Cardiac tissue engineering is an emerging field. The suitability of engineered heart tissue (EHT) for both in vitro and in vivo applications will depend on the degree of syncytoid tissue formation ...and cardiac myocyte differentiation in vitro, contractile function, and electrophysiological properties. Here, we demonstrate that cardiac myocytes from neonatal rats, when mixed with collagen I and matrix factors, cast in circular molds, and subjected to phasic mechanical stretch, reconstitute ring-shaped EHTs that display important hallmarks of differentiated myocardium. Comparative histological analysis of EHTs with native heart tissue from newborn, 6-day-old, and adult rats revealed that cardiac cells in EHTs reconstitute intensively interconnected, longitudinally oriented, cardiac muscle bundles with morphological features resembling adult rather than immature native tissue. Confocal and electron microscopy demonstrated characteristic features of native differentiated myocardium; some of these features are absent in myocytes from newborn rats(1) highly organized sarcomeres in registry; (2) adherens junctions, gap junctions, and desmosomes; (3) a well-developed T-tubular system and dyad formation with the sarcoplasmic reticulum; and (4) a basement membrane surrounding cardiac myocytes. Accordingly, EHTs displayed contractile characteristics of native myocardium with a high ratio of twitch (0.4 to 0.8 mN) to resting tension (0.1 to 0.3 mN) and a strong β-adrenergic inotropic response. Action potential recordings demonstrated stable resting membrane potentials of −66 to −78 mV, fast upstroke kinetics, and a prominent plateau phase. The data indicate that EHTs represent highly differentiated cardiac tissue constructs, making EHTs a promising material for in vitro studies of cardiac function and tissue replacement therapy.
Here we aimed to establish an in vitro engineered heart tissue (EHT) co-morbidity mimicking model of ischemia-reperfusion injury and diabetes. EHTs were generated from primary neonatal rat ...cardiomyocytes. Hyperglycemic conditions or hyperosmolar controls were applied for one day to model acute hyperglycemia and for seven days to model chronic hyperglycemia. 120 min' simulated ischemia (SI) was followed by 120 min' reperfusion (R) and 1-day follow-up reperfusion (FR). Normoxic controls (N) were not subjected to SI/R. Half of the EHTs was paced, the other half was left unpaced. To assess cell injury, lactate-dehydrogenase (LDH) concentration was measured. Beating force and activity (frequency) were monitored as cardiomyocyte functional parameters. LDH-release indicated relevant cell injury after SI/N in each experimental condition, with much higher effects in the chronically hyperglycemic/hyperosmolar groups. SI stopped beating of EHTs in each condition, which returned during reperfusion, with weaker recovery in chronic conditions than in acute conditions. Acutely treated EHTs showed small LDH-release and ∼80% recovery of force during reperfusion and follow-up, while chronically treated EHTs showed a marked LDH-release, only ∼30% recovery with reperfusion and complete loss of beating activity during 24 h follow-up reperfusion. We conclude that EHTs respond differently to SI/R injury in acute and chronic hyperglycemia/hyperosmolarity, and that our EHT model is a novel in vitro combination of diabetes and ischemia-reperfusion.
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•A novel in vitro co-morbidity mimicking model of hyperglycemia and ischemia-reperfusion was established.•Engineered heart tissues responded differently to ischemia-reperfusion in hyperglycemia.•Chronic treatments resulted in significantly greater cell injury than acute treatments.•The degree of cell injury correlated with weaker beating activity.
Cardiomyopathies represent an important cause of cardiovascular morbidity and mortality due to heart failure, arrhythmias, and sudden death. Most forms of hypertrophic cardiomyopathy (HCM) are ...familial with an autosomal-dominant mode of inheritance. Over the last 20 years, the genetic basis of the disease has been largely unravelled. HCM is considered as a sarcomeropathy involving mutations in sarcomeric proteins, most often β-myosin heavy chain and cardiac myosin-binding protein C. ‘Missense’ mutations, more common in the former, are associated with dysfunctional proteins stably integrated into the sarcomere. ‘Nonsense’ and frameshift mutations, more common in the latter, are associated with low mRNA and protein levels derived from the diseased allele, leading to haploinsufficiency of the remaining healthy allele. The two quality control systems responsible for the removal of the affected mRNAs and proteins are the nonsense-mediated mRNA decay (NMD) and the ubiquitin-proteasome system (UPS), respectively. This review discusses clinical and genetic aspects of HCM and the role of NMD and UPS in the regulation of mutant proteins, evidence for impairment of UPS as a pathogenic factor, as well as potential therapies for HCM.
