulation requires another signal. We conclude that depending on other stimuli, HS can suppress neutrophil activation by intercepting multiple receptor signals or augment degranulation by enhancing p38 signaling. In patients HS resuscitation may reduce posttraumatic complications by preventing neutrophil activation via chemotactic factors released during reperfusion.

A comparison of intravenous and subcutaneous hydration in elderly acute stroke patients

The aim of this study was to compare the effectiveness of subcutaneous and intravenous fluid therapy in hydrating, elderly acute stroke patients. Thirty-four such patients, needing parenteral fluids because of impaired consciousness or dysphagia, were randomly allocated to receive either subcutaneous or intravenous fluids (2 litres of dextrose-saline/24 hours). Serum osmolality was measured before starting fluid therapy (Day 1) and on Days 2 and 3. An analysis of covariance of the osmolalities showed no statistical difference between the two groups (P = 0.12). The total cost of cannulae used over the 3 days for the subcutaneous route was approximately a third of that for the intravenous route. Complication rates were similar for the two groups. The results suggest that subcutaneous fluid therapy is an effective alternative to the intravenous route.