A cardiac myocyte culture system as an in vitro experimental model for the evaluation of hypothermic preservation

H9c2 and HL-1 cells demonstrate distinct features of energy metabolism, mitochondrial function and sensitivity to hypoxia-reoxygenation

Dysfunction of cardiac energy metabolism plays a critical role in many cardiac diseases, including heart failure, myocardial infarction and ischemia-reperfusion injury and organ transplantation. The characteristics of these diseases can be elucidated in vivo, though animal-free in vitro experiments, with primary adult or neonatal cardiomyocytes, the rat ventricular H9c2 cell line or the mouse atrial HL-1 cells, providing intriguing experimental alternatives. Currently, it is not clear how H9c2 and HL-1 cells mimic the responses of primary cardiomyocytes to hypoxia and oxidative stress. In the present study, we show that H9c2 cells are more similar to primary cardiomyocytes than HL-1 cells with regard to energy metabolism patterns, such as cellular ATP levels, bioenergetics, metabolism, function and morphology of mitochondria. In contrast to HL-1, H9c2 cells possess beta-tubulin II, a mitochondrial isoform of tubulin that plays an important role in mitochondrial function and regulation. We demonstrate that H9c2 cells are significantly more sensitive to hypoxia-reoxygenation injury in terms of loss of cell viability and mitochondrial respiration, whereas HL-1 cells were more resistant to hypoxia as evidenced by their relative stability. In comparison to HL-1 cells, H9c2 cells exhibit a higher phosphorylation (activation) state of AMP-activated protein kinase, but lower peroxisome proliferator-activated receptor gamma coactivator 1-alpha levels, suggesting that each cell type is characterized by distinct regulation of mitochondrial biogenesis. Our results provide evidence that H9c2 cardiomyoblasts are more energetically similar to primary cardiomyocytes than are atrial HL-1 cells. H9c2 cells can be successfully used as an in vitro model to simulate cardiac ischemia-reperfusion injury.

Optimal temperature range for low-temperature preservation of dissociated neonatal rat cardiomyocytes

The increase in demand for primary cardiomyocytes necessitates advanced methods for their stable supply. In this study, we investigated the optimal temperature range for preserving dissociated cardiomyocytes for 72 h while maintaining their normal growth and beating functions. Neonatal rat cardiomyocytes dissociated by collagenase and suspended in the culture medium were preserved at temperatures from -2 to 35°C for 72 h. The cardiomyocytes preserved at temperatures below 20°C maintained the initial dispersed states, whereas they aggregated robustly at higher temperatures. The viability of the dispersed cells after preservation was more than 80%. After the preservation, the microscopic observations during the 7-days cultivation indicated that these dispersed cardiomyocytes grew normally to form a confluent monolayer, and beat spontaneously and regularly during culture, as did the fresh cells. These systematic evaluations indicated that the optimal temperature ranged from 3 to 20°C. Below this optimal temperature range, the cell activities decreased slightly with temperature. The robustly aggregated cardiomyocytes exhibited weak growth and low beating rates, although some cardiomyocytes still survived. The optimal conditions, which consist of a wider temperature range and longer preservation period than the present commercially used conditions, allowed milder temperature control and thus more economical transportation for the dissociated primary cardiomyocytes.

Cold-Storage of Synthetic Human Epidermis in HypoThermosol

There is a growing need for engineered tissues in a wide variety of medical applications and as alternatives to animal tissues for in vitro toxicology testing. While techniques for the preparation of a variety of synthetic tissue constructs have been devised, little attention has been focused upon the optimum conditions necessary for storage and shipping of these tissue devices. This study investigates the effects of hypothermic storage on synthetic human epidermis (EpiDerm, MatTek Corp., Ashland, MA) and specifically examines the quality of storage in keratinocyte growth medium (KGM), a standard skin culture medium, compared with storage in HypoThermosol, a new hypothermic preservation solution. EpiDerm samples were immersed in HypoThermosol for 1 to 13 days at 4 degrees C and were assayed using the noninvasive, viability indicator dye, Alamar Blue (AB). Samples immersed for 1 to 9 days in HypoThermosol retained their viability subsequent to warming to 37 degrees C and for at least 7 days thereafter in culture. During this time samples previously stored in HypoThermosol continued to generate a stratum corneum and their ultrastructural characteristics were similar to EpiDerm that were not exposed to hypothermic solutions. This profile, however, was not apparent in EpiDerm maintained for 1 to 13 days in KGM and subsequently warmed. These samples appeared viable immediately upon warming in most cases, but viability was not retained thereafter. EpiDerm maintained in KGM and allowed to recover at 37 degrees C appeared necrotic and failed to continue to differentiate. The conclusions of this study are the following: (1) HypoThermosol protects the viability of EpiDerm during cold-storage, (2) HypoThermosol preserves EpiDerm's ability to differentiate subsequent to warming, and (3) the inferior preservation of samples stored in KGM was most apparent 24 h after warming.

