Compatible osmolytes modulate the response of porcine endothelial cells to hypertonicity and protect them from apoptosis

The effects of betaine supplementation on fluid balance and heat tolerance during passive heat stress in men

INTRODUCTION

Consuming intracellular osmolytes, like betaine (BET), may attenuate symptoms of heat stress. The purpose of this study was to examine the effects of BET supplementation on fluid balance and heat tolerance after a 7-day loading period and during passive heat exposure.

METHODS

A double-blind, placebo controlled, crossover study compared BET or placebo consumption (50 mg·kg-1 , twice daily) for 7 days in young, recreationally active men (N = 11).

RESULTS

During the loading period, no significant interactions were found for any marker of fluid balance between or within conditions. During heat exposure, significant time effects but no condition x time interactions, were found for plasma characteristics (i.e., volume, osmolality, sodium, albumin, and total protein). Plasma volume was significantly increased by min 30 in both conditions (PLA: +6.9. ± 5.0%, BET: +10.2 ± 7.4%) and remained elevated for the remainder of the experimental trial, but was not significantly different between conditions. After 60 min of passive heat exposure, both conditions experienced a similar increase in core temperature (PLA: +0.32 ± 0.22°C, BET: +0.31 ± 0.21°C; p = 0.912).

CONCLUSIONS

Supplemental BET did not improve markers of fluid balance or heat tolerance during 7 days of loading or during passive heat exposure.

Neutral amino acid transporter SLC38A2 protects renal medulla from hyperosmolarity-induced ferroptosis

Hyperosmolarity of the renal medulla is essential for urine concentration and water homeostasis. However, how renal medullary collecting duct (MCD) cells survive and function under harsh hyperosmotic stress remains unclear. Using RNA-Seq, we identified SLC38A2 as a novel osmoresponsive neutral amino acid transporter in MCD cells. Hyperosmotic stress-induced cell death in MCD cells occurred mainly via ferroptosis, and it was significantly attenuated by SLC38A2 overexpression but worsened by Slc38a2-gene deletion or silencing. Mechanistic studies revealed that the osmoprotective effect of SLC38A2 is dependent on the activation of mTORC1. Moreover, an in vivo study demonstrated that Slc38a2-knockout mice exhibited significantly increased medullary ferroptosis following water restriction. Collectively, these findings reveal that Slc38a2 is an important osmoresponsive gene in the renal medulla and provide novel insights into the critical role of SLC38A2 in protecting MCD cells from hyperosmolarity-induced ferroptosis via the mTORC1 signalling pathway.

Betaine: A Potential Nutritional Metabolite in the Poultry Industry

Poultry industry has been recognized as a fast-developing sector aiming to produce low-cost and high-nutrient foods for human consumption. This review article aimed to focus on the significant roles of dietary betaine supplementation in the poultry industry. In this respect, different effects of betaine on performance and carcass traits, as well as its osmoregulatory, anticoccidial, immune-modulatory, and heat-stress alleviation activities, were discussed. Different concentrations of betaine supplementation can improve the feed conversion ratio, final body weight, breast muscle yield, egg production ratio, and reduce body fat contents in broiler chicken, turkey, duck, geese, and quail diets. Betaine supplemented with methyl groups can eliminate the need to have some methyl-group donors, including choline and methionine, therefore having positive effects on feed conversion ratio in poultry diets. The osmolytic character of betaine can alleviate heat stress and have a positive impact on tonic immobility, which consequently reduces stress in poultry. By inhibiting distinct developmental stages of Eimeria species, betaine reduces the damaging effects of coccidiosis on broiler chickens and improves intestinal structure and function. The immunological, cardiovascular, neurological, renal, and hepatic metabolic systems benefit from betaine's osmo-protective properties. Therefore, betaine has the potential to be considered as an alternative to feed additives and enhances the health status and productive performance of poultry.

The Role of Betaine in Patients With Chronic Kidney Disease: a Narrative Review

PURPOSE OF REVIEW

This narrative review aimed to explore the functions of betaine and discuss its role in patients with chronic kidney disease (CKD).

RECENT FINDINGS

Some studies on CKD animal models have shown the benefits of betaine supplementation, including decreased kidney damage, antioxidant recovery status, and decreased inflammation. Betaine (N-trimethylglycine) is an N-trimethylated amino acid with an essential regulatory osmotic function. Moreover, it is a methyl donor and has anti-inflammatory and antioxidant properties. Additionally, betaine has positive effects on intestinal health by regulating the osmolality and gut microbiota. Due to these crucial functions, betaine has been studied in several diseases, including CKD, in which betaine plasma levels decline with the progression of the disease. Low betaine levels are linked to increased kidney damage, inflammation, oxidative stress, and intestinal dysbiosis. Furthermore, betaine is considered an essential metabolite for identifying CKD stages.

Acute hepatotoxicity and nephrotoxicity risk assessment of the Tibetan medicine 25 flavors of the turquoise pill based on 1H-NMR metabonomics

ETHNOPHARMACOLOGICAL RELEVANCE

25 flavors of the turquoise pill, a traditional Tibetan medicine for the treatment of various types of hepatitis, has not been investigated on its safety, especially the component mineral turquoise, which is believed to be essential but worried for its potential toxicity.

AIM OF THE STUDY

To explore the potential acute toxicity and function of 25 flavors of the turquoise pill and turquoise, the possible mechanism of the effects of turquoise and 25 flavors of the turquoise pill were systematically studied based on 1H NMR metabolomics.

MATERIALS AND METHODS

The rats were administered with turquoise and 25 flavors of the turquoise pill by gavage for 7 days, and samples of serum, liver, and kidney were collected. The potential toxicity and function of turquoise and 25 flavors of the turquoise pill on the liver and kidney of SD rats were evaluated by 1H NMR metabonomics, histopathology, and biochemical indexes.