Objective
The adenosine triphosphate‐binding cassette (ABC) class transporter ABCC2 (MRP2 multidrug resistance related protein 2 or cMOAT canalicular multispecific organic anion transporter) is ...involved in the cellular outward transport and elimination of methotrexate. We hypothesized that common genetic variations may contribute to the variability of high‐dose methotrexate pharmacokinetics.
Methods
Polymorphisms in all 32 exons of the ABCC2 gene were analyzed in a reference group of 59 healthy white subjects by polymerase chain reaction, single‐strand conformation polymorphism, and sequencing. Subsequently, we assessed the association of polymorphisms with the methotrexate plasma concentrations in 44 pediatric patients with acute lymphoblastic leukemia (ALL) (29 male and 15 female patients; mean age, 6.8 ± 4.8 years). Patients received 4 cycles of 5000 mg/m2 body surface area according to the ALL‐Berlin‐Frankfurt‐Muenster (BFM) 95 or ALL‐BFM 2000 protocol.
Results
In the reference group we detected 8 frequent single‐nucleotide polymorphisms. Five of these were in complete linkage disequilibrium. Overall, 5 new polymorphisms are described. The genotype distribution of the patient cohort was not significantly different from the reference collective. The mean plasma methotrexate area under the curve from 36 to 48 hours after the start of the infusion was significantly 2‐fold higher in female patients carrying at least 1 −24T allele as compared with all other patients (14.2 ± 12.8 h · μmol/L versus 6.9 ± 4.2 h · μmol/L, P < .001). The risk to have 2 or more cycles necessitating an intensification of folinate rescue was 9‐fold (95% confidence interval, 1.8‐ to 44‐fold) in female patients carrying at least 1 T allele (P = .0067).
Conclusion
The data suggest a hitherto unknown gender‐specific impact of the −24C>T ABCC2 gene polymorphism on high‐dose methotrexate pharmacokinetics. Whereas a nonfunctional MRP2 variant has been described in a patient with severe impairment of methotrexate excretion, our study is the first to suggest that a frequent ABCC2 polymorphism contributes to variability of methotrexate kinetics.
Clinical Pharmacology & Therapeutics (2006) 80, 468–476; doi: 10.1016/j.clpt.2006.08.012
In vitro assays could replace animal experiments in drug screening and disease modeling, but have shortcomings in terms of functional readout. Force-generating engineered heart tissues (EHT) provide ...simple automated measurements of contractile function. Here we evaluated the response of EHTs to hypoxia/reoxygenation (H/R) and the effect of known cardiocytoprotective molecules. EHTs from neonatal rat heart cells were incubated for 24 h in EHT medium. Then they were subjected to 180 min hypoxia (93% N2, 7% CO2) and 120 min reoxygenation (40% O2, 53% N2, 7% CO2), change of medium and additional follow-up of 48 h. Time-matched controls (40% O2, 53% N2, 7% CO2) were run for comparison. The following conditions were applied during H/R: fresh EHT medium (positive control), the NO-donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP, 10(-7), 10(-6), 10(-5) M) or the guanylate cyclase activator brain type natriuretic peptide (BNP, 10(-9), 10(-8), 10(-7) M). Frequency and force of contraction were repeatedly monitored over the entire experiment, pH, troponin I (cTnI), lactate dehydrogenase (LDH) and glucose concentrations measured in EHT medium. Beating activity of EHTs in 24 h-medium ceased during hypoxia, partially recovered during reoxygenation and reached time-control values during follow-up. H/R was accompanied by a small increase in LDH and non-significant increase in cTnI. In fresh medium, some EHTs continued beating during hypoxia and all EHTs recovered faster during reoxygenation. SNAP and BNP showed small but significant protective effects during reoxygenation. EHTs are applicable to test potential cardioprotective compounds in vitro, monitoring functional and biochemical endpoints, which otherwise could be only measured by using in vivo or ex vivo heart preparations. The sensitivity of the model needs improvement.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
After administration of metoprolol, plasma concentrations of the drug are markedly higher in CYP2D6 poor metabolizers (PMs) than in non‐PMs. In a prospective double‐blind 3‐month study, we ...investigated whether this translates into differences in metoprolol's effects after initiation of therapy. Despite administering equal doses to PMs and non‐PMs, metoprolol plasma concentrations were 4.9‐fold higher in the PM group. Metoprolol evoked significantly and persistently greater reductions in heart rate, diastolic blood pressure, and mean arterial pressure in PMs than in non‐PMs. It appears, therefore, that the CYP2D6 genotype contributes to interindividual differences in metoprolol response.
