Cytoprotective Effects Of Glycine Research Articles

The role of glycine in regulated cell death.

The cytoprotective effects of glycine against cell death have been recognized for over 28years. They are expressed in multiple cell types and injury settings that lead to necrosis, but are still not widely appreciated or considered in the conceptualization of cell death pathways. In this paper, we review the available data on the expression of this phenomenon, its relationship to major pathophysiologic pathways that lead to cell death and immunomodulatory effects, the hypothesis that it involves suppression by glycine of the development of a hydrophilic death channel of molecular dimensions in the plasma membrane, and evidence for its impact on disease processes in vivo.

The epithelial glycine transporter GLYT1: protecting the gut from inflammation

The epithelial glycine transporter GLYT1: protecting the gut from inflammation

Protective effect of glycine in mesenteric ischemia and reperfusion injury in a rat model.

Glycine has a protective effect in renal and skeletal muscle ischemia. The purpose of this study was to evaluate the effect of glycine in mesenteric ischemia and reperfusion injury in a rat model. Twenty-four anesthetized male Sprague-Dawley rats were subjected to 1 hour of mesenteric ischemia followed by 2 hours of reperfusion. Control animals received normal saline solution intravenously at 0.01 mL/g of body weight/h during ischemia and reperfusion. Treated animals received glycine at 0.5, 0.75, or 1.0 mg/g of body weight, dissolved in saline solution and infused at 0.01 mL/g/h for 2 hours. Animals were killed at the end of the experiment, and proximal, middle, and distal segments of the small bowel were isolated. Sections of the segments stained with hematoxylin-eosin were subjected to histologic examination (as per modified Chiu grading system) and morphometric analysis consisting of measurement of bowel wall, muscularis and mucosal thickness, epithelial coverage, and villar circumference. Isometric tension responses to electrical stimulation (10, 30, 50, 100 Hz), high doses of potassium (120 mmol/L), and carbachol (0.1, 0.5, 1.0, 5.0 micromol/L) were recorded in a multimuscle chamber. Statistical analysis was performed with unpaired t test and one-way analysis of variance. The middle and distal segments of the small bowel in glycine-treated animals showed better histologic grade compared with saline solution-treated control rats (P <.05). At morphometric analysis, total thickness, mucosal thickness, and villar circumference ratio were well preserved in the middle and distal segments of the small bowel in the glycine-treated group (P <.05). No significant differences were observed in the proximal bowel segments between glycine-treated and control animals, because the proximal segment was not subjected to much ischemia. No differences were noted in percentage of epithelial coverage. Isometric tension responses evoked by electrical stimulation were greater (P <.05) in the middle and distal segments treated with glycine as compared with control segments. Carbachol-evoked contractions were stronger (P <.05) in the small bowel segments of animals treated with glycine. The responses evoked by 120 mmol/L of potassium were stronger in the distal segments of the small bowel in the glycine-treated group (P <.05). This cytoprotective effect of glycine was not dose-dependent. Glycine improved mucosal viability in the ischemia and reperfusion injury rat model. Mucosal thickness and villous circumference ratio were reliable objective parameters for evaluation of intestinal ischemia injury. Glycine improved the contractile responses of the bowel segments also, probably by altering the physiologic mechanisms underlying force generation. Further studies are required to elucidate the mechanism of the cytoprotective action of glycine.

Cytoprotective influence of ZVAD-fmk and glycine on gel-entrapped rat hepatocytes in a bioartificial liver

Background: This study was designed to determine if an anti-necrotic compound, glycine, and/or an anti-apoptotic agent, ZVAD-fmk, improved the viability and function of hepatocytes in a bioartificial liver. Methods: Isolated rat hepatocytes were entrapped in collagen gel (1.0 –10.0 × 10 6 cells/mL) and cultured in serum-free medium (1:10 ratio of gel:media) supplemented with glycine alone, ZVAD-fmk alone, or glycine and ZVAD-fmk. The cytoprotective effects of glycine and ZVAD-fmk on gel-entrapped rat hepatocytes (GERH) were determined after anoxic exposure (0 – 20 hours). Cell functionality (measured by urea production), cell viability (quantitated by vital staining with fluorescein diacetate:ethidium bromide [FDA:EB]), and the mechanism of cell death (verified by electron microscopy and DNA fragmentation studies) were determined for each condition. Results: The viability of GERH declined gradually and then stabilized 12 hours after hepatocyte isolation. The rate of urea production by GERH was directly proportional to the number of viable hepatocytes. Apoptotic death predominated at low cell density, and necrotic cell death became significant at high cell density. Hepatocyte necrosis became more significant after exposure to longer periods of anoxia (4, 8, 12, and 20 hours). ZVAD-fmk provided dose-dependent cytoprotection to GERH with an optimum benefit at a concentration of 60 μmol/L. After anoxic exposure or under high cell density culture, glycine demonstrated a maximum benefit of inhibiting necrosis at a concentration of 3 mmol/L. The beneficial effects of glycine and ZVAD-fmk were additive. Conclusions: The metabolic activity of a hepatocyte bioartificial liver may benefit from the use of cytoprotective agents such as ZVAD-fmk and glycine. (Surgery 2000;127:447-55.)