RESULTS

The results demonstrated that 25 flavors of the turquoise pill could scavenge free oxygen radicals, strengthen aerobic respiration and inhibit glycolysis in the liver. It did not cause oxidative stress in the kidney with no obvious damage. By modulation of branched-chain amino acids (BCAAs), 25 flavors of the turquoise pill can improve the utilization of glucose and promote aerobic respiration of the kidney.

CONCLUSION

Considering the high dosage and short duration used in this study relative to their typical clinical usage, administration of 25 flavors of the turquoise pill and its component mineral turquoise are safe to livers and kidneys.

Effects of Two-Week Betaine Supplementation on Apoptosis, Oxidative Stress, and Aerobic Capacity after Exhaustive Endurance Exercise

This study evaluated the effects of 2 weeks of betaine supplementation on apoptosis, oxidative stress, and aerobic capacity after exhaustive endurance exercise (EEE). A double-blind, crossover, and counterbalanced design was adopted, with 10 healthy male participants asked to consume betaine (1.25 g of betaine mixed with 300 mL of sports beverage, twice per day for 2 weeks) or placebo (300 mL of sports beverage). All participants performed a graded exercise test on a treadmill to determine the maximal oxygen consumption (VO2max) before supplementation and then performed the EEE test at an intensity of 80% VO2max after 2 weeks of supplementation. The time to exhaustion, peak oxygen consumption, maximal heart rate, and average heart rate were recorded during the EEE test. Venous blood samples were drawn before, immediately after, and 3 h after the EEE test to assess apoptosis and the mitochondrial transmembrane potential (MTP) decline of lymphocytes as well as the concentrations of thiobarbituric acid reactive substance and protein carbonyl. The results indicated that lymphocyte apoptosis was significantly higher immediately after and 3 h after EEE than before exercise in participants in the placebo trial. However, lymphocyte apoptosis exhibited no significant differences among the three time points in participants in the betaine trial. Moreover, apoptosis in the betaine trial was significantly lower immediately after and 3 h after exercise compared with the placebo trial. No differences were noted for other variables. Thus, 2 weeks of betaine supplementation can effectively attenuate lymphocyte apoptosis, which is elevated by EEE. However, betaine supplementation exhibited no effects on MTP decline, oxidative stress, or aerobic capacity.

Betaine Supplementation May Improve Heat Tolerance: Potential Mechanisms in Humans

Betaine has been demonstrated to increase tolerance to hypertonic and thermal stressors. At the cellular level, intracellular betaine functions similar to molecular chaperones, thereby reducing the need for inducible heat shock protein expression. In addition to stabilizing protein conformations, betaine has been demonstrated to reduce oxidative damage. For the enterocyte, during periods of reduced perfusion as well as greater oxidative, thermal, and hypertonic stress (i.e., prolonged exercise in hot-humid conditions), betaine results in greater villi length and evidence for greater membrane integrity. Collectively, this reduces exercise-induced gut permeability, protecting against bacterial translocation and endotoxemia. At the systemic level, chronic betaine intake has been shown to reduce core temperature, all-cause mortality, markers of inflammation, and change blood chemistry in several animal models when exposed to heat stress. Despite convincing research in cell culture and animal models, only one published study exists exploring betaine's thermoregulatory function in humans. If the same premise holds true for humans, chronic betaine consumption may increase heat tolerance and provide another avenue of supplementation for those who find that heat stress is a major factor in their work, or training for exercise and sport. Yet, this remains speculative until data demonstrate such effects in humans.

The Anti-Inflammatory Effect of Taurine on Cardiovascular Disease

Taurine is a non-protein amino acid that is expressed in the majority of animal tissues. With its unique sulfonic acid makeup, taurine influences cellular functions, including osmoregulation, antioxidation, ion movement modulation, and conjugation of bile acids. Taurine exerts anti-inflammatory effects that improve diabetes and has shown benefits to the cardiovascular system, possibly by inhibition of the renin angiotensin system. The beneficial effects of taurine are reviewed.

Multifaceted regulation of the system A transporter Slc38a2 suggests nanoscale regulation of amino acid metabolism and cellular signaling

Amino acids are essential for cellular protein synthesis, growth, metabolism, signaling and in stress responses. Cell plasma membranes harbor specialized transporters accumulating amino acids to support a variety of cellular biochemical pathways. Several transporters for neutral amino acids have been characterized. However, Slc38a2 (also known as SA1, SAT2, ATA2, SNAT2) representing the classical transport system A activity stands in a unique position: Being a secondarily active transporter energized by the electrochemical gradient of Na⁺, it creates steep concentration gradients for amino acids such as glutamine: this may subsequently drive the accumulation of additional neutral amino acids through exchange via transport systems ASC and L. Slc38a2 is ubiquitously expressed, yet in a cell-specific manner. In this review, we show that Slc38a2 is regulated at the transcriptional and translational levels as well as by ions and proteins through direct interactions. We describe how Slc38a2 senses amino acid availability and passes this onto intracellular signaling pathways and how it regulates protein synthesis, cellular proliferation and apoptosis through the mechanistic (mammalian) target of rapamycin (mTOR) and general control nonderepressible 2 (GCN2) pathways. Furthermore, we review how this extensively regulated transporter contributes to cellular osmoadaptation and how it is regulated by endoplasmic reticulum stress and various hormonal stimuli to promote cellular metabolism, cellular signaling and cell survival. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.