Clinical Pharmacology & Therapeutics (2009); 85, 3, 269–272 doi:10.1038/clpt.2008.218
This pharmacogenetic substudy of the prospective, double‐blind, randomized CIBIS‐ELD trial determined the impact of the β1‐adrenoceptor Arg189Gly polymorphism on heart‐rate responses to bisoprolol or ...carvedilol in elderly patients with heart failure (421 with sinus rhythm, 107 with atrial fibrillation). Patients were randomized 1:1 to bisoprolol or carvedilol with a fortnightly dose‐doubling scheme and guideline target doses. Patients with sinus rhythm responded essentially identically to bisoprolol and carvedilol, independent of genotype. Atrial fibrillation patients homozygous for Arg389 had a much smaller response to carvedilol than carriers of at least one Gly389 allele (mean difference 12 bpm, P < 0.00001). Carvedilol up to 2 × 12.5 mg did not reduce heart rate in Arg389Arg homozygotes at all. Interestingly, the immediate response to carvedilol did not differ between genotypes. The Arg389Gly polymorphism has a major impact on the heart‐rate response to carvedilol (but not bisoprolol) in patients with heart failure plus atrial fibrillation.
Clinical Pharmacology & Therapeutics (2012); 92 1, 21–28. doi:10.1038/clpt.2012.18
Most cardiac myosin binding protein C (cMyBP-C) gene mutations causing familial hypertrophic cardiomyopathy (FHC) result in C-terminal truncated proteins. However, truncated cMyBP-Cs were ...undetectable in myocardial tissue of FHC patients. In the present study, we investigated whether truncated cMyBP-Cs are subject to accelerated degradation by the lysosome or ubiquitin-proteasome system (UPS).
By using an adenovirus-based approach, we analyzed expression and localization of myc-tagged truncated proteins (M6t 3%, M7t 80% truncation, both mutations have been identified in FHC patients) compared to wild type (WT) in neonatal rat cardiomyocytes. Despite similar mRNA levels, protein expression of M6t and M7t was markedly lower than WT (70+/-4% and 11+/-5% of WT, respectively, p<0.05). M6t exhibited weak incorporation in the sarcomere, whereas M7t was mis-incorporated at the Z-disk and formed ubiquitin-positive aggregates. The lysosome inhibitor bafilomycin only slightly raised the protein level of M7t, whereas the UPS inhibitors lactacystin or MG132 markedly raised M6t and M7t to WT level. Using an adenovirus encoding a fluorescent reporter of UPS activity, we demonstrate that mutant cMyBP-Cs impair the proteolytic capacity of the UPS.
Truncated cMyBP-Cs are preferentially degraded by the UPS, which, in turn, may competitively inhibit breakdown of other UPS substrates. Since the UPS plays an important role in a variety of fundamental cellular processes, we propose impairment of this system by mutant cMyBP-Cs as a contributing factor to the pathogenesis of FHC.
Mupirocin is used worldwide for topical treatment of infected skin lesions, impetigo, and especially for nasal decolonization of patients with carriage of
Staphylococci
, including ...methicillin-resistant
Staphylococcus aureus
. Nevertheless, data regarding the effects of mupirocin on the nasal mucosa, in particular on ciliary beat frequency (CBF), is lacking to date. We tested the CBF of ciliated nasal epithelial cells under the influence of Mupirocin–calcium dissolved in
tert
-butyl alcohol (TBA) containing media in different concentrations comparable to clinical use. Ringer’s lactate solution and TBA served as negative control. Cells were visualized with a phase contrast microscope, and the CBF was measured with the SAVA system’s region of interest method. Mupirocin–calcium dissolved in TBA led to a statistically significant time- and concentration-dependent decrease in CBF compared to the negative control. TBA addition without mupirocin also led to a significant decrease in CBF, although to a lesser extent than mupirocin/TBA. In conclusion, CBF of human nasal epithelia is significantly reduced by mupirocin–calcium-containing solutions in therapeutic concentrations. Due to our results in this study, mupirocin as a nasal decolonization agent should be used only with care, with a strictly set medical indication, and additional care measures should be considered.
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