Cytoprotective Effect of Glycine in Cold Stored Canine Renal Tubules

Reperfusion injury has been suggested to cause delayed graft function in renal transplantation. Methods to reduce reperfusion injury could lead to improved clinical renal transplantation. Glycine has been shown to suppress reperfusion injury in rabbit renal tubules and rat hepatocytes. In this study we have determined the effects of glycine on viability of isolated canine renal tubules. Renal tubules were cold stored at 4°C under hypoxic conditions for up to 96 h in the UW solution and rewarmed to 37°C for up to 2 h under oxygenated conditions to simulate reperfusion of an organ after cold static storage. Short-term storage (24 to 48 h) did not cause membrane injury (leakage of lactate dehydrogenase (LDH)) on rewarming. However, after 72 and 96 h cold storage reperfusion injury was evident and LDH leakage increased from about 25% to 59 ± 3% and 71 ± 2% at 72 and 96 h cold storage, respectively. The presence of 3 m M glycine in the reperfusion medium suppressed injury to cold-stored renal tubules. After cold storage for 72 and 96 h LDH leakage was reduced to control concentrations (31 ± 3% and 29 ± 1%, respectively). After cold storage for 72 h there was a reduction in ATP concentration in rewarmed renal tubules (3 nmol/mg protein at 48 h to 1.25 nmol/mg protein at 72 h). Also, there was a loss of mitochondrial functions including decreased stimulation of oxygen consumption by uncoupling of oxidative phosphorylation. Although glycine suppressed LDH leakage in renal tubules cold stored for 72 h it had no effect on the regeneration of ATP or mitochondrial functions, which remained depressed. Thus, the cytoprotective effect of glycine does not appear related to maintenance of energy-linked functions in cold-stored renal tubules. This study shows that glycine prevented reperfusion injury to the membranes of cold-stored canine renal tubules and may be a useful agent to improve clinical renal preservation for transplantation.

Glycine cytoprotection during lethal hepatocellular injury from adenosine triphosphate depletion

Glycine protects renal tubule cells from cell death during adenosine triphosphate (ATP) depletion. Although the liver plays a key role in glycine metabolism, information is lacking regarding the effects of glycine on lethal hepatocellular injury. Thus, the aim of this study was to determine the potential cytoprotective role of glycine during ATP depletion of rat hepatocytes. Metabolic inhibition with 2.5 mmol/L potassium cyanide (KCN) was used to produce ATP depletion. Hepatocyte suspensions treated with KCN had a 2-hour viability of 5.9% ± 2.0%, whereas cells treated with KCN in the presence of 2.0 mmol/L glycine had a viability of 80.2% ± 1.5%, which was virtually identical to controls (81.5% ± 1.9%). Glycine cytoprotection was dose dependent and amino acid specific. The cytoprotective effect of glycine was not mediated by protein synthesis, glycine mitochondrial metabolism, cytosolic acidosis, or preservation of either intracellular cellular glutathione or ATP. However, glycine did decrease total cellular proteolysis by 18% ± 2%, 25% ± 3%, and 33% ± 1% after 1, 2, and 3 hours of KCN treatment, respectively (P < 0.01). Inhibition of proteolysis by glycine was dose dependent over the same range as its cytoprotection. The results suggest that glycine protects against hepatocellular injury by inhibiting degradative proteolytic activity. It was concluded that proteolysis may be an important mechanism contributing to lethal injury of hepatocytes during ATP depletion.

Effect of glycine on medullary thick ascending limb injury in perfused kidneys

The addition of 2 mM glycine to the recirculating perfusate of isolated perfused rat kidneys almost completely prevented the severe morphological injury to tubular cells lining the medullary thick ascending limb (mTAL) that normally develops in this preparation. Glycine was similarly effective in reducing mTAL injury associated with hypoxic perfusion, indomethacin and amphotericin. Fractional reabsorption of sodium was increased with glycine, without any change in perfusate flow to the whole kidney and without consistent improvement in GFR. L-alanine demonstrated a similar though less pronounced cytoprotective action, but glutamine, cysteine, glutamate, cysteine plus glutamate, 1-serine and 4-aminoisobutyric acid all had little or no effect in preventing severe mTAL injury. The protective effect of glycine was unimpaired by the arginine analogue NG-monomethyl-l-arginine (L-NMMA), suggesting that the endothelial-derived relaxing factor, NO, was not involved. The action of glycine was not reduced by the addition of a substrate (benzoate) or a product (hippurate) of the glycine N-acyltransferase reaction. Glycine did not depress the respiration of dispersed mTALs prepared from rat kidneys. The cytoprotective effect of glycine in the mTAL of perfused kidneys, shared with l-alanine, appears to be relatively specific for these amino acids and probably unrelated to a diminution in cell work.

Cytoprotective effects of glycine and glutathione against hypoxic injury to renal tubules.

Roles for both the tripeptide, GSH, and individual amino acids in modifying the cellular response to oxygen deprivation-induced injury have been suggested by prior work in kidney and other tissues, but the precise interrelationships have not been clearly defined. We have studied the effects of GSH, its component amino acids, and related compounds on the behavior of isolated renal proximal tubules in a well characterized model of hypoxic injury in vitro. GSH, the combination of cysteine, glutamate, and glycine and glycine alone, when present in the medium during 30 min hypoxia, a duration sufficient to produce extensive irreversible injury in untreated tubules, were protective. Significant effects were detected at 0.25 mM concentrations of the reagents, and protection was nearly complete at concentrations of 1 mM and above. Glutamate and cysteine alone were not protective. The exogenous GSH added to the tubule suspensions was rapidly degraded to its component amino acids. Treatment of tubules with GSH or cysteine, but not glycine, increased intracellular GSH levels. Oxidized GSH was protective. Serine, N-(2-mercaptopropionyl)-glycine, and a panel of agents known to modify injury produced by reactive oxygen metabolites were without benefit. These observations identify a novel and potent action of glycine to modify the course of hypoxic renal tubular cell injury. This effect is independent of changes in cellular GSH metabolism and appears to be unrelated to alterations of cell thiols or reactive oxygen metabolites. Further elucidation of its mechanism may provide insight into both the basic pathophysiology of oxygen deprivation-induced cell injury and a practical way to ameliorate it.