NFAT5 up-regulates expression of the kidney-specific ubiquitin ligase gene Rnf183 under hypertonic conditions in inner-medullary collecting duct cells

We previously reported that among the 37 RING finger protein (RNF) family members, RNF183 mRNA is specifically expressed in the kidney under normal conditions. However, the mechanism supporting its kidney-specific expression pattern remains unclear. In this study, we elucidated the mechanism of the transcriptional activation of murine Rnf183 in inner-medullary collecting duct cells. Experiments with anti-RNF183 antibody revealed that RNF183 is predominantly expressed in the renal medulla. Among the 37 RNF family members, Rnf183 mRNA expression was specifically increased in hypertonic conditions, a hallmark of the renal medulla. RNF183 up-regulation was consistent with the activation of nuclear factor of activated T cells 5 (NFAT5), a transcription factor essential for adaptation to hypertonic conditions. Accordingly, siRNA-mediated knockdown of NFAT5 down-regulated RNF183 expression. Furthermore, the -3,466 to -3,136-bp region upstream of the mouse Rnf183 promoter containing the NFAT5-binding motif is conserved among mammals. A luciferase-based reporter vector containing the NFAT5-binding site was activated in response to hypertonic stress, but was inhibited by a mutation at the NFAT5-binding site. ChIP assays revealed that the binding of NFAT5 to this DNA site is enhanced by hypertonic stress. Of note, siRNA-mediated RNF183 knockdown increased hypertonicity-induced caspase-3 activation and decreased viability of mIMCD-3 cells. These results indicate that (i) RNF183 is predominantly expressed in the normal renal medulla, (ii) NFAT5 stimulates transcriptional activation of Rnf183 by binding to its cognate binding motif in the Rnf183 promoter, and (iii) RNF183 protects renal medullary cells from hypertonicity-induced apoptosis.

Influence of fibre and betaine on development of the gastrointestinal tract of broilers between hatch and 14 d of age

An experiment was designed to determine the influence of fibre and betaine on the development of the intestine, liver and pancreas of broilers from hatch to 14 d of age. A total of 250-day-old Cobb 500 male broilers were allocated to 16 cages with 15 broilers each. Treatments were arranged in a 2 × 4 factorial design, consisting of 2 feed formulations (low and high fibre diets) and 4 levels of betaine (0, 1, 3 or 5 kg/t). At hatch, 10 birds in total were euthanised, and samples of the liver, pancreas, yolk sac and intestine were collected for reference of the analysed parameters before the start of the trial. On d 4, 9 and 14, 5 birds per cage (10 birds per treatment) were selected, euthanised and treated as the same as the birds at hatch. Villus height and width and crypt depth were determined on the duodenum samples, and absorptive area was calculated. The number of enterocytes in mitosis at the villus was determined by a positive reaction to antibody for Ki67 protein, and fused villus was evaluated visually. The relative weight of the yolk sac reduced (P < 0.05) as birds aged while the intestine and liver reached a maximum (P < 0.05) at around d 4 and the pancreas at d 9. Birds fed the high fibre diet had greater feed intake, lower relative weight of the pancreas and higher villus (P < 0.05) than birds fed the low fibre diet. Villus width increased (P < 0.05) at 4 d of age, and this was associated with fused villus. Betaine inclusion reduced (P < 0.05) villus width, increased (P < 0.05) villus size and absorptive area, and reduced (P < 0.05) the number of enterocytes with positive reaction for the antibody Ki-67. Betaine inclusion reduced the width and increased the absorptive area and the villus height of the duodenum of birds up to 14 d of age. The higher fibre diet increased feed intake and villus height, yet reduced pancreas relative weight, while not affecting body weight gain. This response was possibly due to a dilution effect of the fibre, reducing nutrient absorption and consequently stimulating villus growth to improve absorption rates.

The effect of intravitreal injections on dry eye, and proposed management strategies

Intravitreal injection of anti-vascular endothelial growth factor (anti-VEGF) agents has become a commonly used treatment method for a number of ophthalmic conditions, including age-related macular degeneration. Although anti-VEGF therapy has shown promising results for many patients, there are several aspects of its application that have not been thoroughly investigated. One of these is the development and/or escalation of concurrent dry eye syndrome. Many patients undergoing treatment are already predisposed to dry eye disease due to their age and overall ocular health. As dry eye can have a substantial impact on quality of life, it has become increasingly apparent that the clinical signs and symptoms should be closely monitored and aggressively managed. This will allow for the optimization of patient comfort and visual potential. Here, we discuss the reasons why dry eye may develop during the course of repeated ocular anti-VEGF therapy, highlighting the key concerns about current practices and proposing possible solutions to improve the outcome for the patients.

Cap-independent protein synthesis is enhanced by betaine under hypertonic conditions

Protein synthesis is one of the main cellular functions inhibited during hypertonic challenge. The subsequent accumulation of the compatible osmolyte betaine during the later adaptive response allows not only recovery of translation but also its stimulation. In this paper, we show that betaine modulates translation by enhancing the formation of cap-independent 48 S pre-initiation complexes, leaving cap-dependent 48 S pre-initiation complexes basically unchanged. In the presence of betaine, CrPV IRES- and sodium-dependent neutral amino acid transporter-2 (SNAT2) 5'-UTR-driven translation is 2- and 1.5-fold stimulated in MCF7 cells, respectively. Thus, betaine could provide an advantage in translation of messengers coding for proteins implicated in the response of cells to different stressors, which are often recognized by ribosomal 40 S subunit through simplified cap-independent mechanisms.

Evaluation of potential candidate genes involved in salinity tolerance in striped catfish (Pangasianodon hypophthalmus) using an RNA-Seq approach

Increasing salinity levels in freshwater and coastal environments caused by sea level rise linked to climate change is now recognized to be a major factor that can impact fish growth negatively, especially for freshwater teleost species. Striped catfish (Pangasianodon hypophthalmus) is an important freshwater teleost that is now widely farmed across the Mekong River Delta in Vietnam. Understanding the basis for tolerance and adaptation to raised environmental salinity conditions can assist the regional culture industry to mitigate predicted impacts of climate change across this region. Attempt of next generation sequencing using the ion proton platform results in more than 174 million raw reads from three tissue libraries (gill, kidney and intestine). Reads were filtered and de novo assembled using a variety of assemblers and then clustered together to generate a combined reference transcriptome. Downstream analysis resulted in a final reference transcriptome that contained 60,585 transcripts with an N50 of 683 bp. This resource was further annotated using a variety of bioinformatics databases, followed by differential gene expression analysis that resulted in 3062 transcripts that were differentially expressed in catfish samples raised under two experimental conditions (0 and 15 ppt). A number of transcripts with a potential role in salinity tolerance were then classified into six different functional gene categories based on their gene ontology assignments. These included; energy metabolism, ion transportation, detoxification, signal transduction, structural organization and detoxification. Finally, we combined the data on functional salinity tolerance genes into a hypothetical schematic model that attempted to describe potential relationships and interactions among target genes to explain the molecular pathways that control adaptive salinity responses in P. hypophthalmus. Our results indicate that P. hypophthalmus exhibit predictable plastic regulatory responses to elevated salinity by means of characteristic gene expression patterns, providing numerous candidate genes for future investigations.