Long-term hypothermic preservation of cardiac myocytes isolated from the neonatal rat ventricle: a comparison of various crystalloid solutions

In this study, the functional and biochemical effects of crystalloid solutions on immature cardiac myocytes incubated under hypothermic conditions were evaluated. Cardiac myocytes were isolated from neonatal rat ventricles and cultured for 4 days, following which 12.5 x 10(5) myocytes per flask were incubated at 4 degrees C for 3, 6, 12, and 18 h in five types of crystalloid solutions: lactated Ringer's (LR), St. Thomas' Hospital (ST), University of Wisconsin (UW), 5% glucose-based potassium (GK), and normal saline (NS). The levels of creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) in the solutions were measured after each hypothermic incubation, following which the myocytes were cultured for an additional 24 h at 37 degrees C to evaluate the recovery of the myocyte beating rate. In the LR, UW, and NS groups, the recovery ratios of the myocyte beating rate were over 95% of the control (the beating rate prior to hypothermic incubation) at 3 h, but decreased to 20.3, 15.1, and 0%, respectively, at 18 h. The ST and GK groups had significantly lower recovery ratios than the other three groups (72.9% and 63.4%, respectively) at 3 h. The release of CPK and LDH in the LR, UW, and NS groups was significantly suppressed compared to the ST and GK groups, with the greatest suppression observed in the LR group. Moreover, the ST and GK groups had the highest CPK and LDH levels, respectively. Thus, LR solution had the least cytotoxic effects, indicating that it could be the most suitable basic solution of the various cardioplegic or preservation solutions during the neonatal period.

In vitro evaluation of phosphate, bicarbonate, and Hepes buffered storage solutions on hypothermic injury to immature myocytes

In this study we evaluated cardiac myocyte viability and function under hypothermic conditions using three types of buffer solutions: phosphate buffer solution (PBS), Krebs-Henseleit bicarbonate buffer solution (KHB), and Hepes buffered minimum salt solution (MSS). As a control, normal saline solution (NSS) was used. Cardiac myocytes were isolated from neonatal rat ventricles. Myocytes (12.5 x 10(5) myocytes/culture flask) were then incubated at 4 degrees C for 6, 12, 18, and 24 hours in various buffer solutions. After each incubation time, CPK and LDH were measured. The myocytes were then incubated for an additional 24 hours at 37 degrees C to evaluate the recovery of the myocyte beating rate. Group MSS had a significantly better beating rate recovery than group NSS (control) after 18 hours (MSS, 32.7%, NSS, 0.0% of control; i.e., beating rate prior to hypothermic incubation). In contrast, group KHB showed a significantly lower recovery ratio than group NSS at 12 hours (41.0%, 78.8%, respectively), and the lowest recovery was observed in group PBS beginning at 6 hours of hypothermic incubation (27.6%). Group MSS significantly suppressed the release of CPK and LDH compared to group NSS at 24 hours (MSS, 246.7 and 440.2 mIU/flask; NSS, 369.7 and 821.3 mIU/flask, respectively). In contrast, groups PBS and KHB showed significantly increased CPK and LDH levels compared to group NSS after 12 hours (PBS, 388.6 and 721.4 mIU/flask; KHB, 340.5 and 540.5 mIU/flask; NSS, 91.5 and 222.7 mIU/flask, respectively). In conclusion, Hepes buffer has cytoprotective characteristics that may be suitable for long-term hypothermic preservation of immature myocardium compared to phosphate or bicarbonate buffer.

Possible deleterious effects of glucose on immature myocytes under hypothermic conditions

The purpose of the present study was to evaluate the functional and biochemical effects of glucose-based solutions in combination with potassium or insulin (or both) on immature myocytes under hypothermic conditions. Myocytes were isolated from neonatal rat ventricles and cultured for 4 days with MCDB 107 (University of Colorado solution). Initially, myocytes (12.5 x 10(5) myocytes/flask) were incubated at 4 degrees C for 6 hours in 5% glucose solution containing various potassium concentrations ranging from 0 to 80 mEq/L to evaluate the protective effects. Next, myocytes were incubated at 4 degrees C for 3, 6, 12, 18, and 24 hours in three types of solutions: normal saline solution (control), glucose-potassium solution, and glucose-insulin-potassium solution (glucose: 50 g/L; NaHCO3, 20 mEq; potassium, 20 mEq; insulin, 20 IU/L). After each incubation, creatine kinase and lactate dehydrogenase levels were measured in the incubation solutions. The myocytes then were cultured for an additional 24 hours at 37 degrees C to evaluate the recovery of myocyte beating rate. The 20-mEq potassium treatment showed significantly better beating rate recovery and lower enzymal release than the glucose-only control. The saline solution showed the best protection of all three solutions, both functionally and biochemically, by 12 hours. The greatest damage was observed with glucose-potassium solution, beginning at 3 hours of hypothermic incubation. Although potassium and insulin have additional protective effects on hypothermic preservation, the high concentration of glucose has noxious characteristics for immature myocytes that may not be suitable for cardiac preservation in the neonatal period.