Role of hyperosmolarity in the pathogenesis and management of dry eye disease: proceedings of the OCEAN group meeting

Dry eye disease (DED), a multifactorial disease of the tears and ocular surface, is common and has a significant impact on quality of life. Reduced aqueous tear flow and/or increased evaporation of the aqueous tear phase leads to tear hyperosmolarity, a key step in the vicious circle of DED pathology. Tear hyperosmolarity gives rise to morphological changes such as apoptosis of cells of the conjunctiva and cornea, and triggers inflammatory cascades that contribute to further cell death, including loss of mucin-producing goblet cells. This exacerbates tear film instability and drives the cycle of events that perpetuate the condition. Traditional approaches to counteracting tear hyperosmolarity in DED include use of hypotonic tear substitutes, which have relatively short persistence in the eye. More recent attempts to counteract tear hyperosmolarity in DED have included osmoprotectants, small organic molecules that are used in many cell types throughout the natural world to restore cell volume and stabilize protein function, allowing adaptation to hyperosmolarity. There is now an expanding pool of clinical data on the efficacy of DED therapies that include osmoprotectants such as erythritol, taurine, trehalose and L-carnitine. Osmoprotectants in DED may directly protect cells against hyperosmolarity and thereby promote exit from the vicious circle of DED physiopathology.

Cell volume and monovalent ion transporters: their role in cell death machinery triggering and progression

Cell death is accompanied by the dissipation of electrochemical gradients of monovalent ions across the plasma membrane that, in turn, affects cell volume via modulation of intracellular osmolyte content. In numerous cell types, apoptotic and necrotic stimuli caused cell shrinkage and swelling, respectively. Thermodynamics predicts a cell type-specific rather than an ubiquitous impact of monovalent ion transporters on volume perturbations in dying cells, suggesting their diverse roles in the cell death machinery. Indeed, recent data showed that apoptotic collapse may occur in the absence of cell volume changes and even follow cell swelling rather than shrinkage. Moreover, side-by-side with cell volume adjustment, monovalent ion transporters contribute to cell death machinery engagement independently of volume regulation via cell type-specific signaling pathways. Thus, inhibition of Na(+)-K(+)-ATPase by cardiotonic steroids (CTS) rescues rat vascular smooth muscle cells from apoptosis via a novel Na(+)i-K(+)i-mediated, Ca(2+)i-independent mechanism of excitation-transcription coupling. In contrast, CTS kill renal epithelial cells independently of Na(+)-K(+)-ATPase inhibition and increased [Na(+)]i/[K(+)]i ratio. The molecular origin of [Na(+)]i/[K(+)]i sensors involved in the inhibition of apoptosis as well as upstream intermediates of Na(+)i/K(+)i-independent death signaling triggered by CTS remain unknown.

New insights into roles of acidocalcisomes and contractile vacuole complex in osmoregulation in protists

While free-living protists are usually subjected to hyposmotic environments, parasitic protists are also in contact with hyperosmotic habitats. Recent work in one of these parasites, Trypanosoma cruzi, has revealed that its contractile vacuole complex, which usually collects and expels excess water as a mechanism of regulatory volume decrease after hyposmotic stress, has also a role in cell shrinking when the cells are submitted to hyperosmotic stress. Trypanosomes also have an acidic calcium store rich in polyphosphate (polyP), named the acidocalcisome, which is involved in their response to osmotic stress. Here, we review newly emerging insights on the role of acidocalcisomes and the contractile vacuole complex in the cellular response to hyposmotic and hyperosmotic stresses. We also review the current state of knowledge on the composition of these organelles and their other roles in calcium homeostasis and protein trafficking.

Taurine and atherosclerosis

Taurine is abundantly present in most mammalian tissues and plays a role in many important physiological functions. Atherosclerosis is the underlying mechanism of cardiovascular disease including myocardial infarctions, strokes and peripheral artery disease and remains a major cause of morbidity and mortality worldwide. Studies conducted in laboratory animal models using both genetic and dietary models of hyperlipidemia have demonstrated that taurine supplementation retards the initiation and progression of atherosclerosis. Epidemiological studies have also suggested that taurine exerts preventive effects on cardiovascular diseases. The present review focuses on the effects of taurine on the pathogenesis of atherosclerosis. In addition, the potential mechanisms by which taurine suppress the development of atherosclerosis will be discussed.

Hyperosmotic stress induces aquaporin-dependent cell shrinkage, polyphosphate synthesis, amino acid accumulation, and global gene expression changes in Trypanosoma cruzi

The protist parasite Trypanosoma cruzi has evolved the ability to transit between completely different hosts and to replicate in adverse environments. In particular, the epimastigote form, the replicative stage inside the vector, is subjected to nutritional and osmotic stresses during its development. In this work, we describe the biochemical and global gene expression changes of epimastigotes under hyperosmotic conditions. Hyperosmotic stress resulted in cell shrinking within a few minutes. Depending on the medium osmolarity, this was followed by lack of volume recovery for at least 2 h or by slow recovery. Experiments with inhibitors, or with cells in which an aquaporin gene (TcAQP1) was knocked down or overexpressed, revealed its importance for the cellular response to hyperosmotic stress. Furthermore, the adaptation to this new environment was shown to involve the regulation of the polyphosphate polymerization state as well as changes in amino acid catabolism to generate compatible osmolytes. A genome-wide transcriptional analysis of stressed parasites revealed down-regulation of genes belonging to diverse functional categories and up-regulation of genes encoding trans-sialidase-like and ribosomal proteins. Several of these changes were confirmed by Northern blot analyses. Sequence analysis of the 3'UTRs of up- and down-regulated genes allowed the identification of conserved structural RNA motifs enriched in each group, suggesting that specific ribonucleoprotein complexes could be of great importance in the adaptation of this parasite to different environments through regulation of transcript abundance.

Role of taurine in the vasculature: an overview of experimental and human studies

Taurine is a sulfur-containing amino acid-like endogenous compound found in substantial amounts in mammalian tissues. It exerts a diverse array of biological effects, including cardiovascular regulation, antioxidation, modulation of ion transport, membrane stabilization, osmoregulation, modulation of neurotransmission, bile acid conjugation, hypolipidemia, antiplatelet activity and modulation of fetal development. This brief review summarizes the role of taurine in the vasculature and modulation of blood pressure, based on experimental and human studies. Oral supplementation of taurine induces antihypertensive effects in various animal models of hypertension. These effects of taurine have been shown to be both centrally and peripherally mediated. Consistent with this, taurine produces endothelium-dependent and independent relaxant effects in isolated vascular tissue preparations. Oral administration of taurine also ameliorates impairment of vascular reactivity, intimal thickening, arteriosclerosis, endothelial apoptosis, oxidative stress and inflammation, associated primarily with diabetes and, to a lesser extent with obesity, hypertension and nicotine-induced vascular adverse events. In rat aortic vascular smooth muscle cells (VSMCs), taurine acts as an antiproliferative and antioxidant agent. In endothelial cells, taurine inhibits apoptosis, inflammation, oxidative stress and cell death while increasing NO generation. Oral taurine in hypertensive human patients alleviates the symptoms of hypertension and also reverses arterial stiffness and brachial artery reactivity in type 1 diabetic patients. However, despite these favorable findings, there is a need to further establish certain aspects of the reported results and also consider addressing unresolved related issues. In addition, the molecular mechanism (s) involved in the vascular effects of taurine is largely unknown and requires further investigations. Elucidation of the mechanisms through which taurine affects the vasculature could facilitate the development of therapeutic and/or diet-based strategies to reduce the burdens of vascular diseases.

Gap junctions favor normal rat kidney epithelial cell adaptation to chronic hypertonicity

Upon hypertonic stress most often resulting from high salinity, cells need to balance their osmotic pressure by accumulating neutral osmolytes called compatible osmolytes like betaine, myo-inositol, and taurine. However, the massive uptake of compatible osmolytes is a slow process compared with other defense mechanisms related to oxidative or heat stress. This is especially critical for cycling cells as they have to double their volume while keeping a hospitable intracellular environment for the molecular machineries. Here we propose that clustered cells can accelerate the supply of compatible osmolytes to cycling cells via the transit, mediated by gap junctions, of compatible osmolytes from arrested to cycling cells. Both experimental results in epithelial normal rat kidney cells and theoretical estimations show that gap junctions indeed play a key role in cell adaptation to chronic hypertonicity. These results can provide basis for a better understanding of the functions of gap junctions in osmoregulation not only for the kidney but also for many other epithelia. In addition to this, we suggest that cancer cells that do not communicate via gap junctions poorly cope with hypertonic environments thus explaining the rare occurrence of cancer coming from the kidney medulla.

Effects of Osmoprotection on Symptoms, Ocular Surface Damage, and Tear Film Modifications Caused by Glaucoma Therapy

Purpose

TO determine the effects of 2 artificial tear formulas on the ocular surface in patients with glaucoma using topical preserved beta-blockers (BB) or prostaglandins (PG).

Methods

This was a prospective, comparative, randomized, double-blind study with a crossover design. Twenty patients with dry eye were divided into 2 groups based on glaucoma treatment: BB (10 subjects) or PG (10 subjects). Each group was administered a 4-week course of unpreserved isotonic (300 mOsm/L) solution containing 0.2% sodium hyaluronate (SH) or a preserved isotonic (295–305 mOsm/L) solution containing 0.5% carboxymethylcellulose and 0.9% glycerin as compatible solute (CMCs) administered QID. After a 2-week washout period, the course of treatment was reversed. The primary efficacy criteria consisted of assessing symptoms according to the Ocular Surface Disease Index© (OSDI); the secondary efficacy criteria consisted of evaluating tear film confocal microscopy, central corneal thickness (CCT), and lissamine corneal and conjunctival staining (Oxford Grading System Score [OGSS]).

Results

Within each group, only CMCs induced a significant improvement in OSDI and OGSS compared to baseline values: OSDI-20.5, p<0.0001; OGSS-0.9, p<0.0001. Tear film confocal microscopy improved after treatment, especially in case of patients who were administered CMCs. No difference in CCT was noticed for any subject.

Conclusions

This study demonstrates for the first time that the use of concomitant CMCs in the management of glaucoma undergoing treatment with BB or PG may assist in tear film production and could lead to better compliance with intraocular pressure-lowering medication and ultimately better prognosis.

Central pontine myelinolysis: historical and mechanistic considerations

Central pontine myelinolysis (CPM) is a demyelinating condition affecting not only the pontine base, but also involving other brain areas. It usually occurs on a background of chronic systemic illness, and is commonly observed in individuals with alcoholism, malnutrition and liver disease. Studies carried out 25-30 years ago established that the principal etiological factor was the rapid correction of hyponatremia resulting in osmotic stress. This article reviews progress achieved since that time on its pathogenesis, focusing on the role of organic osmolytes, the blood-brain, barrier, endothelial cells, myelinotoxic factors triggered by osmotic stress, and the role of various factors that predispose to the development of CPM. These advances show great promise in providing novel therapeutic options for the management of patients afflicted with CPM.