An in vitro evaluation of prostaglandin E1 and I2 on hypothermic injury to immature myocytes

The purpose of this study was to evaluate the functional and biochemical effects of Prostaglandin E1 (PGE1) and prostaglandin I2 (PGI2) on cardiac myocytes incubated under hypothermic conditions. Cardiac myocytes were isolated from neonatal rat ventricles and cultured for 4 days with MCDB 107 medium. Following this, 12.5 x 10(5) myocytes/flask were incubated at 4 degrees C for 24 h in media with PGE1, at concentrations of 0 M (group E0), 10(-9) M (group E1), 10(-8) M (group E2), 10(-7) M (group E3), or 10(-6) M (group E4); or with PGI2 at concentrations of 0 M PGI (group I0), 10(-9) M (group I1), 10(-8) M (group 12), 10(-7) M (group I3), or 10(-6) M (group I4). After hypothermic incubation, creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) were measured, and the myocytes were then cultured for 24 h at 37 degrees C to evaluate the recovery of the myocyte beating rate. Of the PGI2 groups, only group I2 recovered significantly more than the control group (group I0), at 47.9 +/- 28.5% (mean +/- SD) of the control, being the beating rate prior to hypothermic incubation, whereas it was 18.1 +/- 9.7% in group I0 (P < 0.025); however, there were no significant differences among the PGE1 groups. Moreover, the release of CPK and LDH was significantly suppressed in group 12 compared to the control, being 57.7 +/- 27.6 mIU/flask (P < 0.05) and 275.1 +/- 83.0 mIU/flask (P < 0.025), respectively, in group I2, and 96.8 +/- 38.3 mIU/flask and 439.6 +/- 147.1 mIU/flask in group I0. Again, no significant differences were observed among the PGE1 groups. In conclusion, PGI2 was found to have a direct cytoprotective effect on immature myocytes which suggests that PGI2 may promote cardiac preservation in the neonatal period.

In vitro protective effects of nicorandil on hypothermic injury to immature cardiac myocytes: comparison with nitroglycerin

The purpose of the present study was to evaluate the functional and biochemical effects of nicorandil and nitroglycerin on cardiac myocytes incubated under hypothermic conditions. Nicorandil is a coronary vasodilator with mixed nitrate-potassium channel agonist activity. Cardiac myocytes were isolated from neonatal rat ventricles and cultured for 4 days with MCDB 197 medium. Myocytes (12.5 x 10(5) myocytes/flask) were then incubated at 4 degrees C for 24 hours in media containing various concentrations of nicorandil (NRD) or nitroglycerin (NTG). After hypothermic incubation, CPK and LDH were measured. The myocytes were cultured for an additional 24 hours at 37 degrees C to evaluate the recovery of the myocyte beating rate. In the nicorandil group, 10(-4) M NRD showed a significant beating rate recovery compared to control (44.2% vs. 24.6%, respectively, as a percent of control; i.e., beating rate prior to hypothermic incubation). Nitroglycerin treatment had no effect on either beating rate recovery or release of CPK and LDH from myocytes. However, the release of CPK and LDH was significantly suppressed by 10(-4) M nicorandil compared to the control (10(-4) M NRD: 24.1, 257.2; control: 125.4 mIU/flask, 459.5 mIU/flask, respectively). Thus nicorandil showed an approximate two-fold recovery of myocyte functional activity after hypothermic incubation with only minor biochemical effects, and therefore may be suitable for cardiac preservation.

In vitro evaluation of diltiazem on hypothermic injury to immature myocytes

The purpose of the present study was to evaluate the functional and biochemical effects of diltiazem (DTZ) on cardiac myocytes incubated under hypothermic conditions. Cardiac myocytes were isolated from neonatal rat ventricles and cultured for 4 days with MCDB 107 medium. Then, myocytes (12.5 x 10(5) myocytes/flask) were incubated at 4 degrees C for 24 hours in media with or without DTZ at concentrations of 0 M (group C), 10(-7) M (Group D1), 10(-6) M (group D2), 10(-5) M (group D3), or 10(-4) M (group D4). After 24 hours at 4 degrees C, CPK and LDH were measured. The myocytes were then cultured for 24 hours at 37 degrees C to evaluate the recovery of the myocyte beating rate. In group C (n = 7), the recovery ratio of the myocyte beating rate was 29.9% of control (beating rate prior to hypothermic incubation). Groups D1 and D2 (n = 7 each) had approximately the same recovery ratios as group C (24.0% and 24.7%, respectively); however, groups D3 and D4 (n = 7 each) showed no beating rate recovery. Release of CPK and LDH in group C was 112.3 mIU/flask and 457.4 mIU/flask, respectively. Groups D1 and D2 showed no significant differences in both enzymes compared to group C. However, the levels of CPK were significantly higher in group D4 (203.3, p < 0.05), and LDH levels were significantly higher in groups D3 and D4 (669.3, p < 0.05; 883.4, p < 0.02). In conclusion, DTZ showed no protective effects on hypothermic injury to immature cardiac myocytes; moreover, it accelerated cellular injury at the concentrations of 10(-5) and 10(-4) M both functionally and biochemically. Therefore, diltiazem may not be suitable for cardiac preservation during the neonatal period.