Proline and glycinebetaine induce antioxidant defense gene expression and suppress cell death in cultured tobacco cells under salt stress

Salt stress causes oxidative damage and cell death in plants. Plants accumulate proline and glycinebetaine (betaine) to mitigate detrimental effects of salt stress. The aim of this study was to investigate the protective effects of proline and betaine on cell death in NaCl-unadapted tobacco (Nicotiana tabacum) Bright Yellow-2 suspension-cultured cells subjected to salt stress. Salt stress increased reactive oxygen species (ROS) accumulation, lipid peroxidation, nuclear deformation and degradation, chromatin condensation, apoptosis-like cell death and ATP contents. Neither proline nor betaine affected apoptosis-like cell death and G(1) phase population, and increased ATP contents in the 200mM NaCl-stressed cells. However, both of them effectively decreased ROS accumulation and lipid peroxidation, and suppressed nuclear deformation and chromatin condensation induced by severe salt stress. Evans Blue staining experiment showed that both proline and betaine significantly suppressed increment of membrane permeability induced by 200mM NaCl. Furthermore, among the ROS scavenging antioxidant defense genes studied here, mRNA levels of salicylic acid-binding (SAbind) catalase (CAT) and lignin-forming peroxidase (POX) were found to be increased by proline and betaine under salt stress. It is concluded that both proline and betaine provide a protection against NaCl-induced cell death via decreasing level of ROS accumulation and lipid peroxidation as well as improvement of membrane integrity.

Ultraviolet A induces transport of compatible organic osmolytes in human dermal fibroblasts

Compatible organic osmolytes, such as betaine, myo-inositol and taurine, are involved in cell protection. Human dermal fibroblasts accumulate these osmolytes and express mRNA specific for their transporting systems betaine-/gamma-amino-n-butyric acid (GABA) transporter (BGT-1), sodium-dependent myo-inositol transporter (SMIT) and taurine transporter (TAUT). Taurine uptake was about sixfold higher than that of betaine and myo-inositol. Compared with normoosmotic (305 mOsm/l) control, hyperosmotic exposure (405 mOsm/l) led to a twofold induction of osmolyte uptake. Ultraviolet A (UVA) upregulated osmolyte transporter mRNA levels and increased osmolyte uptake. Taurine inhibited UVA-induced interleukin-6 (Il-6) mRNA expression by 40%. Furthermore, Il-6 accumulation in the supernatants of UVA-irradiated dermal fibroblasts was much slower when cells were preincubated with taurine. These data indicate that taurine accumulation seems to be part of the fibroblast response to UVA radiation and may protect against UVA-induced Il-6 overexpression.

Potential nutritional and physiological functions of betaine in livestock

The present review summarises the potential nutritional and physiological functions of betaine as a feed additive in relation to performance criteria in livestock production. Betaine, the trimethyl derivative of the amino acid glycine, is a metabolite of plant and animal tissues. In plants, betaine is particularly synthesised and accumulated as an osmoprotectant against salt and temperature stress. In animals, betaine is the product of choline oxidation or it originates from nutritional sources. Over the past decades, numerous studies have been carried out to investigate the potential effects of betaine supplementation on animal performance. Due to its chemical structure, betaine shows the characteristics of a dipolar zwitterion resulting in osmoprotective properties. Promoting effects on the intestinal tract against osmotic stress occurring during diarrhoea or coccidiosis have been reported following betaine supplementation in pigs and poultry. There is also some evidence that dietary betaine may improve the digestibility of specific nutrients. As a product of choline oxidation, betaine is involved in transmethylation reactions of the organism. Betaine as a methyl donor provides its labile methyl groups for the synthesis of several metabolically active substances such as creatine and carnitine. Supplementation with betaine may decrease the requirement for other methyl donors such as methionine and choline. There is also some evidence for enhanced methionine availability after dietary supplementation of betaine resulting in improved animal performance. Alterations in the distribution pattern of protein and fat in the body have been reported following betaine supplementation. A more efficient use of dietary protein may result from a methionine-sparing effect of betaine, but also direct interactions of betaine with metabolism-regulating factors have to be considered. Though the mode of action of betaine as a carcass modifier remains open, there is, however, growing evidence that betaine could have a positive impact both on animal performance and carcass quality.

Effects of orange juice and proline betaine on glycine betaine and homocysteine in healthy male subjects

BACKGROUND

Proline betaine (PB), a glycine betaine (GB) analogue found in citrus foods, increases urinary GB loss and plasma total homocysteine (tHcy) concentrations in rats. Its presence in human plasma is associated with increased GB excretion.

AIM

To compare the effects of dietary levels of PB on GB excretion, and on plasma tHcy and GB concentrations in healthy volunteers.

METHODS

In a randomized crossover study, eight healthy males (18-50 years) ingested either 750 mL orange juice (containing 0.545 g PB), a PB supplement (0.545 g PB dissolved in 750 mL apple juice), or 750 mL apple juice (control). Plasma PB, GB and tHcy, and urine PB, GB and creatinine concentrations were measured hourly for 6 h and at 24 h post-treatment.

RESULTS

Plasma tHcy concentrations were not increased (relative to control) following ingestion of either orange juice or PB supplement. Both treatments produced a significant increase in plasma PB concentrations (P < 0.001), this effect being greater following orange juice compared with PB supplement (P < 0.05, 1-2 h). Urinary excretion of PB was greater than the control following both orange juice (P < 0.001) and PB supplement (P < 0.001), from 2 to 24 h post-treatment. This increase in PB excretion was significantly greater following orange juice compared with PB supplement with higher peak excretion (Cmax difference, P = 0.008). GB excretion was significantly greater following ingestion of orange juice compared with PB in apple juice (P = 0.007) and apple juice control (P < 0.001) in the first 2 h post-ingestion.

CONCLUSIONS

PB administered in dietary doses had little effect on plasma tHcy concentrations in healthy humans. Ingestion of PB in orange juice compared with PB alone resulted in greater increases in the urinary excretion of PB and GB.

Sex differences in the control of plasma concentrations and urinary excretion of glycine betaine in patients attending a lipid disorders clinic

OBJECTIVES

To find whether the control of betaine metabolism differs between male and female patients and identify the effects of insulin and other hormones.

DESIGN AND METHODS

Data from non-diabetic lipid clinic patients (82 female symbol and 76 male symbol) were re-analyzed by sex. Data on insulin, thyroid hormones and leptin were included in models to identify factors affecting the circulation and excretion of betaine and its metabolites.

RESULTS

Different factors influenced plasma concentrations and urinary excretion of betaine, dimethylglycine and homocysteine in males and females. In males, apolipoprotein B (negative), thyroid stimulating hormone (positive) and insulin (negative) predicted circulating betaine, consistent with betaine-homocysteine methyltransferase mediated control. In females, insulin positively predicted plasma dimethylglycine. Urinary betaine excretion positively predicted circulating homocysteine in males (p<0.001), whereas dimethylglycine excretion (also indicating betaine loss) was a stronger positive predictor (p<0.001) in females. Carnitine affected betaine homeostasis.

CONCLUSIONS

Betaine metabolism is under endocrine control, and studies should use sex stratified groups.

Protective effects of taurine on endothelial cells impaired by high glucose and oxidized low density lipoproteins

BACKGROUND

Endothelial dysfunction, common to diabetes and cardiovascular diseases, is an early step in the development of atherosclerosis and diabetic angiopathies. Deficiencies of taurine have been related to diabetes and cardiovascular diseases.

AIMS OF THE STUDY

We investigated whether taurine provides protective action against endothelial dysfunction induced by hyperglycemia and/or oxidized low density lipoproteins (oxLDL).

METHODS

Quiescent human umbilical cord venous endothelial cells were exposed for 20 h to high glucose (35 mM) and/or oxLDL (60 microg/ml) alone and in presence of taurine (0.5-2.5 mg/ml). Apoptosis, caspase-3 activity, soluble(s) and cell surface expressions of vascular cellular (VCAM-1) and intercellular (ICAM-1) adhesion molecules were determined. Results are given as a percentage of the low glucose medium control. Apoptosis, VCAM-1 and ICAM-1 expressions were related to cell number.

RESULTS

Hyperglycemia increased apoptosis to 162.5 +/- 19.2%, caspase-3 activity to 153.2 +/- 10.3%, cell-surface expression of VCAM-1 to 125.1 +/- 5.8%, the expression of ICAM-1 to 123.7 +/- 2.8% and sICAM-1 to 146.5 +/- 7.9%. Taurine (0.5-2.5 mg/ml) restored apoptosis, caspase-3 activity and expressions of VCAM-1 and ICAM-1. OxLDL (60 microg/ml) increased apoptosis to 114.8 +/- 3.1%; taurine (2.5 mg/ml) reduced this apoptosis to 40.5 +/- 4.1%. The combination of hyperglycemia and oxLDL increased apoptosis to 211.7 +/- 11.6%. This increase was normalized by taurine (2.5 mg/ml) to 97.9 +/- 12.8%.

CONCLUSION

Taurine protects HUVECs from endothelial dysfunction induced by hyperglycemia through down-regulation of apoptosis and adhesion molecules. Counteracting the combination of oxLDL and hyperglycemia requires pharmacological concentrations of taurine.

Evaluation of an isotonic tear in combination with topical cyclosporine for the treatment of ocular surface disease

PURPOSE

To determine whether a new category of artificial tear product, carboxymethylcellulose 0.5% with compatible solutes (CMC-solutes) (Optive, Allergan, Inc., Irvine, California) improves clinical outcomes when used adjunctively with topical cyclosporine 0.05% (Restasis, Allergan, Inc., Irvine, California) for the treatment of ocular surface disease.

METHODS

Nineteen patients with ocular surface disease treated with cyclosporine 0.05% for at least 3 months and who had previously used other artificial tears adjunctively were enrolled. Patients discontinued their previous artificial tear and used CMC-solutes, concomitant with topical cyclosporine 0.05%. Corneal evaluation and tear production parameters were evaluated before and during combined CMC-solutes/cyclosporine treatment. Patients also completed a questionnaire before and during treatment with combined CMC-solutes/cyclosporine. Follow-up was at 1 and 3 months.

RESULTS

Most objective measures of ocular surface health were unchanged, but an improvement in conjunctival lissamine green staining and tear break-up time was found. Conjunctival lissamine green staining scores improved from 3.4 +/- 2.5 to 1.9 +/- 2.5 by Month 3 (p = 0.004). Tear break-up time improved from 4.6 +/- 3.9 s pre-treatment to 5.3 +/- 3.8 s post-treatment (p = 0.049). Ocular Surface Disease Index (OSDI) scores improved from 16.2 +/- 9.4 at baseline to 11.5 +/- 8.9 at month 3 (p = 0.007). Subjectively, patients graded their ocular discomfort as 2.7 at baseline and as 2.3 at Month 3 (p = 0.049). At Month 3, 89.5% of patients said they liked CMC-solutes as well or better than previous drops they had used. All patients said CMC-solutes provided similar or improved relief of symptoms of dry eye than previous eye drops. There were no tear-related adverse events reported.

CONCLUSIONS

In this study, CMC-solutes, when used in conjunction with cyclosporine 0.05%, provided patients with an improvement in objective signs and subjective symptoms of ocular surface disease compared to their previous artificial tears. Further studies are warranted.

Pegylated interferon-alpha plus taurine in treatment of rat liver fibrosis

AIM: To investigate the antifibrotic effects of peginterferon-alpha 2b and taurine on oxidative stress markers and hepatocellular apoptosis.

METHODS: Sixty rats with CCl4-induced liver fibrosis were divided into 4 groups (n = 15). Group 1 was left for spontaneous recovery (SR). Groups 2-4 received peginterferon-alpha 2b, taurine, and their combination, respectively, for four weeks. Histological fibrosis scores, histomorphometric analysis, tissue hydroxyproline, tissue MDA, GPx and SOD activities were determined. Activated stellate cells and hepatocellular apoptosis were also evaluated.

RESULTS: The degree of fibrosis decreased in all treatment groups compared to spontaneous recovery group. Taurine alone and in combination with peginterferon-alpha 2b reduced oxidative stress markers, but peginterferon-alpha 2b alone did not. Apoptotic hepatocytes and activated stellate cells were higher in groups 2-4 than in group 1. Combined taurine and peginterferon-alpha 2b further reduced fibrosis and increased activated stellate cell apoptosis, but could not improve oxidative stress more than taurine alone.

CONCLUSION: Peginterferon-alpha 2b exerts anti-fibrotic effects on rat liver fibrosis. It seems ineffective against oxidative stress in vivo. Peginterferon-alpha 2b in combination with taurine seems to be an antifibrotic strategy.

Inter- and intra-individual variations in normal urinary glycine betaine excretion

OBJECTIVES

To establish whether normal human subjects excrete glycine betaine at a constant rate.

DESIGN AND METHODS

Urine was collected from ten normal healthy male subjects for 14 days, during which fluid intake was systematically varied from <800 mL to >3 L per day. Glycine betaine, sorbitol and creatinine excretions were estimated per day and as millimole per mol creatinine.

RESULTS

The intrasubject SD of urine glycine betaine was 3.5 mmol/mol creatinine, and the intersubject SD 5.8 mmol/mol creatinine. The intrasubject SD of plasma glycine betaine was 10.2 mol/L and the intersubject SD 14.2 mol/L. Water load had little effect on glycine betaine excretion and plasma glycine betaine. After 12 years, excretions and plasma concentrations tended to parallel the initial results.

CONCLUSIONS

Normal subjects have consistent individual glycine betaine excretions that are not strongly influenced by urine volume. Abnormal excretions, or significant changes in excretion, can be interpreted as indicating a pathological process.

Hyperosmotic stress response: comparison with other cellular stresses

Cellular responses induced by stress are essential for the survival of cells under adverse conditions. These responses, resulting in cell adaptation to the stress, are accomplished by a variety of processes at the molecular level. After an alteration in homeostatic conditions, intracellular signalling processes link the sensing mechanism to adaptive or compensatory changes in gene expression. The ability of cells to adapt to hyperosmotic stress involves early responses in which ions move across cell membranes and late responses characterized by increased synthesis of either membrane transporters essential for uptake of organic osmolytes or of enzymes involved in their synthesis. The goal of these responses is to return the cell to its normal size and maintain cellular homeostasis. The enhanced synthesis of molecular chaperones, such as heat shock proteins, is another important component of the adaptive process that contributes to cell survival. Some responses are common to different stresses, whereas others are specific. In the first part of the review, we illustrate the characteristic and specific features of adaptive response to hypertonicity; we then describe similarities to and differences from other cellular stresses, such as genotoxic agents, nutrient starvation and heat shock.

Hypertonicity triggers RhoA-dependent assembly of myosin-containing striated polygonal actin networks in endothelial cells

Endothelial cells respond to mechanical stresses of the circulation with cytoskeletal rearrangements such as F-actin stress fiber alignment along the axis of fluid flow. Endothelial cells are exposed to hypertonic stress in the renal medulla or during mannitol treatment of cerebral edema. We report here that arterial endothelial cells exposed to hypertonic stress rearranged F-actin into novel actin-myosin II fibers with regular 0.5-microm striations, in which alpha-actinin colocalizes with actin. These striated fibers assembled over hours into three-dimensional, irregular, polygonal actin networks most prominent at the cell base, and occasionally surrounding the nucleus in a geodesic-like structure. Hypertonicity-induced assembly of striated polygonal actin networks was inhibited by cytochalasin D, blebbistatin, cell ATP depletion, and intracellular Ca(2+) chelation but did not require intact microtubules, regulatory volume increase, or de novo RNA or protein synthesis. Striated polygonal actin network assembly was insensitive to inhibitors of MAP kinases, tyrosine kinases, or phosphatidylinositol 3-kinase, but was prevented by C3 exotoxin, by the RhoA kinase inhibitor Y-27632, and by overexpressed dominant-negative RhoA. In contrast, overexpression of dominant-negative Rac or of dominant-negative cdc42 cDNAs did not prevent striated polygonal actin network assembly. The actin networks described here are novel in structure, as striated actin-myosin structures in nonmuscle cells, as a cellular response to hypertonicity, and as a cytoskeletal regulatory function of RhoA. Endothelial cells may use RhoA-dependent striated polygonal actin networks, possibly in concert with cytoskeletal load-bearing elements, as a contractile, tension-generating component of their defense against isotropic compressive forces.

Creatine as a compatible osmolyte in muscle cells exposed to hypertonic stress

Exposure of C2C12 muscle cells to hypertonic stress induced an increase in cell content of creatine transporter mRNA and of creatine transport activity, which peaked after about 24 h incubation at 0.45 osmol (kg H(2)O)(-1). This induction of transport activity was prevented by addition of either cycloheximide, to inhibit protein synthesis, or of actinomycin D, to inhibit RNA synthesis. Creatine uptake by these cells is largely Na(+) dependent and kinetic analysis revealed that its increase under hypertonic conditions resulted from an increase in V(max) of the Na(+)-dependent component, with no significant change in the K(m) value of about 75 mumol l(-1). Quantitative real-time PCR revealed a more than threefold increase in the expression of creatine transporter mRNA in cells exposed to hypertonicity. Creatine supplementation significantly enhanced survival of C2C12 cells incubated under hypertonic conditions and its effect was similar to that obtained with the well known compatible osmolytes, betaine, taurine and myo-inositol. This effect seemed not to be linked to the energy status of the C2C12 cells because hypertonic incubation caused a decrease in their ATP content, with or without the addition of creatine at 20 mmol l(-1) to the medium. This induction of creatine transport activity by hypertonicity is not confined to muscle cells: a similar induction was shown in porcine endothelial cells.